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Compliments
of

THE C. V. MDSBY COMPANY

NEW YORK, N. Y. — SAN FRANCISCO, CAL.
ST. LOUIS, MO.

SENT AT THE REQUEST
OF

MR. FRANK A. VOLK

Your opinion of this book ivill be

appreciated when your revieiv of it

has been completed.

THE SCIENCE OF BIOLOGY

WILLIAM C. BEAVER, Ph.D.

Head of the Department of Biology, Wittenberg College,

Springfield, Ohio

With 375 Text Illustrations

FOURTH EDITION

l^vr

ST. LOUIS

THE C. V. MOSBY COMPANY

1952

Third Edition Reprinted

November, 1946

June, 1947

November, 1948

February, 1951

Printed in the
United States of America

Press of

The C. V. Mosby Company

St. Louis

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MARY MATZ BEAVER

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PREFACE TO FOURTH EDITION

Numerous changes have been made throughout this revision. Mate-
rial has been rearranged for better organization and presentation, and
additions and deletions have been made in the light of the needs in
various courses as presented. A wide selection of material is given so
that a proper balance can be secured in the various courses. Many of
the benefits of a course in biology are to be derived from a laboratory
or field study of the phenomena of living organisms. Consequently, it
seems that a textbook in such a science should make available those per-
tinent facts which will assist the instructor to help the student to help
himself to understand these phenomena better and to develop the many
attributes of scientific study, including the scientific method. The
instructor must attempt to initiate and maintain in the student a curi-
osity and fundamental interest in the phenomena of the living world.
Through proper techniques and constant practice, the student should
develop a method of working and thinking whereby he is able to formu-
late logical conclusions from scientifically observed and recorded data.
He should become familiar with the technique of proving important
principles for himself rather than merely reading about them or being
told about them. The student should ascertain the facts, and with «a
minimum of help from the instructor, he should formulate his own con-
clusions and prove the more important principles based on the scientific
interpretation of his collected facts and data.

A textbook is not intended to be a book of entertainment, and illus-
trations are not included necessarily for beauty or esthetic purposes but
to assist the student to gather and evaluate facts scientifically. The joy
and entertainment come from scientific discovery of new facts and
phenomena with which he may not have been familiar. The joy and
satisfaction of learning anything new is an essential basis upon which
profitable educational progress is built.

Pronunciations and derivations of terms are more widely considered
than in previous editions in order that the student may understand bio-
logic terminology better and increase his command of the English lan-

4 Preface

guage. Numerous topics have been presented in tables so that facts
may be learned easily and compared and contrasted with other facts.
A new classification of plants is used since it is based on more natural
plant relationships, but a contrast with the older method is given in
the Appendix. Several new illustrations are included and several others
have been revised. Questions and Topics are added at the ends of the
chapters to assist the student in testing himself as well as to guide him
in his study. Selected References are included for additional reading
in case it is deemed necessary. The glossary is extended to include
many of the new materials and principles treated in the text.

To acknowledge all persons who have made contributions toward im-
proving the text would make a prohibitive list. Consequently,- the
author shall limit his acknowledgments to his immediate colleagues,
Professors E. T. Bodenberg, C. A, Brand, and Evelyn Wagner Neal,
whose contributions are greatly appreciated. Permission to reproduce
numerous illustrations from various sources are acknowledged in connec-
tion with each one. The author is indebted to Charles A. Brand and
Gerald R. Bradford for certain new illustrations and for corrections in
others. The Table of Contents is given in some detail so that the stu-
dent may derive a certain degree of orientation and the instructor may
be guided in placing major emphasis on certain topics. Justification for
the somewhat extensive treatment of the various phases of plant and
animal biology is based on presumption that one must understand some-
what the various parts of the science of biology in order to comprehend
more completely any particular portion of it. The human implications
of biology have been presented without attempting to make of this a
text in human anatomy, physiology, or psychology.

William C. Beaver
Wittenberg College
Springfield, Ohio

PREFACE TO FIRST EDITION

If an attempt were made to include in a textbook much of the infor-
mation accumulated in the field of biology, the beginning student would
have difficulty in properly selecting the important parts as well as prop-
erly visualizing and retaining the fundamentals as he should. This
book is written with the hope that it will be of greater service to the
instructor and the student by presenting the more important biological
facts briefly enough to permit a complete comprehension of the subject
as a whole and also to serve as a skeleton to which such additional data
may be added as seem desirable. An attempt is made to systematize
and condense our biological knowledge so that it can be more easily
taught, visualized, and mastered.

Particular attention is called to the following features: (1) Greater
emphasis is placed on the economic importance of animals and plants.
(2) A generalized discussion of the location and functions of the impor-
tant ductless (endocrine) glands, especially in man, is included. (3) A
comparative study of the ten systems of twenty-eight representative
animals, including man, is made in Chapters IX to XVIII. The method
of presentation permits the study to be made either on a comparative
basis or by studying the various systems of a particular animal by
selecting the proper parts of each of these chapters which deal with the
animal being studied. This method of presentation better illustrates the
general principles of the science as well as the unity and various rela-
tionships within the biological world and gives the student the oppor-
tunity of basing his conclusions and formulating his principles upon the
study of representative animals. (4) A comparative study of the vari-
ous structures and functions of fifteen representative plants is made in
Chapters XXIV to XXIX. These plants may be studied on a com-
parative basis, or the proper parts of each of these chapters may be used
in studying the plants in the usual manner. (5) A detailed reference
list of illustrations and drawings in other texts will be of service to the
student in his attempt to understand certain points. (6) The general
consideration of the phyla of animals and plants includes their general
characteristics, a brief but satisfactory classification, and a summary of

6 Preface

the number of species in each phylum. (7) A consideration of the more
important types of the various orders of insects, including a simple key
for the identification of such forms with which the beginning biology
student might wish to become familiar, is given. (8) A summary of
the metamorphosis and life cycles of various types of animals and plants
is given to acquaint the student with this very important phase of the
living world. (9) The embryologic development of animals is illus-
trated by the frog because such demonstration materials are inexpen-
sive and easily secured. (10) The more important theories, laws, and
facts of heredity are discussed, with examples from the plant, animal,
and human fields. (11) A survey of representative animals of the past
and their records is made; a study of geographical distribution of
present-day animals in space, a survey of animal and plant ecology,
and a summary of the science of paleobotany are included. (12) Liv-
ing organisms are discussed as to their origins, continuity, development,
variations, and descent with change. (13) There are pertinent discus-
sions of the properties of living protoplasm, the structures and functions
of various cells and tissues, the process of cell division in animals and
plants, the differences between living and nonliving materials, and the
fundamental dififerences between living animals and plants. (14) There
is a comprehensive summary of the embryologic origin, distinguishing
characteristics, and- functions of the epithelial, connective, muscular, and
nervous tissues of animals. (15) A history of the development and
progress in the field of biology includes many contributions made by
earlier workers in the science. (16) A list of pertinent questions and
topics is found at the end of the chapters to teach the student to sum-
marize his knowledge, to more completely emphasize the important
points, and to stimulate the beginning student to do some original
thinking. (17) Suflficient emphasis is placed on the structures and
functions of the human body to be of value to students of physical edu-
cation, preprofessional students, and the general student who may or
may not take special courses in human anatomy and physiology. (18)
A separate chapter summarizes the more important theories and prin-
ciples of biology. From this the student may easily review and retain
those generalizations which will be of greatest use in his future activities.
(19) A special consideration is made of the application of biology in
various fields in order to show the contributions which this science has
made in the past and to suggest its applications in the future. (20) A
separate chapter is devoted to photosynthesis. (21) An appendix in-
cludes: (a) important prefixes and suffixes frequently used in biology

Preface 7

by means of which the student may readily acquire his necessary bio-
logical vocabulary; (b) methods for starting and caring for a balanced
aquarium which may be applied in the care of out-of-door pools; (c)
directions for collecting, preserving, and mounting insects, which may
be profitably continued long after a formal course in biology is com-
pleted; (d) a glossary which includes the derivation and definitions of
the important terms used in biology.

The essentials of biology are so arranged as to permit an easier and
more effective mastery of the fundamentals. In brief, the book is
designed to "help the instructor help the student to help himself."
Zoological phases of the text may be emphasized more than the botani-
cal, or the latter may be reduced to a minimum to suit the type of
course. The author believes that beginning students in biology should
become familiar with both plant and animal fields because a majority
of them will not take specific courses in both fields. With the proper
foundation in both fields, those who desire may take specific courses in
either zoology or botany or both. The author is also of the opinion
that the principles of biology best can be learned by a rather careful
study of well-selected types of animals and plants. This conclusion is
the basis for the variety of animal and plant types considered. The
variety is sufficiently great as to permit the instructor to select those
which best fit the needs of the course as it is being offered.

No attempt can be made in a work of this type to give due credit to
the many sources of information which through many years of common
use actually have become a part of the science. Cordial thanks are
extended to the authors, publishers, colleagues, and students who in
various ways have supplied the necessary materials and suggestions for
such a work as this. Special acknowledgments are made to Dr. E. T.
Bodenberg, Dr. C. G. Shatzer, Dr. C. A. Lawson, Dr. J. W. Barker,
Professor R. P. Thomas, and Professpr B. B. Young for their many help-
ful suggestions; and to Miss Adrien Jingozian for preparing Figs. 95,
95A, 96, and 132; to Dr. O. L. Inman, of the C. F. Kettering Founda-
tion for the Study of Chlorophyll and Photosynthesis, for his many help-
ful suggestions in Chapter XXXVIII; and to many others who directly
or indirectly have helped in various ways.

William C. Beaver

Wittenberg College
Springfield, Ohio

CONTENTS

TART I

IXTROinr rc^RV lUOlAH^V

CHAPTER PAGE

1. The Science of Bioiah.v a\o vhk Scumhu-. Mi ruon _____ 17

\Vl\v Study Biolojiv _______________ 17

How to Study Bioioi^A ______________ 19

riic ScitMititic Motliod _______________ 20

The Clonr Rcooj^nition and Accurate Statcmrtit of the rrobleni to

Bo Solved ______________ :\

rUe Fonuulntiou ot Working llvpotheses >Vhieh Appear to Explain

the Problem and the Suiigestion ot Methods ot" Investigation _ 22

The Accurate C\^llection and Recording ot" Tertinent Data _ _ _ 2;^
riic Formulation ot" Loj^ical Conclusiotis by the Scientitic Analysis

and Connect Interpretation of the Data and Facts _ _ _ _ 23

The Science of Biology and Its Subdivisions ________ '24

2. Microscopes— Early ano Pkksi nt Day _________ 27

:v Cells and the Cell Principle ___________ 37

rhe Cell Principle and Its Importance _________ 37

Detailed Structure and Fvmctions of Cells _________ 39

I Celluiar C'Jrcamzatiox of Plants ano Animals— Ammai ano

Plant Tissues ________________ Ih

Animal Tissues ________________ 4t)

Kinds of Animal Tissues _____________ 46

Epithelial Tissues _______________ 47

Connective (, Supportive"* Tissues __________ 49

Muscular ;.Coi\tractile) Tissues __________ 53

Nervous Tissues ______________ 54

Parts of the Nervous System ____________ 54

Plant Tissues _________________ 55

Kinds of Plant Tissues _____________ 56

Mcristematic _______________ 56

Epidermal ________________ 56

Parenchyma _______________ 56

CoUenchvma _______________ 56

Schlerenchvma _______________ 59

Cork _'________________ 59

Xvlem _________________ 59

Phloem _________________ 60

Organs __________________ 60

S\-stems __________________ 60

5. How Cells Divide — Indirect Cell Division or Mitosis (Animal

AND Plant) _________________ 62

Mitosis in Animal Cells ______________ 62

Mitosis in the Cells of FTowerinc: Plants _________ 66

Important Facts Regarding Mitosis'- __________ 70

Contenty 9

CHAl'TER PAGE

6. Pkoprkties and Activities of Living PkOTOPLASM . _ _ _ _ 73
Physical Propcrtieg of Protoplasm ___________ 73

J hcorics R^:garding Physical Structure _________ 74

CJoUoidal Systems _______________ 75

Maltf;r, Atorn5, Molcrrulcs, and Elemrmts ________ 78

Chemical Compx^sitiori of l*roUj\j]ixsrn __________ 84

Glucidcs ^Including Carbohydrat/rs; _________ 86

Lipids ''Including Fatsj _____________ 87

Proteins _________________ 88

Mineral Clnorganicj Salts ____________ 89

Water __________________ 90

Vitarnin-j ________ ________ 90

Enzymes _________________ 91

Metabolism, Autosynthesis, Autocatalysis _________ 92

Growth, Assimilation, and Differentiation _________ 94

Reproduction _________________ 96

Adaptation and Irritability i_____________ 96

^Organization and Individuality ____________ 97

Rf i/eneration _________________ 98

Living and Nonliving Things Contrasted ______ __ 99

7. Living Plants and Animals Contrasted ________ 104

PART 2

PLANT BKJLOGY

8. Slrvky op the Plant Kingdom ___________ 108

Classification of Plants f Kingdom Plantae, ________ 109

Number of Species of Plants (Kingdom Plantae; ______ 110

Summary of Distinguishing Characteristics of Plants '^Kingdom Plantae; 111

Subkingdorn 7'hallophyta _____________ 111

General Characteristics of Thallophytes ________ 111

General Characteristics of Algae __________112

Phylum Cyanophyta _____________ 113

Phylum Chlorophyta ____________ 114

Phylum Chrysophyta ____________ 116

Phylum Phaeophyta _^ __________ 116

Phylum Rhodophyta _ ____________ 118

General Characteristics of Fungi __________ 119

Phylum Schizomycophyta _'"_ _ ____ _ _ __ 120

Phylum Myxomycophyta ___________ 122

Phylum Eumycophyta ____________ 124

Subkingdorn Embryophyta _____________ 129

General Characteristics of Embryophytes ________ 129

Phylum Bryophyta _____________ 130

Phylum Tracheophyta ____________ 133

9. Simple Plants With Chlorophyll — Algae _______ 150

General Characteristics of Thallophytes _________ 150

General Characteristics of Algae ______ -_____151

Blue-Green Algae (Phylum Cyanophyta) _________151

Gleocapsa _________________ 152

Oscillatoria ________________ 152

Nostoc __________________154

AnaVjena _________________ 155

^(3W

10 Contents

CHAPTER PAGE

Green Algae (Phylum Chlorophyta) __________155

Chlamydomonas _______________ 156

Protococcus ________________ 157

Spirogyra _________________ 157

Ulothrix _________________ 157

Desmids _________________ 159

Yellow-Green Algae, Golden-Brown Algae, and Diatoms (Phylum Chrys-

ophyta) _______________ 159

Diatoms _________________ 159

Brown Algae (Phylum Phaeophyta) __________ 160

Laminaria _________________ 161

Fucus __________________ 161

Red Algae (Phylum Rhodophyta) ___________ 162

Nemalion _________________ 164

Polysiphonia _____________'___ 164

10. Simple Plants Without Chlorophyll — Fungi ______ 167

General Characteristics of Fungi ___________ 167

Bacteria (Phylum Schizomycophyta) __________ 168

Slime Molds (Phylum Myxomycophyta) _________ 172

True (Higher) Fungi (Phylum Eumycophyta) _______ 173

Class Phycomycetes ______________ 173

Black Bread Mold ______________ 173

Water Mold _______________ 173

Class Ascomycetes ______________ 175

Penicillium ________________ 175

Aspergillus ________________ 175

Cup Fungus _______________ 176

Yeasts _________________ 176

Mildews _________________ 177

Blights _________________ 177

Class Basidiomycetes ______________ 177

Mushrooms ________________ 177

Bracket Fungi (Pore Fungi) ___________ 179

Smuts _________________ 179

Rusts _________________ 181

11. Mosses and Their Allies — Bryophytes (Phylum Bryophyta) _ 185

General Characteristics of Bryophytes _________ 185

True Mosses _________________ 186

Polytrichum ________________ 186

Sphagnum _________________ 187

Liverworts _________________ 188

Marchantia ________________ 188

Porella __________________ 189

12. Ferns and Their Allies _____________ 191

General Characteristics of Ferns and Their Allies (Club "Mosses" and

Horsetails) ______________ 191

Club "Mosses" ________________ 192

Lycopodium ________________ 192

Selaginella _______ _________ 193

Horsetails (Scouring Rushes) ____________ 194

Equisetum _________________ 194

Ferns ___________________ 195

Pteridium _________________ 195

Polypodium ________________ 198

Contents 11

chapter page

13. Gymnospermous Plants — Conifers and Their Allies _ _ _ _ 200

General Characteristics of Gymnosperms _________ 200

Conifers __________________ 201

Pine Tree _________________ 201

Cycads (Sago Palms) ______________ 203

Zamia __________________ 203

14. Angiospermous Plants — Flowering Plants _______ 206

General Characteristics of Angiosperms _________ 206

Indian Corn (Zea mays) _____________ 209

Garden Bean (Phaseolus) _____________ 211

Sunflower (Helianthus) _ _ _ _ _ _ _ _ _ _ _ _ __ 213

15. Biology of Higher Plants — Anatomy and Physiology _ _ _ _ 219

The Root __________________219

General Regions _______________ 219

The Stem _______________<___ 222

Study of a Stem of a Dicotyledonous Plant _ _ _ _ _ _ _ _ 222

Study of a Stem of a Monocotyledonous Plant _______ 222

The Leaves _________________ 223

The Flower _________________ 224

Absorption by Plants ____________ ___2 26

Water __________________ 226

Inorganic Salts _______________ 226

Transpiration by Plants ______________ 226

Conduction of Liquids ______________ 227

Manufacture, Distribution, and Storage of Foods by Plants _ _ _ _ 227

General Consideration of Photosynthesis ________ 228

Theories and Early Work on Photosynthesis _ _ _ _ _ _ _-231

Biochemical Aspects of Photosynthesis _________ 232

Biophysical Aspects of Photosynthesis _________ 233

Influential Factors in Photosynthesis _________234

Applied and Commercial Aspects of Photosynthesis _____ 237

Respiration by Plants ______________ 239

Correlation and Plant Hormones ___________ 239

Growth of Plants, Polarity, Morphogenesis _________ 241

Plant Tropisms (Reactions) _____________ 242

Plant Pigments ________________ 243

16. Economic Importance of Plants __________ 249

Economic Importance of Algae ____________ 249

Economic Importance of Fungi ____________ 250

Economic Importance of Bryophyteg _ _ _ _ __ _ __ _ 256

Economic Importance of Ferns and Their Allies _______ 256

Economic Importance of Gymnosperms _________ 257

Industrial Plants ________________ 257

Fuels __________________ 258

Oils __________________ 259

Plant Fibers ________________ 260

Cork __________________ 261

Woods __________________ 261

Gums and Resins _______________ 262

Coloring Matters (Dyes) _____________ 263

Foods __________________ 264

Beverages _________________ 264

Flavoring Substances ______________ 266

Spices __________________ 266

Savory Substances ______________ 267

Medicines and Poisons _____________ 267

12 Contents

PART 3

ANIMAL BIOLOGY

chapter page

17. Survey of the Animal Kingdom ___________ 272

Phylum 1 — Protozoa ______________ 274

Phylum 2— Porifera ______________ 279

Phylum 3- — Coelenterata _____________ 286

Phylum 4 — Ctenophora _____________ 291

Phylum 5 — Platyhelminthes ____________293

Phylum 6 — Nemathelminthes ____________ 295

Phylum 7 — Trochelminthes _____________ 297

Phylum 8 — Echinodermata ____________ 299

Phylum 9 — Annelida ______________ 304

Phylum 10 — Mollusca ______________ 309

Phylum 11 — Arthropoda _ _ _ _ _ _ _ __ _ _ _ _ 314

Phylum 12— Chordata ______________ 325

18. Unicellular, Microscopic Animals (Phylum Protozoa) _ _ _ 344
Amoeba _ ________________ 344

Paramecium ______.^__________ 349

Euglena __________________ 357

Volvox __________________ 360

Plasmodium _________________ 363

19. Flatworms and Roundworms (Phylum Platyhelminthes and
Phylum Nemathelminthes) ____________ 368

Planaria (Dugesia) _______________ 368

Liver Fluke _________________ 373

Tapeworm _________________377

Ascaris ___"_______________379

20. A Segmented Worm — Earthworm (Phylum Annelida) _ _ _ _ 384

21. Common Insects — Grasshopper and Honeybee (Phylum Arthrop-
oda; Class Insecta) ______________ 393

Grasshopper _________________ 393

Honeybee __________________ 398

22. Identification and Classification (Taxonomy) of Insects _ _ 409
No Metamorphosis _______________ 410

Incomplete Metamorphosis _____________411

Orders of the Class Insecta (Insects) of the Phylum Arthropoda _ _ 414
Gradual Metamorphosis ______________419

Complete Metamorphosis ______ _______419

23. The Frog — An Amphibious Vertebrate Animal ______ 421

24. Embryologic Development of Animals ________ 442

Ontogeny; Phylogeny; Recapitulation (Biogenetic) Theory; Morpho-
genesis __________________ 442

Embryology of the Frog ______________ 444

Embryology of Man (Mammal) _ _________ 450

25. Biology of Man _____ __________ 458

General Organization of the Human Body ________ 458

Integument (Skin) and Skeleton ___________ 459

Motion and Locomotion in Man ___________ 467

Foods and Nutrition ______________ 472

Contents 13

CHAPTER PAGE

Circulation in Man _______________ 477

Functions of the Blood System ___________ 483

Blood __________________ 484

Clotting (Coagulation) of Human Blood ________ 486

Structure and Functions of Human Lymph _______ 487

Human Blood Groups _____________ 489

Respiration in Man ____________--- 489

Excretion of Wastes _______________ 492

Coordination in Man and Sensory Equipment _______ 494

Endocrine (Ductless Gland) System of Man ________ 506

Human Reproduction and Development _ _ _ _ _ _ _ _ - 513

Diseases of Man ______________-_516

Inheritance of Human Traits ____________ 522

Improvement of the Human Race — Eugenics ___ ____526

26. Economic Importance of Animals __________ 530

Phylum 1 — Protozoa (Single-Celled Animals) _______ 530

Phylum 2 — Porifera (Sponges) ___________ -535

Phylum 3 — Coelenterata (Hydra, Corals, Sea Anemone, Sea Cucumber) 536

Phylum 4 — Ctenophora (Comb Jellies or Sea Walnuts) _____ 537

Phylum 5 — Platyhelminthes (Flatworms) _________ 537

Phylum 6 — Nemathelminthes (Roundworms) ________538

Phylum 7- — Rotifera or Trochelminthes (Rotifers) ______ 539

Phylum 8 — Echinodermata (Starfish, Sea Urchin, Sand Dollar, etc.) _ 540

Phylum 9 — Annelida (Segmented Worms) ________ 540

Phylum 10 — Mollusca (Oysters, Clams, Squids, Snails, Devilfish, Oc-
topus) ______________ 541

Phylum 11 — Arthropoda (Crayfish, Lobster, Centipede, Millipede, In- ■

sects. Ticks, Mites, Spiders, etc.) ______ 543

Class Crustacea ________________ 543

Class Diplopoda and Class Chilopoda _________ 544

Class Arachnoidea ______________ 544

Class Insecta or Hexapoda ____________ 547

General Usefulness of Beneficial Insects _______ 547

Injurious or Detrimental Insects in General ______ 549

Economic Importance of Representatives of the Orders of Insects 550
Phylum 12 — Chordata (Lampreys, Sharks, Fishes, Frogs, Reptiles,

Birds, and Mammals) _________ 572

Class Cyclostomata (Cyclostomes) _ _ _ _ _ _ _ _ _ 573

Class Elasmobranchii (Sharks) ___________ 573

Class Pisces (True Fishes) ____________ 573

Class Amphibia (Frogs and Toads) _ _ _ _ _ _ _ _ _ 573

Class Reptilia (Reptiles) ____________ 573

Class Aves (Birds) ______________ 574

Class Mammalia (Mammals) ___________ 574

27. Homology; Analogy; Autotomy; Regeneration; Morphogenesis 576

28. Early Man and His Records ____________ 585

History of Mankind and Human Society _________ 585

Early Man and His Records ____________ 586

Java Ape-Man (Pithecanthropus erectus) ________ 586

Peking Man (Sinanthropus pekingensis) ________ 588

Piltdown Man or Dawn Man (Eoanthropus dawsoni) _ _ _ _ 588

Heidelberg Man ( Palaenthropus [Homo] Heidelbergensis) _ _ _ 588

Neanderthal Man (Homo neanderthalensis) _______ 589

Cro-Magnon Man or Modern Man (Homo sapiens) _____ 589

14 Contents

PART 4

GENERAL AND APPLIED BIOLOGY __________ 591

chapter page

29. Geographic Distribution of Animals and Plants — Biogeography
(Zoogeography and Phytogeography) _________ 591

Why Study Geographic Distribution? __________ 591

Types of Geographic Distribution in Space ________ 592

Principles of Geographic Distribution __________ 593

Geographic Regions of the World ___________ 597

Regions of Geographic Distribution of Vegetation of North America _ 599

General Factors Influencing the Distribution of Organisms _ _ _ _ 602

30. Animals and Plants of the Past and Their Records _ _ _ _ 605

Records of Life ________________ 605

Nature and Kinds of Fossils ____________ 605

Conditions for Fossil Formation ___________611

Significance of Fossils ___________ ___612

Geologic Time Chart ______________618

31. An Ecologic Study of Living Organisms — Plants and Animals _ 620
Ecology of Living Organisms (Plant and Animals) ______ 620

Heredity _________________ 622

The Specific Genes of the Organism Being Studied Ecologically _ 622
The Inherited Abilities and Reactions of the Organism Being

Studied ________________ 623

Mutations and New Types of Organism _______ 624

The Inheritance of Specific Structures by Organisms Being Studied 624
The Rates of Metabolism of the Organism Being Studied Ecologi-
cally _________________ 625

Environment ________________ 625

Physical Factors ______________ 625

Chemical Factors ______________ 630

Biologic Factors ______________ 633

Human Factors ______________ 63 7

Typical Environments and Their Fauna and Flora ______ 639

Ecology of a Portion of a Lake Shore __________ 643

Ecologic Study of a Portion of Your Campus _______ 643

32. Unity and Interdependence in the Living World _____ 646
Unity in the Living World _____________ 646

Unity Within Each Living Organism _________ 646

Unity Within the Individual Cell _________ 646

Unity Between the Various Cells of Each Tissue _____ 647

Unity Between the Various Tissues of Each Organ _ _ _ _ 647

Unity Between the Various Organs of Each System _ _ . ^ 647
Unity Between the Various Systems of a Living Organism _ ^ 648
Similarity of Structures and Functions Between Closely Related Spe-
cies of Organisms _____________ 648

Unity and Cooperation Between Various Types of Living Organisms 649

Nitrogen Cycle _______________ 649

Carbon Cycle _______________ 651

Oxygen Cycle _______________ 652

Biologic Communities (Associations) and Successions of Plants and

Animals _________-_---_- 652

Dependence of All Living Animals and Most Plants on Photosynthesis 654

Web of Life and Balance in Nature __________ 655

Plant and Animal Migrations (Dispersal) ________ 655

Contents 15

chapter page

33. Parasitism and Pathogenesis; Symbiosis; Commensalism; Gregari-

OUSNESS AND COMMUNAL LiFE ; PrEDACIOUSNESS ] INSECTIVOROUS

Plants; Epiphytism; Saprophytism __________ 658

34. Heredity^ — Genetics ______________ 673

Definitions and Methods of Studying Genetics _______ 673

Chromosomes, Polyploidy, and Mitosis _________ 673

Chromosomal Aberrations _____________ 679

Genes and Genie Action _____________ 680

Mendel's Experiments and Laws ___________ 683

Monohybrid, Dihybrid, and Trihybrid Crosses _______ 686

Incomplete Dominance ______________ 690

Multiple Genes and Interaction of Genes _________ 692

Lethal Genes ___________--_--- 694

Mutations _ _________________ 695

Linkage and Crossing Over _____________ 695

Sex Determination and the Sex Ratio __________ 698

Sex-Linked Traits ____________--- 699

Sex-Influenced Traits __ ____________ 703

Inbreeding and Outbreeding ____________ 703

Genetic Improvements of Plants and Animals _______ 705

Production and Maturation of Germ Cells ________ 706

Inheritance or Noninheritance of Acquired Characters _ _ _ _ - 712

Human Inheritance _______________ 712

Eugenics and the Future _____________ 715

35. Variations and Adaptations in Animals and Plants _ _ _ _ 721

Importance of Variations _ _ __ _ _ _ _ _ _ _ - _.721

Classifications of Variations _____________ 722

Causes of Variations ________________ 726

Results of Variations ______________ 727

Adaptations _________________ 727

36. Living Organisms — Their Origin, Continuity, Development, and
Descent With Change _____________ 732

Origin of Life ________________ 732

Abiogenesis (Spontaneous Generation) _________ 732

Biogenesis (Life From Life) ____________ 733

Origin of Life on the Earth ____________ 733

Theories for the Origin of Life on the Earth _______ 734

Continuity of Life _______________ 735

Development of Living Organisms _-,_______--- 736

Descent of Organisms With Change (Evolution) _______ 736

Evidences of Descent With Change _________ 736

Theories of Descent With Change __________ 746

37. Biochemical and Biophysical Phenomena ________ 750

Chemical and Physical Properties of Living Protoplasm "_____ 750

Atoms and Molecules ___________--- 750

Electrolytic Dissociation ______________ 751

Permeability of Membranes and Osmotic Pressure ______ 752

Diffusion and Conduction _____________ 754

Surface Tension ___________--_-- 755

Energy __________________ 756

Radiant Energy ________________ 757

Plant and Animal Colorations ____________ 758

Production and Use of Heat ____________ 760

Production and Reception of Sound ___________ 761

16 Contents

CHAPTER PAGE

Bioluminescence and Light _____________ 762

Bioelectric Phenomena ______________ 764

Enzymes __________________ 766

Plant and Animal Hormones, Including the Ductless (Endocrine)

Gland Secretions _______________ 767

Vitamins __________________ 769

Toxins, Split Proteins, Antibodies, and Hypersensitiveness (Allergies) _ 772

38. Applied Biology _______________ 775

Biology and Its Relation to Agriculture and Hydroponics _ _ _ _ 775

Biology and Its Relation to Foods, Clothing, Furniture, and Fuels _ _ 776
Biology and Its Relation to Human Welfare ________778

Medicine and Health _____________ 778

Biology and Wealth ______________ 779

Water Supplies and Sewage Disposal _________ 781

Diseases Caused or Transmitted by Animals ________ 784

Human Diseases _______________ 784

Diseases of Animals Other Than Human ________ 786

Diseases Produced by Plants ____________ 789

Diseases Caused by Viruses _____________ 789

39. Conservation of Natural Resources _________ 792

Destruction and Conservation of Forests _________ 793

Loss and Conservation of Soils ____________ 794

Loss and Conservation of Water ___________ 795

Loss and Conservation of Animal and Plant Wild Life _____ 796

Loss and Conservation of Minerals and Fuels _______ 797

Conservation of Human Resources ___________ 797

40. Biologists and Their Work ___________ 800

History and Development of Biology __________ 800

How Scientists Have Solved Problems _________ 804

PART 5

APPENDIX __________________ 807

Important Prefixes and Suffixes Used in Biology _______ 807

Glossary, Biologic Principles, and Theories _ _ _ _ _ _ _ _ 813

New and Old Systems of Classifying Plants Contrasted _____ 865

^/^ .. '<,<^ '^

iwv*:o!S"^«:

THE SCIENCE OF BL

LIBRARY ."

Part 1

INTRODUCTORY BIOLOGY

Chapter 1

THE SCIENCE OF BIOLOGY
AND THE SCIENTIFIC METHOD

I. WHY STUDY BIOLOGY

When beginning a study of a new subject, it is desirable to know
some of the reasons for making such a study and to have in mind some
of the valuable and more important results of such an undertaking.
One of the reasons for studying biology is to become familiar with the
various properties and phenomena of living animals and plants, par-
ticularly the structure and functions of living protoplasm in representa-
tive animals and plants. With this information one can profitably
attempt to explain the various living processes of organisms as a whole.

No matter what his future profession may be, a human being can live
a more complete and happy life if he is somewhat familiar with the
wonderful phenomena and laws of nature. Biology helps us to ap-
preciate and understand nature and natural laws by making a com-
prehensive survey of the animal and plant kingdoms.

The present time has aptly been called the age of science. No mat-
ter what an individual may choose to do in the future, he should have
a certain amount of training in science in order to work and to think
more scientifically and accurately. Biology is one of the sciences which
will give the individual an opportunity to acquire scientific training and
technique and to collect data which may be properly systematized and
evaluated, from which proper and logical conclusions may be drawn.

18 Introductory Biology

One of the most important and valuable assets to be acquired for
successful living is an understanding of human beings^ both collectively
and as individuals. Much of the lack of success in the family, in society,
in government, in business, and in the world at large is due to a mis-
understanding of human beings by other human beings. A biologic
study of such phases as heredity, endocrine secretions, personal and
public heahh, sanitation, abnormalities and diseases, normal and abnor-
mal human behavior, as well as balanced and perspective viewpoints
in the fields of society and government, can help materially in our at-
tempt to live happily and successfully. A consideration of the relative
effects of environment and heredity on the various types of human-
beings can aid us in our understanding of education, social progress,
crime, and human diseases and abnormalities. The science of eugenics
contributes quite materially to our proper understanding of the prob-
lems and progress of human welfare. A biologic study of variations
makes us realize that all living things are constantly changing; that the
"most invariable thing in nature is variability." This one factor can
go far in explaining many of the results of human conduct. In spite
of this variation in the living world, biology will reveal also a unity
within the animal and plant kingdoms, a method for living happily and
harmoniously, if we are able to acquire from nature the rules and regu-
lations. One of the most important contributions of biology is our
familiarity with the more important biologic theories and laws which
have materially aided in man's progress and thinking. In other words,
the cultural values of a natural science, such as biology, are immeasurable.

We have recently come to realize the great importance of our natural
resources. Biology will help us understand and will encourage the
enactment of such economic regulations as will tend to conserve our
natural resources, such as health, forests, wild animals, fish, and wild
plants. Such a study also will help us to learn the economic importance
of animals and plants, particularly as they relate to medicine, industry,
landscaping, agriculture, horticulture, and plant and animal diseases.
Such a study also will increase our appreciation and interest in the
great out-of-doors. Because of the enormous numbers of insects and
their destructive habits, the present time has been called the age of
insects. It is only through a study of insects that we will understand
'their role in nature, their economic importance beneficially and detri-
mentally, and desirable methods of control. In order to make worth-
while progress in conservation work, we must understand the causes and

Science of Biology and Scientific Method 19

effects of geographic distribution of living organisms^, and we must be
familiar with some of the geologic records left by organisms of the past
in the various strata of the earth.

Biology can also serve as a foundation for such professions as medi-
cine, dentistry, pharmacy, nursing, agriculture, forestry, education, en-
tomology, horticulture, landscape gardening, and the "profession of
living." In our preparation for such professions, we will appreciate
the interrelationship of all the sciences, such as chemistry, biology,
physics, geology, geography, psychology, sociology, history, paleontology,
and many others.

A conscientious and extensive study of the natural sciences will aid
us in one of the most worth-while problems of our existence — the forma-
tion of such a philosophy of life that we shall live long, happy, and
prosperous lives, ready to attack willingly the problems of the day and
not to shirk our many responsibilities. It may suggest that each of us
has a mission, no matter how great or small, and that there is a cer-
tain responsibility for our individual life which is loaned to us at birth,
taken away at death, and for which we should feel somewhat account-
able during our existence.

II. HOW TO STUDY BIOLOGY

Undoubtedly to some persons such a topic as the above seems some-
what superfluous, but experience shows that students frequently have
difficulty in mastering a science in college whether they have had a
similar course in high school or not. A great part of this difficulty may
be attributed to a lack of knowledge as to how best to study a par-
ticular science. Consequently, a few suggestions as to the best pro-
cedures to follow may not be amiss. Naturally, there can be no rules
which can be applied by all individuals with equal success. Some of
the following rules are somewhat general and can be applied profitably
in the study of any subject. Others are more specifically related to the
mastery of such a science as biology.

Have a particular time and place for study. Permit nothing to
interfere with your program of study. Make study a habit which can-
not be broken. Start your work promptly; do not waste valuable time
in getting started. Before studying a new assignment spend some time
reviewing previous work with which you have had particular difficulty.
Attempt to associate the various parts of the assignment into a unified
whole. Associate the work of the classroom, laboratory, and books in

20 Introductory Biology

such a way that you have a clear, vivid picture of what has been done.
Really to understand a thing you must be able to describe it properly
in your own words. Practice this faithfully in your various phases
of work.

One of the attributes of science is accuracy. Strive to be as accurate
as possible in your descriptions, dissections, drawings, and examinations.

One of the chief difficulties encountered in the study of any new
subject, such as biology, is a mastery of the vocabulary or new terms.
Make it a rule to look up the derivation of each new word. Pay par-
ticular attention to its correct pronunciation. Recall other words with
similar derivations. Use all newly acquired words as repeatedly and
accurately as possible to ensure familiarity.

Read an assignment through for the purpose of getting a general idea
of its contents. Then reread the same assignment more carefully, em-
phasizing the details and weaving them into a unified whole. When
studying, it may be desirable to make notes of the most important
points, placing them in such form as to be most serviceable in retaining
the valuable ones. Seeing these facts in your own handwriting makes
them more lasting and valuable. Certain statements must be copied
verbatim, but many should be written in your own words. This latter
point is important, because, if you can write it correctly in your own
words, you probably will really understand it. When studying an
assignment, always refer to diagrams, graphs, and illustrations which
pertain to the topic in question. Correlate these as much as possible
with your laboratory work.

When attempting to remember something, take the attitude of "intent
to remember." We may read a paragraph and at its conclusion be
unable to tell its contents. Read with the intent to remember. In
this attempt associate your new ideas with those you already know.
Utilize your new information as frequently as possible in your thinking,
conversation, and writing.

TIL THE SCIENTIFIC METHOD

One of the most valuable results of a study of such a science as
biology is the development of the so-called scientific method. A course
in biologic science should give the student a correct idea of the aim and
nature of science, the methods employed, and the value and limitations
of it. Science attempts to observe and describe facts and relate them to
each other. Its conclusions are always subject to revision in the light

Science of Biology and Scientific Method 21

of newly discovered facts which may not have been available when the
original generalizations were made. There are numerous popular, but
erroneous, conceptions concerning the limitations and advantages of
science and what science tries to do, or can do. Some uninformed per-
sons may think that science can do anything, can solve all problems.
While this may not be completely true, the employment of the scientific
method in the solution of most problems will give more logical and
accurate answers than if an unscientific method is used. However, even
when the scientific method is used, if the proper precautions are not
followed in the use of its rules, erroneous conclusions or results may be
obtained.

The failure to appreciate and understand the true nature of science
and its methods has caused much misunderstanding and some unjusti-
fied criticism of the value of the methods of science. Some misinformed
persons may criticize science because biology cannot explain fully what
"life" is. Here, as elsewhere, scientists can use only the tools which are
available to them — they can investigate scientifically the chemical reac-
tions and the physical processes inherent in living things and attempt to
explain life in terms of such investigations. This may not give the com-
plete explanation of life, possibly because the investigations are as yet
incomplete or somewhat inaccurate or because the ultimate problem is
not solvable by science. Even if scientists cannot solve the problem com-
pletely, they may gradually come closer and closer to the ultimate solu-
tion by the correct application of the scientific method.

There may be variations in the steps to be followed in the use of the
scientific method but the following are representative:

A. The Clear Recognition and Accurate Statement of the Problem to
Be Solved

There are enormous numbers of -unusual, or previously unobserved,
problems or circumstances which are constantly present in the labora-
tory as well as in daily life. These may be simple and easily solved,
or complex, requiring laborious observations and experiments for their
solution. Before attempting a solution there must be a proper aware-
ness and clear recognition of the specific problem or situation. It should
be clearly in mind and accurately stated so that irrelevant, yet closely
related, problems do not enter in. In order to have the particular
problem clearly in mind, the investigator should organize his present
knowledge of the problem and familiarize himself with additional, perti-
nent information with which he may not now be familiar. The aware-

22 Introductory Biology

ness of a specific problem may be stimulated (a) by a mere, general
curiosity, (b) by an actual need for the solution of the particular prob-
lem, or (c) by thinking or reading about a similar problem or situation.
After the problem or situation is clearly stated, the next step follows:

B. The Formulation of Working Hypotheses Which Appear to Explain
the Problem and the Suggestion of Methods of Investigation

lVorki?ig hypotheses may be considered as unproved assumptions,
hypothetical explanations, or reasonable speculations which at present
are without proof but which upon scientific investigation may be helpful
in securing the relevant information or data necessary for the eventual
solution of the problem. Undoubtedly, as the problem is being stated
clearly, one or more working hypotheses suggest themselves. No hy-
pothesis or probable cause, no matter how unimportant it may appear,
should be omitted. Each hypothesis is considered in turn, and either it
is rejected because evidence proves it to be faulty or it is investigated as
far and as scientifically as possible because it is giving reliable, pertinent
information with which to work.

After all possible hypotheses have been made, the investigator must
determine the specific methods of investigation which should be followed
in order to secure reliable, pertinent information or data. In general,
methods of investigation include ( 1 ) accurate observations of facts and
phenomena, (2) controlled scientific experiments, (3) or a combination
of the two. The correct solution of the problem may be determined in
great measure by the use of the proper method of investigation. To
devise and use the latter properly may require broad practical training,
imagination, special techniques, or possibly elaborate and intricate ap-
paratus and equipment. If possible, the method of investigation should
be such that it may be repeated sufficiently to secure truly representa-
tive, typical results. In other words, the procedure should be such that
it can be checked and rechecked in order to reduce the chance effects
of unusual dififerences, or variations, found in a few instances or indi-
viduals. Limited observations, or too few investigations, especially if
not checked and rechecked, may give unreliable information.

When using the experimental method of investigation it is highly
desirable to utilize, when possible, the so-called control group in which a
separate group of organisms or data is observed under conditions identi-
cal with the experimental group except that the one condition (rarely
two or three) being examined is not applied to the control group. These
so-called controls are extremely important in the experimental method

Science of Biology and Scientific Method 23

and should be used whenever possible. After the working hypotheses
have been completed and the proper method of investigation decided
upon the next step follows :

C. The Accurate Collection and Recording of Pertinent Data

This may be done by the careful observation of facts or by scientific
experimentation in order to prove or disprove the working hypotheses.
As pertinent data are accurately collected or as observations are scien-
tifically made, they should be precisely recorded in such ways that sig-
nificant and meaningful interpretations can be made. All measure-
ments, observations, records, interpretations of data, or "case histories"
must be scientifically accurate and sufficiently comprehensive to be re-
liable. The accurate collection and recording of data and information
may make the difference between the problem being solved correctly or
incorrectly. The investigator must be honest, open-minded, and faith-
ful, his observations must be correct, his instruments must be accurate
and accurately read, and his records must be comprehensive and com-
plete and contain only relevant materials. After the reliable data have
been recorded and the correct observations have been made, the next
step follows:

D. The Formulation of Logical Conclusions by the Scientific Analysis
and Correct Interpretation of the Data and Facts

After the data and facts have been properly recorded, they must be
analyzed scientifically and interpreted logically in order to solve the
problem correctly. Data and facts must be rechecked several times to
prove their validity and relevance to the specific problem being investi-
gated. Certain data may be found neither to prove nor disprove the
hypotheses; hence they may be discarded as irrelevant or possibly rein-
vestigated in a different manner so as to give additional data which are
relevant. A check should be made repeatedly to keep errors to a mini-
mum. Facts are always present around us, but their proper collection
and logical interpretation form the basis upon which scientific knowl-
edge is built.

The conclusions, if drawn logically, (1) may merely substantiate the
validity and accuracy of previously known facts or observations or (2)
may be entirely new conclusions which could be formulated only in the
light of the data collected or from observations made. Be careful not
to draw conclusions which are broader than the collected data will

24 Introductory Biology

actually and logically warrant. It is important to review the entire
problem step by step to check whether errors have been made, or if a
new procedure has presented itself whereby more accurate data may
be acquired.

Possibly, one might say all this is merely a "common sense" method,
that it is merely a simple blueprint for mental reasoning. Be that as it
may, if the method is properly and carefully used on many types of
problems, it cannot help but result in more reliable conclusions and
results. If the scientific method is not followed, what better one can
be? The fault is not in the scientific method itself but in its improper
use, or possibly in not using it at all. The method becomes more useful
and usable the more it is used.

IV. THE SCIENCE OF BIOLOGY AND ITS SUBDIVISIONS

Biology, which is the "science of living things," is divided into (1)
zoology, which deals with the biology of animals, and (2) botany, which
deals with the biology of plants. Botany and zoology have grown so
extensively that such subdivisions as the following are really sciences
in themselves.

Anatomy* (a-nat'omi) (Gr. anatetnno, cut up) — A study of gross structures,

especially by dissection.
Histology (his -tol' o ji) (Gr. histos, tissue; logos, study)^ — A microscopic study of

tissues.
Cytology (si -tol' o ji) (Gr. kytos, cell; logos, study) — A detailed study of cells and

their protoplasm.
Taxonomy (taks -on' o mi) (Gr. taxis, arrangement; nomos, law) — The science of

systematic classification of organisms.
Embryology (em bri -ol' o ji) (Gr. embryon, embryo; logos, study) — A scientific

study of the formation and development of an embryo.
Physiology (fizi-ol'oji) (Gr. phusis, function; logos, study) — A study of the

functioning or working of an organism or its parts.
Heredity or Genetics (he-red'iti) (L. heres, heir); (je-net'iks) (Gr. genesis,

origin) — A scientific study of the inheritance or transmission of char-
acteristics from members of one generation to those of another.
Evolution (ev o -lu' shun) (L. e, out; volvere, roll or develop) — A scientific study

of developmental changes undergone by organisms whereby they change

from time to time.
Ecology (e-kol'o ji) (Gr. oikos, house or home; logos, study) — A scientific study

of the interrelations of living organisms and their living and nonliving

environments.

^Pronunciations and derivations are based on Webster's New International Dictionary; Hender-
son's Dictionary of Scientific Terms; or Dorland's American Illustrated Medical Dictionary. Only
the major emphasis is shown by the symbol '.

Science of Biology and Scientific Method 25

Biogeography (bi o je -og' ra fi) (Gr. bios, life; geo, earth; graphein, to write) —
The science of geographic distribution of organisms in space or throughout
a particular region.

Paleontology (pa le on -tol' o ji) (Gr. palaios, ancient; onta, beings; logos,
study) — The scientific study of the distribution of organisms in time as
revealed by their records in the strata of the earth's surface.

Pathology (pa-thol'oji) (Gr, pathos, suffering; logos, study) — The scientific
study of diseases and abnormal structures and functions, including causes,
symptoms, and effects.

Economic Biology — A scientific study of organisms which results in the improve-
ment of desirable types or the destruction or hindrance of undesirable ones,
including the value of beneficial organisms and the losses due to detri-
mental ones.

QUESTIONS AND TOPICS

1. List all the reasons why a study of living organisms (plants and animals, in-
cluding man) might well be made.

2. List the rules which you will follow in your method of studying biology. Make
the rules specific and meaningful and post them on the wall of your study
where you may refer to them until you follow them completely. Revise these
rules when you have discovered a better procedure to be followed.

3. Define the so-called scientific method. Explain how it may be used in the
solution of many problems even in daily life. Make it a practice of using this
method whenever and wherever possible.

4. List and describe completely each step to be followed in the scientific method,
including enough details to ensure that you know the purpose and correct use
of each step.

5. Define biology, zoology, botany,

6. Define and learn the correct derivation and pronunciation of each subdivision
of biology as listed in this chapter. Learn the correct pronunciation and
derivation of each new term as you encounter it in your study and include a
definition to be sure that you understand the meaning of the term. If this
is done carefully and conscientiously, some of your difficulties with scientific
terms as well as with other words will be materially reduced.

SELECTED REFERENCES

Avery: Survey of Biological Progress, Academic Press, Inc.

Baitsell: Science in Progress, Yale University Press.

Baker: The Scientific Life, The Macmillan Co.

Bawden: Man's Physical Universe, The Macmillan Co,

Cannon: The Way of an Investigator: A Scientist's Experiences in Medical

Research, W. W, Norton & Co., Inc.
Cohen and Nagel: An Introduction to Logic and the Scientific Method, Har-

court. Brace and Co., Inc.
Conant: On Understanding Science, Yale University Press.
Driesch: The Science and Philosophy of the Organism, A. & C. Black, Ltd.
Fisher: The Rhesus Factor: A Study in the Scientific Method, Am. Scientist

35: 95-103, 1947.

26 Introductory Biology

Haldane: Science and Human Life, Harper & Brothers.
Haldane: Adventures of a Biologist, Harper & Brothers.
——^Haldane: The Philosophical Basis of Biology, Hodder & Stoughton, Ltd.,
London.
Jeans: The Universe Around Us, The Macmillan Co.
Jeans: The Mysterious Universe, The Macmillan Co.

Knobloch: Readings in Biological Science, Appleton-Century-Crofts, Inc.
Lewis: The Anatomy of Science, Yale University Press.
Rapoport: Science and the Goals of Man, Harper & Brothers.
Wells et al.: The Science of Life (4 volumes), Doubleday & Co., Inc.
Woodruff: The Development of the Sciences, Yale University Press.

Chapter 2

MICROSCOPES— EARLY AND PRESENT DAY

Because so much scientific progress of the past, present, and future
has been and is dependent upon the development and use of the micro-
scope, it seems desirable that an understanding of the history of micros-
copy, as well as a brief understanding of modern microscopes, should be
attempted. No elaborate details can be given, and all contributors to
improvements of microscopes cannot be mentioned. The various stages
in the development of microscopes illustrate the scientific method.
Since problems presented themselves which had to be solved, working
hypotheses for their solution were proposed, data were collected and
experiments were performed, and finally conclusions were drawn and
the particular problems were solved, or if not completely solved the
additional information secured may have led other workers to come
nearer the true solution.

It is unknown who invented the first simple microscope which was
really a magnifying glass with a lens thicker at the center than at the
edge. Layard excavated a rock crystal at Nineveh which may have been
a "lens" of the eighth century B.C. Even though burning glasses were
used, probably magnifying glasses were not used extensively until the
invention of spectacles at the end of the thirteenth century. The early
simple microscopes (magnifying glasses) were commonly called ''flea
microscopes^^ because a flea was a specimen commonly investigated. Ac-
cording to present information, Anthony van Leeuwenhoek (1632-1723),
a Dutch microscopist, developed a simple microscope (about 1673) by
mounting a lens between two flat pieces of metal and adding a pivoted
point for holding the specimen (Fig. 1). He ground lenses which had
magnifications of 40 to 160 diameters. With his lenses he studied bac-
teria, protozoa, molds, red blood corpuscles, plants, animals, the circu-
lation of blood in the tadpole tail, etc.

A compound microscope, was invented by Zaccharias Janssen and his
son Hans about 1590 in Middleburg, Holland. These spectacle makers

28 Introductory Biology

combined lenses when viewing objects and discovered that a second lens
would magnify the enlarged image from a magnifying glass. Their
microscope was made of three tubes, had a size of 2 by 18 inches, and
magnified about nine times.

ml'
mm

xm^

fif^fi

Fig. 1. — Leeuwenhoek's microscope (1673). This simple microscope consisted
of a lens mounted between two flat pieces of metal, with an adjustable point for
holding the specimen and focusing purposes. (From the Evolution of the Micro-
scope, American Optical Company, Instrument Division.)

Fig. 2. — Hooke's microscope (1665). The body tube contained a series of
lenses which magnified the image in the manner of a compound microscope.
Illumination was provided by a lamp and a bull's-eye condenser. The instrument
was sixteen inches high and had a maximum magnification of 42 x. (From the
Evolution of the Microscope, American Optical Company, Instrument Division.)

Robert Hooke (1635-1703), an English microscopist, constructed an
outstanding microscope in 1665 which consisted of an objective lens, a
field lens, and an eye lens. The latter two magnified the image of the

Microscopes 29

former in the manner of a compound microscope. He provided a lamp
for illumination and a bull's-eye condenser for intensifying the light. His
microscope had magnifications of 14 to 42 diameters (Fig. 2). He
studied many types of natural objects, and from his investigations of
cork he saw minute, hollow, boxlike structures to which he first applied
the word cell.

Marcello Malpighi (1628-1694), an Italian scientist and physician, is
considered the father of histology because he systematically based his
research on the use of magnifying apparatus in his studies of animals
and plants. His studies included the detailed structure of lungs, kidneys,
spleen, and other organs, the capillary circulation in frogs, and the cellu-
lar structure and anatomy of different plants.

Nehemiah Grew (1628-1712), an English physician, microscopically
studied plants and carefully described the cells, tissues, organs, and ves-
sels in plants. Malpighi and Grew described the microscopic anatomy of
plants so well that it was over a century before any important additions
were made to their work.

Jan Swammerdam (1637-1680), a Dutch physician and student of
Nature, studied the anatomy of lower animals by dissection and injec-
tions, and his results were unequalled for over one hundred years. He
showed a remarkable mastery of the most complicated details in the
many lower animals which he dissected.

The first binocular microscope was designed by Rheita in 1645, two
microscopes were held together by three links at the eye end and two
links at the specimen end. This arrangement accommodated people who
differed as to distance between the eyes and permitted the use of both
eyes in viewing objects.

Bonannus improved the microscope in 1691 and developed a hori-
zontal type which included a source of light, a condenser to concentrate
light, and a rack and pinion mechanism for more efficient focusing
(Fig. 3).

Wilson, about 1710, developed a screw-barrel type of microscope (Fig.
4) which was made of ivory and had a handle. The body had threads
on the observing end into which lenses of different magnifying powers
might be placed. The opposite end contained a condensing lens to con-
centrate light. The specimen was pushed against a spring for focusing.
A Wilson type of microscope was received at Harvard College in 1732
and may have been one of the first compound microscopes used in
American colleges, although simple microscopes probably were used
earlier.

30 Introductory Biology

Cuff, in 1744^ made a microscope of brass which was only twelve
inches high and had a fine screw adjustment and an eyepiece for meas-
uring the size of objects.

Wollaston developed a camera lucida in 1807 for making drawings of
microscopic objects.

■n.M'h"iM

'""'■'-"IMMitMlMlimlMlltlMHi'lMH ,1 ,11, ,,,,, 1 1,...,, II.,

■ "''i'ii"iiimiiiiiiiil|||iiiiP

Fig. 3. — Horizontal microscope of Bonannus (1691). This type included a
source of light, a condenser to concentrate light on the specimen, and a rack-and-
pinion focusing mechanism on a horizontal stand. (From the Evolution of the
Microscope, American Optical Company, Instrument Division.)

Fig. 4. — Wilson's microscope (about 1710). This model w^as made of ivory,
and the body was cut open and the ends threaded for the attachment of lenses.
The specimen was held by a spring for focusing. The handle was unscrewed
when carried in the pocket. (From the Evolution of the Microscope, American
Optical Company, Instrument Division.)

' Microscopes 3 1

The need for better lenses led to work on achromatic lenses in an
attempt to eliminate the undesirable color fringes (various color bands)
seen around objects being observed with high power, single lens objec-
tives. Vincent and Charles Chevalier made an improved achromatic
microscope in 1824 with a magnification of 1800x.

Robert Brown discovered the general occurrence of the nucleus in
plant cells in 1831. ^

Dujardin, the French zoologist, in 1835 observed the jellylike, slimy
material in animal cells which later was found in living plant cells, and
the term protoplasm was applied to this material by von Mohl in 1846.

Jacob Schleiden and Theodor Schwann, through microscopic studies
of many plants and animals, promulgated the cell principle in 1839.

There were only about a dozen microscopes in the United States in
1831. Instructors were using them by 1850, and students began using
them as early as 1875, but they were not in general student use until
about 1890.

Charles A. Spencer (1813-1881) built the first American microscope
(1847) and built several models for instructor and student. Robert B.
Tolles (1824-1883) was another early American microscope builder; he
started as an apprentice of Spencer but established his own business in
1858. He is famous for his improvements on objectives and for his
invention of the homogeneous immersion objectives. In the latter, a
drop of the proper type of liquid is placed on the cover slip on the slide
and the immersion objective is made to contact the liquid, which acts as
a type of lens to assist in higher magnifications. We may use oil immer-
sion objectives for high magnifications. Riddell invented a binocular
microscope in New Orleans in 1851 so that both eyes could be used in
viewing an object. Edward Bausch (1854-1944) made his first micro-
scope in 1872; he was the son of /. J.^Bausch (1830-1896), the founder
of the Bausch & Lomb Optical Company.

Ernst Abbe (1840-1905) joined the Carl Zeiss Co. in Germany in 1866
and invented the Abbe condenser (1872) and a camera lucida (1882)
for making drawings of microscopic objects.

From our brief and necessarily incomplete consideration it is apparent
that many individuals over a long period of time have made their con-
tributions to the improvements of the microscope (Fig. 5). This is
characteristic of science — one person merely takes the work a short dis-
tance, to be carried forward by others who will profit by the errors and
discoveries of their ancestors-in-science.

32 Introductory Biology

Until the end of the nineteenth century the making of complete micro-
scopes was largely done by individuals who made one microscope at a
time. The metal parts were made by hand and the lenses ground and
polished with rather simple equipment. Increasing demands for more
microscopes suggested to manufacturers that specialists (scientists, design-
ers, engineers, specialized workers, etc.) must be trained and standards
set and that microscopes must be built on an assembly line basis. The

EYEPIECE

COARSE ADJUSTMENT

BODY TUBE

DUAL-CONE

NOSEPIECE

OBJECTIVES

COVER GLASS
AND SLIDE

CONDENSER

LOWER IRIS
DIAPHRAGM

FORK-TYPE
SUBSTAGE
MOUNTING

MIRROR

MICROMETER-TYPE
FINE ADJUSTMENT

STAGE CLIP

STAGE

ARM

NCLINATION
JOINT

SUBSTAGE
ADJUSTMENT

PILLAR

-BASE

Fig, 5. — Modern microscope with more important parts labeled. (Courtesy of
Spencer Lens Co. [Scientific Instrument Division of American Optical Co.])

twentieth century has seen many improvements in the manufacture and
usefulness of the various types of microscopes (Figs. 5 and 6). Some of
the more recent improvements include ultramicroscopes, ultraviolet
microscopy, dark-field microscopy, phase microscopy, and electron mi-
croscopy.

When particles too small to be seen with a microscope under ordinary
conditions are illuminated by a strong beam of light parallel to the sur-

, Microscopes 33

face of the stage (at right angles to the direction of vision through the
microscope), they appear as bright specks due to their reflection of light,
but do not show their outline or shape. The apparatus used for such
study is called an ultramicroscope (L. ultra, beyond).

In an ultraviolet microscope invisible ultraviolet rays (of shorter wave
lengths and beyond the visible violet light waves) are used instead of
ordinary light. Because of the invisibility of the ultraviolet rays, photo-
graphs must be made since the image cannot be seen. Special quartz
lenses must be employed which permit the passage of the ultraviolet rays.

Fig. 6. — Correct position when using a microscope. The microscope should
stand upright on the table directly in front of the observer. The left hand should
be used on the fine adjustment to maintain the proper focus, thus leaving the
right hand for other work while looking through the eyepiece. Both eyes should
be kept open in order to minimize eyestrain. This microscope has three objectives
on the nosepiece and a mechanical stage to move the slide on the stage. (From
Carter: Microbiology and Pathology, The C. V. Mosby Co.)

In dark-field microscopy the term dark field refers to a method of
illuminating a specimen brightly while the surrounding background
(field) remains dark. The most practical dark field is obtained by a

34 Introductory Biology

special dark-field condenser (dark-field illuminator) whereby direct light
rays do not enter the specimen; the oblique light rays are focused on the
specimen^ which thus appears as a luminous body against a dark field.
A very small, bright object is more easily seen in a dark background
(field) than is a very small, dark object in a bright field. This is similar
to the phenomenon of seeing small dust particles in a beam of light
when the reo"ion back of the lioht beam is dark.

Fig. 7. — An electron microscope capable of magnifying thousands of times. (Cour-
tesy RCA Victor Corporation.)

Phase microscopy was proposed by Zernike of Holland in 1932 and
has been studied by many, including Richards and others in America
(1944). Phase contrast is a new factor in image formation that permits

Microscopes 35

the study of living organisms and other transparent materials which in-
herently have low contrast properties. By the use of special objectives
and other equipment a greater contrast between the transparent speci-
men and its surrounding medium is secured.

Electron microscopy employs the use of electron (magnetic) micro-
scopes. Electrons produced by special apparatus are used instead of
light, magnetic fields ("electron lenses") are used instead of glass lenses,
and photographic plates are used to record the image since it cannot be
seen. The specimens being photographed must be very thin and in a
vacuum (Fig. 7). The fact that axially symmetrical magnetic and elec-
tric fields could be employed as lenses was discovered by H. Busch in
1926. Hence, by the proper use of magnetic fields (acting as lenses),
the charged particles (electrons) can be made to do what light waves
accomplish in ordinary, optical microscopy. Electron microscopes were
made by Knoll and Ruska (Germany) in 1932, by Marton (Belgium)
in 1934, and by Prebus and Hillier (Canada) in 1938. The Radio Cor-
poration of America in 1941 manufactured a commercial electron micro-
scope of the magnetic type. Many kinds and models have been made
• and used in various parts of the world since that time. Magnifications
of thousands of diameters are possible with such apparatus.

QUESTIONS AND TOPICS

1. Define the following types of microscopes: simple, compound, binocular,
monocular.

2. List the important stages in the general history of the development of micro-
scopes, including the persons and their specific contributions.

3. Explain how scientific progress may depend on the efficient use of microscopes
in such fields as medicine, agriculture, industries, chemistry, water purifica-
tion, metallurgy, and similar ones.

4. Why can ultraviolet and electron microscopes not be used for viewing objects
with the eye ?

5. What are chief differences between the following types of microscopes: light,
ultraviolet, electron ?

6. How does the study of the history of the development of microscopes illus-
trate the use of the various stages of the so-called scientific method? Be as
specific as possible.

7. How can a knowledge of the efficient use of a microscope be of value to us
in everyday life, even though we do not plan to follow a scientific career?

8. Can one learn to use a microscope efficiently without some fundamental knowl-
edge of how the various parts of it really function?

9. Is it true that a microscope can be no more efficient than the optical lenses
of which it is made ?

36 Introductory Biology

10. Learn the location and proper functions of all the essential parts of the micro-
scope.

11. Before using such a delicate and expensive instrument as a microscope be
certain that you know and observe all the rules for its proper use and care.
Carelessness may cause severe damage which may require expensive repairs.

SELECTED REFERENCES*

Burton and Kohl: The Electron Microscope, Reinhold Publishing Corporation.

Carpenter: The Microscope and Its Revelations, J. & A. Churchill, Ltd.

Corrington: Working With the Microscope, McGraw-Hill Book Co., Inc.

Cosslett: The Electron Microscope, Interscience Publishers, Inc.

Gabor: The Electron Microscope, Chemical Publishing Co., Inc.

Gage: The Microscope, Comstock Publishing Co., Inc.

Marton: The Electronic Microscope, J. Bact. 41: 397, 1941.

Wyckoff: Electron Microscopy; Technique and Applications, Interscience Pub-
lishers, Inc.

Zworykin, Morton, Ramber, Hillier, and Vance: Electron Optics and the Elec-
tron Microscope, John Wiley & Sons, Inc.

*Also numerous publications by Bausch & Lomb Optical Co., Spencer Lens Co. (Scientific
Instrument Division of American Optical Co.), E. Leitz, Inc., etc.

Chapter 3

CELLS AND THE CELL PRINCIPLE

I. THE CELL PRINCIPLE AND ITS IMPORTANCE

The cell principle states that all living animals and plants (or those
which were once alive) are made of cells and that all life phenomena
and abilities are fundamentally cellular in nature (Figs. 8 and 9). This
principle is important in biology because since its formulation it has
stimulated the study of a wide range of living phenomena under a com-
mon point of view.

The cell principle was clearly and definitely formulated by the Ger-
man botanist Schleiden and the German zoologist Schwann in 1839, al-
though cells had been rather crudely and inaccurately studied previously.
An Englishman named Hooke had studied cells as early as 1665.

The original formulators of the cell principle did not have accurate
and detailed accounts of cells, but much of that information has been
contributed by multitudes of scientists since. The principle has been
proved repeatedly by these later investigators, but its general purport
and content are much the same today as at the time of its adoption.

A study of this principle shows that plants and animals, although ap-
parently different, are really organized and constructed along common
lines or units. It shows that the functions of a normal animal or plant,
as well as those of an abnormal, diseased organism, are but the expres-
sions of the activities of the individual cells. This principle also influ-
enced the study of physiology by showing that cells and their activities
are at the foundation of this phase of ^science. It also paved the way for
much of the unified scientific experimentation of hundreds of biologists,
thereby profitably influencing their progress and research. It also laid
the foundation for the modern specialized branch of biology known as
cytology, which deals with the study of the finer parts of cells.

Early investigators used the term cell because they saw the cell wall
or container and practically ignored the extremely important substance
within. To them tissues looked like the cells of a honeycomb, or some-
thing in which other things might be placed. Felix Dujardin (1801-
' 1860) studied and recognized the real importance of the cell contents,
especially among the lower animals. Hugo von Mohl in 1846 found

38 Introductory Biology

plant tissues to be made of cells which in turn were composed of that
essential material which he named protoplasm. Max Schultze (1825-
1874) stated that all living cells are made of similar protoplasm or, in
fact, that this mass of organized protoplasm really is the cell and that
bone, chitin, and similar products are manufactured by the active, living
protoplasm.

The cell is now considered as the unit of structure of animal and
plant tissues; that is, units of which they are constructed, as bricks are
the units of which brick walls are made. The cells are also units of
function or physiology because the functions and activities of any living
organism are the sum of the individual cell activities composing that
organism. Each cell works as a unit, performing its particular duty.
However, there must be, and is, a proper interdependence, interfunction-
ing, coordination, and subordination if the organism as a whole is to
function normally and efficiently. The cell is also a unit of develop-
meiit and growth because even a complex animal or plant with its many
cells has grown and developed through the division and increase in size
of its individual cells. Thus, the development of an organism is due to
the properties and activities of its various cells, each acting as a unit,
each contributing its part to the development of the organism as a whole.
Cells are also units of heredity because the embryo receives from each
parent a single sex cell which carries the characteristic determiners. The
embryo grows and its future cells are given these determiners through the
process of mitosis (indirect cell division). There is in this manner a
direct hereditary continuity between the parents of one generation, their
germ cells, and the newly formed offspring of the next generation. Cells
not only transmit hereditary determiners from one generation to the
next, but also through successive cell divisions they retain those hereditary
characteristics with which the young embryo is endowed. If it were not
for this efficiency of our cells, we might at certain periods in our life
fail to retain the characteristics given us by our parents.

Since biology is one of our oldest sciences, one might wonder why the
cell principle was not formulated before 1839. Undoubtedly the follow-
ing will help us to answer such a question : ( 1 ) There was a lack of
scientific instruments with which to study cells effectively before that
time. (2) Experimental science as we know it today was not yet preva-
lent. (3) Gross or macroscopic anatomy demanded the attention of
biologists previous to that time so that a detailed knowledge of cells was
not extremely vital. Biology was studied more or less in a general way
and a greater emphasis was placed on nature study than on detailed
work. (4) A revival of interest in the embryology of organisms in the

Cells and Cell Principle 39

early part of the last century shifted attention from the gross and super-
ficial aspects to the detailed study of cells and their inherent organiza-
tion. All of these, and probably many others, paved the way for the
formulation of the cell principle at that particular time.

II. DETAILED STRUCTURE AND FUNCTIONS OF CELLS

ANIMAL CELLS

PLANT CELLS

I. Cytosome or Cell Body (si' to som)
(Gr. kytos, cell; soma, body) (Fig.
8)

1. Cytoplasm (si' to plazm) (Gr. kytos,
cell; plasma, liquid). — This is that
part of the living protoplasm lo-
cated outside the nucleus. The cy-
toplasm may be separated, more or
less distinctly, into an outer ecto-
plasm (Gr. ektos, outer) and an in-
ner endoplasm (Gr. endon, inner).
The cell sap or cytolymph (si' to
limf) (L. lympha, liquid) forms the
fluid, ground substance of the cyto-
plasm. The cytoplasm is usually
colorless, somewhat granular, and
varies in its viscosity.

Plasma Membrane (and Cell Wall).
— In a few animal cells there may
be a cell wall, although it is rarely
present. Surrounding the cyto-
plasm there always is a thin, clear,
filmlike, rather rigid, plasma mem-
brane. The rather dense plasma
membrane closely adheres to the
cytoplasm and regulates the passage
of materials to and from the cell.
Plasma membranes are semipermea-
ble because certain liquids and dis-
solved materials can pass through
while others cannot. Diffusion
through a semipermeable membrane
is called osmosis (os -mo' sis) (Gr.
osmos, push). IDiffusion occurs
from the region of higher concentra-
tion of a substance to a region of
lower concentration of a substance.

I. Cytosome or Cell Body (Fig. 9)

1. Cytoplasm. — This varies in viscosity
from a thin syruplike liquid to a
gelatinous semisolid. It is usually
colorless, elastic, slightly granular,
and somewhat mucilaginous. Fre-
quently, the cytoplasm forms a layer
next to the cell wall with strands of
it extending across the internal vac-
uole and also surrounding the nu-
cleus. The watery cell sap fills the
vacuole in the cytoplasm and fre-
quently contains salts, sugars, pig-
ments, organic acids, etc.

2. Cell Wall and Plasma Membrane. —
The cell wall is transparent, pliable,
semirigid, and nonliving and gives
strength and support to the plant
body. The cell wall is secreted by
the protoplasm and may be com-
posed of layers, the thickness vary-
ing with the tissues. Adjacent cells
adhere to each other because of a
layer common to them, known as
the middle lamella (la-mel'a) (L.
lamella, small plate). The most
abundant constituent of a plant cell
wall is cellulose (sel'ulos) (L. cell-
ula, small cell). Other materials in
various cell walls are lignin (lig' nin)
(L. lignum, wood), a hard organic
substance found especially in wood;
cutin (ku'tin) (L. cutis, skin), a
waxy substance in epidermal tissues
to make then somewhat impermea-
ble to water; suberin (su'berin) (L.
suber, cork), a waxy substance in
cork tissues to waterproof them.
The thin plasma membrane lies be-
neath the cell wall and, being semi-
permeable, regulates the passage of
materials in and out of the cell.
Osmosis probably occurs much as
in animal cells.

40 Introductory Biology

Centriole ^
Cjo/gi body -*<c:Z7T^

Centro5phcre

?\asma membrane

NudeoJus

{Plasmojomej

Lin'm i^^

Mebaplasmk body

Fibnila

Cytoplasmic Cjranule

_ -.hitophsm
A-. - _ ^ridoplasm

-Xhromabin (granules
-^:- —JVuclear memhrane

V'.'

— Chromatin knob
(karyosomej

.-^Mitochor)dna

(chomdr'iosomej

- Vacuole

Fig. 8. — An animal cell (diagrammatic and generalized). Not all of the struc-
tures shown will be found in any one cell. Special preparation of a variety of
cells is necessary to see all of these structures.

Eiodeo plant

CeHwal/ ^

Plasma

membrane

Cytoplasm _\

Chloropld^.

Cytoplasmic

^ granules

Nucleolus ,

Nucleoplasm N

Nuclear

memhrone

Cyiophsmic

strand

Single cell

Fig. 9. — A common fresh water plant known as Elodea (Anacharis). Only a
thin section of a single cell of a leaf is shown at the right. In the living cell the
chloroplasts are green and floating in the cytoplasm. The vacuole contains cell sap.

Cells and Cell Principle 41

ANIMAL CELLS

PLANT CELLS

3. Protoplasmic Strands ("Bridges").
— In both plant and animal cells
there may be fine protoplasmic
strands extending from one cell to
another to assist in the continuity
between adjacent cells (Figs. 10
and 175).

3. Protoplasmic Strands ("Bridges"). —
The walls of certain plant cells are
not uniformly solid but contain mi-
nute, thin areas called pits which
permit the passage of water and dis-
solved materials between adjacent
cells. In other cell walls, numerous
small canals contain very delicate
protoplasmic strands called plasmo-
desmata (plaz mo -dez' ma ta) (Or.
desma, bond) for the exchange of
foods, the coordination of adjacent
cells by the transmission of stimuli,
etc. (Fig. 10).

4. Centrosome or Central Body. — Just
outside the nucleus there often is
centrosome consisting of a small,
granular, deeply stained centriole
(frequently two) surrounded by a
denser area of cytoplasm, the faintly
stained centrosphere. This body
takes part in cell division and is not
present in all animal cells and is
not present in higher plant cells.

4. Centrosome or Central Body. — This
small body near the nucleus of cells
of certain lower plants (algae, fungi,
etc.) is absent in higher plant cells.
When present, it is associated with
cell division.

5. Mitochondria or Chondriosomes (mi
to -kon' dria) (Or. mitos, thread;
chondr OS, granular) (kon' dre o som)
(Or. chondros, granular; soma,
body). — These cytoplasmic bodies
occur in most cells and appear as
granules, rods, filaments, and some-
times as networks, of variable shapes
and sizes. They are common in
young cells and are thought to be
forerunners of other structures in
adults cells. It has been suggested
that they may assist in cell respira-
tion.

5. Mitochondria or Chondriosomes. —
These small, granular or rod-shaped
structures are commonly present in
plant cells, being visible when prop-
erly stained. It is thought that
they may have the following func-
tions: centers of protein formation
and digestion; assist in cell division;
form and develop certain plastids.

Golgi Apparatus or Golgi Bodies
(gol'je) (after Golgi, Italian scien-
tist).— This is frequently a netlike
structure at one side of the nucleus,
although in certain cells it may be
diffused. It often surrounds the
centrosome. It is thought to have
a secretory function, or to assist in
the metabolism of certain foods.

Golgi Apparatus or Golgi Bodies. —
It is not certain, in the light of pres-
ent investigations, whether struc-
tures comparable to Golgi bodies of
animal cells are present in plant
cells.

42 Introductory Biology

Fig. 10. — A section demonstrating the numerous long protoplasmic strands
(plasmodesmata) which pass through the cell walls and connect adjacent cells,
as found in the Philippine persimmon. (Copyright by General Biological Supply
House, Inc., Chicago.)

Cells and Cell Principle 43

ANIMAL CELLS

PLANT CELLS

7. Vacuoles (vak' u ol) (L. vacuus,
empty). — Spherical vesicles (ves' i-
kal) (L. vesica, bladder) of liquid,
and of various sizes, are known as
vacuoles and may be present or ab-
sent in the cytoplasm of animal
cells, A vacuolar membrane sep-
arates the vacuole contents from the
cytoplasm. Vacuoles may contain
materials to be digested and ab-
sorbed or wastes to be excreted.

Vacuoles. — The central region of a
plant cell usually contains one or
more rather clear vacuoles contain-
ing cell sap. The vacuolar mem-
brane lines the vacuole. In general,
in younger cells the vacuoles are
smaller and more numerous, but as
the cell grows the smaller vacuoles
coalesce and become larger and
fewer in number.

8. Plastids (Or. plastos, to form). —
These are special bodies of various
sizes and shapes and are capable of
forming certain substances. They
are common in plant cells but are
occasionally present in some of the
lower animals.

8. Plastids. — These are specialized,
definitely organized bodies, usually
oval or spherical in shape, which
may be visible in the living condi-
tions. They are of three types: (a)

* chromoplasts (kro' mo plast) (Or.
chroma, color; plastos, moulded)
are red, yellow, or organe and are
common in flowers, fruits, etc.; (b)
leucoplasts (lu'ko plast) (Or. leukos,
white) are colorless and occur most
commonly in storage cells of roots
and underground stems; (c) chlor-
oplasts (klor' o plast) (Or. chloros,
green) are greenish because of
chlorophyll and occur in virtually
all green cells where they photo-
synthesize foods.

Metaplasm (Cell Inclusions) (met' a-
plazm) (Or. meta, between; plasma,
moulded). — This is a lifeless, pas-
sive structure of the cytoplasm and
includes fat droplets, reserve foods
(proteins, glycogen, yolk, etc.),
excretory materials, crystals, etc.

9. Metaplasm '(Cell Inclusions). — This
is a lifeless, passive inclusion and
includes stored foods (starch, pro-
teins, fats), waste materials, crystals,
etc.

II. Nucleus (nu'kleus) (L.
kernel, or nucleus)

nucleus.

1. Nuclear Membrane. — The thin nu-
clear membrane separates the nu-
cleus from the cytoplasm and ad-
heres closely to the nucleus.

II. Nucleus

1. Nuclear Membrane. — The thin, liv-
ing membrane separates the nucleus
from the cytoplasm. Living plant
nuclei are usually rather large, color-
less, and viscus and may be spheri-
cal, oval, or elongated.

44 Introductory Biology

ANIMAL CELLS

PLANT CELLS

2. Chromatin (kro' ma tin) (Gr.
chroma, color). — When killed and
stained, there is a minute, thread-
like network of linin (lin' in) (L.
linum, fiber) to which is attached
the granular chromatin, so named
because it stains deeply with certain
dyes. The chromatin plays an im-
portant role in the transmission of
hereditary characteristics. Modern
investigations suggest that the
chromatin granules are merely thick-
ened regions of the delicate thread
known as the chromonema (kromo-
ne' ma) (Gr. chroma, color; nema,
thread). Eventually the chromatin
forms chromosomes which are con-
sidered in cell division (mitosis).

2. Chromatin. — The chromatin is usu-
ally present in the form of a diffuse,
irregular network or nuclear reticu-
lum (re -tik' u lum) (L. reticulum,
small net) whose principal function
is the transmission of most heredi-
tary characteristics. The chromatin
will eventually form chromosomes
which are considered in cell division
(mitosis).

3. Chromatin Nucleoli (Karyosomes)
(nu -kle' o li) (L. nucleolus, little nu-
cleus) (kar'iosom) (Gr. karyon,
nucleus; soma, body). — One or more
rather large, knotlike (or spherical)
aggregates of chromatin material
may be present (especially in rest-
ing cells).

3, Chromatin Nucleoli (Karyosomes).
— These structures have not been
described for plant cells.

4. True Nucleoli (Plasmosomes) (plaz'-
mo som) (Gr. plasma, form; soma,
body). — Frequently, one or more
small, spherical, lightly stained plas-
mosomes (true nucleoli) exist and
differ from the chromatin nucleoli
in staining reactions.

4. True Nucleoli (Plasmosomes). —
One or more spherical nucleoli may
be present. It is thought that they
may play a role in inheritance, in
cell division, and may synthesize
and store certain protein foods.
They are usually difficult to see in
living cells but may be observed if
stained properly.

Nucleoplasm or Nuclear Sap. — This
makes up the colorless, fluid, ground
substance of the nucleus and fills
the spaces not occupied by other nu-
clear structures. It must be re-
membered that all parts of a cell
work together and the life of the
cell depends on the balanced inter-
actions between the various parts
of the nucleus and cytosome. Some-
times the term protoplast is applied
to all living parts of a cell, in con-
trast to the nonliving metaplast (in-
clusions).

Nucleoplasm or Nuclear Sap. — The
rather viscous, liquid material with-
in the nucleus is the nuclear sap.
Sometimes it is called karyolymph
(Gr. karyon, nucleus; L. lympha,
water). A cell can function nor-
mally only when all parts of the nu-
cleus and cytosome interact prop-
erly. Sometimes the term proto-
plast is applied to all the living parts
of the cell.

Cells and Cell Principle 45
QUESTIONS AND TOPICS

1. Why are there various theories regarding the physical structure of protoplasm?
In what ways are they similar? Which theory do you prefer? Why?

2. List all the parts of the nucleus and of the cytosome (cell body) with the
functions of each.

3. In what general ways do cells of animals and plants differ?

4. Is a certain cell of a living organism always the same chemically, structurally,
and functionally? Give proofs for your answer.

5. List all the important results of the formulation of the cell principle.

6. Discuss each of the ways in which the cell is considered a unit.

7. In what ways might a better understanding of cells aid in the prevention
and cure of such diseases as tumors and cancers?

8. Explain how the functions of cells are influenced by their structure. Explain
how the structure of cells may be modified by the functions which they per-
form. Give examples.

9. What role does heredity play in determining the size, shape, and functions
of the various cells and tissues in a living organism? Do living organisms
inherit cells from which such structures as digestive apparatus or excretory
systems are developed?

10. List several environmental factors telling how each may influence cells in
one way or another.

11. List the names of the men who have made the greatest contributions to the
study of cells, including the thing for which each is noted.

12. Define a cell (in your own words if possible). How was a cell originally
defined?

13. Why are cells usually cut into thin sections and stained before they are stud-
ied? Does a study of such a section reveal the structure of an entire cell?
Might certain structures of an entire cell be absent from certain sections?
Explain the importance of the latter fact.

14. Are all the structures usually found in diagrams of cells in textbooks to be
found in each cell studied on a slide ? Explain.

SELECTED REFERENCES

Amberron and Smith : Outline of Physiology, F. S. Crofts & Co.

Baker: Cytological Technique, John Wiley "& Sons, Inc.

Caspersson: Cell Growth and Cell Function, W. W. Norton & Co., Inc.

De Robertis, Nowinski, and Saez: General Cytology, W. B. Saunders Co.

Gerard: Unresting Cells, Harper & Brothers.

Guillermond: Cytoplasm of the Plant Cell, Chronica Botanica.

Heilbrunn: An Outline of General Physiology, W. B. Saunders Co.

Hober: Physical Chemistry of Cells and Tissues, The Blakiston Co.

Sharp: An Introduction to Cytology, McGraw-Hill Book Co., Inc.

Sharp: Fundamentals of Cytology, McGraw-Hill Book Co., Inc.

Wilson: The Cell in Development and Inheritance, The Macmillan Co.

Chapter 4

CELLULAR ORGANIZATION OF PLANTS AND
ANIMALS— ANIMAL AND PLANT TISSUES

I. ANIMAL TISSUES

A tissue is a group of similar cells differentiated so as to perform cer-
tain functions. According to the cell principle, all living organisms are
composed of cells. Consequently, all tissues and organs of an organism
are composed of cells. Upon casual and hurried observation all tissues
may appear to be made in the same manner, but scientific, microscopic
examinations show that the various tissues differ in structure and func-
tions. In order that the functions of an organism, or its parts, may be
properly understood, it is necessary to be familiar with the cellular struc-
ture of its tissues. In other words, a knowledge of anatomy must precede
physiology. The characteristics of the more important animal tissues
will be given in table form in order that they may be compared and con-
trasted more easily.

Kinds of Animal Tissues

EPITHELIAL
(ep i -the' li al)
(Gr. epi, upon;
thele, nipple)
(Fig. 11)

A layer of tissue composed of flat, cuboidal, or column-
shaped cells, depending on the type of epithelium; there
is a minimum of intercellular space between cells; they
compactly cover the surface and line the cavities of the
body which usually lead to the outside; they are not sup-
plied with blood vessels but must absorb nourishment
from the blood and lymph as they pass the cells.

Functions: Protective, absorptive, secretive, excretive,
sensory.

B. CONNECTIVE
(SUPPOR-
TIVE)

(ko -nek' tiv)
(L. cum, to-
gether; nectere,
to bind) (Figs.
12 and 13)

Fibers are usually present, and much nonliving material
(fibers, plates, masses, etc.) is produced by the cells;
there is a maximum of intercellular space; they are
common in most parts of the body; they all arise em-
bryologically from the same source (mesenchyme cells).

Functions: bind body parts together; some kinds form
semirigid, or rigid, structures for protection and attach-
ment of other tissues and organs.

Cellular Organization of Plants and Animals 47

Kinds of Animal Tissues (Cont'd)

MUSCULAR
(CONTRAC-
TILE)
(mus' ku lar)
(L. musculum,
muscle) (Figs.
14 and 15)

Cells (muscle fibers) are usually elongated and specialized
for contraction because of their tendency to shorten when
stimulated. Special, internal, contractile fibrillae pro-
duced by the cells are responsible for the contraction.

Functions: Move the body as a whole, or its various parts.

D. NERVOUS

(ner' vus)
(L. nervus,
sinew or fiber)
(Figs. 16 and
17)

Highly specialized tissue whose cells (neurons) possess fine
cytoplasmic processes (axons and dendrites) to conduct
nerve impulses; neurons vary in size and length of their
processes; fine neurofibrils in the cytoplasm conduct the
impulses in the proper direction; Golgi bodies are par-
ticularly visible in neurons; Nissl's granules in the cyto-
plasm are probably nutritive as they tend to disappear
after prolonged neuron activity.

Functions: Receive, interpret, and redirect nerve impulses.

A. Epithelial Tissues (Fig. 11)

1. SQUAMOUS
(PAVEMENT)

Broad, fiat cells arranged like the stones in a pavement.

(a) Simple squamous is composed of one layer of cells
which line cavities which do not connect with the out-
side; examples — the endothelium (Or. endo, within)
lining the blood vessels and the peritoneum (Or. peri,
around) lining the body cavity.

(b) Stratified squamous composed of more than one layer
of cells and found in the mouth and nose cavities,
esophagus, outer layer of the skin of higher (verte-
brate) animals, etc.

2. CUBOIDAL

Cells are cube shaped and line glands, tubules of kidneys,
etc.

3. COLUMNAR

Cells are tall and column shaped but may be somewhat
irregular with a. ^nucleus in the base of each cell.

(a) Simple columnar composed of one layer of cells and
lining the intestines of most higher animals.

(b) Stratified columnar composed of more than one layer
of cells and found in the trachea (windpipe), etc.

4. CILIATED,
FLAGEL-
LATED, and
COLLARED

When the free surface of columnar epithelium contains
hairlike cilia, whiplike flagella, or "collars," they are
named accordingly. Ciliated epithelium is found in
the gills of clams, in the roof of the frog's mouth, in
the lining of air passages of vertebrates, in which the
cilia move materials from the surface. Flagellated
epithelium is present on the inner, entodermal layer of
Hydra, etc. Collared epithelium is found in the canals
of sponges, etc.

48 Introductory Biology

A. Epithelial Tissues (Cont'd)

5. SENSORY

Forms the sense organs (receptors) which are affected by
different stimuH; for example, the retina of the eye,
the hning membrane of the nose, etc.

6. GLANDULAR
(SECRETORY)

Usually modified columnar epithelium for the secretion of
specific secretions; examples — intestinal tract, etc.
Certain glands may be composed of unicellular, goblet
cells; others may be complex and multicellular.

7. GERMINAL
(REPRODUC-
TIVE)

Epithelium which is modified for the formation of sex
cells in the reproductive organs (testes and ovaries).

Cuboida]

A Simple _S<^uamoas

qiand cell

Simple qiandular

qIand cells-

L glandular

Q Flaqellabed

r- sensory
^ (nosej

^Sensory (taste)

Simple columnar

F Ciliated columnar

^ Flagellated
with collar

Cjerminal (reproductive)

Fig. 11. — Epithelial tissues. The sensory cells (taste) are connected with a
nerve below and have sensitive hairs above. In the germinal tissue the origin
of the reproductive cell from the epithelial cells can be seen.

Cellular Organization of Plants and Animals 49

B. Connective (Supportive) Tissues (Figs. 12 and 13)

1. RETICULAR

Fine white fibers in the form of a network for supporting
the cells of other tissues in certain organs; examples —
spleen, liver, lymph glands, etc.

2. FIBROUS

(a) Areolar — Minute white fibers frequently in bundles
which form a network with a homogeneous, ground
substance in which are scattered the connective tissue
cells (rounded, irregular, or spindle shaped) ; may
contain thicker, single, yellow, elastic fibers; found
surrounding muscles, nerves, etc.

(b) Tendons and ligaments — White fibers which run
parallel to each other, with cells between them; ten-
dons connect muscles to bones; ligaments connect
bones to bones.

(c) Elastic (yellow) — A preponderance of single, thick,
yellow, elastic fibers over the less numerous white
fibers; found in the blood vessel walls, vocal folds,
lungs, etc.

3. ADIPOSE

Certain rounded cells are filled with fat globules of various
sizes; found in various places beneath the skin, around
certain organs, etc.

4. CARTILAGE

(a) Hyaline ("gristle") — This consists of a clear, firm,
gelatinous, homogeneous matrix with scattered spaces
called lacunae (la-ku'na) (L. lacuna, cavity) in
which are one or more rounded cartilage cells which
secrete the cartilage; examples — ends of long bones
and ribs, nose, trachea (windpipe), etc.

(b) Fibrocartilage — Numerous fibers are present in the
matrix of this cartilage; examples — external ear, be-
tween the vertebrae, etc.

5. BONE

The ground substance, or matrix, is hardened with calcium
carbonate and calcium phosphate; bone cells are pres-
ent in the lacunae which are connected with fine
canals. The units of bone construction, known as
Haversian systems, consist of (a) a central canal with
an artery, vein, and nerve; (b) lamellae made of layers
of bony flakes so arranged as to form rough-walled
canals which are arranged concentrically in circles or
ovals, around the central canal; (c) the lacunae or
enlarged spaces associated with the lamellae and con-
taining the irregularly shaped bone cells; (d) the tiny,
wavy, canal-like canaliculi which radiate from the
lacunae and connect the lacunae with each other and
with the central canal; (e) the hard matrix (bone)
which occupies spaces not previously described and is
secreted by the bone cells by the incorporation of lime
salts.

Bones protect, support, assist in locomotion, serve for at-
tachment of muscles and other tissues, assist in hearing
(ear bones), etc.

50 Introductory Biology

-Elastic fibers
%--Cell
Ground substance

-White flbers-->crT

-Cell

Elastic fibers-VH¥

Cell —
White fibers

Ground substance ..^.^

-Bone (Matrix)
— Lamella

-Haversian canal
- Lacxma

-Canaliculi

"" Bone (Matrix)

Red corpuscle

Polymorphonuclear
leucocyte

Small lymphocyte

Large mononuclear leucocyto

Fig. 12. — Connective tissues. A, Areolar (from beneath skin) ; B, adipose
(fat) ; C, reticular (from lymph node) ; D, fibrous (from longitudinal section of
a tendon) ; E, elastic (yellow) ; F, hyaline cartilage (from end of bone) ; G,
osseous (bone) cross section of Haversian system; H, blood corpuscles (human).
The red blood corpuscle is also known as an erythrocyte; the large mononuclear
leucocyte is known as a monocyte.

B. Connective (Supportive) Tissues (Cont'd)

BLOOD

AND

LYMPH

(Fig. 12, H)

The liquid intercellular matrix is mobile and is the blood
plasma. The modified plasma which is outside the
blood vessels is the lymph. The colorless plasma con-
tains enzymes, hormones, vitamins, foods, wastes, anti-
bodies, and three general types of blood corpuscles:
(a) erythrocytes (red blood corpuscles) ; (b) leuco-
cytes (white blood corpuscles) of various kinds, which
vary as to size, shape and size of the nu'cleus, kinds of
granules in the cytoplasm, etc.; (c) blood platelets
which are small, irregular, nonnucleated (in mam-
mals) and comparable to the nucleated spindle cells
of the frog; the various corpuscles are considered in
greater detail in another chapter.

Blood carries foods to the cells and wastes from the cells;
carries oxygen to the cells and carbon dioxide from
the cells of the body; carries foods to the endocrine
glands which secrete specific hormones which are
transported to various body parts by the blood;
equalizes temperature between various body parts; con-
tains antibodies which are chemical substances which
assist in the body defense in certain diseases; maintains
the acid-alkaline balance between various body parts;
transports water and other substances from one part
of the body to another; destroys bacteria and other
foreign particles by phagocytosis on the part of certain
leucocytes; assists in blood clotting, etc.

'Of^

Fig. 13. — Human bone shown in cross section. Note the arrangement of
lacunae in concentric lamellae around the Haversian canals. Observe the thread-
like canaliculi associated with the lacunae. The bone cells are not clearly visible
in the lacunae of such a ground section of bone. (Copyright by General Biological
Supply House, Inc., Chicago.)

52 Introductory Biology

^SARCOLEMMA
--NUCLEUS

-DARK BAKD
LIGHT BAND

-.-.NUCLEUS

'CYTOPLASM —

-NUCLEUS

•EPIMYSIUM

Fig. 14. — Muscle tissues. A, Striated (cross-striped) ; portion of a single cell
or fiber; B, nonstriated (smooth); several cells; C, cardiac (indistinctly striated);
several cells. Observe the branchings between the various cardiac cells and the
several nuclei in the striated type.

Fig. 15. — Bas relief photomicrograph of striated muscles showing the banded
condition at a magnification of 1,000 X. (Copyright by General Biological Supply
House, Inc., Chicago.)

Cellular Organization of Plants and Animals 53
C. Muscular (Contractile) Tissues (Figs. 14 and 15)

1. SKELETAL

These muscles are skeletal (attached to the skeleton) and
voluntary (subject to the control of the will). Each
cylindroid cell (muscle fiber) may have rather curved
ends and contains several peripheral nuclei (multinu-
cleated). Fine, internal fibrillae (myofibrils) run parallel
to each other and lengthwise of the cell. These cells, at
regular intervals, possess alternate dark and light bands
of different densities which give them their characteristic
striations. During contraction the light bands increase
in width, while the dark bands decrease. Skeletal mus-
cles may contract more rapidly than other types of mus-
cles, although they may fatigue easily. Each fiber is
covered with an elastic membrane, the sarcolemma (sar
ko -lem' a) (Or. sarx, flesh; lemma, covering), and vari-
ous fibers are bound together into muscles by connective
tissues. Muscles are attached to the skeleton by connec-
tive tissues known as tendons (L. tendo, stretch). The
more stationary end of a muscle is its origin and its
more movable part the insertion. Skeletal muscles are
usually attached in opposition so that one may perform
a function opposite the other.

2. VISCERAL
OR
SMOOTH

These muscles are visceral (help to form internal, visceral
organs) and involuntary (not controlled by. the will).
Each elongated, spindle-shaped cell has one central
nucleus (mononucleated). Fine, internal, contractile,
homogeneous fibrillae run parallel to the long axis.
These muscle do not have striations (nonstriated) ; hence
the name smooth or nonstriated. Visceral muscles con-
tract slowly under normal conditions and do not seem to
fatigue easily. Each fiber is covered with an epimysium
(epi -miz' i um) (Or. epi, upon; mys, muscle) which is
not a true sarcolemma. They are present in the walls of
the bladder, blood vessels, etc.

3. CARDIAC

•

These muscles form the wall of the heart (Or. kardia,
heart) and are known as cardiac. They are involuntary.
These smaller cells are often branched and may be con-
nected with each^ other to form a syncytium (sin-
sit' i um) (Or. syn, with; kytos, cell), which is a mul-
tinucleated association of cells which permit impulses
to travel from one cell to another. The internal, con-
tractile fibrillae possess striations for contraction pur-
poses. The speed of contraction may be rapid, or rather
slow, depending upon circumstances, with the rate of
fatigue being intermediate between the other two types.
In this connection it must be remembered that cardiac
muscles have alternate periods of contraction, rest, and
expansion. There is no true sarcolemma. Cardiac mus-
cles are found only in the hearts of vertebrate animals.
The striations may not be quite as discernible as in the
skeletal muscles.

D. Nervous Tissues (Figs. 16 and 17)

NERVOUS

Nervous tissues are composed of nerve cells (neurons),
each with a single nucleus. The cells vary greatly in
size and shape, as well as in their cytoplasmic processes
(axon and dendrite). The axon (axis cylinder) is long
and usually unbranched except for occasional side col-
laterals. The dendrites (Gr. dendron, tree) are usually
much branched, especially near the neuron, although
branches appear to be absent in some instances. The
dendrite carries impulses toward the neuron, while the
axon carries them away. The minute gap between con-
secutive neurons regulates the transmission of impulses
between them and is known as the synapse (sin' aps)
(Gr. synapsis, union). Neurons, depending on the num-
ber of cytoplasmic processes, may be classed as unipolar
(one), bipolar (two), multipolar (more than two proc-
esses). A nerve consists of the processes of nerve cells
united into a sort of "cable." A ganglion is an enlarge-
ment composed of the nerve cells and serves as a center
of nerve influence outside of the central nervous system.

Nerve fibers (processes of neurons) may be classed as (a)
medullated (myelinated) when they are surrounded by
a noncellular, fatty medullary sheath (myelin sheath)
with constrictions at intervals by the nodes of Ranvier and
(b) nonmedullated (unmyelinated) , in which the nerve
fiber lacks the medullary sheath. A thin nucleated
neurilemma (nu ri -lem' a) (Gr. neuron, nerve; lemma,
cover) may cover certain nerve fibers, such as peripheral
nerves going to skin, muscles, viscera. A brain (cerebral
ganglion) and spinal cord are composed of various kinds
of neurons with processes of various types.

Parts of the Nervous System (Figs. 16 and 17)

Central nervous
system

Peripheral
nervous
system

[Cerebrum
Cerebellum
Brain -j Midbrain

Medulla oblongata
*■ Pons varolii
Spinal cord
f Cranial (brain) nerves and their end organs
Spinal nerves and their end organs
Sympathetic nerv^ous system with its various
subdivisions

l^-Demdnte

/Jijjl <^rQnu]e

y '' ^MucYeas

Axon //eurolemma

yAxon brush

;^''. ■"■"■'-" ^^^^^wHwTi*^^^i?*^Mii.j.j...:i)i;5^g

Medullary Jheabh /Jode oi Ranvier

Fig. 16. — Nervous tissue. A nerve cell or neuron is shown much enlarged and

somewhat diagrammatically.

Cellular Organization of Plants and Animals 55

White matter

dorsal horn

MnS

lateral horn

Musda

] Ventral root
5pinal nerve

\jQr\bra\ horn

qray matter

Fig. 17. — Spinal cord in cross section, showing the pathways through the cord
and the origin of the spinal nerves. Arrows indicate the pathways over which
impulses might travel from the skin through the cord and back to a muscle.

II. PLANT TISSUES

A plant tissue is a group of cells commonly of similar structure and
performing essentially the same function. An organ is composed of vari-
ous tissues which together perform interrelated functions. For example,
a leaf is an organ composed of various types of tissues. Naturally, the
simpler, lower types of plants do not have tissues, or, if they do, the tis-
sues are quite simple. The cells of plants show great variations in struc-
ture and size, both of which influence the functions of these cells in the
physiology of the plant. Plant tissues may be simple or complex (Fig.
18). The phloem and xylem tissues are considered to be complex be-
cause several kinds of cells occur in their construction, while other tissues
described below are considered to be simple because they are composed
of a single kind of cell. Certain tissues, such as the rapidly growing
meristematic tissues, give rise to other tissues and might be considered
temporary, while the other tissues remain much the same after being
formed and might be considered permanent tissues. When tissues are
studied casually and hurriedly, they may appear to be alike, but a scien-
tific, microscopic study shows that because of differences they may be
classified into rather different types (Fig. 18).

Types of Plant Tissues (Figs. 18 and 19)

1. MERISTEMATIC (mer is te -mat' ik) (Gr. meristes, divide)

2. EPIDERMAL (ep i -der' mal) (Gr. epi, upon; derma, skin)

3. PARENCHYMA (par -eng' ki ma) (Gr. para, beside; engchyma, infusion)

4. COLLENCHYMA (kol -eng' ki ma) (Gr. kolla, glue; engchyma, infusion)

5. SCLERENCHYMA (skier -eng' ki ma) (Gr. skleros, hard; engchyma, infusion)

A. SCLERENCHYMA FIBERS

B. STONE CELLS (SCLEREIDS)

6. CORK (kork) (Span, alcorque, cork)

XYLEM (zi' lem) (Gr. xylon, wood)

A. TRACHEIDS (trak'eid) (L. irac/izfl^ windpipe, or tube)

B. TRACHEAL VESSELS (TUBES)

C. XYLEM PARENCHYMA

D. XYLEM (WOOD) RAY CELLS

E. XYLEM (WOOD) FIBERS
PHLOEM (flo'em) (Gr. phloios, smooth bark)

A. SIEVE TUBES

B. COMPANION CELLS

C. PHLOEM PARENCHYMA

D. PHLOEM RAY CELLS

E. PHLOEM FIBERS

Kinds of Plant Tissues (Figs. 18 and 19)

SHAPE, SIZE, AND ARRANGE-
MENT OF CELLS

LOCATION AND
FUNCTIONS

L MERISTE-
MATIC

Small, thin walled, frequently cube
shaped, actively dividing by cell
division (mitosis) to form and dif-
ferentiate permanent, mature tis-
sues; cells closely packed and usu-
ally with no intercellular spaces.

Found near the tips of roots
and in buds of stems (ter-
minal, or apical meri-
stems), between bark and
wood of trees (cambium),
in bark of trees (cork
cambium), or where ex-
tensive growth occurs;
commonly called
"growth" tissues.

2. EPIDER-
MAL

Usually one cell thick; outer cell wall
often thickened with a waxy, water-
proofing substance, cutin; cells
usually colorless, except crescent-
shaped guard cells, which contain
green chloroplasts and which con-
trol the epidermal pores, or stomata
(stom'ata) (Gr. stoma, opening)
for exchange of gases; occasionally,
red, purple, or bluish pigments in
cell sap may give color to leaves,
etc. (Figs. 18, 19).

Found on surface of leaves,
flower parts, fruits, young
roots, and stems; conserve
moisture and give me-
chanical protection
against injury, entrance
of parasites, and poison-
ous materials.

PAREN-
CHYMA

Usually spherical or ovoid, but some-
times cylindroid, with large central
vacuole; usually thin cell walls;
numerous intercellular spaces; pro-
toplasm inay remain alive for long
periods of time.

Very common and abun-
dant, occurring in prac-
tically all parts of higher
plants; colorless paren-
chyma of roots and stems
store water and foods;
green, chloroplast-bearing
cells of internal tissues of
leaves photosynthesize
foods; when parenchyma
contains chloroplasts, it is
called chlorenchyma
(klor -eng' ki ma) (Gr.
chloros, green; engchyma
infusion) .

4. COLLEN-
CHYMA

May be somewhat elongated, with
pointed, blunt, or oblique ends;
cell walls thickened with cellulose
at corners or elsewhere; protoplasm
may remain alive for long periods.

Commonly occur beneath
the epidermis in younger
parts of plants as well as
in certain older parts
(petiole of leaf) ; give
support and strength.

Cellular Organization of Plants and Animals 57

EPIDERMAL

Chloroplast

pi.

Stoma

Nucleus
Gua^d Cell

SCLERENCHYA

Nucleus

I ^

l^o.V V® -J

{:®^'l]^

;j©/

■®^-

'■<>;

■:#:

'<3 \;£!;

'«.

MERISTEMATIC

CO"RK

PARENCHYMA

Spiral.

® 4 © ® "® (S ■ ®_"0'(i"'^"'^';i'J i'^'i)

_ _ _ _ *

Z'"

Tracheid

Tracheal "Tubes

Sieve Tube

CONDUCTING

Sieve Plate

Fig. 18. — Plant tissues shown somewhat diagrammatically. The sclerenchyma
tissue shown is a stone cell (sclereid) type of mechanical tissue. The conducting
tissues shown include three types of tracheids (found in xylem), three types of
tracheal tubes (found in xylem), and sieve tubes with their adjacent, nucleated
companion cells (found in phloem). L, Longitudinal section; X, cross section.

58 Introductory Biology

Fig. 19. — Surface view of the epidermis of a plant (Sedum), showing the open-
ings called stomata with their surrounding guard cells. (Copyright by General
Biological Supply House, Inc., Chicago.)

Kinds of Plant Tissues (Cont'd)

SHAPE, SIZE, AND ARRANGE-
MENT OF CELLS

LOCATION AND
FUNCTIONS

SCLEREN-
CHYMA

Cell walls tough and extremely
thickened by cellulose and lignin;
walls possess thin areas, known as
pits, whose borders or edges are
simple and unthickened (unhor-
dered pits); protoplasm dies when
cell reaches maturity. Two types
of sclerenchyma cells:

(a) Sclerenchyma fibers, which are
elongated, pliable, elastic 'cells
with pointed ends and great
strength.

(b) Stone cells (sclereids) , which are
not elongated but may be irregu-
lar in shape, with length and
width about equal; minute pit
canals extend through thickened
walls.

Provide mechanical support
and strength; stone cells
abundant in shells of
nuts, in gritty masses in
fruits (pears), in seed
coats, and in bark of
trees, etc. ; because of
flexibility, strength, and
cohesive ability of fibers,
some of them are used in
making ropes, twine, mats,
and other textiles (fibers
of flax, hemp, etc. ) .

6. CORK

Cell wall contains a waxy, water-
proofing material called suberin;
cells frequently rectangular and
regularly arranged; arise from
cork cambium; protoplasm dies
soon after cell is formed.

Forms outer bark of stems
and roots of woody plants
to give protection against
mechanical injury and
excessive evaporation;
may also be present in
other plant structures for
same purposes.

7. XYLEM

Complex, woody tissues composed of
several kinds of cells which are
usually elongated and with thick-
ened walls. Xylem composed of:

(a) Tracheids, which are elongated,
tapering, single cells with a fairly
large lumen (cavity) ; cell walls
thickened by spirals or rings of
cellulose and lignin and often
possess thin areas called bordered
pits (edge of pit thickened) ;
protoplasm frequently short-lived ;
common in cone-bearing trees,
etc.

(b) Tracheal vessels (tubes), which
are long, multicellular tuies com-
posed of chains of long, cylin-
droid cells whose adjacent ends
have dissolved and fused; cell
walls have thickenings and bor-
dered pits as do tracheids.

(d) Xylem (wood) ray cells which
are chiefly parenchymatous tissue
to conduct materials radially in
stems, etc,

(e) Xylem (wood) fibers which are
elongated, fiberlike cells charac-
terized by bordered pits.

Xylem (wood) functions as
conducting tissue, trans- '
porting water, mineral
salts, etc., upward; thick-
ened areas of tracheids,
vessels, etc., give strength
and support; tracheids
common in cone-bearing
evergreens; tracheal ves-
sels most abundant in
higher plants; xylem
parenchyma stores foods;
ray cells store foods and
conduct materials radially
across stems, etc. ; xylem
fibers give strength and
support.

60 Introductory Biology
Kinds of Plant Tissues (Cont'd)

SHAPE, SIZE, AND ARRANGE-
MENT OF CELLS

LOCATION AND
FUNCTIONS

8. PHLOEM

Complex tissues composed of several
kinds of cells; phloem always
contains sieve tubes and paren-
chyma, and other three kinds of
cells described may, or may not,
be present, depending on specific
tissue. Phloem may be com-
posed of:

(a) Sieve tubes, which are elongated
rows of thin-walled, cylindroid
living cells whose end walls
(sieve plates) contain sievelike
pores; protoplasm continuous
from cell to cell through sieve
pores; in mature sieve tube cells
living protoplasm lacks nuclei.

(b) Companion cells, which are ad-
jacent to sieve tubes, are some-
what shorter and smaller than
latter, and possess prominent
nuclei.

(d) Phloem ray cells which are
parenchymatous to conduct ma-
terials radially.

(e) Phloem fibers which are elon-
gated cells whose structure gives
strength.

Phloem conducts foods
manufactured in leaves
downward through stems
and roots; companion
cells common in flowering
plants and because of
pores between them and
sieve tubes, former may
assist in conducting and
storing foods; phloem
parenchyma stores foods;
phloem ray cells store
foods and conduct mate-
rials radially in stems,
etc. ; phloem fibers give
support and strength.

III. ORGANS

An organ is an association of different tissues which act together to
perform some specific function. For instance, the human arm is an
organ of motion consisting of such tissues as bone, cartilage, muscle,
blood and lymph, connective, vascular (blood vessels), nervous, epithe-
lial, and adipose. Many organs are usually required for performing a
particular function, each organ contributing some part, large or small,
to the functioning of the whole. All organs tend to function together
in a more or less harmonious manner if the living organism is normal
and healthy. If ill or defective, there is a maladjustment of the interac-
tion and interdependence of the various organs of that individual.

The leaf of a plant is an organ, composed of such tissues as epidermal,
chlorenchyma, collenchyma, xylem, phloem, etc.

Cellular Organization of Plants and Animals 61

IV. SYSTEMS

A system is an association of different organs which perform a specific
function. For instance, the digestive system consists of such organs as
the tongue, teeth, saHvary glands, pharynx, esophagus, stomach, large
and small intestines, liver, pancreas, and the gall bladder.

QUESTIONS AND TOPICS

1. Define (1) tissue, (2) organ, and (3) system.

2. What role does heredity play in the process of tissue formation?

3. Give the distinguishing characteristics and location of the following tissues:

(1) epithelial, (2) nervous, (3) connective, and (4) muscular.

4. In nervous tissue describe the structure and functions of (1) neuron, (2)
dendrite, (3) axon, (4) synapse, (5) nerve, (6) nerve pathway, (7) ganglion,
and (8) brain.

5. Why is blood considered a tissue? How does it differ from other tissues?
Should it be classed with the connective tissues or separately? Why? Why
might blood be called a compound rather than a simple tissue ?

6. Contrast and give examples of involuntary and voluntary muscle tissues. Do
involuntary muscles react without a stimulus ? Why should the muscles of
the heart be involuntary ? Which of the three groups of muscles are striated ?

7. Do you consciously send impulses to your skeletal muscles when you walk?

8. What types of muscles are used in each of the following: (1) breathing,

(2) pumping blood, (3) swimming, and (4) digesting foods?

9. Explain what happens in muscles when a so-called habit has been formed.

10. Contrast animal tissues with plant tissues. Which plant tissues perform
functions which resemble those performed by animal tissues ? Give specific
examples.

11. What role does mitosis play in the development of tissues?

12. Give the distinguishing characteristics and functions of each kind of plant
tissue.

SELECTED REFERENCES

Cameron: Tissue Culture Technique, Academic Press, Inc.

Child: Individuality in Organisms, University of Chicago Press.

Cowdry: General Cytology, University of Chicago Press.

Dawson: Lambert's Histology, The Blakiston Co.

Elwyn and Strong: Bailey's Textbook of Histology, Williams and Wilkins Co.

Haden: Principles of Hematology, Lea & Febiger.

Maximow and Bloom: Histology, W. B. Saunders Co.

Nonidez and Windle: Histology, McGraw-Hill Book Co., Inc.

Sharp: An Introduction to Cytology, McGraw-Hill Book Co., Inc.

Sharp: Fundamentals of Cytology, McGraw-Hill Book Co., Inc.

Stiles: Handbook of Microscopic Characteristics of Tissues and Organs, The

Blakiston Co.
Weiner: Blood Groups and Transfusions, Charles C Thomas, Publisher.

Chapter 5

HOW CELLS DIVIDE-
INDIRECT CELL DIVISION OR MITOSIS
(ANIMAL AND PLANT)

One of the most interesting and important phenomena in living cells
is the process of mitosis in which the cells undergo a series of very com-
plicated stages of division. The so-called resting stage occurs between
two successive periods of mitosis. The cell during this stage is resting
only as far as actual cell division is concerned, but metabolism and other
cellular activities are progressing normally. It is during this stage that
young cells grow to their normal, mature size. Mitosis in animal and
plant cells occurs in much the same general way, although, as might be
expected, there are certain fundamental differences. Both of these
methods of mitosis will be described and contrasted.

A resting cell in animals may be characterized by the following: (1)
the nucleus is more or less spherical (Fig. 8) ; (2) irregular granules of
chromatin of various sizes and shapes are suspended in netlike fashion
within the nucleus; (3) a pair of granular centrioles is usually found
within the centrosome (central body) ; (4) the nuclear membrane and
the nucleolus are present; (5) the cytoplasm appears to be normal.

I. MITOSIS IN ANIMAL CELLS (Figs. 20 and 21)

The entire process of mitosis in animal cells is a continuous one but
for convenience is divided into four phases (Fig. 20): (1) prophase,
(2) metaphase, (3) anaphase, and (4) telophase.

A. Prophase (Gr. pro, before or first; phasis, appearance) (Fig. 20,
A-D)

In animal cells the divided centrosomes migrate away from each other
around the nuclear wall until finally they are at opposite sides of the
original nucleus. Each centrosome is surrounded by a halo of radiating,

How Cells Divide — Indirect Cell Division 63

Fig. 20. — Animal cell mitosis in which the chromosome number is assumed to
be 8. A, Prophase (beginning), with chromatin granules in netlike arrangement;
centrosome dividing and surrounded by the astral rays (asters) ; B, prophase
(early), with the chromatin consolidating and beginning to form a definite num-
ber of threadlike bodies; centrosomes moving farther from each other; spindle
figure (spindle) arising between them; C, prophase (late) with nuclear membrane
disappearing; each chromosome, under highest magnification, appearing as a
double structure because of its two parallel strands (chromatin elements) in con-
tact with each other; D, prophase (later), with nuclear membrane absent, cen-
trosomes at opposite ends of the cell, chromosomes distributed on the spindle;
E, metaphase, in which the chromosomes are arranged in equatorial plate, and
each chromosome splits lengthwise into two similar parts; F, anaphase (early),
in which half of each original chromosome moves ov'er the spindle toward o.p-
posite centrosomes; G, anaphase (later), in which the two sets of chromosomes
continue to travel over the spindle toward each centrosome and aster; H, telophase
(early), in which the chromosomes reach their respective centrosomes and there
gradually lose their distinctive chromosome characteristics; spindle and asters
disappearing; cytoplasm starts to divide; /, telophase (later), in which the cyto-
plasm is completely divided by the newly formed cell membrane ; nuclear wall and
entire nuclear contents reappear; centrosomes are already dividing in prepara-
tion for the next cycle of cell division. Each of the newly formed cells will now
grow to normal size and, sooner or later, will undergo the process of mitosis.

64 Introductory Biology

semlbroken lines of force, known as the aster, which emanate out into
the cytoplasm. The centrosomes also form a small, lightly staining set
of fibers, known as the spindle, between them as they migrate. This
spindle becomes more clearly defined in later stages. The asters and
spindle both stain lightly and may be called the achromatic (ak ro-
mat' ik) figure or amphiaster (Gr. a, without; chromatin, staining well).
The spindle eventually occupies the position where the original nucleus
has been.

P4i * _ T^

Fig. 21. — Photograph of a section of the embryo of a whiteftsh showing many
figures of the various stages of mitosis. Note particularly the chromosomes, spindle,
asters, etc. (Copyright by General Biological Supply House, Inc., Chicago.)

The nuclear membrane disappears about this time. The chromatin
granules within the original nucleus lose their netlike appearance and
form a specific number of bodies known as chromosomes. Each cell of a
specific species of animal or plant has a definite number of characteristic
chromosomes, provided the cell is normal. The chromosomes carry the
genes or determiners of heredity.

Finally, the chromosomes migrate in an orderly manner toward the
middle of the original nucleus and arrange themselves on the center of

How Cells Divide — Indirect Cell Division 65

the spindle^ known as the equatorial plate. The latter lies approximately
equidistant between the two centrosomes.

B. Metaphase (Gr. meta, between or after; phasis, appearance) (Fig. 20,
E)

This stage Is known as the equilibrium phase with the chromosomes
lined up across the middle of the equatorial region and balanced between
the two opposing forces of the opposite centrosomes. Each chromosome
now splits lengthwise into two equal parts. This Is very necessary If the
linear arrangements of the hereditary genes contained within the chromo-
somes are to be equally divided between the two future cells. The chromo-
somes which have each divided lengthwise now separate into two exactly
similar groups.

C. Anaphase (Gr. ana, up; phasis, appearance) (Fig. 20, F-G)

In this stage the two equal halves of each chromosome migrate from
the equatorial region along the spindle toward the opposite centrosomes.
Some of the newly formed chromosomes move slowly, while others go
rapidly. The part of the spindle to which the chromosomes are attached
is known as the attachment fibers of the spindle. The part of the spindle
over which the chromosomes have already traveled Is known as the used
spindle or interzonal connecting fibers which are visible between the two
groups of migrating chromosomes. In later anaphase stages the cell mem-
brane constricts, still later to divide the cell proper into two parts. In
certain cells, at least, a plate of small granules appears at the position of
the former equatorial plate. This plate becomes more pronounced and
may play a part In dividing the cell at that point (Fig. 20) .

D. Telophase (Gr. telos, end; phasis, appearance or aspect) (Fig. 20 H-I)

This stage Is a reconstruction stage. The entire cell now Is divided
at the equatorial plate of the spindle. Each half cell (daughter cell)
eventually becomes entire and normal with the characteristics of the
original parent cell. The nucleus again becomes spherical. The nuclear
membrane reappears. The asters disappear completely. The chromo-
somes change Into an Irregular network of chromatin granules again as
found in the original nucleus. The spindles disappear by the end of this
stage. Each daughter cell now grows to approximately the same size as
the original parent cell. Later, the process of mitosis will repeat Itself
in each of the two previously formed daughter cells.

66 Introductory Biology

II. MITOSIS IN THE CELLS OF FLOWERING PLANTS (Figs.

22 and 23)

Mitosis in the cells of the higher or flowering plants resembles the
process described for animals, except for minor differences in certain
stages (contrast Figs. 20 to 23).

A. Prophase (Fig. 22, 2-5)

In the so-called resting stage (nondividing), the nucleus is separated
from the surrounding cytoplasm by the nuclear membrane; the deeply
stained nuclear granules are in the form of chromatic strands. When a

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Fig. 22. — Mitosis in plants. 1, Before mitosis begins, strands of chromatin ap-
pear as a granular network within the nucleus. Prophase stages: 2-5, Network
tends to disappear and the chromatic strands thicken and shorten, eventually
forming a specific number of chromosomes; each chromosome consists of two
darkly stained chromatids more or less in contact with one another and which
will separate when each chromosome divides lengthwise later; in stage 5 the
spindle is forming and the nucleolus disappearing. Metaphase stage: 6, Chromo-
somes line up on equatorial plate in the middle of the spindle which has just
been completed. Anaphase stages: 7 , Each chromosome divides lengthwise into
two equal parts. Each new or daughter chromosome moves along the spindle
toward opposite ends of the cell. 8, Chromosomes at ends of the cell; cell wall
begins to form as minute swellings appear on each spindle fiber at the equatorial
plate. Telophase stages: 9, Chromosomes disintegrate again into a network of
chromatin granules; nuclear membrane appears; cell wall continues to develop;
spindle disappears. 10, Mitosis complete; cells similar to the original cell but
smaller; nuclei and cell wall complete. The two daughter cells will now grow
to normal size. (Copyright by General Biological Supply House, Inc., Chicago.)

How Cells Divide — Indirect Cell Division 67

nucleus is to divide, the chromatic strands thicken and shorten, finally
forming a definite number of strands, known as chromosomes. Each
chromosome contains two parallel chromatids which are more or less in
contact with each other. At times the chromatids are surrounded by
a lighter matrix; at other times the matrix is not visible.

The first visible signs of mitosis in a plant cell is the shortening and
thickening of the granular chromatic strands to form a specific number
of chromosomes (Fig. 22, 5, 6). The number of chromosomes in the
normal cells of any one species of plant is the same. In the onion, for
instance, there are sixteen chromosomes in each cell. In other plants
the number may be different but again specific for that particular plant.
The chromosomes gradually become thicker and shorter (Fig. 22, 6, 7) .
During this stage the nuclear membrane completely disappears, thus
permitting the chromosomes to move somewhat freely within the cell.
In the nuclear region appears a spindle-shaped group of fibers, the
spindle, extending from one end of the cell (cell pole) to the opposite
pole. No asters and no centrosomes are present in higher plants as they
are in animals.

B. Metaphase (Fig. 22, 6)

In this stage the chromosomes localize themselves on the middle or
equatorial plane of the spindle. The halves of each chromosome, formed
by longitudinal dimsion, now move along the spindle toward opposite
poles of the cell. One-half of each original chromosome with its con-
tents goes to each pole.

C. Anaphase (Fig. 22, 7, 8)

In this phase the newly formed chromosomes continue their migration
toward the poles where they will eventually be localized.

D. Telophase (Fig. 22, 9)

In this final stage the chromosomes are crowded together at their
respective poles. Each chromosome changes into a fine network of
chromatin material which somewhat resembles that of the original parent
cell. A new nuclear membrane is formed in each new cell. The remain-
ing nuclear contents are also formed. A partition called the cell plate
forms across the middle of the original cell. The cell plate splits into
two parallel plates between which is formed the new cell wall. The lat-
ter divides the original cell into two daughter cells. There is no indenta-

68 Introductory Biology

Fig. 23. — Various stages of mitosis as shown by photographs of sections of
the root tip of the onion {Allium). A, Low power; B, high power. (Copyright
by General Biological Supply House, Inc., Chicago.)

How Cells Divide — Indirect Cell Division 69

Fig. 23 (Cont'd). — For legend, see opposite page.

70 Introductory Biology

tion of the cell wall as in the mitosis of animal cells (contrast with Fig.
20). The two daughter cells continue to reform their missing parts and
increase in size (Fig. 22, 10).

IMPORTANT FACTS REGARDING MITOSIS

In the process of mitosis new cells always arise from "parent" cells.
The mechanical aspects of mitosis are remarkable, complicated, and at
present not understood completely. The nucleus undergoes the more
visible changes during mitosis. These changes are in all probability
both chemical and physical. Undoubtedly the surrounding cytoplasm
also plays an important role in mitosis, although the exact nature of it
is at present unknown. At certain stages the nucleoplasm and cytoplasm
are not separated by the usual nuclear membrane.

During the entire process of mitosis, there is a continuity of chromatin
in some form or other from the original parent cell to the two daughter
cells. The chromatin is divided accurately and equally between the
newly formed cells. Chromatin transmits hereditary genes from one
cell to others, and also from the parents of one generation to the off-
spring of the next or following generations. In this way chromatin ma-
terials are responsible for the inheritance of certain characteristics which
are passed from one cell to the next and at the proper time will deter-
mine that particular characteristic in the living organism.

The first signs of mitosis (a) in animal cells are the division and
migration of the centrosomes and (b) in plant cells, the formation of
chromosomes from the strands of chromatin granules. Later, in the
telophase stages, the cell membrane of animal cells indents to form the
cell membrane between the daughter cells; the cell wall between daugh-
ter cells of plants is formed by an accumulation of granules along the
equatorial plate without an indentation of the original cell wall (Figs.
20 and 22).

Each species of plant or animal has a definite number of chromosomes
which appear when the cells of that particular organism divide. Most
animals and plants have an even number of chromosomes (occur in
pairs), although a few species have an odd number in their cells. (For
a more complete table showing the numbers of chromosomes in cells,
see the chapter on Heredity.)

Mitosis plays an important role in growth. Living organisms grow
either by an increase in the number of cells (by mitosis) or by an in-
crease in the size of cells already present. In many cases a combination
of these two methods results in the growth of the organism. The forma-

How Cells Divide — Indirect Cell Division 71

tion of the various tissues and organs in an embryo is associated with
properly regulated and controlled mitosis. The rate of cell division is
affected by the age of the organism, usually being more rapid in the
younger and slower in the older.

Mitosis assists in the repair of tissues and restoration of lost parts of
living organisms. Certain tissues are repaired rather easily, while others
are repaired with difficulty or not at all. It is unknown what stimulates
the cells to repair or what stops them at the proper time so that there is
no overproduction of cells.

Certain abnormalities and diseases of animals and plants are due to
abnormal cell divisions. The causes of these abnormal mitoses are prob-
ably internal or external influences which are not well understood at this
time. This type of mitosis is the cause of such conditions as extra toes
and fingers and certain kinds of cancerous growths. One way to attack
the diseases of the latter type is to find out what causes the cells to be-
have abnormally and divide uncontrollably rather than attempt to treat
such diseases after they have started.

Mitosis, at least in certain organisms, shows a marked tendency to
occur at certain hours of the day or night. In the onion root tip the
maximum number of cell divisions occurs around 1 and 11 p.m.; the
minimum number of cell divisions, around 7 a.m. and 3 p.m. In the
root tips of the pea (Pisum) there are three cell division maxima, 1 p.m.,
5 p.m., and 5 a.m., and three cell division minima, 11 a.m., 3 p.m., and
9 P.M. These were described by Friesner in 1919 and 1920.

The duration of the various phases of mitosis has been determined for
a few species. The accompanying table summarizes the results for vari-
ous temperatures. These data are based on the work of Laughlin in
1919.

Duration of Various Phases of Mitosis in Allium

temper-
ature

minutes required

CELL studied

pro-
phase

meta-
phase

ana-
phase

telo-
phase

TOTAL

TIME

Root tip of onion
(Allium)

10° C.

20° C.
30° C.

88.0

74.0
55.0

1.4

1.0
0.3

3.0

2.5
1.0

4.6

4.0
1.5

97.0

81.0
57.8

QUESTIONS AND TOPICS

1. Define mitosis in your own words. What happens in each stage?

2. Is the process of mitosis continuous or does it stop at certain intervals?

3. How long does it take an average" cell to go through each of its stages of
mitosis? What factors might influence this rate of cell division?

72 Introductory Biology

4. Why is it so essential that the individual chromosomes divide lengthwise dur-
ing the metaphase stage?

5. When each chromosome divides lengthwise, what causes each resulting half
to migrate toward opposite ends of the cell?

6. What are the controlling forces which start and stop the process of mitosis?

7. When injured tissues repair themselves by mitosis, what starts and stops the
process? What is happening when injuries fail to repair?

8. What is the probable relationship between mitosis and cancer? Suggest a
method of preventing this disease.

9. Why do we study young tissues in mitosis? What, in general, is the rate of
mitosis in older tissues?

10. What is the relationship between mitosis and heredity?

11. List the chief differences between the process of mitosis in animals and plants.

SELECTED REFERENCES i

Schrader: Mitosis: The Movements of Chromosomes in Cell Division, Columbia

University Press.
White: The Chromosomes, Chemical Publishing Co., Inc.

Chapter 6

PROPERTIES AND ACTIVITIES OF
LIVING PROTOPLASM

L PHYSICAL PROPERTIES OF PROTOPLASM

The "living" substance of plants and animals is known as protoplasm
(pro' to plazm) (Gr. protos, first; plasma, moulded). We consider an
organism to be alive when certain activities within the protoplasm result
in certain specific, discernible properties and reactions or behaviors which
we have decided are characteristic of living beings. Likewise, when
these activities within the protoplasm cease, with the cessation of certain
reactions and properties, we consider the organism to be dead. Life then
might be considered in terms of relative activities of the protoplasm of
which living organisms are composed. It has even been theorized that
life and death may possibly be relative phenomena. Regardless of this,
we know that all things, both nonliving and living, are composed of
matter. Matter might be defined as any solid, liquid, or gas which
occupies space. From this viewpoint the matter which composes a liv-
ing organism is the same matter which that dead organism contains
except that it is probably rearranged and thus has taken on different
properties and activities.

Possibly a beginning student in biology may believe that he will be
able to see "life" if he merely views living protoplasm highly magnified
with a microscope. So far, scientists with the best of equipment have
been unable to do so. What have they seen? They have merely ob-
served certain characteristics displayed by that living protoplasm, as a
consequence of which they conclude that such protoplasm is alive. Just
because scientists cannot see "life" or cannot secure the ultimate answer
as to what life is is no justifiable reason for not studying living protoplasm
to get as much reliable information as possible concerning it. A scientist
takes things as they are and as he finds them, and by careful observations
and experiments, he secures additional data which may take him only a

74 Introductory Biology

small step in advance. Progress is a series of such consecutive, progres-
sive advances. What one scientist discovers may be the stepping-stone
for the discoveries of other scientists.

What are some of the physical properties of protoplasm when viewed
with high magnifications of the microscope? Protoplasm usually ap-
pears to be a colorless, odorless, jellylike material, with granules and
globules of various shapes and sizes, which is constantly varying in ap-
pearance and consistency. Many colorless structures are rendered more
visible by the application of various dyes which stain certain parts and
not others. Protoplasm is slightly heavier than water because of the
additional substances of which it is composed. It is a somewhat viscous
semifluid which under certain conditions may display internal, flowing
("streaming'') movement. Protoplasm diflfers in consistency at different
times and also in appearance. The same protoplasm may appear quite
different when studied by different methods. When the inherent varia-
bilities of protoplasm and the different methods of studying it are taken
into consideration, we may have at least partial explanations for the
differences of opinion among the various investigators as to the physical
structure of protoplasm.

Theories Regarding Physical Structure

Some of the theories which have been proposed from time to time re-
garding the physical structure of protoplasm are (1) granular (gran' u-
lar) (L. granum, grain), in which aggregates of minute granules are
distributed in a liquid medium (Fig. 24, A); (2) fibrillar (fi -bril' ar)
(L. fibrilla, small fiber), in which small fibers are present in a liquid
medium (Fig. 24, B) ; (3) reticular (re -tik' u lar) (L. reticulum, little
net), in which the fibers appear as a network embedded in a liquid
material (Fig. 24, C) ; (4) alveolar (al'veolar) (L. alveolus, small pit,
or hollow), in which a foamlike mass of minute, spherical bubbles are
embedded in a more viscid medium (Fig. 24, D) ; (5) colloidal (kol-
oid' al) (Gr. kolla, glue; eidos, form), in which the many complex sub-
stances of protoplasm are present in a finely divided, or colloidal condi-
tion (Fig. 24, £).

Which of these theories is correct? Or, are they all correct in part,
depending upon the method of investigation used and the particular
characteristic displayed by the specific protoplasm being studied at a
certain time? The chemical and physical changes which are constantly
going on in protoplasm probably explain the different appearances of
the different protoplasms and even the variations in appearance in the
same protoplasm from time to time.

Properties and Activities of Living Protoplasm 75

Fig. 24. — Diagram to illustrate different theories of the physical structure of
protoplasm. A, Granular theory; B, fibrillar or filar theory; C, reticular theory;
D, alveolar theory; E, colloidal theory.

Colloidal Systems

The results of recent scientific investigations suggest that the chemical
constituents of protoplasm are in a finely divided, colloidal state, thus
forming a complex colloidal system. A colloid (Gr. kolla, glue) is a
mixture of invisible, submicroscopic particles of comparatively large size
(usually larger than molecules) which are suspended in a liquid medium.
Colloids often have a sticky, gluelike property; hence the name. The
sizes of colloidal particles may vary from one-millionth (0.000,001) to
one-ten-thousandth (0.0001) of a millimeter (mm.) in diameter. Col-
loids do not diffuse through a parchment or similar membrane, while
crystalloid solutions, like those of sugar or salt, do. When a colloid is
evaporated, it leaves a formless mass, while a crystalloid solution leaves
crystals of definite form. Possibly a better understanding of a colloid
can be gained by stating that such familiar materials as milk, ink, e^g
white, gelatin in water, etc., are colloids. In the language of the chemist,
the particles (solid, liquid, or gas) of a colloid and the medium (solid.

76 Introductory Biology

liquid, or gas) in which the particles exist in a colloidal condition are
known as phases. The colloidal particles are called the dispersed phase,
and the medium in which they are dispersed is called the dispersion
medium. Hence we have a variety of colloidal systems; some of the
more common are given in the accompanying table.

DISPERSED
PHASE

DISPERSION
MEDIUM

EXAMPLES

Gas

Liquid

Foams or froths

Liquid

Gas

Fog or mist (water droplets in air)

Liquid

Emulsions (oil in water; butterfat and milk
which have been "homogenized")

Solid

Gas

Smoke (carbon particles in air)

Solid

Liquid

Ferric oxide in water; colloidal gold in water

Some of the properties and many important reactions of matter which
is in a colloidal state depend upon the great surface displayed by the
enormous numbers of minute colloidal particles which constitute that
particular matter. Possibly the great amount of surface exposed by small
particles may be illustrated as follows: A cube of matter having edges
one centimeter long has an exposed surface of 6 sq. cm, (six surfaces,
each 1 sq. cm. in area). If this cube of matter were divided into simi-
lar, smaller cubes, each having edges only 0.01 cm. long, the total num-
ber of small cubes would be 1,000,000. Each small cube has a surface
area of 0.0006 sq. cm., and the total surface area of all the small cubes
will be 600 sq. cm., or an area one hundred times greater than the origi-
nal large cube. However, if the original large cube were divided into
extremely minute cubes, each with a size of an average colloidal particle
(0.000,001 cm. diameter), there would result one million billion cubes
(each having edges 0.000,001 cm. long), and the total surface areas of
all the colloidal-sized cubes would be 6,000,000 sq. cm., or one million
times as great as the original cube. These 6,000,000 sq. cm. are the
equivalent of over 6,500 square feet, or a city lot 65 by 100 feet. It
should be recalled that the original cube was only 1 cm. square; however,
there is an enormous surface exposure when even a small block of matter
is properly divided into particles of colloidal size.

Protoplasm may exist as a liquid sol (L. solvo, melt) which flows or
as a more solid gel (L. gelu, solid). Under certain conditions it may
change from the sol to the gel state, or from the gel to the sol, or back
again, depending on the relative distribution of the contained colloidal
particles. If particles are more or less uniformly distributed in a liquid
medium, the liquid flows easily (sol state), but if the particles are ar-
ranged in a network which contains the liquid, it would not flow (semi-

Properties and Activities of Living Protoplasm 77

solid, gel state). Certain materials which are considered to be nonliv-
ing, such as gelatin, etc., form colloidal suspensions in water and exhibit
the fluid, sol state when warm and the semisolid gel state when cooler.
These states are reversible, as they may be in living protoplasm.

When a strong beam of light is passed through a colloid, the small
colloidal particles suspended in the liquid reflect the light, and the path
of the light appears as a visible cone known as TyndalVs cone, named
for John Tyndall, the British physicist (1820-1893) who discovered it.
In this manner the same effect is observed when light passes through
fog or smoke. However, if the same strong beam of light is passed
through a true solution of a substance, no such cone is visible.

If the proper colloidal particles suspended in a liquid are viewed
through a microscope, the motion of the light reflected from the colloidal
particles reveals that the latter are moving. This unordered movement
(in all directions, back and forth) is called Brownian movement because
it was first observed in 1827 by the Scotch botanist Robert Brown.

Molecules in the interior of a colloidal particle are attracted equally
in all directions by other surrounding molecules, while those on the sur-
face of a colloidal particle are subject to unequal forces of attraction
(similar to the unequal attraction of molecules on the surface of a
liquid). Because colloidal particles are so small and numerous, they
possess a great total surface area, so that there are great numbers of
molecules on the surface of each particle. As a result, these surface
molecules are able to attract and hold other molecules, atoms, or ions
through a process called adsorption (L. ad, to; sorhere, to draw in).
This property plays an important role in many phenomena in the non-
living and living worlds.

When a colloid is placed between two electrodes of a cell with a rela-
tively high voltage, the colloidal particles migrate either toward the posi-
tive or negative electrodes, depending^ on the specific colloid. Colloidal
metals (and metal sulfides) tend to migrate toward the positive electrode;
hence they must bear a negative electrical charge. Most colloidal hy-
droxides of metals (containing the hydroxyl OH) move toward the nega-
tive electrode; hence they bear a positive charge. The electrical charge
borne by colloidal particles is due to the somewhat selective adsorption
of positive or negative ions from the surrounding medium, the specific
type of ion adsorbed depending on the particular colloid. Ions (Gr.
ion, going) are atoms, or groups of atoms, with either positive or nega-
tive electrical charges. Colloidal particles bearing electrical charges may
explain some of the electrical phenomena of nonliving as well as living
substances.

78 Introductory Biology

Certain colloids, known as emulsoids (L. emulgere, to drain), are
less selective regarding their adsorption of ions and tend to adsorb mole-
cules of the medium in which they are dispersed (dispersion medium).
As these colloidal particles adsorb these molecules of the dispersion
medium, they may swell until the entire colloidal system becomes more
and more viscous, or even semisolid, as in jellies, gelatin desserts, etc. The
swelling of dried fruit in water is another example.

In general, colloids are of great importance because all vital processes
of animals and plants are associated with colloidal materials. The liv-
ing protoplasm of plants and animals is colloidal in character. Many
foods of animals are colloids. The growth of plants, the germinating of
seeds, and many similar phenomena are associated with colloids and
their properties.

Matter, Atoms, Molecules, and Elements

Matter, of which all materials are composed, is made of extremely
small, microscopically invisible molecules (L. molecula, little mass) with
intermolecular spaces between them. A molecule is composed of the union
of two or more atoms and is the smallest unit of matter capable of a
separate, distinct physical existence. A molecule of free oxygen consists
of two atoms (Figs. 25 and 26). A molecule of water consists of two
atoms of hydrogen and one atom of oxygen; hence the molecular formula
for water is H2O (Fig. 27). An atom (Gr. atomos, indivisible) is the
smallest particle of an element capable of taking part in a chemical reac-
tion. There are as many different kinds of atoms as there are elements
(elementary substances), and vice versa. An element is composed of
atoms having the same atomic number, and, by ordinary means, cannot
be built up from simpler or decomposed into simpler substances. There
are over ninety definitely known basic elements, with claims for the dis-
covery of a few more. The chemical elements are known by symbols
which usually are the first or first few letters of the name of the element.
For example, the symbol for hydrogen is H; for oxygen, O; for carbon,
C; for magnesium, Mg.; etc. In some cases the symbol is derived from
the Latin name of the element. For example, the Latin name for iron
is ferrum, and the symbol is Fc; the Latin name for potassium is kalium,
and the symbol is K; the name for sodium is natrium, and the symbol is
Na.; etc. All the known elements are grouped in a table (periodic ar-
rangement of the elements based on their atomic structure) and each
element is given a specific number. Hydrogen has the atomic number 1 ;
helium, 2; carbon, 6; nitrogen, 7; oxygen, 8; magnesium, 12; mercury,
80; uranium, 92; etc.

Properties and Activities of Living Protoplasm 79

Molecules are too small to be visible with the highest magnification of
an ordinary microscope which uses Hght rays, because the smallest par-
ticle visible with such a light (optical) microscope must have a diameter
of 150 millimicrons (1 millimicron is one-millionth of a millimeter and
is abbreviated m/x). The largest molecules probably have a diameter
of approximately only 1 millimicron. The term millimicron is used
here instead of millimeter or centimeter because the latter are too
large for measuring and recording such minute objects. However, an
electron microscope which uses beams of electrons instead of beams of
light can be used to photograph the larger molecules even though they
do not produce an image which can be seen with the eye.

HYDROGEN (h)

cakbon(c)

NITROGEN (n)
7

OXYGEN (O)
8

MAGNESIUM (Wq)

?HOSPHORUS(P)
15

SULFUR (s)

POTASSIUM (k)
19

Fig. 25. — Diagrams representing the structure of the. atoms of certain of the
elements which may be present in protoplasm. The atomic number, which is the
same as the number of nuclear protons, is given below each name. The symbols
in parentheses follow each name. P, proton (+ electrical charge) ; N, neutron
(electrically neutral); small circle with a dash, an electron (- electrical charge).
The inner circle represents the nucleus of the atom; the outer rings represent
one or more orbits ("shells") of the electrons.

Molecules are constantly in rapid motion, moving about in their inter-
molecular spaces. Their speed depends upon certain conditions and
varies over wide ranges, but an average speed is thought to be approxi-
mately 2 million million times their own diameter per second (about
twenty miles per minute) in such a substance as a gas. No matter how
sparsely distributed, molecules cannot travel so fast and so far without
colliding with other molecules also in motion. This energy of molecular
movement is an example of kinetic energy (Gr. kinein, to move). The
intermolecular space between molecules in a gas is greater than the space

80 Introductory Biology

between molecules in a liquid or solid. In the atmosphere the several
kinds of molecules must move about one thousand times their own
diameters before colliding with other molecules. The motion of mole-
cules in a gas is greater than in a solid because in the latter they merely
vibrate back and forth because of the mutual attraction between adja-
cent molecules and probably the closer association of molecules.

If a single molecule could possibly be completely isolated and remain
so, its kinetic energy would remain constant. However, the kinetic
energy of molecules is influenced by the kinetic energy of surrounding
molecules. When molecules increase their speed, they exert greater pres-
sure on other molecules, so that the average distances between them is
increased. Consequently, when heat is applied to certain substances, the
molecules increase their speeds and the substance expands. We measure
the amount of kinetic energy in terms of temperature. Likewise, con-
traction usually is the consequence of reduced molecular speed. If
molecules of two kinds are placed together, the two kinds tend to mix
with each other through the process called diffusion (L. diff under e, to
pour). If a drop of perfume volatilizes (becomes a gas) in a room, its
molecules will move and mix with the various molecules of the atmos-
phere and the odor will diflfuse so as to be detectable some distance away.
Our nose is affected by the molecules of the perfume so we detect the
odor. The odor is not detected immediately because it takes some time
for the perfume molecules to move toward us and the v-arious molecules
of the atmosphere offer resistance (because of collisions). The continual
bombardment of an enclosing wall or membrane by molecules exerts a
pressure which varies with the number of molecules, their movements,
temperature, etc. Likewise, a chemical substance will diffuse through
water in which it is placed. These phenomena of diffusion through gases,
liquids, and solids are common in the nonliving and living worlds.

An atom is the smallest unit particle of an element capable of taking
part in a chemical reaction. There are as many different kinds of atoms
as there are elements (elementary substances), and vice versa. These
submicroscopic atoms are invisible. As a result of recent scientific studies
it is thought that atoms consist of smaller units which are arranged some-
what like a miniature solar system, with much of the atom supposedly
"empty" space. The units which compose atoms are:

1. A large central atomic nucleus consisting of particles smaller but
heavier than the electrons. These nuclear particles are called (a) pro-
tons, which are charged with positive electricity, and (b) neutrons, which
are uncharged electrically (neutral). Each nuclear proton has the power

Properties and Activities of Living Protoplasm 81

to hold one of the whirling electrons in its orbit. Thus, the number of
electrons is determined by the number of positive protons in the nucleus.
The atom as a whole is electrically neutral (neither positive nor nega-
tive). The nucleus of the oxygen atom contains eight positively charged
protons which hold the eight negatively charged electrons in the two
orbits. The nuclear protons and neutrons are held together by intra-
atomic forces (Figs. 25 to 27).

HYDROGEN MOLECULE

OXYGEN MOLECULE

Fig. 26. — Diagram representing the structures of the molecules of the gases
hydrogen and oxygen. In the case of hydrogen, the mutual utilization of one
electron from each atom (total, two electrons) is involved in the combination. In
oxygen, two electrons from each atom (total, four electrons) are involved in the
combination. P, proton (+ electrical charge) ; A''^ neutron (electrically neutral) ;
black circle with dash, an electron (- electrical charge). The inner circle repre-
sents the nucleus of the atom; the outer rings represent one or more orbits
("shells") of the electrons.

2. A series of negatively charged electrons ("planetary" electrons)
which revolve in one or more concentric orbits ("shells") about the nu-
cleus and whirling at inconceivable speed. Modern suggestions state
that electrons may be "whirlpools of energy." Depending on the kind
of atom, there may be from one to seven concentrically arranged orbits,
and each orbit has a maximum of electrons which it can accommodate
(although sometimes an orbit may not have its maximum number). In
general, the inner orbit must be filled to capacity before a second appears.
The maximum numbers of electrons in the various orbits are suggested
below :

ORBIT

First

Second

Third

Fourth

Fifth

Sixth

Seventh

number of electrons

(maximum)

8
18
32
18
12

82 Introductory Biology

The chemical and physical behaviors of the atom are determined
largely by the number and arrangements of the orbital electrons. It is
common knowledge that proper bombardment of certain atoms (with
neutral neutrons, protons, etc.) results in the release of tremendous
amounts of atomic energy by the process of nuclear fission. For example,
the energy released by the fission of one pound of U^^^ (a fissionable
isotope of uranium) is roughly equivalent to that secured from burning
10,000 tons of coal. It is unknown how, or if, comparable energy re-
leases occur in phenomena outside of the artificially conducted experi-
ments of recent years.

Each kind of element has an atomic number which is specific for that
kind of element, but some of these same elements have been discovered
to have different atomic weights and consequently are known as isotopes
fi' so tope) (Gr. isos, equal; topos, place). Isotopes having the same
atomic number are identical as far as their chemical properties and their
extranuclear structures are concerned, but they differ in their atomic
weights and with regard to the structure of the atomic nucleus (number
of neutrons).

Artificially produced radioactive isotopes are extremely valuable in
the study of certain biologic problems. The use of such radioactive
isotopes as "tracers" is valuable because they emit certain radiations
whose presence can be detected in various parts of an organism by sen-
sitive Geiger counters. Hence, the rate of absorption of iodine by the
thyroid gland has been determined by the use of radioactive iodine, and
this has assisted in the treatment of goiter. Radioactive phosphorus
has been traced to the stems and certain parts of the leaves of tomato
plants, while radioactive zinc concentrates in tomato seeds. The many
uses of radioactive isotopes will be of great value in the study of animal
and plant metabolism, diagnosis and treatment of certain diseases, etc.

Atoms with less than one-half of the maximum number of electrons
in the outer orbit mav under certain conditions even lose those which
they have, while atoms with more than one-half the maximum number
of electrons in the outer orbit may add electrons until the outer orbit
is filled to its maximum. The additions or losses of electrons (negatively
charged) in the orbits docs not affect the structure of the atomic nucleus,
but the latter can no longer be electrically neutral after such changes.
Normally, the positively charged protons and the negatively charged
electrons are balanced. Hence, the loss of electrons makes the atom
positively charged and the addition of electrons makes the atom nega-

Properties and Activities of Living Protoplasm 83

tively charged. Such a charged atom is called an ion. Atoms which
have gained electrons have a negative electrical charge and are called
anions; atoms which have lost electrons have a positive electrical charge
and are called cations. Since like charges repel and unlike charges
attract each other, we find that anions and cations combine. The amount
of combining which atoms can undergo is determined by the number of
electrons in the outer orbit at the beginning and the number that can
be gained or lost. Hence, hydrogen, having only one electron, tends to
lose it, becoming a (positive) cation. Oxygen, with six electrons in its
outer orbit, tends to gain two, becoming a (negative) anion. Thus two
atoms of hydrogen and one atom of oxygen combine to form a molecule
of water, since hydrogen loses only one electron and oxygen gains two
electrons (Fig. 27).

HYDROGEN
ATOM

OXYGEN
ATOM

HYDROGEN
ATOM

WATER
MOLECULE

Fig. 27. — Diagrams representing the formation of a molecule of water from two
atoms of hydrogen and one atom of oxygen. The union is represented by the shar-
ing of electrons in the outer orbits of the atoms concerned. P, proton (+ electrical
charge; A^^ neutron (electrically neutral) ; black circle with dash, an electron
(- electrical charge). The inner circle represents the nucleus of the atom; the
outer rings represent one or more orbits ("shells") of the electrons.

Molecules may vary in complexity from the simple water molecule to
the extremely complex long carbon "chains" and "rings" present in
many living, organic materials. Molecules may contain only one kind of
atom (such as O2) or they may contain atoms of two or more different
kinds (such as CO2) ; in the latter case they form a compound. Atoms
are held together either by the attraction of opposite ions or by the shar-
ing of an electron by two different atoms.

Many substances in living organisms are soluble in the large quantity of
water present in the protoplasm, and in solution many of them dissociate
to form ions. Hence, a molecule of common salt, sodium chloride
(NaCl), dissociates into (1) a positive sodium ion (Na^) while losing
its single outer electron and (2) a negative chlorine ion (CI'), gaining
one extra outer electron. A substance which dissociates to form ions is

84 Introductory Biology

called an electrolyte (e -lek' trolite) (Gr. elektron, amber; lysis, loosing)
because of its ability to conduct electric currents. Acids, bases (alkalis),
and salts dissociate in solution. The acids produce the characteristic
hydrogen ions (H^), alkalis produce the characteristic hydroxyl ions
(OH~). The production of ions from salts is of great importance, as is
the nearly equal production of both hydrogen and hydroxyl ions (near
neutrality) necessary in living protoplasm. The production of ions is of
importance in the conduction of electric currents associated with certain
living phenomena as well as in forming and maintaining the proper
acid-base relationship for the various metabolic activities of living proto-
plasm.

Other physical and chemical phenomena of living organisms are con-
sidered in a later chapter.

II. CHEMICAL COMPOSITION OF PROTOPLASM

Attempts to analyze living protoplasm chemically probably cause im-
portant changes in it. Consequently, the results of the chemical analy-
sis may or may not be the same as for living protoplasm. The con-
stituents are known, but we do not know how the complex combinations
of them actually form the basis for life. Protoplasm contains only com-
mon, inexpensive elements. The total value of all the chemicals present
in the protoplasm of the human body is approximately one dollar.
There are no known chemical elements which are present only in proto-
plasm; all of the elements which comprise it are common in the earth,
water, or atmosphere. Of the four most abundant elements in proto-
plasm, free oxygen is common in the atmosphere, most of the carbon
occurs in the bodies of living or dead organisms or their products, hydro-
gen is usually combined with oxygen to form water, and most of the
free nitrogen occurs in the atmosphere, although proteins contain nitro-
gen in their makeup. Even though living protoplasm consists of a few
common, inexpensive elements, they are combined in certain proportions
into compounds which are associated in some unique way so as to help
form the chemical basis of life.

A compound is a chemical union of two or more diflferent elements
which are in definite proportions, and the properties of the compound
are different from those of its constituent elements. In other words, in
a compound all its molecules are composed of the same proportion of
atoms which are combined in a definite way. For example, carbon
dioxide (CO2) and carbon monoxide (CO) are both compounds, but

Properties and Activities of Living Protoplasm 85

the proportion of the atoms difTers. The physiologic effects are differ-
ent also — carbon dioxide stimulates breathing, while carbon monoxide
stops it. Compounds may be divided into organic and inorganic. Or-
ganic compounds are commonly referred to as those which contain car-
bon (with the exception of the carbonates, containing -CO3), while
inorganic compounds are those which have their origin in, or are asso-
ciated with, the mineral world, such as rocks, ores, soils, the constitu-
ents of the natural atmosphere, etc. There are approximately 300,000
carbon-containing compounds known. Examples of organic compounds
are marsh gas or methane (CH4), ethyl alcohol (C2H5OH), and a sugar
(G12H22O11), while examples of inorganic compounds are water (H2O),
table salt (NaCl), sulfuric acid (H2SO4), and lime or calcium carbonate
(CaCOs). A mixture is composed of two or more substances which are
not combined firmly (each of which retains its own properties) and need
not be in any definite proportion. The composition of a mixture may
vary, and the constituents usually may be present in different propor-
tions in different mixtures. For example, the atmosphere is a mixture of
such gases as hydrogen, nitrogen, oxygen, etc., which may vary in their
proportions in different atmospheres.

The following elements (with their symbols) are found in average
protoplasm (those essential to life being indicated by *) :

Oxygen (O) (76.0%)*

Carbon (C) (10.5%)* I qq^ f ,u ■ u.

Hydrogen (H) (10.0%)* f 99% of the weight

Nitrogen (N) (2.5%)* j

Phosphorus (P) (0.3%)*
Potassium (K) (0.3%)*
Sulfur (S) (0.2%)*

Magnesium (Mg) (0.02%)* 1 About 1% of the weight

Iron (Fe) (0.01%)* f ^^^^"^ ^ ^"^ °^ *^^ "^^^^^^

Chlorine (CI) (0.10%) ^

Sodium (Na) (0.05%)

Calcium (Ca) (0.02%) J

Chlorine and sodium do not seem to be essential for most plants, while
calcium is unessential for certain lower animals. In addition to those
listed, certain types of protoplasm at times are found to contain other
elements in small amounts.

In general, the elements listed above are not free in the protoplasm
but are combined as compounds such as the following: glucides (in-
cluding carbohydrates), lipids (including fats), proteins, inorganic salts,
water, vitamins, and enzymes.

86 Introductory Biology

A. Glucides (Including Carbohydrates)

The so-called glucides (glu' sid) (Gr. glykys, sweet) are a large group
of organic compounds which include the commonly known carbohydrates
(kar bo -hy' drate) (L. carho, carbon, coal; Gr. hydor, water) . The term
carbohydrates as used here implies "hydrates of carbon," in which the
ratio of hydrogen to oxygen is 2:1. The simplest carbohydrates in proto-
plasm are the simple sugars with the formula CeHioOe. Carbohydrates
are usually simpler in chemical structure than proteins but they never-
theless have a wide range of complexity among themselves. Like pro-
teins, the more complex carbohydrates may be split into simpler materials
by the action of enzymes. This happens when they are acted upon by
the enzymes of certain digestive juices. Through the proper chemical
action certain carbohydrates may be converted into fats, which explains
the proper selection of foods during prescribed cases of dieting. Carbo-
hydrates furnish elements which may assist in the building of protoplasm,
but their chief role is a readily available supply of heat and energy.
When glucose is oxidized (oxygen united with it), it yields water, carbon
dioxide, and energy; the latter, which originally held the sugar together,
now is available for use :

GLUCOSE OXYGEN WATER CARBON DIOXIDE

CeHaoOe + 6O2 "> 6H2O + 6GO2 + ENERGY

Of the simple sugars, glucose (dextrose) is the only one present in
any quantity in the body for fuel purposes. Carbohydrates are stored
in animals as glycogen (animal starch) because the large molecules can-
not dialyze through the semipermeable cell membranes. Glycogen is
stored in the liver and muscles where it is converted as needed into
usable glucose, which has the following formula :

I
G=0

1
H— C— O— H

1
H— O— G— H

1
H— G— O— H

I
H— G— O— H

I
H

Glucose (A Simple Sugar)

Properties and Activities of Living Protoplasm 87

Glucides may be classified according to their complexity. The follow-
ing examples with their formulas will illustrate:

1. Monosaccharides (mono -sak'' a rid) (Gr. monos, one; sakchar,
sugar), which contain one sugar group: glucose (dextrose or grape
sugar), CsHioOfi.

2. Disaccharides (Gr. di, two), which contain two simple monosac-
charide sugar molecules: maltose (malt sugar), C12H22O11, and sucrose
(cane sugar or beet sugar), C12H22O11.

3. Polysaccharides (Gr. poly, many), which contain several mono-
saccharides united: starch (CeHioOs)!! (in this case n is a rather large
number), cellulose, found in many plants (C6Hio05)x5 glycogen, or ani-
mal starch (CsHioOsIx (in these cases x is a larger number than the n
of starch) .

B. Lipids (Including Fats)

The group of organic compounds known as lipids (lip' id) (Gr. lipos,
fat) includes the true fats and a number of related fatlike substances
which have properties similar to fats but contain things in addition to
the fatty acids. Fats contain the same chemical elements as found in
carbohydrates but possess much less oxygen in proportion to the carbon
and hydrogen. Each molecule of a true fat is composed of one molecule
of glycerol (glycerine) and three molecules of some fatty acid, such as
stearic acid, palmitic acid, or oleic acid, etc. All fats contain glycerol
but differ in the kind of fatty acid combined with the glycerol. One
molecule of glycerol (C3H5[OH]3) plus three molecules of stearic acid
(CigHssOo) produces a common fat (in beef tallow) known as tristearin
(C57H110O6) . In the process, 3(H20) is given off.

Fats contain twice as much heat energy as carbohydrates or proteins.
This accounts for their common use as foods in cold weather. One
gram of protein produces about 4 calories of heat and 1 gram of carbo-
hydrate, about 4 calories, while 1 gram of fat yields about 9 calories.
A calorie is a unit of heat measurement and is the equivalent of the
amount of heat required to raise the temperature of 1 gram of water
(1 c.c.) 1° C.

Fats are used in the body in the construction of the plasma membrane
around the cells and the medullary (myelin) sheath around certain
nerve fibers. Fats are stored in various places as reserve supplies of
energy. Fats are stored under the skin to reduce body heat loss and to
round out the cavities between the tissues. Fats placed around such

88 Introductory Biology

organs as the kidneys help to hold them in place. Fats are not utilized
as a source of body energy as readily as are the carbohydrates. Fats
can be formed from carbohydrates by the body, and, to a limited extent,
fats can be converted into usable glucose. Fats of the animal body are
derived from the carbohydrates and fats consumed as foods. Fats occur
in butter, cream, oils, meats, seeds, and nuts.

C. Proteins

Proteins (pro'tein) (Gr. protos, first) are complex organic com-
pounds which contain carbon, hydrogen, oxygen, and nitrogen, and
usually sulfur and phosphorus. Proteins are present in all protoplasm and
are characterized by the element nitrogen. It is thought that there are
specific proteins for each species of living organism and that each living
organism probably has several specific and unique types. The theory of
species specificity states that due to the constituent proteins, the proto-
plasm of each species of living organism is specific for that species and
differs less slightly from that of related species and markedly from that
of more distantly, or unrelated, species. Studies along these lines have
substantiated the evidence of evolutionary relationships between certain
organisms which has been derived from other facts.

Proteins are the most varied and complex of all the constituents of
protoplasm, each molecule being made of hundreds of atoms. Proteins
contain such elements as:

Carbon

(C)

Approximately

50%

Oxygen

(O)

Approximately

25%

Nitrogen

(N)

Approximately

16%

Hydrogen

(H)

Approximately

*Sulfur

(S)

Approximately

0.3-2%

^Phosphorus

(P)

Approximately

0.0-0.8%

The units of which proteins are made are amino acids, which contain
an amino group (NH2) and an acid (carboxyl) group (COOH). There
are over thirty different amino acids known. The great variety of pro-
teins is made possible by the various combinations and proportions of
the amino acids used in their construction. The various proteins are
formed by joining the acid group of one with the amino group of an-
other amino acid. The protein can act as an acid, and thus com-
bine with alkalis, because of its acid group (COOH) and can act as
an alkali, and thus combine with acids, because of its amino group

*Present only in certain types of proteins.

Properties and Activities of Living Protoplasm 89

(NH2). Hence they are amphoteric (am'foterik) (Gr. amphotere, in
both ways), which is probably important in regulating the proper acid-
base relationship in living protoplasm.

The large size of their molecules causes proteins to assume colloidal
characteristics in water, which explains the colloidal nature of proto-
plasm. Proteins contribute the structural components of protoplasm, as
well as important constituents of enzymes and certain hormones, in addi-
tion to supplying energy and heat. They assist greatly in growth and
repair. Animal protoplasms, in general, seem to be able to manufacture
only a few types of amino acids from raw materials, while plants can
synthesize many of them from simpler substances. In general, animals
are dependent, directly or indirectly, on plants for most of them. When
proteins are digested, they are broken up into amino acids before they
can be absorbed by the blood, which carries them to various parts of the
body where they are made into new proteins. The digestion of proteins
releases energy which was required to hold their components together.
Examples of proteins with their chemical formulas are ( 1 ) albumin of
the white of e^g (C239H389O78N58S2) and (2) zein of corn (CtsbHiisi-

^208Ni84S3) .

D. Mineral (Inorganic) Salts

In spite of the fact that mineral salts are not present in great quan-
tities, they are nevertheless of great importance in maintaining the nor-
mal activities and physiologic equilibrium of living protoplasm. Chemi-
cal analysis of body fluids reveals that the quantity and kinds of salts
in them greatly resemble the concentrations of the mineral salts of sea
water from which the first protoplasm is thought to have originated.
The different salts in ocean water are sodium and magnesium chlorides,
magnesium, calcium, and potassium sulfates, and calcium carbonate, in
addition to minute quantities of other salts. When these salts dissociate
in water (ionize), the sodium, magnesium, calcium, and potassium con-
tribute positively charged ions, and the chlorine, sulfates, and carbonates
contribute most of the negatively charged ions. These positive and
negative ions are probably associated with certain electrical phenomena
of protoplasm.

Normally, the concentration of the various salts in body fluids is quite
constant, because any appreciable deviation will be followed by im-
paired functions, or possibly death in extreme cases. Calcium salts are
important in the building of bones and the coagulation of blood. A
sufficient decrease in the calcium ions in the blood may result in con-

90 Introductory Biology

vulsionSj or even death. Normal contractions of heart muscles can
occur only if there is a proper balance of sodium, potassium, and cal-
cium ions. Mineral salts maintain the normal osmotic balance between
the living protoplasm and the various environmental factors. All in all,
it may be that deficiencies in mineral salts are more important than
temporary deprivations of the organic foods. About fifteen elements are
known to be essential in mineral salts in human diet, although some are
needed only in traces. About 30 grams of these mineral salts are lost
from the human body daily through feces, urine, and sweat, and they
must be replaced. Rich food sources for minerals include vegetables,
milk, cheese, meat, eggs, etc. Iron is necessary to build hemoglobin, and
iodine is necessary to produce thyroxin, the hormone of the thyroid
gland.

E. Water

A rather large part of all protoplasm is water, the percentage varying
with the type of protoplasm, the conditions under which it has lived
previous to the analysis, etc. More water is present in aquatic organ-
isms than in those living in dry environments. Water itself is not alive,
but it forms an arena in which the various nonliving substances which
make up the living protoplasm may perform (Fig. 27). Many of the
movements associated with living protoplasm are influenced in part, at
least, by the water content. Water acts as the dispersing medium of
the colloidal systems of living protoplasm. Water is essential in passing
foods into a living organism and in eliminating wastes from it. Water
also assists in equalizing temperatures throughout an organism as well
as in diluting certain detrimental substances which may have entered.
Water also tends to reduce friction and prevent structures from abnor-
mally adhering to each other. A certain amount of water seems to be
necessary for the reception of certain stimuli, especially those of the
senses of taste and smell.

F. Vitamins

Vitamins (L. vita, life; amine, formed from ammonia) are rather
simple organic compounds which even in small quantities are essential
to life. The various vitamins are quite different chemically and origi-
nally were thought to be amines formed from ammonia; hence the name
is now incorrect from a chemical composition standpoint. In general,
they cannot be manufactured by the animal body (but are produced by

Properties and Activities of Living Protoplasm 91

plants) so must be secured in sufficient amounts in the diet in order to
ensure that the various metabolic processes are performed normally.
Each vitamin which has been successfully analyzed so far has a different
chemical formula, and each has somewhat specific functions. Today we
know the chemical structure of most of the vitamins so far discovered,
and many of them have been prepared synthetically. Vitamins were
discovered about 1912, and much scientific progress has been made since
that time through chemical analyses, animal experimentation, etc.

From recent experiments dealing with the exact functions of a vita-
min it has been observed to act as a catalyst for some fundamental
reaction common to all protoplasm. When there is a vitamin deficiency
below a certain level, certain behaviors and metabolic functions are
impaired, the particular effects being determined by the type of vitamin
involved. Plants probably have their specific vitamin requirements just
as animals, although this has not been studied so extensively as in the
animals. Plants synthesize most of the vitamins so they must play im-
portant roles in their metabolisms. Some of the vitamins are compo-
nents of enzymes which control many physiologic processes in cells or
contribute to the actual formation of certain enzymes. It is probable
that many vitamins in plants act as the components of enzymes or as the
progenitors of enzymes. In green plants, vitamin B is essential for nor-
mal root development. Vitamin K regulates the oxidation-reduction
processes in living cells. The various roles of vitamins in the numerous
processes of living organisms are considered in greater detail in a later
chapter.

G. Enzymes

An enzyme (Gr. en, in; zyme, yeast, or leaven) is a nonliving, complex
organic (protein) catalyst (kat' a list) (Qr. katalysis, dissolving) produced
only by living protoplasm, and controls the speed of a chemical reaction
without taking part in the reaction itself or without being consumed as
the result of it. Because one of the first enzymes was isolated (by the
German scientist BUchner) from crushed yeast cells, the unknown sub-
stance was called an enzyme. Every animal and plant cell contains
many different enzymes, each with a specific function. A pure enzyme is
specific because it controls one type of chemical action and acts on a
specific kind of substance known as the substrate. Many enzymes per-
form their function where they are formed, but some operate outside the
cell which produces them. Digestive enzymes illustrate the latter. Most

92 Introductory Biology

enzymes are soluble in water and can be evaporated to a dry state and
retain their catalytic abilities for a long time. Most enzymes possess an
optimum temperature at which they function best, and most are de-
stroyed by boiling. They are also influenced by acids, alkalis, and
pressure.

As stated previously, some of the vitamins are components of enzymes.
Experimental evidence indicates that the complex chemical reactions
associated with respiration are controlled, at least in part by special
oxidizing enzymes called respiratory enzymes. It is suggested that the
protein genes (hereditary determiners) must have some close relation to
enzymes. Probably specific genes (discussed in a later chapter) deter-
mine the presence of specific enzymes which are essential for the numer-
ous chemical processes in metabolism.

Enzymes are usually classed after the type of chemical action produced
in a particular substance. For example, hydrolytic enzymes (Gr. hydor,
water; lysis, loosing) break down substances by causing them to combine
with water or build up substances by removing a molecule of water from
two simpler molecules of a substance when they combine.

2 molecules of glucose sugar (CeHi^Oe) + hydrolytic enzyme -^
1 molecule of sucrose sugar (G12H22O11) + H2O

Proteolytic enzymes (Gr. protos, first; lysis, loosing) break down, or
possibly build up, proteins. Enzymes are frequently named by adding
-ase to the substance acted on: lipases (Gr, lipos, fat) change fats to
glycerine and fatty acids; amylase (diastase) (L. amylum, starch)
changes starch and dextrins to maltose (sugar) ; maltase (A.S. mealt,
malt) changes maltose to glucose (sugar) ; proteinases convert various
types of proteins into amino acids or intermediate products.

Enzymes are of great economic importance in industries as a few
examples will illustrate : the making of breads, cheeses, syrups, glycerine,
alcoholic beverages, soy sauce, etc.; the retting (removal) of fibers from
the stems of hemp, flax, and other plants; the ripening of tobacco; the
preparation of sizing for paper and textiles; the preparation of skins for
tanning; the preparation of certain medicinal products, etc.

III. METABOLISM, AUTOSYNTHESIS, AUTOCATALYSIS

Metabolism (me -tab' o lizm) (Gr. m^^a^o/^^ to change) includes those
chemical activities of living protoplasm which are associated with growth,
maintenance, repair, and the constant building of new, living, proto-

Properties and Activities of Living Protoplasm 93

plasm from nonliving chemicals. Living protoplasm has the unique and
characteristic ability to change the potential energy of the large mole-
cules of carbohydrates, fats, and proteins into kinetic energy and heat as
the larger molecules are changed to simpler forms. Metabolism may be
divided into (1) anaholism (a -nab' o lizm) (Gr. ana, up; hole, build), in
which the chemical processes unite simpler substances to form more com-
plex substances, with the production of new protoplasm, growth, and the
storage of energy, and (2) catabolism (ka -tab' o lizm (Gr. kata, down;
hole, throw), in which complex substances are broken down, protoplasm
may be used up, and energy released. Both anabolism and catabolism oc-
cur constantly and simultaneously. In young organisms or in younger
parts of older organisms, anabolism predominates over catabolism; during
maturity the two are more or less balanced; in old age catabolism pre-
dominates over anabolism. Certain protoplasms naturally metabolize at a
high rate, while others have a lower rate. The metabolic rate of a partic-
ular individual may vary from time to time, being influenced by age,
height and weight, sex, activity, certain endocrine secretions, general
health, etc.

The hasal metabolic rate is the measurement of the amount of energy
expended (heat given off) just for mere living purposes, with no work be-
ing done and no food being digested. The determination of the hasal me-
tabolism of a human being is of great value in determining certain fac-
tors from a health standpoint. The characteristic ability of living proto-
plasm of organisms to duplicate itself or certain of its parts by synthesizing
complex molecules out of simpler ones, under the influence of specific
enzymes, is referred to as autosynthesis (aw to -sin' the sis) (Gr. autos,
self; synthesis, put together). The duplication of chromosomes, genes,
and possibly filterable viruses, and reproduction itself illustrate this
phenomenon.

Certain forces in the molecules which compose genes enable them to
rearrange the chemical substances in the protoplasm into the same struc-
tural (chemico-physical) pattern which the genes possess. This is essen-
tial if the constancy and stability in the inheritance of an organism are
to be continued through successive generations. However, occasionally
there seem to be changes in the normal structural pattern of genes which
result in certain effects and charges known as mutations (mu-ta'shun)
(L. mutare, to change). These mutations are one source of variations
and form one basis for the statement '^the most invariable thing in life
is variability." These and other variations are the causes and effects of

94 Introductory Biology

the gradual developmental changes (evolution) constantly undergone by
living organisms (evo-lu' shun) (L. evolvere, to unroll or change).

There are certain nonliving, nonprotoplasmic chemical substances such
as giant molecules of proteins which also possess autosynthesis. However,
these molecules of protein are much simpler than those in living proto-
plasm. There seem to be autosynthetic phenomena in both living and
nonliving substances, but in each case the product formed is specific and
unique for that substance.

The ability of a catalyst to synthesize more of its own substance (create
more molecules of its own kind ) , thus gradually increasing the speed of
the chemical action, may be considered as autocatalysis (aw to ka -tal'i
sis) (Gr. autos, self; kata, down; lysis, loosing). Sometimes this term
seems to be used as a synonym of autosynthesis. The disintegration of
cells or tissues by the action of autogenous enzymes (aw -toj' e nus) (Gr.
autos, self; genesis, origin) which they produce may be considered as
autolysis. Life seems to be the result of the interactions and counterac-
tions of these and many other factors, some of which are not yet known.

IV. GROWTH, ASSIMILATION, AND DIFFERENTIATION

True growth is characteristic of all living organisms and consists of
anabolism, in which the protoplasmic substances synthesize more of their
kind from materials which are unlike the protoplasm, thus increasing
their bulk. True growth in living organisms may be the result of the
increase in the size of cells, an increase in the number of cells, or a com-
bination of these two. All living organisms have limits beyond which
they cannot, or do not, grow. Certain organisms do not seem to grow
much after the adult stage, while others continue growth for a longer
period of time. The particular size of each organism is probably due to
its inherent hereditary materials and the influence of environmental fac-
tors both outside and inside the organism. The process of building
smaller particles of chemicals into larger particles of protoplasm which
differ from the original particles (food) is known as assimilation
(a sim i -la' shun) (L. ad, to; similis, alike) .

In the nonliving world there are phenomena which approximate
growth somewhat. A crystal of table salt (NaCl) placed in a super-
saturated solution of table salt (maximum amount of salt which will
normally dissolve in hot water and which will release some of the salt
when the solution cools) will add to its surface some of the dissolved
salt, thereby forming a larger and larger crystal which maintains a fairly

Properties and Activities of Living Protoplasm 95

constant form characteristic for that kind of crystal. In this case the
raw material used in building is essentially the same as the final product,
and the increase in size has been by accretion (ak -re' shun) (L. ad, to;
cr esc ere, to add or grow). This is to be distinguished from true growth
by intussusception (in tus sus -sep' shun) (L. intus, within; suscipere, to
make up), in which chemical rearrangements result in growth from
within. In nonliving things the method of size increase and the chemi-
cal composition are determined by the specific nature of the beginning,
raw material, while in true growth the nature of the final product
formed is determined by the protoplasm of the organism involved. A
cat and dog may be fed the same kind of food, but each animal assimi-
lates and grows in a manner unique for it. There are still many un-
solved problems in connection with how growth is initiated, how it
continues, and also how it ceases. It is not only important to have a
tissue or organ grow to be normal, but it is equally essential to have it
cease growth when normality has been reached. Such abnormal growth
as tumors, cancers, etc., still constitute major problems in this field.

From what has been said it would seem that a cell dividing by mitosis
would always produce two identical cells which eventually would be
similar to the original. Frequently, this does happen, as in the forma-
tion of similar cells in the diflferent tissues. However, if this always
happened, a multicellular man, who develops from an original cell by
repeated mitoses, would be composed of cells which would all be alike,
because the chromosomes, genes, etc., are supposedly alike. From our
studies of tissues it was observed that there are many diflferences in
structures and functions in various tissues, which originally all arose
from the first cell. How can different cells arise from a common origin?

If chromosomes and their genes alone determine the structure and
functions of cells, then should not all cells in a multicellular organism
be alike? It is thought that genes produce enzymes, or act as enzymes,
which influence the behavior of cells under certain conditions. Because
of variations in external and internal environmental factors (such as
foods, enzymes, etc) which can influence groups of cells, or even the
opposite ends of a single cell, differently, even the same genes in the vari-
ous cells will not express their inherent potentialities in the same way in
all cells. In other words, differences in physical and chemical factors
are thought to influence even identical genes in such different ways that
variations in structures and functions are developed. This is the basis
for cellular differentiation (changes in the organization of protoplasm)
which results in difTerent types of cells, tissues, etc. After their differen-

96 Introductory Biology

tiation, the cells and tissues are subjected to still further variations, in
this case possibly by even the same environmental influences, because
now the tissues are even different. It has been experimentally observed
that the embryologic development of a cell or tissue is influenced by its
inherent abilities (genes, etc.) and by the particular environment (chemi-
cal and physical) to which it is subjected. Both of the phenomena are
considered in greater detail in other chapters.

V. REPRODUCTION

Reproduction, or the ability to reproduce themselves, is a character-
istic of living organisms. Most offspring are remarkably like their par-
ents, which suggests there are similar forces which operate generation
after generation in order to ensure this phenomenon of continuity.
Naturally, certain off^spring differ somewhat from their parents, and the
explanations are to be found in differences in the heredity mechanism
or differences in environmental factors, or a combination of both. The
various methods of reproduction of plants and animals, their embryo-
logic developments, the effects of environmental factors, and the opera-
tions of heredity (genetics) are considered in other chapters. Reproduc-
tion is essential if individuals are to propagate their kind and if the race
is to continue existence. The specific methods of reproduction in plants
and animals are numerous and varied as a study of living organisms
will reveal.

VI. ADAPTATION AND IRRITABILITY

Adaptability is the ability of living organisms to undergo changes ap-
propriate to their life needs and to fit efficiently into their environments
so that their life processes may proceed as normally and effectively as
possible. Adaptiveness of living organisms depends upon their irrita-
bility (their capacity to respond to stimuli). Nonliving things may be
more or less affected by external influences, although their reactions are
always more or less the same, while living things do not always react
to the same stimuli in the same way. These differences in reactions are
dependent on the adaptability of the living protoplasm. Naturally, the
specific or definite response to a particular type of stimulus cannot
always be predicted in a living organism as it can in nonliving materials.
Adaptations of living organisms may be of three kinds: (1) changes in
structure (structural); (2) changes in functions (functional); (3)
changes in both structure and function (structural-functional).

Properties and Activities of Living Protoplasm 97

When certain parts of a living organism have been impaired or de-
stroyed, frequently other parts, through the inherent process of self-
regulation, take on compensatory reactions or activities in order to re-
gain a complete, well-balanced normality. Examples of such activities
are as follows: If one human kidney is diseased or destroyed, the other
adjusts or compensates to attempt to do the work of both. If tissues
or organs require more oxygen, the circulatory system attempts to circu-
late the extra amounts necessary. The quantity and quality of the
digestive juices are regulated within certain limits by the variations in
the diet of the organism. When emergencies arise, increased energy is
required. Consequently, larger quantities of foods in various parts of
the organism are liberated and changed to meet the extra demands.

Through some internal recording or regulation, the efforts and reac-
tions of living organisms frequently serve as a kind of experience by
which they are led to avoid similar, undesirable kinds of actions in the
future and attempt to repeat the desirable and successful ones. This
makes for the preservation of the individual, as well as the race, in the
struggle for existence.

VII. ORGANIZATION AND INDIVIDUALITY

All parts of living organisms are so integrated that the whole thing is
a unit or an individual. Individuality is due to the fact that some one
part of the organism which is most active presides or predominates over
the less active parts and thus keeps them all in organized subordination.
In each living organism there are ( 1 ) interdependence and systematic cor-
relation of parts, (2) a variable susceptibility to environmental influ-
ences, (3) inherent self-regulatory tendencies, and (4) a centralized con-
trol. All of these working harmoniously together make the living or-
ganism a unified individual rather than a mere inchoate mass of sepa-
rate and unrelated parts.

Many, if not all, living organisms are organized on one or more axes
along which the various tissues, organs, and physiologic units are ar-
ranged in a somewhat graded series, the more active being at the con-
trolling apical region, and the less active at the opposite end. Between
these two regions is a graded series of decreasing activities extending
from one end to the other on this imaginary line or axis. This arrange-
ment of structures and physiologic units is known as the axial gradient
which to a great extent determines the organization of the organism as

98 Introductory Biology

well as its individuality. Organisms which possess such an organization
are said to possess axiate organization. This phenomenon is studied in
various organisms in other chapters.

VIII. REGENERATION

The protoplasms of all li\ing organisms have the ability to regenerate
to a greater or lesser degree (Fig. 28). If certain parts of an organism
are destroyed or impaired, there is an attempt on the part of the indi-
vidual to regain its completeness and normality.

Fig. 28. — Regeneration of animals as shown by A, Hydra; B, Planaria; C, star-
fish: D, earthworm. The Hnes show the position where the parts were removed
and the darker (stippled) areas are those which have been regenerated. Note
that in the starfish the missing ray is regenerated and the missing ray also re-
generates the four missing rays. The kind of regeneration which develops depends
to a great extent upon where the cut is made.

In general, regeneration in the higher or more complex organisms is
more or less limited to certain structures and regions. If the skin on the
tip of a human finger is lost, it will be replaced, but if the tip of the
entire finger is removed, there is no appreciable restoration of the lost
part. Regeneration thus is relative and is determined or influenced by
the part aflfected. Other illustrations of regeneration of higher organ-
isms are: the healing of wounds of plants and animals, repair of broken
bones, production of new blood corpuscles, replacement of sap lost from
injured plants, and renewal of bark removed from trees.

Properties and Activities of Living Protoplasm 99

In lower types of organisms a part of an organism may have the
abiUty of restoring all the missing parts for an entirely new individual.
For instance, one ray or arm of a starfish may be removed (Fig. 28).
The missing ray will be replaced, and the removed ray has the ability
to add the four rays to itself in order to make two complete individuals,
each with the normal number of five rays. The flatworm (Planaria)
may be cut into several transverse pieces. Each resulting piece has the
inherent ability to regenerate some form of Planaria (Fig. 28). The
earthworm may regenerate a missing "head" or "tail" region. The
Hydra may replace missing tentacles, layers of cells, or even the mouth
region (Fig. 28) .

IX. LIVING AND NONLIVING THINGS CONTRASTED

A survey of various living organisms as a group contrasted with dif-
ferent kinds of nonliving substances reveals certain differences. Many
of these dififerences are quite apparent upon casual observation, and
additional ones will be observed when more detailed studies are made.
Most biologists agree that the phenomena of living organisms are more
complex than comparable phenomena in nonliving substances but that
both are more or less associated with chemical and physical processes. The
mechanistic theory suggests that all vital phenomena are to be explained
by a complete understanding of all the chemical and physical forces
which operate in living protoplasm — that life is merely the result of the
proper interactions and counteractions of these forces. The vitalistic
theory suggests that some unique, supernatural force or power which is
not reducible to the terms of physics and chemistry is responsible for
the initiation, continuity, and control of vital activities — that this "extra
something" differentiates living from nonliving and that science shall
never be able to create life or be able to understand it completely. The
more significant characteristics of living organisms and nonliving sub-
stances are contrasted briefly in the accompanying table.

LIVING (ANIMATE) ORGANISMS

NONLIVING (INANIMATE)
SUBSTANCES

COMPOSITION

A,ll living organisms, both plant and
animal, have been found to be com-
posed of a highly organized, chemi-
cally complex protoplasm with its
unique characteristic chemical and
physical properties.

Even though certain nonliving sub-
stances may have a definite chemical
composition and specific physical
properties, none of them have ever
been observ^ed to be composed of
protoplasm.

100 Introductory Biology

LIVING (ANIMATE) ORGANISMS

NONLIVING (INANIMATE)
SUBSTANCES

STRUCTURE AND ORGANIZATION

All living protoplasm is a complex and
specific organization of structures
and parts which are coordinated so
as to function together as a unit, or
an organism. All living things are
composed of units, called cells, which
have nuclear materials, cytoplasm,
etc., each possessing distinct char-
acteristics and properties. The lat-
ter are constantly changing because
the chemical and physical constitu-
ents are highly organized in a dy-
namic system.

Certain nonliving substances, such as
crystals, may have a definite molecu-
lar structure and organization typical
for each kind of crystal, but this or-
ganization is inert, static, and not dy-
namic. The various structures which
characterize each inanimate sub-
stance are rather simple in compari-
son with complex protoplasm, and
all nonliving substances arc without
cells.

RESPIRATION AND WASTE ELIMINATION

All living organisms respire, or ex-
change oxygen and carbon dioxide at
rather definite measurable rates.
These gases (oxygen for animals;
carbon dioxide for plants) are usu-
ally taken from the atmosphere.
During metabolism, there is respira-
tion and the production and elimina-
tion of wastes. In many living or-
ganisms the latter have rather specific
qualities which characterize the dif-
ferent kinds of living things.

The exchange of gases is present in
certain inanimate substances, but it
is not quite the same kind of phe-
nomenon found in living organisms.
A nail may rust or oxidize (oxygen
added), or a motor may take in
oxygen and give off carbon dioxide,
or carbon monoxide, but these and
similar phenomena are different
from true respiration.

MOVEMENT

Dynamic movements usually result
from rather complex interactions of
physical and chemical forces within
the protoplasm. These independent,
autonomous movements seem to be
responses to stimuli with an expendi-
ture of energy rather than imposed
by external forces. They may be
rapid or slow, depending upon the
organism and the quantity and qual-
ity of stimuli.

Certain inanimate things seem to dis-
play certain movements which may
seem to approximate those of living
organisms, although they are usually
of a simpler nature. Camphor par-
ticles in water may move and modify
their movements in response to cer-
tain external factors. Crystals of
certain types (salts, etc.) dissolve and
diffuse (move) in an aqueous en-
vironment. A drop of mercury in
water to which nitric acid is added
seems to display a type of movement
which somewhat resembles the "flow-
ing" movements of living protoplasm.
Brownian movements are displayed
by such things as particles of dyes
suspended in water etc.

Properties and Activities of Living Protoplasm 101

LIVING (ANIMATE) ORGANISMS

NONLIVING (INANIMATE)
SUBSTANCES

IRRITABILITY AND ADAPTATION

All living protoplasm is typically sen-
sitive to certain environmental fac-
tors {irritability) and tends to react
or respond {adaptation) because of
the labile, dynamic nature of proto-
plasm and the extremely complex
interactions of physical and chemical
forces. Responsiveness to stimuli is
characteristic of living protoplasm
but does not seem to be limited to
it. By adaptation, living organisms
attempt to adjust themselves to their
environments so as to live as suc-
cessfully as possible. Because of ir-
ritability, protozoa, bacteria, the
various parts of animals and plants,
etc., tend to display variable re-
sponses which vary from time to
time and are influenced by the in-
herent nature of the specific proto-
plasm and the quantity and quality
of the stimuli.

Certain nonliving materials which dis-
play movements also seem to display
something which approximates irrita-
bility and responsiveness under cer-
tain conditions. However, the type
of response is usually simpler and
more predictable than in living or-
ganisms. When light rays which fall
on a photoelectric cell are inter-
rupted, they may open doors, set off
alarms, or count cans in a commer-
cial cannery. Pressing a starter but-
ton may result in the movement in
an electric generator. The drop of
mercury in acidified water may "re-
spond" to contacts with certain other
chemicals. The movements dis-
played by certain inanimate objects
may truly resemble some of the sim-
pler movements of certain living or-
ganisms, but on the whole they are
less complicated and rather more
predictable and standardized.

GROWTH AND DEVELOPMENT

All living plants and animals require
foods and they grow, each true to
its type, and jrom within, through
intussusception. Living organisms
also possess the property of assimila-
tion (producing living protoplasm
from nonliving foods ) . The energy-
bearing molecules are taken in, re-
arranged, and delicately adjusted in-
to other more complex molecules of
living protoplasm under the influ-
ences of enzymes and catalysts. Me-
tabolism, which characterizes proto-
plasm, consists of anabolism (con-
structive chemical changes, with the
storage of energy) and catabolism
(destructive chemical changes with
a release of energy). Usually true
growth is accompanied by changes in
structure, form, and functions which
constitute true development. Growth
may be the result of an increase in
the number of cells, an increase of
the size of cells without an increase
in numbers, or a combination of the
two. Certain structures of living or-
ganisms may also be duplicated by
auto synthesis.

Certain inanimate materials may in-
crease in size externally by adding
materials which are essentially simi-
lar to the original materials by the
process of accretion. A crystal of
table salt in a supersaturated solu-
tion of table salt will increase in size
by externally adding more salt. Liv-
ing organisms grow by producing cer-
tain other materials true to type,
while increases in size of inanimate
crystals are influenced by the begin-
ning, raw materials. In other words,
" the final product is the same as the
beginning. Certain chemicals com-
bined to produce the so-called
"chemical gardens" (crystals of
chemicals in water glass) may in-
crease in size and form beautifully
patterned structures which may re-
semble plantlike structures. How-
ever, are these true growth in the
accepted sense?

102 Introductory Biology

LIVING (ANIMATE) ORGANISMS

NONLIVING (INANIMATE)
SUBSTANCES

REPRODUCTION AND HEREDITY (GENETICS)

All living organisms reproduce to form
new units of their own kinds. The
newly formed units or offspring tend
to resemble their parents because of
a continuity pattern carried from
generation to generation through the
numerous phenomena of heredity
(genetics). "All living organisms
arise only from living organisms."
So far, nothing comparable to genes,
etc., has been discovered in the non-
living world. The phenomena of
reproduction and heredity are in-
herent abilities of living protoplasm,
even though they may at times be
influenced by environmental factors
to a certain extent. They seem to be
initiated internally and for the most
part controlled internally. Living
organisms possess the qualities listed
above, but a nonliving object never
has more than a few of them, and
then in a somewhat modified way.

Certain nonliving substances may at
times break into smaller pieces, but
are these phenomena truly compara-
ble to the complicated processes fre-
quently involved in giving origin to
offspring in the animate world? Are
these small bits capable of develop-
ing into a new individual as in the
the living world? Is there inheri-
tance, in the accepted sense, in these
inanimate materials?

QUESTIONS AND TOPICS

1. What is meant by a physical property of protoplasm? List all the physical
properties of protoplasm; attempt to understand the causes for each physical
property and the effects of such a property on the living protoplasm.

2. Learn the correct pronunciation, derivation, and meaning of each new term
used in this chapter.

3. Explain how the chemical composition of a living protoplasm depends on,
and varies with, the chemical substances taken in.

4. What difficulties are encountered in attempting to analyze living protoplasm
chemically? Be sure that the results secured are accurate for the protoplasm
when it was still living (before the analyses were started). Might the chemi-
cal composition of protoplasm differ when dead from what it might be if the
same protoplasm could be analyzed and still be kept alive?

5. Why is nitrogen an essential element for living matter? What general types
of food contain nitrogen?

6. Which are more important, the organic or inorganic foods? Why? Give
the chief sources of mineral salts.

7. Define (1) catalyst, (2) enzyme, (3) vitamin, (4) metabolism, (5) anab-
olism, (6) catabolism, (7) colloidal system, (8) sol and gel, (9) Brownian
movement, (10) adsorption, (11) emulsoid, and (12) diffusion.

8. Describe the structure of an atom, including the characteristics of each of
its parts.

Properties and Activities of Living Protoplasm 103

9. Is the rusting of a nail or the rotting of wood to be considered as catabolisni?
Why? Is the making of concrete from sand, cement, and water to be con-
sidered as anaboHsm? Why?

10. When is an organism considered young? When mature? When old? What
factors influence and determine the age of an organism? Would it have been
desirable if Nature had not placed death in the scheme of things? Why?
Attempt to explain what is meant by death in biologic terms.

11. Do all living organisms possess the same degree of irritability? Is the irrita-
bility of the same organism constant? What factors are responsible for this?
What role does heredity play in this connection?

12. Define individuality. Of what does individuality consist? Explain the rela-
tionships between irritability, adaptability, and individuality.

13. What is meant when we state that an organism is "organized" ?

14. Contrast living and nonliving things in as many ways as you can. Is the dis-
tinction between them always clear? Give examples.

15. Explain each of the traits which we consider to be characteristic of living
organisms.

16. Discuss radioactive isotopes and their roles in the studies of diseases of living
organisms.

17. Discuss the roles which radioactive isotopes may play in tracing certain
chemicals throughout plants.

18. Discuss the electrical properties displayed by protoplasm and how these
phenomena may explain certain functions and abilities in a living organism.

SELECTED REFERENCES

Alexander: Life: Its Nature and Origin, Reinhold Publishing Corp.

Davson and Danielli: The Premeability of Natural Membranes, The Macmillan

Co.
Lotka: Elements of Physical Biology, Williams & Wilkins Co.
Moulton: The Cell and Protoplasm, Science Press Printing Co.
Osterhout: The Nature of Life, Henry Holt & Co., Inc.
Rice and Teller: The Structure of Matter, John Wiley & Sons, Inc.
Schrodinger: What Is Life ? The Macmillan Co.
Seifriz: Protoplasm, McGraw-Hill Book Co., Inc.

Chapter 7

LIVING PLANTS AND ANIMALS CONTRASTED

Living plants and animals possess many characteristics which are com-
mon to both groups, but in many ways they are dissimilar or opposite.
While the distinctive features between higher plants and higher animals
are obvious, discrimination between them becomes quite difficult in some
of the lower forms. In fact, there are certain organisms which are
claimed by the botanists as being plants and by the zoologists as being
animals because of the presence of both plantlike and animal-like traits
in the same individual. Such individuals might be considered as plant-
animals and may be illustrated by such forms as Euglena, Volvox (Figs.
173, 174), etc. One might consider the Tree of Life as consisting of two
main trunks (one plant, the other animal) with numerous branches and
subdivisions to represent the various types in each kingdom. In this case
the roots are hidden from our view (origin in the past), and new
branches are being constantly formed while others are dying. The two
main trunks arise from a common ancestral trunk, which suggests the
close relationships which exist between the two groups, in spite of the
fact that certain individuals on either side may at times be quite dis-
similar. Since it is theorized that plants and animals may have had a
common ancestry, there is no single difference which absolutely sepa-
rates all plants from all animals.

In spite of the fact that no absolute criteria can be established, what
bases, even though they may be somewhat unsatisfactory, can be used
to separate the two groups or to identify individuals in each group?
The following are stated briefly so that contrasts and comparisons can
be made more easily.

CELLULAR STRUCTURE

Outside the plasma memhrane of plant cells there usually is a semi-
rigid cell wall composed of cellulose which gives some rigidity and sup-
port but at the same time prevents excessive movement. Animal cells
also possess a plasma membrane but usually without a semirigid cell wall;
thus support is lacking but certain movements are permitted. Cellulose,

104

Living Plants and Animals Contrasted 105

"to

a carbohydrate, is also present in certain unicellular animals (protozoa)
and even in certain members (such as tunicates) of the highest phylum
of animals. Certain animal cells may secrete hard, rigid intercellular
materials. A few animal cells may even possess a cell wall. When water
is removed from cells by plasmolysis (plaz -mol' i sis) (Gr. plasma, form;
lysis, loosing), the entire animal cell shrinks, while the plasma membrane
usually shrinks away from the cell wall in plants.

CHLOROPHYLL AND PHOTOSYNTHESIS

Plants usually possess green chlorophyll by means of which carbon
dioxide and water, in the presence of energy-supplying light, are com-
bined into carbohydrate foods by the process of photosynthesis. Certain
plants such as the fungi (molds, bacteria, yeasts, mushrooms, etc.) lack
chlorophyll and must depend upon outside sources for their nutrition.
Chlorophyll-bearing plants have the ability to convert kinetic energy
derived from the sunlight into potential energy which is stored in the
plant. True animals do not possess chlorophyll, although a few border-
line organisms (Euglena, Volvox [Figs. 173, 174], etc.) may. Hence, in
general, animals are dependent upon plants either directly (herbivorous
animals) or indirectly (carnivorous animals) for their nutrition. Animals
have the ability to change the potential (stored) energy of foods into
other types of energy, including kinetic, which can be used for movement
and other purposes. The various methods of securing nutrition in plants
and animals will be considered in more detail in later chapters.

GROWTH

In plants and animals, growth consists of an increase in the number
of cells, an increase in size without an increase in the number of cells,
or a combination of the two. Plants might be considered as possessing
unlimited growth in which the ratio ai nonliving tissues to living tissues
gradually increases until the greater part of the plant body may be
composed of dead tissues. The older, dead tissues usually remain in
plants for support and are constantly increasing over a period of time,
while young growing tissues are constantly forming. In most plants,
active, embryonic tissues continue growing over long periods of time, as
in tips of stems and roots. In plants, the maximum size for a certain
species is quite variable and depends greatly upon external environ-
mental conditions.

Animals might be considered as having rather limited growth, in
which the mature individual reaches a certain size and characteristic

106 Introductory Biology

form which do not change to any great extent after maturity is reached.
In limited growth in animals the ratio of nonliving to living tissues is
rather constant, there never being a constant increase of nonliving as in
many plants. By the time animals are mature, most of the embryonic
tissues have disappeared. In general, the plant kingdom shows less
variation in structure than the animal kingdom does, and even higher
plants are less highly organized than comparable higher animals. From
a metabolic standpoint, green plants synthesize their organic foods and
animals must depend upon outside sources for them. There are some
nonchlorophyll plants (fungi) which also depend on outside sources for
their nourishment.

LOCOMOTION AND ACTIVITIES

Most plants are sessile (attached), or floating, and not capable of
locomotion, while most animals are able to locomote; even the few
which are attached (such as sponges, corals, oysters, barnacles, etc.)
have relatively rapid movements of certain body parts. There are
certain lower plants (bacteria, certain algae, etc.) which are motile.
In lower animals the locomotor equipment may be simple cilia, flagella,
or pseudopodia, as may be the case in certain lower motile plants. In
higher animals locomotion is the result of highly developed nervous,
muscular, and skeletal systems.

In general, because of their mode of life, plants store up energy in
organic food materials, while animals generally use up energy which
they have secured ultimately, and directly or indirectly, from plants.
Both plants and animals react to a great variety of stimuli (external
and internal), but the former react relatively more slowly than do ani-
mals. Plants do not possess nerve tissues, but this is also true for many
of the simpler animals. The common sensitive plant (Mimosa pudica)
exhibits a rather high degree of sensitivity and responsiveness, as does
Venus's-flytrap.

EXCRETION OF WASTES

Plants and animals produce wastes as a result of their metabolic ac-
tivities which are frequently eliminated through the general body sur-
face. However, many of the simple animals have distinct excretory
equipments which are not encountered even in the higher plants. The
rather complex methods of waste elimination are common in higher
animals.

Living Plants and Animals Contrasted 107

It is evident that there is no single difference which distinguishes all
plants from all animals, but studies of large numbers of both groups
reveal that they have much in common. In order that comparisons and
contrasts may be made between simple and complex plants on the one
hand and simple and complex animals on the other, it is suggested that
representatives of both groups be studied with these viewpoints in mind.
The higher plants and higher animals may be rather readily available,
but the lower, simpler plants and animals may not be. It would be a
worth-while exercise to study the simple plants and animals that inhabit
a fresh-water pool. These may be supplemented with selected speci-
mens which illustrate points of difference mentioned above.

QUESTIONS AND TOPICS

1. Define a plant and an animal in the light of the knowledge gained in this
chapter;

2. List and explain each of the principal differences between the group of plants
as a whole and the group of animals as a whole.

3. Give reasons why you think animals and plants are closely related and may
have had a common ancestry.

4. Discuss the significance of such organisms which we call plant-animals.

5. Need there be clear-cut differences between plants and animals ? Why ?

6. List some of the more common characteristics possessed by both plants and
animals,

7. If you make a field or laboratory study of the various plants and animals
encountered in a fresh-water pool, what conclusions can you draw?

SELECTED REFERENCES*

Bates: The Nature of Natural History, Charles Scribner's Sons.

Calkins: The Smallest Living Things, The University Society.

Chapman: Animal Ecology, With Especial Reference to Insects, McGraw-Hill

Book Co., Inc.
Comstock: Handbook of Nature Study, Comstock Publishing Co., Inc.
Fasset: Manual of Aquatic Plants, McGraw-Hill Book Co., Inc.
Gates: Field Manual of Plant Ecology, McGraw-Hill Book Co., Inc.
Hausman: Beginner's Guide to Seashore Life, G. P. Putnam's Sons.
Jacques: Living Things — How to Know Them, William C. Brown Co.
Miner: Seashore Life, G. P. Putnam's Sons.

Morgan: Field Book of Ponds and Streams, G. P. Putnam's Sons.
Muenscher: Aquatic Plants, Comstock Publishing Co., Inc.
Needham and Needham: Guide to the Study of Fresh-Water Biology, Comstock

Publishing Co., Inc.
Pratt: Manual of Common Invertebrate Animals, A. C. McClurg & Co.
Ward and Whipple: Fresh Water Biology, John Wiley & Sons, Inc.
Welch: Limnology, McGraw-Hill Book Co., Inc.

*This list of references deals primarily with animals and plants in water. References for
other plants and animals are found in various other chapters.

Part 2
PLANT BIOLOGY

Chapter 8

SURVEY OF THE PLANT KINGDOM

A detailed study of the entire plant kingdom cannot be made in such
a short chapter because there are over 300,000 species (diflFerent kinds)
of more or less well-known plants. Only a few plants which are repre-
sentative of the various subdivisions of the plant kingdom will be con-
sidered. A more detailed consideration of the structures and functions
of certain representative plants will be found in other chapters.

In order to study properly and scientifically the representative mem-
bers of the plant kingdom, a system of classification must be utilized
by means of which investigators in all parts of the world may study the
same species of plants and call them by the same scientific name. With-
out scientific names and classifications, a certain plant might have a
large number of different names given to it by students in various parts
of the world. In the selection of languages for use in classification and
scientific names, Greek and Latin are used because they are more uni-
versally understood and because they are not so susceptible to changes
in each local community. In other words, these languages are more or
less standardized and consequently are very desirable for purposes of
classification and naming. Complete, accurate, scientific descriptions
and classifications of plants also make it possible to identify and correctly
name unknown species of plants. If we did not have specific scientific
terms and classifications, each investigator would more or less have to
make his own classification and follow his own methods of naming and
then would be unable to know if he were studying a form previously
described or if he really had a new species.

For these reasons, the entire plant kingdom is divided into several
main divisions or phyla (singular, phylum). All of the plants included

108

Survey of Plant Kingdom 109

in a particular phylum have one or more characteristics in common.
These characteristics are considered below for each of the phyla of
plants and are described under the heading of General Characteristics.

Naturally, if our classification went no farther than phyla, there would
be too many differences among the various members so that the sys-
tem would be practically useless. Consequently, all the members of a
phylum, having one or more arbitrarily chosen characters in common,
are placed in a subdivision, called a class. Sometimes a phylum is
divided into subphyla. In a similar way classes may be divided into
orders, orders into families, families into genera (singular, genus), and
genera into species. The scientific name of any plant is composed of
its genus and its species; i.e., ordinary corn has the scientific name of
Zea mays, the former being the genus and the latter the species.

Kingdom Plantae

Subkingdom Thallophyta (tha -lof i ta) (Gr. thallos, "leaflike," or young shoot;
phyta, plants) (plants not forming an embryo) (Figs. 29 to 42)

1. 'PhyXnm Cyano phyta (si an -of i ta) {Gr. kyanos,h\viG', phyta, \)\2iwts) (blue-

green algae) (Fig. 29)

2. Phylum Chlorophyta (klor-of ita) (Gr. chloros, green; phyta, plants)

(green algae) (Fig. 30)

3. Phylum Chry so phyta (kris -of i ta) (Gr. chrysos, gold', /? A j^a, plants) (yel-

low-green, golden-brown algae and diatoms) (Fig. 31)

4. Phylum Phaeophyta (fe -of i ta) (Gr. phaios, brown or dusky; phyta, plants)

(brown algae) (Fig. 32)

5. Phylum Rhodophyta (rod -of i ta) (Gr. rhodon, red; phyta, plants) (red

algae) (Fig. 33) _ _ ^ ^

6. Phylum Schizomyco phyta (skiz o mai -kof i ta) (Gr. schizo, split or fission;

mykes, fungus; phyta, plants) (bacteria) (Fig. 34)

7. Phylum Myxomycophyta (mik so mai -kof i ta) (Gr. myxos, slime; mykes,

fungus; phyta, plants) (slime molds or slime fungi) (Fig. 35)

8. Phylum Eumycophyta (yu mai -kof i ta) (Gr. eu, good or true; mykes,

fungus; phyta, plants) (true fungi)

(1) Class Phycomycetes ( fi ko mai -s,e' tez ) (Gr. phykos, algalike; mycetes,

fungi) (algalike fungi) (Figs. 36 and 64)

(2) Class Ascomycetes (as ko mai -se' tez) (Gr. ascus, sac; mycetes, fungi)

(Ascus or sac fungi) (Figs. 37 to 40)

(3) Class Basidiomycetes (basidi omai-se'tez) (Gr. basidium, base or

club; mycetes, fungi) (Basidium or club fungi) (Figs. 41, 42 and
65)

Subkingdom Embryophyta (em bri -of i ta) (Gr. embryon, embryo; phyta, plants)
(plants forming an embryo) (Figs. 43 to 60)

9. Phylum Bryophyta (Atracheata) (bri -of i ta) (L. bryon, moss; phyta,

plants) (a tre ke -a' ta) (Gr. a, without; tracheia, duct or vessel)
(moss plants) (plants without vascular [conducting] tissues)

(1) Class Musci (mu' si) (L. muscus, moss) (true mosses) (Figs. 45 and

46)

(2) Class Hepaticae (he-pat'ise) (L. hepaticus, liver) (Liverworts)

(Figs. 43 and 44)

no Plant Biology

10. Phylum Tracheophyta (Tracheata) (tre ke -of i ta) (Gr. tracheia, duct or
vessel; phyta, plants) (plants with vascular tissues)

A. Subphylum Lycopsida (laik -op' si da) (Gr. lykos,\^o\i; opsis, appearance)

(simple vascular system; small, green leaves)
Class Lycopodineae (lai ko po -din' e e) (Gr. lykos, wolf; pous, foot) (club
"mosses") (Figs. 47 and 48]

B. Subphylum Sphenopsida (sfen -op si da) (Gr. sphen, wedge; opsis, appear-

ance) (simple vascular system; small, scalelike leaves; jointed stems)
Class Equisetineae (ek wi se -tin' e e (L. equus, horse; seta, tail or hair)
(horsetails or scouring rushes) (Fig. 49)

C. Subphylum Pteropsida (ter -op' si da) (Gr. pteris, wing or fern; opsis, ap-

pearance) (complex vascular system; large, conspicuous leaves)

(1) Class Filicineae (fili-sin'ee) (L. filix, fern) (true ferns) (Figs. 50,

51, and 68)

(2) Class Gymnospermae (jim no -spur' me) (Gr. gymno, exposed or

naked; sperma, seed) (exposed, naked seeds) (conifers and allies)
(Figs. 52-54)

(3) Class Angiospermae (an ji o-spur'me) (Gr. angio, enclosed; sperma,

seed) (true flowering plants with seeds enclosed by carpels) (Figs.
55 to 60)

(a) Subclass Dicotyledoneae (di kot i le -do' ne e) (Gr. di, two; kotyle-
don, embryonic, seed leaf) (two cotyledons [embryonic leaves])
(beans, sunflowers, dandelions, etc.) (Figs. 55 to 57)

(b) Subclass Monocotyledoneae (mon o kot i le -do' ne e) (Gr. mono,
one; kotyledon, embryonic, seed leaf) (one cotyledon [embryonic
leaf]) (corn, grasses, etc.) (Figs. 58 to 60)

Number of Species of Plants (Kingdom Plantae)

approximate
number of
Subkingdom Thallophyta species

1. Phylum Cyanophyta (blue-green algae) 1,400

2. Phylum Chlorophyta (green algae) 5,700

3. Phylum Chrysophyta (yellow-green, golden-

brown algae and diatoms) 5,700

4. Phylum Phaeophyta (brown algae) 900

5. Phylum Rhodophyta (red algae) 2,500

Total (Algae) _ 16,200*

6. Phylum Schizomycophyta (bacteria) 2,500?

7. Phylum Myxomycophyta (slime molds) 300

8. Phylum Eumycophyta (true, higher fungi) 75,000

(1) Class Phycomycetes (algalike fungi)

(2) Class Ascomycetes (ascus fungi)

(3) Class Basidiomycetes (basidium fungi)

Total (Fungi) 77,800*

Subkingdom Embryophyta

9. Phylum Bryophyta

(1) Class Musci (true mosses) 13,900

(2) Class Hepaticae (liverworts) 8,500

Total 22,400*

10. Phylum Tracheophyta

A. Subphylum Lycopsida

(1) Class Lycopodineae (club "mosses") 900

B. Subphylum Sphenopsida

(1) Class Equisetineae (horsetails) 25

*Does not include certain groups not being studied.

Survey of Plant Kingdom 111

C. Subphylum Pteropsida

(1) Class Filicinae (ferns) 8,000

(2) Class Gymnospermae (conifers and allies) 640

(3) Class Angiospermae (flowering plants) 195,000

Total

204,565

Grand Total

320,965*

Summary of Distinguishing Characteristics of Plants (Kingdom Plantae)

CHLORO-
PHYLL

TRUE

LEAVES,

STEMS,

AND
ROOTS

Multi-
cellu-
lar

EM-
BRYOS

VASCU-
LAR TIS-
SUES

(phloem

AND

XYLEM )

FLOV^^-
ERS

SEEDS
EXPOSED

(naked)

SEEDS
EN-
CLOSED

£
o

Fungi

—

C/3

Algae

—

■M

-C

a
o

-Q

w
S

Mosses and
Liverworts

—

— •

—

Club

"Mosses,"
Horsetails,
and Ferns

—

Gymnosperms

—

Angiosperms

—

The plant kingdom (Kingdom Plantae) may be divided into two sub-
kingdoms: Thallophyta (tha-lof'ita) (Gr. thallo, sheetlike or "leaf-
like"; phyta, plants) and Emhryophyta (em bri -of i ta) (Gr. embryon,
embryo; phyta, plants) . The former consists of eight phyla whose repre-
sentatives are all rather simply constructed (without true leaves, stems, or
roots), and none produce multicellular ^embryos. The Embryophyta are
primarily land plants which produce multicellular embryos in a female
sex organ. The Embryophyta will be considered later in this chapter.

SUBKINGDOM THALLOPHYTA

General Characteristics of Thallophytes

The thallophytes are simply constructed and are among the oldest of
plants. They usually live in water or moist places. They are without
true leaves, stems, or roots, although in certain species there may be
structures which resemble them in a general way. Some species are

*Does not include certain groups not being studied.

112 Plant Biology

unicellular, some consist of long filaments composed of a linear series
of cells, and others consist of sheetlike masses of cells. Some of the
higher forms are even multicellular. In general, they do not possess
rigid tissues by means of which they can grow upward to any great extent.
Thallophytes do not possess true vascular (conducting) tissues (phloem
and xylem) which are present in higher plants. Spores are produced in
sporangia (spor -an' ji a) (Gr. sporos, spore; angios, vessel) which are
usually unicellular structures. When sex cells (gametes) are formed, they
are produced in gametangia (gam e -tan' ji a) (Gr. gametes, gametes or
sex cells; angios, vessel) which are usually unicellular structures. When
the tgg is fertilized to form a zygote, the latter does not produce a multi-
cellular embryo while still in the female sex structure. Many species of
thallophytes are of great economic importance, both detrimentally and
beneficially. Thallophytes include the algae (al'ge) (L. alga, seaweed)
and the jungi (fun'ji) (L. fungus, fungus, or mushroom). The algae
contain chlorophyll which, in the presence of energy-supplying light, is
able to combine carbon dioxide and water to produce carbohydrates
through the process of photosynthesis (fo to -sin' the sis) (Gr. phos, light;
synthesis, put together). The fungi lack chlorophyll and are unable to
manufacture their foods; they must depend upon outside sources for
their nourishment. The fungi will be considered later in this chapter and
in greater detail in a later chapter.

As will be noted in the classification of plants, the first five phyla of
the subkingdom Thallophyta constitute the so-called "algae," while the
next three phyla constitute the so-called "fungi." Certain species of algae
will be considered more in detail in the next chapter.

General Characteristics of Algae

The term algae is applied to that group of thallophytes which possesses
chlorophyll by means of which photosynthesis may take place (Figs. 29 to
33). The algae vary greatly among themselves, and many of them even
resemble certain fungi in some respects. There are several characteristics
which are common to both algae and fungi, except that the former possess
chlorophyll while the latter do not. Algae are common in fresh water
(aquatic) and in salt water of oceans (marine). They may be free
living in fresh or salt water, where, together with the animals, they make
up the so-called plankton (plangk' ton) (Gr. plangktos, wandering).
Others may live on the bottom, where, together with the animals, they
constitute the so-called benthon (ben' thon) (Gr. benthos, depths of the
sea) . Certain species may grow in moist soils, on moist trees and rocks,

Survey of Plant Kingdom 113

in ice and snow, or in hot springs. Certain species may live symbiotic ally
with other organisms for mutual benefits. Algae may live symbiotically
with certain fungi in an association known as lichens (li' ken) (Gr. lei-
chen, liverwort) , in which case the algae supply foods and the fungi supply
water and give protection (Fig. 327). Some species of algae may be
parasites, others saprophytes, while a few may be found on other plants
as epiphytes (ep'ifite) (Gr. epi, upon, phyton, plant). Certain species
of algae will be considered in greater detail in the next chapter.

C^/orop/ast

Ce(/

.. CeU WqJJ

QJeocapsa

Heherocust

Hormocfon'mm

Cell

Qelaiinoas area

OscUlatona

spore

--^XeJI

Heterocust

Anah

ena

Fig. 29. — Blue-green algae of the phylum Cyanophyta.

In the following pages each phylum of plants will be considered as to
the general characteristics of the phylum as a whole, and a rather brief
classification of certain phyla into subphyla, classes, subclasses, with out-
standing characteristics, examples, and illustrations, will be given.

1. Phylura Cyanophyta (si an -of i ta) (Gr. kyanos, blue; phyta,
plants). — The blue-green algae are simple, unicellular plants, although
certain species may form colonies of similar cells with little differentia-

114 Plant Biology

tion between them. In addition to the green chlorophyll,, there is a blue
pigment called phycocyanin (fi ko -si' anin) (Gr, phykos, alga or sea-
weed; kyanos, blue). Sometimes a red pigment may also be present in
certain species. The chlorophyll is distributed throughout the cell and
is not localized in definite bodies known as plastids, as found in other
algae (Fig. 29). There is ?io definite organized nucleus; the nuclear,
chromatin materials are scattered throughout the center of the cell. The
cells are often surrounded by a slimy , gelatinous sheath. Because of this,
the term Myxophyta (myx-of'ita) (Gr. myxo, slime; phyta, plants)
has been used as the name of the phylum. Foods are stored as glycogen
(gli' ko jeii) (Gr. glykys, sweet) , a starchlike carbohydrate.

Reproduction occurs asexually by fission (cell division). No sexual
reproduction is thought to occur in blue-green algae as it does in certain
species of other algae. None of the vegetative (body) cells, or reproduc-
tive cells, possess threadlike flagella which are present in certain types
of algae of other phyla.

Most species of blue-green algae grow in fresh water, although a few
species grow in salt water. They may cause the water in ponds and
lakes to have a yellowish-green color and may be so abundant that they
are known as ''water blooms," thereby giving the water a "soupy" appear-
ance, a "fishy" taste, and a foul odor. Many species occur in soils, on
moist rocks, in greenhouses, on flower pots, and in other moist places.
Several species grow in hot springs where the temperature may be over
75° G. and where they may precipitate the magnesium and calcium salts
to form travertine (trav' er tin), a whitish, chalklike deposit which may
have bright colors because of the contained algae. Blue-green algae may
precipitate calcium carbonate in lake waters to form deposits of marl
(L. marga, marl) , an earthy mixture of clay and calcium carbonate which
is used as a fertilizer on lime-deficient soils.

Certain species may be associated with certain species of chlorophyll-
less fungi to form plants known as lichens (li'ken) (Fig. 327). A few
species may be parasites in the digestive tracts of animals, including
man. Blue-green algae, together with other algae and animals, are great
sources of foods for aquatic animals. Some species may even be present
on other plants as epiphytes (ep'ifite) (Gr. epi, upon; phyta, plants).
There are approximately 1,400 species.

Examples: Gleocapsa (Fig. 29), Oscillatoria (Fig. 29), Nostoc (Fig.
29), and Anabena (Fig. 29).

2. Phylum Chlorophyta (klor -of i ta) (Gr. chloros, green; phyta,
plants). — In certain species of green algae the chlorophyll may be asso-

Survey of Plant Kingdom 115

ciated with additional pigments known as carotinoids (carotene and xan-
thophyll). The chlorophyll is localized in definite bodies called plastids,
or more specifically known as chloroplasts (klo' ro plast) (Gr. chloros,
green; plastos, moulded or body) (Fig. 30). The cell wall consists of
cellulose (sel'u losz) (L. cellula, little cell)^ and the stored food is starch.
The latter is formed by special structures known as pyrenoids (pi' re noid)
(Gr. pyreuj fruit-stone; eidos, resemblance) located on the chloro-
plasts. The nucleus is well organized^ as is true of all algae except the
blue-green. Green algae vary in structure; the plant body may be U7ii-
cellular, colonial, or multicellular, depending upon the species. When
the vegetative (body) cells or the reproductive cells are motile, each bears
two to jour anterior flagella, usually of equal length.

- Chloroplctrfc
-->Vacl€U5

Protococcus

—Ch\orop]ait

-.//ucleus
-Pyrenoid

Spiroqyra

Ulothrix

..Pyrenoid
-//Ocleus

^-Chlorop]Qst

-.Pyrenoid
I //ucleas

Ch\orop]a5b

Desmids ^

Fig. 30. — Green algae of the phylum Chlorophyta.

Reproduction occurs (a) asexually by cell division, by fragmentation,
by motile zoospores, or by nonmotile spores or (b) sexually by isogamy
(i -sog' a my) (Gr. isos, equal; gamos, marriage) with the fusion of gam-
etes (sex cells) of equal size, by heterogamy (het er -og' a my) (Gr. het-
eros, different) with the fusion of gametes of unequal size, or by oogamy
(o-og'amy) (Gr. oon, egg) which is a special type of heterogamy in
which the female gamete {^g^) is nonmotile. The particular method
or methods of reproduction depend upon the species. The structures

116 Plant Biology

which produce the sex cells in green algae are unicellular; hence they
cannot be called sex "organs" in the true sense.

Most green algae live in fresh water^ although a few live in the water of
the ocean (marine). Other species live in soils, on rocks or trees, in
ice or snow. Some species live in salt lake waters whose concentration of
salt is much greater than that of ocean water. A few species live on
other plants or animals. A few live symbiotically with such animals as
protozoa, sponges, and Hydra. Sometimes certain types may live sym-
biotically with certain species of chlorophyll-less fungi to form plants
called lichens (Fig. 327). Green algae, together with other algae and
animals, may supply foods for fresh-water and marine animals. Certain
marine forms in conjunction with red algae may secrete lime salts which
assist in the formation of reefs in the ocean. There are approximately
5,700 species.

Examples: Chlamydomonas (Fig. 61), Ulothrix (Fig. 30), Protococ-
cus (Fig. 30), Spirogyra (Figs. 30 and 62), and desmids (Fig. 30).

3. Phylum Chrysophyta (kris -of i ta) (Gr. chrysos, gold; phyta,
plants) . — In the yellow-green algae, or golden-brown algae, or diatoms,
the yellowish-brown pigments known as carotinoid pigments are more
abundant than the chlorophyll so that they may have yellowish-green or
golden-brown colors. The pigments are contained in special bodies called
plastids. A well- organized nucleus is characteristic. The cell walls may
be composed of a pair of overlapping halves (valves) which are fre-
quently impregnated with glasslike silica (Fig. 31), Depending upon
the species, these algae may be unicellular, colonial, or, in a few instances,
multicellular individuals. The stored foods are oils and an insoluble
carbohydrate called leucosin (lu'kosin) (Gr. leukos, white).

Asexual reproduction occurs by cell division, by motile zoospores, or by
nonmotile spores. When present, sexual reproduction occurs by isogamy
(fusion of similar gametes). The method or methods of reproduction
depend upon the species. There are approximately 5,700 species.

Example: Diatoms (Fig. 31).

4. Phylum Phaeophyta (fe-of'ita) (Gr. phaios, brown or dusky;
phyta, plants) . — The brown algae are multicellular, some species being
quite large. They are nonmotile (sessile), being attached by rootlike
holdfasts. Depending upon the species, the plant body may be composed
of a few cells or it may be over a hundred feet long, as in some of the
kelps. Brown algae are marine, usually present in colder waters. The
chlorophyll is masked by a golden-brownish pigment called fucoxanthin

Survey of Plant Kingdom 117

(fu ko -zan' thin) (L. jucus, alga or seaweed; xanthos, yellow) . Usually
there are several plastids per cell^ but no pyrenoids are present. Each
cell has a single, organized nucleus and may contain vacuoles. Some of
the cells have an organization similar to that of higher plant cells, some
even having a centrosome similar to that of animal cells. Stored foods
are jats and soluble sugars.

^^'^^■i-

Fig. 31. — Photograph of several species of diatoms of the phylum Chrysophyta.
(Copyright by General Biological Supply House, Inc., Chicago.)

Brown algae possess alternation of generations or metagenesis (met a-
jen'esis) (Gr. meta, over; genesis, origin) in which a free-living, multi-
cellular, gamete-producing gametophyte (gam -me' to fite) (Gr. gamos,
marriage; phyta, plants) alternates with a free-living, multicellular, spore-
producing sporophyte (spor'ofite) (Gr. spora, spore or "seed"; phyta,

118 Plant Biology

plants) . Depending upon the species, asexual reproduction may occur
by fragmentation, by motile zoospores, or by nonmotile spores. Depend-
ing upon the species, sexual reproduction may occur by isogamy, by
heterogamy, or by oogamy. When present, the motile, pear-shaped re-
productive cells bear two lateral flagella of unequal length.

Certain brown algae are of value as sources of iodine, potassium,
fertilizers, and foods for animals and man. There are approximately 900
species.

Examples: The Kelp (Laminaria) (Fig. 32) and Rockeed (Fucus)
(Fig. 32).

Fig. 32. — Brown algae of the phylum Phaeophyta. A, The kelp {Laminaria sp.) ;

B, the rockweed {Fucus sp.).

5. Phylum Rhodophyta (ro -dof i ta) (Gr. rhodon, red; phyta, plants) .
• — The red algae are frequently referred to as "sea mosses" because of
the fancied resemblance of certain forms to true mosses. They contain
plastids with chlorophyll associated with a red pigment called phycoe-
rythrin (fai ko e -rith' rin) (Gr. phykos, alga or seaweed; erythros, red)
and sometimes with a blue pigment called phycocyanin. In most species
the plants are multicellular and may be branched or rather simple, in
the form of a ribbon cylinder, or sheet. Different species vary in size
from a few inches to several feet in length. Each cell contains a nucleus,
central vacuoles, and one or several plastids, some of which possess pyre-
noids. Broad, cytoplasmic strands which connect adjacent cells are fea-
tures of red algae. Stored foods are insoluble ''starches."

Survey of Plant Kingdom 119

Reproduction may occur asexually by nonmotile carpospores produced
in a special structure known as a carpogonium (kar po -go' ni um) (Gr.
karpos, fruit; gonos, birth) . The latter is characteristic of red algae. The
nonmotile sperm (from the antheridia) is carried by water to the female
carpogonium where fertilization results in a zygote. The latter forms
many filaments, the tips of which form the many carpospores. In Poly-
siphonia, the carpospore forms a new plant which produces sporangia
(spor -an' ji a) (Gr. spores, spore; angos, vessel), each with four asexual
tetraspores (tet' ra spor) (Gr. tetra, four; sporos, spore). The nonmotile
tetraspores produce Polysiphonia plants either with male antheridia or
with female carpogonia. Because the sex cells are unlike and the egg is
nonmotile, the process is called oogamy. None of the sex cells, or asexual
reproductive cells, bear fiagella which is characteristic of red algae.

Male orqan

_ Reproduction
Conceptacle

Fig, 33. — Red algae of the phylum Rhodophyta. A, "Irish moss" {Chondrus sp.) ;

B, feathery thallus of Polysiphonia sp.

Most red algae are usually attached m warmer sea waters (marine),
although a few species are inhabitants of fresh water. There are approx-
imately 2,500 species.

Examples: Nemalion (Fig. 63), Polysiphonia (Fig. 33), and Chon-
drus (Fig. 33).

General Characteristics of Fungi

The "fungi," which include the last three phyla [Schizomycophyta,
Myxomycophyta, and Eumycophyta) of the Thallophytes, may be char-
acterized as follows: Fungi lack chlorophyll and consequently must de-
pend upon a heterotrophic mode of nutrition (het ero -trof ik) (Gr.

120 Plant Biology

heteroSj other; trophe, food or nourishment). Because they must secure
foods from outside sources, fungi must live in an environment in which
there is a certain amount of moisture. Heterotrophic fungi may be
(1) saprophytes (sap' ro fite) (Gr. sapros, dead; phyton, plant) living
on dead organic materials or (2) parasites (pa' ra site) (Gr. para, beside;
sitos, food) living in, or on, the body of another living plant or animal.
A few species of fungi are autotrophic, and they will be considered later.
Fungi lack true leaves, stems, and roots; they do not form multicellular
embryos; they lack true vascular (conducting) tissues (phloem and
xylem) which are present in higher plants. Included in the "fungi" are
bacteria, slime molds, yeasts, bread molds, water molds, mushrooms,
bracket fungi, Penicillium, smuts, rusts, etc. The bacteria differ from
the slime molds and other fungi in that the former are unicellular, with
smaller cells, and without an organized nucleus.

6. Phylum Schizomycophyta (skiz o my -kof i ta) (Gr. schizo, split or
fission; mykes, fungus; phyta, plants). — The bacteria (bak -ter' i a) (Gr.
bakterion, small rod) are simple, unicellular (microscopic) plants without
chlorophyll so that a great majority of them must secure foods from out-
side sources, although a few are able to manufacture foods by chemo-
synthesis or by photosynthesis (Fig. 34). The method of nutrition for
a majority of bacteria is heterotrophic (het ero -trof ik) (Gr. heteros,
other; trophe, food or nourishment), securing their foods from outside
sources. Consequently, they may be (1) saprophytes (sap'rofites) (Gr.
sapros, dead; phyton, plant) which obtain foods from dead, nonliving
organic materials or (2) parasites (pa' ra site) (Gr. para, beside; sitos,
food) which live in, or on, the living bodies of plants or animals. In the
latter instance, if a diseased condition is produced, they are known as
pathogenic bacteria (path o -jen' ik) (Gr. pathos, suffering; genos, pro-
duce). A rather small group of bacteria can synthesize organic foods
from carbon dioxide and other simple inorganic substances. Conse-
quently, they are autotrophic (o to -trof ik) (Gr. autos, self; trophe,
nourish). The autotrophic types may be grouped as (1) chemosynthetic
(kem o sin -thet' ik) (Gr. chymos, juice; syn, with; tithenai, to place), in
which the energy required for the synthesis of foods is derived from the
oxidation of certain chemicals, and (2) photosynthetic, in which light
supplies the food-forming energy and the pigments are purplish-red, or
greenish, but are not chlorophyll. The chemosynthetic and photosyn-
thetic bacteria are considered in a later chapter.

Bacteria are considered to be plants rather than animals ( 1 ) because
of their methods of reproduction which resemble those of certain algae

Survey of Plant Kingdom 121

and true fungi, (2) because their cell walls often contain cellulose, a sub-
stance which is quite common in higher plants, (3) because they syn-
thesize vitamins like those of certain plants, (4) because some species are
able to utilize simple, inorganic materials from which more complex
organic compounds may be synthesized.

The forms which bacterial cells may assume include (1) the coccus
(spherical), (2) rod shaped (cylindrical), (3) spiral shaped, (4) fila-
mentous (which may be branched) (Fig. 34). A bacterial cell has a
cell wall which in some species contains cellulose. The protoplasm of
the cell is somewhat homogeneous, contains vacuoles and granules, in-
cluding chromatin. No organized nucleus and no plastids are present.

i^ ^aK

•V

-flaCjQWa ;;^

T-/

C^rar\u]aied ^.^ Banded ,•.

i^ore

Fig. 34. — Various types of bacteria (coccus or spherical, rod-shaped, spirals)
of the phylum Schizomycophyta. A, Staphylococcus aureus (0.8-1.0/^), boils, ab-
scesses, pus, etc.; B, Streptococcus pyogenes (0.6- 1.0m), infections, etc.; C, Strepto-
coccus erysipelatis (0.6-0.8/"), erysipelas; D, Streptococcus scarlatinae (0.6-1.0/i),
scarlet fever; E, Diplococcus pneumoniae (0.5-1.0/i), pneumonia; F, Neisseria
gonorrheae (gonococcus) (0.6-I.Om), gonorrhea; G, Neisseria intracellularis
(meningococcus) (0.6-0.9/i), meningitis; H, Escherichia coli (colon organism)
(0.5 X 1.0/i), intestinal organisms; I, Eberthella typhosa (0.6 x 2.5/x), typhoid
fever; /, Corynebacterium diphtheriae (0.3-0.8 x 1.0-6.0/i), diphtheria; K, hemo-
philus influenzae (0.2 x 0.7 fi), influenza (?); L, Hemophilus pertussis (0.3 x
0.7m), whooping cough; M, Mycobacterium tuberculosis (0.15-0.35 x 0.5-5. 0/i),
tuberculosis; A''^ Clostridium tetani (0.4-0.6 x 2.0-4.0/i), tetanus or lockjaw; O,
Vibrio comma (0.4-0.6 x 1.0-3.0m), Asiatic cholera. Organisms drawn somewhat
on proportionate scale. Actual dimensions are given in microns (/i), which are
each equal to 1/25,000 inch.

122 Pla?it Biology

Not all species are able to locomote in a liquid, but when they do, this
is accomplished by the rhythmic, vibratile actions of whiplike proto-
plasmic structures known as flagella (fla -jel' a) (L. flagellum, whip).

Certain types of bacteria, like higher plants, require free atmospheric
oxygen for their normal activities and are known as aerobes (a'erobe)
(Gr. aer, air; bios, life). Other species do not require free oxygen but
secure it by breaking down certain types of oxygen-bearing foods through
the action of enzymes. These are known as anaerobes (ana' er obe) (Gr.
an, without; aer, air; bios, life).

The various types of bacteria grow at different temperatures. Those
growing best at temperatures of 14° C. or below are known as psychro-
philes (si'krofil) (Gr. psychros, cold; philein, to love) and those having
an optimum temperature between 20° and 40° C. are mesophiles (mes' o-
fil) (Gr. me SOS, middle), while those that grow best above 45° C. are
called thermophiles (ther'mofil) (Gr. thermo, heat).

Bacteria produce enzymes (en'zim) (Gr. en, in; zyme, leaven) with
which they perform various functions. Those which are active within
the cells (intracellular) are called endoenzymes, while those which are
secreted to the outside are called (extracellular) exoenzymes.

Not all bacteria produce diseases; in fact, a great majority of them
do no harm, and a few species are actually beneficial. Pathogenic bac-
teria may produce diseases in other plants, in animals, and in man.
Bacteria reproduce asexually by fission in which the cell divides into two
parts. Frequently, after fission, the cells may remain together to form
a colony. Under favorable conditions fission may occur every twenty to
thirty minutes. Certain species produce resistant endospores by a con-
densation of the cell contents into a spherical or oval mass and the loss of
a certain amount of water (dehydration). A resistant spore wall sur-
rounds the spore (Fig. 34). A few species of bacteria may produce
within their cells a number of small bodies called gonidia (go -nid' i a)
(Gr. gone, "seed"; idion, small), each of which develops into a typical
bacterial cell. Certain species, especially the filamentous types, may
produce tiny conidia (ko-nid'ia) (Gr. konis, dust; idion, small) at the
tips of the filaments, similar to the formation of such structures by cer-
tain true fungi.

Examples: Bacteria (various types of cocci, rods, spirals, and fila-
ments) (Fig. 34).

7. Phylum Myxomycophyta (mik so mai -kof i ta) (Gr. myxos, slime;
mykeSj fungus; phyta, plants). — The slime molds (slime fungi) are

Survey of Plant Kingdom 123

primarily saprophytes on damp, decaying vegetable materials. They
resemble certain fungi in their methods of spore formation and resemble
certain lower animals because of their slimy, amoeba-like bodies, their
amoeboid methods of locomotion by the formation of pseudopodia, and
their ingestion of solid foods. The vegetative plant body is a thin mass
of naked, slimy protoplasm known as the Plasmodium (plaz -mo' di um)
(Gr. plasma, liquid; eidos, form) which contains numerous nuclei (multi-
nucleated) and creeps by a flowing of the protoplasm with the forma-
tion of pseudopodia (su do -po' di a) (Gr. pseudes, false; pous, foot) . It
ingests solid foods in ways which resemble those of certain lower animals.

STEM0NITI5

LYCOGALA

Fig. 35. — Slime molds of the phylum Myxomycophyta. Stemonitis shows a
stalked sporangium (spore case) with its branched capillitium and spores. Ly co-
gala shows, A, fruiting bodies (sporangia) which produce spores internally; B,
germinating spore to form a mononucleated protoplast; C, a mononucleated, pear-
shaped swarm spore with a flagellum at the pointed end; some of the swarm
spores function as gametes to form a zygote which eventually grows to form a
multinucleated, amoeboid plasmodium; from the latter are produced the fruiting
bodies again.

The Plasmodium produces a number of spore cases called sporangia
(spor -anj' i a) (Gr. sporos, spore or "seed"; anggeion, vessel) . The color
of the sporangium varies with the species (colorless, purple, orange,
brown, etc.). Numerous unicellular, nonmotile spores are formed in
each sporangium. Each germinating spore forms one to four swarm

124 Plafit Biology

cells or myx amoebae (mik sa -me' be) (Gr. myxa^ slime; amoibe, change),
each having one to two flagella. Locomotion is by flagella or by the
formation of pseudopodia. Two myxamoebae fuse to form a zygote
(zi'gote) (Gr. zygotos, joined) by a process somewhat like sexual repro-
duction. Several zygotes may join to form a new Plasmodium in which
the nuclei are not fused. There are approximately 300 species. Slime
molds are considered more in detail in a later chapter.

Examples: Stemonitis (Fig. 35) and Lycogala (Fig. 35).

\ounq sporanqlum

' \' Sporanqium

Spore

Beginning of o

sporancjium

Sporan (jiophote

HyphaXi

D L

-Sporartqium Uv^

-Hypha f^:

Fig. 36. — Black bread mold (Rhizopus nigricans) of the phylum Eumycophyta,
class Phycomycetes. A, Portion of mycelium; B, sporangium (enlarged and with
escaping spores) ; C, germination of spore into mycelium; D-F, conjugation of
hyphae (+ and -) to form a zygote; G-J, formation and germination of zygospore.
Stages A-C show asexual spore formation; stages D-J show sexual spore (zygospore)
formation.

8. Phylum Eumycophyta (yu mai -kof i ta) (Gr. eu, true or good;
mykes, fungus; phyta, plants). — These true, higher fungi include the
algalike fungi of the class Phycomycetes, the sac (ascus) fungi of the
class Ascomycetes, and the basidium (club) fungi of the class Basidio-
mycetes.

Survey of Plant Kingdom 125

(1) Class Phycomycetes. — The algalike fungi of the class Phyco-
mycetes (fi ko mai -se' tez) (Gr, phykos, algalike; mycetes, fungi) consist
of filamentous hyphae, with organized nuclei but usually without septae
(cross walls). The threadlike hyphae (hi'fe) (Gr. hyphe, web) fre-
quently form a web known as the mycelium- (mi -se' li um) (Gr. mykes,
fungus). Members of this class are common saprophytes^ some living in
water. Young hyphae may be branched, nonseptate, and contain numer-
ous nuclei. Older hyphae, especially during sexual reproduction, may
show septae. Rootlike rhizoids {yV zoid) (Gr. rhiza, root; eidos, form)
may absorb materials from the substratum and anchor the plant. Spo-
rangiophores (spor-an'ji for) (Gr. sporos, spore; anggion, vessel;
pherein (to bear), bear spore cases called sporangia in the species which

-Nucleus

-CytopJa5^m__
- -Vacuole '

--Aucleus

-Vacuole
-Cytoplasm

Fig. 37. — Bread yeast (Saccharomyces cerevisiae) of the phylum Eumycophyta,
class Ascomycetes. A, Yeast cell; B, three stages showing reproduction by budding
(asexual) ; C, yeast cell which under certain conditions will develop an ascus (Z))
with its ascospores (£). A new yeast cell will develop asexually from each
ascospore.

are not aquatic. The air-borne, nonmotile, asexual spores germinate to
form new hyphae. In aquatic species, .such as Saprolegnia, motile zoo-
spores are formed in zoosporangia. Sexual reproduction may occur by
isogamy or heterogamy, depending upon the species. The sexual method
is known as conjugation and takes place between two different filaments
(as in Rhizopus) or between two different parts of the same filament (as
in Saprolegnia) . In each instance the fertilized egg forms a zygote
(zygospore) which develops a new hypha.

Examples: Rhizopus (black bread mold) (Fig. 36) and Saprolegnia
(water mold) (Fig. 64).

(2) Class Ascomycetes. — The ascus (sac) fungi belong to the
class Ascomycetes (as ko mai -se' tez) (Gr. ascus, sac; mycetes, fungi)
because at some stage in their life cycle all of them may reproduce by

126 Plant Biology

the formation of a saclike ascus in which are formed ascospores. They
all possess organized nuclei and all are filamentous, with such exceptions
as certain types of yeasts. When hyphae are present, they are septate
(cross walls). Many species are ot great economic importance in the

Fig. 38. — Blue-green mold {Aspergillus sp.) of the phylum Eumycophyta, class
Ascomycetes. A, Portion of mycelium, showing spore formation; B-C, spore and
its germination ; D-F, formation of ascospores ; D, hypha twisted into a coil ; E,
coiled hypha surrounded by an ascus (sac) ; F, coiled hypha forming ascospores
within the ascus.

Conidia (spores)

\ »

Sporophore--

Rhi^oid

Fig. 39. — Bluish-green mold {Penicillium sp.) of the phylum Eumycophyta,
class Ascomycetes. Such molds do not frequently form ascospores. although a
few species do so occasionally.

manufacture of foods, as cheeses by such types as Penicillium camemherti
or P. requeforti, in the production of antibiotics by such types as Peni-
cillium notatum, etc., in the fermentation of sugars by yeasts, by para-

Survey of Plant Kingdom 127

sitizing higher plants with the production of such diseases as powdery
mildews, and by the production of such plant diseases as blights, etc.

Certain species reproduce asexually by the formation of conidiospores
(ko -nid' i o spor) (Gr. konis, dust; sporos, spore) in which the tips of

Ascospore

ParapKuses

Ascus
nucelium

Huphae

HumemuTn

Fig. 40. — Cup fungus (Peziza) of the phylum Eumycophyta, class Ascomy-
cetes. A, cup with mycelium for attachment; B, section through the cup show-
ing the hymenium; C, enlarged section of the hymenium showing immature and
mature asci with ascospores, paraphyses, and hyphae.

certain hyphae form chains of colored spores (conidia), as in Penicil-
lium, Aspergillus, etc. Yeasts commonly reproduce by asexual budding
in which a small protuberance is pushed from the cell. The ascomycetes
are considered in more detail in a later chapter.

128 Plant Biology

Pikus

_(^/7/s— >

Hypha -JUI

Basidium.-

^tenqmata--

Button " dasidiospores—
^ypha \

AiyceU

Fig. 41. — Common edible or field mushroom (Psalliota [Agaricus] campestris)
of the phylum Eumycophyta, class Basidiomycetes. A, The so-called mushroom
(sporophyte) ; B, three gills of the mushroom in cross section; C, one gill much
enlarged to show its hyphae and basidia ; D, a basidium with basidiospores; E;
germinating spore; F, immature "button" mushroom; G, later stage in develop-
ment of the immature into the mature mushroom.

Fig. 42. — Shelf (bracket) fungus of the phylum Eumycophyta, class Basidio-
mycetes. A, Attached to a tree; B, section of a sporophore showing three annual
layers of the porous hymenium, with the newest below; C, undersurface showing
openings to pores, beneath which are borne the basidiospores.

Survey of Plant Kingdom 129

Examples: Penicillium (Fig. 39), Aspergillus (Fig. 38), cup fungi
such as Peziza (Fig. 40), yeasts (Fig. 37), powdery mildews, and blights,
etc.

(3) Class Basidiomycetes. — The basidium (club) fungi belong
to the class Basidiomycetes (ba sid i o mai -se' tez) (Gr. basidium, club or
base; mycetes, fungi) because they produce basidiospores on club-shaped
basidia (ba -sid' i a) (Gr. basis, base) . They all possess organized nuclei;
they all are constructed of filamentous hyphae which are septate (cross
walls). In some instances the hyphae may be rather closely compacted
and the interhyphal spaces may even be filled in with rather solid sub-
stances, as in the case of the bracket (shelf) fungi (Fig. 42).

In certain species other types of asexual spores are produced. For
example, certain types of smuts produce conidiospores somewhat like
those produced by certain ascomycetes. In the corn smut (Fig. 66),
the fungi produce heavy-walled, dark-colored smut spores called chlamy-
dospores (klam' i do spor) (Gr. chlamys, cloak; sporos, spore). In the
black stem rust of wheat (Puccinia graminis) several varieties of spores
(Fig. 67) are formed: reddish-orange, summer spores known as uredo-
spores (u -re' do spor) (Gr. uredo, blight; sporos, spore), brownish-black
winter spores known as telios pores (te'liospor) (Gr. telios, end; sporos,
spore), small pycniospores (pik' ni o spor) (Gr. pyknos, crowded), and
spring spores called aeciospores (e' si o spor) (Gr. aecium, injury).
These various types of spores are considered in greater detail in a later
chapter.

Examples: Mushrooms (Fig. 41), bracket fungi (Fig. 42), smuts
Fig. 66), and rusts (Fig. 67).

SUBKINGDOM EMBRYOPHYTA

General Characteristics of Embryophytds

The Embryophytes constitute the remainder of the plant kingdom,
and their representatives, in general, are more complex than the Thallo-
phytes. Embryophyta (em bri -of i ta) (Gr. embryon, embryo; phyta,
plants) produce a multicellular embryo from the fertilized egg (zygote)
which is parasitic for some time in the female sex organ (in the gameto-
phyte in higher plants) . They all produce multicellular sex organs which
are surrounded by a sterile, protective jacket layer. The male sex organ
is the multicellular antheridium (an ther -id' i um) (Gr. anthos, flower;
idion, diminutive), while the female sex organ is the multicellular arche-
gonium (ar -ke go' ni um) (Gr. arche, beginning; gonos, offspring) . The

130 Plant Biology

multicellular spore-forming spore cases, called sporangia (spor -anj' i a)
(Gr. sporos, spore or "seed"; anggeion, vessel) are also protected by a
sterile jacket layer. These protective jacket layers are necessary in land
plants where they are subjected to a variety of environmental influences.
All embryophytes reproduce by oogamy (o -og' a my) (Gr. oon, ^g^;
gamos, marriage) in which unlike sex cells (gametes) fuse and the egg
cell is nonmotile. All have a definite alternation of generations in which
a multicellular sporophyte (spor' o fite) (Gr. sporos, spore; phyton, plant)
alternates with a multicellular gametophyte (gam e' to fite) (Gr. gametes,
spouse; phyta, plants) . '^

Embryophytes are essentially terrestrial (land plants), although a few
species may live in water. They all contain chlorophyll in green plastids.
The aerial parts of the plants may be protected by a layer of waxlike
cutin. Embryo phyta include the two phyla Bryo phyta and Tracheophyta,
both of which are considered in greater detail in later chapters.

9. Phylum Bryophyta (bri -of i ta) (L. hryon, moss; phyta, plants) . —
The Bryophytes include the liverworts, which belong to the class Hepaticae
(he -pat' i se) (L. hepaticus, liver), and the true mosses, which belong to
the class Musci (mu' si) (L. muscus, moss). They are terrestrial plants
which require a certain amount of moisture for their living activities, and
water is required for the transmission of the male sperm to the female
egg. They possess chlorophyll in chloroplasts for the process of photo-
synthesis. Liverworts and true mosses possess similar methods of repro-
duction arid life cycles and are much alike structurally and functionally
in spite of differences which may appear upon casual observation. In
general, the plant body of Bryophytes is never filamentous but is com-
posed of blocks, or sheets, of cells forming a parenchymatous tissue
(par eng -kim' a tus) (Gr. para, beside; engchyma, infusion) composed of
cells with rather thin walls. Consequently, none of the Bryophytes grow
to any great height. 'They lack true roots, true stems, and true leaves,
because they lack the vascular tissues, xylem and phloem, which are
present in higher plants. Rootlike rhizoids anchor the plants and absorb
materials from the substratum.

Bryophytes possess alternation of generations in which a multicellular
gametophyte alternates with a multicellular sporophyte. The latter is
more or less dependent upon the gametophyte. The multicellular,
gamete-producing gametangia (gam e -tan' ji a) (Gr. gametes, gametes,
or spouse; anggeion, vessel) possess a protective layer of sterile cells.
Bryophytes develop a multicellular embryo from the fertilized egg
(zygote), from which the sporophyte develops. No asexual spores are

Survey of Plant Kingdom 131

produced. Asexual reproduction may occur by fragmentation of the
plant or by special bodies known as gemmae (jem'i) (L. gemma, bud),
depending upon the species.

(1) Class Hepaticae (Liverworts). — Many of the liverworts grow
fiat on the substratum and have dorsoventral bodies, with the dorsal
(upper) surface of their gametophyte different from the ventral (lower)
surface. Certain liverworts have flat, lobed, thallose bodies which have
a fancied resemblance to the lobes of a liver of higher animals; for
example, Marchantia (Fig. 43). Other species, called the leafy liver-
worts, have bodies with "leaf like" structures (not true leaves), thus

/^rchegoniophc re

0\jam

ArcheaorYiuvn ^..^rgg^^^

~Kh\7p\ds

gemma

Ar)thend\ophorQ ^ ^ ^p^
(Aiale)

Fig. 43. — Common liverwort {Marchantia sp.) of the phylum Bryophyta, class
Hepaticae. A, Female plant or thallus; B, gemma produced in a cupule; the
gemma will develop into a thallus similar to the one on which it was formed; C,
longitudinal section of an archegonial receptacle (female) ; D, archegonial recep-
tacle in a longitudinal section much enlarged; E, male plant or thallus; F, longi-
tudinal section of an antheridial receptacle (male) ; G, antheridial receptacle in
logitudinal section much enlarged ; H, archegonial receptacle in longitudinal sec-
tion still further enlarged and with a sporophyte (spore-forming plant) attached
to the base of the archegonium; the sporangium is filled with spores; I, spore
germinating into a new thallus with its rhizoids. The thalli will develop into adult
liverwort plants.

resembling certain true mosses, except that these leafy liverworts are
prostrate on the substratum; for example, Porella (Fig. 44). There are
approximately 8,500 species. Liverworts are considered in greater detail
in a later chapter.

Examples: Thalloid liverworts (Marchantia) (Fig. 43) and leafy
liverworts (^Por^//<2J (Fig. 44).

132 Plant Biology

(2) Class Musci (True Mosses). — These are small, green plants
which are usually upright and may grow so densely in some moist places
as to form a mat of vegetation. Such masses of vegetation may consist
of hundreds of individual moss plants. Even though mosses contain

Sporophu'te

f^hizo/a

eauee

ler/d/a

'di\

Se-i

Too't

Elai

Jacket of capsule

rlrchegonium

Spore TnoTne'r cell

Fig. 44. — Leafy liverwort {Porella) of the phylum Bryophyta, class Hepaticae.
A, female plant with an attached sporophyte ; B, portion of a branch of a male
plant bearing antheridia which produce antherozoids (male) ; C, young arche-
gonium from an archegonial branch of a female plant showing an egg and elon-
gated neck; D, developing sporophyte (in longitudinal section) attached to the
parent gametophyte.

Survey of Plant Kingdom 133

rootlike rhizoids and structures which superficially resemble stems and
leaves, they are not true roots, stems, and leaves, because they lack the
vascular tissues (phloem and xylem). Each individual consists of a
stemlike axis with its small, attached leaflike structures. The sporophyte
of most mosses is usually larger than those of liverworts, even though the
sporophytes are parasitic in both. There are approximately 13,900
species. True mosses are considered in greater detail in a later chapter.
Examples: Polytrichum (hairy-cap moss) (Fig. 45) and Sphagnum
(peat or bog moss) (Fig. 46) .

AritheridluYX)

Jporanqium
-Jperr

Fig. 45. — Common moss (Polytrichum sp.) of the phylum Bryophyta, class
Musci. A, Male gametophyte plant with cluster of antheridia at tip; B, tip of
male gametophyte enlarged to show antheridia which produce sperm; C, female
gametophyte plant with cluster of archegonia at tip; D, tip of female gametophyte
enlarged to show archegonia which produce eggs (ova) ; an ovum fertilized by a
sperm is shown developing (at the right) into a sporangium (spore-bearing organ)
which produces numerous spores; E, spore germinating to form a bud which de-
velops into a gametophyte plant (either male or female).

10. Phylum Tracheophyta (tre ke -of ' i ta) (Gr. tracheia, duct or ves-
sel; phyta, plants). — The plants of this phylum all possess a vascular
system composed of phloem and xylem tissues whose complexity varies
with the various groups. This phylum includes the club "mosses" of
the subphylum Lycopsida, the horsetails of. the subphylum Sphenopsida,
and the ferns, gymnosperms, and angiosperms (flowering plants) of the
subphylum Pteropsida.

Tracheophytes possess true leaves, stems, and roots, skeletal materials
for more or less upright growth, stomata (small openings) for the ex-

134 Pla?it Biolooy

change of gases, and a protectixe layer of waxlike cutin, in certain parts.
The sporophyte is larger than the rather inconspicuous gametophyte,
and the former is independent when mature. Hence, there is an alter-
nation of generations. Tracheophytes are primarily terrestrial, although
some live in water. The development of plants with vascular systems is
one of the great steps in the evolution of plants. A recent theory suggests
that the vascular plants may have evolved from some algal ancestor,
probably from the Chlorophyta. All possess multicellular sex organs, and
multicellular embryos are developed from the fertilized egg (zygote).

Fig. 46. — Bog or peat moss (Sphagnum) of the phylum Bryophyta, class Musci.
A, plant showing terminal antheridial (male) branches (at tip) ; B, antheridium
(in section) producing sperm; C, archegonium (in section) showing egg and
elongated neck; D, plant showing terminal sporophytes (at tip) ; E, sporophyte
(in section) showing basal foot for attachment to gametophyte, the seta, and the
production of spores; F, leaflike organ (surface view) showing cells containing
chloroplasts and other clear, dead cells for water storage: the latter connect with
the outside by means of pores; G, protonema (young thalloid gametophyte) from
which the erect, adult gametophyte will arise; rootlike rhizoids are shown.

A. Subphylum Lycopsida (laik -op' si da) (Gr. lykos, wolf; opsis,
appearance). — The club "mosses" belong to the class Lycopodineae
(lai ko po -din' e e) (Gr. lykos, wolf; pous, foot). The sporophyte con-

Survey of Plant Kingdom 135

sists of true root, stem, and leaves. The small, microphyllous leaves
(mi kro -fil' us) (Gr. mikros, small; phyllon, leaf) are usually spirally
arranged. The roots and stems are usually branched dichotomously
(di -kot' o mus ly) (Gr. dicha, in two; temnein, to cut). Spore-produc-
ing sporangia occur singly on the upper surface of specialized leaves
known as sporophylls (spor'ofil) (Gr. sporos, spore; phyllon, leaf).
Usually the sporophylls with their sporangia are grouped at the tips of
the stems to form cones or strobili (strob' il i) (Gr. strobilos, cone) . The
spore-bearing organs are often foot or club shaped. Club "mosses" are
principally perennial, creeping evergreens, which explains their common
name of "ground pines."

Examples: Club "moss" (Lyco podium) (Fig. 47) and smaller club
"moss" (Selaginella) (Fig. 48).

Jtrobilus {cone)

___iL(2aF

Stem

Boots

Sporanqium

Spores

Fig. 47. — Club "moss" or "ground pine" {Lycopodium sp.) of the subphylum
Lycopsida, class Lycopodineae. A, Branches bearing reproductive strobili, each
with sporophylls; B, sporophyll enlarged, showing sporangium and spores.

B. Subphylum Sphenopsida (sf en -op' si da) (Gr. sphen. wedge;
opsis, appearance). — The horsetails belong to the class Equisetineae
(ek wi se -tin' e e) (Gr. equus, horse; seta, tail or hair) . The sporophyte
has true roots, stems, and leaves; the small leaves are scalelike (sometimes
wedgelike) and in whorls at the nodes of the hollow, jointed stems (dis-
tinct nodes) ; stems are usually ribbed and impregnated with silica which
explains the common name of scouring rushes. A horizontal, branched,
underground stem, or rhizome (ri'zom) (Gr. rhizoma, root) in most
species, bears two types of aerial stems: (1) the sterile, green branched

136 Plant Biology

vegetative stem and (2) the colorless, unhranched, fertile, reproductive
stem with its single, terminal cone.

Sporangia (five to ten in number) are borne on a sporangiophore
which is shield shaped or umbrella shaped. Numerous sporangiophores
are grouped to form the cones (strobili). The spores are alike (homo-
sporous), and each has four ribbonlike, hygroscopic elaters (el'ater)
(Gr. elater, driver) which are affected by moisture changes to assist in
the movement of the spores. A germinating spore forms a small, green,
ribbonlike young gametophyte, with rhizoids, and usually with both male
antheridia and female archegonia. The spiral, multiflagellated sperms
swim to the archegonium where the egg is fertilized to form a zygote.

•v-i^-;,.,^^>».;..i;rj;/--

E F

Fig. 48. — Smaller club "moss' (Selaginella) of the phylum Tracheophyta, class
Lycopodineae. A, Part of a mature sporophyte ; B, strobilus (from tip of branch)
consisting of numerous sporophylls, each with a basal sporangium ; C, micro-
sporangium (in section) producing small microspores; D, microsporangium (in
section) in which biflagellated sperms (antherozoids) are produced from mega-
gametophytes, the latter having developed from microspores; E, megasporangium
(in section) producing large megaspores; F, archegonium (in section) with its
egg, in a megagametophyte, and a sperm about to enter; a megaspore (within
the megasporangium) germinates to form a megagametophyte which contains
archegonia (with egg, etc.) ; a fertilized egg forms a zygote from which develops
the parasitic, embryonic sporophyte; G, older sporophyte (still attached to the
megagametophyte) bearing embryonic, primary stem, leaves, and roots.

Survey of Plant Kingdom 137

The latter forms a multicellular embryo which develops into a new sporo-
phyte. Hence, there is alternation of generations. There are approxi-
mately 25 species.

Examples: Horsetail (Equisetum) (Fig, 49).

,£later

^^^^ Archeqonmm

t-Hhi^oid

Fig. 49. — Common horsetail or scouring rush (Equisetum) of the subphylum.
Sphenopsida, class Equisetineae. A, Sterile, vegetative branch (left) and fertile,
reproductive branch (right) ; B, one unit of a strobilus much enlarged to show
several sporangia; C, prothallus with antheridia for sperm production and an
archegonium for egg (ovum) production; D, gametophyte with archegonia for
ovum (egg) production and antheridia for sperm production; E, embryo of horse-
tail plant developing from a fertilized ^%g in the gametophyte. The embryo con-
sists of two primary leaves, a stalklike foot, and a primary root. The prothallus
eventually disappears and the embryo develops into a mature plant with both kinds
of aerial branches, as shown in A.

C. Subphylum Pteropslda (ter -op' si da) (Gr. pteris, wing or fern;
opsis, appearance ) . —

Ferns. — The true ferns belong to'^the class Filicineae (fil i -sin' e e)
(L. filix, fern). The sporophyte consists of true roots, stem and leaves;
the leaves are generally large, or megaphyllous (Gr. me gas, large), and
in ferns are commonly called fronds. The vascular system is rather well
developed (Figs. 50, 51, 68, and 69) .

Multicellular sporangia are borne in clusters, called sori (so' ri) (Gr.
soros, heap), on the lower surface of the leaves or on the margins in cer-
tain species. In the ferns, the sporophyte is large and independent when
mature, while the gametophyte is small, free living, and also independent.
This is in contrast to the higher plants in which the gametophyte is de-
pendent upon the sporophyte. There is an alternation of generations.

138 Plajit Biology

A motile, multifiagellated sperm swims through water to fertilize the egg
(ovum) in the female archegonium, thus forming a zygote. The latter
produces a multicellular embryo which develops a sporophyte. A ger-
minating spore forms a small, thin, green, heart-shaped prothallus (pro-
thallium) with male antheridia and female archegonia.

Examples: Pteridium (Fig. 50) and Poly podium (Fig. 51).

(9<S3

Archeqomum

\ /Antheridi ^

_ 5tGm

0\/urr)\

Toot

"Rhiioids

Fig. 50. — Common fern (Pteridium) of the subphylum Pteropsida, class Fili-
cineae. A, Fern plant or sporophyte; B, sporangium enlarged and emitting spores;
C, two spores developing into prothalli; D, prothallus with archegonia (female)
near the notch with one archegonium enlarged to show the ovum ; antheridia
(male) near the rhizoids; E, similar prothallus with archegonia and antheridia,
with an enlarged antheridium to show the sperm; self-fertilization does not occur;
F, prothallus with a young fern plant growing out of the archegonium from the
fertilized ovum. The prothallus to which this sporophyte is attached eventually
will disappear.

Gymnosperms. — The gymnosperms, or those plants which pro-
duce seeds exposed (naked) on female sporophylls, known as mega-
sporophylls, belong to the class Gymnospermae (jim no -spur' me) (Gr.
gymnos, naked or exposed; sperma, seed). The gymnosperms include
.the cone-bearing evergreens (conifers) and their allies.

Gymnosperms are rather large, woody, perennial plants which are
mainly evergreen (retain leaves more than one growing season). Cer-
tain types may be short and shrubby. They possess true roots, stems, and
leaves; in the cone-bearing evergreens the leaves may be needlelike or
scalelike. The sporophyte generation is large, complex, and independent,
while the gametophyte is small (microscopic) and dependent (parasitic)
upon the sporophyte. Two kinds of cones composed of sporophylls are

Survey of Plant Kingdom 139

Fig. 51. — The polypody fern (Poly podium) of the phylum Tracheophyta, class
Filicineae. A, Showing the horizontal rhizome, the slender adventitious roots, and
the fronds with numerous sori on the lower surface; a young frond is shown
unrolling; B, lower surface of a frond showing three sori (enlarged), each con-
sisting of numerous sporangia which produce spores; C, a sporangium much en-
larged, showing the stalk, the internal spores, the capsule with thin walls, and the
water-sensitive annulus (band of cells, each of which has three thick walls and
an outer thin wall) ; the annulus responds to changes in moisture and bends, back^
thus throwing the spores to the outside.

140 Plant Biology

Microsporophy]]

-Microsporanqium Microspore

c n

Jnbequment

.^ ^ \ Mecjaspore

^^■^—Mlcrosporan^ia

/Aegaqamebophybe
Micropyle /

;

I ^Alecjasporan(j]um
yyieaasporophyll

Meaaaamebophybe
hbQCjumenb

Cotyledons
Food

Ovule

Root

seed "coats

''PoVenqrairy yArchegomum
^ y MQqasporanqium

.L._i ^rcheqomum

yy PoUen cjfrain and tube

Fig. 52. — Pine tree life cycle (Pinus sp.). A, Branch with (male) staminate
cones; B, staminate cone enlarged with upper right section showing microsporo-
phylls, microsporangia, and microspores; C, microsporophyll enlarged (side view)
showing microsporangium and microspores; D, microsporophyll enlarged and
viewed from below; E, microgametophyte (pollen grain) developed from a micro-
spore; F, developing microgametophyte with its pollen tube and nuclei; G, branch
with (female) carpellate cone; H, carpellate cone enlarged with upper right sec-
tion showing megasporophylls, megasporangia, and megaspores; I, megasporophyll
enlarged (side view) showing megasporangium and megaspore; J, megasporo-
phyll enlarged and viewed from above; K, megasporophyll still more enlarged
(side view), showing megasporangium, integument, megagametophyte, and micro-
pyle; L, entrance of microgametophyte (pollen grain) into the megasporangium
through the micropyle. Note the megagametophyte with its archegonia, each con-
taining a megagamete (egg) ; M, as L above, with pollen tube growing toward
archegonium; A^, fusion of the contents of the microgametophyte (pollen grain)
and the megagamete (egg) of the archegonium; O, mature pine seed (longitudinal
section) with two seed coats and food; P, germination of seed (split) showing
cotyledons and root. This young plant is an immature sporophyte which even-
tually will develop into a pine tree.

Survey of Plant Kingdom 141

Cuticle

Epidermis

Cork cambium
Rejin canal.

Medullary ray !^

Cambium

Stoma /Airspace

Epidermis

Resin ducfc

__ Parenchyma
— Phloem
-_XyIem

Cork

,__Corbcx

,__Phloem

, — Xy/em

;, Xylem

Resin canal

—^ndodertnis
— MesophyU

_ SderQnchyma
Cuticle

,-P;th

Fig. 53. — Pine tree (Pinus sp.). A, One-half of a needle (leaf); B, a stem,
both in cross section and somewhat diagrammatically. Note there are two layers
of xylem (one for each year of stem growth) and that the outer cells of each
xylem represent fall wood, while the inner layers of each xylem represent spring
wood. The spring and fall growths of each xylem constitute an annual ring.
The sclerenchyma of the leaf is also known as mechanical tissue ; the mesophyll
contains chlorophyll and is called photosynthetic tissue.

142 Plant Biology

usually present. The male cones are composed of microsporophylls, while
the female cones are composed of megasporophylls. The ovules (im-
mature, unde\eloped seeds), and later the true seeds, are borne exposed
on the female megasporophylls.

Fig. 54. — Cycads. Cycas (above) with a crown of young leaves unfolding;
male plant of Zamia (lower left) at the time of "flowering"; mature fruiting plant
of Zamia (lower right). (From Weatherwax: Plant Biology, W. B. Saunders
Co.)

Two types of spores (heterospory) are formed; namely, microspores,
which develop into male microgametophytes, and megaspores, which
develop into female megagametophytes.

Pollination occurs by wind, the pollen being carried near the micropyle
(mi'kropile) (Gr. mikros, small; pyle, gate) or little opening of the

Survey of Plant Kingdom 143

ovule. A pollen tube is formed through which the male pollen grain
(sperm) may travel to reach the Qgg. In gymnosperms single fertilization
occurs in which one sperm is involved in fertilizing the egg. Gymno-
sperms are considered in greater detail in a later chapter.

Examples: Pine tree (Pinus) (Figs. 52 and 53) and cycad or sago
palm (Zamia) (Fig. 54).

Angiosperms. — The angiosperms, or flowering plants, which pro-
duce their seeds enclosed in an ovary (carpels) , belong to the class Angio-
spermae (an ji o -spur' me) (Gr. angios, enclosed; sperma, seed).

The sporophyte is large and independent (when mature), while the
gametophyte is small and dependent (upon the sporophyte). Angio-
sperms possess true roots, stems, and leaves. A well-developed vascular
system is present. Two kinds of spores (heterospory) are produced;
namely, m,icros pores, which form male microgametophytes, and mega-
spores, which form female megagametophytes. Flowers of some kind are
characteristic. True seeds are enclosed in an ovary (carpels).

Pollination occurs by wind, insects, or birds, rarely by water. A pollen
tube is formed, extending from the stigma of the pistil down through the
style to the ovary, where the male sperm unites with the egg (ovum)
(Fig, 71). In angiosperms double fertilization occurs in which one
sperm (male nucleus) fuses with the egg (true fertilization) to form a
zygote, which will form the multicellular embryo. The other sperm
(male nucleus) fuses with two polar nuclei in the female gametophyte
to form the nutritive, efidosperm tissue to be used by the developing
embryo. Angiospermous plants are considered in greater detail in a later
chapter.

Characteristics of Dicotyledonous and Monocotyledonous Angiosperms

DICOTYLEDONOUS ANGIOSPERMS

Two embryonic seed leaves

Flower parts usually in 4's or 5's or

multiples of these
Leaves net-veined

Some have woody stems, others have
herbaceous stems

Vascular bundles of stems usually ar-
ranged in a circle (cylinder)

Cambium (meristematic tissue) be-
tween the phloem and xylem of vas-
cular bundle

Examples: Beans (Figs. 55 and 56),
sunflowers (Fig. 57), roses, violets,
clovers, snapdragons, potatoes, elms,
oaks, apples, maples, hickories, pop-
lars, lilacs, etc.

MONOCOTYLEDONOUS ANGIOSPERMS

One embryonic seed leaf

Flower parts in 3's or multiples of 3

Leaves parallel-veined, and usually
long and narrow

Most have herbaceous stems (few ex-
ceptions)

Vascular bundles scattered throughout
stem

No cambium between the phloem and
xylem usually

Examples: Corn (Figs. 58 to 60),
wheat, bluegrass, lilies, irises, daffo-
dils, cattails, etc.

144 Plant Biology

.Sepal of calyx
Ovalary

Seed

Hee]

Fig. 55. — Common garden bean or kidney bean (Phaseolus sp.). A, Plant
showing the twining vine, leaves, flowers, and pods (legumes) ; B, one flower very
much enlarged in longitudinal section (somewhat diagrammatic). The ovulary
is also called the ovary.

Hypocotyl--

^._A1icropy/G

3— Hilum Cotyledons ^^-}~::.\:m

leaf___

Plumule
-Hypocotyl

Cotyledons

5talk

Root J

Fig. 56. — Common garden bean or kidney bean (Phaseolus sp.). A, Pod
(legume) with part of wall removed to show bean seeds; B, bean seed with seed
coat in side view; C, same as B in face view; D, face view of bean with seed coat
removed ; E, cotyledons spread to show structures between them ; F, seedling of
bean showing the true leaves and the cotyledons (embryo seed leaves), the latter
being pushed out of the ground during germination.

Survey of Plant Kingdom 145

Cuticle

Upper epidermic

Palisade tissue

iponqry tissue
Stoma

Lower epidcrmii
Quard QcWs

Mechan\ca\ tSssue
.Parenchyma
^MeduHary ray

Stigma ^

Jtyle-

%- -Ovulary
Root hair

<:<-'« (EnSSTif.

,Vasca]ar bundle

Vascular (\ 1 PWocm

bundle \\ Cambium

IXylcm

Pitii / 'iDiral' Pitted
Jpiral 1 duct ,' -»'■'*
duct WoodceJIs

1 iJuct ,' duct I i.ievetubej

Cambium cells

Epidermis /^

Fig. 57. — Sunflower (Helianthus sp.). A, Part of plant showing flowers and
leaves; B, disk floret in bud; C, disk floret further developed with elongated style
and opened stigmas; D, leaf in cross section (somewhat diagrammatic) ; E, stem
in cross section; the mechanical tissue and the parenchyma constitute the cortex;
F, enlarged vascular bundle (such as shown \n E) , showing cross and longitudinal
views; the spiral and pitted ducts are present in the xylem or woody part of the
bundle; the sieve tubes and bast cells constitute the phloem of the bundle; the
embryonic, thin-walled cambium lies between the xylem and phloem; G, root in
diagrammatic cross section in the region of maturation. The ovulary is also
known as the ovary.

146 Plant Biology

5caTc or bract

__ Anther

(immature)
Anther {maturQ)

— Pollen
Hair

Fig. 58. — Indian corn (Zea mays). A, Plant with parts; B, part of tassel
(male) showing an immature flower at the left and a mature flower with three
anthers at the right (very much enlarged) ; C, ear of corn (female) in longitu-
dinal section with one ovary (ovulary) and silk much enlarged; D, female flower
(pistil), much enlarged, showing the hair to receive pollen and the silk (style) to
conduct it to the ovary (ovulary). The corn seed (grain) is shown in Fig. 59.

Survey of Plant Kingdom 147

Endosperm
(Protein)

Endosperm
(starch)

Cotyledon-

-Epicotyl

Seed coat
-Hypo coty J

Embryo

-'--'^dvenfcitipas roots

^--Primary roots__f__^ p

Fig. 59. — Indian corn showing its gi^ain and its germination. A, Longitudinal
section perpendicular to the broad face of the grain (much enlarged) ; B, surface
or face view ; C, surface view with seed coat removed ; D, E, F, stages of germina-
tion and embryo development.

_/4?rjpac(?

Epidermis ^^Jtomatq^^ O

--.Vein

^ Cuticle

'Chloroploitids

Companion cell"

PHoem-

- Sieye tube.

XyfGiD

, Airspace

, Sheath cell

Fig. 60. — Indian corn (Zea mays). A, Leaf (external view) ; B, leaf in cross
section (somewhat diagrammatic) ; C, stalk or stem (cross section) ; D, one vas-
cular bundle very much enlarged (cross section), Chloroplastids are also called
chloroplasts.

148 Plant Biology

The class Angiospermae may be divided into the subclasses ( 1 ) Dicoty-
ledoneae (di kot i le -do' ne e) (Gr. di, two; kotyledon, embryonic, seed
leaf) and (2) Monocotyledoneae (mon o kot i le -do' ne e) (Gr. mono,
one; kotyledon, embryonic, seed leaf). A cotyledon (seed leaf) is a food-
storing and food-digesting part of the embryo which supplies it with food
during its early development.

QUESTIONS AND TOPICS

1. Learn the meaning, correct pronunciation, and derivation of each term used
in this chapter.

2. Define (1) plant kingdom, (2) subkingdom, (3) phylum, (4) subphylum,
(5) class, (6) subclass, (7) genus, and (8) species.

3. Why are Greek and Latin used in composing a system of classification and in
forming a scientific name? Of what does a scientific name consist? Give
several examples.

4. Discuss the needs for a scientific classification of plants. List some serious
objections to the use of common names in scientific work.

5. Tell how so many common names may originate for one and the same plant.

6. Explain what is meant by the binomial system of nomenclature.

7. Give the general characteristics of each plant phylum. What do certain
phyla have in common? Do certain phyla seem to be more closely related
to each other than others? Give specific reasons why.

8. List the total number of species for the plant kingdom. List the number of
species in each phylum. How does the total for the plant kingdom compare
with the animal kingdom?

9. Give specific evidence that the representatives of the various phyla increase
in complexity of structure and function, as we observe them, from the lower
to the higher phyla. What conclusions do you draw from this?

10. Define a life cycle (life history). Do all plants have a life cycle?

11. In general, are plants sessile (attached) or motile? List the affects of at-
tachment on such phenomena as securing foods, development of the organism,
protection, reproduction, etc.

12. Which plant phylum do you consider to be most important? Give specific
reasons why you say so. What makes a plant economically important?

13. Are all economically important plants necessarily of value? List several
plants to prove your point.

14. Discuss alternation of generations in plants, including how this phenomenon
differs from ordinary life cycles. What proportion of plants studied possess
alternation of generations? List advantages and disadvantages of this phe-
nomenon.

15. How do plants illustrate the principle of "struggle for existence"?

16. List a number of ways in which man is influenced (beneficially and detri-
mentally) by plants.

17. Explain the role of plants in a so-called "balanced environment," or "bal-
anced community." Can any living organism live entirely by itself in a state
of complete isolation?

Survey of Plant Kingdom 149

18. Contrast and give specific examples of asexual and sexual reproduction in
plants.

19. Contrast and give an example of each: monocotyledon and dicotyledon,
ovule and seed, rhizoid and root, gymnosperm and angiosperm, antheridium
and archegonium, parasite and saprophyte, chemosynthesis and photosynthesis,
pollination and fertilization, homospory and heterospory, isogamy and heter-
ogamy, algae and fungi, sporophyte and gametophyte.

20. List the conclusions you can logically draw from your scientific study of
the plant kingdom in this chapter.

SELECTED REFERENCES

Armstrong: Western Wild Flowers, G. P. Putnam's Sons.

Asch: The Story of Plants, G. P. Putnam's Sons.

Bailey: How Plants Get Their Names, The Macmillan Co.

Clute: The Common Names of Plants and Their Meanings, W. N. Clute & Co.

Comstock: Handbook of Nature Study, Comstock Publishing Co., Inc.

Coulter: The Story of the Plant Kingdom, University of Chicago Press.

Cuthbert: How to Know the Spring Flowers, William C. Brown Co.

Cuthbert. How to Know the Fall Flowers, William C. Brown Co.

Fuller: The Plant World, Henry Holt & Co., Inc.

Fuller and Tippo: College Botany, Henry Holt & Co., Inc.

Gager: General Botany, The Blakiston Co.

Gibbs: Botany, The Blakiston Co.

Gray: Manual of Botany, American Book Co.

Hausman: Beginner's Guide to Wild Flowers, G. P. Putnam's Sons.

Hill, Overholts, and Popp: Botany, McGraw-Hill Book Co., Inc.

Hylander and Stanley: College Botany, The Macmillan Co.

Hylander: The World of Plant Life, The Macmillan Co.

Jacques: Plant Families — How to Know Them, William C. Brown Co.

Jacques: Plants We Eat and Wear, William C. Brown Co.

Johnson: Taxonomy of Flowering Plants, Century Co.

Kern: Essentials of Plant Biology, Harper & Brothers.

Mathews: Handbook of American Wild Flowers, G. P. Putnam's Sons.

Pool: Basic Course in Botany, Ginn and Co.

Pool: Flowers and Flowering Plants, McGraw-Hill Book Co., Inc.

Robbins and Weier: Botany, John Wiley & Sons, Inc.

Seymour et al. : Favorite Flowers in Color, Wm. H. Wise & Co., Inc.

Sinnott: Botany: Principles and Problems, McGraw-Hill Book Co., Inc.

Smith et al. : Textbook of General Botany, The Macmillan Co.

Swingle: Textbook of Systematic Botany, M.cGraw-Hill Book Co., Inc.

Transeau, Sampson, and TifTany: Textbook of Botany, Harper & Brothers.

Trelease: Winter Botany (published by the author).

Weatherwax: Plant Biology, W. B. Saunders Co.

Wilson and Haber: Plant Life, Henry Holt & Co., Inc.

Chapter 9

SIMPLE PLANTS WITH CHLOROPHYLL— ALGAE

Plants Without True Leaves, Stems, or Roots; Not Forming
Multicellular Embryos; and Without True Vascular (Conduct-
ing) Tissues (Subkingdom Thallophyta)

GENERAL CHARACTERISTICS OF THALLOPHYTES

1. Thallophytes include the algae and fungi. The former contain
chlorophyll which, in the presence of energy-supplying light, is able to
combine carbon dioxide and water to produce carbohydrates through
the process of photosynthesis (fo to -sin' the sis) (Or. phos, light; synthe-
sis, put together). The fungi lack chlorophyll and are unable to manu-
facture their foods but must depend upon outside sources for their
nourishment.

2. Thallophytes are simple plants which lack true leaves, true stems,
and true roots. However, certain species may have structures which
somewhat resemble them, but they do not possess the two vascular tis-
sues (phloem and xylem) of the true organs.

3. This group of plants is vast and varied, ranging from the unicellu-
lar, microscopic types to the large, multicellular forms, some of which
are over 200 feet long. Certain species consist of a linear series of cells,
while others consist of sheetlike masses of cells; hence the name thallo-
phyta (tha -lof'i ta) (Or. thallo, sheetlike or "leaf-shaped"; phyta,
plants) .

4. The sporangia (spor -an' ji a) (Gr. sporos, spore or seed; angios,
vessel), which are structures which produce spores, and the gam,etangia
(gam e -tan' ji a) (Gr. gametes, gametes or sex cells; angios, vessel),
which produce sex cells (gametes), are both usually unicellular.

5. The zygote (fertilized egg cell) does not produce a multicellular
embryo while still within the female sex structure.

6. Thallophytes do not possess the two vascular tissues called phloem
(flo' em) (Gr. phloios, smooth bark) and xylem (zi' lem) (Gr. xylon,
wood ) . These two tissues are present in higher plants.

150

Simple Plants With Chlorophyll — Algae 151

7. Thallophytes usually live in water, or moist places, and do not
possess rigid tissues for extensive upright growth.

8. Many species of thallophytes, both algae and fungi, are of great
economic importance, both beneficially and detrimentally.

GENERAL CHARACTERISTICS OF ALGAE

The term algae does not apply to a natural group of plants, but it is
a desirable name applied to those thallophytes which carry on photo-
synthesis because of the presence of chlorophyll. The algae vary greatly
among themselves, and many of them resemble certain fungi in many re-
spects. There are several characteristics which are common to both
algae and fungi, except that the former possess chlorophyll, while the
latter do not. These facts will be discussed in this chapter and the next.

Algae are common in fresh water and in the salt waters of the oceans
(marine) . They may be free living in fresh or salt water, where, together
with the animals, they make up the so-called plankton (plangk' ton) (Gr.
plangktos, wandering). Others may live on the bottom, where together
with the animals, they constitute the so-called benthon (ben'thon) (Gr.
benthos, depths of the sea). Certain species may grow in moist soils, on
moist rocks and trees, in snow and ice, or in hot springs. Certain species
may live symbiotically with other organisms for mutual benefits. Algae
may live symbiotically with certain fungi in an association known as
lichens (li'ken) (Gr. leichen, liverwort), in which case the algae supply
foods and the fungi supply water and give protection. Some species may
grow on other plants as epiphytes and on animals and may be saprophytes
or parasites.

BLUE-GREEN ALGAE (PHYLUM CYANOPHYTA)

These are simple, unicellular plants although certain species may form
colonies of similar cells among which there is little differentiation. In
addition to the green chlorophyll, there is a blue pigment called phyco-
cyanin (fi ko -si' anin) (Gr. phykos, alga or seaweed; kyanos, blue).
Sometimes a red pigment may also be present in certain species. The
chlorophyll is distributed throughout the cell and not localized in definite
bodies known as plastids (Fig. 29). There is no definite, organized nu-
cleus; the nuclear, chromatin materials are scattered throughout the cen-
ter of the cell. The cells are often surrounded by a slimy, gelatinous
sheath. Because of this, myxophyta (myx-of'ita) (Gr. myxo, slime;

152 Plant Biology

phyta, plants) has been used as the name of the phylum. Foods are
stored as glycogen (starchlike carbohydrate).

Reproduction occurs asexually by transverse fission (simple cell
division). None of the reproductive, or vegetative (body), cells possess
threadlike fiagella which are present in many other types of algae.

Most species of blue-green algae occur in fresh water, although a few
species are marine. They may cause the water in ponds and lakes to
have a greenish-yellow color and may be so abundant that they are known
as ''water blooms," thereby giving the water a "soupy" appearance, a foul
odor, and a "fishy" taste. Many species also occur in soils, on moist
rocks, in greenhouses, on flower pots, and other moist places. Several
species grow in hot springs with temperatures over 75° C, where they
precipitate the magnesium and calcium salts to form travertine, which
may have bright colors due to the contained algae. Blue-green algae
may precipitate calcium carbonate in lake waters to form deposits of
marl on the bottom.

Other species may grow on other plants as epiphytes (ep' if ites) (Gr.
epi, upon; phyta, plants), while still other species are associated with
certain species of chlorophyll-less fungi to form plants known as lichens
{W ken) (Fig. 327). A few species may even be parasitic in the diges-
tive tracts of animals, including man. Blue-green algae, together with
other algae, are great sources of food for aquatic animals. About 1,400
species are classified in 150 genera. The following typical examples will
be considered: Gleocapsa, Oscillatoria, Nostoc, and Anahena (Fig. 29).

Gleocapsa (gle o -kap' sa) (Gr. gloia, glue; kapsa, box). — Simple,
primitive, unicellular plants with each cell composed of (1) an outer,
bluish-green region due to the diflfused chlorophyll and phycocyanin
(blue pigment) and (2) a central region containing scattered chromatin
granules (Fig. 29). There is no organized nucleus and no plastids.
Numerous unicellular plants may be grouped together and surrounded
by a jellylike material. Gleocapsa reproduces by fission (simple cell
division) and is common on wet rocks and other damp places.

Oscillatoria (os i la -to' ri a) (L. oscillare, to swing). — A linear series
of Oscillatoria plants are associated to form a colony which is filamentous
(Fig. 29). Each individual cell is self-sufficient and hence is considered
as a separate plant. The chlorophyll and phycocyanin (blue pigment)
are distributed in the outer region of the cell and not in an organized
plastid. The chromatin granules occupy the central region and do not
form an organized nucleus. Frequently the living filaments may glide
back and forth or may oscillate, hence the name Oscillatoria. Reproduc-

Simple Plants With Chlorophyll — Algae 153

<
o

b
O

w
o

H
w

oi
u
H
O

U
o

I— I

X
m

b
O

CYTO-
PLASMIC
STRANDS
BETWEEN
BODY
CELLS

C
0

None

C!
O

4->
C

lU
en

{/2

c
o

Well or-
ganized

PLAS-
TIDS

Chloro-
plast

Oj
en
OJ
Sh

OJ
en

CL,

OJ
en

OJ
S-i

PIGMENTS IN

ADDITION TO

CHLOROPHYLL

Phycocyanin (and
sometimes a red
pigment)

Carotinoids (carotene
and xanthophyll)

.S
'■(->

2
o

OS
X

Phycoerythrin (some-
times phycocyanin)

c/2

Q
0
0

Q
w

0
H

(/2

Glycogen (starchlike
carbohydrate)

Starch (pyrenoids
present)

Fats and soluble
sugars

"Starch" (insoluble)
(pyrenoids in some
soecies)

MOTILE CELLS
(REPRODUC-
TIVE)

HJ
O

When present, there
are 2 to 4 anterior
flagella usually of
equal length

Present or' absent,
depending on
species

When present, 2 lat-
eral, unequal
flagella

c
o

BLUE-GREEN
ALGAE

(Cyanophyta)

GREEN ALGAE

(Chlorophyta)

YELLOW-GREEN
ALGAE,
GOLDEN-
BROWN ALGAE,
AND DIATOMS
(Chrysophyta)

BROWN ALGAE

(Phaeophyta)

RED ALGAE

(Rhodophyta)

154 Plant Biology

tlon is by cell division (fission). Sometimes, soft gelatinous areas develop
between cells, thereby breaking the filament into pieces known as hor-
mogonia (hor mo -go' nia). (Gr. hormos, chain; gonos, offspring). A
hormogonium may form a new colony. Oscillatoria is common on damp
earth, stones, flower pots, and other damp places.

Nostoc (nos' tok) (F. nostos, return). — This blue-green alga is uni-
cellular, with the individual, globose cells arranged as a chainlike colony,
resembling a necklace of beads (Fig. 29). The strands of cells are en-
closed in a hall of jelly. Each cell contains chlorophyll, phycocyanin,
and chromatin granules as in Gleocapsa and Oscillatoria. At certain
intervals in the chain are thick-walled, transparent cells known as het-
erocysts (het' er o sists) (Gr. heteros, different; kystis, sac or pouch)
which serve to break the filaments into hormogonia, as in Oscillatoria.

REPRODUCTION

ASEXUAL

SEXUAL

BLUE-

Fission (cell division) — Gleocapsa,

None

GREEN

Oscillatoria, Nostoc, Anabena

ALGAE

2.
3.
4.

Hormogonia — Oscillatoria, Nostoc
Heterocysts — Nostoc, Anabena
Spores — Anabena

GREEN

Fission (cell division) — Protococcus,

Isogamy — Chlamydo-

ALGAE

Desmids

monas Spirogyra,

Fragmentation — Spirogyra, Ulothrix

Ulothrix, Desmids

Motile zoospores produced by zoo-

Heterogamy

sporangia — Chlamydomonas, Ulothrix

Oogamy

Nonmotile spores produced by Spo-
rangia

VELLOW-

Fission (cell division)- — Diatoms

I sogamy — D i atoms

GREEN

Motile zoospores

ALGAE,

Nonmotile spores

GOLDEN-

Auxospores — Diatoms

BROWN

ALGAE,

AND

Dr\TOMS

BROWN

Fragmentation — Fucus

Isogamy

ALGAE

Motile zoospores — Laminaria

Heterogamy — Fucus

Nonmotile spores

Oogamy — Laminaria

(Alternation of generations, metagenesis

, with gametophyte

and sporophyte generations)

RED ALGAE

Nonmotile carpospores — Nemalion,
Polysiphonia

Oogamy — male an-
theridia produce non-

Nonmotile tetraspores — Polysiphonia

motile sperm ; female
carpogonia produce
nonmotile egg —
Nemalion; Poly-
siphonia

(Certain species have alternation of generations, metagenesis,

with gametophyte and sporophyte

generations)

Simple Plants With Chlorophyll — Algae 155

Occasionally a heterocyst may germinate to form a new filament, thus
functioning as a spore. Nostoc is common in ponds and pools of fresh
water.

Anabena (ana-be'na) (Gr. anahainein, to go up). — This blue-green
alga resembles Nostoc in its beadlike strands, pigments, heterocysts, and
jelly covering (Fig. 29). It differs in that certain enlarged, thick- walled
cells, known as spores, contain much food and may separate from the
filament and form a new colony.

GREEN ALGAE (PHYLUM CHLOROPHYTA)

In certain species of green algae the chlorophyll may be associated
with additional pigments known as carotinoids (carotene and xantho-
phyll). The chlorophyll is localized in definite bodies known as chloro-
plasts (klo' ro plast) (Gr. kloros, green; plastos, moulded or body). The
nucleus is well organized (Fig. 30). The cell wall consists of cellulose
(sel'ulosz) (L. cellula, little cell), and the stored food is starch. The
latter is formed by structures on the chloroplasts known as pyrenoids
(pi'renoid) (Gr. pyren, fruit-stone; eidos, resemblance). Green algae
vary in structure, and the plant body may be unicellular, colonial, or
multicellular, depending upon the species. When the reproductive or
vegetative (body) cells are motile, each bears two to four anterior flagella,
usually of equal length.

Reproduction occurs (1) asexually by cell division, by fragmentation,
by motile zoospores, or by nonmotile spores or (2) sexually by isogamy
(i -sog' a my) (Gr. isos, equal; gamos, marriage) with the fusion of
gametes (sex cells) of equal size, by heterogamy (het er -og' a my) (Gr.
heteros, different) with the fusion of gametes of unequal size, or by oog-
amy (o-og'amy) (Gr. oon, ^gg) which is a special type of heterogamy
in which the egg (female gamete) is nonmotile. The structures which
produce the sex cells in green algae are always unicellular.

Most green algae live in fresh water, but some are marine, while others
grow in soil, on rocks, or on trees. Several species live in snow or ice.
Some live in salt lake waters whose concentration of salt is much greater
than that of the ocean. A few species may grow on other plants or ani-
mals. A few live symbiotically with such animals as protozoa, sponges,
and Hydra. Certain types may live together with chlorophyll-less fungi
to form plants called lichens (Fig. 327). Green algae, as well as other
algae, supply foods for fresh-water and marine animals. Marine green
algae in conjunction with red algae secrete lime salts which assist in the

156. Plant Biology

formation of reefs in the ocean. About 5,700 species are classified in 360
genera. The following typical examples will be considered : Chlamydo-
monas, Ulothrix, Protococcus, Spirogyra, and desmids.

Chlaniydonionas (klam id o -mo' nas) (Gr. chlamydos, cloak; monas,
one). — This simple, unicellular green alga is common in fresh water and
soils. Each cell is spherical or ovoid and contains a central nucleus, a
single, large, cup-shaped chloroplast with a pyrenoid, an eyespot, two
anteriorly located flagella of equal length, a cell wall of cellulose, and two
excretory contractile vacuoles near the anterior end (Fig. 61). Some in-
vestigators classify this organism as a single-celled protozoan (animal).

FlaaelluTn

Contractije Vacuo/e
Viamenh opoz

Cell Wall

Nucleus
Dense Cutoplas

Plasma Membrane

rurenofd
Chloroplast

Fig. 61. — A green alga (Chlamydonionas) of the phylum Chlorophyta. The
chloroplast is cup shaped ; the pigment spot is also known as the eye spot. Be-
cause of certain characteristics, this unicellular organism is considered by some to
be a protozoan (single-celled animal).

At certain times there may be formed within the cell two, four, or eight
motile swarm spores (zoospores) which resemble the parent cell except
in size and which swim out to form new Chlamydomonas. In some in-
stances the contents of the parent cell may divide into eight, sixteen, or
thirty-two small gametes (sex cells) which resemble miniature Chlamydo-
monas plants. When released into water, two gametes of equal size, but
coming from different parent cells, fuse by the process of fertilization
known as isogamy (i-sog'amy) (Gr. isos, equal; gamos, marriage). In
the fusion of isogamous (alike) gametes, there is no differentiation into

Simple Plants With Chlorophyll — Algae 157

male and female sex cells. The fertilized cell is called a zygote and sur-
rounds itself with a thick, resistant wall to withstand adverse conditions.
Eventually, the single nucleus of the zygote produces four nuclei which
are incorporated into four zoospores, each of which forms a Ghlamydo-
monas plant. The zoospores and the gametes look alike except that the
former are larger.

Protococcus (pro to -kok' us) (Gr. protos, first; kokkus, berry or
round), — This unicellular, thick-walled, round green alga is common on
trees and in moist places. Each cell has a nucleus and a lobed chloro-
plast. Reproduction occurs by cell division, and occasionally several in-
dividual cells may remain together to form a colony (Fig. 30) .

Spirogyra (spi ro -ji' ra) (Gr. speira, coil or spiral; gyros, curved).- —
This green alga is common in fresh water where it may be called "pond
scum" or "water silk." Each unbranched filament is composed of a
linear series of cells and is covered with a slippery, mucilaginous sheath.
Each cell contains a single, organized nucleus located in the center of
the cell and surrounded by cytoplasm (Fig. 30). Strands of cytoplasm
also extend to the pyrenoids located on the chloroplasts. One or more
spiral-shaped chloroplasts may be present in a cell.

Reproduction is by fragmentation (asexual) and by conjugation (sex-
ual). In the latter, the cells in two adjacent filaments form a conjuga-
tion tube between them, and the contents of one cell passes through the
tube to the cell of the other filament. This fusion, or fertilization, pro-
duces a zygote which eventually will produce a new filament. Even
though the gametes are all the same size (isogamous) , the one which
migrates might be considered as male and the other as the female. In
most cases, nearly all the cells of a certain filament produce gametes at
the same time. However, the cells of a single filament may unite at times
(Fig. 62).

Ulothrix (u' lo thriks) (Gr. oulos, wooly; thrix, hair) . — This is a fila-
mentous, unbranched, fresh-water, multicellular green alga with a basal
holdfast cell for attachment to the substratum. The vegetative (body)
cells of the filament are differentiated and interdependent. Each vegeta-
tive cell contains an organized nucleus and a chloroplast which resembles
an open band or ring and which contains numerous pyrenoids (Fig. 30),

Reproduction occurs by fragmentation, by zoospores, and by isogamy.
Certain reproductive structures are known as zoosporangia and each con-
tains two, four, eight, sixteen, or thirty-two large, motile zoospores. Each
zoospore bears four fiagella and forms a new filament by cell division.

158 Plant Biology

Simple Plants With Chlorophyll — Algae 159

Other reproductive cells are formed in gametangia (gam e -tan' ji a) (Gr.
gametes, spouse; angos, vessel) and each contains eight, sixteen, thirty-
two, or sixty- four gametes (sex cells). Each gamete is smaller than the
zoospore and bears only two flagella. The fusion of these gametes of
equal size {isogamy) produces a zygote, the gametes arising from differ-
ent filaments. Each zygote eventually will produce four zoospores, each
of which will attach and form a new filament by cell division.

Desmids (des'mid) (Gr. desmos, chain). — These gree7i algae are
frequently found floating in fresh water and may be solitary or in fila-
mentous or irregular colonies. In most species each cell is divided into
two halves which are joined by a connecting isthmus (Fig. 30). Each
half cell contains a chloroplast. An organized nucleus is located in the
isthmus. Reproduction is by cell division and by conjugation, which
resembles the similar phenomenon in S pirogyra.

YELLOW-GREEN ALGAE, GOLDEN-BROWN ALGAE, AND
DIATOMS (PHYLUM CHRYSOPHYTA)

The yellow, or brown, carotinoid pigments are more abundant than
the chlorophyll so these algae have a golden-brown, or yellowish-green,
color. All pigments are contained in organized plastids. The cell walls
are usually composed of a pair of overlapping halves (valves) which are
frequently impregnated with silica (glasslike) . Depending on the species,
these algae may be unicellular, colonial, or, in a few instances, multicellu-
lar individuals. Stored foods are oils and an insoluble carbohydrate
called leucosin (lu'kosin) (Gr. leukos, white). The nucleus is well
organized.

Reproduction occurs asexually by cell division, by m.otile zoospores, or
by nonmotile spores. Sexual reproduction, when present, is isogamous
(gametes which are alike) . The phylum contains the yellow-green algae,
the golden-brown algae, and the diatoms. About 5,700 species are classi-
fied in 300 genera. Various species of diatoms will be considered as typi-
cal forms.

Diatoms (di' atoms) (Gr. dia, across or two; tome, to cut). — These
unicellular, delicate algae are common in fresh and salt water and may
form filaments or other types of colonies. Different species vary in shape,
including rods, disks, triangles, etc. (Fig. 31). Each cell is composed of
two overlapping halves (valves) like a pill box. The cell walls are trans-
parent and glasslike (siliceous) and do not disintegrate even when the

160 Plant Biology

cell dies. The cell walls are ornamented with patterns of fine dots, or
perforations, which create beautiful designs unique for the various species.
Each protoplast of the cell contains one or many yello\vish-brown plas-
tids which impart the brownish color to most diatoms, although some
species have green or blue plastids. Each cell contains an organized
nucleus. Reserve foods include fats and an insoluble food known as
volutin (vo-lu'tin).

Reproduction may occur asexually by cell division with each new cell
formins: a new valve inside the old one. Eventuallv certain of these
cells will become smaller and smaller. In the latter case certain rejuve-
nescent cells called auxospores (ok' so spor) (Gr. auxe, grow; spora,
spore) are produced. The latter usually result from the fusion of two
diatoms (gametes), and eventually a cell of normal size will be produced
again. The gametes are usually of equal size {isogamous) .

Diatoms are common in fresh and salt ^vaters, although some species
are found in soils, on other plants, and even in hot springs. Diatoms are
important components of the diets of aquatic animals. When diatoms
die, their siliceous shells accumulate on the bottom to form diatomaceous
earth. The latter is used in preparing polishes, tooth powders, filters,
insulatins; materials, etc. It is believed that diatoms mav have aided in
the formation of oil because they are often found to be associated with
oil deposits in the earth.

BROWN ALGAE (PHYLUM PHAEOPHYTA)

The brown algae are multicellular and nonmotile, being attached by
rootlike holdfasts. Depending on the species, the plant body may be
composed of only a few cells or it may be over a hundred feet in length,
as in some of the kelps. They are marine and usually found in colder
waters. The chlorophyll is masked by the golden-brown pigment, fuco-
xanthin (fu ko -zan' thin) (L. fucus, alga or seaweed; xanthos, yellow).
Usually there are several plastids per cell, but no pyrenoids are present.
Each cell has a single nucleus and vacuoles. The cells have an organiza-
tion similar to that of higher plants, some e\en having a centrosome simi-
lar to the centrosome of animal cells. Stored foods are fats and soluble
sugars.

All brown algae possess alternation of generations or metagenesis (met-
a-jen'esis) (Gr. meta, over; genesis, origin), in which a free-livang,
multicellular, gamete-producing gamctophyte (gam -me' to fite) (Gr.

Simple Plants With Chlorophyll — Algae 161

gamos, marriage; phyta, plants) alternates with a free-living, multicellu-
lar, spore-producing sporophyte (spor'ofite) (Gr. spora, spore; phyta,
plants). Reproduction may occur asexually by jragmentatioiij by motile
zoospores, by nonmotile spores; or sexually by isogamy (i -sog' a my) (Gr.
isos, equal; gamos, marriage or gametes) in which gametes of equal size
fuse, by heterogamy (het er -og' a my) (Gr. heteros, different) in which
gametes of unequal size fuse, or by oogamy (o -og' amy) (Gr. oon, egg)
which is a special type of heterogamy with a nonmotile egg. The motile,
pear-shaped reproductive cells bear two lateral flagella of unequal length.

Certain brown algae are important sources of iodine, potassium, fer-
tilizers, and foods for animals and man. About 900 species are classified
in 190 genera. The following typical examples will be considered:
Laminaria and Fucus.

Laminaria (lam i -na' ri a) (L. lamina, flat blade). — These brown
algae or kelps, known as "devil's-aprons," are common on our seacoasts
and may be over six feet long. The sporophyte plants consist of long,
flat blades, stalklike stipes, and branched, rootlike holdfasts. Patches of
zoosporangia (zoo spo -ran' ji a) (Gr. zoon, animal; spora, spore or seed;
angos, vessel) on the blades produce numerous zoospores. The latter
produce two types of microscopic gametophytes: (1) the simple,
branched, filamentous male gametophyte which bears terminal anther-
idia (an ther -id' i a) (Gr. anthos, "flower"; idion, small) and (2) the
female gametophyte which is a short filament with one-celled oogonia
(oo-gon'ia) (Gr. oon, egg; gonos, offspring). Each antheridium pro-
duces a sperm, with two flagella of unequal length. Each oogonium pro-
duces an egg. Oogamous fertilization produces a zygote, which germi-
nates to form the sporophyte plant. Hence, there is alternation between
the large, conspicuous sporophyte and the microscopic gametophytes
(Fig. 32).

Fucus (fiu' kus) (Gr. phykos, seaweed). — This marine brown alga or
rockweed is commonly attached to rocks along seacoasts. The plant is
leathery and dichotomously forked and is attached by a disklike holdfast.
The green chlorophyll is usually masked by a brown pigment called
fucoxanthin (fu ko -zan' thin) (L. fucus, alga or sea weed; xanthos, yel-
low) and carried in special bodies known as chromoplasts (Gr. chroma,
color) . Bladderlike floats filled with gas buoy up the multicellular plant
(Fig. 32). Every body cell has an organized nucleus. Stored foods con-
sist of fats and soluble sugars. Enlarged tips called receptacles (re -sep'-
takl) (L. recipere, to receive) contain numerous openings which lead

162 Pla?it Biology

into cavities known as conceptacles (kon -sep' ta kl) (L. concipere, to
receive) . The latter bear the sex organs. In some species, male and fe-
male sex organs are located within the same conceptacle, while in others
the (male) antheridia (an the -rid' i a) (Gr. anthos, flower; idion, diminu-
tive) are borne on one plant and the {female) oogonia (oo-go'nia)
(Gr. oon, Q^g; gonos, begetting) are formed on another plant.

Each oogonium, is borne on a short stalk and when mature contains
eight eggs. Numerous, m.ulticellular, branched, hairlike paraphyses (pa-
raf'ises) (Gr. para, beside; physis, growth) surround the oogonia. The
paraphyses bear enlarged antheridia, each of which produces numerous
pear-shaped sperms, each with two lateral, unequal flagella. The sperm
and egg unite in the water to form a zygote which forms a new Fucus
plant by cell division. Since the sperm is much smaller than the ^gg,
this process of fertilization is known as heterogamy (het er -og' a my) (Gr.
heteros, different; gamos, marriage or gamete). Fucus may reproduce
asexually by fragmentation. The cells of the plant body contain a double
(diploid) number of chromosomes, while the sex cells contain a single
(haploid) number. The gametophyte generation is reduced to merely
the male sperm or the female egg. Apparently the sperms are attracted
by a chemical substance secreted by the eggs. The sperms swim by the
action of the two unequal flagella. Unfertilized eggs may be induced to
develop by treatment with solutions of acetic or butyric acid, the phe-
nomenon being known as artificial parthenogenesis (par then o -jen' e sis)
Gr. parthenos, virgin; genesis, descent or birth) .

RED ALGAE (PHYLUM RHODOPHYTA)

These plants commonly are called sea "mosses" and contain plastids
with chlorophyll associated with a red pigment called phycoerythrin
(fai ko e -rith' rin) (Gr. phykos, alga or seaweed; erythros, red) and
sometimes with a blue pigment called phycocyanin. In most species the
plant is multicellular and may be branched or relatively simple, in the
form of a cylinder, ribbon, or sheet. Different species vary in size from
a few inches to several feet in length (Fig. 33). Each cell contains a
nucleus, central vacuoles, and one or several plastids, some of which
possess pyrenoids. Broad, conspicuous cytoplasmic strands which connect
adjacent cells are features of red algae. Stored food is an insoluble
"starch." Red algae are usually attached in warmer sea waters, with
a few species in fresh water.

Simple Plants With Chlorophyll — Algae 163

ATitKeridium

crw

Irich'

.IrichoqMTie

CarpocjoniuTd

Carpospore

Fig. 63. — Red alga (Nemalion) of the phylum Rhodophyta. A, Portion of a
forked, cylindrical body (thallus) which grows attached to rocks along the sea-
coast; B, portion of a branch bearing brushlike filaments whose tips divide into
antheridia, each of which contains a nonmotile sperm (spermatium) ; C, portion
of a branch bearing a basal carpogonium (with an egg) and an elongated tricho-
gyne; a nonmotile sperm, carried by water, descends the trichogyne to unite with
the egg to form a zygote ; D, portion of a carpogonium showing asexual, nonmotile
carpospores being produced by the zygote; the released carpospores germinate into
new Nemalion plants.

164 Pla?it Biology

None of the sexual or asexual reproductive cells bear flagella which is
characteristic of red algae. In sexual reproduction the nonmotile male
gamete is carried by the water to the female carpogonium (karpo-
go' ni um) (Gr. karpos, fruit; gonos, offspring). The latter is character-
istic of red algae. Fertilization results in the production of a zygote.
Many red algae alternate between a free-living sporophyte and a free-
living gametophyte. About 2,500 species are classified in 400 genera.
The following typical species will be considered: Nemalion and Poly-
si pho7ii a.

Nemalion (nem -al' i on) (Gr. nema, thread). — This cylindrical,
forked, marine, red alga is attached to rocks on the seacoast. The body
is composed of interwoven, branched threads surrounded by a gelatinous
material (Fig. 63). Some branches bear brushlike filaments whose tips
are divided into short antheridia, each containing one sperm. The tips
of other branches bear female structures consisting of an enlarged, basal
carpogonium (kar po -go' ni um) (Gr. karpos, fruit; gonos, offspring)
with an egg and an elongated, hairlike, tubular trichogyne (trik'ojin)
(Gr. thrix, hair; gyne, female) to receive the nonmotile sperm. The nu-
cleus of the sperm descends the trichogyne to the carpogonium where it
fuses with the ^gg nucleus to produce a zygote. Short projections are de-
veloped from the carpogonium which grow into short filaments at whose
tips are produced the asexual, nonmotile carpospores (kar' po spor) (Gr.
karpos, fruit; spora, spore) . The latter germinate to form a new Nemal-
ion plant.

Polysiphonia (poli si -fo' ni a) (Gr. polys, many; siphon, tube). — This
marine, red alga grows on rocks and is profusely branched. The main
axis and the larger branches consist of a central core made of a single
row of elongated core cells surrounded by a layer of jacket cells (Fig. 33) .
The elongated cells are connected with each other by cytoplasmic con-
nectives which form tubelike structures or ''siphons" ; hence the name
Polysiphonia. Each cell has a nucleus and numerous red plastids con-
taining phycoerythrin (fi kd e -rith' rin) (Gr. phykos, alga or seaweed;
erythros, red) which masks the chlorophyll. Stored foods are insoluble
"starch."

Polysiphonia is diecious (di-e'sius) (Gr. dis, two; oikos, house), the
male gametes being produced by one plant and the female gametes by
another plant. The lateral branches of the male plants bear clusters of
antheridia which produce numerous, nonmotile sperm^ (gametes). On
the side branches of other plants are borne female structures known as

Simple Plants With Chlorophyll — Algae 165

carpogonia (kar po -go' ni a) (Gr. karpos, fruit; gonos, birth). Each
carpogonium has an elongated trichogyne (trik'ojin) (Gr. thrix, hair;
gyne, female) to receive the nonmotile sperm brought by the water. The
nucleus of the sperm travels down the trichogyne to the carpogonium,
where nuclear fusions and cell divisions occur. Eventually this results
in the formation of many filaments, the tips of which produce many
carpospores. Other filaments form an urn-shaped covering which en-
closes the carpospores. When the latter are released through an opening
in the covering, they produce new plants which form sporangia (spor-
an' ji a) (Gr. sporos, spore; angos, vessel), each with four tetraspores
(tet'raspor) (Gr. tetras, four; sporos, spore). The sporangia are borne
on the central core cells just beneath the jacket cells. When liberated,
the tetraspores produce Polysiphonia plants, either with male antheridia
or with female carpogonia. This complex life cycle consists of ( 1 ) male
or female plants, (2) the zygote and its carpospores, and (3) plants pro-
ducing tetraspores. None of the reproductive cells are motile which is
characteristic of red algae.

QUESTIONS AND TOPICS

1. List the general characteristics of the thallophytes (Subkingdom Thallophyta).

2. List the distinguishing characteristics by means of which the following phyla
may be differentiated: Cyanophyta, Chlorophyta, Chrysophyta, Phaeophyta,
and Rhodophyta.

3. In what ways do algae differ from the fungi?

4. List all the asexual methods of reproduction found in the algae, describing
each.

5. List all the sexual methods of reproduction found in the algae, describing
each.

6. Explain what is meant by metagenesis (alternation of generations). Describe
what is meant by a gametophyte. Explain what is meant by a sporophyte.

7. What evidence from your studies of algae can you give for an explanation
for the origin of sex?

8. Describe the increase in complexity of structures and methods of reproduction
as you progress from the simpler to the higher types of algae.

9. What progressive developments take place in the vegetative body of the algae
as we go from the simpler to the higher types?

10. List the evolutionary changes which take place in individual cells of algae
as we go from the simpler to the higher types.

11. List the economic importance of the algae of each phylum, Including bene-
ficial as well as harmful items.

12. Make a list of the habitats for each phylum to which the algae belong.

13. Explain the importance of algae in the lives of fish and other types of aquatic
organisms.

166 Pla?it Biology

14. Diagram a typical life cycle of an alga in each of the phyla.

15. Define all the terms used in the discussion of algae, including the correct
pronunciation and derivation of each term.

SELECTED REFERENCES

Fritsch: The Structures and Reproduction of Algae, Cambridge University

Press.
Smith: Cryptogamic Botany; vol. 1, Algae and Fungi, McGraw-Hill Book Co.,

Inc.
Smith: The Fresh Water Algae of the United States, McGraw-Hill Book Co.,

Inc.
Tiffany: Algae, The Grass of Many Waters, Charles C Thomas, Publisher.
Tilden: The Algae and Their Life Relations, University of Minnesota Press.

Chapter 10

SIMPLE PLANTS WITHOUT CHLOROPHYLL— FUNGI

Plants Without True Leaves, Stems, or Roots; Not Forming
Multicellular Embryos; Without True Vascular (Conducting)
Tissues (Subkingdom Thallophyta)

GENERAL CHARACTERISTICS OF FUNGI

The term fungi is no longer used in the scientific classification but com-
monly refers to that group of thallophytes which lack chlorophyll, which,
in most species, must depend upon a heterotrophic mode of nutrition

Summary of Distinguishing Characteristics of Fungi

bacteria

(schizomy-

cophyta)

SLIME
MOLDS

(myxomy-
cophyta)

true fungi

(eumycophyta)

ALGA-LIKE

FUNGI

(PHYCO-

MYCETES)

ascus fungi
(ascomy-

CETES)

basidium

FUNGI

(basidio-

MYCETES)

Multicellu-
lar em-
bryos

—

Plastids and
chlorophyll

—

Organized
nucleus

—

Filamentous
hyphae

—

Septate
hyphae

—

-t

Amoeboid
Plasmo-
dium

c
o

• I— t

■M

3
X

C/3

Fission
Endospores*
Gonidia*
Gonidia*

Sporangio-

spores
Motile

swarm-cells

(myx-

amoeba)

Sporangio-
spores

Motile
zoospores
(aquatic
species)

Ascospores
Gonidio-
spores*
Budding*

Conidio-

spores*
Ghlamydo-

spores*
Uredospores*
Teliospores*
Pycniospores*
Aeciospores*

None?

Isogamy

Isogamy*
Heter-
ogamy*

Ascospores*
(by fusion)

Basidiospores
(by fusion)

*Certain species.

fExcept certain older hyphae.

167

168 Plant Biology

(het-ero -trof ik) (Gr. heteros, other; trophe, nourishment or food).
Heterotrophic fungi may be (1) saprophytes (sap'rofite) (Gr. sapros^
dead; phyton, plant), living on dead organic materials, or (2) parasites
(pa' ra site) (Gr. para, beside; sitos^ food), living in or on the body of
another living plant or animal. A few species are autotrophic and will
be considered later.

Fungi lack true leaves, stems, and roots; they do not form multicellular
embryos; they lack the two vascular tissues (phloem and xylem) which
are present in the higher plants. The fungi group includes the bacteria
(Phylum Schizomycophyta) , the slime molds (Phylum Myxomycophyta) ,
and the true (higher) fungi (Phylum Eumycophyta) , representatives of
which will be considered in this chapter. The true fungi and slime molds
differ from the bacteria in that the bacteria are unicellular, do not have
an organized nucleus, and usually have smaller cells and their methods of
reproduction differ from those of the slime molds and true fungi.

BACTERIA (PHYLUM SCHIZOMYCOPHYTA)

Bacteria (bak-te'ria) (Gr. bakterion, small rod) are placed in the
phylum Schizomycophyta (skiz o my -kof i ta) (Gr. Schizo, fission; myco,
fungus; phyta, plants) (Fig. 34). Bacteria are simple, unicellular plants
without chlorophyll; thus a majority of them are unable to photosyn-
thesize their foods but must secure them in other ways. The method of
nutrition for a majority of them is heterotrophic (het ero -trof ik) (Gr.
heteros, other; trophe, food or nourish), securing their foods from out-
side sources. Consequently, they may be (1) saprophytes (sap'rofite)
(Gr. sapros, dead; phyton, plant), which obtain foods from nonliving,
organic materials or (2) parasites (pa' ra site) (Gr. para, beside; sitos,
food), which live in or on the bodies of living plants or animals. In the
latter case, if a diseased condition is produced, they are known as patho-
genic bacteria (path o -jen' ik) (Gr. pathos, suffering; genos, produce).

A small minority of bacteria are autotrophic (ot o -trof ik) (Gr. autos,
self; trophe, nourish), being able to synthesize organic foods from carbon
dioxide and other simple inorganic substances. These autotrophic species
may be grouped into (1) chemosynthetic, in which the energy required
for the synthesis of foods is derived from the oxidation of certain chemi-
cals, and (2) photosynthetic, in which light supplies the food-producing
energy and the photosynthetic pigments are reddish-purple or greenish
(not chlorophyll) .

Some of the chemosynthetic bacteria include: (1) the sulfur bacteria
which live in waters, soils, and sewage, and which oxidize hydrogen sul-

Simple Plants Without Chlorophyll — Fungi 169

fide to free sulfur and then to sulfuric acid, thereby releasing energy for
the synthesis of organic compounds from carbon dioxide and other in-
organic substances. The sulfuric acid undergoes chemical changes in
the soil to form sulfates which are the principal sources of sulfur for
green plants; (2) the iron bacteria which live in iron-containing waters
and oxidize the iron compounds, thereby releasing energy for the syn-
thesis of organic compounds; (3) the hydrogen bacteria which live in
soils and oxidize molecular hydrogen to form water, thereby releasing
energy; (4) the nitrifying bacteria which live in soils— one group oxidizes
ammonia to nitrites and the other group oxidizes the nitrites to nitrates,
thus releasing energy. Other bacteria, the symbiotic nitrogen-fixing bac-
teria, live symbiotically in the nodules of the roots of leguminous plants
where they fix the free nitrogen to form nitrates. Still other soil bacteria,
the nonsymbiotic nitrogen-fixing bacteria, fix the free nitrogen to form
nitrates (not in roots). Hence, the essential nitrate supply of the soil is
aflfected by the actions of these various bacteria (Fig. 325) .

Some typical photosynthetic bacteria include: (1) the purple sulfur
bacteria which, because of their purple pigment, are able to synthesize
organic compounds in a manner similar to that used by chlorophyll-bear-
ing plants; (2) the purple nonsulfur bacteria which synthesize organic
compounds by the utilization of molecular hydrogen in the presence of
light; (3) the green bacteria which synthesize organic compounds by
oxidizing hydrogen sulfide and reducing carbon dioxide.

Bacteria are considered to be plants, rather than animals, because
(1) their methods of reproduction resemble those of certain algae and
true fungi, (2) their cell walls often contain cellulose, (3) they synthesize
vitamins like those of certain plants, (4) some species are able to utilize
simple inorganic compounds from which more complex organic com-
pounds may be synthesized.

Bacteria are unicellular and the simplest and smallest of living organ-
isms, being visible only under high magnifications (Fig. 34). When
growing under certain conditions many individuals may associate them-
selves to form a colony whose color and other characteristics are more or
less specific for each species. Typically, bacteria are not over 4 to 5
microns long (a micron is one-thousandth part of a millimeter).

The forms of bacteria (Fig. 34) include: (1) the coccus (spherical
or ovoid), (2) the rod-shaped (cylindrical), (3) the spiral-shaped, (4)
the filamentous (which may be branched). There are various types of
each of the four described above. For example, there are Staphylococci

170 Plant Biology

(masses of cocci forms), Streptococci (chains of cocci), Diplococci (pairs
of cocci), Sarcina (box-shaped mass of cocci) , etc.

Certain types of bacteria, like higher plants, require free, atmospheric
oxygen for their normal activities and are known as aerobes (a'erobe)
(Gr. aer, air; bios, life). Other species do not require free oxygen but
secure oxygen by breaking down certain types of oxygen-bearing foods
through the action of enzymes. These are called anaerobes (ana' er obe)
(Gr. an, without; aer, air; bios, life) . Certain species are at times aerobic
and at other times anaerobic.

A bacterial cell has a cell wall which in some species contains cellulose.
In some species an external, slimy layer or capsule is present. A few
species form a slimy, gelatinous mass called a zooglea (zoo-gle'a) (Gr.
zoon, animal; gloia, glue) in which great numbers of bacteria are em-
bedded in a mucilaginous matrix which is frequently iridescent. The
protoplasm of the cell is fairly homogeneous and contains vacuoles as
well as granules, including chromatin. An organized nucleus and plastids
are absent, although certain investigators maintain that certain species
possess a structure which resembles a nucleus.

Each species of bacteria has a temperature at which it grows best and
is known as its optimum temperature. As this temperature is decreased
or increased, growth is retarded until it eventually ceases. On the basis
of optimum growth temperatures, bacteria are grouped into ( 1 ) psychro-
philes (si'krofil) (Gr. psychros, cold; philein, to love), or those growing
best at temperatures below 14° C; (2) mesophiles (mes'ofil) (Gr.
mesos, middle; philein, to love) , or those having an optimum temperature
between 20° and 40° C, and (3) thermophiles (ther'mofil) (Gr.
therme, heat; philein, to love), or those that grow best at temperatures
above 45° C. Psychrophilic organisms are common in cold, deep waters,
where they exist as saprophytes. Psychrophiles may decompose foods in
cold storage plants. A majority of bacteria are mesophilic. The sapro-
phytic types common in soils, water, etc., grow best at room temperature
(20° to 25° C). Those growing in animals grow best at temperatures
which approximate their animal host. Bacteria which produce human
diseases grow best at body temperature (approximately 37° C). Ther-
mophilic bacteria may be found in many places but particularly in hot
springs, decaying vegetation, etc. Thermophils are not known to pro-
duce diseases, although they can be bothersome in food canning, milk
pasteurization, etc.

Not all bacteria are able to locomote in liquids, but when they do,
this is accomplished by the rhythmic, vibratile action of whiplike proto-

Simple Plants Without Chlorophyll — Fungi 171

plasmic structures known as flagella (fla -jel' a) (L. flagellum, whip).
The number and location of flagella vary with the species (Fig. 34), some
having a single flagellum, others having a tuft of flagella at one end,
others having tufts at each end, and still others having flagella over the
entire surface.

Like other plants, bacteria produce enzymes with which they perform
various functions. Those which are active within cells are called (intra-
cellular) endoenzymes, while those which are secreted to the outside
are called (extracellular) exoenzymes. Bacterial enzymes digest foods
by converting complex, water-insoluble foods into simpler, water-soluble
types. Bacteria also synthesize enzymes which aff"ect processes of oxida-
tion and reduction and hence are influential in respiration.

Probably when most persons think of bacteria they think of diseases.
However, of the total number of bacterial species, only a comparatively
small group produces diseases in animals and other plants. In fact, a
few species are actually beneficial, while a great majority are neither
harmful nor beneficial according to our present knowledge. Some of
the diseases produced by bacteria, yeasts, and fungi, as well as some of the
benefits, are discussed in the chapter on Economic Importance of Plants.

Bacteria cause diseases in plants as illustrated by the following typical
examples: (1) soft rot of cabbage, carrot, cucumber, celery, etc., (2)
the wilt diseases of corn, tomatoes, potatoes, squash, melons, cucumbers,
etc., (3) the root rot of cotton, (4) fire blight of pears and apples, (5)
crown galls of apples, grapes, raspberries, alfalfa, etc., (5) bacterial blight
of beans, (6) bacterial blight of walnut, and many others.

Bacteria may cause such diseases in animals as tuberculosis in cattle
and hogs, chicken cholera, pneumonia, septicemia in cattle, anthrax in
sheep, glanders in horses, goats, and sheep, botulism in chickens and
other animals, rat plague. Bang's disease (brucellosis or undulant fever)
in cattle, tularemia in rabbits, etc.

Bacteria reproduce asexually by fission in which the cell divides into
two parts at right angles to the long axis (Fig. 34) . Mitosis is apparently
not utilized in the process, since no mitotic figures have been observed.
Frequently, after fission, the cells may remain together to form a colony.
Each species forms a colony which has more or less constant character-
istics for that species and thus may be used for identifying them. Under
favorable conditions (proper food, moisture, temperature, etc.) fission
may occur every twenty to thirty minutes. At this rate of fission a single
bacterial cell in twenty-four hours would have nearly 5 million trillion
off"spring whose total weight would be many hundred tons. However,

172 Plant Biology

this rapid reproduction does not occur in nature because of limited food
supplies, the production of poisonous wastes, etc.

Another asexual method of reproduction possessed by certain species,
primarily rods, is by the production of resistant endospores. When a
spore is formed, the cell condenses its protoplasm into a spherical or oval
mass which is quite resjstant to external conditions. This mass forms
the spore with its protective spore wall and its relatively low water con-
tent. When proper environmental conditions are encountered, the spore
germinates to form a new bacterial cell, which will divide by fission.

A few species of bacteria produce within their cells a number of tiny
bodies called gonidia (go -nid' i a) (Gr. gone, "seed"; idion, small), each
of which develops into a typical bacterial cell. Certain species, especially
the filamentous types, may produce tiny conidia (ko-nid'ia) (Gr. konis,
dust; idion, small) at the tips of the filaments, similar to the formation
of such structures by certain true fungi.

SLIME MOLDS (PHYLUM MYXOMYCOPHYTA)

There are about 300 species of slime molds (slime fungi), most of
which are saprophytes on damp, decaying vegetable matter. They re-
semble certain fungi in their methods of spore formation and resemble
certain lower animals by their slimy, amoeba-like bodies, their amoeboid
methods of locomotion, and their ingestion of solid foods. Although the
methods of reproduction and the physiologic activities vary with the
species, the following general description is rather common and typical.

The vegetative body is a thin mass of slimy, naked, viscous protoplasm
known as the Plasmodium (plaz -mo' di um) (Gr. plasm,a, liquid; eidos,
form). The plasmodium contains many nuclei and creeps by a flowing
amoeboid motion through the formation of pseudo podia (su do -po' di a)
(Gr. pseudes, false; pous, foot). It may ingest solid foods in a manner
similar to that employed by certain lower animals (Fig. 35).

After a period of amoeboid locomotion the plasmodium produces a
number of spore cases known as sporangia (spor -anj' i a) (Gr. sporos,
seed; anggeion, vessel) . The sporangia vary in size and form, depending
on the species, and are used in classifying slime molds. Sporangia may
be colorless, purple, orange, brown, etc. As a sporangium matures, the
internal protoplasm forms a network of delicate fibers known as the
capillitium (kap i -lit' i um) (L. capillus, hair), in the meshes of which
are formed numerous unicellular, nonmotile spores (Fig. 35).

The liberated spores germinate, each producing one to four swarm cells
or myxamoebae (mik sa -me' ba) (Gr. myxa, slime; amoibe, change) and

Simple Plants Without Chlorophyll — Fungi 173

each having one to two flagella. The myxamoeba locomotes by flagellar
action or by amoeboid pseudopodia. Two myxamoebae fuse in a form
of sexual reproduction to form a zygote (zi'gote) (Gr. zygotos, joined).
Several zygotes may fuse to form a new plasmodium in which the nuclei
have not fused. Some common slime molds include Stemonitis (Fig. 35),
Lycogala (Fig. 35), Badhamia, Physarum, etc.

TRUE (HIGHER) FUNGI (PHYLUM EUMYCOPHYTA)

A. Class Phycomycetes (fi ko my -ce' tez) (Gr. phykos, seaweed; mykes,
fungus)

1. Black Bread Mold {Rhizopus nigricans) (ri'zopus; ni' gri kans)
(Gr. rhiza, root; pons, foot) (L. nigricans, black). — This mold is typical
of the black molds which are common saprophytes on moist, organic ma-
terials such as bread, fruits, potatoes, animal dung, etc. A few species
may parasitize man and other animals. Certain species parasitize squash,
cowpeas, cotton, and other plants. Other species are used commercially
in the production of alcohol, acids, enzymes, etc. They are called black
molds because of their dark-colored spores.

The irregular, whitish or grayish, mass of threadlike hyphae (hi' fe)
(Gr. hyphe, web) comprise the weblike mycelium (mi-se'lium) (Gr.
myxos, fungus) (Fig. 36). The young hyphae are branched and with-
out cross walls (nonseptate) and contain numerous nuclei, while cross
walls (septa) may be present in older hyphae, especially when reproduc-
ing sexually. Rootlike hyphae known as rhizoids (ri'zoid) (Gr. rhiza^
root; eidos, form) absorb nourishment from the substratum and serve
as anchors. Other hyphae grow over the surface and are called stolons
(sto' Ions) (L. stolo, shoot), from which arise the spore-forming hyphae
known as sporangiophores (spor -an' jio for) (Gr. sporos, spore; ang-
geion, vessel; pherein, to bear). Each- sporangiophore bears a globular
spore case (sporangium) at its tip which becomes darker as it matures.
The air-borne, asexual, nonmotile spores germinate to form hyphae.

Sexual reproduction occurs by the formation of small projections be-
tween two adjacent hyphae. The projections fuse and each forms a sex
cell (gamete). The two gametes fuse in the fertilization process known
as conjugation, thus producing a zygote (zygospore). The latter devel-
ops a new hypha. The two types of hyphae necessary for the sexual
process are called "plus" and "minus" hyphae or strains.

2. Water Mold (Saprolegnia) (sap ro -leg' ni a) (Gr. sapros, rotten;
legnon, edge). — The fungi of this group are primarily saprophytes in

174 Plant Biology

water, securing foods from dead plants or animals. A few species cause
serious damage by parasitizing fish, amphibia, turtles, etc. Goldfish in
aquaria are frequently affected by the white mycelia of water molds.

In Saprolegnia (Fig. 64) the hyphae are branched and the tips bear
enlarged zoosporangia (zo o spor -an' jia) (Gr. zoon, animal; sporos.

E6GS

OOGONIUM

ANTHERIOIAL
TUBE

ANTHERIOIUM

Fig. 64. — A common water mold (Saprolegnia) of the class Phycomycetes.
Left, reproduction by asexual, motile zoospores; right, sexual reproduction by
gametes produced in antheridia and oogonia. The antheridia form antheridial
tubes through which the male gametes pass. (From Fuller and Tippo; College
Botany, Henry Holt and Company.)

spore; anggeion, vessel). The hiciliated zoospores (swarm spores) lib-
erated by the zoosporangia swim ("swarm") in the water, then lose the
cilia, and surround themselves with a wall. Each of these gives rise to
many more zoospores, each of which germinates to form a new hypha.

Simple Plants Without Chlorophyll — Fungi 175

Sexual reproduction in Saprolegnia occurs by developing enlarged
oogonia (o -ogo' ni a) (Gr. oon, egg] gonos, beget) and clublike, male
antheridia (an ther -id' ia) (Gr. anthos, flower; idion, diminutive).
Each oogonium contains eggs. The antheridia penetrate the oogonia
and discharge male nuclei through antheridial tubes. An egg fertilized
by a male nucleus forms a zygote which develops a new hypha. In
Saprolegnia the same plant produces the antheridia and oogonia (mo-
necious).

B. Class Ascomycetes (ask o my -ce' tez) (Gr. askos, sac; mykes, fungus)

1. Penicillium (pen i -sil' i um) (L. penicillus, painter's brush). —
This blue-green mold has a loose mass of hyphae which grows on, or in,
such materials as damp leather, foods, citrus fruits, etc. The spore-bear-
ing hyphae are called conidiophores (ko -nid' io for) (Gr. konis, dust;
idion, diminutive; pherein, to bear), the tips of which resemble tiny
brushes, bearing chains of colored spores (conidia) at the tips (Figs. 39
and 73 ) . The spores are very small, light in weight, and usually present
in the air.

Penicillium is classed as an Ascomycete because certain hyphae may
produce ascos pores (ask'ospor) (Gr. askos, sac; sporos, spore or seed)
within saclike asci.

Species of Penicillium are responsible for food spoilage and destruction
of paper, leather, lumber, etc. Penicillium camemberti and P. roqueforti
impart the flavors and odors to these common types of cheeses. The
bluish-green areas in the cheese are masses of conidia. P. notatum is
widely used as a source for the bactericidal antibiotic penicillin (pen i-
sil'in). Antibiotics (an ti bi -ot' ik) (Gr. anti, against; bios, life) are
organic substances which are synthesized by one type of organism and
which inhibit, or destroy, another type "of organism. This common an-
tagonistic inhibition between two species of organisms (especially fungi)
is called antibiosis (an ti -bio' sis) . In 1940, the possible medical use of
penicillin and other antibiotics in the destruction of pathogenic bacteria
was suggested. Since then, numerous antibiotics, such as streptomycin,
tyrothricin, Chloromycetin, aureomycin, and many others, have been
isolated. These and others are considered elsewhere in the text.

2. Aspergillus (as per -jil' us) (L. aspergere, brush). — This blue-green
mold is composed of a loose mass of hyphae growing on or in damp foods,
leathers, fabrics, fruits, etc. The spore-bearing hyphae are called conidio-
phores which produce chains of colored spores (conidia) on the enlarged,

176 Plant Biology

globose tips of these hyphae (Fig. 38). In many ways the Aspergillus
molds resemble the Penicillium molds, but the tips of the conidiophores
differ in their specific methods of producing the conidia (Figs. 38 and
73).

Aspergillus is classified as an Ascomycete because certain hyphae may
produce ascos pores within saclike asci. Species of Aspergillus cause the
spoilage of bread and other foods, the deterioration of leathers and fab-
rics, the decay of tobacco, and the rotting of fruits. Certain species may
cause lung and ear infections in animals, including man. Certain species
of Aspergillus may be used commercially in the production of alcohols
and organic acids.

3. Cup Fungus (Peziza) (pe-zi'za) (L, pezica, sessile fungus) (Fig.
40). — The so-called cup fungi possess a fleshy, cuplike body {ascocarp)
specifically called an apothecium (ap o -the' si um) (Gr. apo, away;
thece, cup) which is composed of tightly compacted hyphae and which is
often borne on a stalk. Inside the cup is a layer of cylindroid or sac-
shaped asci and sterile hyphae called paraphyses (pa -raf i sez) (Gr.
para, beside; physis, growth). The asci and paraphyses constitute a
layer called the hymenium (hi -me' ni um) (Gr. hymen, skin). The
asci usually contain eight ascospores.

There are over 5,000 species of cup fungi, many of which are sapro-
phytes on decaying vegetable matter, on dead wood, or on the ground.
Some species may be brilliantly colored, and in some the saucer-shaped
fruiting body may be four inches in diameter.

4. Yeasts (ye' st) (A.S. gist, ferment) . — Yeasts are typically unicellular,
saprophytic fungi usually without hyphae, although a few species may
develop a short hypha (Fig. 37) . Each cell is usually ovoid in shape and
contains an organized nucleus. Asexual reproduction is commonly accom-
plished by budding in which a small protuberance {hud) is projected
from the cell. The bud may free itself from the mother cell or remain
attached and produce more buds, eventually forming a many-celled
chain of cells.

Under certain conditions a yeast cell may become a simple, single
ascus in which are formed ascospores (usually four). In other instances
two yeast cells may fuse before the ascospores are produced.

Yeasts are of economic importance in the production of alcohol from
sugars, in the rising of bread by the production of carbon dioxide, in
manufacturing certain vitamins, and by being parasites on higher plants,
animals, and man. A yeastlike organism causes "leaf curl" on peach

Simple Plants Without Chlorophyll — Fungi 111

trees, in which the leaves curl and become yellow. Single asci are formed
on the surface of the diseased leaves. The disease may be prevented by
a thorough application of a ''dormant spray" (Bordeaux mixture and
lime sulfur sprays) two weeks before the buds unfold. The economic
importance of yeasts is considered in the chapter on Economic Impor-
tance of Plants.

5. Mildews (mil' du) (A.S. mildeaw, honeydew). — Powdery mildews
are fungi which are chiefly parasites on the leaves and stems of flowering
plants. The masses of hyphae appear as whitish, or grayish, powdery
areas on the surfaces of the aff'ected plant. Certain hyphae, the haustoria
(hos-to'ria) (L. haurire, to drink) penetrate and absorb food from the
cells of the plant host. Asexual reproduction occurs by forming chains
of spores (conidia) at the tips of the surface hyphae.

Ascospores are formed within the asci. The asci develop within small,
closed ascocarps, known specifically as cleistothecia or perithecia (kli sto-
the'sia) (Gr. kleistos, closed; theke, box) (peri -the' si a) (Gr. peri,
around; theke, box) . The latter are produced by the hyphae on the sur-
face of the host plant. Sometimes the hyphae of the asocarp may be
elongated and delicately branched.

Powdery mildews appear as whitish, dusty patches upon such plants
as lilacs, roses, apples, clovers, dandelions, grapes, maples, berries, and
other flowering plants. Dusting infected plants with flowers of sulfur
may be beneficial in combating these diseases.

6. Blights (blite) (A.S. hlaecan, grow pale).- — Blights are diseases of
plants in which the blossoms, young leaves, or branches die suddenly.
Examples are the fire blight of pears and the blight of chestnut trees.
The latter is produced by the ascomycetous fungus (Endothia parasitica)
which was introduced from China about 1900 and which has killed most
of the chestnut trees in the United States. In these the asci are present
in dark, ovoid ascocarps known specifically as perithecia. Conidia
(spores) may be produced in flask-shaped fruiting bodies called pycnidia
(pik-nid'ia) (Gr. pyknos, dense; idium, diminutive). The mycelium
of the fungus parasitizes the cambium and the living cortex cells of the
chestnut tree.

C. Class Basidiomycetes (ba sid io my -se' tez) (Gr. basis, base or club;

mykes, fungus)

1. Mushrooms. — Mushrooms are saprophytic fungi which derive their
foods from decomposing organic materials in the soil, dead leaves, bark,

178 Plant Biology

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Simple Plants Without Chlorophyll — Fungi 179

wood, etc. The vegetative body consists of masses of septate hyphae
which penetrate the substratum. Fleshy, fruiting bodies called sporo-
phores are produced for reproduction purposes (Fig. 41). Each sporo-
phore typically consists of a broad, caplike or umbrella-shaped pileus
(pil' eus) (L. pileus, cap) and a stalklike stipe (L. stipes, stalk). On
the undersurface of the pileus are gills which are thin plates of compact
hyphal tissues and which bear club-shaped basidia (ba-sid'ia) (Gr.
basis, base). The latter bear numerous hasidiospores (Fig. 65), each
attached by a slender sterigma (ster-ig'ma) (Gr. sterigma, support).
In the case of the common, edible, field mushroom (Psalliota [Agaricus]
campestris), a single sporophore may produce nearly two billion hasidio-
spores, each of which may germinate to form a new hypha. At certam
times there may be fusion between two cells of adjacent hyphae (by a
process equivalent to a sexual process), producing a binucleated cell
which is the hasidium. This nucleus will divide to form four nuclei, one
for each of the four hasidiospores. Each of the latter is pinched off from
the sterigma and scattered by the wind. There are several hundred
species of mushrooms and toadstools but only a comparatively few of
them are poisonous. Most of the latter belong to the genus Amanita.
Unless the collector of wild mushrooms is familiar with the specimens he
collects, he should take no chances with the deadly species. It is better
to forego the use of mushrooms rather than be sorry later.

2. Bracket Fungi (Pore Fungi). — The bracket fungi or shelf fungi are
members of the family known as pore fungi because the underside of the
caps (shelves) contain hundreds of tiny tubes which appear as pores on
the lower surface. The internal tissues around these tubes produce club-
shaped basidia which bear basidiospores (Fig. 42). The latter escape
through the pores.

The hyphae of tree-inhabiting shelf fungi secrete enzymes which digest
the tissues of the wood and bark and absorb organic compounds from
these tissues. The shelflike sporophores described above are often tough
and woody. In certain species they may be perennial, forming new
spore-producing hyphae in annual layers, year after year. Shelf fungi
are common causes of wood decomposition, and parasitic species often
kill living trees. Among the important wood-rotting pore fungi is Meru-
lius lacrymans which causes the common "dry rot" of wood.

3. Smuts. — Smuts are produced by a group of smut fungi parasitic on
flowering plants, in which the irregular masses of septate hyphae pene-
trate the tissues of the host plant. They are called smuts because the

180 Plant Biology

fungi produce heavy-walledj dark-colored, smut spores known as chlamy-
dospores (klam' i do spor) (Gr. chlamys, cloak; sporos, spore or seed).
The latter are especially prevalent in the ovary tissues of the host plant
but may appear in other tissues. The resistant smut spores may be dor-
mant until the next spring when each germinates to form a cylindric
tube of one to four cells known as a basidium. The latter produces
hasidios pores (sporidia). The basidiospores attack host plants, produc-
ing hyphae which eventually form smut spores.

Fig. 66. — Corn smut (Ustilago zeae) showing unbroken tumors at the right but
broken and disseminating spores at the left; insert shows chlamydospores of corn
smut. (By permission from Botany by Hill, Ov^erholts, and Popp. Copyright,
1950, McGraw-Hill Book Company, Inc.)

In some species of smuts, conidia are also found on the parasitized
plant. Thus as many as three types of spores may be formed in certain
life cycles. In certain species the basidiospores conjugate in pairs before
germination.

Smuts constitute a common group of about 400 species and are pri-
marily parasitic on members of the grass family such as corn (Fig. 66),
oats, wheat, rice, rye, barley, etc., where they are responsible for tre-

Simple Plants Without Chlorophyll — Fungi 181

mendous crop losses. In the smut of corn, Ustilago Zaea (us ti -la' go;
ze' a) (L. ustilago, thistlelike plant; zea, kind of grain), the tumorlike
masses of smut may appear on any part of the plant (Fig. 66). When
these tumors mature in the summer or fall, they are masses of black
chlamydospores. The latter usually germinate the next spring or summer
to infect new corn plants. The hasidios pores, formed on the hasidia,
produce germ tubes capable of infecting any part of the corn plant. The
resulting mycelia mass together at definite points and break out as the
smut tumors. The latter are white at first but become black as the
chlamydospores mature. Annual losses in the United States due to corn
smut are estimated at $100,000,000.

4. Rusts. — Rust fungi are parasitic on various flowering plants and
ferns. They are called rusts (A.S. rust, red) because of their reddish-
brown spores on the surface of the leaves and stems. Hyphae penetrate
the tissues of the host plant. A rust may parasitize two unrelated species
of plants, alternating between the two hosts.

A very destructive rust is the black stem rust of wheat (Fig. 67) known
as Puccinia graminis (puk -sin' i a; gram' in is) (Puccini, an Italian
anatomist; L. graminis, grass). The life cycle of this wheat rust may
be briefly described as follows:

In the summer the hyphae live in the stems and leaves of wheat where
the blisterlike uredosori (uredinia) (u -re' do so ri) (Gr. uredo, blight;
soros, heap) contain many unicellular, rough, reddish-orange, wind-
disseminated, summer spores called uredospores (Fig. 67). These spores
may infect other wheat plants and are known as the "red rust" of wheat.

In late summer the hyphae form black pustules known as teliosori
(telia) which produce thick-walled, resistant, brownish-black, winter
spores called teliospores (teleutospores) (te'liospor) (Gr. telios, end;
sporos, spore) (Fig. 67). This is the "black rust" stage. The teliospores
remain dormant on wheat straw and germinate next April or May. Each
germinating teliospore produces a clublike basidium with its four basidio-
spores (ba -sid' i o spor) (Gr. basis, base or club; sporos, spore) which
are wind borne to the common, wild, European barberry (not the culti-
vated Japanese barberry) .

The basldiospores (Fig. 67) germinate and send hyphae into the bar-
berry leaves, while the yellowish-red spots on the upper surface form
small, flask-shaped pycnia (spermogonia) (pik'nia) (Gr. pyknos,
crowded); (sper mo -go' ni a) (Gr. sperma, "seed"; gonos, offspring).
The pycnia produce small, unicellular pycniospores (spermatia) at the

182 Plant Biology

tips of the hyphae which line them. The pycniospores may be carried
by insects and are of two types, known as plus and minus. A plus spore
fuses with a minus spore to form a mycelium which produces chains of
yellowish-red, spring spores called aeciospores (e'siospor) (Gr. aecium,
injury) in small cuplike aecia on the lower surface of the barberry leaves.
The aeciospores are windblown to young wheat plants in the spring,
where their hyphae again form uredospores to complete the life cycle
(Fig. 67).

ureclospores^

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Fig. 67. — Wheat rust (Puccinia graminis). A, Section of leaf through a
pycnium; B, section through an aecium in a barberry leaf; C, section through a
uredinial sorus, showing unicellular, rough uredospores on slender stalks; D, sec-
tion through a telial sorus, showing two-celled teliospores on long pedicels; E,
germinating teliospores — left, both cells of the spore germinating; right, only the
apical cell germinating; the germ tube has been transformed into a basidium,
from each cell of which a basidiospore has been or is being formed. A germinat-
ing basidiospore is also shown. (By permission from Botany, by Hill, Overholts,
and Popp. Copyright, 1950. McGraw-Hill Book Company, Inc.)

Simple Plants Without Chlorophyll — Pungi 183

Common rusts include the cedar-apple rust which parasitizes cedars
and spends the rest of the year on apple trees or hawthorns; the white
pine blister rust in which the fungus alternates between the white pine
tree and wild gooseberries and currants. Other rusts cause diseases of
corn, oats, rye, pears, cherries, plums, peaches, various cone-bearing
trees, many types of garden vegetables, cultivated flowers, and many
other types of economically important plants.

QUESTIONS AND TOPICS

1. Review the general characteristics of the thallophytes (Subkingdom Thallo-
phyta).

2. List the distinguishing characteristics by means of which the following phyla
may be differentiated: Schizomycophyta, Myxomycophyta, and Eumycophyta.

3. Why are slime molds considered as plants? What animal characteristics do
they possess?

4. Describe the life cycle of a typical slime mold.

5. List all the ways you can in which fungi affect man in one way or another.

6. Give reasons why you consider fungi to be higher or lower types of plants
than algae.

7. List and describe each of the asexual methods of reproduction found in fungi.

8. Describe the process of conjugation found in certain fungi. In what ways
does this process resemble sexual reproduction? In which fungi do you find
conjugation?

9. Define and give the derivation of each new term encountered in this chapter.

10. Describe the ways in which sunlight and dry air may be detrimental to fungi.

11. Explain how fungi secure their nourishment and oxygen.

12. Diagram the life cycle of Rhizopus nigricans. Why are the gametes of this
algalike fungus not considered to be true eggs and sperms?

13. Explain how bread molds on the inside of the loaf. What is the source of
the mold?

14. Why are bacteria considered to be plants? Why are they classed as fungi?

15. List all the ways in which bacteria may be ( 1 ) beneficial and (2) harmful.

16. Contrast and give examples of heterotrophic and autotrophic nutrition.

17. List the distinguishing characteristics of the following classes of the true
fungi: Phycomycetes, Ascomycetes, and Basidiomycetes, including examples
of each class.

18. Diagram a typical life cycle of each class of true fungi (Eumycophyta) .

19. Why are yeasts classed as Ascomycetes? In what ways do yeasts differ
from other Ascomycetes?

20. Why are Penicillium and Aspergillus classed as Ascomycetes? Of what
economic importance are these two fungi?

21. Contrast the structure of asci and basidia.

22. Describe the life cycle of the black stem rust of wheat, including the various
hosts, stages, types of spores, damages, etc.

23. Why are the sporophores of many fungi borne upright?

184 Plant Biology

24. Do any of the fungi produce multicellular embryos? Do any of them possess
plastids and chlorophyll?

25. Do all cells of fungi possess nuclear materials? Do they all possess an or-
ganized nucleus?

26. Describe the increase in complexity of structures and methods of reproduc-
tion as we proceed from the simpler to the higher types of fungi.

27. List all conclusions you can logically draw from your study of fungi.

SELECTED REFERENCES

Allen, Holtman, and McBee: Microbes Which Help or Destroy Us, The C. V.
Mosby Co.

Bessey: Textbook of Mycology, The Blakiston Co.

Birkeland: Microbiology and Man, Appleton-Century-Crofts, Inc.

Christensen: Common Edible Mushrooms, University of Minnesota Press.

Clifton: Introduction to Bacteria, McGraw-Hill Book Co., Inc.

Conant et al.: Manual of Clinical Mycology, W. B. Saunders Co.

Dodge: Medical Mycology, The C. V. Mosby Co.

Fitzpatrick: The Lower Fungi (Phycomycetes), McGraw-Hill Book Co., Inc.

Frobisher: Fundamentals of Bacteriology, W. B. Saunders Co.

Greaves and Greaves: Elementary Bacteriology, W. B. Saunders Co.

Jordan and Burrows: Textbook of Bacteriology, W. B. Saunders Co.

Krieger: Mushroom Handbook, The Macmillan Co.

Henrici and Ordal: The Biology of Bacteria, D. C. Heath & Co.

Henrici et al.: Molds, Yeasts, and Actinomycetes, Henry Holt & Co., Inc.

Large: The Advance of Fungi, Henry Holt & Co., Inc.

Lewis and Hopper: Introduction to Medical Mycology, Year Book Publishers,
Inc.

Lindegren: The Yeast Cell, Educational Publishers, Inc.

Nickerson et al. : Biology of Pathogenic Fungi, Chronica Botanica Co. *

Rahn: Microbes of Merit, Jacques Cattell Press.

Rice: Textbook of Bacteriology, W. B. Saunders Co.

Sallee: Fundamental Principles of Bacteriology, McGraw-Hill Book Co., Inc.

Singer: The Agaricales (Mushrooms), Chronica Botanica Co.

Smith et al. : Manual of Phycology, Chronica Botanica Co.

Stitt, Clough, and Branham: Practical Bacteriology, Hematology and Parasitol-
ogy, The Blakiston Co.

Thomas: Fieldbook of Common Mushrooms, G. P. Putnam's Sons.

Waksman: Microbial Antagonisms and Antibiotic Substances, Commonwealth
Fund.

Waksman: Principles of Soil Microbiology, Williams & Wilkins Co.

Wolf and Wolf: The Fungi, 2 vols., John Wiley & Sons, Inc.

Chapter 11

MOSSES AND THEIR ALLIES— BRYOPHYTES
(PHYLUM BRYOPHYTA)

Intermediate Plants With Chlorophyll; Without True Leaves,
Stems, or Roots; Without Vascular (Conducting) Tissues; Form-
ing Multicellular Embryos (Subkingdom Embryophyta)

GENERAL CHARACTERISTICS OF BRYOPHYTES

L The members of the phylum Bryophyta (bri-of'ita) (Or. hryon^
moss; phyta, plants) are terrestrial plants, although they require consid-
erable moisture for growth and fertilization.

2. In general, the adult plant body of Bryophytes is composed of
blocks, or sheets, of cells forming a parenchymatous tissue, in contrast to
the simple construction of the Thallophytes. The adult plant body of
Bryophytes is never filamentous, but the developmental, protonema stage
of mosses may be filamentous.

3. The gamete-producing sex organs, the gametangia (gam e -tan' ji a)
(Or. gametes, spouse or gametes; anggeion, vessel), are multicellular
and possess a protective layer of sterile cells, while the gametangia of
Thallophytes are unicellular (few exceptions).

4. Water is required for fertilization in Bryophytes, as in most algae.

5. All Bryophytes possess an alternation of generations between the
gamete-producing gametophyte generation and the spore-forming sporo-
phyte generation. The latter is more or less dependent on the gameto-
phyte.

6. Bryophytes develop a multicellular embryo from the zygote (fer-
tilized t.gg) , from which the sporophyte develops.

7. No asexual spores are produced by Bryophytes.

8. Asexual reproduction may occur by fragmentation of the plant, or
by special bodies known as gemmae (jem'i) (L. gemma, bud).

9. Bryophytes are without true vascular (conducting) tissues such as
phloem and xylem.

185

186 Plant Biology

10. Bryophytes, including mosses and liverworts, possess chlorophyll in
chloroplasts for the purpose of photosynthesis.

11. Mosses and liverworts possess similar methods of reproduction and
life cycles and are much alike structurally and functionally in spite of
diflferences which may be apparent upon casual observation.

12. True mosses belong to the subkingdom Emhryophyta, the phylum
Bryophyta, and the class Musci (mus' si) (L. muscus, moss).

13. Liverworts belong to the subkingdom Emhryophyta, the phylum
Bryophyta, and the class Hepaticae (he-pat'ise) (L. hepaticus, liver).

TRUE MOSSES

1. Polytrichum (po -lit' ri kum) (Gr. polys, many; thrix, hair) is a
common, true moss known as the hairy cap moss. Mosses are small
terrestrial plants which require a certain amount of moisture for growth
and fertilization processes. They usually grow so densely as to form a
mass of vegetation. Each individual plant consists of a stemlike axis to
which are attached small, leaf like appendages (not true stems or leaves
because of the absence of the vascular tissues, phloem and xylem) (Fig.
45). Rootlike rhizoids absorb materials and anchor the plants.

Several male antheridia (an the -rid' i a) (Gr. anthos, flower; idion,
diminutive) are borne in a cluster at the tips of certain stemlike axes,
while several female archegonia (ar ke -go' ni a) (Gr. arche, beginning;
gonos, offspring) are borne at the tips of other stemlike axes. Poly-
trichum has its sexes in separate plants, being diecious (di -e' si us) (Gr.
dis, two; oikos, house). In other species of mosses the antheridia and
archegonia are borne on the same plant, being monecious (bisexual).

In Polytrichum the antheridia are separated by multicellular, sterile
hairs called paraphyses (pa -raf i sez) (Gr. para, beside; physis, growth),
and both are surrounded by a rosette of leaflike appendages which may
be colored and resemble a "flower." Each antheridium consists of a
short stalk and an enlargement which produces unicellular male sperms.
The sperms are coiled, bear two long, terminal flagella, and escape from
the apex of the antheridium.

The female archegonia are separated by paraphyses, and each arche-
gonium has a stalk supporting an enlarged venter which surrounds the
egg. When mature, a canal leads through the long neck to the venter.
During fertilization the motile sperm swims through water from the
antheridium to the female plant. It travels down the canal to the
venter where a sperm and &gg fuse by the fertilization process known as

Mosses and Their Allies — Bryophytes 187

oogamy (o-og'ami) (Gr. 0072^ egg; gamos^ marriage). In oogamy the
two gametes are unlike and the eg^ is stationary. The fertilized ^^^,
known as a zygote, is retained in the venter where it forms an embryo
by numerous cell divisions. The embryo is parasitic on the female
gametophyte plant, being given water, food, and protection. The embryo
then grows to form a new plant known as the sporophyte (spor'ofite)
(Gr. sporos, spore; phyta, plants). A sporophyte consists of a foot,
which is attached to the female plant, and a stalklike seta, at whose tip
is a spore case or sporangium (spor -an' ji um) (Gr. sporos, spore; ang-
geion, vessel). The sporangium, or capsule is covered with a hairy cap
or calyptra (ka -lip' tra) (Gr. kalyptra, covering) ; hence the common
name of hairy cap. When the calyptra is removed, a lidlike operculum
(o -per' ku lum) (L. operculum, lid) is observed to cover the capsule.
Beneath the operculum is a ring of hygroscopic teeth known as the peri-
stome (per'istom) (Gr. peri, around; stoma, opening). The teeth are
affected by moisture, and their movements expel the spores from the
capsule. When immature, the capsule contains spore mother cells, each
of which undergoes reduction division (meiosis) and produces four
spores. The four spores of each tetrad are of two kinds. One kind con-
tains a small, Y chromosome (sex chromosome) and produces a male'
plant; the other kind contains a large, X chromosome and produces a
female plant. This method of sgx determination is similar to that in
man in which there are also X and Y chromosomes.

Each spore germinates to form a threadlike, branched protonema
(pro to -ne' ma) (Gr. protos, first; nema, thread). The cells of the
protenema bear chloroplasts with which to photosynthesize food. Rhi-
zoids anchor the young plant and absorb materials from the soil. Buds
appear on the protonema, and these, by cell divisions, produce a new
male or female moss plant. There is an alternation of generations be-
tween the gametophyte plant and the sporophyte plant. Under certain
conditions some mosses may reproduce asexually by a fragmentation of
the plant or by the formation of special bodies known as gemmae (jem' i)
(L. gemma, bud) .

2. Sphagnum (sfag' num) (Gr. sphagnos, moss) is the name of a genus
to which belong the peat or bog mosses which are common inhabitants
of bogs, ponds, and other wet places. Their life cycles are similar to that
of Polytrichum. The upright, branched axis may be one foot long and
bears leaflike appendages ("leaves") (Fig. 46). The latter contain two
types of cells — one for water storage and the other containing chloroplasts

188 Pla7it Biology

for photosynthesis purposes. The water storage cells are large and empty
and have openings to the outside. Sphagnum can absorb water up to
twenty times its weight.

Depending on the species, male antheridia and female archegonia may
be present on the same plant (but different branches) or on different
plants. The fertilized egg (zygote) develops into a sporophyte which has
a base embedded in the gametophyte, a short stalklike seta, and an en-
larged capsule. Because of the short seta, the gametophyte develops a
structure known as the pseudopodium (su do -po' di um) (Gr. pseudes,
false; pous, foot) at the base of the foot in order to elevate the spore-
producing capsule above the gametophyte. Alternation of generatio?is
similar to that described above takes place. Unlike Polytrichum, when
a spore germinates, it forms a thin, lobed, platelike prothallus (''proto-
nema"). Sphagnum may frequently reproduce by fragmentation.

Sphagnum and other mosses grow on the edges of ponds and lakes
where they may gradually fill in the entire body of water. During this
process of filling in there may be masses of floating mosses. The water
of such bogs is apparently antiseptic because many things have been
preserved for years in such bog water. This antiseptic property is utilized
when Sphagnum is used for surgical dressings. In addition, the water
absorption properties are useful in this connection.

Sphagnum is also utilized in gardening to keep the soil porous and
to increase the water-retaining capacity. Because of the water-holding
abilities, it is used by florists in packing cut flowers, in the development
of seedlings, etc. Sphagnum and other mosses have accumulated in bogs
and swamps in the past where they have slowly decomposed and become
compacted and carbonized. This process has produced peat which is a
valuable fuel. Vast deposits of peat in the United States could be used
in place of coal.

LIVERWORTS

1. Marchantia (mar -kan' shi a) (after the French botanist. Mar-
chant, who died in 1678) is the genus to which belong the fiat, lobed,
thalloid liverworts commonly found prostrate on moist rocks and soil
along streams. These plants are called liverworts because of their
fancied resemblance to the lobed liver of higher animals.

The surface of the branched thallus body possesses rhomboidal areas,
each of which has a pore in its center for the exchange of gases. Inter-
nally, the thallus has air chambers and columns of cells containing chloro-

Mosses and Their Allies — Bryophytes 189

plasts for photosynthesis. Rootlike rhizoids anchor the thallus and absorb
materials from the substratum (Fig. 43) .

Marchantia is diecious, one thallus bearing male antheridia and an-
other thallus bearing female archegonia. On the male thallus (male
gametophyte) arise the stalklike antheridiophores with lohed disks at the
tip. The male antheridia are borne in cavities which open on the upper
surface of these disks. Each antheridium is an enlarged, oval structure
which produces coiled, bifiagellated sperms (gametes) (Fig. 43).

On the female thallus (female gametophyte) arise the stalklike arche-
goniophores with small, term,inal disks bearing fingerlike rays (Fig. 43).
The female archegonia are borne on the undersurface of these disks.
Each archegonium has a hollow, tubular neck and an enlarged venter
with a single egg (ovum) at the base of the latter.

The sperm swims through the water from the antheridium to the
venter of the archegonium where the sperm and egg fuse (fertilize) to
form a zygote. The latter through numerous cell divisions forms a multi-
cellular embryo from which develops the spore-producing sporophyte.
The latter consists of a foot embedded in the disk of the female gameto-
phyte, a seta, and a capsule (sporangium). The latter produces numer-
ous spores. Elongated, spiral-shaped, hygroscopic elaters {eV a ter) (Gr.
elater, driver) are affected by moisture and expel the spores from the
capsule. The spores germinate to form new male or female gameto-
phytes (thalli).

There is an alternation of generations between the gamete-producing
gametophyte and the spore-forming sporophyte which is quite similar to
that in true mosses. Unlike the moss sporophyte, the Marchantia sporo-
phyte does not possess stomata (stom'ata) (Gr. stoma, opening) and is
usually smaller than in most mosses. Marchantia may also reproduce
asexually by the formation of special bodies known as gemmae (jem'i)
(L. gemma, bud) in little gemma cups or by the process of fragmentation.

2. Porella (por -el' a) is a common leafy liverwort (Fig. 44) which
may form a green mass on moist soil, rocks, or rotten wood. Some
species of leafy liverworts may grow on tree trunks in damp forests. Some
species may resemble true mosses, but the liverworts are prostrate on their
substratum.

Porella has three rows of leaflike structures attached to a stemlike axis.
The latter may be branched and is attached by rhizoids. The leaflike
structures are much simpler than the gametophyte of Marchantia, con-
sisting of one layer of cells and without a midvein. The sporophyte of

190 Plant Biology

Porella is similar to that of Maichantia, consisting of a foot, stalk, and
sporangium (capsule). The latter bears spores and elaters as in the
thalloid liverworts.

QUESTIONS AND TOPICS

1. List the characteristics of (1) Embryophyta, (2) Bryophyta, (3) Hepaticae,
and (4) Musci.

2. Learn the pronunciation, derivation, and a definition of each new term used
in this chapter.

3. Discuss the economic importance of bryophytes.

4. Contrast gametophytes and sporophytes in as many ways as possible as illus-
trated by the bryophytes.

5. Make a diagram of a true moss life cycle showing the stages in correct
sequence and the chromosome numbers in the gametophyte and sporophyte
generations.

6. Make a diagram of a liverwort life cycle showing the stages in correct
sequence and the chromosome numbers in the gametophyte and sporophyte
generations.

7. Why are the axes, "leaves," and rhizoids not considered to be true stems,
leaves, and roots?

8. Why are the mosses and their alhes classed as Embryophytes ?

9. Why are the bryophytes considered not to have true vascular (conducting)
tissues?

10. In what ways do the leafy liverworts resemble certain mosses?

IL In what ways do the leafy liverworts differ from the thalloid liverworts?

12. How do the gametangia of Bryophyta differ from the gametangia of Thal-
lophyta?

13. Why do the bryophytes require a considerable amount of moisture?

14. List some of the more important values of Sphagnum mosses.

15. Explain why most bryophytes are rather short plants, giving specific reasons
because of structures, growing conditions, etc.

16. Describe the structure and functions of elaters.

17. Describe differences in structures of the zygote developments in the mosses
and in the liverworts. (Contrast protonema and prothallus. )

18. Describe the method of determination of sex in bryophytes. In what ways
are these methods similar to the sex determination methods in man?

SELECTED REFERENCES

Conard: How to Know the Mosses, William C. Brown Co.
Evans: Classification of the Hepaticae, Botanical Review 5: 49-96, 1939.
Grout: Mosses With a Hand Lens, A. J. Grout, Newfane, Vt.
Grout: Mosses With a Hand Lens and Microscope, A. J. Grout, Newfane, Vt.
Smith: Cryptogamic Botany (vol. 2): Bryophytes and Pteridophytes, McGraw-
Hill Book Co., Inc.
Verdoorn et al.: Manual of Bryology, Chronica Botanica Co.

Chapter 12

FERNS AND THEIR ALLIES

Higher Plants With Chlorophyll; With True Leaves, Stems,
AND Roots; With Vascular Tissues (Phloem and Xylem) ; With-
out Seeds; Forming Multicellular Embryos (Subkingdom Em-
bryophyta)

GENERAL CHARACTERISTICS OF FERNS AND THEIR ALLIES
(CLUB "MOSSES" AND HORSETAILS)

1. Ferns and their allies belong to the subkingdom Embryo phyta be-
cause they form multicellular embryos and to the phylum Tracheophyta
because they possess true vascular tissues of varying degrees of complexity.

2. The phylum Tracheophyta includes such subphyla as ( 1 ) Lycopsida
(club ''mosses") having simple vascular tissues, small, green leaves, usually
spirally arranged, and branched stems and roots, (2) Sphenopsida
(horsetails), having a simple vascular system, small leaves in whorls
(sometimes scalelike), jointed, and hollow stems which are usually rough-
ened by ribs and silica, and (3) Pteropsida (ferns), having a rather com-
plex vascular system and usually large, conspicuous leaves.

3. Tracheophytes possess true leaves, stems, and roots, skeletal mate-
rials for upright growth, stomata for the exchange of gases, and a pro-
tective layer of cutin.

4. Club "mosses," horsetails, and ferns have somewhat similar methods
of reproduction and life cycles.

5. The gametangia (sex organs) are multicellular, as in the Bryophytes,
but in contrast to the unicellular sex structures of the Thallophytes.

6. Tracheophytes possess an alternation of generations in which a
gamete-producing gametophyte generation alternates with a spore-form-
ing sporophyte generation.

7. The gametophyte bears characteristic multicellular sex organs
known as the male antheridia and the female archegonia.

8. The sporophyte is relatively large and independent (with true
leaves, stems, and roots), while the gametophyte is usually rather small
and inconspicuous (contrast with bryophytes) .

191

192 Plant Biology

9. In ferns and their allies the multicellular sporangia (spore cases)
are usually borne on leaves so that such sporophylls are an important
characteristic.

10. In certain species the sporophylls bear sporangia in which the
spores are all alike (homosporous) ; in others there are two kinds of
sporophylls, two kinds of sporangia, and two kinds of spores (hetero-
s porous).

11. Sporangia may (1) be borne in clusters (sori), as in ferns, (2)
occur in groups of 5 to 10 upon shield-shaped sporangiophores to form
conelike strohili, as in horsetails, or (3) occur singly on the upper sur-
face of the sporophylls to form a clublike strobilus, as in club "mosses."

12. Spores germinate to form different types of young gametophytes :
( 1 ) colorless, rather bulky prothalli with male antheridia and female
archegonia in club "mosses," (2) thin, green, irregular gametophytes,
with antheridia and archegonia in horsetails, (3) small, thin, green,
heart-shaped prothalli with antheridia and archegonia in ferns.

CLUB "MOSSES"

1. Lycopodium (laik o -po' di um) (Gr. lykos, wolf; pous, foot) . — The
club "mosses" belong to the subkingdom Embryo phyta because they pro-
duce multicellular embryos, to the phylum Tracheo phyta because they
possess true vascular tissues, and to the subphylum Lycopsida (laik -op'
si da) (Gr. lykos, wolf; opsis, appearance) .

Plants belonging to the genus Lycopodium (Fig. 47) are small and are
commonly called club "mosses'' because of the mosslike leaves and the
club-shaped cones (strobili) borne on stalks. They are also referred to
as "ground pines" because of their /)ro5/;'<2^^^ creeping habits and their
resemblance to evergreen, miniature pine trees. The main stem (rhi-
zome) is prostrate on the ground and is branched. It possesses roots
and sends up numerous upright stems, usually about eight inches tall.
The upright stems bear small, green leaves, usually spirally arranged.
Lycopodium possesses a simple vascular system consisting of alternate
strands of phloem (sieve tubes and companion cells) and xylem (tra-
cheids). Stomata occur on the leaves and stems for the exchange of
gases.

Sporangia-bearing leaves are known as sporophylls. In some species
the single sporangia are borne on leaves which may be located on any
part of the stem. In other species the sporophylls are concentrated at
the tips of the branches to form conelike strobili. The spores are all

Ferns and Their Allies 193

alike (homosporous) and are wind disseminated. A spore germinates to
form a colorless, rather lumpy prothallus (young gametophyte) which is
usually in the soil. In some cases a small part of the inconspicuous
gametophyte is above the ground and is green.

Male antheridia and female archegonia similar to those of the Bryo-
phytes are embedded on the upper surface of the gametophyte. Rhi-
zoids anchor the gametophyte. The antheridia produce hiflagellated
sperms (like those of true mosses) that swim to the egg which is fer-
tilized to form a zygote.

By cell division the zygote forms two cells, one of which forms a sus-
pensor which pushes the embryo into the food tissues of the gametophyte.
The other cell forms the multicellular embryo which develops into a
young, leafy sporophyte. The latter remains as a temporary parasite
on the gametophyte. The embryo forms a special organ called the foot
which acts as an absorbing organ. A root forms and the gametophyte
tissues eventually decay, thus leaving the herbaceous sporophyte inde-
pendent.

The various species of Lycopodium are common plants of forests and
mountains. They are widely used in the preparation of decorations,
wreaths, and other articles where the evergreen stems can be used.

2. Selaginella (sel i ji -ncF a) (L. selago, shrubby plant). — The deli-
cate, perennial, smaller club "mosses" belong to the genus Selaginella
(Fig. 48) and are widely distributed but are most abundant in the
tropics. One species of Selaginella, known as the "resurrection plant,"
can withstand dry conditions in southwestern United States by rolling up
into a ball. Other specimens are grown as ornamental plants in green-
houses.

Most species of Selaginella are usually creepers, although a few are
erect. The stems are branched, wdth tiny, green, triangular, stomata-
bearing leaves, usually in four rows. Roots anchor the plant and absorb
materials. The vascular system is rather simple and varies with the
species. At the base of each leaf is a membranous ligule (lig' ul) (L.
ligula, little tongue) of unknown function but of value in differentiating
Selaginella from Lycopodium which lacks this structure.

Cones at the tips of the branches are composed of spore-producing
sporophylls. In a cone the upper surface of each microspore phyll has
in its axil (upper angle) a small micros porangium which produces many
small microspores. The larger megasporophylls produce four large mega-
spores in each me gas porangium located in the axil. Frequently, the
microsporophylls are located toward the tip of the cone, while the mega-

194 Plant Biology

sporophylls are located belovv^ but on the same cone. Since Selaginella
produces two kinds of spores (microspores and megaspores), it is hetero-
sporous.

A me gas pore germinates to form a me gagameto phyte (female game-
tophyte) within the megaspore while still in the megasporangium. As
the megagametophyte develops, it forms several female archegonia, rhi-
zoids, stored foods, and chlorophyll.

A microspore develops within the microsporangia to form a small,
parasitic microgameto phyte (male gametophyte) . The latter is sur-
rounded by the microspore wall and consists of one prothalial cell and
one male antheridium. No chlorophyll is formed. The antheridium
produces hiciliated sperms.

When the microsporangial walls rupture, the microspores are carried
to the megasporangia. The sperm swims to the archegonium where the
egg is fertilized to form a zygote. By cell division, the latter forms two
cells, the upper one becoming a suspensor to push the embryo into con-
tact with the stored foods of the megagametophyte. The other cell of
the zygote develops into the embryo. The latter develops a mass of cells
known as the foot by which foods are absorbed from the megagameto-
phyte. Eventually, the embryo produces a stem, root, and two cotyledons
(embryonic "seed" leaves). Later this young sporophyte becomes inde-
pendent by photosynthesizing its own food. The production of a sus-
pensor by the zygote is somewhat similar to a phenomenon in the higher
seed-producing plants.

HORSETAILS (SCOURING RUSHES)

Equisetum (ek wi -se' turn) (Gr. equus, horse; seta, tail). — The horse-
tails belong to the subkingdom Embryo phyta; phylum Tracheophyta;
subphylum Sphenopsida (sf en -op' si da) (Gr. sphen, wedge; opsis, ap-
pearance) because of the wedge-shaped leaves of certain species. All
horsetails belong to the genus Equisetum (Fig. 49) which has the follow-
ing characteristics: hollow, jointed stems, usually ribbed and containing
silica, branches and small leaves (sometimes scalelike) in whorls, and
strobili (cones) composed of whorls of shield-shaped sporangiophores,
each of which bears five to ten sporangia (spore cases) .

The sporophyte of Equisetum consists of a branched horizontal rhi-
zome with nodes. The latter bear whorls of scalelike leaves. In most
species, the rhizomes bear ( 1 ) upright, colorless, unbranched fertile stems
with a strobilus at each tip and (2) upright, green, bushy vegetative
(sterile) stems with many whorled branches at the nodes. Because of

Ferns and Their Allies 195

the rough, silica-bearing stems, they may be used for scouring purposes
and are commonly known as scouring rushes. The vascular system con-
sists of vascular bundles composed of phloem and xylem.

The terminal homosporous strobili (cones) consist of whorls of shield-
shaped (umbrella-like) sporangia phores, each of which bears five to ten
elongated, saclike sporangia (spore cases). The spores possess jour
elators which are ribbon shaped and hygroscopic. The elators respond
to differences in moisture and may assist in spore dispersal (Fig. 49).

Germinating spores form small, green, irregularly lobed, thalloid game-
tophytes. These bear rhizoids and usually both male antheridia and
female archegonia. The antheridium produces coiled, multiflagellated
sperms which swim to the egg in the archegonium where fertilization
produces a zygote. The latter develops into an embryo from which a
new sporophyte with its leaves, stems, and roots is formed. Hence, there
is an alternation of generations (Fig. 49).

FERNS

1. Pteridium (te-rid'ium) (Gr. ptero, wing or feather). — The ferns
belong to the subkingdom Embryophyta; phylum Tracheophyta; sub-
phylum Pteropsida (ter -op' si da) (Gr. pteris, wing, or feather; opsis.,
appearance) because of the winglike or featherlike appearance of certain
species.

The brake ferns (brackens) (bracken, fernj are common species in
temperate regions and many belong to the genus Pteridium (Fig. 50).
The slender, underground stem (rhizome) continues to grow at its an-
terior end, while it dies at the opposite end. It may even separate into
pieces, thus producing independent plants. The underground stem is
quite well developed, consisting of internal parenchyma cells, mechanical
tissues, vascular bundles (with phloem and xylem), and epidermis (Fig.
69). Long, slender roots arise from the underground stem. A young
leaf arises from the stem as a tightly coiled structure which pushes
through the soil. When in the air it uncoils and continues to grow to
form a slender, central petiole and a much-divided blade. The entire
leaf of a fern is referred to as a frond (L. frons, leaf), and the small
leaflets are called pinnae (L. pinnae, feather) (Fig. 68). In general,
the internal structure of the leaf is similar to that of higher plants, being
composed of epidermis, stomata, guard cells with chlorophyll, veins,
spongy tissue, and a palisade layer.

Certain of the green leaves of a bracken bear numerous sporangia
(spore cases) on the edge of the undersurface of each leaflet. Such

196 Plant Biology

spore-producing, green leaves are called sporophylls (Fig. 68). All the
common ferns produce one type of spore and are therefore homosporous.
When sporangia are grouped in clusters, they are known as sori (Gr.
soros, heap). Each sporangium consists of a capsule borne on a stalk.

Fig. 68. — Fruiting fronds of various ferns showing the ways in which spores
are produced. 1, Sensitive fern; 2, cinnamon fern; 3, climbing fern; 4, common
grape fern; 5, common polypody fern (Poly podium) ; 6, bracken fern (Pteridium) ;
7 , maiden hair fern; S, common chain fern; 9, Christmas fern; 10, spinulose shield
fern; //;, common bladder fern; 12, obtuse woodsia fern; 13, boulder fern;
14, walking fern; 15, ebony spleenwort fern. (Copyright by General Biological
Supply House, Inc., Chicago.)

The capsule wall contains a row of special, moisture-sensitive cells known
as the annulus (an' u lus) (L. annulus, ring). The walls of the annulus
cells are thicker on one side and, when affected by moisture, tend to
straighten the annulus, thus throwing the spores from the ruptured
capsule.

Ferns and Their Allies 197

Within the capsule are formed spore mother cells, each of which forms
jour spores, as in the true mosses. At this time the chromosome number
is reduced from 2N to N. When the spores are shed in late summer,
they germinate to form a flat^ green, heart-shaped prothallus (prothal-
lium) with a notch at its anterior end. Rhizoids anchor the prothallus
and absorb water and nutrients. The prothallus matures to form a
gametophyte which may not be over one-fourth inch in diameter. The
same gametophyte may produce male antheridia and female archegonia
on its lower surface.

LATERAL xRIDGE

EPIDERMIS

OUTER SCLERENCHYMA
INNER SCLERENCHYMA

PERICYCLE

PHLOEM

XYLEM

ENDODERMIS

^PARENCHYMA

VASCULAR BUNDLES

Fig. 69. — Rhizone (underground stem) of bracken fern. A, one-half of rhizone
shown in cross section; B, a vascular bundle highly magnified.

The antheridia may form on nearly any part of the undersurface, but
usually they are more numerous on the older, posterior part where the
rhizoids are most abundant. Archegonia are usually limited to the area
just back of the notch. Each antheridium is small and dome shaped.
Internally there are formed numerous, spiral, multifiagellated sperms
(antherozoids) . Each archegonium is small and simpler than it is in
liverworts and true mosses. It consists of an enlarged venter, a neck with
a canal, and an ^crcr within the venter.

During jertilization one sperm unites with the egg to form a zygote
which develops into a parasitic embryo within the venter. The embryo
becomes four lobed and forms the young sporophyte. The lobes develop
into four structures: a temporary joot (absorb food), primary root, stem,

198 Plant Biology

and primary leaf. Although male antheridia and female archegonia are
present on the same gametophyte, most of the antheridia develop and
discharge their sperms before the eggs are mature in the archegonia of
the same plant. Hence, cross-fertilization between different plants
usually occurs. The life cycle of the bracken shows alternation of gen-
erations between the independent sporophyte generation (with 2N
chromosomes) and the independent gametophyte generation (with N
chromosomes). A contrast between ferns and mosses may be observed
below :

SPOROPHYTE

GAMETOPHYTE

Moss

Relatively small
Short lived

Relatively large and

conspicuous
May live for years

Fern

Large and conspicuous
May live for years

Relatively small
Short lived

2. Polypodium (pol i -po' di um) (Gr. polys, many; podion, small
foot).— The common polypody ferns of the genus Polypodium (Figs. 51
and 68) have rather simple but lobed, leaf blades. The thick rhizome
is horizontal and possesses numerous slender, fibrous, adventitious (un-
usual) roots. . Several leaves (fronds) arise from the rhizome. Dotlike
aggregates of sporangia known as sori (Gr. soros, heap) are present on
the undersurface of the leaves. The particular arrangement of the sori
varies with the species. In many ferns each sorus is covered by a pro-
tective, membranous indusium (in-du'zium) (L. induere, to put on).
Each sporangium consists of a thin-walled capsule borne on a stalk. A
hygroscopic annulus is composed of a band of moisture-sensitive cells.
Some of the walls of the annulus cells are thick, while the other walls
are thin. Their response to moisture changes causes the annulus to bend,
thus hurling the spores from the capsule.

QUESTIONS AND TOPICS

1. List the characteristics of (1) the phylum Tracheophyta, (2) subphylum
Pteropsida, and (3) class Filicineae.

2. Learn the pronunciation, derivation, and meaning of each new term used in
this chapter.

3. Discuss the economic importance of ferns, horsetails, and club "mosses."

4. Explain how the sporophytes and gametophytes differ in ferns, horsetails, and
club "mosses."

5. Make a diagram of a typical fern life cycle showing the stages in correct
sequence and the chromosome numbers in the sporophyte and gametophyte
generations.

Ferns and Their Allies 199

6. Why are the leaves of ferns and their alUes considered to be true leaves?

7. Why are ferns and their allies classed as Embryophytes?

8. Why are the ferns and their alhes considered to have true vascular tissues?

9. Contrast the sporophytes and gametophytes of ferns with those of true mosses.

10. In what ways are the gametangia (sex organs) of Tracheophytes similar to
those of the Bryophytes but different from those of the Thallophytes?

11. Describe the structure and function of stomata.

12. Describe the type of young gametophyte formed from a germinating spore
in club "mosses," horsetails, and ferns.

13. Describe how the multicellular sporangia are borne in ferns, horsetails, and
club "mosses."

14. Why is water necessary for fertilization in ferns?

15. Describe the structure and function of the annulus.

16. Compare the alternation of generations in ferns with a similar phenomenon
in horsetails and club "mosses."

17. Describe the structure and function of the suspensor.

18. In what ways do Lyco podium and Selaginella differ?

19. In what ways do Pteridium and Poly podium differ?

20. Why must there be a reduction in the number of chromosomes previous to
fertilization?

21. Describe the structure and function of the "foot."

22. Discuss the functions of spore mother cells.

SELECTED REFERENCES*

Bower: The Ferns (3 vols.), Cambridge University Press.
Durand: Field Book of Common Ferns, G. P. Putnam's Sons.
Small: Ferns of the Southeastern States, Science Press Printing Co.
Smith: Cryptogamic Botany (vol. 2): Bryophytes and Pteridophytes, McGraw-
Hill Book Co., Inc.
Verdoorn: Manual of Pteridology, Chronica Botanica Co.
Wherry: Guide to Eastern Ferns, Science Press Printing Co.

*Also refer to textbooks in list of references on p. 149.

Chapter 13

GYMNOSPERMOUS PLANTS-
CONIFERS AND THEIR ALLIES

Higher Plants With Chlorophyll; With True Leaves, Stems, and
Roots; With Vascular Tissues; With Exposed (Naked) Seeds;
Forming Multicellular Embryos (Subkingdom Embryophyta)

GENERAL CHARACTERISTICS OF GYMNOSPERMS

L The gymnosperms belong to the subkingdom Embryophyta; the
phylum Tracheophyta; subphylum Pteropsida; class Gymnospermae (jini-
no -spur' me) (Gr. gymnos, naked or exposed; sperma, seed) because the
seeds are produced on the exposed (naked) surface of the megasporo-
phylls and are not protected by an ovary w^all, as in angiosperms.

2. Gymnosperms are usually rather large, woody, perennial plants
which are mainly evergreen (retain leaves more than one growing sea-
son) . Certain types may be short and shrubby.

3. Gymnosperms possess true roots, stems, and leaves. In the cone-
bearing evergreens the leaves may be needlelike or scalelike.

4. The sporophyte generation is large, complex, and independent,
while the gametophyte generation is much smaller (microscopic) and
parasitic upon the sporophyte.

5. Cones composed of sporophylls are usually present; in the conifers,
the male and female cones may be present on the same plant {monecious)
or on different plants (diecious) , depending upon the species.

6. Ovules (immature, undeveloped seeds) and true seeds are borne
exposed (naked) on female megasporophylls (a single megaspore is re-
tained within the megasporangium where the female megagametophyte
develops). The sporophylls often form cones.

7. Two kinds of spores are formed (heterosporous) ; namely, micro-
spores, which produce male microgametophytes, and m,e gas pores, which
produce female megagametophytes. (The two spores may be the same
size or the microspores may even be larger than the megaspores, yet they
produce different types of gametophytes.)

200

Gymnospermous Plants — Conifers and Their Allies 201

8. Pollination occurs by wind, the pollen grains landing near, or in,
the micropyle (little opening) of the ovule and forming a pollen tube
leading to the egg.

9. In gymnosperms, single fertilization occurs in which one sperm is
involved in fertilizing the egg, in contrast to double fertilization as it
occurs in the angiosperms (flowering plants).

10. In pine trees, the lapse of time between pollination and subsequent
fertilization (actual union of the sex gametes) is a marked feature. For
example, if pollination occurs in June, fertilization may not ordinarily
occur until July of the next year. This time lapse varies with the species,
locality, etc., but usually a year elapses between pollination and fertiliza-
tion. After fertilization the seed develops rather rapidly, reaching ma-
turity by the end of the year in which fertilization occurs.

11. Gymnosperms are considered to be higher plants than ferns, horse-
tails, and club "mosses" because (1) of the two kinds of cones which
bear, respectively, male microsporophylls and female megasporophylls ;
(2) of a temporary retention of the developing microgametophytes (pol-
len grains) in the microsporangium; (3) of a retention of the megaspore
and the megagametophyte in the megasporangium (nucellus) ; (4) of
the direct parasitism of both male microgametophyte and female mega-
gametophyte upon the large, conspicuous sporophyte; (5) of the develop-
ment of a pollen tube and the establishment of the seed habit.

CONIFERS

Pine Tree [Pinus) (L. pinus, cone bearing) (Figs. 52 and 53).- — The
conifers belong to subphylum Pteropsida, class Gymnospermae (jim no-
spur' me) (Gr. Gymnos, naked; sperma, seed) ; order Coniferales (ko ni-
fer-a'lez) (L. conus, cone; jero, to bear) because most of them bear
cones composed of sporophylls (sporangium-bearing leaves). There are
over 500 species of conifers, including the various species of pine, spruce,
fir, juniper, cedar, hemlock, larch, yew, cypress, redwoods, etc. The
leaves are simple and are either needlelike or scalelike. Conifers are often
referred to as "evergreens" because most of the leaves on many species
remain throughout the year. A few, such as the bald cypress and larch
(tamarack), are deciduous. All are woody and usually are trees, al-
though some are shrubs. Some of the oldest and largest plants are
conifers; for example, the giant sequoia trees of California may be over
30 feet in diameter, 300 feet tall, and 4,000 years old; the redwoods may
be 15 feet in diameter, 300 feet tall, and 1,000 years old.

202 Plant Biology

Pine trees have large, branched stems, and the needlelike leaves are
borne in clusters on short, spurlike branches. The number of leaves per
cluster (2 to 5) and the length of the leaves vary with the species.

In the pines, the male and female cones are borne on the same tree
(monecious) (Fig. 52). In other conifers, the male and female cones
may be borne on separate plants (diecious). The simple, staminate
(male) cones are smaller than the female and are home in a group.
Each male cone is composed of microsporophylls which are spirally
arranged and attached to a central axis. Each microsporophyll bears
two microsporangia on the undersurface, in which are produced numer-
ous microspore mother cells, each of which produces four m,icrospores
(pollen grains). Each pollen grain develops into a microgametophyte
by producing two prothallial cells and an antheridial cell. The latter
divides to form a generative cell and a tube cell. During this process a
pair of ''wings" forms on the four-celled pollen grain to assist in its dis-
semination by the wind, in some cases for hundreds of miles.

The ovulate (female) cones are larger than the male and usually are
borne singly. Each female cone (Fig. 52) is composed of scalelike mega-
sporophylls attached to a central axis. Each megasporophyll bears two
ovules on its upper surface. An ovule consists of (1) an external, pro-
tective integument which has a micropyle (small opening) for the en-
trance of a pollen grain and (2) a central megasporangium. (nucellus).
When young, the megasporangium has one megaspore mother cell which
produces four megaspores, three of which abort. The one megaspore
develops into the female megagametophyte which contains two or three
archegonia. Each archegonium contains an egg within a venter.

During pollination the wind carries the pollen grains (microspores)
to the female cones, where pollen enters through the micropyle and con-
tacts the megasporangium (nucellus) by means of a sticky liquid. The
pollen grains form pollen tubes through the nucellus toward the arche-
gonia. The generative cell and the tube cell pass through the pollen
tube, and the former produces two, nonmotile sperms (m,ale nuclei).

About one year after pollination the fertilization process occurs and
consists of the fusion of one sperm with the ^^cr within the archegonium.
The resulting zygote, by cell division, eventually produces an embryo and
suspensor cells. The latter force the embryo in contact with the food
endosperm (transformed female megagametophyte). Later the embryo
develops an epicotyl (epi-kot'il) (Gr. epi, upon; kotyle, vase or cup)
and a hypocotyl (hi po -kot' il) (Gr. hypo, under), which bears a number
of primary, embryonic seed leaves known as cotyledons (kot i -le' don)

Gymnospermous Plants — Conifers and Their Allies 203

(Gr. kotyle, cup or vase). The embryo is surrounded by the endosperm
(food) which is covered by the seed coat (hardened integument). The
seed thus formed was originally the ovule and contains a wing for wind
dispersal. When a seed germinates, the embryo produces a young seed-
ling which eventually develops into a pine tree (sporophyte generation).
Since gymnosperms produce two different kinds of spores (microspores
and megaspores), they are heterosporous.

Conifers are of great economic value, serving as sources of lumber for
furniture, buildings, boxes, poles, railroad ties, etc., wood pulp for the
manufacture of paper, and numerous other uses. Cedars and their allies
are used in making shingles, pencils, cedar chests, etc. The balsam fir
produces a resin from which Canada balsam is manufactured. The lat-
ter is used to affix coverglasses on slides permanently. Certain types of
pines yield turpentine, rosin, pitch, and similar products.

CYC ADS (SAGO PALMS)

Zamia (za' mi a) (L. zamia, fir cone). — The cycads (sago palms) be-
long to the class Gymnospermae and the order Cycadales (sik a -da' lez)
(Gr. kykas, coco palm). They are palmlike trees or low shrubs with
unbranched stems, terminating in a tuft of thick, pinnate (fernlike)
leaves which are often spiny edged. In Zamia (Fig. 54), which occurs
in Florida, the short, tuberous stem is not over four feet tall and bears
a crown of leathery, pinnate leaves. Sometimes much of the stem is
underground. In general, the cycads are inhabitants of the tropics or
semitropics.

Zamia is diecious since male and female cones are borne on separate
plants. The female carpellate cones are composed of peltate (shield-
shaped) megasporophylls, each of which bears two ovules, with a micro-
pyle (small opening) in the enclosing iyitegument. In the center of the
ovule is the megasporangium (nucellus) . The latter contains one mega-
spore mother cell which produces four megaspores, three of which dis-
integrate. The nucleus of the remaining megaspore divides to form two
nuclei, and further division results in numerous nuclei. Walls separate
the nuclei, so this multicellular tissue becomes the female megagameto-
phyte which produces two to six archegonia. Each archegonium consists
of one large egg and a iieck.

The male staminate cones are smaller than the female and consist of
numerous micros porophylls. Each of the latter bears numerous (thirty
to forty) microsporangia on the lower surface. Each microsporangium

204 Plafit Biology

contains many microspore mother cells which produce many micro-
spores (pollen grains). When still within the microsporangia, the nuclei
of the pollen grains divide to form two, one of which produces a prothal-
lial cell and one of which divides later to form ( 1 ) a generative cell and

(2) a tube cell. These three-celled pollen grains (immature micro-
gametophytes) are carried by the wind to the female cones where, be-
cause of a sticky liquid, they pass through the micropyle of the ovule to
contact the nucellus. The tube cell forms a branched pollen tube through
the nucellus by digesting the latter. The generative cell divides to form
(1) a body cell and (2) a stalk cell. The body cell divides to form two
large multiflagellated (ciliated), m,otile sperms (antherozoids) . This
unique characteristic of wind-pollinated plants is probaby an ancestral
trait no longer needed.

About six months after pollination a sperm fuses (fertilizes) with an
egg in the archegonium, forming a zygote. The latter develops ( 1 ) a
multicellular em.bryo, (2) two cotyledons (primary, embryonic leaves),

(3) hypocotyl, (4) epicotyl, and (5) a long, coiled suspensor to push the
embryo in contact with the endosperm (food) of the megagametophyte.
Thus the original ovule is changed into a seed with its seed coat. Upon
germination the seeds develop either a staminate or a carpellate sporo-
phyte. Certain portions of the stem contain starch and may be used as
food.

QUESTIONS AND TOPICS

1. List the distinguishing characteristics of the subkingdom Embryophyta, the
phylum Tracheophyta, the subphylum Pteropsida, and the class Gymno-
spermae.

2. Learn the meaning, pronunciation, and derivation of each new term used in
this chapter.

3. Discuss the similarities between the conifers and the cycads. Discuss the
ways in which they differ.

4. In what ways are gymnosperms considered to be higher plants than the ferns ?

5. List the ways in which gymnosperms are of economic value.

6. Make a detailed diagram of the life cycle of the pine tree, including the
various stages in correct sequence, with each labeled properly.

7. Do you consider the conifers to be higher or lower plants than the cycads ?
Why?

8. Considering the method of sexual reproduction in Zamia, do the sperm need
to be motile (flagellated) ? What explanation can you give for their motility?

9. In the conifers, the sperm lacks flagella. Of what significance is this?

10. Explain the phenomenon of alternation of generations in gymnosperms.

11. Explain the formation and function of the pollen tube.

Gymnospcrmous Plants — Conifers and Their Allies 205

12. Why would it not be desirable to have the pollen tube preformed rather than
form it just as needed? Explain.

13. What are the chromosome numbers in the sporophyte and the gametophyte?

14. Why must there be a numerical reduction in the number of chromosomes
previous to the union of the sperm and egg?

15. Explain what is meant by "evergreen."

16. Contrast and give an example of monecious and diecious.

17. Contrast between ovules and true seeds.

18. Contrast between pollination and fertilization, giving examples of each.

19. Explain why ovules and true seeds are said to be borne exposed (naked) and
hence are gymnospcrmous.

20. Explain the significance of the phenomenon of heterospory.

21. Describe the structure and function of the micropyle.

SELECTED REFERENCES*

Bowers: Cone-bearing Trees of the Pacific Coast, McGraw-Hill Book Co., Inc.

Chamberlain: The Living Cycads, University of Chicago Press.

Chamberlain: Gymnosperms, Structure and Evolution, University of Chicago

Press.
Eliot: Forest Trees of the Pacific Coast, G. P. Putnam's Sons.
Harlow: Trees of Eastern United States and Canada, McGraw-Hill Book Co.,

Inc.
Harrar and Harrar: Guide to Southern Trees, McGraw-Hill Book Co., Inc.
Jacques: How to Know the Trees, John S. Swift Co., Inc.
Longyear: Trees and Shrubs of the Rocky Mountain Regions, G. P. Putnam's

Sons.
Mathews: American Trees and Shrubs, G. P. Putnam's Sons.

^Also refer to textbooks in list of references on p. 149.

Chapter 14

ANGIOSPERMOUS PLANTS— FLOWERING PLANTS

Higher Plants With Chlorophyll; With True Leaves, Stems, and
Roots; With Vascular Tissues; With Enclosed Seeds; Forming
Multicellular Embryos (Subkingdom Embryophyta)

GENERAL CHARACTERISTICS OF ANGIOSPERMS

L Angiosperms, or flowering plants, belong to the phylum Tracheo-
phyta; subphylum Pteropsida, class Angiospermae (an jio -spur' me)
(Gr. angios, vessel or enclosed; sperma, seed) because the ovules and
seeds are enclosed by megasporophylls (carpels) (Fig. 71). At maturity,
the latter constitute the fruit.

2. Angiosperms constitute the dominant, economically most important,
and the largest class in the plant kingdom, comprising nearly 200,000
species in approximately 10,000 genera.

3. The angiosperms are widely distributed on the earth, where they are
primarily terrestrial, although a few are aquatic (hydrophytes).

4. Angiosperms possess true leaves, stems, and roots.

5. Angiosperm possess flowers and true seeds (Fig. 71) .

6. The angiosperm plant, whether it be corn, bean, sunflower, or a
deciduous tree, is the sporophyte with its roots, stem, leaves, and flowers.
The cells of the sporophyte contain the double number (diploid) of
chromosomes (2N).

7. The sporophyte produces two types of spores (heterospory), al-
though, as in the gymnosperms, the microspores may actually be larger
than the megaspores.

8. The gametophyte generation is represented by the (female) mega-
gametophyte and the (male) microgametophyte. The microgameto-
phyte is represented by the pollen grain and the pollen tube with its
three cells (two sperms and one tube nucleus). The megagametophyte
is the embryo sac consisting of seven cells (one e^g, two nonfunctional
synergid cells, three nonfunctional antipodal cells, and two polar nuclei).
The two polar nuclei fuse with one sperm nucleus to form the endosperm
(food) whose cells contain the unique, triple number of chromosomes
(3N). The two synergid cells are thought to be remnants of the arche-

206

Angiospermous Plants — Flowering Plants 207

gonium. The three antipodal cells are regarded as remnants of the
prothallus tissue. A sex cell contains the N number of chromosomes.

9. The adult sporophyte is large and independent, while the gameto-
phyte is very small and dependent (without chlorophyll) .

10. Pollination occurs by pollen landing on the stigma and a pollen
tube being formed through the stigma, style, and part of the ovary.

11. Water is not required for the fertilization of the ^g^ by the sperm.

12. Pollination may be by wind, insects, birds (rarely by water), de-
pending upon the species.

13. A so-called double fertilization occurs, in which one sperm (IN)
fuses with the egg (IN) (true fertilization) to form a zygote, with its
diploid (2N) number of chromosomes, which will develop into the
embryo. The other sperm (male gamete) fuses with the two polar nu-
clei in the center of the female gametophyte (megagametophyte), thus
forming a nucleus with the unique, triploid (3N) number of chromo-
somes. This triploid nucleus is called the primary endosperm nucleus
because its gives rise to the nutritive, endosperm tissue. The tube nu-
cleus usually disintegrates.

14. The vascular (conducting) system of angiosperms typically con-
sists of long, tubular vessels composed of segments derived originally
from single cells which have been fused at maturity into long, continu-
ous tubes. In contrast, the conducting tissues of the xylem of gymno-
sperms are composed of single-celled tracheids.

15. In the evolution of plants, from the simplest algae to the angio-
sperms, there has been an increase in the size and independence of the
sporophyte, while there has been a reduction in size and independence in
the gametophyte.

16. The Angiospermae are divided into the subclasses (1) Dicotyledo-
neae (di kot i le -do' ne e) (Gr. di, two; kotyledon, embryonic seed leaf)
and (2) Monocotyledoneae (mon o kot i le -do' ne e) (Gr. mono, one;
kotyledon, embryonic seed leaf), which may be differentiated as follows:

DICOTYLEDONEAE

MONOCOTYLEDONEAE

2 cotyledons (embryonic seed leaves)

Net-veined leaves

Vascular bundles of the stems usually arranged in

a circle (cylinder)
Cambium (meristematic tissue) between the

phloem and xylem of the vascular bundle
Some have woody stems; others have herbaceous

stems
Flower parts usually in fours or fives, or multiples

of these

1 cotyledon
Parallel-veined leaves
Vascular bundles scattered

throughout the stem
Usually no cambium
Mostly herbaceous stems

(few exceptions)
Flower parts typically in

three's or multiples of

three.

208 Plant Biology

17. The flowers, which are distinguishing characters of the entire group
of angiosperms, show great diversity of structure. Flowers are concerned
with the sexual reproductive process and lead to the formation of fruits
(matured ovary) and seeds (embryo, food endosperm, and seed coat).
Flowers may be composed of four sets of parts attached to the apex of the
stem and known as the receptacle (Fig. 71). Going from the outside
of the flower toward the center, the four parts are (1) sepals, (2) petals,
(3) stamens for the production of pollen, and (4) pistils for the recep-
tion of pollen and the production of ovules, the latter forming the mature
seeds. The sepals collectively constitute the calyx (Gr. kalyx, cup), while
the petals collectively constitute the corolla (L. corolla, crown). A com-
plete flower has all four sets of parts, while an incomplete flower has any
one of the four sets of parts lacking. Sepals and petals together con-
stitute the perianth (Gr. peri, around; anthos, flower).

The odors of flowers are produced by the formation of chemical sub-
stances in special secreting cells, usually on the petals. The petals of
certain flowers have glands known as nectaries for the secretion of the
sweetish nectar, collected by insects. Flower colors usually result from
the presence of pigments known as anthocyanins (an tho -si' an in) (Gr.
anthos, flower; kyanos, dark blue) or carotenoids (kar' o ten oidz) (L.
car Ota, carrot or yellowish; Gr. eidos, form). The anthocyanins are
blue, red, and purple water-soluble pigments, while the carotenoids are
yellow, orange, and sometimes reddish pigments,

A stamen consists usually of a stalklike filament and an enlarged
anther for the production of pollen. A pistil consists usually of an en-
larged, basal ovary within which seeds are formed, a slender style arising
from the ovary, and an enlarged, pollen-receiving stigma at the tip of the
style. The enlarged, ovary portion of the pistil is composed of one or
more carpels (Gr. karpos, fruit) within which are ovules from which seeds
are formed by fertilization.

The angiosperms are widely distributed and numerous (approximately
200,000 species), so that it is impossible to study all of the many groups.
However, a detailed study of a few, well-selected representatives may
suffice for an orientation in the class as a whole. Consequently, Indian
corn [Zea mays) is selected because it is a large, common monocotyle-
donous type, the garden bean [Phaseolus) is chosen because it is a com-
mon dicotyledonous form, and the sunflower [H elianthus) because it is a
typical dicotyledonous type w ith a composite flower.

Angiospermous Plants — Flowering Plants 209

INDIAN CORN

Zea mays (ze' a) (Gr. zea, corn). — Indian corn has an erect stem
from which adventitious roots are formed at the nodes (L. nodus, knob
or joint) to assist the true roots in the absorption of water and dissolved
materials from the soil as well as to assist in anchoring the plant (Figs.
58 to 60). Consequently, such unusual adventitious roots are called
"brace roots" or "prop roots." Roots which develop directly from stems
or leaves are called adventitious.

Corn has a typical monocotyledonous stem with numerous vascular
bundles (Fig. 60) scattered throughout the stem which is composed of
parenchyma cells (par -eng' kima) (Gr. para, beside; engchyma, infu-
sion) of various sizes and shapes. These can be observed in a cross sec-
tion. The external cover of the stem consists of a layer of epidermis
whose cells are relatively small and thick walled. Beneath the epidermis
is a narrow layer of (mechanical) sclerenchyma tissue (skier -eng' kima)
(Gr. skier OS, hard; engchyma, infusion) whose cells are small and thick
walled with lignin (lig' nin) (L. lignum, wood). Each vascular bundle
is surrounded by a sheath or layer of thick-walled (mechanical) scler-
enchyma tissues. Internally, each bundle consists of (1) phloem (toward
the periphery of the stem) and (2) xylem (toward the center of the
stem). There is no meristematic cambium separating the phloem and
xylem, as in dicotyledonous stems, so there can be no indefinite increase
in size after the primary tissues are mature. Bundles lacking cambium
are called "closed" bundles because of their inability to grow indefinitely
(Fig. 60).

The phloem of a mature bundle conducts liquids downward and con-
sists of regularly arranged, nonnucleated, sieve tubes and companion
cells (Fig. 18). The sieve tubes have their adjacent end walls supplied
with a perforated sieve plate. Often a^ narrow, thin-walled, elongated,
nucleated, companioin cell lies parallel to the sieve tube.

The xylem conducts liquids upward and consists of two large vessels,
with pitted walls, located next to the phloem. Between these two vessels
are a few, hollow, one-celled tracheids (Fig. 18). The innermost part
of the xylem contains one or two vessels whose walls have ring-shaped
or spiral thickenings. Between the latter vessels and the sheath of me-
chanical tissue is a large, hollow intercellular space.

The leaves of corn are characterized by numerous, main veins running
parallel to the long axis, and all connected by a network of fine, incon-
spicuous, branches (Fig. 60). The veins are actually vascular bundles

210 Plant Biology

which are connected with the vascular bundles of the stem. The broad
portion of a leaf is called the blade. The tissues of the corn leaf are as
follows: (1) An epidermis on the upper and lower surfaces composed
of one layer of cells. Openings on the surfaces are known as stomata
(stom'ata) (Gr. stoma, opening) and are for the exchange of gases.
Each stoma is bordered by guard cells to regulate the size of the open-
ing. Just beneath each stoma is an irregularly shaped, intercellular (suh-
stomal) space for the storage of gases. (2) A mass of compactly arranged
cells which contain chloroplasts for photosynthesis. (3) Veins which are
vascular bundles composed of phloem and xylem. The true root system
of corn is fibrous and quite extensive in order to anchor the plant and
to absorb water and nutrients from the soil. Small root hairs are exten-
sions of the epidermal cells of certain regions of the roots and serve to
increase the absorption area of the root system. A nucleus is usually
present near the tip of the hair, and there is a large vacuole.

The flowers of the corn plant are incomplete and on different parts
of the same plant. The tassel at the tip of the stem consists of pollen-
bearing stamens (male flowers). Each stamen consists of a stalklike
filament at the tip of which is the enlarged, pollen-producing anther
(Fig. 58).

The female flowers (pistils) consist of a series of enlarged ovaries
(''kernels") arranged on the corn cob to form the corn "ear." A long
style (the "silk" of corn) is attached to each ovary, and the tip of the
style, called the stigma, is sticky to receive the wind-desseminated pollen.
A pollen tube, for the conduction of pollen, grows through the style to
the ovary. Fertilization takes place within the ovary (Fig. 58).

A grain of corn is really a fruit because it consists of a ripened ovary
(Fig. 59). A mature grain of corn consists of an outer pericarp (per" i-
karp) (Gr. peri, around; karpos, fruit) firmly fused to the seed coat be-
neath. On the concave side of the grain, beneath the pericarp, is the
embryo embedded in the extensive endosperm (food). The endosperm
is composed of three parts : ( 1 ) a single layer of cells next to the nucel-
lus is called the aleurone layer; these cells are filled with grains of pro-
tein known as aleurone (alu' ron) (Gr. aleuron, flour); (2) an inner,
starchy endosperm; (3) an outer, horny endosperm containing proteins.

The embryo (Fig. 59) consists of (1) one broad cotyledon for absorp-
tion of food from the endosperm, (2) a well-developed plumule consist-
ing of a stem and one or more foliage leaves, (3) a very short hypocotyl
(hi po -kot' il) {Gr. hypo, under or below; kotyle, cup), (4) a radicle
(rad' i kel) (L. radix, root) which is the lower part of the hypocotyl and

Angiospermous Plants — Flowering Plants 211

forms the primary root of the seedling, (5) a sheathlike coleoptile (kol' e-
op til) (Gr. koleos, sheath; ptilon, feather) which completely encloses the
plumule, (6) a sheathlike fo/^or/izza (kol e o -ri' za) (Gr. A;o/^oi^, sheath;
rhiza, root) which encloses the radicle.

Upon germination the radicle breaks through the coleorhiza and forms
a temporary primary root. Adventitious, fibrous roots are soon formed.
The plumule breaks through the protective coleoptile to form true leaves
which develop chlorophyll for photosynthesis.

GARDEN BEAN

Phaseolus (fa -se' o lus) (L. fabaceous, bean) (Figs. 55 and 56) . — The
common garden bean belongs to the phylum Tracheophyta; subphylum
Pteropsida, class Angiospermae, the subclass Dicotyledoneae; family
Leguminosae (le gum i -no' se) (L. legumen, to gather) because the
legumes (fruits) are frequently gathered for various purposes. The
family is commonly called the pea or pulse family (L. puis, pottage or
porridge) and includes such foods as peas, beans, peanuts, lentils, etc.,
such forage crops as clovers, alfalfa, vetches, etc., and such ornamental
plants as sweet peas, lupine, lotus, wistaria, Judas tree, etc. Locust trees
are used as timber. The family includes such drug plants as senna, lico-
rice, etc. Leguminous plants add nitrogenous materials to the soils
through the fixation of free nitrogen by the actions of special types of
bacteria which inhabit the enlarged nodules on the roots.

The bean plant may be short, bushlike, or a vinelike annual, depend-
ing upon the variety. The stalks (stems) may be long and slender and,
due to unequal rates of growth on opposite sides, have a tendency to
twine spirally around objects with which they come in contact. The
external epidermis is rather thin and affords limited protection. In cer-
tain parts of the stems and leaves there niay be hairs (outgrowths of epi-
dermal cells) .

The leaves of the bean plant are usually trifoliate (three leaves arising
from one point) and net veined (frequently branched). The thin epi-
dermal layer contains stomata for the exchange of gases. Guard cells
control the size of the opening of the stoma. Below the stomata are air
spaces surrounded by cells which contain chlorophyll in green chloro-
plasts. The chlorophyll, through energy supplied by light, combines the
carbon dioxide and water to form carbohydrates by the process of photo-
synthesis. Part of the manufactured foods may be used by the plant
and the remainder stored, particularly in the developing seeds. The

212 Plant Biology

Siy

stored carbohydrates and proteins in bean seeds make them valuable as
foods. The veins (vascular bundles) of leaves conduct materials through-
out the leaf and are continuations of the vascular bundles of the leaf
petiole, stem, etc.

The rather conspicuous flowers (Fig. 55) of the common bean are
irregular (bilaterally symmetrical, with petals of various sizes and un-
equally spaced), perfect (both stamens and pistils), and complete (all
four sets of flower parts). They are usually small, whitish-purple, and
racemose (flowers along an elongated axis). The calyx is composed of
four to five green sepals, more or less united. The corolla is papilio-
naceous (butterfly-like) and consists of four to five petals, some of which
may be coalesced. In those species with definitely irregular flowers, the
large, recurved, somewhat contorted, upper petal is called the standard,
the two lateral petals are called wings, and the two lower (anterior)
petals are fused to form the keel which may be spirally coiled. There are
usually ten stamens (nine of which may be united into a thin sheath
around the pistil while one is free) . Each stamen bears a pollen-produc-
ing anther at its tip.

The female pistil is composed of a single, elongated ovary (one carpel)
which contains several ovules, a filamentous style, and a pollen-receiving
stigma. When the ovary matures, it becomes a bivalved, multiseeded
pod (legume). Pollen tubes are formed through the style and extend
from the stigma to the ovary. Fertilization occurs in the ovary, and the
fertilized ovules develop into the true seeds (Fig. 56) .

The pod (legume) is linear, usually slightly curved, with two halves
(valves), several internal seeds, and usually with remains of the style.
The seeds (Fig. 56) are composed of two similar halves known as cotyle-
dons in which foods have been stored for use in germination of the seed.
There is ?io endosperm (food), as in the case of corn, but its place is
taken by the two cotyledons. Each seed is attached to the pod by a stalk-
like funiculus (fu -nik' u lus) (L. funiculus, small cord) .

The bean seed is a dicotyledon which lacks endosperm. The seeds, _
like those of other legumes (leg' um) (L. legumen, pulse or "pod"), ^

are developed in a legume (pod), which is the mature, ripened ovary
(Fig. 56). Since a ripened ovary is known as a fruit, the legume (pod)
is a rather special type of fruit.

Each individual seed consists of ( 1 ) a small, prominent scar, the hilum
(hi' lum) (L. hilum, small), where it was attached to the pod; (2) a

Angiospermous Plants — Flowering Plants 213

prominent ridge above the hilum, the raphe (ra'fe) (Gr. raphe, seam),
which is formed by the ovule beneath; (3) the micro pyle below the hilum
(mi'kropile) (Gr. mikros, small; pyle, gate) which is a small opening
in the seed coat for the entrance of pollen; (4) seed coats which form
the protective covering; (5) two cotyledons (kot i -le' don) (Gr. kotyle,
cup) which are the two fleshy halves of the bean for the storage of food;
(6) the plumule (or epicotyl) with its true leaves folded over the grow-
ing tip; (7) the hypocotyl; and (8) the radicle (rad'ikel) (L. radix,
root) which is continuous with the hypocotyl and forms the embryonic
root. The tip of the radicle points toward the micropyle. All of these
structures may best be seen in seeds which have been soaked to initiate
germination.

During germination^ the food of the cotyledons is digested and trans-
ferred to the plumule, hypocotyl, and radicle. The embryonic, primary
root is formed from the radicle which bends downward under the influ-
ence of gravity. The hypocotyl elongates and carries with it the plumule
and the two cotyledons out of the soil. The two cotyledons spread to
allow the developing foliage leaves of the plumule to develop. The
cotyledons may develop chlorophyll for carrying on photosynthesis for
a time, but eventually they shrivel. The roots absorb water and nutrients
from the soil and conduct them to the stalk (stem) .

SUNFLOWER

Helianthus (he li -an' thus) (Gr. helios, sun; anthos, flower). — The
sunflower belongs to the phylum Tracheophyta; subphylum Pteropsida;
class Angiospermae; subclass Dicotyledoneae; family Compositae (kom-
poz'ite) (L. cum, together; ponere, to place) because of the many
closely compacted individual flowers (florets) which form a head, com-
monly mistaken for the flower (Fig. 57-). Common plants with com-
posite flowers include sunflowers, dandelions, ragweeds, cockleburs, gold-
enrods, daisies, asters, zinnias, dahlias, marigolds, lettuce, artichoke, etc.
The enormous production of seeds and the efficient devices for their
dispersal have distributed them widely. The pollen of many of them,
including goldenrods, ragweeds, etc., are causes of pollen (hay) fever.

A sunflower plant consists of a stem with nodes (joints), at which
leaves are borne, and inter nodes, between successive nodes, by which
growth occurs by an elongation process.

Internally, a mature stem of a dicotyledonous plant such as a sun-
flower (Fig. 57) consists of (1) a central, pith region composed of thin-

214 Pla?it Biology

walled parejichyma cells; (2) vascular bundles which are arranged in
a circle toward the periphery of the stem and composed of (a) xylem (to-
ward the pith), composed of thick-walled cells (single-celled tracheids
and vessels), (b) phloem (toward the periphery of the stem), composed
of nonnucleated, sieve tubes (with perforated sieve-plates) and elongated,
nucleated companion cells, and (c) a thin layer of meristematic tissue
called cambium which separates the xylem and phloem; (3) the pericycle
which is a cylinder of mechanical tissue, external to the vascular bundles,
composed of thick-walled cells, with some thin-walled cells; individual
bundles are separated by radial strands or rays, composed of parenchyma
cells to conduct materials across the stem; the entire central core of the
stem described so far constitutes what is called the stele; (4) a layer
of cortex just external to the stele composed of large, thin-w^alled cells;
(5) a layer of mechanical tissue beyond the cortex composed of thick-
walled cells; (6) the epidermis external to the mechanical tissue com-
posed of elongated, flat cells whose outer walls are impregnated with a
waxy cutin to make them impermeable to water. Certain epidermal cells
may produce extensions known as hairs. A connection between a vascu-
lar bundle and a leaf is called a leaf trace.

Dicotyledonous stems (as well as gymnospermous stems) usually pro-
duce so-called secondary tissues in contrast to the monocotyledons which
do not produce secondary tissues. The secondary tissues arise from the
cambium and consist of secondary xylem and secondary phloem. In the
stems of annual plants the secondary xylem and secondary phloem are
formed for only one season, but in perennial plants (especially shrubs
and trees) the cambium forms secondary xylem and phloem year after
year. In stems of woody trees and shrubs, where secondary xylem and
phloem are formed year after year, the xylem formed in the spring is
composed of large, relatively thin-walled elements (spring wood), while
the xylem formed during the summer is composed of small, thick-walled
elements (summer wood). The annual rings are concentric lines of
demarcation between the large-celled, thin-walled spring wood of the
current year and the small-celled, thick-walled summer wood of the pre-
vious year. The number of rings is not always an accurate criterion ofl
age, because under unusual conditions two rings may be formed in onei
year. The thickness of an annual ring is often greatly influenced by
environmental conditions, such as water supply, weather conditions, etc.
The secondary phloem of most woody dicotyledons may contain thick-
walled, elongated cells with pointed ends and are called bast fibers. The

Angiospermous Plants — Flowering Plants 215

secondary xylem may contain rigid, thick-walled, elongated cells with
pointed ends and are called wood fibers.

A mature sunflower leaf (Fig. 57) consists of a broad blade attached
to the stem by a slender petiole. Net veins conduct materials through-
out the leaf. Photosynthesis is carried on by the chlorophyll which ab-
sorbs light energy and combines carbon dioxide and water to manufac-
ture organic compounds, with oxygen as a by-product. Some of the
stored energy is used by the plant for its various metabolic activities, while
some of the energy absorbed is used in the manufacture of the organic
foods. Capture and storage of light energy by chlorophyll-bearing plants
is a unique phenomenon. The leaf blade (Fig. 57) includes (1) an
external epidermis w^hose cells are often irregular when viewed from the
surface but rectangular in cross section; the outer walls of the epidermal
cells contain a waxy cutin; (2) a region of column-shaped palisade cells
beneath the upper epidermis which are compactly arranged and contain
many chloroplasts; (3) a layer of spongy tissue beneath the palisade layer
composed of irregularly shaped, loosely packed cells with numerous in-
tercellular spaces between them {chloroplasts are also present in the cells
of the spongy tissue) ; (4) a lower epidermis similar to the upper epi-
dermis except that it contains openings known as stomata for the ex-,
change of gases. Each stoma is bordered by two bean-shaped guard
cells which contain chloroplasts and regulate the size of the stoma. The
stomata open into intercellular cavities (substomal cavities) in which
gases may be exchanged with the leaf cells. Both epidermal tissues may
bear hairs; (5) veins which are vascular bundles composed of xylem and
phloem as in the petiole and stem; a sheath of variable thickness sur-
rounds the vein.

An older sunflower plant has a primary root with lateral branch roots
which may have an extensive branching root system for anchorage and
absorption.

The regions of a mature root, beginning at the tip, include ( 1 ) the
cup-shaped root cap which protects the root as it is pushed through the
soil; (2) the meristematic region (growing region) which is covered by
the root cap and is composed of small, similar, closely packed, rapidly
dividing cells; (3) the elongation region, just back of the growing region,
which is composed of cells which are increasing in length; (4) next the
maturation region in which the cells are diff"erentiated and are taking on
mature characteristics; and (5) following this the mature region in which
most cells have completed their development. All these regions can be
observed in a longitudinal section.

216 Plant Biology

Internally the mature region of a root (Fig. 57) consists of (1) a cen-
tral stele (Gr. stele, pillar), (2) a surrounding cylinder of tissues called
the cortex, and (3) the external epidermis. These can be observed in a
cross section.

The stele in the center is composed of (1) xylem, (2) phloem., (3)
parenchyma, and (4) pericycle. The xylem is in the form of a + and is
composed of thick-walled cells (tracheids and vessels) of various sizes;
the phloem is located in the angles between the strands of xylem and
consists of sieve tubes with their companion cells; the parenchyma tissues
lie between the xylem and phloem and are composed of rather large,
thin-walled cells; the pericycle (Gr. peri, round; kyklos, circle) sur-
rounds all of the above tissues and is in the form of a cylindrical sheath
(ringlike in cross section), being composed of one or several layers of
thin-walled cells.

The cortex is composed of endodermis and parenchyma tissues. The
endodermis (en do -der' mis) (Gr. endo, within; derma, "skin") is the
innermost, single layer of cortex cells. The parenchyma tissues are just
external to the endodermis and are composed of rounded cells of various
sizes.

The epidermis (ep i -der' mis) (Gr. epi, upon; derma, "skin") covers
the root and is one cell thick. Certain epidermal cells may possess pro-
jections known as root hairs to increase the absorption of the root.
Growth of the root occurs toward the tip rather than in the region with
root hairs, so that the latter are not injured as the root is pushed through
the soil.

The composite flower of the sunflower (Fig. 57) is composed of nu-
merous individual flowers grouped together so as to form a head which
resembles a single flower in a general way. The small flowers are borne
on a disklike peduncle (pe -dung' el) (L. pedunculus, small foot) .

At the edge of the flower-bearing disk are two or more spirals of o\er-
lapping, flat, green bracts (L. bractea, thin plate). On the face of the
disk is an outer circle of closely packed flowers, each in the axil of a
small bract (modified leaf). The two types of flowers on the head are
(1) ray flowers, forming one or two rows at the edge, and (2) disk
flowers, forming the remainder of the head. The marginal, ray flower
consists of a strap-shaped corolla, one side of which is modified into a
broad, flat structure. The stamens and style of the ray flower may be
abortive. These marginal ray flowers may be sterile or they may contain
only pistils. Each inner, disk flower consists of a wedge-shaped, hollow
receptacle partly enclosing the ovary which contains one functional ovule.

Angiospcrmous Plants — Flowering Plants 217

Fused petals {corolla) surround the style, and their tips are recognizable
as five blunt teeth. The pollen-producing anthers are united at their
edges to form an anther tube around the style. The style extends beyond
the corolla tube and the surrounding anther tube and terminates in two
protruding stigmas (Gr. stigma, mark). The calyx is represented by
two scales (pappus) at the top of the ovary.

After fertilization (union of male and female gametes) the ovary
enlarges and contains one seed.

QUESTIONS AND TOPICS

1. List the distinguishing characteristics of the class Angiospermae, subclass
Dicotyledoneae, subclass Monocotyledoneae, and the family Compositae.

2. Learn the meaning, pronunciation, and derivation of each new term used in
this chapter.

3. Discuss the economic importance of angiosperms.

4. Discuss the distribution and habitats of angiosperms.

5,. Make a detailed diagram of a typical angiospcrmous plant life cycle, including
the various stages in correct sequence, with each labeled correctly.

6. Describe the sporophyte generation and the gametophyte generation in angio-
sperms, including their relative sizes and independence.

7. Compare the pollination process in angiosperms with the polhnation as it
occurs in a gymnosperm such as a pine tree.

8. Describe the structures and functions of the v^arious parts of a complete flower.

9. Describe the seed production process of angiosperms.

10. List the chromosome number in the gametes, sporophyte, and endosperm.

11. Contrast monocotyledonous angiosperms with dicotyledonous angiosperms in
as many ways as possible.

12. Describe the formation of the pollen tube and its function.

13. Review all of the plant tissues described in this chapter, including their dis-
tinguishing structural characteristics and functions.

14. Describe the structure and functions of the ovary. Why are angiosperms said
to form enclosed seeds?

15. Contrast what is meant by pollination and fertilization.

16. Discuss the so-called double fertilization process and its significance.

17. Define heterospory and give examples from the angiospcrmous plants.

18. In the botanical sense, contrast a fruit and seed, giving examples of each.

19. Describe the structure and functions of cambium.

20. Describe the construction and functions of cotyledons.

SELECTED REFERENCES

Bailey and Bailey: Hortus, The Macmillan Co.

Britton and Brown: An Illustrated Flora of Northern United States, Canada, and

British Possessions, New York Botanical Gardens.
Clements and Clements: Flower Families and Their Ancestors, The H. W. Wilson

Co.
Coulter and Chamberlain: Morphology of Angiosperms, D. Appleton & Co.

218 Plant Biology

Cuthbert: How to Know the Spring Flowers, H. E. Jacques, Mt. Pleasant, Iowa.
Douglass: Climatic Cycles and Tree Growth, Carnegie Institution of Washington.
Hausman: Beginner's Guide to Wild Flowers, G. P. Putnam's Sons.
Hausman: Illustrated Encyclopedia of American Wild Flowers, Garden City

Publishing Co., Inc.
Hutchinson: Families of Flowering Plants, The Macmillan Co.
Hylander: The World of Plant Life, The Macmillan Co.
Johnson: Taxonomy of Flowering Plants, Century Co.
Mathews: American Wild Flowers, G. P. Putnam's Sons.
Mathews: American Trees and Shrubs, G. P. Putnam's Sons.
Moldenke: American Wild Flowers (illustrated), D. Van Nostrand Co., Inc.
Pool: Flowers and Flowering Plants, McGraw-Hill Book Co., Inc.
Seymour et al. : Favorite Flowers in Color (illustrated), Wm. H. Wise & Co., Inc.
Small: Manual of Southeastern Flora, Science Press Printing Co.
Skene: The Biology of Flowering Plants, The Macmillan Co.
Wherry: Wild Flower Guide, Doubleday & Co., Inc.

Chapter 15

BIOLOGY OF HIGHER PLANTS-
ANATOMY AND PHYSIOLOGY

I. THE ROOT

General Regions. — Very important parts of the roots are the tips of
the finest branches. The surface of these branches is covered for a
considerable distance, from a point slightly behind the tip, with fine,
transparent, hairlike root hairs. Each root hair is really a continuous
extension from one of the outer flattened, epidermal cells of the root.
Each root hair contains a nucleus and a vacuole within the cytoplasm.
The extreme tip of the root is protected by a root cap, the outer cells
of which are constantly destroyed as the root is pushed through the soil.
Some of the growth of the root occurs in the formative region just above
the root cap and is known as the embryonic region. The cells of this
region are small, closely packed, angular, filled with protoplasm, and fre-
quently dividing by mitosis. Just above this region is the elongation
region in which the cells grow in length by taking water into the vacuoles
distributed in their cytoplasm. The next region is the maturation region
(cell differentiation region) in which different cells begin to undergo
specialization and differentiation. In this region the cells of the epi-
dermis form root hairs, and the cells of the central axial part of the root
form conduction tissues for the transportation of plant materials. The
fourth region includes the remainder of the root and is known as the
mature region. The cells here are differentiated into various tissues of
the mature root (Figs. 57 and 70).

The mature root consists of primary and secondary tissues. The
former develop from differentiated cells which arise directly by cell
division from the embryonic region of the root tip. The secondary tis-
sues are produced from the cambium, which develops from undiffer-
entiated cells that retain their embryonic character.

219

220 Pla?it Biology

The mature region of a root consists of the following primary tissues:

(1) epidermis, (2) cortex, (3) stele. The epidermis is an outer pro-
tective layer of one cell thickness. Just beneath the epidermis is the
cortex or differentiated region which surrounds the central stele. The
cortex consists of (1) parenchyma (Fig. 18), composed of thin-walled
cells which usually measure about the same in each direction and which
possess stored food and water in the large vacuoles of their cytoplasm;

(2) endodermis, or the inner boundary of the cortex, formed by a layer
of cells resembling those of the epidermis; (3) mechanical tissues which
are present in certain plant roots and absent in others. The stele, or
solid, central cylindrical portion of the root, consists of (1) pericycle,
(2) primary xylem (woody tissue), (3) primary phloem, and (4) pa-
renchyma. The pericycle surrounds the stele and consists of one or more
layers of cubical cells just inside the endodermis. The primary xylem
extends lengthwise of the stele. The first cells to be differentiated in the
primary xylem are the tracheids (Fig. 18) which are elongated cells
with pointed ends and walls thickened in certain places. The three
most common types of tracheids are the spiral tracheids, in which the
cell wall is thickened along a spiral, the remainder of the wall being thin;
the annular tracheids, in which the cell wall has a series of thickened
rings; pitted tracheids, in which the cell wall is generally thickened with
only pits of thin walls. The protoplasm of the tracheids dies and leaves
them hollow in order to transport water through the root. As the root
develops, the primary xylem also develops spiral vessels, annular vessels,
and pitted vessels. These vessels are formed by joining a number of
elongated cells end to end. The end walls where the cells join are dis-
solved, thus forming a long tubular structure. The side walls of the ves-
sels have thickenings similar to the tracheids. The protoplasm of the
vessels dies and thus a long hollow tube is formed for conducting plant
liquids (Fig. 18). The primary phloem of the mature root is composed
of numerous strands of cells located between the numerous primary xylem
strands and alternating with them. The primary phloem consists of ( 1 )
sieve tubes (Fig. 18) and (2) companion cells. A sieve tube is formed
by uniting a number of elongated cells end to end in a way similar to
that in which a xylem vessel is formed, except that the side walls are not
especially thickened and the end walls are not dissolved. These end
walls develop sievelike pores through which the cytoplasm of adjacent
cells is continuous. Closely associated with the sieve tubes of most plants
are companion cells (Fig. 18), the length of which is equal to or shorter

Biology of Higher Plants — Anatomy and Physiology 221

than the portion of the sieve tube which arises from one cell. The cyto-
plasm and nucleus are present in companion cells, while the nuclei of
cells which form sieve tubes disappear. The tracheids and vessels of the
primary xylem conduct water and other materials from the roots to the
leaves. The sieve tubes and companion cells of the primary phloem con-
duct to the roots organic materials which they have received from the
stems and leaves. The parenchyma of the root is composed of numerous
thin-walled cells which lie between the primary xylem and primary
phloem.

All the tissues just described are primary tissues and arise directly by
cell division from the embryonic region. In the mature region of roots
of dicotyledonous plants (seeds having two cotyledons or seed leaves),
certain cells remain undifferentiated, retain their embryonic character,
and form cambium. The cambium is bounded by the phloem on the
outside and xylem on the inside. Somewhat back of the mature region,
the cambium forms a continuous cylinder between the xylem and phloem.
The cambium consists of small cubical cells which divide rapidly by
mitosis during the growing season. Growth of the cambium causes the
root to increase in diameter. Tissues formed by the cambium are known
as secondary tissues, which include ( 1 ) secondary xylem, ( 2 ) secondary
phloem, (3) medullary rays, and (4) annual rings. The secondary
xylem is formed on the inner side of the cambium, while the secondary
phloem is formed on the outer side. As the root becomes older, the sec-
ondary xylem and phloem occupy most of the stele and form two con-
centric regions separated by cambium. In certain places the cambium
produces parenchymatous strands which extend radially between the
xylem cells toward the center and between the phloem cells toward the
periphery of the stele. These radially arranged strands are the medullary
rays. The secondary xylem produced by a single year's growth is rep-
resented by a so-called annular ring. In the roots of plants which live
several years, the formation of new secondary xylem and phloem con-
tinues year after year, forming concentrically arranged annular rings.
The xylem vessels produced during the early spring are generally large
and thin walled, while the xylem vessels formed near the end of the
growing season are smaller and thick walled. Hence, each annular ring
is composed of two types of xylem vessels described above.

The functions of roots ordinarily include anchorage of the plant, sup-
port of the stem, absorption of water and dissolved materials, and storage
of manufactured foods. In some instances special types of roots per-
form other more specialized functions.

222 Pla?it Biology

II. THE STEM

The development and differentiation of the tissues of a stem occur
in the buds at the ends of the stem and its branches. The growing end
of a stem does not have a root cap as does a root, but it does have an
embryonic region, an elongation region, a maturation region, and a
mature region. The many similar cells of the embryonic region of the
bud divide rapidly by mitosis. Growth and cell differentiation occur in
the bud so that the youngest part of the stem or branch is nearest the
bud. The elongation region develops after the bud opens. The differ-
entiation of the cells of the stem to form xylem, phloem, parenchyma,
etc., is generally similar to the corresponding cells of the root.

Study of a Stem of a Dicotyledonous Plant. — If a thin section of
such a plant as the sunflower is studied, the following structures are
visible (Fig. 57): (1) epidermis, (2) cortex, and (3) stele. The epi-
dermis is composed of a single layer of flattened cells for protection. The
walls are infiltrated with a waxy substance (cutin) to prevent loss of
water. The cortex consists of parenchyma cells and mechanical tissues.
The parenchyma cells of the cortex are continuous with the large pa-
renchyma cells of the pith. These two groups of parenchyma cells sep-
arate adjacent vascular bundles. The mechanical tissue is formed of
elongated, thick-walled cells to give rigidity to the stem. The tissues of
the stele of the stem are quite different from the stele of the root. The
conducting tissues of the stem stele consist of a series of vascular bundles
arranged in the form of a ring, leaving a large central area of pith. Each
vascular bundle is composed of xylem and phloem separated by cambium.
In young stems the large parenchyma cells of the pith and cortex are con-
tinuous between the vascular bundles. The parenchyma forms radiating
medullary rays (pith rays) between the vascular bundles. In each vascu-
lar bundle the phloem lies external to the cambium and the xylem in-
ternal to it. The xylem cells have thick walls as in the root xylem and
conduct liquids from the roots to the leaves, etc. The annular rings are
even more noticeable in stems than they are in roots, although they are
formed in much the same manner in each. The phloem conducts ma-
terials downward toward the roots.

Study of a Stem of a Monocotyledonous Plant. — If a thin section of
such a plant as corn is studied, certain differences will be noted (Fig.
60). In the monocotyledonous stems the vascular bundles are scattered
throughout the parenchyma. Each vascular bundle contains only pri-
mary xylem and phloem but no cambium separating them. It is impos-

Biology of Higher Plants — Anatomy and Physiology 223

sible to distinguish pith and cortex. The vascular bundles and the stem
as a whole do not increase in diameter beyond a certain point. Each
vascular bundle is enclosed by mechanical tissue composed of long, thick-
walled cells. These mechanical tissues, together with those just beneath
the epidermis, give rigidity to the stem.

The functions of a stem include the support of flowers and leaves, the
manufacture of foods (in certain instances), the storage of materials,
and the conduction of materials.

III. THE LEAVES

Leaves vary in size and shape in diff"erent plants (Figs. 53, 55, 57, 60,
and 70) . They vary from the needlelike leaves of the pine, to the large
leaves of certain palms. A typical leaf consists of (1) a flat, expanded
blade (lamina) ; (2) the stalk (petiole) ; (3) the base for attachment.

/ . E

Cross section
of jbem

Carpel (pistil)

cJf Cortical parenchyma
■^{Lndodermis i

Q[Hypoderrnis\ ,\

Pith '

Parenchyma
--ce//f

— £ndodermr5

yylem

Cambium

Phloem

-Xylem

Fibers

^_ Per ('cycle
^_Ph/oom p

Cortex _ _
Epidermis^ ^

Fig. 70. — Buttercup (Ranunculus sp.). A, Leaf; B, flower and its parts
(carpels are also known as pistils) ; C, root in cross section with its central stele
(composed of xylem, phloem, and pericycle) shown enlarged in D; E, stem in
cross section with a portion enlarged in F, showing the detailed structures, par-
ticularly the vascular bundle. Note the difference in the locations of xylem and
phloem in the root and stem. Observe the nectar-producing nectary at the base
of the petal.

224 Pla?it Biology

The blade may be simple, as in the case of the sunflower, or compound
(divided into leaflets), as in the horse chestnut. The margin of the
blade may be smooth or irregular. Within the blade are veins which
consist of vascular bundles. Each vascular bundle contains extensions
of xylem and phloem cells of the stele of the stem.

The internal structure of a leaf may be studied from a thin cross
section. The upper surface is protected by the upper epidermis, the cells
of which contain cutin to prevent rapid loss of water. The lower sur-
face is protected by the lower epidermis. In the lower epidermis, and
less frequently in the upper, are slitlike stomata (Fig. 18) (singular,
stoma) which lead into intercellular air spaces within the leaf. Each
stoma is surrounded by a pair of semicircular guard cells which control
the size of the stoma. The guard cells contain green chlorophyll, while
the epidermal cells do not. The interior of the leaf is composed of meso-
phyll tissue made up of chlorophyll-bearing cells. Just beneath the upper
epidermis, the mesophyll is known as palisade tissue, because the chloro-
phyll-bearing cells are column-shaped and are arranged side by side
perpendicular to the surface of the leaf. The mesophyll below the pali-
sade is known as spongy tissue in which the irregular-shaped cells sur-
round the intercellular air spaces. The veins of the leaf extend through
the spongy tissue. Each vein consists of a vascular bundle with its thick-
walled xylem cells toward the upper side and the thinner-walled phloem
toward the lower. The smaller veins contain only tracheids, while the
larger ones contain tracheids, sieve tubes, and companion cells. The
chlorophyll of the palisade and spongy tissues manufactures plant food
through the process of photosynthesis.

IV. THE FLOWER

A flower is really a series of whorls of modified leaves borne at the
end of a stem (Figs. 55, 57, 58, and 71). Flowers vary greatly In differ-
ent plants, but the more important structures and function may be ascer-
tained from the simple flower of the buttercup {Ranunculus sp.) (Fig.
70). The end of the stem which bears the floral leaves is called the re-
ceptacle. The outer whorl of floral leaves is called the calyx, which is
composed of five small, yellowish-green sepals. Within the calyx is the
more conspicuous corolla composed of five larger yellow petals. The
petals and sepals together constitute the perianth. Passing inward from
the corolla we find numerous filamentous stamens, each of which con-

Biology of Higher Plants — Anatomy and Physiology 225

sists of a stalklike filament and an enlarged anther at its free end. The
hollow anther contains microspores (pollen grains). The pollen grains
develop into male gametophytes. . In the center of the flower are whorls
of small, green, pointed, oval carpels. Each carpel consists of ( 1 ) a
basal saclike ovary, which contains a female ovule; (2) a hooklike,
pointed, distal end, known as the stigma to receive pollen; and (3) a
style, which connects the stigma with the ovary. The stigma, style, and
ovary constitute the pistil. The ovule of the flower is attached to the
ovary and consists of a megasporangium (nucellus). The megasporan-
gium forms four megaspores, only one of which develops into a female
gametophyte. The union of a male gametophyte with the female game-
tophyte within the ovary constitutes fertilization, which results eventually
in the development of a seed.

Pollen oraiTi

ToUen "tube

(J^ilaTneTti-
In'neT IriteaumeTit—

Duter iTtequmerit
^GCjaqaTn^ophyte

Stiana
Style

Ovary

Petal
Ovule

Sepal

FuNiculus
Micropyle
Receptacle

Fig. 71. — Diagram of a flower (in section) to show parts and fertilization.
The anther contains pollen grains which escape to the stigma. The stamens are
also known as microsporophylls. The pistil consists of the stigma, style, and
ovary. The pistil may consist of a single, basal carpel (megasporophyll, or ovule-
bearing "leaf") or of two or more fused carpels. The micropyle permits the en-
trance of the pollen tube into the female megagametophyte (egg sac). Ovules
later become seeds. The pollen tube and its contained pollen grains constitute
the male microgametophyte. The tube nucleus (of the pollen grain) germinates
and forms a pollen tube through which the generative nucleus (of the pollen)
follows to the ovule where fertilization occurs. The generative nucleus divides
into two sperm (male gametes); one sperm unites with the egg to form the
embryo; the other sperm fuses with the two polar nuclei (shown at top of mega-
gametophyte) to form the food endosperm.

226 Pla?it Biology

V. ABSORPTION BY PLANTS

Water. — Higher plants absorb water and inorganic salts by means of
the fine, transparent root hairs located near the tip of their roots (Fig.
57). The root hairs are really extensions of the epidermal cells and are
in close contact with the film of water which surrounds the individual
grains of the soil. Water passes from this film through the cell wall and
plasma membrane of the root hairs and the epidermis of the root tip.
Water is not absorbed by any other part of the root, stem, or leaves. The
absorption of water depends on the osmotic pressure of the soil water
and the osmotic pressure of the protoplasm within the cells. Water sup-
plies two elements, hydrogen (H) and oxygen (O), for plant use, in addi-
tion to serving as a vehicle for the entrance of essential inorganic salts.
Only a small part of the absorbed water remains in a plant as will be
seen when transpiration is considered.

Inorganic Salts. — Soils usually contain a variety of salts, some of
which can be used by a plant. Certain of these salts are selected by the
plant and absorbed for its future use. Plants require certain essential
salts which contain the following chemical elements: calcium (Ca),
potassium (K), nitrogen (N), phosphorus (P), magnesium (Mg), sul-
fur (S), and iron (Fe). These are rarely found in the soil as elements
but are frequently combined into such usable compounds as calcium
nitrate, Ca(N03)2; potassium nitrate, KNO3; potassium phosphate,
KH2PO4; magnesium sulfate, MgS04; iron phosphate, FeP04. The
quantity and quality of the chemicals in the soil, together with its water
content, to a great degree determine the structure and functions of the
plant growing in that particular type of soil.

VI. TRANSPIRATION BY PLANTS

The roots continually absorb water which is conducted by the xylem
through the stems and leaves (Figs. 53 and 55 to 60). Most of this
absorbed water is given off by the leaves through the process of transpira-
tion. The epidermal cells of the leaf contain a waxy substance (cutin)
which prevents any great loss of moisture through those cells. Most of
the transpiration occurs through the minute stomata scattered through-
out the upper and lower epidermis, particularly the latter. The xylem
tissues transport the water to the cells of the mesophyll of the leaf. From
the spongy tissue of the mesophyll, the water escapes into the intercellular
air spaces, from which it evaporates through the stomata. This escape
of water is regulated by the pair of semicircular guard cells which sur-

Biology of Higher Plants — Anatomy and Physiology 227

round each stoma. The opening of each stoma is regulated by the guard
cell and this is influenced by the amount of humidity in the surrounding
atmosphere. Transpiration results in a constant current of water through
the plant. This circulation transports foods and wastes from one part of
the plant to another.

VII. CONDUCTION OF LIQUIDS

The constant absorption of water by roots and the loss of water by
transpiration in the leaves result in a constant flow of water and its
absorbed materials through the plant. Water absorbed by a root hair
is passed into the cortex of the root, then to the endodermis, to the peri-
cycle, and finally into the xylem of the root. From the root xylem it
passes into the xylem of the stem which is connected with the veins of
the leaves. From the veins the water passes to the mesophyll cells of
the leaf. From these cells it escapes into the intercellular air spaces and
hence outside through the stomata.

The three factors which explain the ascent of water and dissolved ma-
terials in a plant are (1) root pressure, (2) tensile strength of water,
(3) transpiration. The differences in osmotic pressures, in the proto-
plasm of the root hair cells and the soil water, result in root pressure,
which causes an absorption of water by the roots and a tendency to force
it upward. A thin, continuous column of water is found in the small
xylem vessels. Under such conditions, the tensile strength of water is
great enough to resist successfully forces tending to pull the column apart.
Hence, the column of water when once started will not be easily broken.
A loss of water by transpiration in the leaf results in its replacement from
deeper tissues. This is accomplished by the upward pull on the water
column in the xylem tissues. The xylem seems to conduct materials
upward, while the phloem transports food materials from the point of
their manufacture to their places of use and storage. This is often down-
ward through the stem. The medullary rays of the stem conduct foods
and water radially (Figs. 53 and 57).

VIII. MANUFACTURE, DISTRIBUTION, AND
STORAGE OF FOODS BY PLANTS

Plants without chlorophyll, such as bacteria, yeasts, and molds, select
and absorb their foods from the materials on which they grow. Chloro-
phyll-bearing plants combine carbon dioxide and water to form carbo-
hydrates in the presence of light through the process of photosynthesis.

228 Plant Biology

In higher plants the carbon dioxide is taken from the air by the leaf and
the water is supplied by the roots. The carbon dioxide enters the leaf
through the stomata and intercellular air spaces (Figs. 53, 57, and 60)
and diffuses into the chlorophyll-bearing mesophyll cells. The chloro-
phyll combines this gas with the water brought to the mesophyll tissues
by the xylem tissues of the root and stem. Less than 4 per cent of the
light energy falling on a leaf is used in the photosynthetic process; part
of the additional energy absorbed by the leaf increases its temperature
and part is eliminated with the water during transpiration.

The green color of the chloroplasts in plants is due to a mixture of
four pigments: two green ones, chlorophyll A (C55H7205N4Mg) and
chlorophyll B (C55H7o06N4Mg), and two yellow ones, carotene (C40H56)
and xanthophyll (C40H56O2). The term chlorophyll is often used for
the mixture of these four pigments. Light is essential for the develop-
ment of chlorophyll as is shown by the pale color of leaves grown in dark-
ness. We do not know how chlorophyll unites carbon dioxide and water,
but since it does not contribute to the product formed and is not itself
used up in the process, it is surmised that it acts as a catalytic agent. The
process may be illustrated by the following chemical equation :

6 molecules 6 molecules Light Carbohydrate ^ Oxygen

water (H2O) carbon dioxide (CO2) energy (CeH^Oe) (6O2)

It will be noted that oxygen is a by-product of the process. Part of
this oxygen may be used by the plant for metabolic purposes and the
remainder eliminated. Part of the carbohydrates is oxidized, thus lib-
erating usable energy for plant use, but a much larger part is chemically
transformed by the plant into (1) components of living protoplasm, (2)
reserve foods, such as sugars, starches, proteins, and fats, and (3) other
substances, such as oils, resins, pigments, enzymes, vitamins, etc. Plants
form proteins by adding to the carbohydrates such elements as nitrogen
and sulfur and, in some cases, phosphorus. The living plant oxidizes
many of its substances, thus liberating energy for its various metabolic
activities.

General Consideration of Photosynthesis. — Photosynthesis is one of
the most important of living processes because, directly or indirectly, it
provides most of the foods, fuels, clothing, and shelter for living organ-
isms. Photosynthesis (Gr. photos^, light; synthesis, put together) is a
constructive or anabolic process. Chlorophyll (Gr. chloros, green; phyl-
lon, leaf) serves as an absorber of the light and no doubt has much to
do with the physical and chemical reactions necessary to transform the

Biology of Higher Plants- — Anatomy and Physiology 229

radiant (kinetic) energy into the potential energy of the sugar. Photo-
synthesis is also known as "carbon assimilation" or "carbon fixation."

The photosynthetic apparatus is made of the chlorophyll-bearing chloro-
plasts which in higher plants are usually most abundant in the chlo-
renchyma (mesophyll) tissues of the leaves (Figs. 57 and 60), although
they may be present in any living plant tissues exposed to light. Recent
investigations with the electron microscope reveal that the chloroplasts
in plant cells contain tiny green bodies of chlorophyll known as grana
(Fig. 72). The latter increase in size until they divide to form two new
chloroplasts. Chlorophyll is also present in the mosses, ferns, and algae.
In certain algae the green chlorophyll may be masked by other pig-
ments which are considered in greater detail in other parts of the book.
In addition to chlorophyll, the chloroplasts may contain two other pig-
ments: a yellow pigment called xanthophyll (Gr. xanthos, yellow;
phyllon, leaf) and an orange pigment called carotene. The latter was
formerly called carotin and was named because of its abundance in car-
rots. The yellow pigments are more resistant than chlorophyll to low
temperatures, drought, minimum light, diseases, and injuries. Conse-
quently, in the fall when some or all of the above factors may be present
and the chlorophyll begins to disintegrate, the yellow pigments may play
important roles. Chlorophyll was first named by Caventou and Pelletier
(1819), but it was isolated and its chemical composition determined in
1912 by Willstatter and his associates.

The chloroplasts in difTerent species of plants vary greatly, some func-
tioning in temperatures above 50° C. Inman found several species of
blue-green algae in Yellowstone National Park growing in a temperature
of 70° C. Other chloroplasts function in temperatures below -25° C.
These are extremes and undoubtedly most chlorophyll functions best in
less extreme temperatures. Some plants photosynthesize in full sunlight
while others function better in shaded environments. Diffuse light for
the necessary period of time is most favorable. It is believed that the
same type of chlorophyll is present in all species of plants. The total
quantity of chlorophyll in a plant averages about 1 per cent of the total
dry weight of that plant. The average plant makes about 1 Gm. of car-
bohydrate per square meter of leaf surface per hour under average
conditions.

Most photosynthesis is accomplished in leaves because ( 1 ) their ar-
rangement and position permit them most effectively to receive air and
light; (2) in form they are relatively thin and broad to enable them to

230 Plaiit Biology

Fig. 72. — Electron micrographs of individual chloroplasts from spinach leaves,
showing the tiny spherical bodies, called grana, within each chloroplast. These
spinach chloroplasts show grana and matrix, while three grana are enlarged,
shadowed with gold. (From Granick, S., & Porter, K. R.: Am. J. Botany 34:
545, 1947.)

Biology of Higher Plants — Anatomy and Physiology 231

absorb a maximum of heat and light; (3) they are well supplied with
transportation vessels (veins ending in the mesophyll tissue) to transport
water and minerals to the photosynthesis apparatus and carbohydrates
away from that apparatus; (4) their transparent cuticle and epidermis
permit the entrance of heat and light but prevent excessive evaporation
of moisture; (5) their spongy mesophyll tissues with their air spaces
communicate through the stomata with the outside to permit the neces-
sary exchange of gases; (6) they possess a maximum of chloroplasts for
uniting carbon dioxide and water. In algae the water and carbon dioxide
enter through the cell membranes.

Theories and Early Work on Photosynthesis. — Our present knowl-
edge of this phenomenon, like that of many of the great concepts, is due
to facts acquired by long, laborious experiments and observations by
many workers over a long period of time. Bonnet (1769) noticed bub-
bles of gas coming from living grape leaves immersed in water but no
bubbles from boiled water. Priesdey (1774) found that plants could
improve the air which had been rendered unfit by animals, hence sug-
gesting the exchange of carbon dioxide and oxygen between animals
and plants. Ingen-Housz, a Dutch physician (1779), showed that this
purification of the air was accomplished only by green plants and only in
light. Senebier (1782) showed that carbon dioxide was absorbed by
plants for nutritional purposes. De Saussure (1804) showed that plants
returned an amount of oxygen to the air which was about equal in
volume to the amount of carbon dioxide they had removed. He also
proved that the absorption and decomposition of carbon dioxide by a
plant resulted in an increase in weight of that plant. Boussingault
(1860-1890) carefully measured the carbon dioxide taken in by a plant
and the oxygen given off, thereby establishing their equality in volume.
Sachs (1862) concluded that starch grains in the green chloroplasts were
the product of photosynthesis in the presence of light. He also suspected
that there were intermediate products leading to the formation of starch.
He discovered that starch disappears from leaves at night and reappears
the next day. He proved that oxygen is a by-product of the process.
Von Baeyer (1870) formulated the formaldehyde hypothesis of photo-
synthesis in which he stated that small amounts of formaldehyde (CHoO)
were formed from water and carbon dioxide.

The theories which have been proposed for explaining photosynthesis
are based on the supposed intermediate products of the photosynthetic
process. One theory is based on the supposition that formic acid and

232 Plant Biology

formaldehyde are intermediate products and, even though they may be
poisonous, it is theorized that they are joined to some other group so
quickly that they do not have time to produce toxic effects on the living
protoplasm. The successive steps might be stated as follows:

(1) CO2 ^ H2O _^ H2CO3

(Carbon dioxide) (Water) (Carbonic acid)

(2) H2CO3 + H2O ^ CH.O; + H2O2*

(Formic acid) (Hydrogen peroxide)

(3) CH2O2 + H2O -^ CH2O + H2O2*

(Formaldehyde)

(4) By adding successive CH2O -> C6H12O6

(Sugar)

Another theory suggests that the intermediate product of photosynthe-
sis may be a complex chlorophyll compound. It is known that chloro-
phyll absorbs certain photons of light (radiant energy), thus becoming
chemically active. When in this state the chlorophyll probably unites
with carbon dioxide and water to form an unstable, intermediate product.
An enzyme converts the chlorophyll compound to sugar. The successive
steps might be stated as follows:

(1) CO2 + H2O + Chlorophyllf + Light energy -^ Chlorophyll
(Carbon (Water) carbonate
dioxide)

(2) Chlorophyll carbonate + Enzymef + H2O -^ Sugar + O2

Recent experiments on photosynthesis by Graffon, Brown, and Fager
utilizing radioactive tracer technics, seem to reveal that there is a pri-
mary, intermediate product of carbon dioxide and water formed which is
known as "Factor B." The latter is chemically unidentified at present
but behaves like an acid and is rapidly used by the plant in its metabolic
processes. Proper identification of this factor and future work with
radioactive chemicals which can be traced may assist in the explanation
of the process.

Biochemical Aspects of Photosynthesis. — Plants do not derive their
foods, as usually stated, from the soil. Plants cannot live alone on the
inorganic salts and water absorbed by the root hairs from the soil but
must have proteins, carbohydrates, and fats just as animals must. Both
plants and animals require much of the same type of food, but the green

*Split by cmzymes into water and oxygen.

fin the process the chlorophyll and enzyme are converted to their original state.

Biology of Higher Plants — Anatomy and Physiology 233

plants can manufacture their own foods from raw materials (water and
carbon dioxide) while animals cannot.

Algae absorb carbon dioxide through their surface from their sur-
roundings, while higher plants usually take it through the regulating
stomata of the leaf epidermis. The water and its contained salts are
osmosed into the roots by means of numerous root hairs. From the
roots these materials are conducted by means of the xylem tissues of the
roots and stems to the veins of the leaves. The carbon dioxide of the
air is being constantly used by the many green plants, but the supply
is replenished by such sources as animal metabolism, the combustion of
luels, industrial combustions, volcanic eruptions, etc.

Willstatter (1912) showed that chlorophyll actually consists of a mix-
ture of two substances which he called chlorophyll A and chlorophyll B.
Both these chlorophylls may form green crystals when extracted with
ethyl alcohol. They may be separated from each other by their differ-
ent solubilities in organic solvents. Chlorophyll A is blue-green in trans-
mitted light and blood red in reflected light. Chlorophyll B is yellowish-
green in transmitted light and brownish-red in reflected light. Chemi-
cally, chlorophyll is an ester (a combination of an acid and an alcohol).
In both chlorophylls about 2.7 per cent of magnesium is the center.
Iron is necessary for the plant to manufacture chlorophyll, but no iron
enters into the composition of the chlorophyll. It is evident that the
two chlorophylls are quite similar in most respects, differing only in the
amounts of hydrogen and oxygen.

Biophysical Aspects of Photosynthesis.^ — Chlorophyll has the physical
property of selectively absorbing certain wave lengths of light while
other wave lengths are transmitted. When a green leaf, or a solution of
chlorophyll, is placed between a source x)f light and a prism, dark bands
appear in the spectrum (Fig. 368), showing that some of the light is
absorbed by the chlorophyll, while the rest of the light is passed through
the chlorophyll or reflected from the leaf surface. The color of a leaf
is green because those wave lengths are not absorbed by the leaf but
are reflected from its surface to the eye. In strong sunlight absorption
is greatest at the red end of the spectrum where the wave lengths are
longer (0.00076 mm. long). In diff"use light more absorption occurs at
the violet end with its shorter wave lengths (0.00039 mm. long). The
red wave lengths arc more efficient because of the presence of more
energy. It is well known that "the photosynthetic work accomplished

234 Plant Biology

varies directly with the energy absorbed from the Ught regardless of the
wave length." The physicist, Langley, determined the distribution of
energy in the spectrum as follows:

SPECTRUM REGION PERCENTAGE OF TOTAL ENERGY

Infrared 62—63
Visible spectrum 37.0
Uhraviolet 0^6

About 63 per cent of the total energy has no value in the photosyn-
thetic process, because none of the infrared waves are used. The rela-
tion between light and photosynthesis is considered in another part of
this chapter.

Chlorophyll also possesses the optical property of fluorescence. In
reflected light it appears blood red due to the fact that part of the light
waves falling on it are transformed and reflected with an altered wave
lens:th.

'O"

Influential Factors in Photosynthesis. —

1. The Carbon Dioxide Supply: The quantity of carbon dioxide in
the air is a very important factor in photosynthesis. The average
amount in the air is about three parts per 10,000 (0.03 per cent). This
amount is usually too small for a maximum of photosynthesis because
experiments show that many of the common plants could use efficiently
up to 1 per cent. Certain plants might even use higher concentrations-
Increased carbon dioxide must be accompanied by corresponding in-
creases in temperature and illumination if maximum use of the gas is
to be made. Approximately 50 per cent of the dry weight of a plant
body is composed of carbon which for the most part must come from
the air. The application of additional amounts of carbon dioxide to
such crops as tomatoes, potatoes, beets, and carrots increased their yield
from 30 to 300 per cent. A tree with a dry weight of 1,000 pounds
must secure 500 pounds of carbon from approximately 1,427,000 cubic
yards of carbon dioxide from the air. Under natural conditions, the
amount of carbon dioxide in the air is probably a limiting factor in the
rate of photosynthesis.

2. Quantity and Quality of Light: The quantity (intensity), quality
(wave lengths), and the duration of light all affect the rate of photo-
synthesis. Certain plants apparently require small amounts of light for
the process. A lighted match held for one second 10 cm. away from a
green alga (Chorella sp.) will initiate the process with the evolution of

Biology of Higher Plants — Anatomy and Physiology 235

oxygen. Moonlight is sufficient to continue the process in certain algae.
While some photosynthesis can occur in all parts of the visible spec-
trum, not all parts of the spectrum are of equal value. In general, the
red end of the spectrum is twice as valuable as the blue end. The lowest
rate occurs in the green region; the highest rate, in the red end; infra-
red radiations (Fig. 368) are not used at all; ultraviolet radiations are
used to a limited extent. While the rate of photosynthesis is highest in
the red end because of its greater energy value in sunlight and stronger
absorption of light by chlorophyll in this region, the absence of blue-
violet light decreases the rate of photosynthesis. This may explain the
lower rates of photosynthesis under artificial lights, which may be de-
ficient in the blue-violet rays.

Brown has shown that in bright sunshine a sunflower leaf receives
600,000 units (gram calories) of radiant energy per square meter per
hour with the formation of 0.8 Gm. of carbohydrate. Of all the light
which falls on a leaf, only about 3.5 per cent is absorbed by the chloro-
phyll proper. Raber states that the chlorophyll apparatus has an
efficiency rate of about 15 per cent.

Up to a certain point the rate of photosynthesis increases as the in-
tensity of light increases. There are variations, but most plants require
light much below the intensity of strong sunlight at noon. Usually there
is more light available in nature than plants use, provided other factors
are normal.

The duration or length of time a plant is in the light aflfects the
amount of carbohydrate produced. This is an important factor in
autumn and winter when light is available for shorter periods. Plants
need for maturation and growth a certain number of light energy units,
the unit being the product of the light intensity and the duration of
time. In general, if other factors are constant, a weak light acting for
a long time may have the same effect as a stronger light acting for
a shorter time. The growth of plants and the ripening of their products
can be speeded up by increasing the duration of light by using artificial
light. Differences in light intensities and duration in various parts of
the country influence the rate of photosynthesis in those different areas.

3. Water Supply: Since carbon dioxide is combined photosyntheti-
cally with the constituents of water, the latter becomes a limiting factor,
especially if present in minimal quantities. However, increasing the
water supply will increase photosynthesis only up to a certain point.
If water is so deficient as to cause wilting of leaves, there probably is
insufficient water for photosynthesis. The wilting may close the stomata

236 Plant Biology

of the leaves, thus inhibiting the normal entrance of carbon dioxide.
Water is also necessary to transport the soil salts in solution.

4. Temperature: In general, the rate of photosynthesis rises in a
geometrical way as the temperature rises from the minimum toward the
maximum. For every 10 degree rise in temperature, the rate of photo-
synthesis increases an average of 2.4 times, until a maximum of about
35° C. is reached, beyond which no increase in the rate occurs. In fact,
bevond 35° C. the rate mav even decrease. Certain conifers accus-
tomcd to cold climates may photosynthesize at -25° C, while the mini-
mum for most plants is about 0° G. The maximum for most plants is
about 45° C.

5. Soil Salts, Including Magnesium and Iron: Iron salts in the cells
probably act as catalyzers in the photosynthesis process, although iron
does not enter into the composition of chlorophyll. Magnesium is the
central constituent of chlorophyll, and consequently the quantity avail-
able wall influence the formation of chlorophyll, and this in turn will
determine the rate of photosynthesis. Excesses of salts in the soil retard
photosynthesis by inhibiting the osmosis of water by the root hairs. Salts
in the plant liquids also may influence the normal functioning of the leaf
stomata, and hence influence the entrance of carbon dioxide.

6. Internal Factors, Including Chloroplasts and Enzymes: Chloro-
phyll is absolutely essential for photosynthesis, and the amount of car-
bohydrate manufactured varies almost directly with the amount of
chlorophyll in the chloroplasts. Fruits and other plant products are
directly influenced by the number and size of the leaves with their
contained chlorophyll. The removal of some of the leaves shows the
important quantitative relation between chlorophyll and the food manu-
factured. Damage to leaves produced by hail, storms, and insects
causes a corresponding decrease in photosynthesis.

Willstatter and Stoll theorize that a specific enzyme is associated with
chlorophyll in photosynthesis. The action of this enzyme is accelerated
as temperature rises, which may explain in part the eff^ect of increased
temperature. However, acceleration of the enzyme leads to increased
photosynthesis only when an abundant supply of chlorophyll is present,
the latter absorbing more of the necessary light energy. Probably in
plants with a minimum of chlorophyll it is the lack of light absorption
that limits the rate of photosynthesis, while in plants high in chlorophyll
content the activity of the enzyme may be the limiting factor. Many
factors operate simultaneously in the photosynthesis process and the

Biology of Higher Plants — Anatomy and Physiology 237

amount of carbohydrate produced depends on their joint action. What
may be a limiting factor in one plant under certain conditions may not
be a limiting factor in another plant under different conditions.

The anatomic construction of the leaves and their stomata influence
photosynthesis. Foreign materials, dirt, and rain in the stomata inhibit
the exchange of gases, and hence influence photosynthesis. The pre-
dominance of stomata on the underside of leaves makes this a factor
of less importance than if the stomata were on the upper surface.

7. Atmospheric Pressure: Variations in atmospheric pressure de-
cidely influence photosynthesis; when the pressure is high, the rate is
increased.

Applied and Commercial Aspects of Photosynthesis. — In most plants
the demonstrable products of photosynthesis are sugars and starch.
Starch is an ideal storage product because it cannot pass through the
cell walls due to its insolubility. Some plants, such as the onion/ pro-
duce no starch, while others produce an oil instead of starch. The
carbohydrates formed by photosynthesis are the building stones of which
the plant builds proteins, fats, oils, etc., as shown by the following:

Carbohydrates + Nitrogen -> Amino acids (each -> Proteins

(glucose, cane Phosphorus molecule has the

sugar, starch) Sulfur amino or NH2 group)

Carbohydrates (by fermentation) -> Glycerin \ p .
Carbohydrates (by oxidation) -^ Fatty acids T'

Most of the radiant energy absorbed by green leaves is transformed
into heat energy which through radiation raises the temperature of the
surrounding air. In this manner some of the heat energy of the sun
is captured and radiated for use by other living organisms. Some of
this heat energy also vaporizes the water within the leaf. Some of the
light energy absorbed by chlorophyll rpay be transformed into electric
energy, which may explain some of the electric phenomena of living
plants.

The close chemical relationship between chlorophyll A and the blood
pigment (hematin) has caused much scientific investigation. When
chlorophyll is decomposed by acids or alkalies, the residue (hemopyrrole)
has a chemical composition similar to that of hematin which is derived
from the decomposition of red blood pigment. In hemopyrrole the
metallic element involved is magnesium; in hematin it is iron.

Chlorophyll has long been considered to be of dietary value to ani-
mals although its exact significance has not been determined. More

238 Plant Biology

experiments on plant pigments, hormones, vitamins, and other bio-
chemical phenomena may give us additional information.

Ganong states that many of our common plants produce as an aver-
age about 1 Gm. of carbohydrate per square meter of leaf surface per
hour. This may seem insignificant, but, when we consider all the green
plants which photosynthesize, the total quantity produced is tremendous.
In 1930, sugar beets and sugar cane produced photosynthetically in the
world about 32,000,000 tons of sugar over and above what they used
themselves. The United States produced about 1,500,000 tons. The
carbohydrates made photosynthetically are used by the plant in diges-
tion, translocation, respiration, assimilation, storage, and synthesis into
proteins, fats and oils, or other types of carbohydrates. When we con-
sume plants we utilize those products which they formed but did not
use for their own needs.

Plants use the products which they have photosynthesized in many
ways as shown by the following: (1) They may be digested into soluble
forms; (2) they may be translocated to other parts of the plant; (3)
they may be synthesized into proteins, fats, oils, or other carbohydrates;
(4) they may be oxidized through fermentation or respiration to liberate

Products Resulting From Photosynthesis*
(Including Years in Which Data Were Selected)

product

world

UNITED STATES

Oats (average 1921-30)

4,491,000,000

bu.

1,285,513,000 bu.

Corn (average 1921-30)

4,144,000,000

bu.

2,712,430,000 bu.

Wheat (average 1921-30)

4,081,000,000

bu.

831,578,000 bu.

Rye (average 1921-30)

1,664,000,000

bu.

56,269,000 bu.

Barley (average 1921-30)

1,636,000,000

bu.

237,395,000 bu.

Rice (1930-31) China excluded

137,000,000,000

1,248,000,000 tb

Beet and cane sugar (1930-31)

64,000,000,000

3,000,000,000 tb

Cotton (average 1927-30)

12,715,000,000

7,000,000,000 tb

Hemp (1927)

1,622,000,000

2,000,000 tb

Coffee

3,000,000,000

Tea

1,760,000,000

Cocoa beans (1926)

1,000,000,000

Beans (dry) (1931-32)

4,004,000,000

1,266,000,000 tb

Apples (1932)

140,000,000 bu.

Oranges (1932)

49,000,000 boxes

Grapefruit (1932)

13,000,000 boxes

Lemons (1932)

7,000,000 boxes

Rubber (average 1925-29)

2,000,000,000

Turpentine (average 1925-29)

6,000,000 gal.

Rosin (average 1925-29)

500,000,000 tb

Lumber

41,000,000,000 bd. ft.

Wood pulp (1930)

7,000,000 cords

*The total value of all farm products in the United States alone averages between 15 and 20
billion dollars annually.

Biology of Higher Plants — Anatomy and Physiology 239

energy; (5) through assimilation and growth they may build new tis-
sues; (6) they may be stored in roots, seeds, or stems for future use or
for the use of animals.

It is believed that coal, peat, petroleum, natural gas, and similar fuels
are the result of decomposition of living organisms of many years ago.
These remains originally were made by the plant through the process of
photosynthesis and the radiant energy stored in these fuels in the form
of potential energy. When these fuels are used today, this energy is
released. The amount of photosynthesis which has taken place in all
the green plants of the past is beyond our imagination. The amount of
material produced each year by present-day plants through the process
of photosynthesis is beyond computation.

IX. RESPIRATION BY PLANTS

During respiration there is an absorption of oxygen and a liberation
of carbon dioxide. Respiration occurs continuously in the living proto-
plasm of all animal and plant cells. In this respect it differs from
photosynthesis which occurs only in chlorophyll-bearing cells of green
plants in a proper source of light energy. These two phenomena have
been contrasted in a previous chapter. During respiration the molecules
of the plant materials are broken down into simpler forms, and the
stored chemical energy is liberated in such a form as to be utilized
by the plant. During photosynthesis, light energy is absorbed and used
by the plant. Animals confiscate energy when plants are consumed.
All the energy used by plants and animals in their activities is derived,
directly or indirectly, from the sunlight. For instance, when such a
sugar as glucose is oxidized by respiration, the equation is as follows:

Glucose (sugar) Oxygen _. Carbon dioxide Water Energy

(CeHiiOe) (6O2) (6CO2) (6H2O) released

In many respects this equation is the reverse of the equation of photo-
synthesis.

X. CORRELATION AND PLANT HORMONES

Correlation in plants by means of chemical hormones recently has
been realized as being of utmost importance. The presence of specific
chemical substances in plants (of certain species, at least) is known to
play an important role in plant metabolisms and in the correlation of
the plant as a whole. Plant hormones might be defined as chemical

240 Plant Biology

substances naturally produced in minute quantities by plants^, stored in
certain regions, and later transported to other regions to produce regu-
latory effects on the development and growth of that organism. The
term hormone (Gr. hormao, excite) ineans "to arouse to activity." Hor-
mones in plants are normally produced in very minute quantities but
apparently are sufficient to perform their specific functions. Much of
the experimental evidence of the past years concerning the activity of
plant growth hormones has helped to explain normal growth, tropisms
(responses) to gravity, tropisms to light, and similar phenomena. Plant
hormones, like animal hormones, are produced in one part of the plant

Characteristics of Plant Growth Hormones

NAME

CHEMISTRY

MELTING
POINT

EFFECTS OF
ACIDS AND
ALKALIES

FUNCTIONS
WITHIN THE PLANT

Auxin A or
auxentriolic
acid

C18H32O6

196° C.

Stable in acid :
sensitive to
alkali

Promotes cell elongation
in the direction of the
long axis of tissues ;
growth of leaves and
stems is dependent on
it, while root growth is
inhibited by it

Auxin B or
auxenolonic
acid

CisHsoOi

183° C.

Destroyed by
acid and by
alkali

Same as above

Heteroauxin
or 3-indole
acetic acid

C10H9O2N

165° C.

Sensitive to
acid ; stable
to alkali

Same as above

(usually young, vigorously growing parts) and transported to another
part of the organism where they actively control specific phenomena,
depending on the type of hormone in question. The tropic responses of
plants to two of the most important environmental stimuli, gravity and
light, are associated definitely with the movement of plant hormones
("auxins") from one region of a stimulated plant organ to another.
This phenomenon is known as the growth hormone explanation of
tropisms. Several different plant hormones have been found naturally
present: (1) auxin A, (2) auxin B, and (3) heteroauxin, which seems
to be the most widely distributed of the present hormones. Another
plant hormone, traumatin (Gr. trauma, wound) seems to initiate and
influence healing of plant wounds.

In young plant tissues the hormones move only in a morphologically
basipetal direction ("polar transportation"), but in older tissues they
move in either direction. In very old inactive tissues there is probably

Biology of Higher Plants — Anatomy and Physiology 241

very little, if any, movement. The plant hormones may be transported
in the following ways : ( 1 ) by diffusion, ( 2 ) by protoplasmic streaming,
(3) by the transportation or circulatory system of the plant, if such is
present, (4) by an electrical phenomenon in which they are moved
toward a positively charged pole because of changes in electrical poten-
tial within the plant. A similar phenomenon in animals has been sug-
gested by recent experimental evidence. In spite of the fact that plant
hormones can be extracted from plants, there is no chemical test which
provides a simple and efficient means of qualitative and quantitative
detection of the minute amounts of them in living plants. However,
certain physiologic methods are now being perfected by means of which
the hormone concentration can be determined.

XI. GROWTH OF PLANTS, POLARITY, MORPHOGENESIS

Plants increase in size by mitosis (cell division) or by an increase of
the size of the cells without increasing the number. In many instances
growth is probably the result of both these phenomena occurring at the
same time. There is a limit to the size to which a cell can grow and
normally carry on its metabolic activities. After a certain size is
reached, mitosis must occur and the two resulting cells must increase in
size by assimilating foods brought to them. It is not known precisely
how the living protoplasm in these plant cells assimilates this food.
Undoubtedly, the various food elements are built up and held together
by energy supplied to the plant, principally through oxidation of food
materials. The actual rate of growth of a particular plant, or any of
its parts, is influenced by such factors as (1) the specific inheritance of
those cells, (2) the quantity and quality of available foods, (3) the age
of the plant, (4) the amount of available oxygen, and (5) the presence
of specific plant hormones.

Generally speaking, plant growth hormones bring about growth if
such conditions as water supply and foods are satisfactory. It is be-
lieved that no plant growths can take place without the presence of the
specific plant hormones previously described. The hormone auxin in
minute quantities promotes the elongation of cells (stretching) in the
direction of the long axis of an organ, such as a stem or branch. In
this case auxin is said to promote "polarized growth"; that is, growth
in length rather than in another direction. This is particularly true in
younger tissues. After tissues have reached a certain age, growth occurs
in such a manner that the tissue increases in diameter. In all instances
growth is dependent on plant hormones.

242 Plant Biology

Polarity (L. polus, pole) is a phenomenon in which there exists struc-
tural and functional direction due to complex internal factors. For
example, experiments show that certain plant stems (such as willow,
etc.) when cut into sections and suspended in humid air will develop
shoots from the distal end and adventitious roots from the proximal end.
This proves that these stems possess a permanent physiologic difference
between the two ends which is called growth polarity. If the experi-
ment is performed in moist soil, roots may form on the original distal
end of the stem (when placed in the soil) but they will form more
slowly and less extensively than on corresponding stems whose proximal
ends are placed in the soil. So these stems seem to have a prospective
"shoot end" and prospective "root end" which shows polarity in the stem.

Polarity seems to be present in individual cells, parts of organs, entire
organs, etc., in which functional polarity accompanies structural polarity.
Hormonal polarity exists in which the movements of plant hormones
(auxins, etc.) are primarily polar, taking place primarily from the more
distal (apical) to the more basal (proximal) parts of a plant structure.
This distribution and presence of hormones in certain regions of plants
explain some of the many growth and behavior phenomena of plants.

Electrical polarity is experimentally proved in which the distal (apical)
end of stems is electropositive, while the basal (proximal) part is electro-
negative. A similar electrical polarity exists in cells. All of these polari-
ties seem to be inherent and usually fixed and ordinarily cannot be
changed materially by environmental conditions.

When living cells pass through their enlargement stages, they undergo
differentiation (L. differe, to differ) in which division of labor and dif-
ferences in structure and form occur, depending on the various functions
to be performed. These causes of differentiations are due to hereditary
determiners in each species of plant, being transmitted from one genera-
tion to the next. Environmental conditions, at times, may modify these
differentiations of cells but only quantitatively and not permanently.
This study of differentiation is called morphogenesis (mor fo -jen' e sis)
(Gr. morphe, form; genesis, origin).

XII. PLANT TROPISMS (REACTIONS)

Each species of plant is affected in specific ways by external and in-
ternal factors. Light, heat, moisture, chemicals, gravity, and atmos-
phere are a few of the influential external factors, while the chromo-
somes and their genes, the chemical constituents of the protoplasm, and
the chemical hormones are important internal factors. External en-

Biology of Higher Plants — Anatomy and Physiology 243

vironmental conditions which cause a plant to react are known as
external stimuli. A reaction to a stimulus which possesses direction is
known as a tropism. The following tropisms are common in plants:

Phototropism (Reaction to Light). — The stems usually grow toward
light (positive phototropism), while roots usually grow away from light
(negative phototropism),

Geotropism (Reaction to Gravity). — Stems are generally negatively
geotropic, while most roots are positively geotropic.

Chemotropism (Reaction to Chemicals). — This reaction is exhibited
by plants in various ways, depending upon the quality and quantity of
the chemical and the species of plant.

Thermotropism (Reaction to Heat). — Certain plant structures grow
toward heat, while others grow away from it, depending on the quan-
tity and quality of the heat and the species of plant. The reaction of
cold (the absence of heat) is also important and characteristic.

Hydrotropism (Reaction to Moisture). — Roots tend to be positively
hydrotropic, or grow toward a supply of moisture, because one of their
functions is to supply water to the plant.

Thigmotropism (Reaction to Contact With Solid Objects). — The
small tendrils of certain plants are stimulated by contact with solid
objects so that the tendrils grow around that object. This contact
stimulates the cells of that particular region so as to produce an un-
equal rate of mitosis in the two sides of the tendril. This unequal rate
of growth results in the curving of the tendril around the solid object.

A young stem always bends toward the light because of a greater
concentration of growth hormone on the darkened side of the stem.
One possible explanation for this is that it is at least partly due to a
light-induced change in the electric potential across that stem. In a
similar manner the various tropisms are thought to be determined and
influenced by the actions of the various hormones present in the plant.
This is known as the hormone explanation of tropisms.

Xni. PLANT PIGMENTS

The structures and functions of pigments in the plant kingdom are
not well understood at the present time. There is no doubt that pig-
ments play important roles, but only future experiments in this field will
reveal their true significance. It is commonly known that a variety of
pigments exist in leaves, flowers, seeds, stems, and fruits. Certain uni-
cellular and simple multicellular plants have pigments whose functions

244 Plant Biology

are not definitely established. The blue-green algae (phylum Cyano-
phyta) contain a blue pigment, phycocyanin, in addition to the green
chlorophyll and yellow pigments. The red algae (phylum, Rhodophyta)
contain a red pigment, phycoerythrin, in addition to the green chloro-
phyll. The brown algae (phylum Phaeophyta) contain a brown pigment,
fucoxanthin, in addition to the green chlorophyll. The green algae
(phylum Chlorophyta) contain green chlorophyll which predominates
over the carotene and xanthophyll pigments. The diatoms (phylum
Chrysophyta) have a yellowish-brown pigment in addition to their green
chlorophyll. A brief summary of the pigments of higher plants is given
in the accompanying table.

Green pigments, such as chlorophyll, may occur in any part of a plant
which is exposed to light, although they also occur without light in such
tissues as lemon and melon seeds, in embryos and endosperm, certain
fruits, and in the wood of many Rosaceae. Chlorophyll A in alcoholic
solution appears blue-green by transmitted light and blood red by re-
flected light and has a blood red fluorescence. Chlorophyll B in alcoholic
solution appears yellow-green by transmitted light and has a brownish-
red fluorescence. The formation of chlorophyll is dependent on ( 1 ) iron,
which is necessary to form chlorophyll but is not a part of the pigment;
(2) at least a minimum of light to develop chlorophyll from the unstable
pigment chlorophyllogen, although certain algae, young ferns, and the
seedlings of certain conifers become green in darkness; (3) moderate tem-
perature for an optimum formation of chlorophyll, because there is no
greening at very low or very high temperatures; (4) an excess of oxygen
which seems necessary for greening; (5) the proper quantity and quality
of carbohydrates; (6) certain mineral salts, especially magnesium, which
is an important constituent of chlorophyll.

Yellow pigments may occur in any part of a plant and their presence
is not related to the presence of light. One important yellow pigment is
xanthophyll (Or. xanthos, yellow; phyllon, leaf), which is common in
the leaves of elms, birches, and poplars. Xanthophyll is also found in
animals in ^^^ yolk and yellow feathers. Xanthophyll is one of several
pigments known as carotinoids which form about 0.5 per cent of the
weight of fresh leaves. In the fall, as chlorophyll decomposes, the caro-
tinoids become visible, often together with the red anthocyanins in
leaves. From its chemical formula xanthophyll appears to be merely an
oxidation product of carotene which is another carotinoid pigment.

Another carotinoid pigment is carotene (Or. karotin, carrot yellow),
which is almost insoluble in alcohol (cold) and which forms flat rhombic

Biology of Higher Plants — Anatomy and Physiology 245

CU
<

■!->

c
JS

CA
O

C
1— (

■M

J2
'3.

X!
bo

-d

■M

l+H
O

Leaves of elm, birch, and pop-
lar; in the fall this pigment
becomes visible when chloro-
phyll disappears

-C

-t-i
c

c3
0)

c/3

Occurs as glucosides (sugar
plus flavone) in such plants
as osage orange, sumac, yel-
low wood, snapdragon, and
onion (skins)

"Delphinidin chloride" in
grape, red hollyhock, red pe-
tunia, violet, etc.

Pelargonin in red geranium,
red and purple aster, scarlet
sage

Cyanidin in red dahlias, pop-
pies, cornflower, fruits of
cherry, currant, and straw-
berry

Peonidin in red peonies

0
H

Bluish-green with a
deep red fluores-
cence in alcoholic
solution

Yellow-green with a
brownish-red fluo-
rescence in alcohol

Nearly insoluble in
alcohol

Deep yellow or
orange-yellow with
alkali

Red or purple in acid
solution and green
or blue in alkaline
or neutral solutions

OCCUR

IN
PLASTIDS

c/5

n-.

No; they
are in
solution
in cell
sap

PERCENT-
AGE IN
LEAVES

O
CM

in
id

CHEMICAL
CHARACTERISTICS

-r

o
-f

Yellow crystals
with high melt-
ing point

Closely related to
the glucosides
(CsHcOs);
usually require
sunlight for
their develop-
ment

S-c

be
c

CS
Sh

"aj

t
o

-C

a
2

>-H

a
o

-C
C

■4-»

"Flavones"
or flavonols

c
c

o
0

-C

246 P!a7it Biology

crystals. It is widely distributed in the green parts of plants, but it is
also found in flowers, fruits, seeds, roots, and certain fungi. It is present
in large quantities in carrots. The carotene content of leaves varies
with the seasons because its formation is dependent on light. Its func-
tion is not clear, but its tendency to unite with oxygen may be significant
in photosynthesis where reduction of compounds containing oxygen
occurs.

Flavones (L. flavus, yellow) are yellow pigments in such plants as
yellow wood (Morus), osage orange (Madura,) and sumac (Rhus).
They are not so common in yellow flowers and leaves where the color is
due to carotinoids. Flavones are probably oxidation products, the exact
functions of which are not clear at present. They are responsible for
the yellow color of onion skins and certain snapdragons. In most plants
they occur as glucosides.

Red pigments known as anthocyanins (Gr. anthos, flower; kyanos,
dark blue) are dissolved in the cell sap of such structures as certain
flowers, fruits, and leaves, beet roots, red cabbage, etc., where they give
red, purple, or bluish colors. Anthocyanins absorb some light energy
which is converted into heat. The latter increases the temperature,
which accelerates the metabolic activities of the cell and probably aids
in protecting the plant from the lowered temperature of the surrounding
air. This is plausible in view of the fact that anthocyanins are more
common in leaves in the fall than in summer. Anthocyanins develop
more abundantly in all parts of a high alpine plant than in the lowland
plant, even in plants of the same species. For example, the common
weed, the yarrow (Achillea millefolium), has white flowers in lowlands
and southern regions but has red flowers on high mountains and in the
far north. Anthocyanin formation depends on ( 1 ) the presence of
sugars, (2) a certain amount of light (they are "sun pigments"), al-
though they also develop in the roots of beets and in the outer part of
radish roots which do not contact light; and (3) a lower temperature,
which naturally must be above freezing. A few examples of anthocya-
nins which occur naturally are red plums, red bananas, red rose, red ber-
ries, red geranium, red hollyhock, red hyacinths and tulips, the bracts
of the Poinsettia, the scarlet oak, scarlet maple, and similar materials.

In general, plant pigments have been credited with such functions as
follows : ( 1 ) An aid in respiration. The relationship between anthocya-
nins and easily oxidizable sugars suggests a possible correlation between
the processes of oxidation and respiration. Carotene is oxidizable into
xanthophyll. Red anthocyanins may be changed to blue ones by oxidiz-

Biology of Higher Plants — Anatomy and Physiology 247

ing and reducing enzymes. (2) An aid in photosynthesis by absorbing
usable Hght. It is known that certain anthocyanins can absorb certain
Hght rays which the chlorophyll cannot, thus supplying the latter with
energy. (3) Absorbers of heat rays which protect chlorophyll against
too strong light and secure a maximum of energy. Red pigments in
autumnal leaves and fruits absorb more energy, which hastens the matur-
ing and ripening processes. (4) Attractions and repellents for animals.
Certain colors and odors attract animals to plant flowers, thus ensuring
their pollination. Most insect-pollinated flowers are brightly colored
and have strong odors. (5) Osmotic constituents of cells. Anthocyanins
and other soluble pigments are important osmotic constituents of cells
and thus are associated with the passing of materials through cell walls.
Plant pigments play a very important role in the autumnal coloration
of leaves. This phenomenon varies from year to year in its duration and
in the degree of its magnificence. As cooler weather comes, the green
chlorophyll disintegrates. This permits the yellow carotinoid pigments
to become visible, and, if sugars are present, the reds and lavenders of
the anthocyanins also appear as they are formed. Bright days in early
fall produce abundant sugars upon which the bright yellows and reds
depend. Plants rich in sugars, such as maples and birches, are likely
to be bright red and yellow. Brown colors are due to flavones, and more
often to tannins in the cell walls. The leaves of oaks and beeches are
rich in tannin, hence are likely to be brown. Although the phenomenon
of autumnal coloration is not completely understood, sufficient data have
been secured to explain the process in a general way.

QUESTIONS AND TOPICS

1. Describe briefly each of the five general regions of the root.

2. Discuss briefly each of the primary and secondary tissues of the mature region.

3. Describe the general anatomy and physiology of (1) stems, (2) leaves, and
( 3 ) flowers.

4. Explain how absorption occurs and the importance of this phenomenon.

5. Discuss the purposes of transpiration in higher plants.

6. How are liquids conducted in higher plants?

7. Discuss the manufacture, distribution, and storage of foods in plants.

8. Describe the method of respiration in plants.

9. Explain the phenomenon of correlation in plants, including the characteristics
and functions of auxins and heteroauxins.

10. Discuss briefly the methods of growth in higher plants.

11. Classify plant tropisms and give explanations for these vital phenomena.

12. Classify plant pigments and give characteristics and functions of each pig-
ment.

248 Plajit Biology

13. Write a brief article explaining the phenomenon of autumnal coloration of
leaves.

14. Describe the process of photosynthesis, including the biophysical and bio-
chemical factors which may influence it.

15. List the sources of foods, fuels, shelter, and textiles which are dependent upon
photosynthesis.

16. Discuss the various types of polarity with examples of each.

17. Define differentiation and morphogenesis, with examples of each.

SELECTED REFERENCES

Avery and Johnson: Hormones and Horticulture, McGraw-Hill Book Co., Inc

Boysen and Jensen: Growth Hormones in Plants, McGraw-Hill Book Co., Inc.

Curtis: The Nature and Development of Plants, Henry Holt & Co.

Curtis: The Translocation of Solutes in Plants, McGraw-Hill Book Co., Inc.

Curtis and Clark: Introduction to Plant Physiology, McGraw-Hill Book Co., Inc.

Dixon: The Transpiration Stream — University of London Press.

Eames and MacDaniels: An Introduction to Plant Anatomy, McGraw-Hill Book

Co., Inc.
Ellis and Swaney: Soilless Growth of Plants, Reinhold Publishing Corp.
Gardner: Basic Horticulture, The Macmillan Co.

Gericke: The Complete Guide to Soilless Gardening, Prentice-Hall, Inc.
Hoagland: Inorganic Plant Nutrition, Chronica Botanica.
Jeffrey: The Anatomy of Woody Plants, University of Chicago Press.
Maximov: The Plant in Relation to Water, The Macmillan Co.
Meyer and Anderson: Plant Physiology, D. Van Nostrand Co., Inc.
Miller: Plant Physiology, McGraw-Hill Book Co., Inc. '

Mitchell and Marsh : Growth Regulators, University of Chicago Press. j

Pool: Flowers and Flowering Plants, McGraw-Hill Book Co., Inc. J

Russel: Soil Conditions and Plant Growth, Longmans, Green & Co.
Schopfer: Plants and Vitamins, Chronica Botanica.
Seifriz: The Physiology of Plants, John Wiley & Sons, Inc.

Sharp: Fundamentals of Cytology, McGraw-Hill Book Co., Inc. - .

Skene: The Biology of Flowering Plants, The Macmillan Co.
Went and Thimann: Phytohormones, The Macmillan Co.
Wodehouse: Pollen Grains, McGraw-Hill Book Co., Inc.

Chapter 16

ECONOMIC IMPORTANCE OF PLANTS

Naturally, not all plants of economic importance or the economic
importance of all plants listed can be fully considered in one chapter.
Economic importance is considered from the beneficial as well as the
detrimental standpoint. Certain phases of economic biology are also
considered in the chapter on Applied Biology. Greater emphasis con-
stantly is being placed on the economic importance of both animals and
plants in everyday life. Consequently, a consideration of a few repre-
sentative phases in courses in biology is essential. The following de-
scriptions are representative but by no means complete. For more
detailed discussions the reader is referred to books on economic botany.

I. ECONOMIC IMPORTANCE OF ALGAE (Figs. 29 to 33)

Certain blue-green algae (phylum Cyanophyta) may become so abun-
dant in fresh water as to produce a distinct color, the so-called "water
bloom." When they die and decay, they may give the water a very
unpleasant taste and odor. Cattle have been known to die by drinking
water in which they were very abundant. The larger brown algae
(phylum Phaeophyta) are a source of such materials as iodine and
potash. The red algae (phylum Rhodophyta) are sources of agar-agar
which is used as a medium for the cultivation of bacteria as well as for
a medicine. A jellylike food is obtained from the red alga known as
"Irish moss." Certain types of red algae become encrusted with lime
and thus help in the formation of the so-called "coral" reefs, atolls, and
islands.

Because of their toughness, certain algae when dried are used in mak-
ing fishing lines, handles for tools, and similar objects. Certain seaweeds
(algae) as well as diatoms (phylum Chrysophyta) are used by various
animals for foods.

249

250 Plant Biology

Fossil diatoms form "diatomaceous earth" which forms the basis of
many scouring or cleaning materials, such as metal polishers and tooth
pastes. Certain diatoms, because of their fine, regular markings, are
used as test objects for calibrating microscope lenses. Diatomaceous
earth is also used as a heat-insulating material. It may also be molded
into hollow cylinders or "bougies" used in making bacteriologic filters.
Dynamite is made by absorbing nitroglycerin in diatomaceous earth.

II. ECONOMIC IMPORTANCE OF FUNGI (Figs. 34 to 42)

Fungi by their growth in foods, clothing, and lumber frequently de-
stroy them or diminish their values. One of the principal wood-rotting
fungi (Merulius lacrymans) attacks wood at rather low temperatures,
about 15° C. These fungi do not thrive in water or water-logged soils
because they are aerobic. Decay of wood thus occurs most rapidly near
the ground- or water-line. Heartwoods are generally more resistant than
sapwoods. Certain fungi, including bacteria, help in the necessary and
desirable decay of plant and animal remains, thus removing them from
the water and soil and rendering their constituents again available for
use by future living organisms.

Certain types of mushrooms (class Basidiomycetes) are used as human
foods. Several species are extremely poisonous and cause severe illness
or death when eaten. Great care should be taken in the selection and
use of mushrooms. Unless the collector is absolutely certain the species
is nonpoisonous, he should discard it. In case of doubt, the specimens
in question should be discarded. The flavors which are characteristic of
certain cheeses are produced by specific fungi. The characteristic odors
and tastes of Roquefort cheese and Camembert cheese are produced by
the molds Penicillium roqueforti and Penicillium camemherti, respec-
tively (Fig. 39).

Penicillium notatum, Aspergillus sp. (Fig. 73), and numerous other
fungi produce penicillin and other antibiotic substances successfully used
in the treatment of many diseases. Recent discovery of the remarkable
curative values of penicillin and other antibiotic substances has stimu-
lated great interest in the entire field of chemotherapy. In 1877, Pasteur
and Joubert discovered that certain airborne organisms inhibited the
growth of anthrax bacilli, and they suggested that antibiotics might be
utilized in the treatment of certain infections. Dr. Alexander Fleming
in London (1929), observing a plate culture of Staphylococcus organ-

Economic Importance of Plants 251

isms, noted the presence of a contaminating mold colony (Penicillium
notatum) (Fig. 73) and noted that the Staphylococcus organisms sur-
rounding the mold colony were undergoing lysis (destruction). Thus
began the steps to obtain, cultivate, and purify the most remarkable
chemical therapeutic agent for the treatment of certain types of bacterial
infections. The progress made in the production and use of penicillin
has been so great and fast that one can only guess of the possibilities of
the future. Some of the characteristics of penicillin are as follows: it is
a light brown powder (as now used) ; appears to be virtually nontoxic
in doses required for therapeutic purposes; is highly selective in its
action, being capable of destroying certain bacteria without injury to
body cells; is highly soluble in water or saline solution; is stable to light
but is affected by heat; when administered, it is rapidly excreted in the
urine; is highly successful in the treatment of many diseases which here-
tofore have been difficult to treat.

Fig. 73. — Two common fungi, (A) Penicillium sp. and (B) Aspergillus sp.,
which produce penicillin and other antibiotic substances used in the treatment of
numerous diseases.

In spite of the wide and successful use of penicillin, scientific workers
are still attempting to discover other antibiotic substances which may be
equally satisfactory. In fact, dozens of antibiotic substances are known
to be produced by molds, bacteria, actinomyces, a certain unicellular
Alga (Chlorella sp.), certain weeds and flowering plants, soybean flour,
common garlic, etc. All of them are being tested, and some show great
promise.

252 Platit Biology

Certain fungi kill insects which are harmful to man. Certain species
of bacteria attack insects and may produce illness and cause death, al-
though their specific pathogenicity has not been definitely proved. Bac-
teria and fungi aid in insect decay after death, thus returning their
chemical constituents to the soil to be used by future organisms. A few
species of slime molds (phylum Myxomycophyta) are parasites on living
seed plants (Fig. 35).

There are two principal groups of yeasts: (1) the Saccharomyces
(sugar fungi), which are harmless (Fig. 37) and (2) the Blastomyces
(germ fungi), which are pathogenic. The harmless yeasts are of great
importance in connection with the manufacture of wines and beers and
in other industries which depend upon the fermentation of sugars and
similar substances. The most common fermentation which yeasts are
able to produce is the so-called alcoholic fermentation in which sugars
are attacked, with the formation of ethyl alcohol and carbon dioxide.
The various species of saccharomyces are able to ferment various sugars
and related substances, forming a large number of end products, many
of which are useful in industrial processes. The familiar "yeast cake"
is composed of yeast cells mixed with a small quantity of starch. When
harmless yeasts are added to bread dough, the cells multiply rapidly (if
proper temperature exists) and ferment the sugars, thus giving ofT car-
bon dioxide. This harmless gas escapes through the dough and causes
it to "rise." The gas leaves countless small holes which make the bread
porous and light.

Certain fungi cause great economic losses by producing diseases of
higher plants. A few representative examples are the white rust of
radish, mustard, cress, and related plants; the chestnut blight, a fungus
disease which has exterminated practically all our chestnut trees; corn
smut; wheat rust; potato scab, which renders the skin of potatoes rough
and unsightly; the ergot of rye, in which the fungus, Ergot (Claviceps
purpurea) parasitizes the rye, resulting in poisonous, hypertrophied
grains. Epidemics of ergotism have been frequent in the past, but mod-
ern methods of cleaning have eliminated it to a great extent. The ergot
is a high-priced drug of high medicinal value.

Certain pathogenic fungi cause diseases in man and other animals.
The following are rather common, representative types: (A) The patho-
genic yeastlike fungus (Blastomyces dermatitidis) (Fig. 74, A) produces
a chronic infection known as North American blastomycosis (Gilchrist' si

Economic Importance of Plants 253

disease) characterized by suppurative and granulomatous lesions any-
where in the body but especially in the skin, lungs, and bone. The causal
organism is a spherical, budding, yeastlike fungus. (B) The pathogenic
yeastlike fungus (Candida [Monilia] albicans) (Fig. 74, B) causes a
great variety of acute or subacute infections known as moniliasis in which
lesions may be present in the mouth, skin, vagina, nails, or lungs, and
even a septicemia, endocarditis, or meningitis. When the mouth is in-
fected there are produced creamy-white patches of ulcers, and this dis-
ease is called thrush. The causal organism is a budding, yeastlike,
mycelium-producing, nonascospore-forming, fungus. (C) The patho-
genic fungus (Coccidioides immitis) (Fig. 74, C) causes a very common

Fig. 74. — Pathogenic fungi, not drawn to scale and somewhat diagrammatic.
A, Blastomyces dermatitidis, showing yeastlike budding cells; B, Candida (Monilia)
albicans, showing yeastlike cells and hyphae; C, Coccidioides immitis, showing
branching hyphae segmented into thick-wailed arthrospores, and a thick-walled
spherical structure (upper right) filled with endospores ; D, Sporotrichum schenckii,
showing branching, segmented hyphae with clusters of terminal conidia; E, Epi-
dermophyton floccosum, showing hyphae with clavate, multiseptate macroconidia;

F, Trichophyton sp., showing hyphae with numerous single-celled microconidia;

G, Microsporum sp., showing hyphae with large multicellular macroconidia
(above) and small, unicellular microconidia (below) ; H, Actinomyces bovis,
showing delicate, branching filaments, very much like those of certain bacteria
such as Mycobacterium tuberculosis. (From various sources.)

infectious disease known as Coccidioidomycosis which may be of two
types: (1) primary (usually acute but benign self-limited respiratory
infection) and (2) progressive (chronic malignant infection involving
the skin, internal organs, or bones) . The causal organism is a fungus

254 Plant Biology

whose hyphae are septate and branched and break into numerous rec-
tangular or oval, thick-walled, infectious arthrospores. In lesions, how-
ever, C. immitis may appear as a spherical, thick-walled, nonbudding
structure filled with numerous small endospores which reproduce the
fungus within the tissues. (D) The pathogenic fungus (Sporotrichum
schenckii) (Fig. 74, D) causes a chronic infection known as sporotricho-
sis characterized by the formation (in skin, lymph nodes) of nodular
lesions which soften and break to form ulcers. The causal oroanism is
a fungus whose hyphae are septate and branched and bear oval or pyri-
form (pear-shaped) conidia laterally or in groups at the ends of the
lateral branches. (E) Several species of fungi, known collectively as
dermatophytes, produce infectious skin diseases known as dermatomy-
coses. The specific clinical symptoms and the causal organism vary with
the particular disease as shown by the following: (1) "Athlete's foot''
(Tinea pedis, ringworm of the feet) is a world-wide infection of the skin
of the feet (especially soles and between toes) caused by such fungi as
Epidermophyton floccosum (Fig. 74, E) or various species of Tricho-
phyton (Fig. 74, F) . Epidermophyton hyphae bear the characteristic,
large, clavate (club-shaped), multiseptate conidia and Trichophyton
hyphae bear numerous, single-celled, thin-walled, oval or clavate conidia
(singly or in clusters). (2) Tinea corporis (ringworm of the body) is
an infection of the skin of the body caused by various species of the
fungi, Trichophyton (Fig. 74, F) or Microsporum (Fig. 74, G), and is
characterized by simple, or granulomatous lesions. Microsporum is com-
posed of hyphae with (a) large, multicellular, thick-walled, rough,
spindle-shaped macroconidia, and (b) small single-celled, clavate micro-
conidia borne on the sides of the hyphae. (3) Tinea capitis (ringworm
of the scalp) is a world-wide infection of the scalp and hair caused by
various species of fungi. Trichophyton (Fig. 74, F) or Microsporum
(Fig. 74, G), and is characterized by scaly, red lesions, and sometimes
deep ulcerative lesions. (F) The pathogenic fungi (Actinomyces hovis)
(Fig. 74, H) and several species of Nocardia cause a chronic, world-wide,
systemic infection called actinomycosis or lumpy jaw, and is character-
ized by granulomatous lesions tending to break down and form abscesses
which drain through multiple openings. The causal fungus, Actinomyces
hovis (Fig. 74, //), is anaerobic, closely related to the bacteria, and com-
posed of tangled masses of delicate, branching hyphae, while the species
of actinomycetes belonging to the genus Nocardia are aerobic and may
be inhaled with dust, straw, and other materials.

Economic Importance of Plants 255

About 150 species of bacteria (phylum Schizomycophyta) are directly
or indirectly responsible for human diseases. The following are a few
common, representative human diseases of bacterial origin (Fig. 34) :

Boils, carbuncles, abscesses, etc.

Internal and general infections

Many cases of "sore throat"

Erysipelas

Scarlet fever

Meningitis

Gonorrhea

Pneumonia

Anthrax or splenic fever

Diphtheria

Typhoid fever

Paratyphoid fevers

Tuberculosis

Leprosy

Malta or undulant fever

Plague or "black death"

Tularemia or "rabbit disease"

Whooping cough

Tetanus or "lockjaw"

Gaseous gangrene

Botulism (toxic food poisoning)

Staphylococcus aureus
Streptococcus pyogenes
Streptococcus hemolyticus
Streptococcus erysipelatis
Streptococcus scarlatinae
Diplococcus intracellularis
Neisseria gonorrhea
Diplococcus pneumoniae
Bacillus anthracis
Corynebacterium diphtheriae
Eberthella typhosa
Salmonella paratyphi (Type A)
Salmonella schottmiilleri (Type B)
Salmonella hirschfeldii (Type C)
Mycobacterium tuberculosis
Mycobacterium leprae
Brucella melitensis
Pasteurella pestis
Pasteurella tularense
Hemophilus pertussis
Clostridium tetani
Clostridium welchii and others
Clostridium botulinum

From the consideration given above, one might imagine that all bac-
teria are harmful. This is not the case. Most bacterial organisms are
neither harmful nor beneficial; less than three hundred have been spe-
cifically proved pathogenic, and an ever-increasing number is found to
be very beneficial in many ways. Bacteria are valuable in decomposing
plant and animal remains so that the original constituents may again
be used by future living organisms. Bacteria arc also employed in the
process of tobacco curing as well as in the retting process followed in
the preparation of flax for industrial purposes. Certain species of bac-
teria play an important role in the fermentation of sauerkraut, giving it
the characteristic odor and flavor. Other species of bacteria are bene-
ficially associated in the manufacture of butter, cottage cheese, and
other cheeses. Specific bacteria are responsible for the use of free nitro-
gen of the air by the plants of the legume family. This is more fully
discussed in the nitrogen cycle. Other organisms are also associated
with other nitrogen transformations in the soil. The manufacture of
vinegar is also dependent upon the fermentation of certain juices by
acetic acid bacteria. It is thought that bacteria, and possibly other
microorganisms, are responsible for the decomposition of the remains of
organisms with the formation of crude oil and natural gas. It is also

256 Plant Biology

stated that certain specific kinds of bacteria are necessary for the desirable
decomposition of waste materials in the human large intestine. Naturally,
not all types would be desirable for this important work. If the bac-
terial flora of the large intestine is not normal, there may result a variety
of abnormal conditions.

III. ECONOMIC IMPORTANCE OF BRYOPHYTES

(Figs. 43 to 46)

Peat mass (Sphagnum) (Fig. 46) is used for packing materials in ship-
ping, in surgical dressings, in gardening, and similar ways. In gardening
the peat moss retains soil moisture and prevents weed growth. One
species of sphagnum can absorb approximately twenty times its weight of
water. Certain kinds of coal were formed by an accumulation of the re-
mains of sphagnum mosses in swamps and open waters of past ages. Peat
is formed by sphagnum moss and, when dried, is used as fuel in certain
communities where other materials are not available. A few species of
bryophytes are the sources of certain chemicals and medicines. Undoubt-
edly certain bryophytes are of some importance in the destruction of
rock into soil. They may also aid in preventing soil waste by erosion.
As compared with other phyla of plants, bryophytes are of small eco-
nomic importance to man.

IV. ECONOMIC IMPORTANCE OF FERNS AND
THEIR ALLIES (Figs. 50 and 51)

The larger roots of certain species of ferns contain considerable
starch and are consequently used as food. Certain species of ferns con-
tain a substance known as coumarin which is used in making certain
perfumes. Other ferns contain such chemicals as tannin, aconitic acid,
or ethereal oils which may be used for commercial purposes. Ferns
have been used in the preparation of certain medicines. Certain varie-
ties of ferns produce stock poisoning when eaten by domestic animals.
The horsetails or scouring rushes (Equisetum sp.) (Fig. 49) may be
used for scouring or polishing purposes. The growing of these plants
along certain slopes of land may prevent soil erosion. The presence of
horsetails along the edges of swamps may help in the transformation of
the swamp into a marshlike area by retaining soil particles around them.
They add to the land area in this manner at the expense of the water
area.

Certain tropical club "mosses" are used for medicinal purposes. The
spores of certain club "mosses" (Lycopodium clavatum) (Fig. 47) because

Economic Importance of Plants 257

of their oil content, are used in the manufacture of burning flashlights
as well as certain kinds of dusting powders. The spores of certain club
"mosses" or "ground pines" are very inflammable, for which reason they
are used in fireworks under the name of vegetable sulfur. Certain types of
coal were deposited in past ages through the carbonized remains of cer-
tain treelike club "mosses," scouring rushes, and primitive seed plants. In
general, the ferns and their allies are of small economic importance to-
day, although at one time they dominated the vegetation of the earth.

V. ECONOMIC IMPORTANCE OF GYMNOSPERMS

(Figs. 52 to 54)

The cone-bearing trees, known as conifers, are ranked high in the
production of valuable timber, as is verified by the use of yellow pines,
redwoods, pitch pines, firs, cedars, hemlocks, and white pines. In 1930
over 7,500,000,000 board feet of yellow pine alone were cut in the
United States. Pine lumber is one of the most valuable and widely used
kinds because it is durable due to its composition, it is easily worked,
and it is quite resistant to the attacks of insects, probably because of its
resin content. Certain conifers are used extensively in the manufacture
of wood pulp. Red cedars are used in making pencils, cigar boxes,
chests, trunks, and posts. Conifers yield large quantities of resins, oils,
and amber products used in arts, industries, and medicine. Examples
are turpentine, balsam, spruce gum (for chewing gum), oil of juniper,
and oil of savin. Certain species of pine provide edible seeds used by
human beings for foods. The edible or nut pine of western United
States and the sugar pine of California are examples. The barks of such
conifers as hemlock and spruce furnish important materials for use in
the tanning of skins of animals for leather. Thousands of youngsters,
and probably as many adults, are made happy at Christmas time by the
decorated conifers. This use of conifers for this purpose has become so
extensive that the cultivation of desirable types has become necessary in
order to supply the ever-increasing demands. The wood of spruce trees
is particularly resonant so that it is used in making certain types of
musical instruments. The remains of conifers are often found as fossils
and as fossil-resin amber in which other fossils may have been imbedded.

VI. INDUSTRIAL PLANTS

Industrial plants may be considered as those which yield materials
used in such industries and arts as spinning, weaving, dyeing, painting,
paper making, building, tanning, sculpture, carving, manufacture of
foods, medicines, etc.

258 Plant Biology

Of the immense number of plants more or less important to man,
only a few which yield such products and materials as fuels, oils, plant
fibers, cork, woods, gums and resins, dyes or coloring materials, foods,
beverages, flavoring substances, spices, savory substances, medicines and
poisons will be considered.

Fuels. — A fuel may be defined as a plant substance which has stored
the energy of the sun during its life and releases it upon burning or
combustion.

Wood (when perfectly dry) consists of nearly 99 per cent combustible
materials and 1 per cent inorganic matter, which remains as ash when
burned. An increase in the water content of wood reduces its fuel
value by taking the place of combustible material and also by using
some of the heat produced to evaporate the water. Wood is the most
widely used of all plant fuels.

Peat is a deposit of more or less carbonized plant substances which
have accumulated and decomposed under pressure in wet marshes and
bogs. Peat is a useful and efficient fuel in regions where coal is scarce.
When buried a long time, the peat may resemble a soft brown coal.

Coal is the remains of ancient and extinct plants so changed under
pressure that the resulting material is much harder and more completely
reduced to carbon than peat. Coal has much more heating power than
peat or wood.

Charcoal, which is nearly pure carbon, is made by burning wood in a
minimum of oxygen, usually by burning piles of wood in mounds cov-
ered with earth. Charcoal is mixed with sulfur and saltpeter to make
gunpowder. It is also used in making charcoal drawings and for a great
variety of other purposes.

Coke, which is nearly pure carbon, is made by burning coal in a
minimum of oxygen, usually by covering piles of burning coal, or in
special coke ovens. Coke produces very little smoke.

Artificial gas is made by subjecting wood or coal to a high tempera-
ture and collecting and purifying the gases evolved. This gas is used in
communities where natural gas is not available.

Natural gas is the product of plant decomposition in which there is
produced a gas, the important constituent of which is methane (CH4).
It is used to a great extent for heating and cooking purposes, being
transported many miles from "gas wells" to the consumer. This gas is
usually formed under great pressure and rapidly and forcefully comes
to the surface when a gas "pocket" is tapped by drilling.

Economic Importance of Plants 259

Petroleum or crude oil is a dark-brown or yellowish-green inflam-
mable liquid formed by the partial decay of organic ooze (foraminifera,
diatoms, algae, etc.) by bacterial action, thus liberating fats and waxes
to produce petroleum.

Kerosene is an inflammable liquid obtained by the distillation and
purification of petroleum. It is used for heating, lighting, and cooking
purposes where gases are not available.

Gasoline is a volatile and highly inflammable liquid obtained by the
distillation and purification of petroleum. Its principal use is for motor
fuel.

Oils. — Oils are very generally present in the plant kingdom as either
volatile or fixed oils. Generally speaking, the volatile oils easily and
quickly vaporize at ordinary temperatures, while the fixed oils do not.
The fixed oils are chemical mixtures in various proportions of glycerides
(glycerine and an acid). Examples of the volatile oils are oil of winter-
green, oil of cloves, oil of peppermint, etc. Examples of fixed oils are
oil of almonds, peanut oil, olive oil, etc.

Plant oils are used (1) in flavoring materials, (2) as foods, (3) as
medicines, (4) in industries in the manufacture of paints, printing inks,
soaps, perfumery, lubricants, illuminants, etc.

Certain fixed oils are used to hold particles of coloring matter in sus-
pension in paints. The oil permits the even application of the paint and
its prompt hardening through the process of oxidation. Linseed oil,
which is pressed from the seeds of flax, is an excellent "drying" oil
whose properties may be improved by boiling (boiled linseed oil). For
fine paints, such oils as nut oil (from nuts of English walnut) and
poppy oil (from seeds of opium poppy) may be superior to linseed oils.
In certain printing inks the linseed oil is boiled until it is very thick.
Linseed oil is used extensively when united with resins to make varnish.

Any fixed oil with its contained glyceride (glycerine plus an acid)
when combined with an alkali will form a soap. In this process the
glycerine is given off" as a by-product. A fixed oil plus potash or lye
forms a "soft" soap. A fixed oil plus soda forms a "hard" soap.

As lubricants, only fixed oils which are nondrying can be used. The
oil must be thin enough to penetrate to all parts and at the ^ame time
have a consistency which will withstand high temperatures and friction.
Examples of such oils are crude oils, motor oils (refined crude oils),
castor oil (from castor bean), olive oil, cotton-seed oil, rape oil (from
certain varieties of turnip).

260 Plant Biology

As illumlnants, the fixed, nondrying oils serve best. Illuminating oils
must volatilize but not too quickly; they must be inflammable but not
dangerous or explosive. Among the illuminating oils are crude oils,
kerosene, olive oil, peanut oil, rape oil, etc.

Plant Fibers. — Plants which produce fibers have contributed greatly
to the advancement of civilization, and plants providing foods have
been the most useful of all plants.

Plant fibers as well as animal fibers and skins have been utilized since
prehistoric times for clothing, baskets, fish lines, bowstrings, snares, nets,
etc. More recently such materials have been utilized for making brushes,
paper, cellulose products, cordage, mattings, wickerwork, fabrics, pack-
ings, awnings, tapes, laces, straw hats, etc.

Cotton fibers cover the seeds of several species of cotton plants. These
fibers are separated from the seeds by the machine known as the cotton
gin. These fibers are then cleaned, combed, and spun into threads. The
latter are woven into fabrics. The cleaned cotton fibers, when rolled
into sheets, are known as cotton batting. The cotton fibers in the raw
state are more or less covered with an oil which repels water. When
this oil is removed, the end product is known as absorbent cotton. Ab-
sorbent cotton plus nitric acid plus sulfuric acid produces nitrocellulose
(guncotton). Nitrocellulose dissolved in alcohol and ether forms col-
lodion. Collodion when forced through fine openings into running
water hardens into silklike fibers.

Flax fibers are practically pure cellulose which is obtained from the
stems of the flax plant by a process of retting or rotting. These fibers
are strong and fine and are used widely in making fine lace, linen, duck,
canvas, and better qualities of paper. The retting process is a decom-
position process due to the action of certain species of bacteria.

Hemp fibers, secured from the hemp plant, are coarser, longer, and
stronger than flax and are used in making rope, twine, sailcloth, bags,
and similar coarse fabrics.

Jute fibers are obtained from plants (linden family) closely related to
flax, but the fibers are not so strong or durable and contain less cellulose.
They are used in making burlap, bags, and similar coarse fabrics.

Manila hemp fibers are coarse and fine fibers obtained from the edge
of the fleshy leaf stalks of the Manila hemp plant (banana family).
The principal source is from the Philippine Islands. The fibers are
much stronger than those of ordinary hemp and are used in making
bags, mats, sailcloth, Manila paper, and similar materials.

Economic Importance of Plants 261

Straw, which is the stalk, leaves, etc., of wheat, oats, rye, barley, and
rice, is used for making hats, mats, baskets, paper, pasteboard, etc.

The ripened branches of the flower cluster of broom corn (grass fam-
ily) yields a flexible, tough material from which various kinds of brooms
are made.

The fibers split from the stems of rattan (palm family) are called reeds
and are used in making baskets, cane seats, wickerware, coarse brushes,
etc. The stems of the bamboo (grass family) are used quite extensively
for various purposes. The fibers from the leaves and nut husks of the
coconut palm (palm family) are used in the manufacture of door mats,
cables, etc. Punk is a mass of slender fibers found within the rind of
certain shelf fungi. It is used to stop bleeding in dentistry, as tinder to
kindle fires, for making mats, etc.

Cork. — Cork is a light, compressible, nonfibrous, waterproof mate-
rial secured from the outer bark of the cork oak (beech family). It
contains about 75 per cent of a tallowlike, waxy substance known as
suberin. The pores of the cork are channels through which air may
enter the plant. The cork grows in layers, and unless the outer lay-
ers are carefully removed at certain intervals, the product is inferior.
Slabs of cork of various thickness may be removed about every eight
years, with the result that abundant quantities of homogeneous cork are
obtained. The removal of this cork does not injure the tree; in fact, re-
moval seems to be beneficial to it. There are many uses for cork, but
the following are typical: floor coverings, lining for shoes and hats, stop-
pers, packing for fruits, and the making of artificial limbs, life preservers
and fish-net floats.

Woods. — Wood is a comparatively hard mass of fibrous material
cemented together and contains, in addition to the common substance
cellulose, more or less of the substance lignin. The lignin is of unknown
chemical composition, although it is similar to cellulose. The cellulose
is distinguished from lignin by turning blue instead of yellow when
treated with sulfuric acid and iodine.

The texture, strength, durability, and hardness of woods depend on
the arrangement of the various materials of which the diff"erent varieties
are composed.

The following are a few typical and representative uses of wood:
wood pulp from certain trees, such as poplar and spruce, is used in the
manufacture of paper; certain woods as spruce and white pine are
shredded into excelsior; splints split from such hard woods as hickory
and ash, which split easily, are used in making baskets and similar ob-

262 Plant Biology

jects; houses and roofs; furniture and musical instruments; ships and
canoes; barrels and casks; vehicles; road materials; railroad ties; poles,
piling, and posts; industrial implements and tools; recreational equip-
ment; toys, canes, pencils, matches, toothpicks, clothespins, etc.

The woods of many trees are of two kinds: sap wood and heart wood.

The sap wood is formed in certain trees next to the bark in succes-
sive layers as new wood. It conducts sap and consequently is called sap
wood. Some of the plant foods are stored in this kind of wood. It is
usually more massive and resistant in larger trees.

Sap wood after a certain time becomes stronger, more compact, and
somewhat drier. It no longer carries sap and is known as heart wood.
It differs in color from the sap wood because of the stored, useless plant
by-products. This color of heart wood frequently makes it more desir-
able for manufacturing purposes.

Gums and Resins. — The two most common elastic gums are India
rubber or caoutchouc (pronounced koo'chuk) and gutta-percha. Both
are tough, waterproof, somewhat elastic solids which separate as a curd
from the milky juices of a number of tropical plants and of several of
our native plants, particularly goldenrod. It becomes hard when dried
or heated. The principal source is the Brazilian rubber tree (spurge
family) .

Rubber was early used to rub out pencil marks; hence the name rub-
ber; the India part of the name was derived from the fact that it was
imported from the West Indies.

Rubber has a great variety of uses, among which are manufacture of
boats, overshoes, waterproof garments, tires, bands, toys, bottles, cushions,
insulators, fountain pens, etc.

The quality of rubber was improved by Charles Goodyear in 1844 by
adding sulfur to the caoutchouc and subjecting the mixture to consider-
able heat. This process was known as vulcanization. When a large
amount of sulfur is added to caoutchouc, a hard rubber known as vul-
canite is produced.

Gutta-percha difTers from India rubber in being more firm and rather
inelastic below 50° C. Like caoutchouc, it is flexible, tough, a poor con-
ductor of electricity and heat, and impervious to moisture. It is obtained
from juices by tapping several dififerent species of trees closely related to
the taban tree (sapodilla family). It is similar in chemical composition
to caoutchouc in that they both contain hydrogen and carbon. Gutta-
percha contains in addition certain resinous substances which are formed

Economic Importance of Plants 263

by oxidation. Gutta-percha is used in making surgical instruments, orna-
ments, golf balls, coverings of cables, tubes, etc.

Resins are like the elastic gums in that they are secured from certain
plants by tapping them for their juices. Resins are mixtures of several
different oxidized hydrocarbons (hydrogen and carbon). They are
inflammable, insoluble in water, usually liquids which harden when
oxidized. The common resin is obtained from the pitch or resinous sap
of pine trees. Sometimes a gum and resin are united as a gum resin,
such as asafetida. Resinous materials of various types are common in
many plants. Two common examples are rosin and copal. Rosin is the
most widely used of resinous materials. It is one of the products which
remain when turpentine is distilled. Turpentine flows from the pine
and other cone-bearing trees. Rosin is used in the manufacture of var-
nish, yellow soap, certain cements, sealing wax, cheap candles, certain
medicinal ointments, etc. Copal is the name applied to a large variety of
resins which occur naturally in hard, amberlike masses. Corpal is used
in the manufacture of certain types of varnish. Amber is a yellowish,
translucent, fossilized resin resembling copal. It is used in the manufac-
ture of pipe stems, amber beads, and certain types of varnish. When
polished by friction, it becomes highly electric.

Coloring Matters (Dyes). — Coloring matters of various kinds are
quite common in the plant kingdom but often of questionable or un-
known benefit to the plant which produces them, in which case they are
probably waste products of their metabolic activity.

Indigo blue (CieHioNsOo) was first used in India many hundreds of
years ago and is derived from indican (C26H31NO17), an aqueous extract
from the leaves of the indigo plant (pulse family) .

Haematin (CieHisOe) is a violet -purple dye derived from the color-
less material haematoxylin (C16H14O6) obtained from the logwood tree
(pulse family) .

Gamboge is a resinous, gummy material secured from the bark of
various species of gamboge trees (gamboge family). When solidified,
the bright, transparent, yellowish material is used as a coloring material
in lacquers, varnishes, and certain paints.

Tanbark is obtained from the bark of such trees as chestnut, oak,
willow, spruce, hemlock, and larch. The bark is rich in tannin
(C14H10O9 + 2HoO), which is used in medicine, in dyeing, and in the
manufacture of ink and leather. In the preparation of skins by the

264 Plant Biology

process of tanning, the tannic acid combines with the skins of animals
to render them soft, pliable, and useful.

Foods. — Foods may be defined as chemical substances which, when
taken into an animal body, supply energy, help build body materials, or
regulate metabolic processes. Vitamins are of the latter group and the
various types are quite well represented in the plant kingdom. In fact,
our chief natural sources of the various types of vitamins depend directly
and indirectly on plant materials.

Of the great varieties of foods, only the following will be considered
briefly: cereals, nuts, legumes, vegetables, and fruits.

The cereals most commonly used are corn, wheat, oats, rice, barley,
rye, and buckwheat. Corn (Figs. 58 to 60), which was originally grown
principally for food, has become the basis of a large number of com-
mercial products such as corn syrup, corn starch, corn oil, dextrine (for
pastes), and cellulose for paper pulp and building materials (from stalks
and husks). The hulls of oats contribute an important chemical solvent
known as furfural, from which plastic materials used in manufacturing
phonograph records, etc., are made.

Nuts are edible kernels protected by shells. Among the more common
are birch family (filbert or hazelnut), beech family (chestnut), walnut
family (black walnut, butternut, or white walnut, hickory nut, pecan,
etc.), myrtle family (Brazil nut), palm family (coconut).

Among the various legumes used for food are pulse family (garden
peas, garden beans (Figs. 55 and 56), lima beans, etc.)

Among the common vegetables are nightshade family (white potato),
morning-glory family (sweet potato), sunflower family (artichoke, let-
tuce, etc.), parsley family (celery), goosefoot family (spinach), lily fam-
ily (onion, asparagus, etc.), mustard family (cabbage, cauliflower, kohl-
rabi, Brussels sprouts, etc.)

Some of the common fruits are gourd family (pumpkin), nightshade
family (tomato, egg plant), rose family (apples, pears, quinces, plums,
cherries, raspberries, etc.)

Beverages. — Coffee (Coffea arahica) is obtained from green, oblong
berries which grow on an evergreen plant. The plant grows to a height
of 20 feet but usually is pruned to 6 or 8 feet in order to secure uniform
flavor and ripeness, as well as to make it easier to harvest. The plants
bear when four years of age. The plants produce a great number of
white flowers with a jasmine-like fragrance which rivals that of an orange
blossom. The flowers produce the green berries, which develop in six

Economic Importance of Plants 265

months into bright red berrylike cherries. When ripe, their color is dark
red. The coffee "cherries" each contain two seeds of coffee beans with
their flat sides face to face. The three coverings are removed in the prep-
aration process. These evergreen coffee plants grow at high altitudes
(lj500 to 6j000 feet above sea level) . One tree yields from one to twelve
pounds, depending on its size. The coffee plant is indigenous to Eastern
Africa and is cultivated in tropical countries, such as Brazil, Central
America, Java, Sumatra, and Ceylon. Coffee was probably first used
in Arabia or Abyssinia in the ninth century. The Arabians called it
"kawah" from which the names kaffee and coffee eventually were de-
rived. By 1696 it had reached the island of Java which was destined to
continue its contribution for many years. In fact, even today some say
a "cup of Java" instead of a "cup of coffee."

When dried, ground, and boiled, the coffee beans contain 1 to 2 per
cent of a crystalline alkaloid known as caffeine which acts as a poison
when taken in larger doses. They also contain from 3 to 5 per cent of
tannin, 10 to 12 per cent of fatty oils (palmitin and olein), 15 per cent of
glucose and dextrin, 12 per cent of proteins. The aroma is due to a
volatile oil known as coffeol which is developed during the roasting
process.

Tea is made by steeping the dried leaves of the tea plant {Thea sinen-
sis) which is an evergreen shrub or tree indigenous to Eastern Asia and
extensively cultivated in China, Japan, Java, Brazil, France, and to some
extent in the southern United States. The dried leaves contain from
1 to 3 per cent of the crystalline alkaloid theine and 10 per cent of the
astringent tannin. The flavor is due to a volatile oil developed during
the curing process.

Cocoa is prepared from a dark-brown powder which is obtained from
the seeds of the small tree Theobroma cacao. The fruit is large, fleshy,
yellowish-red, ovoid, and contains five rows of ovoid seeds, ten or twelve
in each row. The seeds contain from 1 to 3 per cent theobromine (a
crystalline alkaloid), 15 per cent proteins, 15 per cent starch, 40 to 50
per cent of a fixed oil known as cacao butter, 0.3 per cent caffeine, 0.5
per cent sugar, and a red color due to the process of fermentation. The
aroma of cacao arises during the process of fermentation. The flavor is
mild, and frequently spices and vanilla are added to make chocolate.

The cacao tree is indigenous to the countries on the Gulf of Mexico
and is cultivated in several tropical countries. The raw seeds are bitter;
a great part of the bitterness is eliminated by the process of fermentation
to which the seeds are subjected in preparing them for use.

266 Plant Biology

Alcoholic beverages are made by the fermentation action of certain
yeasts and bacteria on the sugars in the grains, flowers, berries, or fruits
of various plants. The alcoholic content of the so-called spirituous
liquors (whisky, gin, brandy, rum) is much higher (40 to 60 per cent)
than that of beer and wine and they are made by a process of distilla-
tion. Whisky is distilled from liquors made from corn, rye, or wheat.
Gin is distilled from beer made from the above grains, to which a flavor
(usually the volatile oil of juniper berries) is added. Brandy is distilled
from wine. Rum is distilled from molasses.

Flavoring Substances. — Flavoring substances are extracted from plants
and are usually in liquid forms. The flavor is due to the presence of
certain volatile oils. The following will suffice to illustrate:

Vanilla is obtained from the pods of vanilla beans borne on a high-
climbing plant (Vanilla planifolia) of the orchid family. The mature,
yellow fruits are cured by alternately steaming and drying, until they
acquire the odor and dark-brown color of the commercial product.
Lemon flavor is obtained from the peel or rind of the fruit of the lemon
which yields the oil of lemon. The lemons are borne on shrublike trees
(Citrus medica, subspecies Limonia). Rose flavor is obtained from the
petals of roses. Wintergreen flavor is obtained from the leaves and fruit
of the plant Gaultheria procunibens. The leaves contain the true oil of
wintergreen, which consists almost entirely of methyl salicylate. It con-
tains alcohol and an ester orivins: the characteristic odor.

Peppermint flavor is obtained from an herb (Mentha piperita) of the
mint familv.

Spearmint flavor is obtained from the leaves and flowers of an herb
(Mentha spicata) of the mint family.

Orange flavor is obtained from the rind of the fruit of the orange tree
(Citrus aurantium). The oil contained in the rind of the fruit is known
as oil of orange peel.

Spices. — Spices are usually powdered, aromatic substances secured
from certain plants. The aroma is due to specific volatile oils which
evaporate easily, dissolve readily in alcohol, and leave no oily stain on
paper. The following list will illustrate the members of this group:

Black mustard is obtained from the seed of Brassica nigra of the
mustard family. Nutmeg is a berry obtained from the evergreen tree
Myristica jragrans of the nutmeg family. Mace is the dried, fleshy net-
work which surrounds the nutmeg seed or kernel. Ginger is obtained

Economic Importance of Plants 267

from the rootlike, underground stem of the plant Zingiber officinale of
the ginger family. Cinnamon is the young bark of the tree Cinnamo-
mum zeylanicum of the laurel family. Cloves are the dried flower buds
of the tree Carybphyllus aromaticus of the myrtle family. Red pepper
is obtained from the dried, berrylike fruits of the shrub Capsicum annum
of the nightshade family. Black pepper is obtained from the dried, un-
ripe berry of the plant Piper nigrum of the pepper family. Allspice is
obtained from the dried fruit of the evergreen tree Pimenta officinalis
of the myrtle family.

Savory Substances. — Savory substances are aromatic and are either
the herbs, seeds, or seedlike fruits of plants which possess specific volatile
oils. They are usually used whole rather than in powder form. The
following will illustrate this group:

Garden sage is the fresh or dried herb of the plant Salvia officinalis
of the mint family. Sweet marjoram is the fresh or dried herb of the
plant Originum marjorana of the mint family. Parsley (garden) is the
fresh or dried herb of the plant Petroselinum sativum of the parsley fam-
ily. Thyme is the fresh or dried herb of the plant Thymus vulgaris of the
mint family. Summer savory is secured from the fresh or dried plant
Satureia hortensis of the mint family. Caraway is the seedlike fruit of
the plant Carum carvi of the parsley family. An.ise is the seedlike fruit
of the plant Pimpinella anisum of the parsley family. Coriander is ob-
tained from the plant Coriandrum sativum of the parsley family.

Medicines and Poisons. — A medicine may be defined as any sub-
stance to prevent, relieve, or cure a disease. A poison may be defined
as any substance or agency (exclusive of injurious physical, mechanical,
or bacterial agencies) which is capable of destroying life or injuring
health when applied externally or administered in moderate doses in-
ternally.

Some plants contain certain substances which, unless taken in large
doses, are not poisonous, but on the other hand may be somewhat stimu-
lating, soothing, slightly irritating, or even more or less nutritious. Sub-
stances of this kind may be illustrated by the following: .

Castor oil is secured from the seeds of the castor oil plant (Ricinus
communis) of the spurge family. It acts as an irritant and lubricant.
Cacao butter is the fixed oil of cacao seed obtained from the plant
Theohroma cacao (silk-cotton family). It is used for soothing or lubri-
cating purposes. The oils of olives and almond may be used for the
same purposes. Asafetida is obtained by drying the juices from the roots

268 Plant Biology

of the asafetlda plant (Ferula assafoetida) of the parsley family. Asa-
fetida is an ill-smelling substance used for medical purposes and some-
times used in small quantities as flavoring for sauces and gravies.

Numerous plants produce gelatinous materials used as medicines them-
selves or used in the preparation of medicines. The following will illus-
trate a few of this type:

Gum arable is made principally from the juice of the gum arable tree
(Acacia Senegal) of the pulse family. This gum contains a carbohydrate
called arabin (C12H22O11) which has the same formula as cane sugar.
When arabin is boiled with dilute acid, the sugar, arabinose, is formed.
Gum tragacanth is made from the juice of the stem of the tragacanth
shrub {Astragalus gummifer) of the pulse family. This gum contains
a carbohydrate tragacanthin (C6H10O5). Licorice is secured from the
roots of the licorice plant (Glycyrrhiza glabra) of the pulse family.
Gelatinous materials are obtained from Irish ''moss" (Chondrus crispus)
(Fig. 33) and from Iceland "moss" (Cetraria islandica).

Certain plants contain various poisonous substances which prove
harmful when eaten. The following examples are typical:

Jimson weed or thorn apple (Datura stramonium) of the nightshade
family is quite common around farm buildings. It is sometimes mistaken
for other plants and eaten with fatal results. Indian poke (Veratrum
viride) of the lily family has been mistaken for other plants and eaten
with dangerous results. Common pokeweed (Phytolacca decandra) of
the pokeweed family is often eaten like asparagus. Unless the leaves,
roots, seeds, and fruits are thoroughly boiled in many changes of water,
death may result. Monkshood (Aconitum napellus) of the crowfoot
family is common in gardens and has produced fatal results when eaten.
Deadly water hemlock (Cicuta maculata) of the parsley family is fre-
quently confused with other plants found in swampy regions. Poison
hemlock (Conium maculatum) of the parsley family is very common
along roadsides and may prove fatal when the seeds, leaves, or roots are
eaten. The roots and bark of the elder (Samhucus canadensis) of the
honeysuckle family and the locust (Robinia pseudacacia) of the pulse
family are sometimes fatal. Every part of the Indian tobacco plant
(Lobelia inflata) of the bellflower family, which is common in pastures,
is highly poisonous. The wilted leaves and the kernels of the cherry
stones of the wild black cherry contain prussic acid, which is very dan-
gerous to man and cattle. Sheep laurel (Kalmia augustifolia) and moun-
tain laurel (Kalmia latifolia) of the heath family are among the most

Economic Importance of Plants 269

deadly of our poisonous plants. Poisonous mushrooms, such as the death
cap (Amanita phalloides) and the fly amanita (Amanita m,uscaria) , are
extremely dangerous. Unless one knows mushrooms very well, there is
a great possibility of eating the poisonous varieties.

A few poisonous drugs of plant origin may be listed as follows:
Opium is obtained from the dried, milky juice of the seed pods of the
opium poppy (Papaver somniferum) of the poppy family. Opium con-
tains numerous alkaloids and is used to induce sleep, to relieve pain, and
for certain relaxations. Morphine (C17H19NO3) is one of the most im-
portant alkaloids present in the opium poppy. Tobacco is the dried and
cured leaves of the tobacco plant. The tobacco plant of Virginia is
Nicotiana tabacum of the nightshade family. The tobacco leaves possess
an aroma which is due to a volatile substance. The chief active con-
stituent of tobacco is an alkaloid known as nicotine (C10H14N2) which
is a very potent poison. Quinine (C12H24N2O2) is an alkaloid obtained
from the bark of the calisaya tree (Cinchona calisaya) of the madder
family. Quinine is a deadly poison to the protozoan parasites which
cause malarial fever (Fig. 176). Strychnine (C21H22N2O2) is an alkaloid
obtained from the seeds of the nux vomica tree (Strychnos nux-vomica)
of the logonia family. Atropine (G17H21NO3) is an alkaloid obtained
from the roots and leaves of the belladonna plant (Atropa belladonna)
of the nightshade family. It is used in the examination of the eyes.
Cocaine (C17H21NO4) is an alkaloid secured from the dried leaves of
the coca shrub (Erythroxylon coca) of the coca family. It is used to
counteract pain. Aconitine (C33H45NO12) is the active alkaloid prin-
ciple derived from the dried tubers of the monkshood plant (Aconitum
napellus) of the crowfoot family. It is used as a cardiac and respiratory
sedative.

Certain of our plants poison the skin when they or their products
come in contact with it. The following examples are typical:

Poison ivy (Rhus toxicodendron) of the sumac family produces the
well-known effects of itching, and eruption, swelling of the skin of sus-
ceptible persons, especially women and children. Poison ivy plants may
be distinguished from other viny plants by their white fruits and three
leaflets. The poisonous principle is a fixed oil known as cardol. Poison
sumac (Rhus vernix) of the sumac family produces itching, eruption, and
swelling of the skin of susceptible persons. The active principle is a fixed
oil similar to the one in poison ivy if it is not identical. Poison sumac
plants can be distinguished from common sumacs by (1) greenish- white

270 Plant Biology

color of their drooping fruit or flower clusters, (2) their smooth twigs
and leaves, and (3) the even edges of the leaflets. The application of a
concentrated solution of sugar-of-lead in 60 per cent alcohol every few
hours is useful in poison-ivy and poison-sumac poisoning. Instead, a
strong solution of baking soda (sodium bicarbonate) may be applied as
soon after exposure as possible. Parsnip and carrot roots and herbs
affect certain persons much in the same manner as described above.
Some persons are poisoned when preparing them for eating. Certain
of our common orchids, known as yellow lady slipper (Cypripedium
parviflorum) and showy lady slipper (Cypripedium hirsutum) of the
orchid family produce symptoms similar to those described above because
of a fixed oil similar to cardol.

QUESTIONS AND TOPICS

1. What is meant by an economically important plant?

2. In which phylum are the plants of greatest economic importance? Give
proof to justify your conclusions.

3. List the various ways in which a knowledge of economically important plants
may be of value.

4. Can you think of any plants which might be improved? What methods would
you suggest for such improvements?

5. Define bacteria. Why are they classed as plants?

6. How many species of bacteria are fairly well known? What percentage of the
total is in one way or another detrimental to man? How many are beneficial
to man?

7. List the more common diseases of ( 1 ) man, (2) animals, and (3) plants which
are caused by bacteria, giving the causal organism for each disease.

8. Write an article on the so-called galls of plants, including the causes and
economic importance.

9. Give the values of a knowledge of plants in such professions as ( 1 ) medicine,
(2) dentistry, (3) horticulture, (4) agriculture, (5) landscaping, (6) forestry,

■

(7) pharmacy, (8) business, and (9) everyday living by nonprofessional
people.

10. Write an article on antibiotics, including the specific organism from which
each is derived, and including their uses in the prev^ention and treatment of
certain diseases.

11. List some important diseases produced by (1) yeasts and (2) fungi, giving
the causal agent for each disease.

SELECTED REFERENCES

Bessey: Textbook of Mycology, The Blakiston Co.

Brown, Panshin, and Forsaith: Textbook of Wood Technology, McGraw-Hill

Book Co., Inc.
Dorrance: Green Cargoes, Doubleday, Doran & Co., Inc.

Economic Importance of Plants 271

Fernald and Kinsey: Edible Wild Plants of Eastern North America, Idlewild

Press.
Heald: Introduction to Plant Pathology, McGraw-Hill Book Co., Inc.
Hill: Economic Botany, McGraw-Hill Book Co., Inc.
Horn: This Fascinating Lumber Business, Bobbs-Merrill Co., Inc.
Jones: Economic Geography, The Macmillan Co.
Peattie: Cargoes and Harvests, D. Appleton-Century Co., Inc.
Record: Identification of the Timbers of Temperate North America, John Wiley

& Sons, Inc.
Robbins: Biology of Plant Crops, The Blakiston Co.
Robbins and Ramaley: Plants Useful to Man, The Blakiston Co .
Stanford: Economic Plants, D. Appleton-Century Co., Inc.
Stevens: Plant Disease Fungi, The Macmillan Co.
Westcott: Plant Disease Handbook, D. Van Nostrand Co., Inc.
Wilson: Trees and Test Tubes, Henry Holt & Co., Inc.
Wilson et al. : New Crops for the New World, The Macmillan Co.
Wolf and Wolf: Fungi (2 vols.), John Wiley & Sons, Inc.

Part 3
ANIMAL BIOLOGY

Chapter 17

SURVEY OF THE ANIMAL KINGDOM

A detailed study of the entire animal kingdom cannot be made be-
cause there are over 800^000 species (different kinds) which are more
or less well known. Only a few species which are representative of the
various subdivisions of the animal kingdom will be considered.

In order to study representative species of the animal kingdom scien-
tifically, a system of classification must be used whereby all investigators
in all parts of the world may study the same species of animal and call
them by the same scientific name. Without scientific names and classifi-
cation, students in various parts of the country may apply dozens of
entirely different names to the same animal. For instance, such names
as night crawlers, fishworms, or groundworms might be applied in dif-
ferent localities to the same earthworm, which, by biologists the world
over, is known by its scientific name of Lumhricus terrestris. On the
other hand, if the term night crawler were applied in various communities
to any animal which crawled at night, there would be great confusion
and many entirely different animals would have the same common name.

Greek and Latin are used in classification and scientific names be-
cause they are universally understood and because they are not suscep-
tible to changes in each local community. Because of their standardiza-
tion throughout the world, they are extremely desirable for scientific
purposes.

Complete scientific descriptions and classifications of animals also
make it possible to identify accurately unknown animal species no matter
when or where found. Without scientific terms and classifications, each
investigator would have to make his own classification and follow his in-
dividual ideas of naming. If this procedure were universally followed, an

272

Survey of the Animal Kingdom 273

investigator would be unable to know if he were studying a previously
described species or if he really had a new one.

For convenience, the entire animal kingdom is divided into several
main groups or phyla (singular, phylum). All the animals included in
any particular phylum have certain characteristics in common. These
characteristics in the future will be considered as general characteristics
in each phylum.

If our classification were carried no further than phyla, there would
be so many differences among the various members that the system would
be practically useless. Consequently, all the members of a phylum which
have in common one or more arbitrarily chosen characters are placed in
a subdivision known as a class. In a similar manner each class is divided
into orders, each order into families, each family into genera (singular,
genus), each genus into species. The scientific name of any particular
animal is composed of its genus and species. For instance, man has the
scientific name of Homo sapiens, the former being the genus, the latter
the species.

Approximate Number of Species in the Animal Kingdom

TOTAL FOR

PHYLA

CLASS

PHYLA

Protozoa

15,000

Porifera

3,000

Coelenterata

9,500

Ctenophora

100

Platyhelminthes

6,000

Nemathelminthes

8,000

Trochelminthes (Rotifera)

1,000

Echinodermata

6,000

Annelida

7,500

MoUusca

75,000

Arthropoda

Crustacea

20,000

Onychophora

Diplopoda (Millipedes)

1,000

Chilopoda (Centipedes)

1,000

Insecta

625,000

Arachnoidea

28,000

675,050

Chordata

Miscellaneous

2,000

Pisces (Fishes)

14,000

Amphibia

2,000

Reptilia

4,000

Aves (Birds)

14,000

Mammalia

4,000

40,000
846,150*

*Does not include all individuals or groups.

274 Animal Biology

In a general survey of the animal kingdom each phylum of animals
will be considered from the following standpoints: general character-
istics of the phylum and classification of each phylum into classes or other
subdivisions.

Phylum 1. Protozoa (pro to -zo' a) (Gr. protos, first; zoon, animal)
General Characteristics

Most Protozoa are microscopic although a few are visible to the naked eye,
some forms being two-thirds of an inch long. All Protozoa are animals, each of
which is composed of a single cell (unicellular). This makes them the most sim-
ply constructed of all animals. Protozoa exhibit most of the activities which char-
acterize the higher, multicellular animals although in a simpler manner. Certain
types of Protozoa are colonial ; that is, a number of individuals of one species may
be more or less associated in the form of a colony. All Protozoa are complete
animals but are without true tissues and organs. Structures similar to true organs
of higher animals or which perform functions comparable to organs of higher
types are known as organelles. Protozoa were first discovered by Leeuwenhoek,
a Dutch naturalist (1632-1723). Many types of Protozoa are parasitic, thus
living in or on the bodies of living plants or other living animals. Under such
conditions they sometimes produce disease and thus are known as pathogenic
Protozoa. For a more detailed discussion consult the chapter on economic im-
portance of animals, and the chapter on unicellular, microscopic animals. Number
of species of Protozoa, 15,000.

Classification of the Phylum Protozoa

Class 1 — Sarcodina (sar ko -di' na) (Gr. sarx, protoplasm or f^esh). — These
unicellular animals possess protoplasmic pseudopodia ("false feet").

Subclass A — Rhizopoda (ri-zop'oda) (Gr. rhiza, root; pous, appendage
or foot). — These Protozoa "creep" by means of pseudopodia of one kind or an-
other.

Examples: Amoeba proteus (Figs. 75, 157, and 159), Endamoeba histolytica
(Fig. 264), and various other amoeboid types (Fig. 75).

Subclass B — Actinopoda (ak ti -nop' od a) (Gr. aktin, ray; pous, ap-
pendage).— These amoeboid Protozoa are spherical, floating forms with radiat-
ing, raylike, unbranched pseudopodia.

Examples: Actinophrys (Fig. 75) and Thalassicola (Fig. 75).

Class 2 — Mastigophora (mas ti -gof o ra) (Gr. mastix, whip; phoreo, to
bear) or Flagellata (flaj el -la' ta) (L. flagellatus, whip). — These Protozoa travel
by means of one or more whiplike flagella, and are commonly called flagellates.

Subclass A — Phytomastigina (fi to mas ti -ji' na) (Gr. phyton, plant; mas-
tigion, whip or flagellum). — These flagellated Protozoa somewhat resemble plants.
Colored bodies known as chromatophores (kro' ma to fors) (Gr. chroma, color;
phoreo, to bear) are usually present.

Examples: Euglena (Figs. 76 and 173), Phacus (Fig. 76), Trachelmonas
(Fig. 76), Paranema (Fig. 76), Volvox (Figs. 174 and 175), Chlamydomonas

Survey of the Animal Kingdom 275

(Fig. 76), also considered as a plant, Ceratium (Fig. 76), Chilomonas (Fig. 76),
Uroglena (Fig. 259), Dinohryon (Fig. 260), and Synura (Fig. 261).

Subclass B — Zoomastigina (zo o mas ti -ji' na) (Gr. zoon, animal; mas-
tigion, whip or flagellum). — These flagellated Protozoa are animal-like and do
not possess chromatophores.

Examples: Mastigamoeba (Fig. 76), Tetramitus (Fig. 76), Monosiga (Fig.
76),' Bodo (Fig. 76), Cercomonas (Fig. 76), and such pathogenic species as
Trypanosoma gambiense (Fig. 263), which causes African sleeping sickness, and
Trypanosoma brucei (Fig. 266), which causes a serious disease in animals in
Africa (see chapter on Economic Importance of Animals).

— Pseudopodltun — t:^^.^"','

Shell-

eudopodium -|f jy| |/|Y'I '^'^

^ — Pseudopodliim— , — ^ f

Fig. 75. — Representative protozoa of the class Sarcodina. A, Protomonas
amyli; B, Rotalia beccarii; C, Globigerina bulloides; D, Allogromia sp.; E. Amoeba
proteus; F, Arcella vulgaris; G, Difflugia oblonga; H, Centropyxis aculeata; I,
Actinophrys sol; J, Thalassicola nucleata. - (All enlarged and somewhat dia-
grammatic.

Class 3 — Sporozoa (spo ro -zo' a) (Gr. spora, spore or seed; zoon, animal).
— These Protozoa possess no locomotor organelles in the adult stages, although
in certain immature stages they may move about by different means. All species
reproduce by spores which are small bodies surrounded by a resistant membrane
(sporocyst). All species are parasitic and none appears in fresh water. The adults
absorb foods through their cells. Many Sporozoa have a very complicated life
cycle, spending part of their life in one species of animal and probably another
part of the cycle in a different species. The animals in which such parasites live
are known as hosts.

Examples: Monocystis (Fig. 77), a parasite of worms and arthropods; Plas-
modium malariae (Fig. 176), which causes human malaria (quartan type) with an

276 Animal Biology

attack of fever every seventy-two hours; Plasmodium vivax, which causes human
malaria (tertian type) with an attack every forty-eight hours; Plasmodium fal-
ciparum, which causes human malaria (subtertian or estivo-autumnal type) with
a daily attack, or more or less constant fever; and Babesia bigemina (Fig. 267),
which causes Texas fever of cattle. Sporozoan diseases are considered in greater
detail in other chapters.

Class 4 — Infusoria (in fu -so' ri a) (L. infusus, crowded or poured into). —
These Protozoa, comm^only called "infusorians," are very numerous in fresh water

s — Flagell\ani

Stigma^

^Contractile
vacpole —

Reservoir—

"Pelllcle-

^■Nucleus

Chromatophore—

Pyrenold

Phar:^:c

"Plagelltun— -^—

Pharynx

Pyrenold IKXi

X^hromatophore ''^^

Nucleus —

Contractlle-ife'*
vacuole

o , :,--• Nucleus

• •• ■

<iM^^ Flagellum

Oontractlle
vacuole

Fig. 76. — Representative protozoa of the class Mastigophora. A, Chilomonas
Paramecium; B, Ceratium hirundinella ; C, Chlamydomonas monadina; D, Euglena
viridis; E, Phacus longicaudus; F, Monosiga robusta; G, Trachelomonas hispida;
H, Peranema trichophorum; I, Mastigamoeba aspera; ], Bodo caudatus; K,
Cercomonas longicauda; L, Tetramitus rostratus. (All enlarged and somewhat
diagrammatic. )

Survey of the Animal Kingdom Til

and in cultures or infusions of decomposing materials. Hairlike cilia are present
at some stage in their life.

Subclass A — Ciliata (sili-a'ta) (L. cilium, hairlike cilia). — Numerous
hairlike cilia are present in the adults for locomotion and for securing food.
A permanent mouth and gullet are usually present.

rcs^

171 1

^Xt.

Fig. 77. — Life cycle of Monocystis, a gregarine protozoan of the class Sporozoa.
This is a common parasite in the seminal vesicle of the earthworm. A, Mature
individual (trophozote) attached to the seminal funnel of the earthworm; B, two
gametocytes, having formed a cyst around them; C, formation of gametes (sex
cells) ; D, conjugation of gametes to form a zygote; E, zygotes which have become
encysted spores; F, single spore whose original nucleus has divided into eight
nuclei; G, fully developed spore containing eight sporozoites; H, eight sporozoites
escaping from the sporocyst (spore case) into the intestine of a new earthworm
and eventually into its seminal vesicles; I, infestation of the sperm mother cells
of the seminal vesicle of the earthworm; spe, tails of withered sperms adhering
to the parasite; gam, gametes (sex cells) ; res, residual protoplasm; int, endocyst
(internal coat of the gamocyst) ; ext, epicyst (external coat of the gamocyst) ;
zy, zygote; spz, sporozoites; spc, sperm mother cells of the seminal vesicle. (From
Borradaile and Potts: The Invertebrata. By permission of The Macmillan Com-
pany and the Cambridge University Press, Publishers.)

278 Animal Biology

- Mouth
Cytopharynx-

I Cilia

?- Pellicle

••— Mouth
---Cilia

Nucleus

: Contractile

~~ vacuole -~

Trichocyst-

Cllla

Contractile
vacuole '

Mouth Q

_^^- Mouth
^-^-Cytopharynx

Nucleus

"Pellicle
Contractile-
vacuole
, Cilia — -.

-Cytopharynx

Nucleus-- __
-Pelllcle--
Contractlle
vacuole

Cilia

Nucleus--

— Cytopharynx

• Nucleus

Pellicle

_Contractlle
vacuole

-Pellicle
— Cllla-

/ Food vacuole— ^>;'^«'.r-'y!

-Cirri

Contractile
vacuole

Pelllcle--
Cytopharynx-- _^

cleus-- -|:i;i^^^

Cirri

Cilia—
-Nucleus

. Pellicle

Cytopharynx ^

Suctorial_
tentacle

--.Cytopharynx

"Contractile

vacuole
Stalk

Fig. 78.— Representative protozoa of the class Infusoria. A, Lacrymaria olor;
B, Prorodon griseus; C, Didinium nasutum; D, Lionotus fasciola; E, Urocentrum
turbo; F, Frontonia leucas; G, Colpoda campyla; H, Paramecium caudatum; I,
Spirostomum ambiguum; J, Stentor sp.; K, Halteria grandinella; L, Stylonychia
mytilis; M, Euplotes charon; N, Vorticella campanula; O, Carchesium poly-
pinum.; P, Podophrya fixa. Cirri are fused cilia. All protozoan forms are shown
enlarged and somewhat diagrammatically.

Survey of the Animal Kirigdom 279

Examples: Paramecium (Figs. 78, 163, 170, and 171), Vorticella (Figs. 78,
79, and 80), Stentor (Fig. 78), Lacrymaria (Fig. 78); Prorodon (Fig. 78),
Didinium (Fig. 78), Lionotus (Fig. 78), Urocentrum (Fig. 78), Frontonia (Fig.
78), Colpoda (Fig. 78), Opalina (Fig. 265), Spirostomum (Fig. 78), Bursaria
(Fig. 258), Balantidium (Fig. 262), Halteria (Fig. 78), Stylonichia (Fig. 78),
Euplotes (Fig. 78), Carchesium (Fig. 78).

Subclass B — Suctoria (suk-to'ria) (L. suctum, suck or attach). — The
adults are sedentary and without cilia, but they have tubelike sucking structures
with which to secure food. The immature larval stage is ciliated; hence, free
swimming; eventually it attaches itself and transforms into an adult.

Example: Podophrys (Fig. 78).

Cilia

J'"

Macronucleus

Undulating rnewbrane

CorttractUe vacuole

Micronudeus

Pharynx

food vacuoles

Stalk

M\^onQrY)e with elaibic fibres

Point of attachment

Fig. 79. — Vorticella, a protozoan of the class Infusoria, subclass Ciliata (highly

magnified) .

Phylum 2. Porifera (po-rif'era) (L. porus, a pore; ferro, to bear)

General Characteristics

This phylum includes all the animals known as sponges. They all contain
systems of canals which are connected with pores located in the body wall.
Sponges are multicellular and usually have irregular habits of growth. Depend-
ing upon the species, they have either radial symmetry (Scypha) (Grantia) or
asymmetry (commercial sponges). With the exception of about fifty species, most

280 Animal Biology

sponges live in salt waters of the ocean (marine). They are attached to rocks
and other submerged objects. Many species contain gray, red, green, or brown
pigments. The type of skeleton of the sponge depends upon the species. The
following kinds of skeletons are common: (1) spicules of silicon (siliceous),
(2) spicules of calcium carbonate (calcareous), (3) fibers of spongin (horny).

Fig. 80. — A number of Vorticella (class Infusoria) shown attached to an object
by means of the contractile stalk. (Copyright by General Biological Supply House,
Inc., Chicago.)

The various classes into which the phylum is divided are determined by the type
of skeleton. The body wall of sponges is diploblastic (two layers of cells) ; a non-
cellular middle layer is known as the mesenchyme (mesoglea). The external
cellular layer is known as the ectoderm; the internal cellular layer, as the ento-
derm. Number of species of Porifera, 3,000.

Survey of the Animal Kingdom 281

Classification of the Phylum Porifera

Class 1 — Calcarea (kal -ka' re a) (L. calcarius, lime). — The skeleton is
composed of spicules of calcium carbonate (calcareous). The sponges are mostly
gray or white, living in shallow sea water.

Examples: Scypha (Grantia) (Figs. 81, 82, and 87) and Leucosolenia (Figs.
83 and 84).

Class 2 — Hexactinellida (hek sak ti -nel' i da) (Gr. hex, six; aktin, rays). —
The skeleton of these deep-sea sponges is composed of six-rayed spicules of silicon
(siliceous) which may in certain species be fused into a continuous skeleton re-
sembling spun glass.

Example: Venus's flower basket (Fig. 85).

OSCULUM.

SPICULES

BASE

Fig. 81. — A simple sponge, Scypha (Grantia) of the class Calcarea. A young
bud is also shown. The entire organism is somewhat diagrammatic and enlarged.
(From Parker and Clarke: Introduction to Animal Biology, The C. V. Mosby Co.)

Class 3 — Deniospongiae (de mo -spon' ji e) (Gr. demos, people; spongos,
sponge). — These commercial sponges usually possess skeletons of spongin fibers
alone or spongin fibers associated with spicules of silicon. These sponges have a
complicated system of canals.

282 Animal Biology

SPICULES
GASTRAL CAVITY

-OSTIUM

gjj^^g^^^RADlAL CANAL

^^Sy^lNCURRENT CANAL
^ PROSOPYLE

APOPYLE

Fig. 82. — Cross section of a sponge, Scypha (Grantia), somewhat diagram-
matic. The ostium is also known as the incurrent pore, the radial canals as the
excurrent canals, the prosopyle as the connecting canal (between radial and in-
current canals), the apopyles as excurrent pores. (From Parker and Clarke: In-
troduction to Animal Biology, The C. V. Mosby Co.)

OscuJam

.- — Sieve membrane
- - Spicule

POKQ

Fig. 83. — Leucosolenia, a small colony of a simple sponge of the class Calcarea.
In the upper right quarter the outside covering has been removed to show the
structures beneath. (See also Fig. 84.)

Survey of the Animal Kingdom 283

qastra\
cavit-

qastra]
epitheliurn

F/agellam
-CoUar

;^Xhoariocyte

Porocybe ^^^^

jpicule yAmoebocyte

leroblast
derma] ^pifcheliam

Fig. 84. — x\ cross section of part of a simple sponge (Leucosolenia sp.), showing

the structures in detail.

Fig. 85. — Twelve different species of sponges: A, Euplectella sp. (Venus's
flower basket, from the Philippine Islands) ; B, Suberites domuncula (from the
Mediterranean) ; C, Phyllospongia velum (paper sponge, from Africa) ; D, Pan-
daros sp. (finger sponge, from the West Indies) ; E, Euspongia officinalis (grass
sponge, from Nassau) ; F, Tuba plicifera (tube sponge, from the Bahamas) ; G,
Pachychalina rubens (purple sponge, from the Bahamas) ; H, Euspongia sp. (hard
head sponge, from Nassau) ; /, Hyalonema sieboldii (glass rope sponge, from
Japan) ; /, Hircina ignobilis (Hircina sponge, from Africa) ; K, Verongia sp.
(Verongia sponge, from the West Indies) ; L, commercial sheep's wool sponge
(from Nassau).

ei^-tocyUs- .Vlv.;{vA jMocjfea conj-edaie ^ \ ) ^ J ^ I

^ v.: V .' J to jorm ^emmulcs ®^5^ VenUt^ea jgemmufe*

Fig. 86. — Spongilla, a fresh water sponge. Diagrams show the congregation
of special cells (statocytes) to form gemmules from which a new colony of
Spongilla may arise. (Copyright by General Biological Supply House, Inc.,
Chicago. )

Fig. 87. — Types of sponges shown in section with the pores and canals repre-
sented somewhat diagrammatically. Arrows show the direction of water flow
A, Asconoid type, such as Leucosolenia; E, syconoid type, such as Scypha
(Grantia) ; C, leuconoid (Rhagon) type, as in commercial sponges.

7, Incurrent pore (ostium).

2, Incurrent canal.

.?, Connecting structure (prosopyle).

4, Excurrent (radial) canal.

5, Flagellated cell (choanocyte).

6, Apopyle (excurrent pore).

7, Gastrocoel or spongocoel (central cloacal
cavity).

8, Osculum.

9, Dermal epithelium.
\0, Mesenchyme.

II, Gastral epithelium.

72, Subdermal cavity.

13, Dermal pore or ostium.

Survey of the Animal Kingdom 285

tnedusoe-
I
I

hydnanth dud i

"^ ® 1

Oi/a/T? 3perm

Fig. 88. — Life cycle of Obelia, a coelenterate of the class Hydrozoa, showing
alternation of generations. A, Portion of a colony with its medusae and the ovum
and sperm. The sperm fertilizes the ovum to form the zygote, a, which divides
by mitosis to form two cells, b, then four cells, c, then a mass of cells known
as the blastula, d, and eventually the ciliated planula. B, Developing a new
colony from the attached planula. (From Curtis and Guthrie: Textbook of Gen-
eral Zoology, published by John Wiley & Sons, Inc.)

286 Animal Biology

Examples: Bath (commercial) sponges (Fig. 85, L) ; Spongilla, a fresh-water
sponge (Figs. 86 and 87).

Phylum 3. Coelenterata (se len ter -a' ta) (Gr. koilos, hollow; enteron, digestive
tract)

General Characteristics

This phylum includes a number of frequently unnoticed marine animals and a
few fresh-water forms, such as Hydra and a few fresh-water medusae. The ani-
mals are multicellular and possess a single, hollow, central gastrovascular cavity

Nemabocyst--

flaaeWam

Testis

Sperm

Entoderm celL
with yacmole

Rseudopodium-

Ovary

Ovum

Ectoderm

-Tentacle

Gastrovascular

cavity

^::l -Older bud

Mesoqlea

Young bud

M Entoderm

^. Basal disk

Fig. 89. — Hydra, a fresh-water coelenterate, in section, much enlarged and some-
what diagrammatic.

(enteron). There is no anus. The body wall is diploblastic, being composed of
two layers of cells, the outer ectoderm and the inner entoderm. Between these
two is a noncellular layer, the mesoglea. Tentacles are characteristically around
the mouth. The tentacles and body wall contain peculiar structures known as
nematocysts (stinging cells). Coelenterates possess radial symmetry, there being
from four to six antimeres (parts of a radially symmetrical animal). Many of
the coelenterates are sedentary, while certain species are sessile for at least part
of the time. The life cycle typically involves an alternation of generations (meta-

Survey of the Animal Kingdom 287

ECTODERM

EPITHELIO-

MUSCU1_AR

CELL

1 MXER-
SXI XI AL
CELL

NEMAXOCYST
CN I OOBLAST

MES03LOEA

DIOESTIVE

CELLS

G LAND
CELL

Fig. 90.- — Cross section through the body of Hydra. The central space is the
gastrovascular cavity (enteron). (Drawn by Titus C. Evans, from Potter: Text-
book of Zoology, The C. V. Mosby Co.)

Fig. 91. — Nervous system of a coelenterate. (From Herrick: Neurological
Foundations of Animal Behavior, published by Henry Holt and Company.) (After
Max Wolf, 1904.)

288 Animal Biology

3-i

<CJ

■M

t- f

^N*

-a

</>

«TJ

U-l

4—
O

5 >-

Pi^

d -»5i

!^j

o <«

•^^

PiD

i r ' ''"^1 umilW'^T^^

r- O

■^

1' !■

^i.' ' > •'^Ps^Sjv*^

Survey of the Animal Kingdom 289

genesis) between the hydroid (hydralike) and medusoid (medusa-like) stages.
Not all coelenterates have metagenesis. Obelia illustrates a type which has meta-
genesis by having both a hydroid and medusoid stage in its life cycle (Fig. 88).
Number of species of Coelenterata, 9,500.

Classification of the Phylum Coelenterata

Class 1 — Hydrozoa (hidro-zo'a) (Or. hydra, water; zoon, animal). —
These coelenterates possess a gastrovascular cavity which is not held in position
by membranous mesenteries. They do not possess a true gullet or stomodaeum
as do the Anthozoa. Sex cells are discharged directly to the exterior. Certain
species have alternation of generations (metagenesis), while others do not. When
a medusa is formed in the life cycle, it has a velum (membrane on the under
surface).

jr.- ■ ■■it :.;r'-*^ -^ •■-■■»■:•- *r-:-.>^S** ■ -vS. '3

Tloat h]adder

Polyps -..-^

Jentade--

Hg. 93. — Portuguese man-of-war {Physalia sp.) of the phylum Coelenterata,
class Hydrozoa. This colonial coelenterate floats on the surface of the sea. Male
and female zooids, vegetative polype, and long tentacles with nematocysts are
suspended from the float bladder.

Examples: Hydra (Figs. 89, 90), Obelia (Fig. 88), many of the smaller
jellyfishes (medusae) , Gonionemus (Fig. 92), and Portuguese man-of-war (Fig.
93).

Class 2 — Scyphozoa (sifo-zo'a) (Or. skuphos, cup; zoon, animal). — These
types have their gastrovascular cavity held in position by membranous mesenteries.

290 Animal Biology

A stomodaeum (gullet) is present in certain species and absent in others. All
scyphozoa are carnivorous and marine. They are usually free floating, although
at times they may be sedentary. Sizes range from one inch to four feet in diam-
eter. They have a very inconspicuous hydroid stage in their life cycle. The
medusa stage is large and without a velum. The medusa of the scyphozoa can
be distinguished by notches (usually eight) in the margin of the umbrella.
Examples: larger jellyfishes such as Aurelia (Fig. 94).

Fig. 94. — Diagram of the life history of the jellyfish {Aurelia aurita) of the
phylum Coelenterata, class Scyphozoa. 1 , Adult jellyfish (medusa) ; T, tentaculo-
cyst (for equilibrium) ; F, gastric filaments (with nematocysts) ; O, oral arm;
M, mouth; P, gastric pouch; 2, egg; 3, sperm (from another adult) ; 4, zygote
(fertilized e.gg) ; 5, planula (ciliated larva) ; 6, 7, stages in the development of
the scyphistoma; 8-10, stages in the development of the strobila; 11, ephyra (im-
mature medusa). (From White: General Biology, The C. V. Mosby Company.)

Class 3 — Anthozoa (antho-zo'a) (Or. anthos, flower; zoon, animal). — The
hydroid polyps have a well-developed stomodaeum (gullet) which is fastened to
the body wall by a number of radially arranged membranous mesenteries. Most
of the polyps produce a colony by budding, although a few are solitary. This
colonial organization gives the efTect of a flower; hence, the name Anthozoa.
Several species secrete a calcareous skeleton known as coral. There is no medusa
stage in the life cycle.

Examples: Sea anemone (Metridium) (Fig. 95) and most of the stony corals,
sea pens, sea fans, precious corals (Fig. 96).

Survey of the Animal Kingdom 291

Phylum 4. Ctenophora (te-nof'ora) (Gr. ktenos, comb; phoreo, to bear)
General Characteristics

Ctenophores are jellyfish-like marine animals which are found in warm seas.
They are free swimming because of eight bands of vibratile swimming plates com-
posed of rows of fused cilia radially arranged. Many Ctenophores possess solid,
contractile tentacles. Beroe sp. (Fig. 97) is an exception. With one exception,
Ctenophores possess no nematocysts (stinging hairs). Ctenophores are nearly

Fig, 95. — Sea anemone (Metridium sp.) of the phylum Coelenterata, class
Anthozoa, dissected to show internal structures. 1, Siphonoglyphe or ciliated
groove in the side of gullet; 2, tentacle; 3, inner ostium through which water
passes; 4, outer ostium; 5, ring muscle; 6, ectoderm; 7, entoderm; 8, gullet; 9,
primary mesentery extending from gullet to the body wall; 10, cinclides or spe-
cial apertures in body wall; 11, gastrovascular cavity or radial chambers, six in
number; 12, mesenteric filament; 13, acontia or special threads armed with
nematocysts (acontia may be protruded through the mouth or cinclides) ; 14,
secondary mesentery; 15, tertiary mesentery; 16, retractor, muscle; 17, gonads or
sex organs (diecious) ; 18, directive mesenteries, one pair at each end of the
gullet (stomodaeum), opposite the siphonoglyphe, having their longitudinal mus-
cles turned away from one another; 19, basal disk (Copyright by General Bio-
logical Supply House, Inc., Chicago.)

292 Animal Biology

transparent with changeable colors and are often phosphorescent at night. They
are triploblastic (ectoderm, mesoderm, entoderm), while the Coelenterates are
diploblastic (ectoderm, entoderm). Ctenophores possess bilateral symmetry in
part and radial symmetry in part (biradial symrrietry). They are hermaphroditic;
one row of testes lies beside a row of ov-aries against each longitudinal canal.
Ctenophores are also called comb jellies because of their eight rows of comblikc

^^^^^^l^B

^^^^^^^B

^^^^Z^I

H^^^^^^B

^Ib '''''''''•' ''^^H

^^^^^^^^B

^^^^^^H

^^L^^jB

^^^^i^^^B

■^-^^

^B^£~^B

^r^^^^^l

Hir^ H

^^r*^^^^B

H^^^i^^^^H

^■^■■B^H

Hlhli^HHMHHI

Fig. 96. — Twelve different species of corals of the phylum Coelenterata, class
Anthozoa. A, Stylaster sanguinea fhydroid coral, from Samoa) ; B, Dichocoenia
porcata (from Andros Island); C, Oculina sp. (eyed coral, from the Bahamas),
D, Fungia sp. (mushroom coral from the Fiji Islands) ; E, Distichophora nitida
(hydroid coral, from Samoa) ; F, Manicina areolata (from the Bahamas) ; G,
Pocillopora sp. (from the East Indies) ; H, Siderastroea galaxea (star coral, from
the Bahamas) ; I, Millepora sp. (hydroid coral, from the West Indies) ; /. Isophyl-
lia dipsacea (rose coral, from the Bahamas) ; K, Madrepora sp. (branching coral
from the Indian Ocean) ; L, Tubipora musica (organ-pipe coral, from Singapore).

Mouth _:

Testes

Ovaries

i^--.Comb

Fig. 97. — Thimble comb-jelly {Beroe sp.) of the phylum Ctenophora.

Survey of the Animal Kingdom 293

locomotor organs (Fig. 97) and their jellylike bodies. Other species are called
sea walnuts because of their walnutlike shapes. Number of species in the phylum
Ctenophora, 100.

Classification of the Phylum Ctenophora

Class 1 — Tentaculata (ten tak u -la' ta) (L. tentare, to feel). — These Cte-
nophores possess contractile, sensory tentacles.

Class 2 — Nuda (nu' da) (L. nudus, bare or devoid of). — These Ctenophores
are without tentacles; the body is thimble-shaped; mouth and pharynx are large.
Example: Be roe (Fig. 97).

Phylum 5. Platyhelminthes (plat i hel -min' thez) (Gr. platus, broad or flat;
helmins, intestinal worm)

General Characteristics

These animals are flattened dorsoventrally and possess bilateral symmetry.
The body is elongated and unsegmented (nonmetameric) . The animals are
triploblastic, having three primary germ layers, the ectoderm, mesoderm, and
entoderm. There is no true body cavity (coelom). Certain species have
branched, tubular intestines (gastrovascular cavity) with a mouth. The spaces
between the organs and the body wall are occupied by a connective tissue called
parenchyma. No anus is present. Certain species are parasites and pass through
a number of complex stages in the bodies of several species of animals during their
life cycle. Some flatworms live in fresh water; others, in salt water; a few are
terrestrial. Number of species of Platyhelminthes, 6,000.

Classification of the Phylum Platyhelminthes

Class 1 — Turbellaria (tur be -la' ri a) (L. turbo, disturb). — These turbel-
larians are free living in fresh, salt, or brackish water or moist soils. They possess
a ciliated ectoderm or epidermis. Special ectodermal cells produce rodlike bodies
known as rhabdites or they secrete mucus. They possess two prominent light-sen-
sitive eye spots. In general, they have remarkable powers of regeneration of lost
parts (Fig. 28) and also illustrate the phenomenon of axial gradient.

Example: Planaria (Figs. 177, 178, and 179).

Class 2 — Trematoda (tre ma -to' da) (Gr. trema, a pore; eidos, resemblance).
— ^The trematodes are flat and leaflike in shape and possess one or more ventral
suckers at or near the posterior end and in the anterior or mouth region. The
ectoderm is nonciliated but hardened in the adult. They are either endoparasites
or ectoparasites.

Example: Liver fluke (Figs. 180, 181, and 374).

Class 3 — Cestoda (ses -to' da) (Gr. kestos, a girdle; eidos, resemblance). —
The cestodes possess a scolex and a body made of a linear series of proglottids.
Each of these proglottids is really an individual in itself, so that the entire cestode,
strictly speaking, is unsegmented. All cestodes are endoparasites. They have no
mouth and no alimentary canal because of their parasitic habits. They inhabit
the alimentary canals of a great variety of vertebrate animals during some stage of
their life cycle. The cuticle of the adult is not ciliated.
Examples: Tapeworms (Figs. 182, 183, and 268).

294 Animal Biology

Life Histories of a Few Typical Flukes (Trematodes)

IMMATURE

PARASITE

ADULT STAGES

stages

DISTRIBUTION

Sheep Liver Fluke

Sheep (liver).

Snail (Lymnea),

Present in United

(Fasciola

cattle, hogs.

water, soil.

States; common

hepatica)

man

grass

in Europe

Chinese Liver

Man (liver), cat,

Snails, fresh-

China, Japan,

Fluke

dog, mammals

water plants.

Korea, Indo-

(Clonorchis

( flesh-eating )

water

China

sinensis)

Oriental Intestinal

Man (China),

Snails, fresh-

China, Formosa,

Fluke

pigs ( Formo-

water plants.

India, Indo-

(Fasciolopsis

sa)

water

China, Sumatra

buski)

Human Blood

Man (large in-

Snails, water

Africa, West In-

Fluke

testine)

dies, North and

(Schistosoma

South America

mansoni)

( tropics )

Human Blood

Man, dog, cat.

Snails, water

Japan, China,

Fluke

pig, cattle

Philippines

(Schistosoma

japonicum)

Egyptian Blood

Man (bladder.

Snails, water

Near East, Africa,

Fluke

rectum), mon-

Portugal, Aus-

(SchistosoTna

key

tralia

haematobium)

Oriental Lung

Man (lung), dog.

Snails, fresh-

America, Japan,

Fluke

cat, pig, tiger

water crabs

Philippines,

(Paragonimus

and crayfish

China, Peru

westermani)

Life Histories

OF A Few Representative Tapeworms (Cestodes)

PARASITE

ADULT

STAGE

IMMATURE STAGE

Pork Tapeworm

(Taenia solium)
Beef Tapeworm

(Taenia saginata)
Dog and Cat Tapeworm

(Taenia pisiform.is)
Dog Tapeworm

(Dipylidium caninum.)
"Gid" Tapeworm

(Multiceps multiceps)

Hydatid Tapeworm
(Echinococcus
granulosus)

Fish Tapeworm

(Diphyllobothrium

latum)
Rat Tapeworm

(Hymenolepis

diminuta)
Sheep Tapeworm

(Moniezia expansa)

Man (intestine)

Pig

Man

Cattle

Dog, cat

Rabbit, mouse

Dog, cat, man (intestine

Lice and fleas of dog, cat.

occasionally)

man

Dog

Sheep (brain and spinal

cord) (causing "gid"

or "staggers"

Dog, cat, wolf and other

Man, monkey, cattle.

carnivorous mammals

sheep, pig, cat, dog.

etc. (in liver, lungs.

brain)

Man, cat, dog, fox and

Fresh-water fishes and

other fish-eating

copepod Crustacea

mammals
Rat, mice, man (occa-
sionally)

Sheep, goat, etc.

Such insects as flea, ear-
wig, flour beetle, meal
moth, etc.

Free-living mite
(Galumna)

Survey of the Animal Kingdom 295

Phylum 6. Nemathelminthes (nem a thel -min' thez) (Gr. nema, thread or round;
helmins, intestinal worm)

General Characteristics

These worms are elongated, slender, cylindroid, and with no internal or ex-
ternal segments (nonmetameric). They are bilaterally symmetrical. The animals
are triploblastic, having three primary germ layers: ectoderm, mesoderm, and
entoderm. The alimentary canal has a mouth at the anterior end and an anus on
the ventral side near the posterior end. There are no cilia on any part of the
body. The cavity between the internal organs and body wall is filled with loose,
mesenchymal tissue and probably is not a true coelom. The tubular sex organs
(gonads) are usually in separate individuals (diecious). Different species vary
in length from 0.01 to 1 meter. Nemathelminthes live in fresh and salt water,
damp earth, decaying matter, or parasitically in animals and plants. Certain
forms (Trichinella) live for a time embedded in the tissues, producing the disease
trichinosis in man, pigs, and rats. Such forms as the hookworm and Ascaris are
parasites in man and lower animals. Certain microscopic forms (vinegar eel)
live in vinegar. Number of species of Nemathelminthes, 8,000.

Classification of the Phylum Nemathelminthes

Class — Nematoda (nem a -to' da) (Gr. nematos, thread; eidos, form). —
The body is elongate, slender, cylindrical, and often tapered at the ends. There
are no segments but lateral lines are present. The digestive tract is straight and
nematodes have no proboscis. A resistant cuticle is shed (moulted) at intervals.
As a group they inhabit almost every possible habitat, many species living freely
in fresh water, salt water, or soil, while many other species parasitize other animals
and plants. (See table on p. 298.)

Order 1 — Ascaroidea (as kar -oid' e a) (Gr. askaris, intestinal worm) . —
These organisms are free living in soils, fresh water, or salt water, or they may be
parasitic. The mouth usually has three lips. This order includes the majority
of the nematodes.

Examples: Human ascaris (Ascaris lumhricoides) (Fig. 184), sheep ascaris
(Ascaris ovis), human pinworm (Enterohius vermicularis) , horse pinworm
(Oxyuris equi), a parasite of hundreds of plants (potato, tomato, lettuce, trees,
and weeds) (Heterodera [Caconema] radicicola), and "vinegar eel" (Turbatrix
[Anguillula] aceti) (Fig. 98), living in vinegar, stagnant water, and decaying
materials.

Order 2 — Strongyloidea (stron jil -oid' e a) (Gr. strongylos, round). —
All of these worms are parasitic. They frequently enter the body through the
skin or in water. The esophagus is club shaped and is without a posterior bulb.
Males have caudal bursae; they are supported by rays. These parasites produce
many common diseases.

Examples: American hookworm (Necator americanus) (Fig. 99), European
hookworm ( Ancylostoma duodenale), ground itchworm ( Ancylostoma braziliense) ,
and bird gapeworm (Syngamus trachea).

Order 3 — Filarioidea (fil ar -oid' e a) (L. filum, thread).— All of
these worms are parasitic, living in the blood, lymph, connective tissues, or mus-
cles of higher animals (vertebrates) ; they require an insect host for their trans-

296 Animal Biology

Embryo

Pharynx

Fntesfcinc

Cuticle

.Moath

Uterus

Fig. 98. — "Vinegar eel" {Turbatrix [Anguillula] oceti) of the class Nernatoda,

phylum Nemathelniinthes (much enlarged).

Ijophacjus Ovary qenitalpore

Mouth Nerve rincj

Mouth

Tema]Q
Te5t\3 TrttQstine Somha) vesicle Ar)us Bursa

Male

Fig. 99.^ — American hookworm {Necator americanus) , adults, of the phylum,
Nemathelniinthes. The actual length of the female is 10 mm., and of the male,
7 mm.

Muscle fibres

Cyst for
protection

Muscle fibre?

Orqans of attachmeryt

\rtesbne j^'^.^

Ferf orated cell bodies of intestine Pharynx

/^erve rmq

\' \

Fig. 100. — Trichina or "pork worm" (Trichinella spiralis) of the phylum
Nemathelniinthes. A, Trichina between muscle fibers; B, trichina between muscle
fibers and surrounded by a cyst; C, trichina (male); D, trichina (female).

Survey of the Animal Kingdom 297

mission. The esophagus is without a bulb; the mouth has a pair of lateral lips or
may be lipless. They are the cause of many diseases.

Examples: Human filarial elephantiasis worms, Wuchereria (Filaria) bart-
er of ti (Fig. 101), which causes human elephantiasis by obstructing the flow of
lymph, especially through the lymph glands (is transmitted by nocturnal mos-
quitoes), guinea worm or "fiery serpent" (Dracunculus medinensis) which is an
inhabitant of the skin of human beings, dogs, etc., and the "eye" worm (Loa loa)
which affects the human eye.

Order 4 — Trichinelloidea (trik i nel -oid' e a) (Gr. trich. hairlike). —
All are parasitic. The body is divided into a more or less distinct esophageal region
and a posterior region; the esophagus is a nonmuscular tube of cuticle embedded
in a single layer of epithelial cells. Females have a single ovary with a duct;
males have one spicule or may have none.

-Mouth- -rt

Female

Anas

VJjBS.

Male

Anus

Fig. 101. — Wuchereria {Filaria) bancrofti of the class Nematoda, phylum
Nemathelminthes. A, Causes of human elephantiasis; B, a chronic enlargement
and hardening of the skin, particularly of the legs. Note the comparative sizes of
the male and female.

Examples: Human Trichina or pork roundworm (Trichinella spiralis) (Fig.
100) which causes human trichinosis when improperly cooked pork is eaten (the
saclike cysts in which the immature stages are spent may be so numerous that
100,000 may be present in one cubic inch of meat). The worms may be present in
the muscles of man, dogs, rats, pigs, rabbits, and mice. Human whipworms
(Trichuris trichiura) inhabit the cecum and appendix of man.

Phylum 7. Trochelminthes (trok el -min' thez) (Gr. trochos, wheel; helmins,
worm) or P. Rotifera (ro -tif era) (L. rota, wheel; fero, to bear)

General Characteristics

Rotifers (Fig. 102) are very common, small, aquatic animals found mostly in
fresh water, although some are marine and a few are parasitic. They are charac-
terized by a bandlike disk of cilia (trochal disk) around the mouth at the anterior

298 Animal Biology

Life Histories of a Few Representative Nematodes
(Unsegmented Roundworms)

parasite

ADULT stages

immature stages

Human or Pig Roundworm

(Ascaris lumbricoides)
Human Pinworm

(Enterobius vermicularis)
American Hookworm

(Necator americanus)
European Hookworm

(Ancylostoma duodenale)
Elephantiasis (Filarial)
Worm

(Wuchereria bancrofti)
Guinea (Filarial) Worm or
"Fiery Serpent"

(Dracunculus medinensis)
Pork Roundworm or
Trichina

(Trichinella spiralis)
Bird Gapeworm

(Syngamus trachea)

Human Whipworm

(Trichuris trichiura)
Common Garden Nematode

Heterodera [Caconema]

radicicola)
Vinegar "eel"

(Turbatrix [Anguillula]

aceti)

Man, pig

Man (intestine, cecum)

Man (skin, intestine,
heart, lungs, trachea)

Man (blood stream,
lymph, lungs, skin)

Man (beneath skin)
Man (intestine, muscles)

Fowls, wild birds

(trachea) (cause of
gapes )

Man (cecum, appendix)

Hundreds of plants,

crops, trees, etc.

(especially in roots)
Vinegar

Soil, water, pig, man
(lung)

Soil (moist)
Soil (moist)
Mosquito

Fresh-water crusta-
cean (Cyclops),
water

Pig, rat, cat, dog,
flesh-eating animals

Soil, earthworms

Soil

end. Because of the wheel-like movements of these cilia, the animals are com-
monly called rotifers or wheel animalcules. The body is somewhat cylindrical,
bilaterally symmetrical, and covered with a transparent cuticle. The latter is
divided into sections which may be telescoped into each other when the animal
contracts. The movements of a pair of chitinous, chewing jaws (mastax) dis-
tinguish the living rotifers. A cavity (probably not a true coelom) contains the
alimentary canal and a pair of excretory tubes which empty their wastes into a
bladder which contracts at intervals, expelling them through the anus (cloacal
opening). A forked posterior tail ("foot") is provided with pedal (cement)
glands for adhesion. Certain rotifers may resist drying for years and be carried
by dust particles in their dried state. Hence, rotifers are among the most widely
distributed of animals. Different species of rotifers vary in shape from the free-
swimming spheroid forms that float near the surface to the wormlike bottom
dwellers or the flowerlike attached types. In certain species, several individuals
are grouped in a colony. Some species dwell in tubes of materials made from
their surroundings. The life cycles are quite complicated. Three types of eggs
are produced : ( 1 ) large, thin-shelled summer eggs which develop parthenogeni-
cally (without fertilization) into females, (2) small, thin-shelled summer eggs
which develop parthenogenically into males, and (3) thick-shelled winter eggs
which when fertilized develop into females. The winter eggs may remain alive
in a dormant state for years, developing when suitable conditions occur. Number
of species of Rotifers, 1,000.

Survey of the Animal Kingdom 299

Classification of the Phylum Trochelminthes (Rotifera)* (Fig. 102)

In the classification of the rotifers, the following characteristics are used: (1)
the presence of one or a pair of ovaries; (2) whether males are usually present
but degenerate; males unknown; or males fully developed; (3) absence or pres-
ence of lateral antennae on the body. If desired, the student is referred to a
more complete classification in other books.

CiUa

Mouth . ^^£

MastaK

(jasttic <j1ar)d -. .

Excretory canal

Bladder

Intestine

Cloacal opening _

Toot

Flame cell

Brain

Esophaqus

Stomach

Ovary

Oviduct

^Pedal glands

Fig. 102. — A female rotifer (much enlarged) of the phylum Trochelminthes

(Rotifera).

Phylum 8. Echinodermata (e ki no -dur' ma ta) (Gr. echinos, spiny; dermos, skin
or covering)

General Characteristics

The echinoderms have a spiny skeleton of calcareous plates which usually
covers the body. The adults have radial symmetry with five antimeres (divisions
of a radially symmetrical animal). The larvae have bilateral symmetry. The
adult animals are triploblastic, having three primary germ layers: ectoderm,
mesoderm, and entoderm. An anus is usually present. The coelom (body cavity)
is well developed. The type of locomotion which is peculiar to many types of
echinoderms is accomplished by tube feet. These are branches of the water
vascular system which is a division of the coelom. All echinoderms are marine.
Many species have great powers of regeneration, particularly after autotomy (Gr.

*Sometiines the term Rotifera is used as a class under the phylum Trofhelminthes,

300 Animal Biology

Fig. 103. — Brittle star (oral view) of the phylum Echinodermata, class Ophiuro-

idea.

TUBE FEET

Fig. 104. — Starfish from the oral or under side, showing the rows of tube feet
extending from the ambulacral grooves. The long, movable ambulacral spines
protect the tube feet when the latter are retracted within the groove. Similar
oral spines surround the mouth for protection. (From Parker and Clarke: An
Introduction to Animal Biology, The C. V. Mosby Co.)

Survey of the Animal Kingdom 301

autos, self; tome, cutting or mutilating) (Fig. 28). The eggs of many species
lend themselves admirably for experiments on artificial parthenogenesis (develop-
ment of the egg without fertilization). Number of species of Echinodermata,
6,000.

Classification of the Phylum Echinodermata

Glass 1 — Asteroidea (as ter -oi' de a) (Gr. aster, star; eidos, resemblance). —
These are typically free-living, five-rayed (pentamerous) types with the five rays

Ambulacral Braces
(Skeletal)

Hepatic Caeca —

Ampullae of
Tube Feet

yr;>y, :'::^'"'*-~~r-^- '^i,^,r-_^<^^^^^ £ toiTia ch

(Pyloric)
^-Rectal Caeca

Duct to

Radial Canal

Eye

Fig. 105. — Common starfish (Asterias forbesi) dissected from the aboral sur-
face to show the digestive, locomotor, reproductive, and skeletal systems. I, Arm
or ray, showing aboral surface covered with spines; // and III, arms with aboral
surface removed; IV, arm with aboral surface removed and the hepatic caeca
moved to show the bulblike ampullae of the tube feet, etc.; V, arm with internal
organs and vertebral ridge removed to show the four rows of ampullae of the
tube feet, the connecting canals, and the radial canal (all of the water vascular
system).

302 Animal Biology

or arms not sharply marked off from the central disk. The internal visceral
organs extend into the arms. There is a distinct ambulacral groove on the ven-
tral side of the arms. There is a true coelom (body cavity). The body is some-
what flattened. The anus and madreporite plate (entrance of water vascular
system) are located on the dorsal, upper aboral side.
Example: Starfish (Figs. 104 to 107 and 328).

MADREPORITE

STONE CANAL

RING CANAL

TIEDEMANN'S BODIES
LATERAL CANALS

Fig, 106. — Water-vascular system of starfish somewhat diagrammatic. The
madreporite is a porous plate on the upper surface of the starfish, between the
bivium rays, through which the water enters. The ring canal is also known
as the circular or circumoral canal. There are nine Ticdemann's bodies (the
tenth is replaced by the stone canal), which produce the amoebocytes found in
the fluid within the water-vascular system. The lateral canals are also known as
connecting canals. (From Parker and Clarke: An Introduction to Animal Biol-
ogy, The C. V. Mosby Co.)

OSSICLE

BODY WALL

AMBULACRAL RIDGE

" OSSICLE

RADIAL CANAL

LATERAL CANAL

COELOM-
AMBULACRALGROOVE

ADAMBULACRAL OSSICLE

PAPILLA

DERMAL BRANCHIA

PYLORIC CAECA

PEDICELLARIA

AMPULLA
RADIAL NERVE
GONAD

PERITONEUM

TUBE FOOT

AMBULACRAL
SPINE

Fig. 107. — Cross section of a starfish arm or ray, somewhat diagrammatic. (From
Parker and Clarke: Introduction to Animal Biology, The C. V. Mosby Co.)

Survey of the Animal Kingdom 303

Class 2 — Ophiuroidca (of i u -roi' de a) (Gr. ophis, snake; oura, tail;
eidos, resemblance). — These are typically free-living, five-rayed (pentamerous)
types with the five flexible rays or arms sharply marked off from the central disk.
There are no caeca and reproductive organs in the arms. There are no am-
bulacral grooves. The body is somewhat flattened. There is no anus. The
madreporite plate is on the dorsal upper surface. The tube feet are modified
and serve only as tactile organs.

Examples: Brittle or serpent star (Fig. 103) and basket star.

Fig. 108.- — Purple sea urchin (Arbacia punctulata) of the phylum Echinoder-
mata, class Echinoidea, from the oral or under side. Note the five sharp white
teeth (Aristotle's lantern) in the center. (From Coe: Echinoderms of Connecti-
cut, State Geological and Natural History Survey of Connecticut, Bulletin 19.)

Class 3 — Echinoidea (ek i -noi' de a) (Gr. echinos, hedgehog; eidos, resem-
blance).— These are free-living types but may be sedentary. There are no free
arms or rays, the space between them being more or less filled in. The test or
skeleton is composed of twenty columns of firmly united calcareous plates bearing
movable spines. These include five pairs of ambulacral rows (perforated for the
exit of tube feet) and fiv^e pairs of interambulacral rows of plates.

Examples: Sea urchin (Figs. 108 and 109), sand dollar (Fig. 110), and heart
urchin.

Class 4 — Holothurioidea (hoi o thu ri -oi' de a) (Gr. holos, whole; thurios,
rushing). — These echinoderms have soft, elongated, ovoid, muscular bodies with

304 Animal Biology

rather isolated, small, calcareous plates. Branched, contractile tentacles surround
the mouth. Five rows of radially arranged rows of tube feet extend the length
of the body. The external surface is free from spines, cilia, and pincerlike pedi-
cellaria. The madreporite is internal. The sea cucumbers move about freely in a
lateral position near the bottom of the sea. They possess remarkable powers of
autotomy and regeneration. When stimulated, the muscles of the body wall con-
tract and set up an enormous pressure in the fluid of the body cavity. As a result,
many of the internal organs are pushed out and surround an attacking enemy.
The lost organs are usually soon regenerated.
Example: Sea cucumber (Fig. 111).

Fig. 109. — Diagram of the skeleton or "test" (with spines removed) of purple
sea urchin (Arbacia punctulata) of the class Echinoidea. Outline of plates of the
aboral surface, showing the four plates of the periproct (center) surrounded by
the five ocular and five genital plates at the ends of the ambulacral, R, and
interambulacral, /, zones, respectively; one genital plate marked M is the
madreporite plate; the ocular plate is smaller than the genital plate and is lo-
cated in the angle between two of the latter; T, tubercles for attachment of
spines; P^ pores for the tube feet. (From Coe: Echinoderms of Connecticut, State
Geological and Natural History Survey of Connecticut, Bulletin 19.)

Class 5 — Crinoidea (kri -noi' de a) (Or. krinos, lily; eidos, resemblance). —
The five arms generally are branched with many smaller pinnules which give a
lilylike appearance. The tentacles are like tube feet but without the pouchlike
ampullae. The aboral plate usually has a heavy jointed stalk for temporary or
permanent attachment. Certain species have small holdfasts; others are second-
arily free swimming. Fossil remains of crinoids are very common in limestone
strata.

Examples: Stone lily, feather star (Fig. 112) and sea lily.

Phylum 9. Annelida (a -nel' i da) (L. annellus, a little ring; eidos, resemblance).

General Characteristics

These worms are elongated with a linear series of internal and external ring-
like segments (metameres). They possess bilateral symmetry. Setae, or skin

Survey of the Animal Kingdom 305

Fig. 110. — Sand dollar {Echinarachnius parma) oi th.& -phylnva Echinodermata,
class Echinoidea. Upper view shows aboral surface; lower, the oral surface. In
the aboral view, the darker ambulacral areas, or "petals," are shown. In the oral
view, the ambulacral areas are shown as narrow furrows radiating from the
central mouth. (From Coe: Echinoderms of Connecticut, State Geological and
Natural History Survey of Connecticut, Bulletin 19.)

306 Animal Biology

bristles, are common in many species. The animals are triploblastic, having three
primary germ layers: ectoderm, mesoderm, and entoderm. All species possess a
true coelom (body cavity), although it may be small in some types, such as
leeches. They possess a complex closed circulatory system. Some species are
aquatic, some terrestrial, and others marine. Number of species of Annelida,
7,500.

Calcareous

Ring canal

Madrepor'ite cana] . .
and plate .^

tsophaqus
(^nita) duct

Stomach
(Jonad...

Oral tcntades

Retractor muscle

Polian vesicle

Respiratory'
tree

'-Mesenteries
'-- Intestine

v.. ..Longitudinal
muscles

Cloaca muscle

Cloaca....

Lloaca aperture

Fig. 111. — Sea cucumber (Thyone briareus) of the phylum Echinodermata,
class Holothurioidea, shown in longitudinal section and somewhat diagrammatically.
(From Coe: Echinoderms of Connecticut, State Geological and Natural History
Survey of Connecticut, Bulletin 19.)

Classification of the Phylum Annelida

Class 1 — Archiannelida (ar ki a -nel' i da) (Or. archi, primitive; annelida).
— These are primitive marine annelids which lack both bristlelike setae and para-
podia (flat organs of locomotion and respiration).

Survey of the Animal Kingdom 307

Fig. 112. — Feather star (Antedon sp.) of the class Crinoidea, phylum Echino-
dermata. Oral view showing only four of the five branched arms, each with
many small pinnules. The "hold fasts" attach it to the ground.

Fig. 113. — Sandworm {Nereis virens) of tHe class Chaetopoda, phylum An-
nelida. A, Anterior and posterior ends (dorsal views) ; B, parapodium removed
from side of body and enlarged; 1 , palp; 2, terminal (prostomial) tentacle; 3, pros-
tomium; 4, eye; 5, lateral tentacles; 6, peristomium; 7, segment (somite) ; 8, para-
podium (respiratory locomotor organ) ; 9, anus; 10, anal cirrus; 11 , dorsal cirrus;
12, gill plate (respiratory lobe) ; 13, setae (chaetae) ; 14, notopodium; 15, neuro-
podium; 16, ventral cirrus; 17, aciculum. (Copyright by General Biological Sup-
ply House, Inc., Chicago.)

308 Animal Biology

Example: Polygordius (about two inches long, and internally resembles the
earthworm).

Class 2 — Chaetopoda (ke-top'oda) (Gr. chaite, bristle; pons, appendage).
— Terrestrial, marine, or fresh-water annelids possessing chitinous bristlelike setae
(chaetae) embedded in pits of the integument and moved by means of attached
muscles. The coelom is divided by numerous intersegmental septa (partitions).

f ye 6pobs
-Cerebral qana]]a
Nerve rincj

Head--.

Pharynx

/-^e Diverticulum (crop)

_ Ventral nerve cord
Lateral blood vessels

Anterior and posterior
Sachers

Jtomach H _

U^Divertkulum (crop) -\_

Rectum

Anus.

Fig. 114. — Common leech of the class Hirudinea, phylum Annelida, dissected
from the dorsal side to show the nervous and circulatory systems, A, and the
digestive system, B. The anterior and posterior suckers of the ventral side are
shown separately.

Order 1 — Polychaeta (pol i -ke' ta) (Gr. poly, many; chaeta, hrisiles) .
— Marine types with many setae situated on flat, fleshy lateral outgrowths known
as parapodia (used for locomotion and respiration). These worms usually have a
well-developed head bearing appendages. The sexes are separate. There is a
free-swimming, ciliated larval stage known as a trochophore (Gr. trochos, wheel;
phoreo, to bear).

Example: Sandworm (Clamworm) (Fig. 113).

Order 2 — Oligochaeta (ol i go -ke' ta) (Gr. oligo, few; chaeta,
bristles). — This order consists mostly of terrestrial and fresh-water annelids with
few setae, no parapodia, and no distinct head with appendages. Both sexes are

Survey of the Animal Kingdom 309

in the same individual (hermaphroditic or monecious). There is no trochophore
larval stage in its embryologic development.
Example: Earthworm (Figs. 185 to 190).

Class 3 — Hirudinea (hir u -din' e a) (Gr. Hirudo, leech). — Leeches have
dorsoventrally flattened bodies with anterior and posterior suckers for attachment
and blood sucking. There are no setae or parapodia. The real and visible seg-
ments have from two to fourteen external grooves to each real segment (depend-
ing on the species). The coelom may be small because of the growth of
mesenchyme cells. Both sexes are in the same individual.
Example: Leeches (Fig. 114).

Phylum 10. Mollusca (mol -lus' ka) (L. ynollis, soft)

General Characteristics

Mollusks have soft bodies with no true skeleton, although many types secrete
one or more external calcareous shells from a fold of the body wall. These

dorsal

Ventral

Fig. 115. — Chiton {Katharina sp.) of the class Amphineura, phylum Mollusca.

animals are nonmetameric (unsegmented) -and possess either bilateral symmetry
or asymmetry, depending on the species. The animals are triploblastic, having
three primary germ layers: ectoderm, mesoderm, and entoderm. The coelom
(body cavity) is secondarily obliterated and is divided into a pericardial cavity
(around the heart) and a cavity around the reproductive organs. Mollusks
possess a mantle cavity between the main body and the mantle (enclosing en-
velope). A ventral muscular foot for locomotion is usually characteristic. Num-
ber of species of Mollusca, 75,000.

Classification of the Phylum Mollusca

Class 1 — Amphineura (am-fi-nu' ra) (Gr. amphi, on both sides; neura,
nerves). — These forms are widely distributed marine types which possess bilateral
symmetry with two nerves running the length of the animals. They often have

310 Animal Biology

a series of calcareous plates (usually eight) on the dorsal side. Several pairs of
gill filaments may be present for respiration.
Example: Chiton (Fig. 115).

Class 2 — Gastropoda (gas -trop' o da) (Gr. gaster, belly or stomach; pous,
foot). — The body is more or less spirally coiled with part of the digestive tract in
the muscular foot. Gastropods possess a distinct head, foot, and mantle cavity.

Respiratory
aperture

Velum
I

T ' 1 '

Gcnita/apertur. ^^^^^^

Mouth

nespiratory aperture

stalked eye

Zdqz of vnantie
foot — :^^- —

-Tenfcacfc

' Mouth

Genital aperture

Fig. 116. — A, Fresh water snail {Lymnea sp.) ; B, land snail (Humboldtiana
sp.). Bodies are expanded from the shell. (From Potter: Textbook of Zoology,
TheC. V. Mosby Co.)

The latter contains a mantle for respiration. The shell is in one piece and coiled.
In such types as the slugs the shell is absent. The shell is asymmetrical, but
the head and foot show bilateral symmetry.

Examples: Snails (Figs. 116, 117, and 119), slugs, limpets, and whelks.

Survey of the Animal Kingdom 311

Class 3 — Pelecypoda (pel e -sip' o da) (Gr. pelekos, hatchet; pons, foot) or
class Lamellibranchiata (L. lamina, thin sheet; bronchiatus, having gills). — The
mantle cavity has gills which are usually lamellate (sheetlike). The muscular
foot, which is used for locomotion, somewhat resembles a hatchet. The calcareous
shell consists of paired valves, which are secreted by the bilobed mantle. The
pelecypods are bilaterally symmetrical. They are all aquatic and most of them
are marine. None possess head, tentacles, or eyes.

Examples: Mussels, clams (Figs. 118, 120, 121), oysters, scallops, and ship-
worms (Fig. 122).

Olfactory tentacle

Pharynx.

PeniV .

Salivary duct

stomach.. ^ _ai

Salivary qland -
TlaqeUum . |

Jeminol

receptacle

Vas deferens

Oviduct

Albumen

Cjland

Ovotest\s_ t

Liver 1

Eye tentacle

Brain

^ 9^n{fcal pore

Finger q/ond

p Dart sac

Maqina

Anal opening

Ureter opening

^Pulmonary
^ Veins

Lang

.:^^i^U^ -Auricle and
z^^j^lf- -Ventricle of
r^±-W heart

'^ kidney

\ Ureter

Aorta
Intestine
Foot

Fig. 117. — Anatomy of the snail [Helix pomatia) , the roof of the pulmonary
sac cut at the left and turned to the right; the pericardium and visceral sac
opened and the viscera or internal organs somewhat separated. The finger gland
is also called the accessory or mucous gland.

Class 4 — Cephalopoda (sef al -op' o da) (Gr. kephale, head; pons, foot). —
The head and foot are fused to form a tentacled secondary head. Suckers are
present on the tentacles. They possess external bilateral symmetry. The nervous
system is well developed in the head.

Examples: Squid (Fig. 123), octopus (Fig. 124), cuttlefish, and nautilus.
Class 5 — Scaphopoda (ska -fop' o da) (Gr. skapho, a boot; pous, foot). —
These elongated marine types possess a trilobed foot for boring in the sand. The

312 Animal Biology

,, , ... Ligamentous hinqe
Ventral Siphon -^

I lior 5 q\ siphon
I

Umbo

_, 7 Growth linzs

ypctnded
%ot

Posterior adductor
musclz

/Interior adductor

Ij---'- ~-:^i/-Anterior
protractor
y&. retractor
muscle

PaHial Urn

Fig. 118. — Fresh water clam (Lampsilis anodontoides) of the phylum Mollusca,
class Pelecypoda. External, A, and internal, B, shell features. (From Potter:
Textbook of Zoology, The C. V. Mosby Co.)

Kidney-

Ven trick.
Auricle

Pulmonary vein

iver
Hermaphroditic duct
-0 I/O test is

C!:^^?^^&^2^ Seminal receptaclj

Tentacl'e

Salivary duct-
Buccal mass

Vas deferens
Oviduct

hdutb I 'Cenitai }>oTe\'^i^)na\Kr>hs\ hucoas glands
Pedal ^an^l/a Penis Fla^ellufT) ^Oart sac

Fig. 119. — Internal anatomy of a snail {Helix sp.) with shell removed. (From
Potter: Textbook of Zoology, The C. V. Mosby Co.)

Survey of the Animal Kingdom 313

Mantle cut frez

Perkardlai cavity Rectum

Ant. retractor

Anterior i
adductor i

Poit. retractor
Po5t. adductor
£.x. siphon

In. siphon

Protractor Ext. labial palp Left qill plate

Fig. 120. — Fresh water clam {Lampsilis anodontoides) with the left mantle
partially removed and turned back to expose the underlying organs. (From
Potter: Textbook of Zoology, The C. V. Mosby Co.)

Pericardial \\/a\l Reno -pericardial pore
Post, aorta I Ventricle [ Excretory pore
Vertical ^^^^- odductor M. ! ! AuUle 1 i Ant.aorta Liver

water tubes

Exholant
Siphon

I Hidn(2y

stomach \ cerebral

commissure

[ Ant. adductor
muscle

Inhalant
siphon

» Oill
Mantle ^^^^^

Visceral Q.

Labial

Qonad \ I root \ '^'^''^^ ^^'^'^

Intestine Pedal Q. Cerebro pleural G-.

Fig. 121. — Fresh water clam (Lampsilis anodontoides) showing internal organs,
(From Potter: Textbook of Zoology, The C. V. Mosby Co.)

314 Animal Biology

tuskshaped, calcareous shell is secreted by the mantle. They possess bilateral sym-
metry and the head is rudimentary.

Example: Tooth shell (Dentalium) (Fig. 125).

Phylum 11. Arthropoda (ar -throp'o da) (Gr. arthron, jointed; pous, appendage,
or foot)

General Characteristics

Paired, jointed appendages are present on all or some of the segments of the
body. An exoskeleton of chitin is secreted by the cells just beneath it. Chitin
(Gr. chiton, a tunic or covering) is a protein material and has the formula
(C50H30O19N4) . The external, dissimilar segments (metameres) are well defined,
but the internal segments are largely obliterated. The body possesses regional
specialization (certain regions for specific purposes) and is bilaterally symmetrical.

\ Vh(?j; forbonnq

Ihcurrenb siphon-^^^S^-^ipnon

Fig. 122. — The shipworm (Teredo navalis) of the class Pelecypoda, phylum
Mollusca. The shipworm is shown somewhat diagrammatically in its burrow in
a piece of wood. The modified bivalve shell and the siphons are characteristics
of mollusca.

The animals are triploblastic, having three germ layers: ectoderm, mesoderm,
and entoderm. The coelom (body cavity) is rather poorly developed, it being
replaced by a hemocoel (Gr. hema, blood; koilos, cavity) filled with blood. The
mouth and anus are on opposite ends of the animal. A tubular heart and its
aorta are dorsal to the alimentary canal. Blood sinuses are commonly distributed
throughout the tissues. The nerve cord with its ganglia is ventral to the alimen-
tary canal. The paired cerebral ganglia are anterior and dorsal to the alimentary
canal (as in the earthworm). The cerebral ganglia are connected with the ven-
tral nerve cord by a nerve ring. The muscles of the body are usually striated
(striped). Number of species of Arthropoda, 675,050.

Classification of Arthropoda (see table on pp. 318 and 319)

Hectjocotylhed arm^

Jcjcker

Cartilage

Siphon

Anus

Niucle

Esophaau5 H

Rectutn

Ink5ac

Ant. aorta

Systemic hearts
Pen.

Penis

'CI Left g/ll

U\ Branchial heart

p£S^ Lt. post cava

t& c \ ^■
^j^A: Spermabopnoric sac

?1\ Stomach

Pen

iL-iiZi, Liver

.stomach-
poach

.Cut edge of
body wall

Fin

Fig. 123. — The squid {Loligo sp.) of the class Cephalopoda, phylum Mollusca.
Dissected to show internal anatomy. (From Potter: Textbook of Zoology, The
C. V. Mosby Go.)

316 Animal Biology

Fig. 124. — Octopus or "devilfish" of the class Cephalopoda^ phylum Mollusca.

-Foot

>Mouth— -(

Kidney- -
Digestive gland

qonad '

.-Shew

Fig. 125.— Tooth shell {Dentalium sp.) of the class Scaphopoda, phylum Mollusca.
At the right the shell is removed to show the internal organs.

Survey of the Animal Kingdom 317

Fig. 126.

Fig. 127.

Fig. 126. — Sowbug (Porcellio laevis) of the class Crustacea, phylum Arthropoda.
Much enlarged. A terrestrial type common in dark, damp places. (From
Popenoe : Mushroom Pests and How to Control Them, U. S. Department of Agri-
culture, courtesy of Bureau of Entomology and Plant Quarantine. )

Fig. 127.— Copepod water flea {Cyclops) of the class Crustacea, phylum Arthro-
poda. The paired egg sacs are shown near the tip of the body of the female.
Found in fresh water. (Copyright by General Biological Supply House, Inc.,
Chicago.)

318 Animal Biology

Q
O
a<
o
oi

<
O

w
z

u
o

Body composed of
head, thorax, and
abdomen ; head and
thorax may be fused
into a cephalothorax

Primitive, tropical,
or semitropical
arthropods; possess
paired, annelid-like
nephridia; limited
in distribution

Long, slender bodies
flattened dorsoven-
trally, having 15 to
173 segments; swift
moving

Long, slender bodies
subcylindrical, hav-
ing 25 to 100 seg-
ments ; slow moving

0
Ui
■J

en
3
O

Numerous
( 1 pair
on most
segments)

Numerous
(2 pairs
on most
segments)

o
z

c
o

iz:

RESPIRA-
TION

Gill breath-
ing

Trachea
(air
breath-
ing)

Trachea

(air

breath-
ing)

Trachea
(air
breath-
ing)

5
<

Aquatic for
most spe-
cies (few
are para-
sitic)

Terrestrial
(moist
places)

z
z

z
<

C/3

1 pair
(long)

1 pair
(short)

w
cu

<
X

Crayfish (Figs.

128 to 130

and 307)
Lobster
Shrimp (Fig.

131)
Crab (Fig. 132)
Barnacle (Fig.

133)
Water flea (Fig.

134)
Sow bug (Fig.

126)'
Cyclops (Fig.

127)

Peripatus (Fig.
135)

Centipedes
(Fig. 135)

Millipedes

(Fig. 135)

1. Crustacea

(krus -ta' she a)
(L. crusta,
skin)

2. Onychophora
(on i -kof o ra)
(Gr. onux,
claw; phoreo,
to bear)

3. Chilopoda*
(kai -lo' po da)
(Gr. cheilos,
lip; pous, foot)

4. Diplopoda*
(dip -lo' po da)
(Gr. diploos,
double; pous,
foot)

Survey of the Animal Kingdom 319

Body composed of
head, thorax, and
abdomen ; wings, if
present, attached to
thorax; many species
are harmful; a few,
beneficial; most spe-
cies, as far as known,
are neither

Certain species have
wings at certain
stages of their lives
and not at others
(wingless)

Head and thorax fused
into a cephalothorax ;
abdomen present;
no true jaws but 1
pair of nippers; some
species are detrimen-
tal; a few, beneficial;
most are neither

3 pairs on
thorax

. 1— (

2 pairs,
1 pair,
or none
(depend-
ing on the
species)

C
O

Trachea
(air

breath-
ing)

Trachea
and book
lungs
(air
breath-
ing)

Terrestrial
(some
species
live in
water)

Bees (Figs. 195

to 200)
Wasps (Fig.

306)
Butterflies (Fig.

207)
Moths (Figs.

300 to 302)
True bugs

(Fig. 287)
Grasshoppers

(Figs. 191 to

194 and 206)
Flies
Cicadas

(Fig. 292).
Beetles (Figs.

272,295-297)

etc.

Spider (Figs.

137 and 138)
Scorpion (Fig.

138)
Horseshoe crab

(Fig. 136)
Mites (Fig. 138)
Daddy long legs

(Fig. 138) etc.

5, Insecta\
(in -sek' ta)
(L. insectus,
cut into)
or

Hexapoda
(hecks -ap'
o da)

(Gr. hex, six;
pous, feet)

6. Arachnoidea
(ar ak -noi'
de a)

(Gr. arachne,
spider)

3
■«1.

,~,

-0

■

• F^

t-l

■ — '

"«

trt

■a.

*-<

• *•«

«i

■4-*

c/^

'„

<1)

4-*

Ifl

-0

a; u
o c

"^ c

« .2

o ft

•Si. 'U

o o

•O. 1^
0;

-«

■a.

-c

-1—

MALE

Fig. 128. — Crayfish, ventral view. The opening of the green gland (excretory
organ) is on the base of the antenna. The first two pairs of appendages (antenna
and antennule) are labeled; the third pair (mandibles), the fourth and fifth
(maxillae), the sixth, seventh, and eighth (maxillipeds) are not labeled (except

the ninth to the thirteenth (five pairs of walking legs) are
the fourteenth and fifteenth (modified swimmerets) are
the transfer of sperm to the female (these swimmerets in
the female are much smaller or vestigial) ; the sixteenth to the nineteenth (swim-
merets or pleopods). The last pair of swimmerets, sometimes called the uropods,
together with the telson constitute the tailfin for swimming backwards. (See
Fig. 307.) (From Parker and Clarke: An Introduction to Animal Biology, The
C. V. Mosby Co.)

the third maxilliped)
shown only in part ;
large in the male for

Survey of the Animal Kingdom 321

a
a

S >^

I >^

O b€

■X, O

(/I ,—1

^H •t-H

c
c o
o-i2

• f-H

322 Animal Biology

Carapace
removed

Sternal

artery
hascle —

Ventral thoracic
artery

Ventral sinus

Pericardial s/nus

Heart

Ostium

hasc/e

Gonad

Intestine
Oigest/i^e jland
Efferent /esse/

Gill

Neri/e cord
Carapace

Fig. 130. — Diagram of cross section through the posterior thoracic region of a
crayfish. Arrows show direction of blood flow. (From Potter: Textbook of
Zoology, The C. V. Mosby Co.)

■^^^^^^^

!I^^!^^|^H

JK^R

^^^^B

i ''fl^^^^^^^^l

^^Vii- -^aSQ

i^^^^i

^B^^^H

. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^1

KMB>«»^nJQM^

t^j^^^^^^^^^^^^^^^^^^^^^^^^^^^l

E^^PH

^BJ

^Hjl

^^nl^^^^^^^^^^^l

T ^^^^^^^^^^^^^^^M

^^^M

^^^^^^m: '-'-

^'J^^^^^^^H

■*-■- iV

Fig. 131. — Fresh-water shrimp (Palaemonetes sp.) of the class Crustacea,
phylum Arthropoda. (From a photograph by P. S. Tice. Copyright by General
Biological Supply House, Inc., Chicago.)

Survey of the Animal Kingdom 323

FAGURU5

LIBINIA

Fig. 132. — Representative crabs of the class Crustacea, phylum Arthropoda.
Fiddler crab {Uca); blue edible crab (Callinectes) ; hermit crab { Pa gurus.) ;
spider crab (Libinia) . (Copyright by General Biological Supply House, Inc.,
Chicago. )

Cirri --

■> shell plates .

_-3talK

Fig. 133. — Barnacles of the class Crustacea, phylum Arthropoda.

Sfvod- chamber

J>/yesf/ye tract
Abdominal processes **^

Abdominal setae —

Heart

Abdominal cfav/S^ *

I
$
I

post- abdomen

Mandfbtd

Antenna

Hepatic caeca

1—1 Compound eye

'"•Oce//(/«

^Arrtennvl^!

^ItQbnjffn

rrofttal organ
^tiedian eye
^'Isf antenna
^"^Po/red eyes
^g.<i antenna

'^Caudal sfy/ats

Fig. 134. — Representatives of the class Crustacea, phylum Arthropoda. Above,
The water flea [Daphnia pulex). Below, The fairy shrimp {Branchinecta pack-
ardii) , lateral view of female showing appendages and uterus filled with eggs;
left, anterior view of a male showing the second antennae modified as clasping
organs. (From Curtis and Guthrie: Textbook of General Zoology, published by
John Wiley & Sons, Inc.)

Fig. 135. — A, Peripatus sp., an arthropod of the class Onychophora, with sev-
eral annelid characters; B, a millipede of the class Diplopoda, phylum Arthro-

_r ii- - _i /^7- .•;

Survey of the Animal Kingdom 325

Phylum 12. Chordata (kor-da'ta) (L. chordatus, having a rodlike chord)

General Characteristics

A dorsal, rodlike notochord (Gr. noton, back or dorsal; chorde, chord) is
present as a cartilaginous or bony structure at some stage of life. A central,
tubular nerve cord is located dorsally. Paired pharyngeal clefts (gill slits) are

Fig. 136. — Horseshoe crab or king crab (Limulus polyphemus) of the class Arach-

noidea, phylum Arthropoda (dorsal view).

Heart

Pericardium

Sucking Stomach
Dorsal Muscle Of Sucking Stomach
Eve Cerebral Ganglion

Malpighian Tubules
StercoralPocket

Poison Glan

Pedipalp

Dendriform Silk Glands

Anus

Spinneret
And
Pyriform Silk Glands
Ampuliforra Silk Glands

Tubuliform Silk Glands

Fig. 137. — Spider, shown diagrammatically from the side, somewhat enlarged.
(From Metcalf: Economic Zoology, published by Lea & Febiger. )

present for respiration purposes at some stage. In certain species, these clefts are
no longer visible, as such, in the adult. The coelom (body cavity) is well de-
veloped. Bilateral symmetry is generally characteristic. The animals are triplo-
blastic (ectoderm, mesoderm, entoderm). The body is metameric (segmented).

326 Animal Biology

Fig. 138. — Representatives of the class Arachnoidea, phylum Arthropoda. A,
Scorpion; B, jumping spider {Attus sp.) ; C, human itch mite {Sarcoptes scabiei) ,
male, much enlarged; D, hair follicle mite {Demodex jolliculorum) , much en-
larged; E, daddy-long-legs or harvestman {Phalangium sp.).

Proboscis / /V/oafeK
Noiochord

Ventral ve'sse) t^ nerve

Fig. 139. — Balanaglossus, a. marine chordate of the subphylum Hemichordata.
Observe in the chordate characters, the gill slits, dorsal notochord, and dorsal nerv-
ous system in the section below.

Survey of the Animal Kingdom 327

although at certain stages the segments may be somewhat fused and difficult to
distinguish. Mouth and anus are present. Number of species of Chordata,
40,000.

Classification of the Phylum Chordata

Subphylum 1 — Hemichordata (hem i kor -da' ta) (Gr. hemi, half; chorde,
chord) or Enteropneusta (en ter op -nus' ta) (Gr. enteron, digt%\.\v& tvdict; pneuma,
breathe). — These marine, wormlike animals have a short, dorsal notochord in
the anterior end. Several pairs of permanent gill slits serve as respiratory organs,
with the internal gills. The anterior end of the body usually has a collar and a
fleshy proboscis. No cranium (brain case), jaws, vertebrae, or paired ap-
pendages.

Arms

--Tentacle

Proboscis

/Notochord

CoUarnerve

//iouth ^/^

tsophacfus.

Ventral nerve

TranU coe\om _

Trunk

Intestine

Fig. 140. — Rhahdopleura, a colonial chordate of the subphylum Hemichordata.
Enlarged, partially dissected, and somewhat diagrammatic. Actual length, 0.1
The collar nerve is also called the dorsal nerve.

mm.

Examples: Balanoglossus (Fig. 139), Cephalo discus, and Rhahdopleura (Fig.
140).

Subphylum 2 — Urochordata (u ro kor -da' ta) (Gr. aura, tail; chorde, chord)
or Tunicata (tuni-ka'ta) (L. tunica, a mantle). — These marine animals have
small tadpolelike larvae with paired gill slits and both dorsal notochord and nerve
cord in the tail. In the adult stage the body may be tubular, globose, or irregu-
lar in shape (depending upon the species), covered with a transparent tunic which
is made of cellulose (a material common in plants). The adults are usually
sessile (attached), with many gill slits, but the notochord is usually absent and the
nervous system reduced. There are no cranium, jaws, vertebrae, or paired ap-
pendages.

Examples: Ascidians and Appendicularians (Fig. 141).

328 Animal Biology

— /ncurrent siphon
- — txcurrent siphon

Mantle

Tunic

Qonqlion

AncJ5

^ Genital duct

Testis

•%\ — Ovar-y

— Digestive glands

— Isophagus
--Intestine

— -Stowach
— Branchial fold

- - tndostyle

- - yttrium

- - Pharynx

Fig. 141. — A typical ascidian or sea squirt (Molgula manhattensis) of the sub-
phylum Urochordata (Tunicata) . The diagram is from the left side of the body.
The courses of water and food through the body are shown by arrows. (From
Potter: Textbook of Zoology, The C. V. Mosby Co.)

Fig. 142. — Amphioxus, a simple chordate, subphylum Cephalochordata (general
structure of a lateral view), nc, Notochord; s.c, spinal cord (nervous); my,
myotomes (muscle segments); r, fin rays; d.f-, dorsal fin; c.f-, caudal fin; cir,
cirri on edge of vestibule leading to the mouth; m, mouth surrounded by a fringed
velum; g, gills (branchiae) constructed of alternate slits for the passage of water
and supporting plates in the walls of which are blood vessels; o, ovaries; /, liv^er;
a. p., atrial pore; in, intestine from which the liver arises as a pouchlike diverticu-
lum; v.f., ventral fin; a, anus. (From Galloway: Textbook of Zoology. Copy-
right P. Blakiston's Son & Co., Inc., publishers.)

"FiJ^v

:??

">■•

NostrW

Pharyngeal clefts Mouth

Fig. 143. — A lamprey of the class Cyclostomata, phylum Chordata. Note the
circular, sucking mouth, the median unpaired nostril, the seven pharyngeal clefts
("gill slits"). Lampreys frequently attack fishes, causing their death.

Survey of the Animal Kingdom 329

Subphylum 3 — Cephalochordata (sef a lo kor -da' ta) (Gr. kephale, head;
chorde, chord). — These marine animals have small, slender, elongate "fishlike"
bodies which are distinctly segmented. The permanent dorsal notochord and nerve
cord extend from the head to the tail (entire length of body). Many permanent,
paired gill slits (pharyngeal clefts) are present in the pharynx. No cranium,
jaws, vertebrae, or paired appendages.

Example: Amphioxus or lancelet (Branchiostoma sp.) (Fig, 142).

Fig. 144. — Representatives of the class Elasmobranchii, phylum Chordata (not
drawn to scale). A, Spiny dogfish shark (Squalus acanthias) ; B, sawfish (Pristis
antiquorum) ; C, hammer-head shark {Sphyrna zygaena) ; D, Southern sting ray
{Dasyatis americana) , common in the Gulf of Mexico.

Subphylum 4 — Vertebrata (vur te -bra' ta) (L. vertebratus, jointed) or Cra-
niata (Kra ni -a' ta) (Gr. kranion, cranium or head). — All vertebrates have a noto-
chord at some stage of development. This is replaced by an axial skeleton com-
posed of vertebrae in higher species. Both the axial and appendicular skeletons
are internal. They all have a coelom (true body cavity) and are bilaterally
symmetrical. The body is divided into head, thorax, and abdomen, A hollow

330 Animal Biology

Fig. 145. — Representative fishes of the class Pisces (not drawn to scale). A,
Small-mouth bass (Micropterus dolomieu) ; B, yellow perch {Perca flavescens) ;
C, black bullhead (catfish) (Ameiurus melas) . (From WicklifF and Trautman:
Some Food and Game Fishes of Ohio, State of Ohio Division of Conservation and
Natural Resources.)

Survey of the Animal Kingdom 331

central nervous system is dorsal to the digestive tract. All vertebrates have a ven-
tral heart with two to four chambers, depending on the species (Figs. 364 and
365).

Class 1 — Cyclostomata (si klo -sto' ma ta) (Gr. kyklos, circle or round;
stoma, mouth). — These possess a jawless, circular sucking mouth with a rasping
tongue. They are aquatic, fishlike, and have a median unpaired nostril. There
are no lateral appendages or fins. They possess no scales and a permanent noto-
chord.

Examples: Hagfishes and lampreys (Fig. 143).

Class 2 — Elasmobranchii (e las mo -brang' ki i) (Gr. elasmos, plate; branchia,
gills). — These types possess vascular gills or branchia supported by cartilaginous,
platelike structures known as gill plates. They are fishlike animals with jaws,
paired fins, and placoid (platelike) scales. They have a persistent notochord and
a permanently cartilaginous skeleton. There is no air bladder. They are cold
blooded (temperature varies with their surroundings).

Examples: Sharks and skates, rays (Fig. 144).

Lateral line

Spinous dorsal fin

Nasal
1

Soft dorsal fin
Caudal fin

Mandible I

< I .

I I Maxillary j

I Opercle
Branchiostegal

Premaxillary

Fig. 146. — External features of the perch. (From Hegner: College Zoology.
By permission of The Macmillan Company, publishers.)

Class 3 — Pisces (pis' ez) (L. piscis, fish). — These true fish have gills through-
out life which are supported by bony or cartilaginous gill arches. Jaws are present.
The two pairs of pectoral and pelvic fins and unpaired median fins are supported
by fin rays. The skeleton is principally bony, although cartilage may also be found
in certain regions. Scales are present in the skin. The air bladder (swim blad-
der) is primarily for hydrostatic purposes, for maintaining a certain level in water
without muscular effort. They are cold blooded (their temperature varies with
their aquatic surroundings). Their heart is two chambered (1 auricle and 1 ven-
tricle). There are about 14,000 species of true fishes.

Examples: True fishes (Fig. 145), as perch (Figs. 146 and 147), trout, bass,
minnow, carp, and goldfish.

Class 4 — Amphibia (am -fib' i a) (Gr. amphi, both; bios, life). — These
aquatic or semiaquatic animals have gills during larval stages and paired lungs
in adults (hence amphibious). The skin is slimy, smooth, moist, and usually

332 Animal Biology

bO
c4

.to
iiJ

«5

(4-1 O

e _

■to "Tw

<to.5

==• c

^ — ' ■(->

in O

.2tj
•^ c

c
^^

a; O

I. S

Survey of the Animal Kingdom 333

scaleless. The paired legs usually have five digits. They are cold blooded. The
heart is three chambered (2 auricles and 1 ventricle). There are about 2,000
species of Amphibia.

Examples: Frog (Figs. 208 to 219), toads, salamanders, and newts (Figs. 148-
150).

Fig. 148. — Representatives of the class Amphibia (not to scale). A, bullfrog
(Rana catesbiana) ; B, common toad {Bufo sp.). (Copyright by General Biological
Supply House, Inc., Chicago.)

Class 5 — Reptilia (rep -til' i a) (L. reptilus, reptile, from repere, to crawl).
— These animals have horny plates (scales) covering their body. They have paired
lungs in the adult with no gills. They are cold blooded. Their heart is three
chambered (2 auricles and 1 ventricle, the latter being partially divided). The
cranium (brain case) articulates with the vertebral column by a single occipital
condyle. Reptiles possess both amnion and allantois. There are 4,000 species
of reptiles.

334 Animal Biology

Fig. 149. — Representatives of the class Amphibia (not to scale). A^ Red-
spotted newt {Triturus uiridescens) ; B, tiger salamander (Ambystoma tigrinum).
(Copyright by General Biological Supply House, Inc., Chicago.)

Survey of the Animal Kingdom 335

A. B.

Fig. 150. — Representatives of the class Amphibia (not drawn to scale). A,
"Hellbender" salamander (Cryptobranchus allegheniensis) ; B, "mud puppy" (Nec-
turus maculosus) . (Copyright by General Biological Supply House, Inc., Chicago.)

336 Animal Biology

Fig. 151. — Representative reptiles of the class Reptilia (not to scale). A,
Horned "toad" {Phrynosoma cornutum) ; B, giant collared lizard {Crotaphytus
collaris) . (Copyright by General Biological Supply House, Inc., Chicago.)

Survey of the Animal Kingdom 337

%, ■ ""V

,.^:.;^^v^^..-iV..-/^

Fig. 152. — Representative reptiles of the class Reptila (not to scale). A, Black
snake {Zamenis constrictor); B, box turtle {Cistudo Carolina). (Copyright by
General Biological Supply House, Inc., Chicago.)

338 Animal Biology

Fig. 153. — Representative reptiles of the class Reptilia (not to scale). A, True
chameleon {Chameleon vulgaris) ; B, American alligator {Alligator mississippi-
ensis). (Copyright by General Biological Supply House, Inc., Chicago.)

Fig. 154. — Representative birds of the class Aves (not to scale). A. Mourning
dove {Zenaidura macroura carolinensis) ; B, common tern (Sterna hirundo) ;
C, green heron [Butorides virescens virescens) ; D, ring-neck duck (Marila col-
laris) ; E, brown pelican (Pelicanus occidentalis) ; F, great horned owl (Bubo
virginianus virginianus) ; G, cardinal {Cardinalis cardinalis) ; H, cedar waxwing
(Bombycilla cedrorum). (Copyright by General Biological Supply House, Inc.,
Chicago. )

340 Animal Biology

Examples: Turtle (Fig, 152) , snakes (Fig. 152) , lizards (Fig. 151) , crocodiles,
chameleons (Fig. 153), and horned "toads" (Fig. 151).

Class 6 — Aves (a'vez) (L. avis, bird). — Feathers are distinctive of birds.
Paired lungs are found in the adult. They are warm blooded with a more or less
constant temperature which is usually 10° C. higher than mammals. The fore-
limbs are wings which are small in the ostrich and auk. All birds are terrestrial,
although some may be associated with water. The heart is four chambered (2
auricles and 2 ventricles). There are 14,000 species of birds.

Examples: Wrens, owls, sparrows, pigeons (Fig. 155), chickens, robins, eagles,
turkeys, ducks, terns, gulls, hawks, coots, penguins, and ostrich (Fig. 154).

Optic Nerve
Cerebrum
Olfactory Lobe

Poeterior Nostril
Tongue

» . .. Pulmonary Artery

-Medulla i p„i„ ' v •

rulmonary Vein

Dorsal Aorta

Glandular StomacL.

Spermary

Spleen

Oil Gland

Second Digi
Third Digi

•Aperture Of Ureter
Aperture Of
^ClMca Sperm Duct

Duodenum
Pancreas

Fig. 155. — Diagram of the internal structures of a bird of the class Aves. (From
Metcalf: Economic Zoology, published by Lea & Febiger. )

Class 7 — Mammalia (ma -ma' li a) (L. mamma, breast). — The young mam-
mals are suckled by mammary glands (few exceptions). They have paired lungs
in the adults. They are warm blooded with a temperature around 37° C. regard-
less of surroundings. They possess hair (wool in some types) at certain stages.
They heart is four chambered (2 auricles and 2 ventricles). The cranium (brain
case) articulates with the vertebral column by means of two occipital condyles.
There is a well-developed, usually conv^oluted brain. A muscular diaphragm
separates the thorax and abdomen. A tubelike placenta attaches the unborn
young to the mother. There are 4,000 species of mammals.

Examples: Man (Figs. 228 to 256), cat, bat, whale, seal, monkey, kangaroo,
elephant, dog, bear, antelope, and prairie dog (Fig. 156).

Survey of the Animal Kingdom 341

Fig. 156. — Representative mammals of the class Mammalia (not to scale). A,
Orangutan {Simla satyrus) ; B, llama [Lama huanacos) ; C, American bison or
buffalo {Bison bison); D, red fox {Vulpes sp.) ; E, Bactrian camel (shedding)
{Camelus bactrianus) ; F, Russian bear {Ursus sp.) ; G, beaver {Castor canaden-
sis); H, armadillo {Dasypus sp.). (Copyright by General Biological Supply
House, Inc., Chicago.)

342 Animal Biology
QUESTIONS AND TOPICS

1. Define the following terms: species, genus, class, and phylum.

2. Give all the reasons you can why a classification of animals must necessarily
be a scientific one. Why can we not depend on the use of common names for
particular animals in a classification? Why are Greek and Latin used in com-
posing scientific names and classification?

3. Give the distinguishing characteristics of each phylum into which the animal
kingdom is divided. Which phyla seem more closely related than others?
What suggestions can you offer for this?

4. How many species of animals are there in each phylum? How many species
are there in the animal kingdom? Tell how this number may vary.

5. Tell how the representatives of the various phyla increase in complexity as
we observe them from the lower to the higher and complex phyla. What
conclusions do you draw from this phenomenon?

6. Define the following types of symmetry: (1) asymmetry, (2) radial sym-
metry, and (3) bilateral symmetry. List the phyla and give the type or types
of symmetry found in each. What conclusions can be drawn from these data?

7. What effect does attachment (nonlocomotion) of an animal have on (1) its
general development, (2) its method of reproduction, (3) the dispersal of
its offspring, and (4) the securing of food and elimination of wastes?

8. List the advantages and disadvantages of having the offspring dispersed in
many directions from their place of birth.

9. What is meant by alternation of generations (metagenesis) ? List all the ad-
vantages and disadvantages of metagenesis.

10. Which phylum do you think contains the most important animals? Why do
you choose as you do? What makes an animal important?

11. Upon what does the economic importance of a particular animal depend?

12. In which phyla do we find a true body cavity (coelom) ? Discuss the advan-
tages and disadvantages of such a structure.

13. In which phyla do we find metamerism (segmentation) ? What are the ad-
vantages and disadvantages of such construction?

14. Define (1) chordate, (2) invertebrate, and (3) vertebrate. Do all the ani-
mals in the phylum to which man belongs closely resemble man? Why do
we place man, whales, bats, horses, cats, and monkeys in the class mammalia?
Must all animals be absolutely alike in all respects to be classified together?

SELECTED REFERENCES

Alexander: Birds of the Ocean, G. P. Putnam's Sons.

Anthony: Animals of America ("Mammals of America"), Doubleday, Doran &

Co., Inc.
Anthony: North American Mammals, G. P. Putnam's Sons.
Barbour: Reptiles and Amphibians, Houghton Mifflin Co.
Borrodaile and Potts: The Invertebrata, The Macmillan Co.
Breder: Marine Fishes of the Atlantic Coast, G. P. Putnam's Sons,
Brown: Selected Invertebrate Types, John Wiley & Sons, Inc.
Buchsbaum: Animals Without Backbones, University of Chicago Press.
Bullough: Practical Invertebrate Anatomy, The Macmillan Co.
Caiman: Classification of Animals, John Wiley & Sons, Inc.

Survey of the Animal Kingdom 343

Ditmars: Reptiles of the World, The Macmillan Co.

Driver, E. C. : Name That Animal, Northampton, Mass., published by the author.

Eliot: Birds of the Pacific Coast, G. P. Putnam's Sons.

Guyer: Animal Biology, Harper & Brothers.

Hamilton: American Mammals, McGraw-Hill Book Co., Inc.

Hausman: Field Book of Eastern Birds, G. P. Putnam's Sons.

Hegner: Parade of the Animal Kingdom, The Macmillan Co.

Hegner: Invertebrate Zoology, The Macmillan Co.

Hegner: College Zoology, The Macmillan Co.

Hyman: The Invertebrates (Protozoa Through Ctenophora), McGraw-Hill

Book Co., Inc.
Jacques: How to Know the Land Birds, William C. Brown Co.
Jordan: Fishes, D. Appleton-Century Co., Inc.
Kyle: Biology of Fishes, The Macmillan Co.

LaMonte: North American Game Fishes, Doubleday & Co., Inc.
Lutz: Field Book of Insects, G. P. Putnam's Sons.
MacGinitie and MacGinitie: Natural History of Marine Animals, McGraw-Hill

Book Co., Inc.
Mathews: Field Book of Wild Birds and Their Music, G. P. Putnam's Sons.
Morgan: Field Book of Animals in Winter, G. P. Putnam's Sons.
Norman and Eraser: Field Book of Giant Fishes, Whales and Dolphins, G. P.

Putnam's Sons.
Palmer: Field Book of Natural History, McGraw-Hill Book Co., Inc.
Pough: Audubon Bird Guide, Doubleday & Co., Inc.
Pearson: Birds of America, Doubleday, Doran & Co., Inc.
Pratt: Manual of Common Invertebrate Animals, A. C. McClurg Co.
Pratt: Manual of Common Land and Fresh Water Vertebrate Animals of the

United States, P. Blakiston's Son & Co.
Rand: The Chordates, P. Blakiston's Son & Co.
Romer: The Vertebrate Body, W. B. Saunders Co.
Schmidt and Davis: Field Book of Snakes of the United States and Canada,

G. P. Putnam's Sons.
Schrenkeisen: Fresh Water Fishes of North America, G: P. Putnam's Sons.
Swain: The Insect Guide, Doubleday & Co., Inc.
Walter and Sayles: Biology of the Vertebrates, The Macmillan Co.

Chapter 18

UNICELLULAR, MICROSCOPIC ANIMALS
(PHYLUM PROTOZOA)

Amoeba; Paramecium; Euglena; Volvox; Plasmodium

AMOEBA

Amoeba (a-me'ba) (Gr. amoihe, change) is a common fresh-water
protozoan (pro to -zo' an) (Gr. protos, first; zoa^ animals) about 1/100
inch (0.2 mm.) in length. Under the microscope it appears as an irregu-
lar, colorless, jellylike, granular mass which is changing its shape by the
formation of small fingerlike processes called pseudopodia (su do -po' di a)
(Gr. pseudes, false; pous, foot). A disk-shaped nucleus, containing
chromatin granules, is not easily observed in living specimens. With
high power, it will be observed that the living protoplasm has a flowing
(streaming) movement. Many structures are more easily observed if the
protozoan is killed and stained with a dye. Some of the more important
characteristics of the common species {Amoeba proteus) are given briefly
(Figs. 157 to 162).

Integument (Covering). — An outer, thin, clear ectoplasm layer (ek' to-
plazm) (Gr. ektos, outside; plasma, mould) is just external to the inner,
granular endo plasm (en'doplazm) (Gr. endon, within). Within the
endoplasm are the nucleus, granules, vacuoles, etc., described below.

Ingestion and Digestion. — Food may be ingested at any point on the
body surface but usually at the anterior end (part toward the direction of
locomotion) . Minute animals and plants are selected and surrounded by
the pseudopodia. Then thin sheets of cytoplasm cover the food, even-
tually forming a jood vacuole (vak' u ol) (L. vacuus, empty) . This tem-
porary structure contains water and digestive enzymes. Digestion within
the food vacuole takes place in an acid environment (as in the stomach
of a higher animal) and later in an alkaline environment (as in the in-
testine of a higher animal). The digested foods are absorbed into the

344

Unicellular^ Microscopic Animals 345

cytoplasm, and the food vacuole disappears. Within the cytoplasm the
absorbed foods are assimilated (made into living protoplasm) , Complex
molecules of protoplasm are oxidized to release the energy needed for
movement, locomotion, the production of heat, and other physiologic
activities.

FOOD
VACUOLE

COMTRACTIL.E
VACUOUE

NUCU.EUS

ENDOPl_ASM

^ PSEUDO PODIUM

ECXOPUASM

Fig. 157. — Amoeba proteus of the class Sarcodina (magnified and somewhat dia-
grammatic). (From Potter: Textbook of Zoology, The C. V. Mosby Co.)

Fig. 158. — Amoeba proteus showing various shapes revealed by a photomicrograph.
(From White: General Biology, The C. V. Mosby Co.)

Motion and Loconiotion. — Amoeba moves from place to place (loco-
motes) and captures foods by the fingerlike pseudopodia, commonly
referred to as "pseudopods." They may form on any surface by pushing
out a blunt projection of clear ectoplasm into which flows the granular
endoplasm. Two theories regarding the formation of pseudopodia are
( 1 ) the surface tension theory, based on changes in the tension of the sur-
face of the amoeba, and (2) the viscosity theory, based on the tendency
to resist changes in the shape or arrangement of parts.

346 Animal Biology

Circulation. — There is no circulatory system, but the flowing of the
protoplasm naturally circulates the contents of the cell by a process
known as cyclosis (sik -lo' sis) (Gr. kyklosis, whirling around) .

Respiration. — Oxygen, required for various metabolic activities, is dis-
solved in the water and is taken in through the body surface. Carbon
dioxide passes out through the surface as well as being expelled by the
contractile vacuoles.

Fig. 159. — Amoeba ingesting another protozoan, an encysted Euglena. (From
Jennings: Behavior of the Lower Organisms, pubhshed by the Columbia Univer-
sity Press.)

Fig. 160. — Negative reaction of Amoeba to contact or mechanical stimulation.
Arrows show the movement before and after stimulation with a glass rod at the
anterior end, a. As a result, the part is contracted, the currents are changed, and
a new pseudopodium is sent out at b. (From Jennings: Behavior of the Lower
Organisms, published by Columbia University Press.)

Excretion and Egestion. — A clear, spherical contractile vacuole col-
lects wastes and, at somewhat regular intervals, it is carried to the body
surface where it contracts and forces its fluid contents out of the body.
The contractile vacuole is not permanent and it disappears at each con-

Unicellular^ Microscopic Animals 347

traction. A new one forms by the fusion of droplets of liquid. Indigesti-
ble and partially digested food particles are egested at any point of the
surface, there being no special opening to the outside. Ordinarily, the
wastes include solids, fluids, minerals, urea, carbon dioxide, etc.

Fig. IGl. — Reaction of Amoeba to light, in which it moves away from the
source of light. The arrows at a, b, c, and d indicate the successive directions of
the light and the numbers indicate the successive positions occupied by the
Amoeba. (From Jennings: Behavior of the Lower Organisms, published by
Columbia University Press.)

Coordination and Sensory Equipment. — Even though an amoeba is
small and rather simply constructed, its different parts must be properly

348 Animal Biology

coordinated in order that it may perform the numerous activities essential
for its life. This is accomplished by the properties of its living protoplasm
without the benefit of any specialized sensory or nervous equipments.
Amoeba responds to a number of types of stimuli (en\ironmental fac-
tors), and its reactions to them are called its responses. Such activities
as changes in shape, formation of pseudopodia, locomotion, capture of
foods, etc., constitute its behavior. These changes may be due to ex-
ternal, as well as internal, factors. Movement toward a stimulus is called
a positive reaction; movement away from a stimulus, a negative reaction.
These two reactions may be influenced by the quantity and quality of
the particular stimulus. The following reactions are typical:

1. Contact (thigmotropism or thigmotaxis) (thig -mot' ro pizm; thig-
mo-tak'sis) (Gr. thigema, touch; trope, turn; taxis, arrangement) : At
first the Amoeba may cease locomotion and then move away.

FISSION 1" STAGE

NUCLEAR DIVSION
COMPLETED

FlSSiCN COMPLETED

FISSION 2"»STAGE

Fig. 162. — Reproduction of Amoeba by binary fission. Note how the nucleus
divides and how the cells eventually separate to form two Amoebae. (From
Parker and Clarke: Introduction to Animal Biology, The C. V. Mosby Co.)

2. Chemicals (chemotropism ov chemotaxis) (ke -mot' ro pizm; kem o-
tak' sis) (Gr. chymos, juice) : The reaction is negative to such chemicals
as sodium chloride, cane sugar, and acetic acid, but it is positive to cer-
tain foods and other chemicals, depending upon the concentration, etc.

3. Temperature {thermotaxis or thermotropism) (ther mo -tak' sis;
ther -mot' ro pizm) (Gr. therme, heat): The reactions vary with the
temperature, but movements stop if the temperature is decreased suffi-
ciently. Response is negative to higher temperatures.

4. Light [phototaxis or phototropism) (fo to -tak' sis) (fo-tot'ro-
pizm) (Gr. phos, light). The response is negative to strong light but
may be positive to weak light.

Amoeba may also be affected by such stimuli as gravity, electrical
currents, water currents, etc.

Unicellular, Microscopic Animals 349

Reproduction. — The principal method of reproduction is by binary
fission, in which a full-sized Amoeba divides into two parts. The nucleus
divides by mitosis (Fig. 162) and the cytoplasm elongates and divides into
two parts. The entire process occurs in less than thirty minutes at 30° C.
After fission, the young amoebae grow rapidly, reaching mature sizes
about three days after fission.

PARAMECIUM

Paramecium (par ah -me' se um) (Gr. paramekes, oblong) is a large,
fresh-water protozoan commonly called the "slipper animalcule" because
of its fancied resemblance to a slipper. A common type, Paramecium
caudatum (ko-da'tum) (L. cauda, tail) has a tuft of tail-like cilia at
the posterior end and may be about 0.3 mm. long, while P. aurelia
(o-re'lia) (L. aurum, gold or brown) may be less than C.2 mm. long.
Most of the infusoria (in fu -so' ri a) (L. infusus, poured into or crowded)
possess (1) a large macronucleus (Gr. makros, large) composed of a
number of small, complete nuclei and (2) a small micronucleus (Gr.
mikros, small). P. caudatum has a blunt anterior end, and the posterior
end is somewhat pointed (Figs. 163 to 172).

Integument (Covering). — Two types of cytoplasm, as in Amoeba, are
(1) an outer, clear layer, the ectoplasm, and (2) an inner endoplasm
with larger granules. A distinct pellicle (pel'ikel) (L. pellis, skin)
covers the ectoplasm. If a drop of 35 per cent alcohol is added to a
drop of Paramecium culture, the pellicle may be observed to separate
from the ectoplasm. Under high power, the pellicle is seen to be made
of six-sided hexagonal areas (noncellular) produced by ridges on the
surface (Fig. 170). One cilium projects from the center of each hexag-
onal area. The cilia arise from basal granules within the protoplasm
and are called microsomes ( mi' kro_^som ) (Gr. mikros, small; soma,
body). Spindle-shaped cavities called trichocysts (trik'osist) (Gr. thrix,
hair; kystis, sac) are embedded in the ectoplasm just beneath the surface.
These baglike cavities are filled with a liquid which solidifies into long,
jellylike threads when expelled to the exterior. Each trichocyst opens
through a pore on the ridges of the hexagonal areas. The poisonous
trichocyst fibers serve as weapons of defense. They may be observed to
discharge if a small amount of acetic acid is added to a drop of culture.
The basal granules are connected by longitudinal fibers.

Motion and Locomotion. — Fine, hairlike cilia (sil'ia) (L. cilium,
hair) are regularly arranged over the entire external surface. These

350 Animal Biology

beat rhythmically and backward, thus propelling the animal forward.
The rhythmic strokes are diagonal; hence, the body is rotated on its long
axis. The greater rate of action of cilia in the oral groove tends to swerve
the Paramecium to the left. All these actions locomote the animal in a
spiral path, usually to the left.

^Anterior

Contmctilc--
\/acuo\Q

-C\\\a

-PeJIJcle

-Trichocyifc

Macror)uc]eus
MicroriadiQi _.

Tlad\at\r)q

canals ^

Conbractile __
vacuole

^: . :. ',o ■^- ■'.[«:->i%3M- jiv- ^

• • .■ •■'.■'o - ."^l* '^'V. /.'•q •.-•

*:o::.<!i^5-^:..-#;.;'.;;;'6:?.q fi
■».'.-.-P. V xZxo • •. vo • -i^' j*. ; : o

Oralcjroove

Moabh

„__gall<2fc

^-.- Food vacuole

£^ Anas

Posterior

Fig. 163. — Paramecium aurelia, a protozoan of the class Infusoria.

Ingestion and Digestion. — A funnel-shaped oral groove extends from
the anterior end backward and obliquely toward the middle of the ani-
mal. The cell mouth or cytostome (si' to stom) (Gr. kystis, hollow;
stoma, mouth) is at the posterior end of the oral groove and opens into a

Unicellular^ Microscopic Animals 351

short, tubelike gullet or cytopharynx. The side of the animal with the
oral groove is known as the oral or ventral side; the opposite, as aboral
or dorsal. The cilia within the oral groove and gullet propel certain
foods toward the food vacuole. Foods consist principally of bacteria and
other small protozoa. Numerous food vacuoles (droplets of water with

Fig. 164. — Paramecium showing spiral locomotion. 1 , 2, 3, 4, 1 show successive
positions occupied. Dotted areas show currents of water drawn from the front.
(From Jennings: Behavior of the Lower Organisms, published by the Columbia
University Press.)

352 Animal Biology

suspended foods) of various sizes and in \arious stages of food digestion
can usually be seen. Food vacuoles are formed at the posterior end of
the gullet. When filled, the food vacuole is pinched off by the cytoplasm
and it moves away in the flowing cytoplasm. Digestion occurs within

Fig. 165. — The "avoiding reaction" of a Paramecium. A, Solid object a source
of stimulation; 1-6, successive positions occupied by the Paramecium in attempting
to avoid the object; rotation on its long axis also occurs but is not shown in the
diagram. (From Jennings: Behavior of the Lower Organisms, published by
Columbia University Press.)

I I

:•/.'.' -^-^'--^ ' -

. I - /
^ /

I ■

• \ "■

Fig. 166. — Reaction of Paramecium to salt solution. A, Method of introducing
a drop of 0.5 per cent of NaCl solution; B, four minutes later. (From Jennings:
Behavior of the Lower Organisms, published by Columbia University Press.)

Unicellular, Microscopic Animals 353

the food vacuoles because of the contained digestive enzymes secreted
by the cytoplasm. Foods are absorbed and assimilated into living proto-
plasm.

Circulation. — There is no special circulatory equipment, but the foods,
wastes, etc., are circulated by the natural streaming of the cytoplasm
and is known as cyclosis.

Fig. 167. — Neuromotor mechanism (in part), trichocysts, and cilia of Parame-
cium sp. A, Section showing trichocysts attached to the ridges of the hexagonal
depressions of the pellicle ; B, surface and side view, showing the coordinating
fibers which connect the basal granules which control the actions of the cilia. 1,
Cilium; 2, basal granule of cilium; 3, interciliary fibril to connect basal granules;
4, trichocyst pore; 5, trichocyst; 6, discharged trichocyst; 7, hexagonal area of
pellicle. (From various sources, from data discovered by Lund.)

Fig. 168. — Galvanotropism (reaction to electricity) shown by Paramecia. A,
General appearance of the apparatus and Paramecia reacting to electric current.
The current is passed through a cell with porous walls by means of unpolarizable
brush electrodes. Paramecia have moved toward the negative pole or cathode.
B, Magnified view showing movement toward the cathode. (From Jennings:
Behavior of the Lower Organisms, published by Columbia University Press.)

354 Animal Biology

Respiration. — Oxygen is taken in from the water through the body
surface. Carbon dioxide passes out through the body surface as well as
through the contractile vacuoles.

Excretion and Egestion. — A large contractile vacuole is usually located
near each end of the body. Each contractile vacuole has radiating canals

f-j^

PARAMOECIJM
PREPARING FOR FISSION

FISSION COMPLETED

Fig. 169. — Paramecium reproducing by asexual, binary fission (transverse divi-
sion), shown diagrammatically. Note the division of the nuclei, gullet, and con-
tractile vacuoles. (From Parker and Clarke: Introduction to Animal Biology,
The C. V. Mosby Co.)

t^"7trl l^ba-g'i.

rid. tri. fi:

(»«^^

•■'■A

Fig. 170. — Structure of the ectoplasm of typical Protozoa of the class Infusoria.
A, Frontonia leucas (cross section) ; B, Paramecium sp. (cross section) ; C, Para-
mecium sp. (surface v^iew) ; pel., pellicle; cor., cortex; tri., trichocyst; enp., endo-
plasm; fl., cilium; ha. gr., basal granule (microsome) at the base of each cilium;
alv., alveolar layer of minute regular vacuole; rid., surface ridges of the pellicle;
fi' ., point of insertion of cilium in the middle of each hexagonal area; hexagonal
areas are formed by the striations of the pellicle. (From Borradaile and Potts:
The Invertebrata. By permission of The Macmillan Company and the Cambridge
University Press, publishers.)

Unicellular, Microscopic Animals 355

(from six to eleven) which collect wastes and transport them to the con-
tractile vacuole. The latter discharges wastes to the exterior through a
pore. After each discharge, a new contractile vacuole is formed. Con-
tractions may occur every twenty to thirty seconds, depending upon nu-
merous factors. Wastes may also diffuse through the pellicle. An anal
spot posterior to the oral groove may be observed as it discharges solid
particles.

Coordination and Sensory Equipment. — Paramecia respond to stimuli
as do many other protozoa. When certain stimuli are encountered, a
Paramecium may reverse its cilia and swim backward a short distance.
Using its posterior end as a pivot, the anterior end then swings about in
a circle, testing for the stimulus. When no longer stimulated, the cilia

Fig. 171.- — Paramecium. Photomicrograph of specimens in conjugation. (Copy-
right by General Biological Supply House, Inc., Chicago.)

move the animal forward again. This is the so-called ''avoiding reac-
tion." The optimum temperature for paramecia is slightly less than
30° C. When stimulated by heat, a paramecium displays the avoiding
reaction, moving toward less heat. Sodium chloride gives a negative
chemotaxic reaction, while a weak solution of acetic acid may even attract
paramecia. They do not seem to be visibly affected by ordinary light.
The longitudinal fibers at the basal granules of the ciHa are probably for
the purpose of coordinating the actions of the cilia (Fig. 170).

Reproduction. — Paramecium divides transversely by binary fission
(Fig. 169). Occasionally, this is interrupted by a temporary union of
two individuals through a process called conjugation (L. com, together;
jugare, to join) (Fig. 171) in which there is a reciprocal fertilization.

356 Animal Biology

MEGANUCLEUS
MICRONUCLEUS

FUSION NUCLEUS

FISSION

FUSION NUCLEUS

FISSION

\0 \ t)\ FISSION
» \/ »

C •CONJUGANT CARRIES ON

NORMAL OFFSPmNa OF

Fig. 172. — Paramecium caudatum reproducing by conjugation, shown diagram-
matically. The meganucleus is also known as the macronucleus. (From Parker
and Clarke: Introduction to Animal Biology, the C. V. Mosby Co.)

Unicellular, Microscopic Animals 357

Two individuals construct a ''protoplasmic bridge'' between their oral
surfaces, and certain of their reorganized nuclear materials migrate to
the opposite paramecia (Figs. 171 and 172). Fusion of nuclear mate-
rials results in fertilization, which is somewhat like sexual reproduction,
although no sex cells are actually formed. Paramecium aurelia has been
carried in a culture continuously for a period of over forty years, and
neither conjugation nor death from age have occurred, yet fission took
place at a vigorous, normal rate. It has been found that there are eight
distinct races of paramecia, each with its inherited characteristics. Para-
mecium aurelia has been found to have at least two mating types called
types I and II. Neither of these will conjugate with one another, but
mating type I must conjugate with mating type II. In order to rejuve-
nate certain paramecia, conjugation must take place between different
strains, while in other species rejuvenation is accomplished by inbreeding
or even self-fertilization.

It has been discovered recently that the cytoplasm contains a system
of particles which have the property of self-duplication, a property simi-
lar to that of chromosomes and genes of the nucleus. Such a system of
cytoplasmic genes are called plasma genes to distinguish them from nu-
clear genes. The plasma genes play important roles in the heredity _ of
paramecia.

Another method of reproduction is known as autogamy (o -tog' a my)
(Gr. autos, self; gamos, marriage) and consists of a nuclear reorganiza-
tion of a single individual. It involves meiosis (mio' sis) (Gr. meion,
smaller) in which there is a reduction of nuclear materials from the dip-
loid (double) to the haploid (single) condition. It also includes self-
fertilization. This method is used by paramecia under certain conditions.

It has been discovered recently that there are races of paramecia which
produce and liberate a substance in their cytoplasm which kills animals of
other races. The two races have been called ''killers'' and "sensitives."
This killer substance is called "paramecin," and one particle of it {kappa
particle) can kill a sensitive Paramecium. Killers may have hundreds
of these kappa particles in their cytoplasm, while sensitives have none.
Hence, these kappa particles are cytoplasmic genes called plasma genes.

EUGLENA

Euglena (u -gle' na) (Gr. eu, good; glene, pupil of the eye) is a com-
mon, fresh-water flagellated protozoan. Two common species are Eu-
glena viridis (vir'idiz) (L. viridis, green) 2ind Euglena gracilis (gras'il-

358 Animal Biology

is) (L. gracilis, slender). These flagellates belong to the class Masti-
gophora (mas ti -gof o ra) (Gr. mastix, whip; phoreo, to bear) because
of a whiplike flagellum (L. flagellatus, whip). Because Eugle Ji a has
certain plantlike characteristics, it is frequently claimed to be a plant by
the botanists. We might well compromise and call it a plant-animal,
E. viridis is about 0.1 mm. long, blunt at the anterior end, and with a
pointed posterior end. An ovoid or spherical nucleus contains a central
body, the endosome (Fig. 173).

Mouth

Gullet-M'

Stigma

Granules

Pyrenoid'
Nucleus—

Striation

Reservoir

-Contractile
vacuoles

Nucleus,

Cuticle

Chromatophore ^

y Flagellum -^

[($^t^)— Chromatophore-

-Reservoir —

—Nucleus
Cyst

Fig. 173. — Euglena viridis, a protozoan of the class Mastigophora. A, Free-
swimming adult (highly magnified) ; B, reproduction by longitudinal binary fis-
sion; C, euglena rounded and protected by cyst; D, longitudinal fission within
cyst; E and F, shapes (in outline) assumed by Euglena. (All enlarged and some-
what diagrammatic.)

Integument (Covering). — A tough, flexible, external pellicle (cuticle)
has longitudinal, parallel, thickened striations which give the body
rigidity.

Ingestion and Digestion. — A funnel-shaped cytostome (cell mouth)
leads to a cytopharynx (gullet). The latter has an enlarged reservoir

Unicellular, Microscopic Animals 359

at its base. A contractile vacuole next to the permanent reservoir arises
by the flowing together of several smaller vacuoles, and it discharges
wastes into the reservoir.

Suspended in the cytoplasm are numerous green, chlorophyll-bearing
chromatophores (kro' mat o for) (Gr. chroma, color; phorein, to bear)
known specifically as chloroplasts. In each chloroplast is a pyrenoid (pi-
re' noid) (Gr. pyren, fruit-stone; eidos, like) which probably forms a
starchlike paramylum (pa -ram' i lum) (Gr. para, beside; amylon,
starch). The latter may be free in the cytoplasm in the form of rods,
disks, etc. Euglenae photosynthesize most of their foods (holophytic
nutrition) in a plantlike manner, although they may absorb certain foods
through the general body surface by saprophytic nutrition. It is debated
whether Euglenae ingest solid foods through the cytopharynx.

Motion and Locomotion. — A long, vibratile flagellum, arising from two
axial filaments within the body, extends out through the cytostome. The
flagellum consists of a contractile axial filament, or myonemes (mi' on-
em) (Gr. myo, muscle; nema, thread), composed of a bundle of fibers
and surrounded by a sheath of protoplasm. A Euglena may be propelled
in a spiral path by the actions of the flagellum at the anterior end. Eu-
glena may also contract the body to assume a variety of shapes and to
move by what is called euglenoid movement.

Circulation. — Foods, wastes, etc., are circulated through the cytoplasm
by the flowing of the protoplasm and is known as cyclosis.

Respiration. — Respiration takes place through the general body sur-
face. Possibly some of the carbon dioxide is used in photosynthesis, and
some of the oxygen from photosynthesis is used for its various activities.

Excretion. — A contractile vacuole, next to the permanent reservoir,
arises by the flowing together of several smaller vacuoles and collects and
discharges wastes into the reservoir. From the latter the wastes pass to
the gullet and out the cytostome. It is not unusual for wastes to be elim-
inated through a mouthlike opening in lower types of animals.

Coordination and Sensory Equipment. — A light-sensitive, red, eye spot
or stigma (Gr. stigma, mark) is near the anterior end of the body. A
fine, delicate, fiberlike rhizoplast (ri'zoplast) (Gr. rhiza, root; plastos,
formed) extends from the nucleus to the reservoir. Euglenae swim to-
ward ordinary light (positive phototaxis) to assist in photosynthesis but
swim away from direct sunlight which may be harmful. The avoiding
reaction is frequently observed.

360 Animal Biology

Reproduction. — Binary longitudinal fission occurs by a splitting of the
body at the anterior end which continues posteriorly until completed.
The nucleus, chloroplasts, etc., also divide. Occasionally, a Euglena
throws off its flagellum and surrounds itself with a thick, gelatinous cyst
(Gr. kystis, bag) to resist drying conditions. Sometimes longitudinal
fission may occur while the animal is encysted and new flagella are
formed. As many as thirty-two Euglenae in one cyst have been observed.
When proper conditions are encountered, the cyst breaks and the Eu-
glenae emerge to assume an active life again.

VOLVOX

Volvox (vol' vox) (Gr. volvo, turn) is a colonial protozoan in which
thousands of body (somatic) cells are associated to form a hollow, water-
filled, globe-shaped colony. A common species is V. globator (L. globus^
ball). Because Volvox contains certain plantlike characteristics (chloro-
phyll, cellulose), it might be considered as a plant-animal (Figs. 174 and
175).

Integument. — The body wall consists of cellulose, a material common
in plants. A gelatinous matrix (mat' riks) (L. mater, mother) serves as
an intercellular substance to bind adjacent cells together. The cells are
arranged in a single layer, and many of them bear two flagella.

Motion and Locomotion. — Most of the body cells bear two flagella
whose lashing movements give the colony a rotating locomotion. The
male sperm are also supplied with flagella.

Ingestion and Digestion. — Most of the body or somatic cells (so-
mat' ik) (Gr. soma, body) contain chlorophyll by means of which car-
bon dioxide and water may be combined to form foods by photosynthesis
in the presence of energy-supplying light. There is no cytostome so solid
foods cannot be ingested. Chlorophyll is borne in chloroplasts.

Circulation. — There is no special circulatory equipment, but materials
are probably circulated by the flowing of the cytoplasm (cyclosis).

Respiration. — Respiration probably takes place through the general
body surface. Possibly some of the carbon dioxide is used in photosyn-
thesis, and some of the oxygen from photosynthesis is used for its various
activities.

Excretion. — Most of the body cells contain a contractile vacuole which
collects wastes and throws them to the outside. Since the colony is only
one cell in thickness, possibly each cell can easily rid itself of its waste
materials.

with
hich
n of

-o

•M

o C ci

- CO

J2 o ^

^^ • •— t ^

4J
*->

> -t-j • -^

•-I i-l ^-V

• »-1

-t-> ^^

<U •>-> lU

bo 3 u

j:i

of ve
witho

(sex

eds
sis (
etes

^ (U c

§^^

-c o D

c -^

_, ij c3

:§f6

*|o

0-Q.2

O o o

t^ o " g

•^ S c ^

■ O-Z! .

" n N • -

•5tt5

o.c

:= 2?

o-^c/^

■ ■-I C/3

t/2

O •" —

a o jD 5

,—1 C3

-^ O ai

^ a o

I bc^ Oj_^

;^ > ."S bo ^

o
'o

bo =" 55
bo o

o c:

q3 c3 k!

S-i

362 Animal Biology

Unicellular^ Microscopic Animals 363

Coordination and Sensory Equipment. — The thousands of body cells
in the colony are connected by protoplasmic strands (Fig. 175) to estab-
lish physiologic (functional) continuity between these cells. Through
these structures, coordination between the various parts of the colony
may be accomplished. Most body cells contain an eye spot (stigma)
which is light sensitive and probably assists in orientation for photosyn-
thesis.

Reproduction. — Reproduction occurs by asexual and sexual methods.
In asexual reproduction, certain cells of the colony without flagella in-
crease in size and are called parthenogonidia (par then o go -nid' i a)
(Gr. parthenos, virgin; gonos, offspring; idion, diminutive). These di-
vide to form numerous cells which form a new colony. This method of
developing an egg without unioji with a sperm is known as partheno-
genesis (par then o -jen' e sis) (Gr. parthenos^ virgin; genesis^ origin or
descent) .

The sexual method consists in the formation of flagellated male sperm
and nonflagellated female eggs. Within the colony, certain cells, by
simple division, form a sperm bundle which may contain over 100
spindle-shaped sperm (male gametes). Other cells divide and produce
as many as 50 large eggs (female gametes). One sperm fuses with
(fertilizes) an egg (inside the colony) to form a zygote (zygospore)
which surrounds itself with a resistant wall to withstand the winter.
When proper conditions are encountered, the zygospore breaks the wall
and by division forms a new colony. In Volvox the colony consists of
two types of cells; the true somatic body cells and the true reproductive
germ cells (either male or female) .

PLASMODIUM

Plasmodium (plaz -mo' di um) (Gr. plasma, mold or form; eidos,
like) belongs to the class Sporozoa because it reproduces by means of
spores. Plasmodium vivax (vi' vax) (L. vivere, long live) causes the
so-called tertian type of human malaria (L. tertianus, thrice) with an
attack of fever every forty-eight hours (third day) ; P. malariae causes
quartan malaria (L. quartus, fourth) with an attack every seventy-two
hours (every fourth day); P. falciparum (L. falix, sickle) produces
aestivo- autumnal malaria (L. aestivus, summer) with daily attacks or
more or less constant fever. The life cycles of these three species of
Plasmodium differ only in minor details. Malarial fever is transmitted
by the bite of the diseased female mosquito (not the male) of certain

364 Animal Biology

a
a

a
o

(X4

Unicellular^ Microscopic Animals 365

366 Animal Biology

species which happen to carry the sporozoite (spore) stage of the malarial
parasite. The female mosquito of the genus Anopheles (an -of el ez)
(Gr. anopeles, hurtful) transmits malaria, while the ordinary mosquito
of the genus Culex (ku'leks) (L. culex, gnat) does not (Figs. 176, 202,
and 303).

Motion and Locomotion. — In the adult stages Plasmodium, does not
possess locomotor organelles, although certain immature stages may be
motile. These will be noted later in the discussion of reproduction.

Ingestion and Digestion. — Sporozoa have no digestive organelles but
they absorb foods from their surroundings. Since they are parasitic, they
undoubtedly enjoy many "precooked" meals at the expense of the hosts.

Circulation. — The Sporozoa are so small that they do not require
circulatory equipments but can rely upon the flowing of protoplasm
(cyclosis) within their cells.

Respiration. — The limited oxygen requirements are probably sup-
plied by taking it in through the general body surface.

Excretion. — The parasitic sporozoa, taking in foods from their hosts,
probably do not need to excrete great quantities of wastes and do so
through the general body surface.

Coordination and Sensory Equipment. — The parasitic habits probably
explain the absence of specific sensory equipments.

Reproduction. — The spindle-shaped spores, called sporozoites (spo ro-
zo'ites) (Gr. sporos, spore; zoon, animal) (Fig. 176), in the saliva of
a diseased female mosquito are thrust into the human wound by the bit-
ing mouth parts and enter the human red blood corpuscles where they
become amoeba-like trophozoites (trof o -zo' ite) (Gr. trophe, nutrition;
zoon, animal) which feed at the expense of the red blood corpuscles. In
about fifty hours the trophozoite becomes a schizont (shiz' ont) (Gr.
schizein, divide), which divides (sporulates) to form from fifteen to
twenty-four merozoites (me ro -zo' ite) (Gr. meros, part; zoon, animal).
The merozoites are liberated into the blood stream in about eight hours
and attack other red blood corpuscles. The time of liberation of mero-
zoites parallels the attack of fevers and chills. Some merozoites develop
into additional schizonts again, while other merozoites became sex cells,
called gametocytes (gam' et o site) (Gr. gamos, spouse; kytos, cell).
These m.ale and female gametocytes may be picked up by the biting
female mosquito from the blood stream of a malarial patient. The
female gametocyte forms a macrogamete (egg). The male gametocyte
forms from six to eight elongated microgametes (sperm). A sperm and
egg fuse to form a zygote which changes into a motile, wormlike ookinete

Unicellular^ Microscopic Animals 367

(oo-kin'et) (Gr. oon, egg; kine, motile) which enters the wall of the
mosquito stomach. Here the ookinete forms a round oocyst (o'osist)
(Gr. oon, egg; kystos, sac) which, after six to seven days, forms hundreds
of spindle-shaped sporozoites which eventually go to the salivary glands
of the mosquito, ready to be transferred by a bite. Formation of spores
from a fertilized zygote is called sporogony (spo -rog' o ne) (Gr. sporos,
spore; gonos, to produce), but if formed from unfertilized cells it is called
schizogony (skiz -og' o ne) (Gr. schizein, to cleave).

QUESTIONS AND TOPICS

1. List all the characteristics which protozoa, as revealed by your studies, have
in common.

2. Make a table of the protozoa studied, showing all differences between them.

3. Explain specifically why certain protozoa are considered as plant-animals.

4. Describe each of the following for the protozoa studied: (1) integument,
(2) motion and locomotion, (3) ingestion and digestion, (4) circulation, (5)
respiration, (6) excretion and egestion, (7) coordination and sensory equip-
ment, and (8) reproduction.

5. Why do unicellular protozoa not have organs and tissues? What are such
structures called in protozoa?

6. What characteristics of living protoplasm did you observe in your studies
of protozoa?

7. In the light of the numerous abilities of protozoa to live successfully, would
you consider them simple or complex? Explain.

8. Discuss the economic importance of protozoa, both detrimentally and bene-
ficially.

9. Explain the complex life cycle of such a protozoan as Plasmodium, including
the stages in proper sequence, the different hosts, and the detrimental effects
of the different stages.

10. Explain the significance of parthenogenesis as revealed by certain protozoa.

11. List the conclusions you can draw from the observations made on protozoa.

SELECTED REFERENCES

Calkins: Biology of the Protozoa, Lea & Febiger.

Calkins: The Smallest Living Things, The University Society.

Calkins and Summers: Protozoa in Biological Research, Columbia University

Press.
Hegner: Invertebrate Zoology, The Macmillan Co.
Hegner: College Zoology, The Macmillan Co.

Hegner and Taliaferro: Human Protozoology, The Macmillan Co.
Hyman: The Invertebrates (Protozoa to Ctenophora), McGraw-Hill Co., Inc.
Kudo: Handbook of Protozoology, Charles C Thomas, Publisher.
Minchin: An Introduction to the Study of Protozoa, Lea & Febiger.
Morgan: Field Book of Ponds and Streams, G. P. Putnam's Sons.
Needham and Needham: Guide to the Study of Fresh Water Biology, Comstock

Publishing Co., Inc.
Ward and Whipple : Fresh Water Biology, John Wiley & Sons, Inc.

Chapter 19

FLATWORMS AND ROUNDWORMS

(PHYLUM PLATYHELMINTHES and
PHYLUM NEMATHELMINTHES)

Planaria (Dugesia) ; Liver Fluke; Tapeworm; Ascaris

Planaria (Dugesia) (pla-nar'ia) (Gr. pianos, wandering) and the
liver fluke Fasciola hepatica (fas -i' o lah) (L. jasciola, a band) (he
pat'ika) (Gr. hepar, liver) belong to the Phylum Platyhelminthes (plat
i hel -men' thez) (Gr. platus, flat; helmins, worm).

PLANARIA (DUGESIA)

The common, free-living, fresh- water planarian is Dugesia tigrina, for-
merly called Planaria maculata. Its upper surface is spotted, brown and
white, while the lower is grayish. The body has bilateral symmetry and
may be 20 mm. long (Figs. 177 to 179) .

Integument. — The ectoderm, a thin layer of external, ciliated cells,
called the epidermis, secretes mucus which may give protection and
diminish friction. Rodlike rhabdites (rab' dite) (Gr. rhabdos, rod) em-
bedded in the epidermis are discharged for offensive purposes. The
entoderm is a single layer of elongated, epithelial cells and lines all
branches of the digestive tract. The middle, cellular mesoderm is com-
posed of large amoeboid cells. Hence, planaria is triploblastic, being
composed of cellular ectoderm, mesoderm, and entoderm. There is no
true body cavity.

Motion and Locomotion. — The entire surface is covered with hairlike
cilia, although they are more numerous on the flat, ventral side. Three
sets of muscles, longitudinal, circular, and oblique, in the body wall aid
in locomotion. Mucus secreted at the anterior end reduces friction dur-
ing locomotion.

Ingestion and Digestion. — The pharyngeal chamber, with its cylindri-
cal, muscular pharynx and mouth at its tip, is located midway between

368

Flatworms and Roundworms 369

the anterior and posterior ends of the body (Fig. 177). The intestine
joins the pharynx and has one anterior and two posterior main branches,
each with numerouSj smaller^ lateral branches or diverticula (di ver -tik'
ula) (L. de, d^Mdiy; vertere, to turn). The intestine serves as a gastro-
vascular cavity (gas tro -vas' ku lar) (Gr. gaster, stomach or digestive;
L. vasculum, vessel or circulatory) in which both digestion and circula-
tion take place. The pharynx may be everted and protruded through the
ventral surface as a tubular proboscis (pro -bos' is) (Gr. proboskis.

Transverse tube

Excretory tube

Labera] branches

Excretory pore —

Anterior wbestine

with lateral branches

Pharynx

flame cell with cilia.
to propel wastes

-Opentna of pharynx.
_>Moafch

.Posterior
intestine

Flame eel (

(enlarged)

Fig. 177. — Planaria of the phylum Platyhelminthes, class Turhellaria, showing the
digestive system, A, and the excretory system, B.

trunk) when feeding. Part of the foods are digested within the intestine
by digestive juices secreted by cells which line it. This is called extra-
cellular digestion (outside of cells). Other foods are digested by diges-
tive juices within food vacuoles within these cells. This is called intra-
cellular digestion (within cells). There is no anus, and wastes are elimi-
nated through the mouth, which is a rather common practice in many
lower animals.

370 Animal Biology

Circulation. — There is 7io special circulatory system, but the branched
intestine serves as a gastrovascular cavity in which foods, wastes, water,
etc., circulate.

Respiration. — Respiration takes place through the general body sur-
face as well as through the surface of the intestine (gastrovascular
cavity) .

Excretion and Egestion. — Wastes are eliminated from the intestine
through the mouth. Coiled excretory tubes run lengthwise along the

Eye spot

Auricle

Brain

~Zz.-\-^^ '^^^^<^ cords

r^rr^r^ =.- Transverse nerves

Fig. 178.— Nervous system of Dugesia (Planaria). Observe the nerves leading

from the brain to the auricle.

two sides of the body and are connected near the anterior end by a
transverse tube. This system opens exteriorly through small excretory
pores on the dorsal surface behind the eye spots. Additional openings
along the excretory tubes may exist. The small lateral branches of the
tubes divide, redivide, and terminate in a large, hollow, flame cell. The
latter contains a bunch of motile cilia to propel wastes. The motile cilia
tend to flicker like a flame; hence, "flame cell" (Fig. 177).

Flatworms arid Roundworms 371

Coordination and Sensory Equipment. — A bilobed, diffuse mass of
nerve cells known as the cerebral ganglion (brain) is located beneath the
pair of sensitive eye spots just posterior to the pair of sensitive auricles.
Numerous nerves connect the brain with the sense organs in the anterior
part of Planaria. Two ventral nerve cords extend backward, laterally

Cerebrals
(jatKjIion

LonqitudinaL
nerve cord

Testis

VasQ

efferentia

Lateral

nerve

Auricle

_^_-Eyc
_\ Ovary

Vos J

deferens

Mouth \_^^

Sem'mcl

vesicle

Sern'inal

receptacle

— .Yolk cjlar)ds

Lateral nerve

Intestine

_J)/Vcrticula

lumen of

pharynx

N_. Intestine

_Oviduct

Pharyngeal

chamber

Penis

Qenitalpore

Fig. 179. — Dugesia (Planaria) (reproductive system). The male organs are
shown on one side only. (From Potter: Textbook of Zoology, The G. V. Mosby
Co.)

372 Animal Biology

and longitudinally, to the posterior part of the body. Several transverse
nerves connect the two ventral nerve cords (Fig. 178) Ciliated pits on
either side of the head contain special sensory cells.

Planaria illustrates axiate organization. It has (1) a primary antero-
posterior axis and (2) a secondary ventrodorsal axis. When the primary
axis is considered, we find an axial gradient of metabolic activity which
decreases as we proceed from the anterior end toward the posterior end.
In other words, the more highly active areas of the anterior regions,
because of their activity, assume a control over the less active posterior
regions as we progress in sequence from anterior to posterior. When
the secondary ventrodorsal axis is considered, we find the greatest activ-
ity in the ventral side. Activity gradually decreases as we go toward
the dorsal side. When these two axes are considered at the same time,
the region of greatest activity is located at the anterior end near the
ventral side. Planaria also has bilateral symmetry in which the right
and left halves are similar to each other. Because of the axial gradient,
Planaria may be cut transversely into pieces and each segment under
proper conditions will regenerate and eventually assume its normal ac-
tivities with new centers of control established in each piece (Fig. 28).

Planaria responds to a variety of stimuli. One pair of dorsal eye spots
are sensitive to light. One pair of lateral tactile olfactogustatory auricles
connected with the brain are affected by touch and certain chemicals (L.
tactus, touch; L. olfacio, smell; L. gustus, taste).

Reproduction. — Both male and female sex organs are present in the
same Planaria; thus it is monecious or hermaphroditic (mo -ne' si us;
her maf ro -dit' ik) (Gr. monos, one; eikos, house) (Gr. hermaphroditos,
combining both sexes). However, self-fertilization probably does not
occur, but cross fertilization is used (Fig. 179). The male organs include
numerous spherical testes scattered throughout the body. The testes are
connected by sperm ducts or vasa deferentia (singular, vas deferens).
Each of the pair of large sperm ducts enlarges at its posterior end into a
seminal vesicle (L. semen, seed; vesica, bladder) . The latter connect with
the muscular copulatory penis. The sperm produced by the testes are col-
lected by the vasa deferentia and carried to the seminal vesicles until
transferred by the penis to the opposite animal during copulation. The
penis projects into the genital chamber located posterior to the pharynx.
The sperm are transferred by the penis to the seminal receptacle (copu-
latory sac) of the opposite animal during copulation. The saclike semi-
nal receptacle is connected by a tube with the genital chamber.

Flatworms and Roundworms 373

The female organs include a pair of spherical ovaries near the anterior
end. Each is connected by means of an oviduct with the genital cham-
ber. A series of yolk glands empty yolk (food) for the eggs into the
oviduct. After copulation the sperm leave the seminal receptacle, travel
up the oviducts toward the ovaries, and fertilize the eggs as they leave
the ovary. As the fertilized eggs pass down the oviducts, they are sur-
rounded by yolk cells from the yolk glands. In the genital chamber
clumps of eggs and yolk cells are surrounded by a shell-like egg capsule
(cocoon). Each cocoon may contain as many as ten eggs and hundreds
of yolk cells for nourishment. The cocoons are passed to the outside
through a genital pore. The eggs develop in two to three weeks into
miniature worms without a reproductive system. The reproductive or-
gans of adults degenerate after each breeding and are later regenerated.
This might explain the absence of reproductive systems in certain adults.

Planaria also reproduces asexually by transverse fission. Ordinarily
Planaria constricts just behind the pharynx, and after several hours the
two parts separate. The anterior part regenerates the missing posterior
part, while the posterior part regenerates an anterior part, with all miss-
ing structures eventually replaced. Because of axiate organization,
Planaria shows a remarkable ability to replace missing parts. This axiate
gradient of metabolic activity can be demonstrated by the relative
amounts of oxygen used, and the amounts of carbon dioxide given off",
by the different levels from one end of the animal to the other. Planaria
may be carefully cut into pieces to illustrate this remarkable ability to
regenerate. If properly conducted, this makes one of the most interest-
ing exercises in the laboratory.

LIVER FLUKE

The liver fluke, Fasciola (Distomum) hepatica, is a parasitic trema-
tode (tre'matode) (Gr. trema, pore; eidos, resemblance) which in its
adult stages may live in the liver of sheep, cows, pigs, and occasionally
man. The immature stages are found in the bodies of a specific kind
of water snail, with a few special stages in water, or on vegetation. The
adults are flat and leaf like. The body is triploblastic (Figs. 180, 181,
374).

Integument. — The ectoderm is a thick, heavy, elastic cuticle which
protects the adult from the host which it parasitizes. The entoderm
lines the alimentary tract. The mesoderm is represented by muscles,
excretory organs, reproductive organs, and parenchyma. The paren-

374 Animal Biology

Mouth

Pharynx

Esopha(jus

__;nfcc5t?n<?

. Excretory

canal

-.Pharynx
—Nerve rinq
--Esophacjus

vesiclQ

Ovary &.
duct

Openincj of excretory

Mouth

Penis^ withaP^r.

^ Vaccina tures

2X Uterus

Longitudinal
^nerve

Jhcll Cjland
.Sperm duct

-Anterior
testes

.-Posterior
testes

-Yolk qlands

Fig. 180. — Liver fluke (Fasciola hepatica) of the phylum Platyhelminthes.
A, Digestive system; B, excretory system; C, nervous system; D, reproductive sys-
tem. All are much enlarged and somewhat diagrammatic.

Flatworms and Roundworms 375

Proboscis (extruded)

Nerve-ganglion

Eerg,.

Yolk-cella

„ Intestine

- Germ-cellfi

Cercaria

Ventral sucker
Nephridium

Germ-cells

Fig. 181. — Diagrams to show the life cycle of the liver fluke (Fasciola hepatica).
A, Egg in a case; B, miracidium (ciliated larva); C, sporocyst; D, redia (early
stage) ; E, redia (later stage containing cercaria) ; F, cercaria with motile tail;
G, cercaria (encysted and without tail) ; H, adult fluke in the liver of the sheep,
where it produces, perhaps, 500,000 eggs when sexually mature. Only digestive
and excretory systems are shown in this adult. (Consult Fig. 180, D for reproduc-
tive system.) (From Hegner: College Zoology. By permission of The Macmillan
Company, publishers.)

376 Animal Biology

chyma (par -eng' ki ma) (Gr. para, beside; engchyma, infusion) is a
loosely organized tissue between the alimentary tract and the body wall
in which the internal organs are embedded, there being no true coelom.

Motion and Locomotion. — The body consists of three layers of mus-
cles: circular, longitudinal, and diagonal (oblique).

Ingestion and Digestion. — A mouth lies in the center of a muscular,
disk-shaped anterior (oral) sucker. A ventral sucker serves for attach-
ment. The mouth leads into a short pharynx, the latter connects with
the esophagus, and the esophagus leads to the intestine, with its two
main branches and numerous smaller ones. The digestive cavity serves
as a gastrovascular cavity for digestion and circulation.

Circulation.— There is no special circulatory system, although circu-
lation is accomplished by the digestive tract (gastrovascular cavity).

Respiration. — Respiration occurs through the general body surface.
Being parasitic, the oxygen needs are probably not great.

Excretion. — The external excretory pore (nephridial opening) is lo-
cated at the posterior end of the body. There is only one main excretory
canal with its numerous branches which extend to all parts of the body.
Undigested materials may be eliminated through the mouth.

Coordination and Sensory Equipment. — The nervous system consists
of a brain (nerve ring) in the anterior part of the body. Two longitudi-
nal nerves extend posteriorly from the brain. The general structure
resembles that in Planaria.

There is no special sensory equipment in the adult stage which is
parasitic within the body of the host.

Reproduction. — The external genital opening is located between the
mouth and the ventral sucker. Both male and female reproductive or-
gans are present in the adult fluke; hence, it is mo?iecious (hermaphro-
ditic). Their arrangements may be studied in Fig. 180, D.

The various stages in the life cycle in the two hosts may be studied in
Figs. 181 and 374. One adult fluke may produce over 500,000 eggs, and
200 flukes in the bile ducts of a sheep liver may thus produce 100,000,000
eggs. The eggs pass from the sheep liver to the intestine where they are
passed with the feces. When in water, an egg produces a ciliated larva
called a miracidium (mir a -sid' i um) (Gr. meirakion, stripling). The
latter swims until it bores into the body of a certain species of fresh-
water snail (Lymneae). In two weeks it changes to a saclike sporocyst
(spor'osist) (Gr. sporos, spore; kystis, sac). Each of the numerous
germ cells within a sporocyst develops into a second type of larva called

Flatworms and Roundworms Zll

the redia (re' di a) (after Redi, an Italian scientist). Redia in turn
give origin to one or more generations of daughter redia, after which they
form a third type of tailed larva called a cercaria (ser-ka'ria) (Gr.
kerkos, tail). The cercaria leave the body of the snail, swim for a time
if water is available, and then encyst on grass or other vegetation. If the
vegetation is eaten by a sheep, the cyst wall is dissolved by the digestive
juices and the cercaria travel to the bile ducts of the liver where mature
flukes develop in about six weeks.

TAPEWORM

The pork tapeworm lives as an adult in the alimentary canal of man.
It has the scientific name Taenia solium (te' ni a; soMi um) (L. taenia,
ribbon; solus, alone). A closely related species, the beef tapeworm

ProqJottid

SheU

^ Hooks

Fig. 182. — Development and life history of the pork tapeworm {Taenia so-
lium). A, The anterior part of the tapeworm, showing the scolex with its suckers
and hooks, as well as young proglottids; B, mature proglottid with multibranched
uterus containing eggs; C, egg with embryonal shell (striped) ; D, larva with
three pairs of hooks and without shell; E, cyst stage (shown in section) with
scolex inside; F, more advanced stage with scolex everted and the bladder at-
tached. Stage F develops into the first stage, thus completing the life cycle.
Stages A and B are present in the human intestine; stages C and D in the pig
intestine; stage E in pig tissues; stage F, again in human body.

(which also parasitizes man), is called T. saginata (sagi-na'ta) (L.
saginare, to fatten). T. solium has an enlarged scolex (sko' lex) (Gr.
skolex, worm) which contains hooks and suckers. T. saginata has no
hooks. A large string of linearally arranged parts known as proglottids
(pro -glot' id) (Gr. pro, before; glottis, tongue) are attached to the
neck. One worm may become several feet long and contain hundreds of
proglottids. The latter are formed by budding (strobilization) from the

378 Animal Biology

S-i

CO
CO

-J ^

I— I i/i

3
X

br; c^

C 4J

Flatworms and Roundworms 379

neck, so that the newest proglottids are nearest the neck. The older ones
at the opposite end of the worm may break from the series and be passed
with the feces (Figs. 182 and 183).

Integument. — An external, very thin cuticle may give slight protection
to the parasite against the host.

Motion and Locomotion. — The tapeworm is moved primarily with
the contents of the alimentary canal, although the hooks and suckers on
the scolex attach the anterior end.

Ingestion and Digestion. — There is no alimentary tract, and the gen-
eral body surface absorbs digested foods from the intestine of the host.
There is no true coelom,.

Circulation. — There is no circulatory system required because foods
are absorbed through all surfaces of the body.

Respiration. — What little oxygen that is probably needed because of
its parasitic habits may be taken in through the general body surface.

Excretion. — A pair of longitudinal excretory canals whose branches
end in flame cells open to the exterior, at the posterior end of the pro-
glottid, where wastes are eliminated.

Coordination and Sensory Equipment. — The nervous system is simi-
lar to that of Planaria and the liver fluke (cerebral ganglia, lateral nerve
cords), although not so complex. The parasitic habits probably explain
the absence of sensory equipment, although suckers and hooks are present
for attachment.

Reproduction. — A mature proglottid contains both male and female
sex organs which may be studied in Fig. 183. The eggs develop into six-
hooked embryos. If eaten by a pig, they bore through the wall of the
digestive tract and enter the skeletal muscles or other organs where they
encyst. Within the protective cyst, a. scolex develops from the cyst wall
and then everts. The larva is called a bladderworm or cysticercus (sis-
ti-ser'kus) (Or. kystis, bladder; kerkos, tail). If insufficiently cooked
pork containing cysticerci is eaten by man, the bladder part is cast off
and the scolex attaches to the human intestine and a series of proglottids
is formed by budding at the neck.

ASCARIS

A common roundworm, parasitic in the human intestine, is Ascaris
lumbricoides (as'karis lum bri -koid' ez) (Gr. askaris, intestinal worm;
L. lumbricus, earthworm; Gr. eidos, form). It has a long, slender,

380 Animal Biology

Mouth

Excretory pore

Pharynx

iJii

Excretory tubes _ _ ^___

Intestine

Muscles _

Epiderm is _

qcnital pore

Vaqi'ma

v/Qs deferens .

Tejt'i^

- -Uterus

• I

Seminal vesicle

Ovary Anus

Penial setae

Ejaculatory duct

Rectum

Sac containincj setae — ^

Male

female

Fig. 184. — The parasitic human roundworm, Ascaris lumbricoides, phylum Nema-
thelminthes, dissected to show internal structures.

Flatworms and Roundworms 381

smooth, unsegmented body with somewhat pointed ends. The sexes are
separate, the female being larger (five to eleven inches long) ; the male is
usually smaller with a bend in the posterior part of the body. Because
the two sexes can be distinguished by means other than the sex organs,
they are said to illustrate sexual dimorphism (di -mor' fizm) (Gr. di,
two; morphe, form). A pair of broad lateral lines on either side point
out the pair of excretory tubes beneath. No cilia are present on the out-
side of the adults (Fig. 184).

Integument. — The external, transparent cuticle is usually smooth and
glistening, with very fine striations. A cellular hypodermis lies beneath
the cuticle. Between the body wall and the digestive tract is a cavity
which contains large, giant cells loosely arranged to form mesenchyme
tissue (mes' eng kime) (Gr. mesas, middle; engcheim, pour in). The
latter contains spaces known as vacuoles, but there is probably no true
coelom.

Motion and Locomotion. — Muscle cells in the body walls may cause a
limited amount of locomotion as the worms are moved along by the
intestinal contents of the host.

Ingestion and Digestion. — The mouth at the anterior end has one
dorsal and two ventral lips which are finely toothed and which bear
nipplelike papillae (pa-pil'i) (L. papilla, nipple). A straight pharynx
connects with the muscular, sucking esophagus which joins a straight,
nonmuscular intestine, ending in the arms at the posterior end of the
animal. The muscular esophagus sucks fluids from the intestine of the
host. The posterior part of the intestine is the rectum (rek' tum) (L.
rectus, straight) .

Circulation. — Because of the slender body and the absorption of foods
through the long intestine, 7io special circulatory system is required.

Respiration. — The parasitic habits^ and the comparative inactivity
preclude any need for a special respiratory system.

Excretion. — The pair of longitudinal excretory tubes embedded in the
pair of lateral fines open to the exterior by one excretory pore on the
ventral surface near the anterior end. There are no flame cells. Un-
digested materials may be eliminated by the intestine.

Coordination and Sensory Equipment. — A ring of nervous tissue en-
circles the esophagus and gives off a large dorsal nerve cord and a large
ventral nerve cord. The two cords may be connected by other nerve
rings. There is no special sensory equipment.

382 Animal Biology

Reproduction. — The sexes are in separate animals; hence, they are
diecious (di -e' si us) (Gr. di, two; oikos, house). The m,ale reproduc-
tive organs include one coiled, threadlike testis which leads into a tubular
vas deferens. The latter joins a wider seminal vesicle which connects
with a muscular ejaculatory duct, opening into the rectum. One pair of
spicules, called penial setae, protrude from the anus and assist in trans-
ferring sperm to the female during copulation.

The female reproductive organs include one pair of coiled, threadlike
ovaries, each connected with a larger uterus. The two uteri unite to
form a short, muscular vagina (va-ji'na) (L. vagina, sheath). The
latter empties through the genital pore about one- third the length of the
body from the anterior end.

Fertilization occurs in the uteri and each egg is then enclosed by a
shell of chitin (ki' tin) (Gr. chiton, tunic or covering), after which it
passes from the genital pore. One female may possess more than
25,000,000 eggs, and a mature female may lay 200,000 daily. They are
laid inside the host intestine and pass with the feces. The eggs are re-
sistant and may remain alive in the soil for months. When eggs which
contain embryos are ingested through the mouth, infestation may result.
The ingested eggs hatch in the intestine, where the embryonic larvae
bore through the intestinal wall into the lymphatic vessels or capillaries.
They eventually enter the right side of the heart, from which they pass
in successive stages to the lungs, trachea, esophagus, stomach, and in-
testine. This entire journey requires a little more than a week.

QUESTIONS AND TOPICS

1. List all the ways in which Platyhelminthes and Nemathelminthes differ.

2. List the characteristics which planaria, the tapeworm, and the liver fluke
have in common.

3. Make a table of the animals studied, including all the ways in which they
differ.

4. Describe each of the following for each animal studied: (1) integument,
(2) motion and locomotion, (3) ingestion and digestion, (4) circulation,
(5) respiration, (6) excretion and egestion, (7) coordination and sensory
equipment, and (8) reproduction.

5. Discuss the significance of ( 1 ) bilateral symmetry, (2) triploblastic, (3) sexual
dimorphism, and (4) hermaphroditism.

6. Discuss specifically what effects prolonged parasitism seems to have had on
such systems as the digestive, circulatory, and sensory of the parasite.

7. Discuss the phenomenon of axiate organization and its significance.

8. Discuss specifically the structures and abilities which certain parasitic worms
possess whereby they are able to live successfully in spite of many obstacles.
Explain how the production of large numbers of offspring enters into this
consideration.

Flatworms and Roundworms 383

9. Explain the complex life cycle of the liver fluke, including the stages in cor-
rect sequence, the different hosts, and the detrimental effects of the various
stages.

10. Discuss the economic importance of flatworms and roundworms.

11. Explain why the digestive system is considered a gastrovascular cavity in
certain types of worms.

12. List the conclusions you can draw from your studies of flatworms and round-
worms.

SELECTED REFERENCES

Cameron: The Internal Parasites of Domestic Animals, London.

Chandler: Introduction to Human Parasitology, John Wiley & Sons, Inc.

Craig and Faust: Clinical Parasitology, Lea & Febiger.

Faust: Human Helminthology, Lea & Febiger.

Gamble: Platyhelminthes; in vol. 2, Cambridge Natural History, The Macmillan

Co.
Hegner, Root, Augustine, and Huff: Parasitology; With Special Reference to

Man and Domestic Animals, D. Appleton-Century Co., Inc.
Mackie, Hunter, and Worth: Manual of Tropical Medicine, W. B. Saunders Co.
Ward and Whipple: Fresh Water Biology, John Wiley & Sons, Inc.

Chapter 20

A SEGMENTED WORM— EARTHWORM
(PHYLUM ANNELIDA)

The common earthworm is Lumbricus terrestris (lum'brikus te -res'-
tris) (Gr. lumbrikus, earthworm; L. terra, earth). Its body is elongated,
soft, and segmented. It burrows in the soil by forcing the soil through
its alimentary tract and passing this soil on the surface as ''castings." A
conspicuous saddlelike clitellum (kli -tel' um) (L. clitellae, pack-saddle)
is present (segments XXXI to XXXVII) . A true body cavity or coelom
(se' lom) (Gr. koilos, hollow) exists internally and communicates with
the exterior by means of dorsal pores in the mid-dorsal line at the an-
terior edge of each segment from VIII to the posterior end of the body.
Membranous, internal septa (L. septum, partition) separate adjacent
segments (Figs. 185 to 190).

Integument. — -The thin, noncellular, transparent cuticle of ectodermal
origin is iridescent because of its striations to refract light to produce
various colors. The cuticle contains pores of glands located in the epi-
dermis (hypodermis) just beneath. Four pairs of chitinous, bristlelike
setae (se' ti) (L. seta, bristle) are located in seta sacs in each segment
(Fig. 187).

Motion and Locomotion. — An outer layer of circular muscles and an
inner layer of longitudinal muscles in the body wall aid in locomotion.
Four pairs of bristlelike setae per segment are moved by protractor (pro-
trak' tor) (Gr. pro, forth; tractus, to draw) and retractor muscles
(re -trak' tor) (L. retrahere, to draw back) at their bases. Each seta
is set in a seta sac. The setae are set at certain angles to provide friction
or to reduce it as desired.

Ingestion and Digestion. — The foods of earthworms consist of dead
plant and animal materials and soils rich in organic substances. Living
materials are rarely molested. A fleshy prostomium (pro -sto' mi um)
(Gr. pro, before; stoma, mouth) projects over the mouth at the anterior
end. The mouth leads into a buccal pouch which connects with a thick,

384

A Segmented Worm — Earthworm 385

Aiouth

Circumpharyn-
geol ring

Mephndiurri-

Seminal

receptacle \y

Seminal

vesicle

-Frojtomum

Bra\n

_ Pharynx

. Pbaryrii^eal
muscles

Esophagus

Heart

Caldferous
cjland

Crop

Cji^^ard

Dorja] hhod
yessel

.Jntestine
_ Septa

Fig. 185. — Earthworm (Lumbricus terrestris) dissected from the dorsal side to
show internal structures of the anterior end somewhat diagrammatically. I, V ,
X, XV, Number of segments or somites. Nephridia are shown only in a few
segments. There may be slight variations in the location of certain structures
in different earthworms.

386 Animal Biology

muscular, sucking pharynx. Muscles attached to the outside of the
pharynx contract and expand it to cause suction. A narrow esophagus
connects the pharynx with the large, thin-walled crop which is used for
storage. Posterior to the crop is the thick, muscular gizzard for grinding
by means of grains of sand and similar materials. The gizzard leads to
the long intestine, with its deep, dorsal fold, the typhlosole (tif'losole)
(Gr. typhlos, blind; solen, channel). The latter increases the absorbing
surface of the intestine and is filled with chlorogen cells (klo-rog' o jen)
(Gr. chloros, greenish-yellow) which probably aid in digestion of foods
and elimination of wastes. The anus is at the posterior end of the earth-
worm.

•Dorsal vessel

eart intestino-tegumentary
— vessel
-Ventral vessel

Heart

■y =f Sub-neural vessel

'!Sw.,iiiSaBa;:iJ^ T^'Ci^iaitJlEailc^iatx

X SepU j^ IX Septa

Septa

Dorsal vessel intestino-tegumentary

vessel

CEsophagiis

VIII
Dorsal vessel

Ventral vessel
Sub-neural vessel

Nephridium
Lateral-neural vessel

Parietal
ve«sel

i^ Typhlosolar
vessel

Ventral
vessel

Efferent intestinal vessel

T-v ^Sub-neural vessel

Afferent intestinal vessel

Dorsal vessel

Typhlosolar vessel

-'Ventral vessel
Sub-neural vessel

Parietal vessel

Fig. 186. — Earthworm circulatory system (somewhat diagrammatic). A, Longi-
tudinal view in segments VIII, IX, and X; B, cross section of same region; C,
longitudinal view in region of intestine; D, cross section of same region. (From
Hegner: College Zoology. By permission of The Macmillan Company, publishers.)

Three pairs of calciferous glands (kal -sif e rus) (L. calx, lime; ferro,
to carry) near the esophagus secrete calcium carbonate (lime) into it to
neutralize acid foods as well as to line the tunnels (burrows) through

A Segmented Worm-

-Earthworm 387

^-'

,.— ^

a >^

(U ^

t«

t/2

-tJ

o j:3

~~— '

■M

o 13

ii o
o

Si
4J

• ■1

•M

388 Animal Biology

which the worm crawls. These plastered tunnels prevent their collapse
and allow moisture and air to penetrate the soil. In this way the earth-
worms cultivate the soil.

Enzymes of the digestive juices act on foods in a manner similar to
that of higher animals, as shown by the following table :

ENZYME

FOOD ACTED ON

PRODUCTS FORMED

Trypsin
Diastase
Steapsin

Proteins

Carbohydrates

Fats

Peptones

Sugars

Fatty acids and glycerin

Absorption in the earthworm occurs through the walls of the
intestine, being assisted by the amoeboid action of some of the lining
epithelial cells. Some absorbed foods are placed in the coelomic
cavity where they are circulated by the coelomic fluid. Other ab-
sorbed foods are placed in the circulatory system to be taken to various
parts of the body.

Prostominm

Buccal cavity
\

Circumpharyngeal
Cerebral gransrlion connective

In-

in
I.

Seermental nerve

Month

Subpharynfireal ^nslion

Septal nerve

Fig. 188. — Earthworm nervous system. Side view of anterior end with the
cerebral gangHon and larger nerves. (From Hegner: College Zoology. By per-
mission of The Macmillan Company, publishers.) (After Hess.)

Circulation. — A complex system of blood vessels forms a so-called
''closed type'' of circulatory system. A closed system is one in which
the blood flows, more or less continuously, in the vessels, with only a
limited amount of its constituents passing in and out through their walls.
The more important parts of the system are: (1) a dorsal blood vessel
dorsal to the digestive tract, (2) a ventral vessel ventral to the digestive
tract, (3) five pairs of pulsating, looplike heart arches in segments VII

A Segmented Worm — Earthworm 389

to XI which connect the dorsal and ventral vessels, (4) a subneural vessel
beneath the ventral nerve cord, (5) two lateral neural vessels on either
side of the nerve cord, (6) numerous branches from the vessels with
their thin-walled capillaries (kap'ilari) (L. capillaris, hair) to supply
all body parts. The blood is propelled through the vessels by the peri-
staltic contractions of the hearts and dorsal blood vessel, thus forcing it
from the posterior part of the dorsal vessel toward the anterior end.

Testis ^

X-

Vas deferens- -

Ovary

Oviduct

XV-

^<]<j Sac

Seminal
receptacle

Sewinal
vesicle

Fig. 189. — Earthworm reproductive system with the seminal vesicles on the left
dissected to show the male and female organs (see Fig. 185).

OPENINGS OF SEMINAL RECEPTACLES- 2 PAIRS
OPENING OF VASA OEFERENTIA-I PAIR

ENCASING TUBE
[ (CLITELLUM

OPENINGS OF SEMINAL

RECEPTACLES

CLITELLUM

SEMINAL CHANNELS

OPENINGS OF VASA DEFERENTIA-I PAIR

Fig. 190. — Reproduction in earthworms by copulation, shown somewhat dia-
grammatically. During copulation, the ventral surfaces of the two worms are in
contact, with the anterior ends pointing in opposite directions. A sHmy tube se-
creted by the clitellum of each animal surrounds the two worms, and a pair of
temporary seminal channels is formed on the ventral surface of each worm, so
that sperm expelled from the vasa deferentia of one worm travel to the openings
of the seminal receptacles of the other, within which they are stored. (From
Parker and Clarke: An Introduction to Animal Biology, The C. V. Mosby Co.)

390 Animal Biology

Valves in the hearts and dorsal vessel prevent the backward flow. Blood
is returned from the body wall to the lateral neural vessels, in which it
flows posteriorly, eventually re-entering the dorsal blood vessel.

The blood of the earthworm consists of ( 1 ) liquid plasma with its
oxygen-carrying red pigment, hemoglobin, dissolved in it and (2) nu-
merous colorless white blood cells resemblins, those of human blood and
with possibly similar functions. The blood carries absorbed foods from
the digestive tract to all parts of the body, transports wastes rapidly from
the tissues to the organs of elimination, and exchanges oxygen and car-
bon dioxide by coming near the body surface.

When the liquid portion of the plasma of the blood passes out through
the walls of the blood vessels into the tissues and organs, it is known as
lymph. The latter consists of (1) liquid plasma of the blood which has
osmosed from the blood vessels, (2) numerous colorless leucocytes, (3)
foods contained within the lymph plasma and secured from the blood,
(4) wastes secured from the tissues, which are either carried by the
lymph toward the organs of excretion or placed into the circulatory sys-
tem to be carried to the excretory organs, and (5) oxygen on its way
from the blood to the tissues and carbon dioxide on its way from the
tissues to be eliminated.

The lymph fills the coelom (body cavity) and occupies smaller spaces
within the tissues and organs. It is from these cavities that the lymph
functions. Lymph is circulated by the muscular movements of the body
or of the internal organs.

Respiration. — There is no respiratory system but oxygen is obtained
and carbon dioxide eliminated through the moist body surface. Many
thin-walled capillaries just beneath the cuticle make the exchange of
gases possible. Excess water around the animal interferes with respi-
ration, which partly explains why earthworms are "rained out" after a
rain.

Excretion and Egestion. — A pair of nephridia (ne-frid'ia) (Gr.
nephroSj kidney) is present in each segment (metamere) except the first
three and the last one. The internal, free end of each is a ciliated,
funnel-shaped nephrostome (nef rostome) (Gr. nephros, kidney; stoma,
mouth) which selects the wastes from the coelomic fluid. The nephridia
select the wastes and pass them through the ciliated tubes to the exterior
through openings called nephridio pores. The latter are located on the
ventral side of the body just posterior to the segment in which their par-
ticular nephridia are located. Chlorogogen cells covering the intestinal

A Segmented Worm — Earthworm 391

-b

wall and filling the typhlosole may act to eliminate wastes. Solids are
eliminated through the anus.

Coordination and Sensory Equipment. — A bilobed brain (supra-
pharyngeal ganglion) is located dorsal to the pharynx near segment III.
The circumpharyngeal ring or commissure encircles the pharynx and
connects the brain with the subpharyngeal ganglion below the pharynx.
The ventral nerve cord extends posteriorly from the subpharyngeal gan-
glion and has an enlarged ganglion (gang' li on) (Gr. ganglion, little
tumor) which gives origin to three pairs of nerves in each segment.
These ganglia serve as subordinate ''brains" where nerve impulses may
be received and redirected. Nerves connect the various body segments
to coordinate their various activities. The muscles of the setae are con-
trolled in order to make them perform their functions properly.

There are epidermal sense organs in the peripheral tissues which when
stimulated send impulses over nerves. Sensory hairs penetrate the cuticle
and are connected with the nervous system. Earthworms react to light,
contact, moisture, chemicals, sound, etc.

Reproduction. — Both male and female sex organs are present in the
same earthworm; hence, it is monecious (hermaphroditic ) . The female
organs include one pair of small ovaries (segment XIII) not visible from
the dorsal side, one pair of small oviducts which are modified nephridia
(segment XIII), one pair of egg sacs connected with the oviducts (seg-
ment XIV), one pair of oviduct openings on the ventral side (segment
XIV), two pairs of seminal receptacles (spermatheca) in segments IX
and X, and two pairs of seminal receptacle openings between segments
IX and X and X and XI. The male organs include two pairs of hand-
shaped testes (segments X-XI) covered by the seminal vesicles and not
visible from the dorsal surface, one pair of vasa deferentia (sperm ducts)
with ciliated funnels (segments X to XV), one pair of vasa deferentia
openings on the ventral surface (segment XV), and three pairs of large,
conspicuous seminal vesicles (segments IX to XII). The bases of these
vesicles are attached in these segments, although they may extend beyond
them.

During copulation the ventral surfaces of two earthworms are in con-
tact, with the anterior ends pointing in opposite directions. A slimy,
bandlike cocoon (kokoon') (Fr. cocon, cocoon) secreted by the clitellum
encircles the two worms. A pair of temporary seminal channels is formed
on the ventral surface of each worm, so that sperm expelled from the
vasa deferentia of one worm travel to the openings of the seminal recep-
tacles of the other, within which the sperms are stored. Copulation

392 Animal Biology

results in a mutual exchange of sperms but no discharge of eggs or fer-
tilization at this time. One earthworm cannot fertilize its own eggs, but
there is a mutual, cross-fertilization in the cocoon.

After copulation, the worms pull away from each other and half of
the slimy band is slipped over the anterior end of each worm. In doing
so, the eggs from the oviducts are discharged into the slimy tubes which
also receive sperms from the seminal receptacles (segments IX and X).
The elastic ends of the cocoons close to imprison sperm, eggs, and a
liquid food for the developing embryos. A young worm eventually
breaks from the cocoon and shifts for itself in the soil. After a few
weeks the embryo becomes an adult.

QUESTIONS AND TOPICS

1. List the distinguishing characteristics of the phylum Annelida.

2. In what ways is the earthworm to be considered a higher type of animal than
those studied previously? Be specific in your answer.

3. Explain and give the significance of ( 1 ) metamerism, (2) coelom, (3) "closed
type" of circulatory system, (4) typhlosole, (5) hemoglobin, (6) lymph,
(7) setae with their muscles, (8) calciferous glands, (9) triploblastic, and
(10) clitellum.

4. Explain why earthworms appear to be "rained out" after a rain.

5. Discuss the economic importance of earthworms.

6. Explain the advantage of having both male and female sex organs in the same
earthworm, especially when the method of copulation is taken into considera-
tion.

7. In what specific ways are the nervous system and sensory equipment more
highly developed than in animals studied previously? What is the significance
of this?

8. Describe each of the following in the earthworm: (1) integument, (2)
motion and locomotion, (3) ingestion and digestion, (4) circulation, (5)
respiration, (6) excretion and egestion, (7) coordination and sensory equip-
ment, and (8) reproduction.

9. Why do you think an earthworm needs so many pairs of nephridia? Explain.
10. List the conclusions you can draw from your studies of the earthworm.

SELECTED REFERENCES

Beddard: Earthworms and Their Allies, Cambridge University Press.

Buchsbaum: Animals Without Backbones, University of Chicago Press.

Darwin: The Formation of Vegetable Mould Through the Action of Worms,

London, John Murray Co.
Hegner: Invertebrate Zoology, The Macmillan Co.

Chapter 2 1

COMMON INSECTS— GRASSHOPPER AND
HONEYBEE (PHYLUM ARTHROPODA;
CLASS INSECTA)

GRASSHOPPER (figs. 191 to 194)

Insects are air-breathing arthropods with bodies divided into head,
thorax, and segmented abdomen. The head bears one pair of antennae
and the thorax bears three pairs of jointed legs. The grasshopper is a
rather desirable type for study because it is large and less specialized than
many other types. Although there are many different species of grass-
hoppers which vary in certain respects, the following descriptions apply
in general to most species which are available for study: Grasshoppers
have enlarged hindlegs, sound-producing and sound-receiving structures,
leathery forewings, and membranous hindwings. On either side of the
head is a compound eye. On top of the head are simple eyes, called
ocelli (o-sel'i) (L, ocellus, little eye). Grasshoppers have chewing
mandibles (mandibulate mouth parts) which may be studied in Fig. 192.
Grasshoppers belong to the order Orthoptera (or -thop' ter a) (Gr.
orthos, straight; ptera, wings).

Integument and Skeleton. — A flexible, noncellular, chitinous cuticle
also serves as an exoskeleton (ek so -skeF e ton) (Gr. exo, external; skele-
tos, hard) to which organs, muscles, ^and tissues are attached on the
inside. The cuticle is secreted by a cellular hypodermis beneath it. The
chitin chemically has the formula C30H50O19N4. Beneath the hypoder-
mis is a basement membrane.

Internally the cavity in the body is not a true coelom but a hemocoel
(he'mosele) (Gr. haima, blood; koilos, hollow), being filled with or-
gans and a colorless blood. When the animal grows, it sheds its chitin
at intervals by the process of moulting or ecdysis (ek' di sis) (Gr. ekdyein,
to shed) . The liquid secreted by the hypodermis hardens into new chitin.

Motion and Locomotion. — Grasshoppers may walk or jump by means
of the three pairs of jointed legs or fly by means of two pairs of wings.

393

394 Animal Biology

Each leg consists of a series of segments: the coxa (kok' sa) (L. coxa,
hip) attached to the thorax, trochanter (tro -kan' ter) (Gr. trochanter,
runner), femur (fe' mur) (L. femur, thigh), tihia (tib' ia) (L. tibia,
shin), and tarsus (tar' sus) (Gr. tarsos, sole of foot). The latter is seg-
mented, the proximal segment bearing three pads and the distal one a
pair of claws. Between the claws is a fleshy pulvillus (pul-vil'us) (L.
pulvilus, small cushion). The forewings are leathery and unfolded and
cover the folded membranous hindwings. Chitinized, tubular vei7is in
the wings give strength. The fine, strong, striated muscles attached to
the inside of the chitinous skeleton help to move wings, legs, mouth,
parts, etc.

V\Qad

ooeWus

p.tax

abd

3.0 men

j compound cue
I /proT\o\um

' ■■''

Fig. 191. — Grasshopper (Melanoplus vittatus) with wings removed. Female.
(From Walden: Orthoptera of Connecticut, State Geological and Natural History
Survey of Connecticut, Bulletin 16.)

Ingestion and Digestion. — The foods of grasshoppers consist of vege-
tation which is chewed by the pair of chitinized mandibles (man'dibel)
(L. mandibulum, jaw) which move from side to side rather than up and
down. The principal parts of the digestive system include (in sequence)
( 1 ) a mouth, with a pair of salivary glands to secrete digestive juices,
and the various mouth parts (Fig. 192), (2) a tubular esophagus, (3)
an enlarged crop for storage, (4) a gizzard (proventriculus) for grinding,
(5) a stomach with eight double, glandular, cone-shaped gastric caeca
(se' ka) (L. caecus, blind) for the secretion of digestive juices, (6) a
large intestine wdth its delicate Malpighian tubes (after Malpighi, an
Italian scientist), and (7) a small intestine which expands into a rectum

Common Insects — Grasshopper and Honeybee 395

(rek'tum) (L. rectus, straight) opening through the anus (a'nus) (L.
anus, anus) . Other types of insects have different kinds of mouth parts.
Some have a sucking (siphoning) mouth part (Fig. 201), while others
have a piercing-sucking type (Fig. 202) .

Fig. 192. — Chewing mouth parts of the grasshopper (Rhomaelia microptera) .
L, Labrum (upper Hp) ; M, mandible (jaw) ; Mx, maxilla; La, labium; CI,
clypeus; C, cardo; St, stipes; Lac, lacinia; Ga, galea; Mp, maxillary palp; Pa,
palpifer; Me, mentum; Sm, submentum; Li, ligula; LP, labial palp. (From
White: General Biology, The C. V. Mosby Co.)

Circulation. — A single, tubular heart in the dorsal side of the abdo-
men is divided by valves into a series of chambers, each with a pair of
ostia (os'tia) (L. ostium, door) for the entrance of blood from the sur-
rounding pericardial sinus (Gr. peri, around; kardia, heart) (si'' nus)
(L. sinus, cavity). Valves close the ostia when the heart contracts. A

396 Animal Biology

tubular aorta (Gr. aorta, the great artery) extends anteriorly from the
heart and opens into the body cavity known as a hemocoel in the region
of the head. The hemocoel contains the internal organs and circulates
the colorless blood. This so-called "open system" of circulation causes
the blood to flow in vessels only part of the time; most of the time it
flows in tissue spaces or sinuses in the body and appendages. The blood

Hearts Alalpiqhian tubes

Rectum

--Anus

^ Pharynx SaVw/ary Qastric Stomach Irttest'ine

c^land caeca

Oviduct
i

Cement gland
/

\ ^ 1

Id Suhesophacjeal qanqJion AbdorninaJ aanqlion

(jenital opening

Trachea
/
/

Air sac

Spiracle

Fig.

193. — Internal anatomy of the grasshopper. A, Digestive and circulatory
systems; B^ reproductive and nervous systems; C, respiratory system.

flows from the heart through the aorta into the hemocoel from which
the various systems receive nourishment. Eventually the blood returns
to the pericardial sinus. The liquid plasma of the blood contains color-
less white blood corpuscles or leucocytes (lu'kosite) (Gr. leukos, white;
kytosj hollow or "cell").

Common Insects — Grasshopper and Honeybee 397

Respiration. — The thorax is divided into three segments (anterior,
prothorax; middle, mesothorax; posterior, metathorax) . Ten pairs of
external openings or spiracles (spi' ra kel) (L. spiraculum, air -hole)
open into the tracheal (respiratory) system on either side of the meso-
thorax and metathorax. The spiracles permit the entrance of oxygen
and the exit of carbon dioxide. The tubular tracheae ramify to all parts
of the body and may have enlargements called air sacs. The blood does
not play an important role in respiration (Fig. 194) .

Excretion and Egestion. — The coiled Malpighian tubules in the
hemocoel collect wastes and empty them into the large intestine. Solid
materials are eliminated through the anus.

Fig. 194. — Photomicrograph of a portion of grasshopper trachea with its
branching tubules, both large and small. The tracheal rings and nuclei are quite
distinct. (Copyright by General Biological Supply House, Inc., Chicago.)

Coordination and Sensor^^ Equipment. — A dorsal brain (three pairs
of ganglia) is connected by a pair of circumesophageal connectives with
a subesophageal ganglion. The ventral nerve cord continues posteriorly,
with a pair of large ganglia in each thoracic segment and five pairs of
ganglia in the abdomen. A sympathetic nervous system supplies the
spiracles, muscles of the digestive system, etc.

The compound eyes are covered with a cuticular cornea (L. corneus,
horny) divided into numerous hexagonal facets (L. facies^ face). Each
facet is the external surface of a unit called an ommatidium (om a -tid'-
ium) (Gr. ommation, little eye; idion, diminutive). Each ommatidium

398 Animal Biology

is composed of a long visual rod, and the various ommatidia are separated
from each other by a layer of dark pigment cells. Such an arrangement
gives mosaic vision in which each ommatidium receives a portion of the
image.

Each simple eye or ocellus consists of a group of cells, the retinulae (L.
rete, net) ; a central optic rod, the rhahdom (Gr. rhahdos, rod) ; and a
transparent, cuticular "lens." The ocelli probably function as light-per-
ception organs.

The pair of jointed, threadlike antennae (an -ten' i) (Gr. ana, up;
teino, stretch) bear sensory bristles probably for olfactory (ol -fak' to ri)
(L. olere, to smell; facere, to make) purposes. Organs of taste (gusta-
tory) are located on the mouth parts. Hairlike organs of touch (tactile)
are present on various body parts but particularly on the antennae. The
pair of sound-receiving auditory organs located on the sides of the first
abdominal segment consists of a membranous tympanum (tim' pa num)
(Gr. tympanon, drum) which covers an auditory sac.

Reproduction. — The sexes are in separate grasshoppers (diecious).
The female possesses a conspicuous ovipositor (o vi -poz' i tor) (L. ovum,
egg; ponere, to place) at the tip of the abdomen for depositing eggs. In
the female, one pair of ovaries produce eggs which are discharged into a
pair of oviducts. The latter unite to form a vagina connected with the
genital pore between the parts of the ovipositor. A seminal receptacle
(spermatheca) connected with the vagina receives sperm from the male
during copulation and releases them to fertilize eggs. A secretion of the
cement gland may stick eggs together as they are deposited.

In the male, one pair of testes discharge sperm into a pair of vasa
defer entia (sperm ducts) which unite to form the ejaculatory duct that
opens at the posterior end of the abdomen. Accessory glands secrete a
fluid into the ejaculatory duct to aid in the transfer of sperm to the
female. Eggs are fertilized by sperm when they are deposited. A young
grasshopper which hatches from an egg is called a nymph (nimf) (Gr.
nymphe, immature stage) and resembles an adult without wings. As
the grasshopper grows, it must shed its chitinous exoskeleton at certain
intervals by the process of ecdysis (moulting). Adult wings are event-
ually formed from wing buds.

HONEYBEE (Figs. 195 to 200)

The honeybee, Apis mellifica (L. apis, bee) (me-lif'ika) (L. mel-
lificus, honey), belongs to the order Hymenoptera (hi men -op' ter a)
(Gr. hymen, membrane; ptera, wings) because of its two pairs of mem-

Common Insects — Grasshopper and Honeybee 399

branous wings. Honeybees are more highly specialized in life habits and
structure than grasshoppers. Colonies of honeybees consist of ( 1 )
workers which are females with undeveloped reproductive organs, (2)
male drones, and (3) female queens. A typical colony may contain
50,000 workers, a few hundred drones, and one adult queen. The

Fig. 195. — Castes and development of the honeybee {Apis mellifica) of the
order Hymenoptera. In A, the adults, a is a worker; b, a queen; c, a drone. In
B, the immature stages, a is an egg; h, young larva; e, old larva; d, pupa. (From
Phillips: Bees, U. S. Department of Agriculture, courtesy of Bureau of Ento-
mology and Plant Quarantine.)

drones and queen are for reproductive purposes. Hymenoptera are char-
acterized by having their mouth parts modified for both sucking and bit-
ing (chewing) . The body is divided into head, thorax, and abdomen.

400 Animal Biology

The thorax is divided into an anterior prothorax, a middle mesothorax,
and a posterior metathorax. The abdomen is also segmented.

Integument and Skeleton. — A tough, flexible cuticle covers the body
and serves as an exoskeleton to which muscles and organs are attached
internally. Chitin is a protein substance (C30H50O19N4) . The cavity is
a hemocoel, which carries blood.

Motion and Locomotion. — Locomotion is accomplished by two pairs
of wings and three pairs of jointed legs (Fig. 197). The wings consist
of a double layer of transparent membranes between which is a network
of veins to strengthen them. When at rest, the wings are folded. Dur-
ing flight they are extended, and the fore- and hindwings are locked
together by a row of tiny hooks on the front margin of the hindwings.
Wings may vibrate over 400 times per second during flight.

Fig. 196. — Comb cells made by the honeybee. Note the baglike cells on the
surface in which the queen develops. (From PhilHps: Bees, U. S. Department
of Agriculture, courtesy of Bureau of Entomology and Plant Quarantine.)

The three pairs of legs are much more specialized than those of the
grasshopper (Fig. 197). Because of their complexity and differences,
each leg will be considered separately.

Prothoracic Leg (First): (1) An oblong coxa next to the thorax, (2)
a short trochanter^ (3) a long femur with branched, pollen-carrying
hairs, (4) a tibia with pollen-carrying hairs and a flat, movable, spinelike
velum, (ve' lum) (L. velum, covering), (5) a segmented tarsus, the
proximal segment of which may be called the metatarsus and which

Common Insects — Grasshopper and Honeybee 401

Probhoradc leo

Mesotboraac leg

Temijr

Velum

Antenna comb
Metatarsus

Coxa

Trochanter >

Tfbia

-Pollen brush &Jpur.

Metatarsus-

Eye brush

Tarsus

PuW'iWus

~ C/aw

..PoUen
brash

Tarsus

Metathoradc ieq
(inner surface )

Metathoradc leg
(Outer surface)

Trochanter

Coxa V

Metatarsus

Claw

- -femur

Pollen
basket -

_Pccten
yAuriclG

Pollen comb
. -Tarsus^ .

Pulvillus A_

/Metatarsus
__Cfaw

Fig, 197, — Legs of a worker honeybee (Apis mellifica) of the order Hymenoptera.

402 Animal Biology

bears a semicircular antenna comb. The latter together with the velum
constitute the antenna cleaner , through which the antenna may be drawn
to remove materials. On the opposite margin of the tibia from the velum
is the pollen brush, composed of curved bristles. The last (distal) tarsal
segment has claws with a padlike pulvillus between them. The latter
secretes a sticky substance for adhering.

CARDO

*!mentum

PREMENTUM

MAXILLARY PALPUS

PALPIFER
PARAGLOSSA

ALEA-LACINIA

LieULA

FLABELLUM

Fig. 198. — Honeybee worker mouth parts, much enlarged. The galea-lacinia is
also known as the maxilla. The ligula is known as the glossa or tongue. The
flabellum is also known as the bouton or labellum. The labial palps and the
ligula together constitute the lower lip or labium. (From Parker and Clarke:
Introduction to Animal Biology, The C. V. Mosby Co.)

Mesothoracic Leg (Second): The segments are the same as on the
first pair of legs. A long pollen spur on the distal end of the tibia is used
to remove pollen from the pollen basket and to clean wings. For other I
structures^ see Fig. 197. ^

Common Insects — Grasshopper and Honeybee 403

Metathoracic Leg (Third) : The pollen basket is located on the outer,
concave surface of the tibia, and long hairs curve over its depression some-
what to cover it. A pincerlike structure between the tibia and metatarsus

Trachea

Z- Air sac

Pharynx

Salivary cjlands
Esophaqus

Honey sac

—imall intesiine

J Jtomach

^- ^^Rectalqiands
Rectum

^—.Malpiqhian tub<25

Air sac

_t<( Aorta

Afusdes

^M__Airsac

iracJes

Anbenna

_ Compound
eye

-Jhoracic

cjanqlion

.-Cords
_ Nerves

^Ahdorninal
oancjUa

Fig. 199. — Internal anatomy of a worker honeybee. A, Digestive system; B,
circulatory system; C, respiratory system; D, nervous system.

is composed of rows of spines, the pecten ('pek' ten) (L. pecten, comb),
and a liplike auricle (or' i kel) (L. auricula, small ear) . The pecten and
auricle convey pollen to and pack pollen into the pollen basket. On the
inner surface of the metatarsus are numerous, transverse rows of stiff,

404 Animal Biology

bristlelike pollen combs to comb out pollen from various body parts and
to handle wax. The wax is secreted in flat scales by a glandular area on
the underside of the abdomen. The wax is masticated by the mandibles
before it is used in building the "cells" of the honeycomb.

Ingestion and Digestion. — The mouth parts may be studied from Fig.
198. One pair of smooth mandibles lies beneath the upper lip (labrum)

The sucking mouth parts assist the

and are used in masticating wax.

Poison sac

Alkaline (jland ^Poison)

^--P/ofces (Levers tx> move barbs)

Sheath (TohoJd retracted lancets)

Lancets

Fa]pus ofstin^

Barbs on lanccb

Fig. 200. — Sting apparatus of the worker honeybee (Apis mellifica) . Drawn with

the parts somewhat separated.

suction of the pharynx to convey fluids into the digestive tract. A long
esophagus extends from the pharynx to the large honey sac (crop) in
the abdomen. A large cylindrical stomach leads into the intestine and
the latter joins the rectum which ends in the anus.

The nectar of flowers is sucked up and stored in the honey sac where
it chemically changes into honey. The latter is regurgitated into the
"cells" of the honeycomb. Here the honey is still further dehydrated by
currents of air which are caused by the rapid vibrations of the wings.

Common Insects — Grasshopper aiid Honeybee 405

A minute drop of poison from the sting helps to preserve the honey. An
average colony of bees in an average season may collect about forty
pounds of honey.

Pollen is rich in protein which honey lacks, so pollen {''bee bread'') is
essential in the diet of bees. The pollen collected in the pollen basket
is placed in certain "cells" of the honeycomb. "Bee-glue" or propolis
(Gr. pro, for; polis, city) is a resin collected from plants and is used in
filling cracks, cementing loose parts, etc. Various types of cells con-
stitute the honeycomb (Fig. 196).

Circulation. — A long, delicate, tubular, muscular heart in the mid-
dorsal region of the body discharges the colorless blood toward the head
region. Blood enters the heart through five pairs of ostia, each pair lead-
ing into a chamber of the heart. Valves prevent the backflow into the
body during contraction. Blood discharges at the head region and passes
through the hemocoel (body-circulatory cavity). From the latter it
reenters the heart chambers. The blood plasma contains white blood
corpuscles.

Respiration. — Respiration occurs through pairs of very small spiracles
located along the sides of the thorax and abdomen and leading into a
branched system of tracheae to convey air to all body parts. Certain,
trachea may possess enlarged air sacs.

Excretion. — Numerous, hollow, glandular, threadlike Malpighian tu-
bules excrete wastes into the intestine much in the same manner as in
grasshoppers.

Coordination and Sensory Equipment. — A large "brain (supraesopha-
geal ganglion) in the dorsal part of the head supplies nerves to the eyes,
antennae, etc. The brain is connected by a riiig (nerves) to the sub-
esophageal ganglion which supplies nerves to the mouth parts. A ventral
nerve chain extends posteriorly from the subesophageal ganglion along
the midventral side of the body. The chain is a double nerve strand and
connects with two thoracic ganglia and five abdominal ganglia (Fig.
199,2)).

The hairlike end organs of the sense of touch (tactile) are present on
various body parts but are particularly numerous on the tip of the an-
tennae. The pair of jointed, hairy antennae have numerous, sound-sen-
sitive pits which are thought to be for auditory purposes. Other pits
on the antennae are thought to be for olfactory purposes. Bees seem
to use the scent-detecting mechanism for discovering food and for mat-
ing between drone and queen. A worker bee is able to transmit to the

406 Animal Biology

antennae of other workers the "scent information" necessary to direct
the latter to newly discovered food supplies. The so-called "tongue"
bears numerous, bristlelike taste setae. Bees can be trained to estimate
time intervals, because some have been trained to come to a source of
food at regular intervals. The pair of large compound eyes, on the top
and side of the head, are constructed and function similar to those of the
grasshopper previously described. The color sense of bees is better ad-
justed to the shorter wave lengths of the light spectrum; that is, toward
the blue end of the spectrum. Three small simple eyes (ocelli) are pres-
ent on the dorsal side of the head.

The stijig is a modified ovipositor which is used for protection (Fig.
200). Males do not have a sting. It is composed of two straight,
grooved lancets (darts) with barbs at the tips and with muscles for their
operation. A large, storage poison sac is connected with the base of the
sting. Two acid glands and an alkaline gland mix their secretions to
form the poisonous material which is injected when the bee stings. After
stinging, the worker leaves the sting, poison sac, glands, etc., and the bee
dies.

Reproduction.— The worker honeybee contains only vestigial (ves-
tij' i al) (L. vestigium,, trace) reproductive organs since It Is an unde-
V'cloped female. The reproductive organs of the m.ale (drone) include
one pair of bean-shaped testes which produce sperm, that are carried
away by one pair of slender vasa deferentia. The latter expand to form
the sem,inal vesicles for sperm storage. The two seminal vesicles combine
to form one ejaculatory duct which leads to the copulatory mechanism,.
One pair of large accessory glands secrete and empty nourishment Into
the ejaculatory duct.

In the female (queen), one pair of large ovaries produces eggs which
are carried by one pair of oviducts. The latter unite to form one tubu-
lar vagina leading to the exterior. A spermatheca attached to the vagina
stores sperm received from the male during copulation. The queen is
fertilized once In a lifetime, during a nuptial flight during swarming, and
the sperms remain alive for years In the spermatheca. As an egg passes
down the ovary toward the oviduct, its receives a shell with a small open-
ing, the micropyle, through which a sperm may enter. A queen may lay
an unfertilized egg to develop a drone or fertilized eggs to develop fe-
males, either queens or workers. A queen may lay 1,500 eggs per day
for weeks at a time, and she may live several years. The eggs are small,
oblong, and bluish-white. Fertilized eggs are placed in worker or queen
cells of the honeycomb; unfertilized eggs, in the drone cells. A worm-

Common Insects — Grasshopper and Honeybee 407

like^ whitish larva ("grub") hatches from the e^g in four days. All
larvae are fed on a specially prepared and predigested mixture of honey
and pollen ("royal jelly") for a few days^, after which the drone and
worker larvae are fed on plain honey and pollen, while the queen larva
is kept on the "royal jelly" diet. This continuity of special food causes
the larva to develop into a queen instead of a worker. After six days
a larva develops into a pupa (pu' pa) (L. pupa, puppet) enclosed in a
silken cocoon. A worker pupa changes into an adult bee in about thir-
teen days, a queen in about seven days and a drone in about fifteen days
(Figs. 195 and 196).

QUESTIONS AND TOPICS

1. List the distinguishing characteristics of the class Insecta.

2. List the characteristics which grasshoppers and honeybees have in common.

3. List the ways in which grasshoppers and honeybees differ, being specific in
the various details.

4. Why are insects placed in the phylum Arthropoda?

5. Explain and give the significance of (1) ecdysis, (2) chitin, (3) hemocoel,
(4) spiracle, (5) ostia, (6) Malpighian tubules, (7) ommatidia, and (8)
sinus.

6. Explain each of the following for the grasshopper and honeybee: (1) integu-
ment, (2) motion and locomotion, (3) ingestion and digestion, (4) circula-
tion, (5) respiration, (6) excretion and egestion, (7) coordination and sensory
equipment, and (8) reproduction. In what specific ways have these shown
an improvement over the same i n lower types of animals?

7. Contrast the types of mouth parts in the grasshopper and honeybee.

8. Contrast each of the three legs of the grasshopper with the same leg of the
honeybee, including the major differences. Which insect would you consider
the more specialized in this connection?

9. Describe the structure and function of a compound eye.

10. Contrast the types of metamorphosis in the grasshopper and honeybee.

11. Discuss the economic importance of grasshoppers and honeybees.

12. Discuss the colonial life and the various castes of honeybees.

13. Discuss the structure and functions of the so-called "open type" of circulatory
system.

14. List the advantages and disadvantages of a separate tracheal system of respira-
tion.

15. Why is it scientifically incorrect to say honeybees gather honey?

16. List the conclusions you can draw from your studies of the grasshopper and
honeybee.

SELECTED REFERENCES

Brues: Insects and Human Welfare, Harvard University Press.

Blatchley: Orthoptera of North-eastern America, Indianapolis, Nature Publishing
Go.

408 Animal Biology

Duncan and Pickwell: The World of Insects, McGraw-Hill Book Co., Inc.

Fabre: Book of Insects, Tudor Publishing Co.

Hegner: Invertebrate Zoology, The Macmillan Co.

Hermes: Medical Entomology, The Macmillan Co.

Matheson: Medical Entomology, Comstock Publishing Co., Inc.

Matheson: Entomology for Introductory Courses, Comstock Publishing Co., Inc.

Michener: Comparative External Morphology, Phylogeny and Classification of

Bees, Bull. 82, American Museum of Natural History.
Phillips: Beekeeping, The Macmillan Co.
Ross: Textbook of Entomology, John Wiley & Sons, Inc.
Snodgrass: Anatomy and Physiology of the Honeybee, McGraw-Hill Book Co.,

Inc.
von Frisch: Bees, Cornell University Press.
Wellhouse : How Insects Live, The Macmillan Co.

Wheeler: Social Life Among the Insects, Harcourt, Brace and Co., Inc.
Wheeler: Foibles of Insects and Men, Alfred A. Knopf, Inc.

Chapter 22

IDENTIFICATION AND CLASSIFICATION
(TAXONOMY) OF INSECTS

Since insects are of such great economic importance, so numerous and
ubiquitous in their distribution, it seems desirable that one should know
something about them. Even from such a limited study as suggested
here, many benefits from esthetic and practical standpoints may be
derived. Possibly, a maximum of benefits, with a minimum of time
expended, may be secured by a study of the various representative orders.
The information is given in table form in order to expedite the work and
to make pertirient contrasts and comparisons more easily. The more
important features used in the differentiation of the orders include wings,
mouth parts, and type of metamorphosis.

Depending on the species, the sex, or even the particular stage of the
life cycle, insects may have two pairs of wings or one pair of wings or
may be wingless. Typically, most insects have two pairs of membranous
wings which vary as to shape, construction, venation, foldings, etc.
When at rest each species has a particular method of holding the wings
which is taken into consideration in classification. Typically, only one
order [Diptera) has one pair of wings, the second pair being repre-
sented by a pair of threadlike knobbed halters (hal-te' rez) (Gr. halter,
weight or balancer). The forewings of such forms as the Orthoptera,
Coleoptera, and Dermaptera are thickened for protection. The fore-
wings of the Hemiptera are thickened only at the base. The particular
type of wing venation is also taken into consideration in classification. In
some species, one sex has wings, while the opposite sex is wingless. For
example, the male canker worm moth has two pairs of wings, while the
female is wingless.

Insect mouth parts may be for (1) chewing (mandibulate) (Fig. 192)
or (2) sucking. Mouth parts consists typically of a flaplike upper lip
{labrum) , a pair of upper jaws (mandibles) , a pair of lower jaws (maxil-
lae), and a lower lip (labium). In addition, there may be, in certain

409

410 Animal Biology

species^ one or two organs, the membranous epipharynx and the tongue-
like hypopharynx (Fig. 202). The jaws operate horizontally rather than
up and down. The maxillae and labium are each supplied with a pair
of sensitive feelers {palpi). Mouth parts vary greatly with the different
species. Among certain insects with sucking mouth parts, there are varia-
tions. For example, in the mosquito (order Diptera) (Fig. 202) the
mouth parts are modified for piercing in addition to sucking, while the
butterfly (order Hymenoptera) (Fig. 201) sucks nectar from flowers with
a tubular proboscis.

Antennae
A

_ CorDpound eye

:^ Labial palpus

_ Proboscis

Fig. 201. — Butterfly head and mouth parts, the latter in the form of a siphoning
(sucking) proboscis which may be uncoiled when used.

Many insects in their life cycles undergo remarkable changes in form
and size. These changes in structure and form undergone by an organism
from the embryo to the adult stage constitute metamorphosis (met a-
mor'fosis) (Gr. meta, change; morphe^, form). The life cycle (Gr.
kyklos, circle) includes the various stages through which an individual
passes from one adult stage to the next aduU stage. There are diff"erent
systems of classifying the types of insect metamorphosis but the following
is typical:

i. No Metamorphosis. — In this type the egg develops into a form
which is practically the same as the adult, although smaller. Briefly, the
stages are egg, adult, egg (Figs. 203, 204, 273, 274) .

Identification and Classification of Insects 411

2. Incomplete Metamorphosis. — In this type the egg develops into a
nymph, specifically known as a naiad (ni' ad) (Gr. naias, water nymph),
which does not resemble the adult in general characteristics or in man-
ner of life. In each of the orders that possess incomplete metamorphosis
the naiads develop in water, with aquatic respiratory organs, while the
adults are terrestrial (aerial) with air-breathing organs. The changes
in body form are more marked than in gradual metamorphosis but are
much less marked than in complete metamorphosis. Briefly, the stages
are egg, aquatic naiad, terrestrial, aerial adult, egg (Fig. 205).

Thorax
I Eye

Antenna

Hypopharynx

^lahiufn

„ ^pipharynx
.--.Mandible
— Maxilla

Fig. 202. — Piercing-sucking mouth parts of a mosquito (Culex sp.) of the order
Diptera. Mouth parts are separated and enlarged.

Fig. 203.

Fig. 204.

Fig. 203. — Snow flea (Achorutes nivicola) of the order Collembola, much en-
larged. (From Kellogg: American Insects, Henry Holt & Co.)

Fig. 204. — Springtail (Achoreutes armatum) of the order Collembola, much
enlarged. A spring beneath the tip of the abdomen for springing purposes is not
shown. (From Popenoe: Mushroom Pests and How to Control Them, U. S.
Department of Agriculture, courtesy of Bureau of Entomology and Plant Quaran-
tine.)

Mymph

Adult

Fig. 205. — Dragonfly of the order Odonata (class Insecta) illustrating incom-
plete metamorphosis (development). The nymph (naiad) has large eyes and
dev'eloping wings. The naiad stage is aquatic in incomplete metamorphosis. The
adult shows large compound eyes and the characteristic jointlike nodus at the
front margin of the wing.

Fig. 206. — Gradual metamorphosis of a grasshopper {Rhomaelia sp.). A, Egg;
B, n>TTiph just hatched; C-F, successive stages in development. (Original drawing
by Eleanor Sloan Hough, from White: General Biology, The C. V. Mosby Co.)

Identification and Classification of Insects 413

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Identification and Classification of Insects 415

Larval naiads live in water un-
der stones ; 1 pair of tail-
like, jointed cerci at tip of
abdomen; serve as fish food

Flat, broad, louselike body with
broad head; sharp claws;
parasites on skin, hair, and
feathers of birds and mam-
mals

Flat, broad body with free hor-
izontal head ; fleshy, un-
jointed proboscis; parasitic
and feed on blood of mam-
mals; eggs called "nits"

Most species live on vegetation;
mantes feed on other insects

Social insects living in a colony
with several castes (usually
4) ; abdomen broadly at-
tached to thorax; workers
and soldiers usually dirty
white in color; build earthen
tubes for passageways

•M

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none)

-a

Piercing-
sucking

2 pairs ; membranous,

netted ; hindwings usually
longer than forewings and
folded when at rest

"he
c

"ho

2 pairs (usually) ; forewings
leathery (wing covers)
but with veins ; hindwing.
delicate, folded like a far
when at rest; some specier
have vestigial wings, oth
ers are wingless

2 pairs ; long, narrow, simi-
lar, and lie flat on back
when at rest and shed
after swarming; certain
castes with small wing
buds ; workers and soldierr
wingless

Stoneflies (Fig.
278)

Biting bird lice
such as chicken
lice, cattle lice,
etc. (Fig. 280)

True lice such as
human head lice,
human body
lice, dog lice,
rat lice, etc.
(Fig. 287)

Grasshoppers, ka-
tydids, cock-
roaches, crick-
ets, walking
sticks, praying
mantis, etc.
(Figs. 191, 192,
283, 284, and
329)

Termites (Fig,
279)

5. Plecoptera
(pie -kop'-
tera) (Gr.
plekos, folded;
ptera, wings)

6. Mallophaga
(ma -lof a ga)
(Gr. mallos,
wool ; phagein,
to eat)

7. Anoplura
(an o -ploo'-
ra) (Gr. an-
oplos, un-
armed ; oura,
tail)

8. Orthoptera
(or -thop' ter-
a) (Gr. orthos,
straight ;
ptera, wings)

9. Isoptera

(i -sop' ter a)
(Gr. isos,
equal; ptera,

wings)

416 Animal Biology

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Booklice are minute, soft-
bodied, and grayish-yellow in
color; barklice have oval
bodies with free head; feed
on vegetation

Minute, slender body; feet have
bladderlike organs for cling-
ing

Beak arises from front of head;
many species on vegetation

Beak arises from hind part of
lower side of head; many
species on vegetation

METAMOR-
PHOSIS

•—1

3
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-^
u

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PARTS

Piercing-
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Piercing-
sucking
(beak)

73
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Booklice wingless; barklice
have 2 pairs of mem-
branous with few cross-
veins; forewings larger
than hindwings; wings
held rooflike when at rest

2 pairs (usually) ; long,
similar, narrow, mem-
branous, not folded ; few
veins; fringed with long
hairs; some species wing-
less

2 pairs or wingless; fore-
wings thickened at base,
with thinner extremities
which overlap on back;
hindwings membranous
and folded

2 pairs or wingless; mem-
branous wings are usually
of same thickness through-
out; usually held sloping
at side of body when at
rest ; many wingless form'"

Booklice (found in
old papers),
barklice (feed
on plants)
(Figs. 285 and
286)

Thrips, such as,
grass thrips,
onion thrips,
fruit thrips,
wheat thrips,
etc. (Fig. 281)

True bugs, such as
stink bugs,
squash bugs,
assassin bugs,
chinch bugs,
water striders,
back swimmers,
bedbugs, etc.
(Figs. 288 and
290)

Cicadas, leaf-hop-
pers, tree-hop-
pers, plant a-
phids, scale-bugs,
spittle-insects,
etc. (Figs. 289
nnd 291 to 293)

NAME OF
ORDER

10. Corrodentia
(kor o -den'-
shia) (L.
corrodens,
gnawing )

11. Thysanoptera
(thi sa -nop'-
tera) (Gr.
thysanos,
fringe ; ptera,
wings)

12. Hemiptera
(he -mip'-
tera) (Gr.
hemi, half;
ptera, wings)

13. Homoptera
(ho -mop'-
tera) (Gr.
homos, same ;
ptera, wings)

Identification and Classification of Insects 417

One pair of pincerlike cerci at
tip of abdomen; narrow, flat
body; not common in U. S.

Many species are predacious;
larvae may suck blood from
their prey

Chitinous covering is usually
heavy; vary in size from mi-
nute to very large; very com-
mon in many places

Male abdomen resembles that
of a scorpion but not a
sting; long, slender anten-
nae ; head prolonged into a
long beak with mouth parts
at tip

Soft, mothlike insects; live near
water; frequently attracted
by light; larva resembling an
aquatic caterpillar usually
dwells in caddice cases
formed of stones

Gradual (or
none)

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beak)

Vestigial (in
adults)

Some forms wingless, others
with 2 pairs; forewings
short, leathery, veinless,
and meet in middle of
back; hindwings large,
membranous, folded cross-
wise and lengthwise

2 pairs; thin, similar, mem-
branous, with many nerve-
like veins; held rooflike
when at rest

2 pairs; forewings greatly
thickened (wing covers,
or elytra) ; hindwings
membranous, folded ;
elytra usually meet in line
down the back; in some
species hindwings absent;
few species are wingless

2 pairs or wingless; wings
long, similar, narrow,
membranous with many
cross veins and dark
spotted; some species ves-
tigial or wingless

2 pairs; membranous with
long, silky hairs ; hind-
wings usually shorter and
broader; wings folded
rooflike when at rest

Earwigs (Fig.
282)

Dobson flies, ant
lions, aphis
lions (lacewing
flies) (Fig. 294)

Beetles, such as
tiger beetles,
ladybird beetles,
June beetles,
click beetles,
ground beetles,
weevils, curcu-
lios, etc. (Figs.
295 to 297)

Scorpion flies
(Fig. 298)

Caddice flies (Fig.
299)

14. Dermaptera
(dur -map'-
tera) (Gr.
derma, skin;
ptera, wings)

15. Neuroptera
(nu -rop'-
tera) (Gr.
neuron, nerve;
ptera, wings)

16. Coleoptera
(ko le -op'-
tera) (Gr.
coleos, sheath;
ptera, wings)

17. Mecoptera
(me -kop'-
tera) (Gr.
mecos, long;
ptera, wings)

18. Trichoptera
(tri -kop' ter a)
(Gr. trichos,
hair; ptera,
wings)

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3. Gradual Metamorphosis. — In this type of development the changes
are gradual (Fig. 206) and the egg develops into a young nymph which
resembles the adult in general body form and lives in the same general
kind of environment as the adult. There is a gradual growth of the body,
wings, and appendages. Briefly, the stages are egg, nymph (air breath-
ing), adult (air breathing), egg.

4. Complete Metamorphosis. — In this type the egg hatches into a
"wormlike" larva (lar' va) (L. larva, mask) which changes into a quies-
cent pupa (pu'pa) (L. pupa, baby), and the latter in turn develops into
an adult (Fig. 207). The larva bears almost no resemblance in form
to the adult. Commonly, the larvae of the Coleoptera are known as
grubs, those of the Diptera as maggots, and those of the Lepidoptera as
caterpillars. Even though the pupa stage is usually nonmotile, internally
great changes occur. For example, the larva enters to become the pupa,
but an entirely different adult emerges from the pupa. Great structural
and physiologic changes take place in this so-called "inactive" pupa. At
the same time, the pupa always "knows" the specific kind of adult it is
to produce. The markings on adults of certain species are so accurately
formed that they are used in classification and identification. In com-
plete metamorphosis, the stages are egg, larva, pupa, adult, egg.

QUESTIONS AND TOPICS

1. What are the principal points used in the classification of insects into orders?

2. Learn the exact spelHng, correct pronunciation, derivation and examples of
each order of insects.

3. From a study of the table and typical, representative insects, describe each of
the following: mouth parts, types of metamorphosis, number and structure
of wings.

4. Describe each of the types of metamorphosis in detail with examples of each.

5. How can we differentiate between the biting bird lice {Mallophaga) and the
true lice (Anoplura) ?

6. How can we differentiate between fleas (Siphonaptera) and lice?

7. How can we differentiate between termites (Isoptera) and true ants (Hyme-
noptera) ?

8. Do all insects have the same type of mouth part in the embryo and adult
stages? Give specific examples to prove this point.

9. How many pairs of legs do all adult insects possess? How many antennae?

10. Why are insects classified as arthropods?

1 1. What is the method of respiration of adult insects?

12. How can we differentiate in general between moths and butterflies?

13. List all the benefits which you have derived from such a study of insects.

SELECTED REFERENCES

Brues and Melander: Classification of Insects, Harvard University Press.
Chu: How to Know the Immature Insects, William C. Brown Co.
Comstock: An Introduction to Entomology, Comstock Publishing Co., Inc.

420 Animal Biology

Essig: College Entomology, The Macmillan Co.

Frost: General Entomology, McGraw-Hill Book Co., Inc.

Jacques: How to Know the Insects, William C. Brown Co.

Lutz: Fieldbook of Insects, G. P. Putnam's Sons.

Metcalf and Metcalf: A Key to the Principal Orders and Families of Insects,
North Carolina State College.

Needham et al. : Culture Methods for Invertebrate Animals, Comstock Publish-
ing Co., Inc.

Peterson: A Manual of Entomological Equipment and Methods (Part I), Ed-
wards Bros., Inc.

Peterson: A Manual of Entomological Equipment and Methods (Part II), John
S. Swift Co., Inc.

Swain: The Insect Guide, Doubleday & Co.

Chapter 23

THE FROG— AN AMPHIBIOUS
VERTEBRATE ANIMAL

The common leopard frog is known as Rana pipiens (ra' na pip' i enz)
(L, rana, frog; pipiens, piping). Its body is smooth and covered with
mucus secreted by glands in the skin. Like many lower vertebrates, the
frog has the ability to change color due to changes in the black and yel-
low pigment cells in the skin. Because of its coloration the frog is af-
forded a certain degree of protection from enemies. This is known as
protective coloration. When in water, the frog need keep only the tip
of the nose above the surface because of the location of the nostrils (ex-
ternal nares) . Two large eyes are located on the top of the head. The
tympanum (eardrum) is external and just posterior to each eye. The
body may be divided into head and trunk. The latter bears two pairs of
appendages, but there are no claws upon the toes.

Integument and Skeleton. — The skin does not fit tightly and is com-
posed of (1) a rather thin outer layer called the epidermis and (2) a
thicker, inner layer the dermis (corium) (Fig. 208). The epidermis con-
sists of several layers of cells: (1) the outer ones, composing the stratum
corneum (stra' tum kor'neum) (L. stratum, layer; corneus, horny),
are flat, compact, and horny (shed several times during the active season
when the frog moults) and (2) the inner ones, next to the dermis, com-
posing the Malpighian layer, are columnar and by mitosis give origin to
the outer layer. The dermis consists of connective tissues in which are
glands, blood vessels, pigments (Fig. 209), nerves, muscle fibers, and
lymph spaces. The dermis is made of (1) an outer layer, called the
stratum spongiosum, consisting of loose connective tissue and containing
(a) pigment bodies which give the frog its spotted pattern (pigments may
also be present in the epidermis), (b) small spherical mucous glands
which pour a slimy secretion out upon the surface of the skin, (c) larger
spherical poison glands which secrete a whitish, acrid fluid for protection,
and (d) numerous sensory and tactile papillae (just below the epidermis)

421

422 Animal Biology

for sensory purposes and (2) the stratum compactum consisting of dense
connective tissues in which the fibers run somewhat parallel to the sur-
face of the skin and among which are blood vessels. The smooth, scale-
less, hairless skin functions as an organ of respiration as well as gives pro-

STRATUM CORNEUM ^^

MALPIGHIAN LAYER ^'f

fPIGMENT BODIES jjf'

MUCOUS GLAND

STRATUM SPONGIOSUM -

POISON GLAND

2
K
bJ

2
3

STRATUM COMPACTUM
BLOOD VESSELS

Fig. 208. — Skin of frog (cross section and somewhat diagrammatic). Com-
pare this with human skin (Fig. 228). (From Parker and Clarke: An Introduc-
tion to Animal Biology, The C. V. Mosby Co.)

^a-^rf/

Fig. 209. — Pigment melanophore from the frog (Rana temporia) . A, Pig-
ment distributed in response to Hght; B, pigment contracted. (From Potter:
Textbook of Zoology, The C. V. Mosby Co.; redrawn and modified from Noble:
Amphibia of North America, McGraw-Hill Book Co., Inc.)

The Frog — An Amphibious Vertebrate Animal 423

tection and serves for sensory purposes. The pigment bodies are respon-
sible for some protective coloration.

The bony endoskeleton (Fig. 210) consists of (1) an axial skeletoti
(skull and vertebral colum?i) and (2) appendicular skeleton (pectoral
girdle with its forelimbs and pelvic girdle with its hindlimbs). The frog
has no ribs. Most of the bones of the skull, except those of the upper

Premaxilh-

Maxilla

Sphehothmoid

fronbopaneba}

Squamosal

Atlas or /sfc cer- ^

v'lcal vertebra

Transverje process,
of vertebra

Jn^ -Phalanges

Metacarpals

^y Carpals

Radioulna

Prootid

Humerus

— Suprascapula
— Sacral or 9^ vertebra

Urosiyle
Ilium

hchium

Acetabulum

— femur

--.Tihiofibula

~--Asbraqa\us
Colcar

Calcaneum

Tarsals

Metatarsals.
Phalancjes

Fig. 210. — Skeleton of frog (dorsal view, appendages of left side not shown). The
acetabulum is not a bone but the joint at the proximal end of the femur.

and lovuer jaws and the hyoid bone to which the tongue is attached, form
the brain case (cranium). The brain and spinal cord connect through
a large opening (foramen magnum) at the base of the cranium. The
cranium articulates with the first vertebra (atlas) by means of a pair of

424 Animal Biology

rounded prominences, the occipital condyles. The pair of prootid bones,
one on either side of the posterior part of the cranium (Fig. 210), forms
the rounded auditory capsule that encloses the inner ear. Forming the
dorsal roof of the cranial cavity are two bones, the frontoparietals, each
formed by the fusion of a frontal and a parietal bone in the young frog.
At the anterior end of the brain case is the tubular sphenethmoid which
is divided by a transverse septum into two chambers. The anterior
chamber is divided longitudinally by a median septum and con-
tains the posterior part of the olfactory sacs (nasal capsules). The
posterior chamber is part of the cranial cavity and contains the
olfactory lobes of the brain. A pair of triangular nasal hones help to
form the dorsal wall of the olfactory sacs. A pair of vomer hones helps
to form the ventral wall of the olfactory sacs and also helps to form the
roof of the mouth. The vomer bones bear vomerine teeth on the ventral
surface. The upper jaw (maxilla) consists of a pair of premaxillae, a
pair of maxillae, and a pair of quadratojugal hones (Fig. 210). The first
two bear teeth. The lower jaw (mandihle) is the only part of the two
jaws that moves. The jaws are attached to the cranium by a suspensory
apparatus, of which the squamosal (Fig. 210) is a part. The hyoid ap-
paratus consists of a large flat, diamond-shaped plate of cartilage in the
floor of the mouth cavity. Rods of cartilage and bone extend anteriorly
and posteriorly from its central plate. The posterior rods extend back-
ward to the glottis which they help to support.

The vertebral column consists of nine vertehrae (Fig. 210) and a blade-
like posterior urostyle. A typical vertebra consists of (1) an oval, basal
centrum (for articulation), (2) neural arch through which the spinal
cord passes, (3) a single dorsal spine (neural spine) attached to the
neural arch and (4) a pair of transverse processes (except on the atlas)
which extend laterally for the attachment of muscles. The articulating
processes at each end of the neural arch are called zygapophyses. Liga-
ments hold the vertebrae together but allow a certain amount of move-
ment.

The pectoral girdle to which the forelimbs are attached is not attached
to the vertebral column by bones but by means of muscles. Compare
this attachment with that in man (Fig. 229). The sternum ("breast
hone) is located on the ventral median line and is composed of a number
of bones and cartilages. The ventral part of the pectoral girdle consists
of an anterior clavicle and a posterior coracoid. Other smaller bones go
to make up this part of the girdle. The dorsal part of the girdle is com-
posed of the bony scapula dorsal to which is the cartilaginous supra-

The Frog — An Amphibious Vertebrate A?iimal 425

scapula (Fig. 210). The glenoid fossa is the cavity with which the hu-
merus of the forelimb articulates. The radioulna of the forearm is a
fusion of radius and ulna bones. Contrast this with man (Fig. 229).
The wrist consists of six bones (car pals). The hand is supported by
five metacarpals. Distal to the hand are the bones of the digits or fingers
(phalanges).

The pelvic girdle (Fig. 210) to which the hindlimbs are attached is
attached to the transverse processes of the ninth or sacral vertebra. The
girdle is composed of a pair of long ilium bones (plural ilia), a pair of
ischium bones, and a pair of pubis bones. These three pairs of bones
articulate so that a cavity is formed {acetabulum) with which the femur
of the hindlimb joins. The anterior part of the acetabulum is formed by
the ilium and the posterior by the ischium, while the ventral part is
formed by the cartilaginous pubis. The tibio fibula is a fusion of the
tibia and fibula bones. Contrast this with man (Fig. 229). The tarsals
(ankle bones) are arranged in two rows, the proximal one consisting of
long bones, the astragalus and calcaneum. Contrast this with man. The
distal row contains a series of smaller bones. Distal to this are the five
elongated metatarsals (foot). Of the five toes (digits or phalanges), the
first and second contain two phalanges each, the third and fifth, three
phalanges each, and the fourth, four. On the tibial side of the first toe
there is an additional or accessory digit called the calcar or prehallux.
There are no claws.

Motion and Locomotion. — Well-developed and complex muscles are
present in the body, appendages, and head (Fig. 211). Minor muscles
move the lower jaw, aid in breathing, pump blood, secure foods, eliminate
wastes, and produce sounds by means of the vocal apparatus. The mus-
cles attached to the skeleton are called skeletal muscles. Each has an
origin which is the more fixed end and an insertion which is the more
movable end. Pulsating lymph ''hearts" (two near the third vertebra and
two near the end of the vertebral column) force lymph into the trans-
verse iliac and internal jugular veins.

Ingestion and Digestion. — Living insects, worms, and similar organ-
isms are captured by a rather sticky, extensile tongue attached at its
front end (Figs. 212 and 213). The tongue is thrown forcibly forward
by the rapid filHng of a lymph space beneath it. The large mouth cavity
bears cone-shaped teeth on the upper jaw. The two vomer bones in the
roof of the mouth bear vomerine teeth. A constricted, horizontal slit
separates the mouth cavity from the esophagus. The stomach is crescent

426 Animal Biology

shaped and is composed of a large, anterior cardiac part and a con-
stricted, posterior pyloric part which connects with the coiled small intes-
tine. The latter consists of an anterior duodenum, and a much coiled

Jc/bmax;/lary_

Deltoid _

Pectorahs major
fAnb, portion^

Tricep5 ^

Pecboralis majorL .

[Middle portion'^

Pectoral 15 major

^yJbdominal portion)

Rectus abdominis

External oblique

Tissue septum

Bectus abdominis

Linea alba

Addactor \onqas

Adductor macjnus

Sartorius

Triceps -femoris

gracilis major

gracilis minon

gastrocnemius

Extensor cruris

Tibicjlis posticus

nblo-fibula (hone)

Tibialis antlcus )onqus^

Tendon of- Achilles

Fig. 211. — Muscles of the frog (ventral view). Only the superficial muscles
are shown. The linea alba is a white line separating the right and left rectus
abdominis muscles. The triceps femoris has three heads one of which is the
vastus internus. The gracilis major is sometimes called the rectus internus major.
The gracilis minor is sometimes called the rectus internus minor. The muscles are
drawn somewhat diagrammatically, and some variations may be observed in dif-
ferent frogs.

The Frog — An Amphibious Vertebrate Animal 427

VomQrhQ teeth

floor of orbit

Esophagus _J''

Vocal iac

Maxillary teeth
_ _ Internal nares

_ Jc//a/5 marqinalis

_ E.Uitach'ian tuoe
— Glottii

€ Tonijae

Fig. 212. — Mouth of bullfrog opened to show internal structures. (From Potter:

Textbook of Zoology, The C. V. Mosby Co.)

iivcr M

Qall bladder

Commor\ bile dact ,,

Pancreatic duct _

large mtesb'me-
Ureter

Oviduct J

Anus

Bsophaqus
— Liver

..Cardiac erxi
of stomach

Pyloric end

of stomach

Pancreas

Ileum

Jplecn

Urinary

bladder

W^.. Cloaca

Fig. 213. — Frog digestive system with associated organs.

428 Animal Biology

ileum which widens into the large intestine. The latter connects with
the saclike cloaca. The latter also receives tubes from the kidneys and
reproductive system. The cloaca empties to the exterior through the
anus which is located between the two hindlegs.

The pancreas is a much-branched, tubular organ which lies between
the stomach and the duodenum. It passes its alkaline digestive juices
into the common bile duct (Fig. 213). The large, reddish, trilobed liver
secretes an alkaline bile which is carried to the gall bladder from which
it enters the duodenum together with the pancreatic juices through the
common bile duct.

The Physiology of Digestion: Digestion breaks down complex, insolu-
ble foods, such as proteins, fats, and carbohydrates, into simple, soluble
compounds capable of being absorbed by the cells and assimilated into
living protoplasm. The foods in the cells are constantly being used and
must be replaced in order to supply energy and chemical substances to
carry on the various life activities.

Uses of Foods in the Body of the Frog

FOOD
TYPES

USES

HOW USED

WHERE
STORED

BY-
PRODUCTS

Carbohy-
drates

Serve as fuel and
furnish energy;
may help build
certain tissues

Unite with oxygen
through the
process of oxida-
tion

As glycogen (animal
starch) in the
liver, muscles,
ovaries, nerves,
and skeleton

Carbon
water
dioxide.

Fats

Same as abov-e

Same as above

As adipose tissue in
the body, in the
liver, in the fat
bodies

Carbon
dioxide,
water

Proteins

Build living tis-
sues; repair de-
stroyed tissues

Broken down for
the release of
energy and their
constituent ele-
ments

Probably all parts of
the body

Urea, car-
bon diox-
ide, water

The various foods are acted upon by specific enzymes (ferments) which
hasten the above conversion processes without being used up themselves.
Because enzymes are so important, it may be well to list briefly some of
their more important characteristics. Enzymes are manufactured by liv-
ing protoplasm from foods and other materials which are brought to it.
Enzymes are specific for certain substances. For example, the enzyme
pepsin acts only on proteins and not on carbohydrates or fats. Enzymes
have an optimum temperature at which they can act most efficiently. A
temperature of 100° C. usually destroys the action of enzymes, while at
0° C. they are usually rendered very inactive. They also usually react

The Frog — An Amphibious Vertebrate Animal 429

best in a definite acid or alkaline environment. If too much acid or too
much alkali is present, a specific enzyme may not function, while it might
do so if the acid-alkaline reaction were changed to its specific optimum.
They are powerful chemical substances because a small amount may pro-
duce a large reaction. Their chemical composition is unknown, but they
are probably of protein makeup. They cause chemical changes in other
substances without, or with very slight, destruction of their own substance.
Many, if not all, enzymes may be stored in an inactive state in cells until
they are needed later.

Changes Which Foods Undergo: In the mouth there are no mastica-
tion, no digestion, and no enzymes (no glands). In the esophagus cer-
tain glands produce an alkaline mucous secretion which becomes active
when mixed with the acid gastric juice secreted by the glands in the walls
of the stomach. The cardiac end of the stomach has long, tubular,
branched, deeply set glands for the secretion of mucus. The pyloric end
of the stomach has short, tubular, shallow glands for secreting gastric
juice which contains the enzyme pepsin and about 0.4 per cent hydro-
chloric acid (HCl). In other words, the reaction is as follows:

Pepsin + HCl + Proteins —> Soluble Peptones

After the partially digested foods pass the pyloric valve from the stom-
ach into the duodenum, they are mixed with the alkaline pancreatic juice
which is secreted by the pancreas and brought to the duodenum by the
pancreatic ducts. The alkalinity of the pancreatic juice is due to sodium
carbonate (Na2C03). The three specific enzymes of the pancreatic
juice are (1) amylopsin, (2) trypsin, and (3) steapsin. Their specific
actions are shown:

Amylopsin + Starch -^ Maltose (double sugar)
Trypsin + Proteins or Peptones (in an alkaline

reaction) -^ Amino Acids
Steapsin + Fats — > Glycerin + Fatty Acids

The hepatic cells of the tubular glands of the liver secrete a green-
ish bile which is stored in the gall bladder until needed. The bile is
mixed with the pancreatic juice in the common bile duct before they
enter the duodenum. Certain bile enzymes convert fats, when in an
alkaline environment, into a soapy emulsion capable of osmosing through
the intestinal walls into the blood and lymph systems. The liver also
stores glycogen or animal starch (CeHioOs)!!. This is changed by cer-
tain liver enzymes into usable sugar when needed. Wastes are also elimi-
nated with the bile from the liver.

430 Animal Biology

The production and roles of intestinal juices and their enzymes in the
frog are not well known, but they are probably similar to those in higher
animals. Possibly starches may be converted into sugars in the intestine.
The various types of foods acted upon by specific enzymes in their proper
environments are eventually absorbed by the cells of the intestine and
passed into the lymph and blood vessels by which they are transported
to body tissues to be utilized.

External carotid

Palatine

Auricularis

Cutaneous
Carotid oiand

Conus arteriosus
Pulmonary

Systemic arch

Lateralis
Dorsa lis

Ophthalmic
Cerebral

a^lnternaf carotid

Brachial

Vertebral

Hepatic

Cocliaco^rn-escnteric

Left qastric

PANCREAS

IRiqht qastric
C celiac
Anterior
mesenteric

Splenic

Recto.vesical
Sciatic

/RECTUM I Pac,t^rior mesenteric

Fig. 214. — Arterial system of the bullfrog (ventral view). (Drawn by Ruth M.
Sanders, from Potter: Textbook of Zoology, The C. V. Mosby Co.)

Circulation. — The heart, located within the thin, saclike pericardium,
is three chambered, being made of two thin-walled auricles (right and
left) and one muscular, cone-shaped ventricle (Figs. 214, 215, 364, and
365). A thick- walled, tubular truncus arteriosus (conus arteriosus) arises

The Frog — An Amphibious Vertebrate Animal 431

from the base of the ventricle. A thin-walled, triangular sinus venosus,
located on the dorsal side of the heart, is connected with the right auricle.
In the adult frog the blood is pumped from the ventricle into the truncus
arteriosus which has branches as shown in the diagram of the arterial
system on page 432. Study this diagram, noting the relationships of the
various parts of the arterial system.

Linqual

■ ■ Mandibular
/■■ ^

^ Internal jagalar

Brachial.

Sinus

venosus

External jugular

. Subscapular

Innominate

Cardiac-

Hepatic

Cutaneous —

Posterior
vena cava.

■ '' / vtA-'f V' ^^

-: ' y l.-v\V<S*'. . ;.<?•>.- V

Free aval

Spermatic.

Dorso. lumbar.

Renal

^^\ Hepatic

'> nnrf/!l

[Gasfric

'.Splenic

\\ \\ !^_ /Mesenteric

Abdominal —
Renal portal.
Vesical

External iliac.— ^

Femoral

Fig. 215. — Venous system of the bullfrog (ventral view). (Drawn by Ruth M.
Sanders, from Potter: Textbook of Zoology, The C. V. Mosby Co.)

After passing from the arteries into thin-walled capillaries, the blood
is returned from the various tissues and organs of the body by a system of
veins (Fig. 215). The right and left pulmonary veins return the oxy-
genated (aerated) blood from the right and left lungs to the left auricle.
The blood from all other parts of the body is returned to the sinus veno-
sus through three large veins known as (1) the posterior vena cava (post-

432 Animal Biology

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The Frog — An Amphibious Vertebrate Animal 433

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434 Animal Biology

caval) with its branches^ (2) the right anterior vena cava (right pre-
caval) and its branches and (3) the left anterior vena cava (left pre-
caval) and its branches. The blood from the sinus venosus enters the
right auricle. The right and left auricles send their blood into the one
ventricle which forces its mixture of oxygenated blood (from the left
auricle) and nonoxygenated blood (from the right auricle) into the
truncus arteriosus through three pocket-shaped semilunar valves. The
venous part of the frog circulatory system is shown in the diagram on
page 433. Compare and contrast the diagram of the venous system with
the diagram of the arterial system.

Frog blood (Fig. 12) is quite complex and consists of: (1) Oval,
biconvex, nucleated red blood corpuscles (erythrocytes) which contain
hemoglobin. The latter unites temporarily with oxygen in the lungs and
skin to form oxyhemoglobin, which in turn gives up its oxygen to cells
and tissues when or where it is needed. (2) Amoeboid white blood
corpuscles (leucocytes) which are able to move independently and are
of different sizes. They pass through the walls of blood vessels and tis-
sues. They destroy bacteria and other organisms by ingesting them,
thus serving to prevent infections. (3) The spindle cells are frequently
spindle shaped and upon their disintegration assist in the clotting of blood.
Blood corpuscles originate principally in the marrow of the bones but
may also increase in numbers by division within the blood vessels after
being formed. (4) The plasma or liquid part of the blood carries foods,
wastes, proteins, mineral salts, etc. Blood coagulates, especially after in-
juries, to form a clot which includes fibrin, red and white corpuscles, tis-
sue cells, etc.

Respiration.— In the earlier, tadpole stages, external gills are present
for respiration, but these are later covered to form internal gills which
communicate with the exterior through a small opening. The internal
gills are eventually absorbed and typical lungs develop in the air-breath-
ing adult frog. In the adult frog respiration takes place through the skin
and lungs, probably more through the former than the latter. During
hibernation the lungs are inactive, yet skin respiration continues, even
though the rate may be reduced (Fig. 208). In lung respiration the air
is admitted into the mouth cavity (Fig. 212) from the outside through
the external nares (nostrils) and then through the slitlike glottis into the
short, tubular larynx: from the latter the air passes into the trachea
(windpipe) and finally into the thin-walled, saclike, paired lungs. The
lungs are ovoid, distensible, and internally divided by folds (septae) into
a number of compartments known as alveoli (al-ve'oli) (L. alveolus,

The Frog — An Amphibious Vertebrate Animal 435

small cavity) to increase the surface exposed to the air. Thin-walled
capillaries line the inner surfaces of the alveoli and permit the exchange
of oxygen and carbon dioxide between the air in the lungs and the blood
in the circulatory system. The amount of exchange of these gases
depends upon the concentration of each on either side of the lung and
blood vessel membranes. Air is forced into the lungs through the slit-
like glottis by closing the nares and contracting the floor of the mouth.
It is expelled from the lungs through the glottis into the mouth cavity
by the contraction of the muscles of the body walls. Air may be expelled
or drawn into the mouth through the nares by closing the glottis and
alternately raising or lowering the floor of the mouth. Sounds may be
produced by forcing air back and forth through the glottis (Fig. 212).

Oxygen unites temporarily with the hemoglobin of the red blood cor-
puscles, forming oxyhemoglobin. The latter carries oxygen to the tissues
and cells where it is given up if needed. The latter is determined by the
amount of oxygen present in the tissue, the activity of the tissue, etc. The
carbon dioxide is removed from tissues by the plasma.

Excretion. — Some of the wastes are excreted by the frog skin and in-
testine (Figs. 208 and 213), but many are taken from the blood by a pair
of elongated kidneys in the dorsal abdominal cavity. Internally, a kid-
ney contains a number of Malpighian bodies, each consisting of an en-
closing membrane known as Bowman s capsule, which surrounds a coiled
mass of thin- walled capillaries known as a glomerulus (glo -mer' u lus)
(L. glomus, ball). Wastes are collected from the blood in the glomeruli
and carried by urinijerous tubules to collecting tubules and thence to the
tubular ureter and finally to the saclike cloaca (klo -a' ka) (L. cloaca,
sewer) (Fig. 213). From the latter the urine may be stored in the thin-
walled, distensible urinary bladder, which voids only at certain intervals.
Ciliated, funnel-shaped nephrostomes in the ventral part of the kidney
open into the coelom, from which wastes may be secured and later
eliminated.

Coordination and Sensory Equipment. — The nervous system may be
divided into ( 1 ) central nervous system, consisting of brain and spinal
cord, (2) peripheral nervous system, consisting of ten pairs of cranial
nerves and ten pairs of spinal nerves, and (3) sympathetic nervous sys-
tem, consisting of nerves and ganglia which supply the internal (visceral)
organs (Figs. 216 and 217) .

The brain has the following structures: (1) two small, fused olfac-
tory lobes for the sense of smell, (2) two large, elongated cerebral hemi-
spheres of uncertain function, (3) two large optic lobes for the sense of

436 Animal Biology

sight, (4) the well-developed midbrain, (5) the small, narrow cerebellum
of uncertain function, and (6) the wide medulla oblongata which con-
nects with the enlarged portion of the spinal cord. When the brain
(except the medulla oblongata) is removed, the frog is still able to
breathe, jump, swim, swallow food, and use its sense of equilibrium.

O/factory tract
.Olfactory lobe

Trigeminus

facials ^
Auditory

Optic nerve

Pineal body

J)/(2ncephalon

^pfcic lobe

CembellurD

Medulla oblongata

4y? ventricle

J?lo550pbaryngeG/

Vaqus nerve

J^ spinal nerve
22^ spinal nerve

Thoracic
enlaraement

Spind cord

Lumbar.
en/argemenb

.Cerebmm

}

Brachial
plexuf

V 3- 5pinal nerve

.+^ jpinal nerve

jCalcarsoos body
5S?>splnal nerve

_.6^* ipina/ nerve

.7^ spinal nerve

,3 ^-t! spinal nerve

S— spinal nerve

lOib ip\na\ nerve

\ Jciatic pkKus

Jdatic nerve

Fig. 216. — Nervous system of a frog (dorsal view). (From Potter:

Zoology, The C. V. Mosby Co.)

Filumt^rminale

Textbook of

On the ventral side of the brain, the following structures are distin-
guishable: (1) optic chiasma, or the crossing of the optic nerves, (2) the
hypophysis (pituitary body), and (3) infundibulum.

The Frog — An Amphibious Vertebrate Animal 437

The spinal cord has a dorsal median fissure and a ventral median fis-
sure. The cord is composed of a central mass of gray matter (principally
nerve cells) in the shape of the letter H and an outer mass of white mat-
ter made up of nerve fibers. The hollow central canal extends through-
out the entire cord and may be seen in the middle of the crossbar of the
H in a cross-section of the spinal cord (Fig. 17). The central canal con-
nects anteriorly with the cavities (ventricles) of the brain. The spinal
cord has two surrounding membranous meninges, the outer one being
called the dura mater and the inner, the pia mater.

There are ten pairs of spinal nerves, each arising from the gray matter
of the spinal cord by a dorsal root and a ventral root (Fig. 17). The
union of these two roots at the side of the cord forms a spinal nerve.
Each spinal nerve passes out between the bony arches of adjacent
vertebrae.

OLFACTORY LOBE

OPHTHALNAIC

PALATINE

;v\AX\LLARY
MANDIBULAR

FACIAL

OLFACTORY

EYE

EAR

CLOSSOPHARYNGEAL-
CEREBELLUM

VAGUS

FOURTH VENTRICLE

RRST SPINAL-

CEREBRUM
GASSERIAN
GANGLION

OPTIC LOBE

JUGAL GANGLION

MEDULLA

SYMPATHETIC
NERVES

SPINAL CORD

Fig. 217. — Brain and cranial nerves of the bullfrog {Rana catesbeiana) shown
somewhat diagrammatically from the dorsai side. 1 to 10 show the cranial nerves;
11, the first pair of spinal nerves. Certain cranial nerves show some of their
branches. (From Atwood: A Concise Comparative Anatomy, The C. V. Mosby
Co.)

The sympathetic nervous system consists of two main trunks which
parallel the spinal cord, one on either side of it. Each trunk has ten
ganglia or enlargements where the ten pairs of spinal nerves unite with it.

The skin, because of its contained sensory nerve endings, receives
tactile, chemical, heat, and light stimuli (Fig. 208). The paired eyes
have a large, spherical lens which, in other respects, resembles the eyes
of other vertebrates. There are three eyelids: the rather motionless

438 Animal Biology

upper lid, the lower, which is fused with the third eyelid or nictitating
membrane (L. nictare, to beckon). The lens permits objects to be seen
at definite distances, especially moving objects. The pupil contracts and
regulates the amount of light which enters. The sensitive retina within
the eye is stimulated by light and transfers the impulses to the optic nerve
which carries them to the brain to give the sensation of sight. The eyes
lie in orbits (sockets) at the side of the skull and are moved by six eye
muscles known as external and internal recti, the superior and inferior
recti, and the superior and inferior oblique muscles.

The Number, Name, Origin, Distribution, and Function of the Cranial

Nerves of Vertebrates

NUM-
BER

NAME

ORIGIN

DISTRIBUTION

FUNCTION

Olfactory

Olfactory lobe

Mucous membrane lin-
ing the nose

Sensory (smell)

Optic

Second vesicle of
forebrain
(diencephalon)

Cells of the retina of
the eye

Sensory (sight)

III

Oculomotor

Ventral part of
midbrain

Superior, inferior, in-
ternal recti; and in-
ferior oblique mus-
cles of the eye

Motor (move-
ment of the
eye)

Trochlear
(Pathetic)

Dorsal part of
midbrain

Superior oblique muscle
of the eye

Motor (eye
movement)

Trigeminal

Laterally from
the medulla
(hindbrain)

Face, tongue, and
mouth, and to the
muscles of the jaws
or mandibles

Sensory and
motor

Abducens

Ventral part of
the medulla

External rectus muscle
of the eye

Motor

VII

Facial

Laterally from
the medulla

Muscles of face, roof of
mouth, hyoid, etc.

Motor (princi-
pally)

VIII

Auditory
(Acoustic)

Laterally from
the medulla

Cells of the semicircu-
lar canal and other
parts of the inner ear

Sensory (hear-
ing and equi-
librium?)

Glossopharyn-
geal

Laterally from,
the medulla

Membranes and mus-
cles of tongue and
pharynx

Sensory and
motor

Vagus ^
(Pneumo- V
gastric) J

Laterally from
the medulla

Heart, lungs, pharynx,
stomach, intestine,
visceral arches, etc.

Sensory and
motor

XI*

Spinal acces-
sory

Laterally from
the medulla

Muscles of the shoulder,
etc.

Sensory and
motor

XII*

Hypoglossal

Ventral part of
the medulla

Tongue and neck
muscles

Motor

*The XI and XII pairs are not present in fishes and amphibia.

The tympanic membrane of the outer ear communicates with the inner
ear by a bony columella which vibrates with the sound stimuli received

The Prog — An Amphibious Vertebrate Animal 439

(Figs. 216 and 217). The auditory nerve carries the impulses to the
brain, where the sensation of hearing is really produced. There are no
external ears. The middle ear communicates with the mouth cavity by
means of the Eustachian tube. The latter aids in equalizing air pres-
sures on the eardrums. The inner ear also contains organs of equilibrium.

Esophagus

ClUatGd mouth of
oviduct

. Egrg

Fat body

Ovary

-Adrenal (j]and

Hidney

Ovidact

Ureter

.—Rectum

Bladder

Uterus

Cloaca

.Anus

Fig. 218. — Urinogenital system of female frog (ventral view).

The olfactory sense is located in a pair of nasal cavities lined with
folds of sensitive, epithelial, nasal membranes. The external nares (an-
terior nares) connect with the nasal cavity. The internal nares (posterior
nares) connect the nasal cavity with the mouth cavity. The nares in
amphibia and other vertebrates (above the fishes) are used for both
respiratory and olfactory purposes. The olfactory nerves connect the
epithelial nasal membranes of the nasal cavities with the olfactory lobes
of the brain (Figs. 216 and 217). The elevated papillae of the mouth

440 Animal Biology

and tongue contain organs of taste, especially if foods and chemicals are
in solution. Lateral sense organs are present in the tadpole stages only
and are stimulated by vibrations of rather low frequency. Adult frogs
do not have a lateral line.

Reproduction. — The sexes are separate (diecious) (Figs. 218 and 219) .
The sperm of the male arise in paired, small, oval testes. The sperm pass
through the vasa effere?itia into the kidneys ^ then by means of Bidder's
canal, into the ureter, thence into the cloaca, and out through the anus.

Fat body

Testis

■^ VQsa effcrentia

y — Collecting tubules

Bidders canal

/drenal cjiand

Kidney

Ureter

Rectum

h]addQr

Omdacb

Cloaca

Anus

Fig. 219. — Urinogenital system of male frog (ventral view). On the right,
the testis has been moved and the kidney dissected to show the internal tubes.
The sperm pass from the testes through the vasa efferentia into Bidder's canal
from which they pass out through the ureter. Part of the circulatory system and
the adrenal (ductless) glands are also shown. Note the poorly developed rudi-
mentary oviduct in the male.

The eggs arise in the large paired ovaries, and later break out through
the walls of the enlarged ovary into the coelom (body cavity) . From the
latter the eggs eventually find their way into the much-coiled, paired
oviducts, the funnel-shaped openings of which are located near the an-
terior edge of the abdominal cavity. The oviducts lead into the thin-
walled uterus which leads into the cloaca. The latter leads to the anus.
The eggs are given a coat of gelatinous food which is produced by glan-

The Frog — An Amphibious Vertebrate Animal 441

dular cells of the oviduct. There are no copulatory organs. A yellowish,
hand-shaped organ, known as the fat body, is located in front of each
reproductive organ for the storage of food. There are no amnion and
no allantois attached to the developing embryo as in reptiles and mam-
mals. The embryology of the frog is considered in a special chapter.

QUESTIONS AND TOPICS

1. List the characteristics which place the frog in the phylum Chordata, sub-
phylum Vertebrata, and class Amphibia.

2. Explain and give the significance of (1) protective coloration, (2) internal
bony skeleton, (3) closed system of arteries, veins, and capillaries, (4) lymph,
(5) lymph hearts, (6) three-chambered heart, (7) paired appendages with
digits, (8) well-developed skeletal muscles which function in opposition, (9)
erythrocytes which contain hemoglobin, and (10) special cells to assist in the
clotting of blood.

3. Describe the structure and functions of the following for the frog: (1) in-
tegument, (2) motion and locomotion, (3) ingestion and digestion, (4) circu-
lation, (5) respiration, (6) excretion, (7) coordination and sensory equip-
ment, and (8) reproduction. In what specific ways have these shown im-
provements over the same in lower types of animals?

4. Explain (1) the origin and insertion of a muscle, (2) pectoral and pelvic
girdles, (3) auricle and ventricle, (4) vasa efferentia and ureter, and (5)
ureter and oviduct.

5. Describe the structure and functions of the various parts of the digestive
system, including the physiology of digestion in detail.

6. Discuss the advantages of a three-chambered heart over a two-chambered one.

7. Explain how blood is carried to and from the lungs and skin.

8. Describe the blood of the frog, including advantages over blood of animals
studied previously.

9. Explain how the circulatory system must be changed when a system of respi-
ration (lungs and skin) is present.

10. Explain how the circulatory system must be developed when only one pair of
kidneys excrete wastes.

11. Discuss the improvements in structure^ and functions of the nervous system
and sensory equipment of the frog over animals studied previously.

12. List the number, names, origin, distribution, and functions of the ten pairs of
cranial nerves in amphibia. In what ways do reptiles, birds, and mammals
differ from amphibia and fishes in regard to cranial nerves?

13. List the conclusions you can draw from your studies of the frog.

SELECTED REFERENCES

Dickerson: The Frog Book, Doubleday, Page & Co.

Holmes: The Biology of the Frog, The Macmillan Co.

Kingsley: The Frog (Guide for Dissection), Henry Holt & Co., Inc.

Marshall: The Frog, The Macmillan Co.

Noble: Biology of the Amphibia, McGraw-Hill Book Co., Inc.

Shumway: The Frog (Laboratory Guide), The Macmillan Go.

Stuart: Anatomy of the Bullfrog (Laboratory Guide), Denoyer-Geppert Co.

Chapter 24

EMBRYOLOGIC DEVELOPMENT OF ANIMALS

Ontogeny; Phylogeny; Recapitulation (Biogenetic) Theory
Morphogenesis

The embryologic stages undergone by an individual in its development
from the zygote to the adult are considered as the life history of the in-
dividual or ontogeny (on -toj' e ni) (Gr. on, being; genos, develop). A
race of organisms, made up of successive generations of individuals also
changes and evolves, and this developmental history of a race is known
as phylogeny (fi-loj'eni) (Gr. phylon, race; genos, descent). The
recapitulation (biogenetic) theory states that the life history of the stages
of embryologic development of the individual (ontogeny) briefly recapit-
ulates (repeats), in a modified manner, the evolution or stages of devel-
opment of the race (phylogeny) . Each organism tends in its individual
life history to recapitulate the various stages through which its ancestors
have passed in the development and evolution of their particular race.
In other words, ontogeny recapitulates phylogeny.

Each multicellular animal begins its life as a single, fertilized cell which,
according to the recapitulation theory, corresponds, in a general way, to
the unicellular Protozoa in animal ancestry. Most multicellular animals
(few exceptions) pass through an embryologic two-layered stage which
is comparable to such two-layered organisms as Hydra, sponges, etc. In
the higher multicellular animals there follows an embryologic three-
layered stage which is comparable to the three-layered organisms, such
as annelids, arthropods, chordates, etc. Many structures are developed
in individual organisms which are similar to comparable structures in
lower ancestral types of organisms. Embryonic pharyngeal clefts ("gill
slits") appear in the developing embryos of all mammals because they
developed in their ancestors. In certain adults, such as man, there are
no visible pharyngeal clefts remaining, but the embryologic stages of the
human being pass through these pharyngeal cleft stages nevertheless.
The development of a four-chambered heart in a higher animal em-
bryologically recapitulates the types of hearts found in the fishes, am-

442

Emhryologic Development of Animals 443

phibia, reptiles, and birds. The fishes have typical two-chambered hearts,
the amphibia have three-chambered hearts, the reptiles have three- or
four-chambered hearts (depending on the type), the birds and mammals
have four-chambered hearts.

One of the most important phenomena in the embryologic develop-
ment of individual organisms is the actual origin and development of the
definite structures and forms of specific tissues, organs, and systems.
How do so many different kinds of structures originate within a single
embryo? A study of the origin and development of the form and struc-
ture in organisms is known as morphogenesis (mor fo -jen' e sis) (Gr.
morphe, form; genesis, origin) . Naturally, the specific inheritance of the
particular embryo, together with the influences of environmental factors,
both external and internal, are influential in determining morphogenesis.
Many of these are not well understood, but the action and interactions
of specific genes, as well as the action of the cytoplasm,, assist in laying the
groundwork or blueprint for the detailed construction of the individual.
These are affected by physical and chemical factors (environmental) so
that specific traits are developed. The earliest stages in the development
of an animal seem to be influenced by the cytoplasm of the ^^g, which is
maternal. Within each species of animal there is a certain pattern of
development which is typical and normal. When this pattern is disturbed,
either by genetic or environmental factors, there follow abnormal proc-
esses which cause abnormalities in growth and developments. The
specific abnormalities depend upon the particular genetic materials in-
volved or the quantity and quality of the environmental factors at work
or both. Just after fertilization, various currents appear in the cytoplasm
of the cells which initiate the developmental pattern unique for that
species. Environmental influences may modify the normal cytoplasmic
currents and thus alter normal development. Later developments appear
to be influenced by chemical factors of the genes and cytoplasm and may
also be affected by environmental factors. However, unless these condi-
tions are extreme, development proceeds according to the normal pat-
tern for that species.

It is thought that genes possess a high degree of autonomy (o -ton'-
omi) (Gr. autos, self; nemo, distribute) and that they consist of highly
specific nucleoproteins which may be constructed from the simple mole- ^
cules of the nutrients of the cells. Many processes which occur in cells
are the result of the actions of various enzymes which in turn are thought
to be produced by gene action. It is believed that these enzymes are also
protein in composition. It is thought that genes reproduce themselves.

444 Animal Biology

thus perpetuating their hereditary potentialities. There seems to be a
relationship between the synthesis of enzymes and of new genes. It is
theorized that an undifferentiated cell in a particular region gives origin
to different and specialized cells (differentiated cells) because of cyto-
plasmic differences and that these differences which produce cells of
different sizes, shapes, and functions are the result of plasmogenes in the
cytoplasm. It is suggested that plasmogenes in the cytoplasm are pro-
duced by genes found in the nucleus.

EMBRYOLOGY OF THE FROG

The embryologic development of many of the animals is much the
same, with only minor differences in certain stages. The embryology
of the frog has been chosen to illustrate the general principles because
( 1 ) the frog has a rather typical, representative method of development
and (2) the materials are usually available and rather inexpensive.

The sexes of the frog are in different animals (diecious). The male
gametes (spermatozoa or sperm) produced by the male sex organs (male
gonads or testes) unite with the female gametes (ova or eggs) produced
by the female sex organs (female gonads or ovaries). This union forms
the first cell of the embryo known as the zygote. The eggs are found in
jellylike masses in fresh water pools and ponds in early spring. Each eg^
has several, thick, concentric layers of jelly known as the vitelline mem-
brane and is about the size of a buckshot.

In two or three hours after fertilization the zygote divides by mitosis
to form the two-cell stage, the two cells remaining in contact. Division
in this case is known as total cleavage or holoblastic (Fig. 220, A). A
second division occurs by mitosis in about one hour and at right angles
to the first plane of division, thus forming the four-cell stage. These
four, more or less equal, cells are called blastomeres (Fig. 220, B) .

The next plane of cleavage is horizontal and slightly above the middle
or equator, thus dividing each of the four previous cells by a transverse
division to form the eight-cell stage. Of these eight cells, four are pig-
mented, smaller, located at the animal pole, and known as micromeres;
the other four are unpigmented, larger, located at the vegetal pole, and
known as macromeres (Fig. 220, C) .

These cells continue to divide until there are a large number of cells,
all of which are closely packed together in a somewhat solid mass known
as the morula stage. The micromeres continue to divide more rapidly
than the macromeres at this time. It is evident that growth cannot con-
tinue indefinitely in this manner, or the animal would be solid without

Embryologic Development of Animals 445

Gray crescent

Animal pole

Yolk cells

Enteron

Vegetal pole

Blastocoel

Endoderm
Ectoderm

Neural groove

JR-EH

Yolk plug

Blastopore

Neurenteric canal

Notochord-^
Blastopore

Recttim

Yolk
Ectoderm

Yolk plug
Spinal cord

Midbrain
Forebraiai

Enteron
Sucker plats
Endoderm
Mesoderm

Fig. 220. — Embryology of the frog. A, B, C, Two-, four-, and eight-cell stages
of dividing egg; D, early blastula; E, section of D; F, late blastula; G, early
gastrula with very small ectodermal cells overgrowing other cells; H, section of G,
showing germ layers, blastocoel {Bid), etc.; /, late gastrula with neural groove;
/, older gastrula with neural groove closed and assuming a tadpole form; K, sec-
tion of / (see also Fig. 221). (From Woodruff: Animal Biology. By permission
of The Macmillan Company, publishers.)

446 Animal Biology

cavities in which tissues and organs could be placed. Consequently, at a
certain stage in the cleavage process, the cells of the morula stage all line
up in a very definite fashion to form a one-layered, hollow sphere known
as the hlastula or hollow sphere stage (Fig. 220, D, E, F) . This sphere
has a central, fluid-filled cavity known as the blastocoel or segmentation
cavity. This hlastula stage consists of ( 1 ) an outer, transparent, jellylike
capsule; (2) a dark, pigmented animal hemisphere, composed of smaller
and more numerous cells (ectoderm) ; and (3) a light-colored, unpig-
mented vegetal hemisphere which floats downward and is composed of
larger and fewer cells (entoderm). The vegetal cells are quite large and
contain yolk or food which is supplied to the cells of the animal hemi-
sphere. This arrangement makes the wall of the hlastula on the vegeta-
tive side much thicker than it is on the upper or animal side. The active
growth in this stage occurs, primarily, in the animal hemisphere region.

The gastrula or yolk plug stage follows the hlastula and is formed as
follows : At a certain point between the animal and vegetal hemispheres,
the vegetal cells turn inwardly into the blastocoel or segmentation cavity
(Fig. 220, G, H). The pigmented animal cells (ectoderm) grow over
the lighter colored, unpigmented vegetal cells (entoderm) and fold in
with them to some extent at that point. Thus, an inner area or layer
of cells is continuous with the outer layer. Because of more rapid mitosis,
the animal hemisphere continues to grow almost entirely over the vegetal,
leaving a small, light yolk plug exposed. The space between the bound-
aries of the infolded layers of cells, which surrounds the yolk plug, is
the blastopore or primitive mouth. The ingrowth of the latter is shown
on the surface by a thin, crescent-shaped fold or groove. The outer
layer of cells is known as the ectoderm and is continuous with the inner
inturned layer or entoderm. The point where the entoderm cells of the
vegetal region turn in is one side of the yolk plug and is known as the
dorsal lip of the blastopore. This inturned entoderm forms a cavity
known as the archenteron or primitive intestine (primitive gut). The
blastocoel now appears as a reduced cavity at the opposite side and is
gradually being crowded out by the developing archenteron and the
entoderm. The indentation on the opposite side of the yolk plug from
the dorsal lip of the blastopore is known as the ventral lip of the blasto-
pore.

The neural groove stage (Fig. 220, 7) follows the gastrula stage. The
neural groove, which is the forerunner of the future nervous system, be-
gins as a small depression on the dorsal side of the blastopore and grows
anteriorly along the dorsal side of the embryo as a thickened neural plate

Emhryologic Development of Animals 447

(medullary plate) in the ectoderm (Fig. 222). During this time, the
embryo grows longer and has definite anterior and posterior ends. A
thickened fold at each margin of the original neural plate forms a neural
fold (medullary fold). These folds at first are flat and far apart. Later
they arch toward the median dorsal line and unite to form the future
neural tube. At this time the neural plate sinks to form a definite neural
groove along the middorsal side of the embryo. The neural groove is
composed of ectoderm cells (Fig. 222) .

An elongated mass of cells dorsal to the archenteron forms the long,
rodlike notochord which may still be connected with the entoderm from
which it originates. The mass of cells at either side of the neural groove
is known as the mesoderm (middle germ layer) (Fig. 222) .

The neural tube stage closely follows the neural groove stage (Fig.
220, /) . The two neural folds on the dorsal surface of the embryo at
this time have met and fused into an elongated neural tube (Fig. 222).
At this stage the latter probably will be free from the outer ectoderm
from which it originated. The anterior part of the neural tube constricts
and enlarges by well-regulated mitosis to form the future fore-, mid- and
hindbrains. The notochord is now free from the archenteron and is just
below the neural tube (Fig. 222) .

The mesoderm completely surrounds the archenteron ventrally, arid
near the middorsal part there appears a small split or break which is the
forerunner of the coelom (body cavity). This break continues ventrally,
thus forming the body cavity between the two layers of the mesoderm.
The inner layer of the mesoderm, known as the splanchnic layer, lies
next to the entoderm, while the outer layer, known as the somatic layer,
lies next to the ectoderm. The cells of both ectoderm and entoderm are
now quite distinct (Fig. 222).

The larval stage with external gills follows the neural tube stage. A
pair of oval, thick-lipped suckers on the ventral side of the tadpole serve
for attachment purposes. The stomodeum (primitive mouth) appears as
an oval pit in front of the suckers. The olfactory pits are a pair of small
depressions above and anterior to the stomodeum. The three pairs of
external gills are fingerlike processes on either side of the head which act
as specialized organs of respiration. The proctodeum (primitive anus)
is located on the dorsoposterior part of the tadpole. A tail and a pair
of eyes are also present (Fig. 221 ) .

The larval stage with internal gills (Fig. 221) follows the stage with
external gills. The external gills are now covered by a fold of skin known
as the operculum (gill cover) which has a single opening called the

448 Animal Biology

spiracle. As the three pairs of external gills are resorbed, there are
formed four pairs of internal, fishlike gills (Fig. 222). In this stage the
suckers are small projections just behind the mouth. The mouth is sur-
rounded by a number of small projections known as the circumoral
papillae. The mouth also has a pair of horny jaws. The intestine shows
through the transparent ventral body wall as a long, coiled tube. This
great length of intestine suggests a typical vegetarian animal which the
tadpole really is at this stage. The hindlimb buds appear as small out-
growths on either side of the anal opening. These buds will continue to
grow by mitosis into the real hindlimbs.

Fig. 221. — Metamorphosis of the frog (for previous stages, see Fig. 220). 1,
Tadpole just hatched; 2, 3, older tadpoles, side view; 4, 5, later stages, dorsal
views showing external gills; 6, tadpole with gills practically covered; 7, older
stage, right side showing hind limb; 8 and 10, later stages, lateral view showing
hind limb de\elopment; 9, tadpole dissected to show internal gills, spiral intestine,
and anterior legs developed within the operculum; 11, advanced tadpole just be-
fore metamorphosis; 12, 13, 14, stages in metamorphosis, showing gradual resorp-
tion of tail; 15, young frog after metamorphosis. (From Woodruff: Animal Biol-
ogy. By permission of The Macmillan Company, publishers.)

Embryologic Development of Animals 449

Neuraf plat?

Neuraf groove

Notochot-d

Mesoderm

Endoderm

Neural tube

1 Notochord

Mesoderm

Somatic
mesoderm

a Ectoderm Endoderm i Ectoderm ^"docJerm

Spinal cord

Notochord *'*^''te

,/ \

Notochord ^

tctoderm

Splanchnic ^
mesoderm /

Spinal cord
Vertebra ' Dorsal root

■» ' OandJinn

i Sanglion

Genital
ridge

f ndflderm d
Brain

Muscle
segment

^Primitive
kidney

^■^Mesenchyma-

Coeion

Digestive

Ectoderm (Body cavity) "" tf^ct

<^n;K,.,i ,-r..A Notochord Neurenteric

t)pinal|COrd > canal

Anal pit

Digestive tract

smaA

Liver
outgrowth

Coelonr*
(Body cavity)

Fig. 222. — Development of a vertebrate, shown somewhat diagrammatically.
Stages a-e are cross section of mid-body region, a. Neural plate stage; b, neural
groove stage; c, neural tube stage; d, spinal cord stage; e, spinal cord stage still
later; f, embryo cut lengthwise to show internal structures. (From Being Well
Born, by Michael F. Guyer. Copyright 1927. Used by special permission of the
publishers, The Bobbs-Merrill Company.)

450 Animal Biology

The so-called later stages of dev^elopment (Fig. 221) follow the stages
described above. The front limb buds appear and develop into typical
front legs. The tail gradually is resorbcd and disappears, the materials
beins^ taken to the liver and stored. The internal "ills are resorbed and
their place taken with rapidly growing lungs. The adult frog is not
aquatic but has lungs similar to other land-living (terrestrial) animals.
The coiled intestine gradually shortens, which suggests a typical carniv-
orous (flesh-eating) animal, which the frog has now become.

EMBRYOLOGY OF MAN (MAMMAL)

Sperm which are produced by the male testes (Figs. 223 and 254) are
deposited at copulation in the female vagina and swim by means of their
whiplike flagellum through the glandular secretions along the wall of the
uterus and finally to the paired Fallopian tubes (oviducts) (Fig. 255).

e?t»S-Head

Neck

-TaLI

Zona pellucida

Cijtoplasm
Nucleus

Fig. 223. — Reproductive cells. A, Sperm (spermatozoon or male gamete) ; B,
ovum (egg or female gamete). The head of the sperm is primarily nuclear mate-
rial; a thin layer of cytoplasm surrounds the nucleus and fills the remainder of
the cell. The tail is also known as the flagellum by means of which the sperm
moves. The zona pellucida of the ovum is an albuminous envelope. (From
Francis, Knowlton, and Tuttle: Textbook of Anatomy and Physiology, The C. V.
Mosby Co.)

The production of ova (eggs) by the female ovary is called ovulation.
When the Graafian follicle which develops and encloses the developing
ovum collapses and the wall of the ovary breaks (Figs. 223 and 255), the
ovum is passed from the ovary into the abdominal cavity near the open-

Embryologic Developmerit of Animals 451

Fig, 224. — Cleavage, blastulation, gaslrulation, and formation of three primary
germ layers (ectoderm, mesoderm, entoderm) of mammalian embryo. The early
stages have never been actually observed in human beings but probably resemble
those of other mammals.

/, Fertilized cg^ cell; 2, two-celled stage; 3, three-celled stage; 4, morula stage;
5, morula stage in half-section, showing outer trophectoderm {T) and inner cell
mass (/) ; 6, blastocyst stage in half-section," showing amniotic cavity {A.C.) above,
and a single layer of entoderm {En.) ; 7, later blastocyst in median section, show-
ing amniotic cavity {A.C.) and yolk sac {Y.S.) separated by a cellular mass consti-
tuting the embryonic disc or shield {E.D.), the latter eventually forming the em-
bryo. The amniotic cavity is lined with ectoderm {Ec.) and the yolk sac with
entoderm {En.) Observe the two types of mesoderm known as the somatic meso-
derm {S.M.) and the splanchnic mesoderm {Sp.M.). Two layers of mesoderm
form the extraembryonic coelom {E.C.) between them. 8, Blastocyst containing
human embryo {E.) about twenty-one days old, showing chorionic villi {C.V.)
for securing nourishment; the allantois {A.) \ splanchnic mesoderm {Sp.M.); so-
matic mesoderm {S.M.) ; 9, blastocyst containing human embryo about thirty-three
days old and about 5.0 millimeters long, showing eye, pharyngeal clefts, front
and hind limb buds, tail, and umbilical cord {U.C.). For older embryos see Fig.
225. The above stages are represented somewhat diagrammatically; from various
sources.

452 Animal Biology

ing (ostium) of the Fallopian tube. Through the action of the cilia
which line the Fallopian tube the ovum, is drawn into it, and fertilization
usually takes place there, although, on rare occasions, the ovum may be
fertilized while still in the abdominal cavity. In the latter case the de-
veloping embryo must be removed surgically. Unless the ovum is fer-
tilized within a week after it is produced, it usually will not be. The
ovum, (egg) extrudes its first polar body at the time of ovulation and a
second polar body upon fertilization. The o\um is now ready to divide
(cleave).

Cleavage of the fertilized ovum, (zygote) probably occurs in the Fallo-
pian tube. The first cleavage, extending from the animal pole to the
vegetal pole, results in two equal cells (blastomeres) (Fig. 224) which ad-
here to each other and are surrounded by an albuminous layer called the
zo7ia pellucida. The second cleavage is accomplished by one of the
blastomeres dividing longitudinally at right angles to the first cleavage,
to be followed by cleavage of the other blastomere, thus forming the four-
blastomere stage. Cleavage continues until a small sphere of blastomeres
the size of a pinhead is formed; this is known as the morula stage. The
morula is still in the Fallopian tube but probably is approaching the
fundus (base) of the uterus. It is thought that approximately one hun-
dred hours are required for the fertilized ovum to develop to the sixte en-
cell stage of the morula. The morula consists of (1) an outer layer of
cells called the trophectoderm or trophoderm (Gr. trophe, nourishment;
ecto, external; derm., covering) and (2) an inner cell mass. The cells of
the trophectoderm increase so that the outer surface is much enlarged,
thereby forming a saline-filled cavity (blastocoel) within the morula,
which is now known as the blastocyst (blastodermic vesicle) (Fig. 224).
Within ten days after fertilization the blastocyst has moved into the
uterus. The latter has developed a thick, glandular layer which is stimu-
lated by a ductless gland secretion, known specifically as progestin, to
produce a sticky fluid by means of which the blastocyst adheres to the
uterine wall. After a few hours the blastocyst begins to sink beneath the
mucous layer of the uterus (endometrium) because the latter is eroded by
cytolytic action of the trophectoderm cells of the blastocyst. This phe-
nomenon is for the purpose of ensuring nourishment for the developing
embryo until it can secure its own food.

The inner cell m.ass, near the point where it contacts the trophecto-
derm, forms the hollow amniotic cavity (Fig. 224). The free or un-
attached region of the inner cell mass forms a yolk sac cavity along the
inner surface of the trophectoderm. The space betwen the yolk sac

Embryologic Development of Animals 453

cavity and the trophectoderm is quite large. The yolk sac cavity con-
tains no yolk (food), but its upper region will later form the roof of the
alimentary canal. The amniotic and yolk sac cavities are separated by
a cellular embryonic disk (embryonic shield) which will form the em-
bryo. Its ventral layer is entodermal, its dorsal layer ectodermal, and
the cells between the two are mesodermal (Fig, 224). Mesoderm is also
formed between the yolk sac cavity and the trophectoderm and between
the ectodermal lining of the amniotic cavity and the trophectoderm. The
trophectoderm is now lined on the inside by a layer of mesoderm (Fig.
224), known specifically as somatic mesoderm. The trophectoderm and
somatic mesoderm combined are known as the chorion because the lat-
ter, through minute projections (villi), contacts the blood vessels of the
uterus in order to supply nourishment until the future blood system of
the embryo is developed. Hence, the entoderm of the yolk sac cavity
is covered with splanchnic mesoderm, while the ectoderm of the amniotic
cavity is covered with somatic mesoderm (Fig. 224) . The blastocyst also
develops a third cavity, the extraembryonic coelom, located between the
two separating layers of mesoderm. These two layers were originally
one layer which was located between the entoderm of the yolk sac cavity
and the trophectoderm.

In the next stages of development the embryonic mass (embryo)
detaches itself partially from the inner surface of the chorion, grows rap-
idly, and forms a tubular outgrowth from the upper region of the yolk
sac (Fig. 224) . This outgrowth, called the allantois (Gr. allanto, sausage
or tubular; eidos, form), grows toward the chorion and through the body
stalk, by means of which the embryo is attached to the chorion. The
yolk sac and allantois do not play as great a role in human embryologic
development as they do in lower forms of organisms.

Between the third and fourth week of gestation (L. gestatio, carry-
ing, pregnant) the blastocyst has enlarged so as to form a bulge on the
surface of the uterus. The embryo soon pushes into the cavity of the
uterus, being surrounded by the amnion membrane of the embryo (Gr.
amnion, embryo covering) . The body stalk now functions as the um-
bilical cord, the latter being continuous with the highly vascular, disk-
shaped placenta which in turn is in contact with the blood vessels of the
walls of the uterus.

About two- thirds of the embryonic shield (embryonic disk) previously
mentioned will form the future head, while the remainder will form the
neck, trunk, and tail. The two cellular layers of the embryonic shield
consist of (1) the lower entoderm layer (nearest the yolk sac cavity) and

454 Animal Biology

(2) the upper ectoderm layer which gives rise to the brain, spinal cord,
outer skin, etc. Between the ectoderm and entoderm, on either side of
the median Une, and originating from both, there are formed two groups
of cells: (1) the membranous mesoderm (mesothelium) and (2) a
loosely arranged meshwork of cells called the mesenchyme. The ecto-
derm, mesoderm, and entoderm are known as the three primary germ
layers, because from them arise all the tissues and organs of the future

oroanism.

The tissues of the adult are derived from the primary germ layers as
follows :

1. From the Ectoderm — The epidermis and its derivatives, as hair,
nails, glands, lens of the eye; nervous tissues, including the neuroglia;
the epithelium of the organs of special sense, of the mouth and its oral
glands, of the hypophysis, of the anus, the amnion; the chorion; the
smooth muscles of the iris (eye), and the sweat glands.

/I.

Fig. 225. — Human embryos. The membranes (amnion and chorion) have
been removed to show the embryo. The approximate sizes and ages are given for
each one. Drawn somewhat diagrammatically and somewhat enlarged. A, Thirty-
three days old and 5 mm. long, showing the umbilical cord, pharyngeal clefts,
tail, limb buds, eye, etc.; B, thirty-eight days old and 7.5 mm. long, showing the
enlarging heart (shown just below the pharyngeal clefts), the beginning of the
external ear, the myotomes (muscles) in the dorsal region; C, seven weeks old
and 17 mm. long; D, about eight weeks old and 24 mm. long. (Modified from
various sources.)

2. From the Mesodenn — The epithelial lining of the pericardium,
pleura, peritoneum, urogenital system; striated muscles; smooth mus-
cles; notochord; connective tissues, including cartilage and bone; bone
marrow; blood; lining (endothelium) of the blood vessels and lymph
system; lymphoid organs; the cortex of the suprarenal gland.

3. From the Entoderm — The epithelium of the pharynx and its deriva-
tives, the thyroid, parathyroids, thymus, tonsils and auditory tube; the

Embryologic Development of Animals 455

digestive tract, including the liver and pancreas; the respiratory tract,
including the lungs, trachea, and larynx; the bladder; the prostate; the
urethra; the yolk sac; the allantois.

The detailed description of the embryologic origin of each tissue
and organ cannot be given, but a few typical examples will be suffi-
cient. As the embryo develops, the upper part of the yolk sac forms the
tubular primitive m,id- and hindgut with its outgrowth, the liver, when
the embryo is about three weeks old. The saclike "hearf begins to beat
soon after this time. By the third week the yolk sac has numerous

Yo/k Sac

Muscu/ar Layer-
of Uterus

Basal Plate-
of Placenta

Umbilical Coraf-

Amnion

Chorion & Oecidua
Copsularis

Fig. 226. — Human fetus shown in normal position in a section of the uterus.
The chorion is the outer embryonic membrane and the amnion is the inner. (From
Potter: Textbook of Zoology, The C. V. Mosby Co.; modified after Ahlfeld.)

' blood islands" for developing the embryonic vitelline circulation. The
embryonic disk infolds (invaginates) to form a troughlike groove (neural
groove) , the open, upper side of which later closes to form a hollow tube
(neural tube). From the anterior end of the tube will develop the vari-
ous parts of the brain and cranial nerves, while the remainder forms the
spinal cord with its spijial nerves.

Before five weeks the embryo externally shows a head with rudimen-
tary eyes, an external tail, and a neck with four pairs of gill arches and

456 Animal Biology

four pairs of incompletely formed slits which somewhat resemble the gill-
bearing arches of a fish (Figs. 224 to 227 and 363). There are numerous
blood vessels here, but no true gills. These gill arches give rise to such
structures as the following: from the arches arise muscles used in chew-
ing foodj middle ear bones, hyoid bone (at base of tongue), certain
facial nerves and muscles, part of the cartilage of the larynx and its mus-
cles; from the slits between the arches arise such structures as the Eusta-
chian tubes, external ear passage, part of the tonsils, thymus, and para-
thyroids.

conjunctiva —
aqueous humor,
crystalline lens
lower lid — —

vitreous humor —
retina ' — - — "

pigment layer —

optic nerve — •

Fig. 227. — Stages in the development of the eye in embryos of a vertebrate ani-
mal shown somewhat diagrammatically. A, Thickening of the ectoderm of the
side of the head as the optic cup begins to form on the end of the optic stalk;
B, formation of the lens and the retina in the optic cup; C, later stage with parts
labeled. (From Atwood and Heiss: Educational Biology, The Blakiston Co.)

QUESTIONS AND TOPICS

1. Describe the frog egg before development begins. Where and when can you
find such eggs? Why are such eggs not deposited in the fall? What is the
relationship between the dark pigment of the eggs and the source of heat
energy for the development of the eggs?

Embryologic Development of Animals 457

2. Define (1) zygote, (2) morula, (3) blastula, (4) gastrula, (5) ectoderm, (6)
entoderm, (7) blastocoel, (8) blastopore, (9) archenteron, and (10) cleavage.

3. Contrast micromeres and macromeres as to size, location, rate of division, and
functions.

4. What system is first definitely differentiated in the developing frog? In man?
Explain how and why it arises early.

5. Explain the origin of the notochord and its relationship to the nervous system.

6. Review the discussion on tissues and tell which tissues arise from each of the
three germ layers.

7. What forces cause certain cells of an embryo to divide and dev^elop at certain
times and to rem.ain rather inactive at other times?

8. Why is it undesirable for all cells of an embryo to divide at the same time?
Explain the relationship between this and food supphes, waste accumula-
tions, etc.

9. Explain the role of heredity in determining the time and rate of development
of certain tissues at specific periods.

10. What controls the rate of mitosis in the anterior part of the neural tube,
which through enlargements develops into the various regions of the brain?

11. Can the age of an embryo be approximately determined by the presence of
specific embryonic structures?

12. In what ways do the various stages of the frog embryo and human embryo
resemble each other? In what ways do they differ?

13. Describe the embryologic origin and development of such human tissues and
organs as the instructor suggests.

14. Give a definition and an example of ontogeny, phylogeny, recapitulation
(biogenic) theory, and morphogenesis.

SELECTED REFERENCES

Arey: Developmental Anatomy (Embryology), W. B. Saunders Co.

Bailey and Miller: Textbook of Embryology, William Wood & Co.

Corner: The Hormones in Human Reproduction, Princeton University Press.

Corner: Ourselves Unborn, Yale University Press.

Dodds: Essentials of Human Embryology, John Wiley & Sons, Inc.

Huettner: Fundamentals of Comparative Embryology of Vertebrates, The Mac-

millan Co.
Marshall: Vertebrate Embryology, G. P. Putnam's Sons.
McEwen: Vertebrate Embryology, Henry fiolt & Co., Inc.
Parshley: The Science of Human Reproduction, W. W. Norton & Co., Inc.
Patten: Human Embryology, The Blakiston Co.
Patten: Embryology of the Chick, The Blakiston Co.
Patten: Embryology of the Pig, The Blakiston Co.

Potter: Fundamentals of Human Reproduction, McGraw-Hill Book Co., Inc.
Richards: Outline of Comparative Embryology, John Wiley & Sons, Inc.
Rugh: Experimental Embryology, John Wiley & Sons, Inc.
Weiss: Principles of Development, Henry Holt & Co., Inc.
Wieman: Introduction to Vertebrate Embryology, McGraw-Hill Book Co., Inc.

Chapter 25
BIOLOGY OF MAN

I. GENERAL ORGANIZATION OF THE HUMAN BODY

All human beings arise embryologically from a single cell (zygote)
which is the result of the fertilization of an ovum (egg) by a male sperm.
This zygote and all succeeding cells divide by mitosis to produce the
organs, tissues, and cells of which the body is composed. When a child
is born its body already is composed of approximately 26 trillion cells.
It is suggested that the reader review the discussions of cells and tissues in
previous chapters as well as the embryologic development of a human
being.

In spite of the fact that there are so many cells in the human body,
they are not all alike. In fact, early in the development of the embryo
various cells are set aside (differentiated) to form the future organs and
tissues. The human body is composed of the following systems of organs
with their functions briefliv stated.

Integumentary (Skin) System. — Protection, support, heat regulation,
absorption, excretion, stimuli reception (Fig. 228).

Skeletal System. — Support, protection, posture, motion, locomotion,
manufacture of blood corpuscles (by bone marrow), transmission of
sound waves (ear bones) (Figs. 229 and 250).

Muscular System. — Locomotion, movements of parts of the body or
organs, as stomach, heart, intestines, etc. (Figs. 232 and 233).

Digestive System. — Ingestion, digestion, and absorption of foods (Fig.
236).

Circulatory System. — Transportation of foods, wastes, heat, oxygen,
carbon dioxide, and various secretions (Figs. 237 to 242).

Respiratory System. — Furnish oxygen and eliminate carbon dioxide
and other waste products (Fig. 244).

Excretor)^ System. — Secretion and elimination of waste products of
cell and tissue metabolism (Fig. 245).

458

Biology of Man 459

Nervous and Sensory System. — Receive stimuli; transmit and interpret
impulses for purposes of correlation^ secretion, movement, locomotion,
behavior, etc.; centers of sight, hearing, taste, smell, equilibrium, etc.;
memory; imagination (Figs. 246 to 251).

Endocrine (Ductless) Gland System. — Production of ductless gland
secretions for the correlation and regulation of various body processes
(Figs. 252 and 253).

Reproductive System. — Production of sex cells by the growth and
development of which the species as well as the race will continue (Figs.
223to225, 254, and255).

II. INTEGUMENT (SKIN) AND SKELETON

There are two distinct layers of the human skin: (1) the external
epidermis (cuticle) and (2) the deeper dermis (corium) (Fig. 228).
The epidermis is stratified squamous and columnar epithelium, contains
no blood vessels, but has fine nerve fibrils. The hair, nails, and numerous
glands are all modified epidermis. When we "peel" after a sunburn, the
epidermis comes oflF in sheets or strips.

The human epidermis is composed of the following four layers : ( 1 )
The outer, thin stratum corneum is made of layers of cells, the lower
layers of which are living and which replace the upper dead layers. The
protoplasm of these cells contains a protein material, keratin, to prevent
the excess loss of water. Many bacteria are probably harmed by the acid
of this layer. (2) The next layer, the semitransparent stratum lucidum,
is made of cells which are practically dead and which are renewed from
below. (3) The next layer, the thick, granular stratum granulosum, con-
tains some dead cells which are also replaced from below. (4) The
lowest layer of the epidermis, the stratum mucosum or Malpighian layer,
is made of several layers of columnar <:ells and contains the pigments ol
the skin. This layer gives rise to the upper layers of the epidermis.

The dermis or corium is well developed, thicker than the epidermis,
and contains blood vessels, lymph vessels, nerves, and sense organs as well
as hair follicles, glands, and papillae. The dermis is attached to the
deeper tissues by a type of connective tissue known as subcutaneous
tissue. The dermis is characteristic of vertebrates and is used when
leather is "tanned." The dermis is composed of the following: (1)
The superficial papillary layer contains numerous slight elevations called
papillae in order to increase the surface for nerves, blood vessels, lymph
vessels, sense organs, and glands. (2) The deeper reticular layer con-

460 Animal Biology

sists of bands of yellow elastic and white fibrous connective tissues which
contain adipose tissue ("fat") and sweat glands.

In some parts of the human body the skin is very tightly attached
to the deeper tissues, while in other parts it is loosely attached to permit
free movements. On the inner surface of the hands and fingers and on
the soles of the feet there are many minute ridges which increase fric-
tion and form the individually distinctive fingerprint and footprint
patterns which remain constant throughout life. The dermis contains
thousands of sensory nerve endings for the reception of heat, cold, pain,
pressure, and touch (tactile) stimuli. Receptors for each of these sen-
sations are present in all parts of the skin but some are much more
concentrated in certain regions than in others. For example, tactile
receptors (touch) are much more numerous on the finger tips than on
the back of the hand.

Sweat- Duct

Sebaceous Glancl>

Bomy layer
Pigment layer

Tactile Organs"
Nerve —
Blood Vessels '

Sweat Gland^zirS-^

Fat

Epidermis

)> Dermis

Fig. 228. — Human skin shown in cross section. The horny layer of the epi-
dermis is composed of three parts: the outer part, stratum corneum, made of
layers of flat cells containing keratin to prevent water loss; a middle part, stratum
lucidum, composed of transparent cells; and a lower part, stratum granulosum,
whose cells contain granules. The pigment layer of the epidermis is also known
as the Malpighian layer or stratum mucosum. The dermis or corium has an upper
or papillary layer containing papillae (elevations), nerves, tactile organs (sense
of touch), blood vessels, sebaceous glands, etc.; and a lower or reticular layer
containing sweat glands, fat (adipose tissue), etc. Contrast human skin with
that of the frog (Fig. 208). (From Guyer: Animal Biology, Harper & Brothers.)

Accessory structures of the skin include hairs, oil glands, nails, teeth,
and sweat glands (Fig. 228). The Malpighian layer of the epidermis
is extended (invaginated) downward into the dermis to form the tube-
like hair follicles. The cells at the base of a follicle produce the hair

Biology of Man 461

which is a fusion of epidermal cells supplied with keratin (a horny, pro-
tein material). When a hair is being formed, it first appears as a tiny
elevation below the skin surface, later to be erupted. As more is pro-
duced, the hair is shoved farther from the skin surface. The part of
the hair within the folHcle is called the root, while the remainder is
called the shaft. All skin is provided with folHcles, except the palms of
the hands, the soles of the feet, and the last portion of the fingers and
toes. The consistency of the hair depends upon the structure of the
follicle; a round follicle (in cross section) gives rise to straight hair, an
oval follicle to curly hair, and a rather flat, ribbon-shaped follicle to
wavy (kinky) hair. The color of the hair is determined by the quantity
and quality of pigments present and their relation to the transparent air
spaces within the hair. Loss of hair may be due to inheritance, certain
diseases, or other environmental factors. Certain types of baldness are
due to heredity. Fewer women than men are bald because the former
more rarely inherit the necessary baldness-producing determiners. The
base of each hair is supplied with a nerve and blood vessels for its nour-
ishment. Smooth muscle fibers in the dermis are attached to the hair
follicle so that the hair can be moved.

Sebaceous (oil) glands are formed by the invagination of the Mal-
pighian layer of the epidermis into the dermis and are nearly every-
where associated with the hair follicles, being especially numerous on
the face and scalp. The oily secretion passes from the glands into the
hair follicle from which it passes to the surface, where the oil keeps
the hair and skin from becoming dry and brittle and prevents undue
evaporation or absorption of water and other liquids by the skin. Some-
times the glands become infected with pus-producing bacteria.

Nails are produced from closely packed epithelial cells along the
furrow at the base of the nail. The nail is formed by a fusion of clear,
dead, horny, keratinized cells to produce a solid plate.

Teeth are derived embryologically from epithelial tissues and are im-
bedded in the upper and lower jawbones for support and strength.
The part of the tooth above the gum is called the crown and is covered
with very hard enamel. The remainder of the tooth is composed of
softer dentine with its central canal (pulp cavity) which in turn con-
tains blood vessels and nerves. The teeth are attached to the jawbone
by a substance called cementum. Man, like all mammals, has a tem-
porary, "baby" set of teeth, twenty in number, which appear between
six months and two and one-half years of age. The permanent set,
thirty-two in number (Figs. 230, and 231), is composed (on each side

462 Animal Biology

CRANIUM

MANDIBLE

CLAVICLE

SCAPULA

STERNUM

RIBS

HUMERUS
SPINAL COLUMN

PELVIC BONE

RADIUS

ULNA

CAVITY OF PELVIS

CARPALS
METACARPALS

PHALANGES
FEMUR

PATELLA

TIBIA
FIBULA

TARSALS

METATARSALS

PHALANGES

Fig. 229. — Human skeleton. The clavicle is commonly called the collarbone:
the scapula, the shoulder blade; the patella, the kneecap. (From Parker and
Clarke: An Introduction to Animal Biology, The C. V. Mosby Co.)

Biology of Man 463

"eye" tooth

of each jaw) of two incisors ("front" teeth), one canine
or cuspid), two premolars (bicuspids), and three molars. The last pair
of molars ("wisdom teeth") is frequently not erupted until later in life,
or not at all. Hence, the normal dental formula for man is:

(for each jaw)

The incisors are flat and sharp for cutting food as they overlap; the
pointed canines correspond to the tusks of carnivorous animals and are

CENTRAL
NCISOR

LATERAL
NCISOR

CUSPID

FIRST
BICUSPID

SECOND
BICUSPID

FIRST
MOLAR

SECOND
MOLAR

THIRD MOLAR
(WISDOM TOOTH)

SECOND
MOLAR

FIRST
MOLAR

SECOND
BICUSPID

FIRST
BICUSPID

CUSPID

LATERAL
NCISOR

CENTRAL
NCISOR

Fig. 230. — Chart showing the thirty-two permanent human teeth. (Courtesy of

the American Dental Association.)

used for tearing foods; the broad-surfaced premolars have two elevations
for grinding purposes; the larger molars have four or more elevations
for grinding.

Sweat glands are present in all skin but are most numerous under the
arms, on the forehead, on the soles of the feet, and on the palms of the
hands. The coiled, tubular glands are located in the dermis and empty

464 Animal Biology

their excretions (sweat or perspiration) through pores on the skin sur-
face. Over two million sweat glands in the entire skin eliminate over a
quart of sweat per day under normal conditions. Under abnormal con-
ditions, more or less than this amount may be excreted. Perspiring
eliminates body wastes and regulates body heat through the evapora-
tion of water. Heat which is produced in various tissues, especially
muscles, is distributed b)- the blood throughout all parts of the body,
thus producing an average, normal body temperature of 98° to 99° F.

Adamant

or
enamel

Crouin —

Neck

Root -

Dentine

or
Wory

Dental pub

Cement
Gum

Alveolar
process

Peridental
membrone

Jont M.Hopf

Fig. 231. — Human incisor tooth in vertical section. (From Francis
tion to Human Anatomy, The C. V. Mosby Co.)

Introduc-

Since the skin is well supplied with blood, it can efficiently act as a heat-
regulating and heat-eliminating mechanism. Dilation (enlargement) of
the blood vessels and relaxation of the muscle fibers of the dermis allow
more blood to lose more heat, while a contraction of these blood vessels
and muscles has the opposite effect. In addition to this loss of heat, the
skin may also be cooled by the evaporation of sweat from the skin surface.
The functions of the human skin and its accessory structures may be
summarized as follows: (1) regulation and elimination of heat; (2)
excretion of wastes; (3) protection against injury, harmful light rays,

Biology of Man 465

loss of water, disease-producing organisms (bacteria, molds, parasites,
etc.), (4) prevention of the absorption of various deleterious materials
from our environment, (5) aid in normal respiration, (6) supply infor-
mation about our environment through the various types of sensory
end organs, and (7) to produce hair, nails, glands, and teeth each with
their specalized functions.

The skeletal system consists of 206 named bones, cartilage, and liga-
ments, the latter to hold the other parts together and bind them into an
efficient structure. The bones are illustrated in Fig. 229 and the names
and numbers are given in table form so as to be easily memorized. It
will be observed that the bones may be classified as to shape as follows:
(1) long (arms, legs), (2) short (wrist), (3) flat (shoulder blade,
patella, etc.), and (4) irregular (vertebrae). It will be noted that the
teeth are not listed as part of the skeleton but are included with the
integument because of their epithelial origin. By studying a human
skeleton it will be evident that there are several types of joints, each
with its specific functions. Joints may be classed as ( 1 ) immovable
(irregular, dovetail connections [sutures] of the bones of the cranium)
and (2) movable, with movements of various types for specific purposes.
Movable joints may be further classed as (1) ball and socket (femur
and pelvic girdle, humerus and pectoral girdle), (2) hinge (femur arid
tibia, humerus and ulna), (3) sliding (most of vertebrae), and (4)
rotating (radius and ulna).

Bones, for the most part, originate in the embryo as cartilage; hence
they are known as cartilage bones in contrast to the less common mem-
brane bones which are formed by the gradual ossification of soft, fibrous,
membranous tissues (skull bones). Certain parts of the skeleton remain
as cartilage, such as the external ear, tip of the nose, tip of the breast
bone, between the vertebrae, and articulatory surfaces of movable joints.
The great strength, elasticity, and reduced friction make cartilage an
efficient part of the skeleton.

Briefly stated, the functions of the human skeleton are (1) to form a
framework to support other organs and give posture to the body, (2)
to give protection to vital organs (such as brain, spinal cord, heart and
lungs), (3) to form solid attachments for muscles so that they may act
as a system of levers in motion and locomotion, (4) to store fat in the
"fat" marrow, (5) to store certain mineral reserves, (6) to form blood
corpuscles by the bone marrow, and (7) to transmit sound waves as
accomplished by the hammer, anvil, and stirrup bones of the ears (Fig.
250).

466 Animal Biology

Human Skeleton (see Fig. 229)

Axial (80)

Skull

Cranium ( 8 )

(Brain Case)

Face (14)

Ear bones (6)

Vertebral column (26)

'Occipital (base of skull)

Parietal (top of head)

Frontal (forehead)

Temporal (above ears)

i Ethmoid (back of nose)

[Sphenoid (back of eye)

Mandible (lower jaw)
Maxilla (upper jaw)
Palate

Malar or zygomatic (cheek)
Lacrimal (inner orbit)
Inferior turbinated (nose)
Vomer (nasal septum)
, Nasal (bridge of nose)

rMalleus (hammer) (2)
<. Incus (anvil) (2)
I Stapes (stirrup) (2)

Cervical (neck) (7)
Thoracic (chest) (12) with ribs
•{ Lumbar (lower trunk) (5)
Sacral (sacrum) (1)*
Coccygeal (caudal or tail) (l)t

Hyoid (base of tongue) (1)
Sternum (breastbone) (1)

Ribs (24)

Pectoral (shoulder) girdle j ^^^p„'/^' ("houlde^r'^blidi

(1)
(2)

(1)
(1)

(1)

(2)
(2)
(2)
(2)
(2)

(1)
(2)

Appendicular (126)

2)
) (2)

Arms

Humerus (2)

Radius (2)

Ulna (2)

Carpals (wrist) (16)

Metacarpals (hand) (10)

Phalanges (fingers) (28)

Pelvic (hip) girdle (2)|

fFemur (thigh) (2)
Tibia (shin) (2)
Fibula (2)

Tarsals (ankle and heel) (14)
Metatarsals (foot) (10)
Phalanges (toes) (28)

Knee cap (patella) (2)

Legs

This does not include the variable number of sesamoid hones (ses' a moid) (L. sesamnn, ses-
ame seed; eidos, like) embedded in the tendons of tiie hand, knees, and foot, or the wormion
bones (wur' mi an) (after Worm, a Danish anatomist) which are isolated bones in the sutures or
joints, especially of the skull.

The figures in parentheses give the number of bones of each type.

*Five bones fused.

fFour bones fused.

JThree bones (ilium, ischium, pubis) fused.

Biology of Man 467

III. MOTION AND LOCOMOTION IN MAN

The living bones of the human skeleton are the passive structures to
which the active muscles are attached and by means of which various
parts of the body are moved or the body as a whole is moved from one
place to another (Figs. 229, 232, 233, and 249). There are over 400

S-ternodetdomastoid'

', V^„ PpftArali^ major
• • -"k (rIavicLildr portion)

Deltoid.

^Pectoralis rnajor
*f(stGrnal portion)

Spermatic Cord

Fig. 232. — Human muscles (front view). (From Francis: Fundamentals of

Anatomy, The C. V. Mosby Co.)

named muscles attached to the skeleton for the movement of parts of
the body or for locomotion. These are the skeletal muscles and each is
composed of cells with several nuclei (multinucleated). Skeletal mus-
cles are under the control of the will (voluntary), are distinctly striated.

468 Animal Biology

have a rather rapid rate of action, and fatigue, rather quickly. Many
unnamed, unstriated (smooth), mononucleated, muscle cells compose
the muscles of the internal organs (viscera), such as the esophagus,
stomach, intestines. These visceral muscles are not under the control of

TrapezlixS

Deltoid

■ i-^Tferea minor

Teres mdjor
Fascia over ^
infraspinatus

Rhomboideus
major

LatiasLmus dorsl

■Triceps

> 'ii/

Irt — External obVuJue muscle Of abdonnen

— * Lun

imbodorsal fascia

,S"

'Gluteus medius

-Gluteus maLxlmus

^V^M

/^.l^llll»:.^

Fig. 233. — Human muscles (back view). (From Francis: Fundamentals of Anat-
omy, The C. V. Mosby Co.)

the will (involuntary), have a rather slow, rhythmic rate of action, and
do not fatigue easily. Numerous, indistinctly striated, mononucleated,
cardiac muscle cells compose the walls of the heart and arteries. Cardiac

Biology of Man 469

muscles have a variable rate of action and under normal conditions do
not fatigue quickly. They are involuntary because our will cannot make
them contract just so many times per minute. These various types of
muscle tissues have been described earlier and the reader might w^ell
review them.

FROMTAL AIR SIN

SUPERIOR
TURBtMAT

MIDDLE
TURBINATE

IMFERIOR
TURBIMATE

ETHMOID AIR CELL

SELLA TURCICA

HARD PALATE

SPHEHOID AIR

smus

EUSTACHIAn TUBE

h /a^i=;'TORUS TUBARIUS
' 'SOFT PALATE

T0M6UE

MAnOIBL

GEMIOHYOIO
MUSCLE —

ll^ "^ ESOPHAGUS

MYLOHYOID
MUSCLE

THYROID CARTILAGE

VOCAL CORD

TRACHEA

Fig. 234. — Face and neck in section showing parts of the respiratory and diges-
tive systems. The common cavity where the two systems cross is known as the
pharynx. The leaf-shaped epiglottis prevents food from entering the larynx from
the pharynx. (From Zoethout and Tuttle: Textbook of Physiology, The C. V.
Mosijy Co.)

Skeletal muscles have one end rather solidly attached and known as
the origin, while the other end is more movable and is known as the
insertion. Study some muscles (Figs. 232 and 233), observing the origin
and insertion of each. It will be noted that muscles of the body do not
cross the median line; hence they are in pairs. Muscles which move a

470 Animal Biology

part away from the median line are called abductor muscles, while those
which move a part toward the median line are called adductor muscles.
Skeletal muscles are named in various ways: (1) after the name of the
structure, or bone, with which they are associated {triceps hrachii.

.Carotid Artary^
.Trachea

Subclavian V.

Precaval V.

Oorsiil Aorta

Pulmonary A.

Left Aur'ick

Lef tVcntr/cte

Lana

Diaphracjin

Liver

Duodenum

Stomach

Gal/Blflddep

Jranis/erseColon

.Usscendlnc] Colon
..Ajcendin^ Colon

Ileum

Fig. 235. — Human internal organs of the thoracic and abdominal cavities
which are separated by the muscular diaphragm (see Fig. 236). (Drawn by
Edward O'Malley, from Potter: Textbook of Zoology, The C. V. Mosby Co.)

muscle on the back of the upper arm, or brachium), (2) after the num-
ber of "heads" with which they originate {triceps hrachii, meaning three
heads; biceps hrachii, two heads and located on the front of the upper
arm), (3) after the shape of the muscle {deltoid, delta-shaped muscle of

Biology of Man 471

the top of the shoulder; trapezius, trapezoid-shaped muscle of the back),
(4) after the direction in which they run (external oblique, strong muscle
of the abdominal wall which lies obliquely), (5) after the length and size
of the muscle (peroneus longus, large muscle attached to the fibula;
peroneus hrevis, smaller muscle attached to the fibula bone), (6) after

SUBMAXILLARY CLAND

$U&UHCUAL SALIVARY
CLAHD

PAROTID
SALIVARY CLAMO

LIVER

CALL
BLADDER

DUODEMUM

HEPATIC
FLEXURE

ASCEtlDIMC
COLON

CECUM

APPEND

ILEUM
SICMOID FLE

STOMACH
PANCREAS

LEFT COLIC
"FLEXURE

TRANSVERSE
COLON

DESCENDING
COLON

JEJUNUM
CMOID

CTUM

Fig. 236. — The human digestive system with accessory organs. (From Zoethout
and Tuttle: Textbook of Physiology, The C. V. Mosby Co.)

the origin and insertion [sternocleidomastoid, which arises from the
sternum and clavicle, and is inserted into the mastoid portion of the tem-
poral bone of the skull), (7) after their location [external intercostals,
superficial muscles between the ribs; internal intercostals, deeper muscles
between the ribs), and (8) after their function [adductor longus, adduct
the thigh toward the median line) .

472 Animal Biology

Muscles play an Important role in the movements of many organs as
will be observed by a study of such systems as the digestive (Fig. 236),
respiratory (Figs. 234 and 244), circulatory (Figs. 237 to 241), excre-
tory (Fig. 245), reproductive (Figs. 254 and 255), and special sense
organs (Fig. 249). Certain movements are caused by cilia which line
various areas, such as those of the nose and reproductive tubes.

IV. FOODS AND NUTRITION

A food may be defined as any substance which when ingested in the
proper amount is absorbed from the digestive tract and contributes to
the normal maintenance of the body. Foods are composed of such or-
ganic compounds as carbohydrates, fats, proteins, and vitamins and
such inorganic substances as water and various inorganic salts. These
food constituents are considered in detail elsewhere and the reader is
referred to them. Of all the thousands of organic and inorganic sub-
stances, only a few serve as satisfactory human foods, probably because
of man's limited number of enzymes by means of which he can digest
them. Any animal in utilizing a substance for food purposes must get
that substance into a condition which can be absorbed through the small
openings in the semipermeable membranes which enclose the absorptive
cells of the digestive tract. These openings may be of the size to permit
the absorption of water molecules (two atoms of hydrogen and one
atom of oxygen) but too small to permit the absorption of other foods
the molecules of which are larger. Consequently, certain foods whose
molecules are large (because of a great number of atoms which form
these molecules) must be changed (digested) before they can be ab-
sorbed. For example, the molecule of sucrose (cane sugar) (C10H22O11)
must be digested to form two simpler monosaccharide molecules before
it can be absorbed, while the simple molecule of glucose (CeHijOe) is
absorbed unchanged. Digestion is primarily a chemical process whereby
the molecules of foods which are too large to be absorbed are changed so
that they may be. This phenomenon is accomplished by hydrolysis
which means "a change by the action of water." Hydrolysis is based on
enzyme action in which water is added to the complex molecular ar-
rangements of foods, thus disassociating the complex molecules into
simpler, absorbable ones. The summary of the digestion of foods in
man is given so that the stages can be easily memorized. For example,
when one molecule of water (H2O) is added to a molecule of sucrose
(cane sugar) (G12H22O11), the hydrolytic action results in two separate,
absorbable molecules, each with the formula of (C6H12O6). It must be

Biology of Man 473

remembered that the mere addition of water to a food will not result in
digestion, but the specific action of digestive enzymes is necessary (con-
sult table on Summary of Digestion, showing the enzymes and their
roles).

After foods are digested and absorbed they can be made into a part
of the living protoplasm. This phenomenon is called assimilation. In
all probability assimilation, as well as other phenomena, is affected by
certain specific vitamins, some of the better known being listed in a
summary to expedite their mastery (Figs. 369 to 372). Vitamins may
be considered as essential accessory substances present in variable
amounts in different foods. Each vitamin has its unique function in the
maintenance of normal body processes (consult summary of vitamins).
Unlike other food components, such as carbohydrates, fats, proteins,
and minerals, they do not provide energy or build tissues directly. Their
function is to enable the body to use other foods properly in addition to
performing other very essential functions. Vitamins vary in their chemi-
cal composition, their solubility in fat or water, their resistance to heat,
and their inactivation by oxygen. The term vitamin, which was coined
when vitamins were erroneously thought to be amines (containing an
amine, NH2) essential to life (vita), is still used today but may even-
tually be supplanted when more is learned about them and their chemi-
cal compositions are completely ascertained. Minerals are nutritional
substances (inorganic) which, in combination with other food constitu-
ents, promote the formation and maintenance of various parts of the
body structure. Each mineral not only aids in metabolic processes but
actually forms a part of certain body fluids and tissues. Calcium aids
in blood clotting and bone formation, while iron enters into the con-
struction of the hemoglobin of the red blood corpuscle.

The human digestive system (Figs. 234 and 236) consists of: (1)
The mouth with its numerous taste organs, a muscular tongue, thirty-
two teeth (two incisors, one canine, two bicuspids, and three molars in
each half of each jaw), and three pairs of salivary glands (the parotid,
submaxillary, and sublingual glands) for the secretion of saliva (Fig.
236). (2) A tubelike esophagus with two layers of circular and longi-
tudinal muscles for the peristaltic movement of foods. (3) The stomach
with its three layers of muscles (the circular, oblique, and longitudinal),
the anterior cardiac part (nearest the heart) in which foods are stored,
and the posterior pyloric part principally for digestion. The stomach
secretes gastric juice and mucin. (4) The small intestine for digestion
and absorption which is composed of the duodenum (one foot long), the

474 Animal Biology

Summary of Important Vitamins

VITAMIN

1 IMPORTANT SOURCES

FUNCTIONS

1 EFFECTS OF DEFICIENCY

Fish li\'er oils, animal

General health

Retarded growth, dry skin.

C20H30O

livers, egg yolk.

and vigor.

inflammation of alimen-

Fat-soluble

butter, carrot, yel-

resistance to

tary tract, kidneys and

Antiophthalmic

low squash, sweet

skin infec-

respiratory system, "dry

potato, green vege-

tions, normal

eyes" xerophthalmia)

tables

vision

(Fig. 370), night bhnd-

Precursor is carotene

ness (partial loss of

(C40H56) in green

sight in dim light)

vegetables

Yeast, whole grains

Promotes nor-

Beriberi (human nervous

Thiamin

(cereals), vege-

mal appetite.

disease) or polyneuritis

Ci2Ha7N4SO

tables (raw), fruits.

digestion,

(birds) (Fig. 371), loss

Water-soluble

egg yolk, liver.

and carbo-

of appetite and vigor,

Antineuritic

meats, milk, corn

hydrate

stunted growth, stiff,

meal, peanuts

metabolism

painful muscles, irrita-

Manufactured

bility and fatigue

synthetically

Yeast, egg white.

Normal nutri-

Scaly skin defects around

Riboflavin

liver, kidney, green

tion and

ears and angles of

(Vitamin G)

vegetables, fruits.

growth

mouth, itching, red eyes.

CUH.0N4O6

milk, corn meal

disturbed metabolism.

Water-soluble

retarded growth

Yeast, wheat and

Assumed to be

Little is known for man.

Pyridoxin

corn germ, rice

essential for

dermatitis in chicks and

CsHnNOa

polishings, milk.

man but

rats, paralysis in

livers of mammals

little is

chickens

Manufactured

known ; may

synthetically

assist in oxi-
dation of
food

Niacin

Liver, yeast, wheat

Normal skin

Pellagra (lesions of the

Nicotinic acid

germ, meat, egg

and diges-

mucous membranes of

P-P Vitamin

yolk, green vege-

tion; affects

mouth, gastrointestinal

C«H5N02

tables, adrenal

cellular

disturbances, mental

Water-soluble

gland

functions

disorders) in man (Fig.

Antipellagric

Manufactured

372) and monkeys.

synthetically

pellagra in hogs, black-
tongue in dogs

Pantothenic

Liver, kidney, rice

Functions un-

Not known for man, causes

acid

bran, milk, yeast.

known but

pellagra-like symptoms

C.HitNOs

molasses

seems essen-

in chickens, graying of

Manufactured

tial for

black hair (rats)

synthetically

growth

B12

Liver, liver extract

Treatment of

Anemia which in certain

Rubramin

pernicious

cases may involve de-

Water-soluble

anemia (by

generation of spinal

Antianemic

increasing

cord and inflammation

red blood

of tongue, loss of

corpuscles.

strength, possible loss of

hemoglobin.

appetite

and plate-

lets), prob-

ably assists in

maturing

erythrocytes

Biology of Man 475

Summary of Important Vitamins — Cont'd

VITAMIN

IMPORTANT SOURCES

FUNCTIONS

EFFECTS OF DEFICIENCY

Citrus fruits (lemon.

Protection

Scurvy (affects bones.

Ascorbic acid

orange), fresh

against infec-

joints, mucous mem-

C«H.06

fruits, certain fresh

tions, assist

branes; bleeding mucous

Water-soluble

vegetables (cab-

in wound

membranes and beneath

Antiscorbutic

bage, lettuce,

healing, nor-

skin), fatigue, loss of

potato, spinach,

mal teeth

weight, retarded growth,

tomato, peppers)

tooth decay

Manufactured

synthetically

Animal fats, fish liver

Normal bone

Rickets (bone disease) in

Calciferol

oils, milk, butter,

growth, regu-

children, retarded

C2hH440

egg yolk, oysters.

lates calcium

growth, weak muscles,

Fat-soluble

Occurs in animals

and phos-

soft bones and defective

Antirachitic

which manufacture

phorus

teeth

it from ergosterol

metabolism

of plants when

exposed to ultra-

violet or sunlight
Wheat germ, egg yolk.

Not known for

Sterility in rats and fowls.

Tocopherol

meats, lettuce, corn

man, normal

death of rats in uterus

C29ri5oC)2

oil, cotton seed oil,

production of

Fat-soluble

alfalfa

male and

Antisterility

female sex
cells in rats

Vegetables, grains

Growth of man

Dry mucous membranes

Biotin

(cereals), nuts.

and other

and skin

C10H16N2SO3

eggs, liver, kidney

animals, oc-

Manufactured

curs in

synthetically

higher ani-
mals and
plants

Liver, leafy vege-

Normal blood

Excessive bleeding because

C3iri4602

tables (spinach, cab-

clotting by

of delayed clotting

Fat-soluble

bage, etc. ) , soy-

producing

Antihemor-

bean oil, alfalfa.

prothrombin

rhagic

grass

by the liver

jejunum (eight feet long), and the ileum (twelve feet long). There are
two layers of circular and longitudinal muscles for the peristaltic move-
ment of foods. The inner walls of the small intestine are covered with
large numbers of small, finger-shaped villi located on numerous circular
folds. The villi and folds retain the foods for absorption and increase
the absorbing area. (5) The large intestine or colon (five feet long)
has two layers of circular and longitudinal muscles for the movement of
foods and waste materials toward the anal opening. Faulty elimination
of waste materials at the proper times from the large intestine results in
their being reabsorbed. The large intestine has an enlarged pouchlike
cecum, at the junction of the small and large intestines, from which the
pencil-shaped vermiform appendix arises. Inflammation of the latter is

476 Animal Biology

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Biology of Man 477

known as appendicitis. Extending upward on the right side from the
cecum is the ascending colon. The transverse colon connects the latter
with the descending colon which descends down the left side of the lower
abdominal cavity. The sigmoid connects the lower end of the descending
colon with the rectum. The latter empties externally through the anus.

(6) The liver is the largest gland in the body and is divided into the right
and left lobes. It is located just below the diaphragm and in the adult
weighs about 2.8 per cent of the total body weight. The liver arises
embryologically as an outgrowth of the duodenum and migrates to its
normal position below the diaphragm. The liver manufactures bile from
the red blood corpuscles and pours it into the gall bladder through the
cystic duct. The bile duct leads from the gall bladder to the duodenum.

(7) The pancreas is an elongated organ, about two by six inches, which
lies between the stomach and the duodenum. In adult human beings it
weighs about 2/2 ounces. Certain cells of the pancreas secrete the pan-
creatic juice which is carried by the duct of Wirsung to the common bile
duct. In some cases the duct of Wirsung and the common bile duct
open separately into the duodenum.

V. CIRCULATION IN MAN

The circulatory system is a so-called "closed system" composed of a
heart, contractile arteries, capillaries, and veins. The muscular, cone-
shaped heart is about the size of a fist and is divided by a partition into
right and left sides. Each side is divided into an upper chamber called
the atrium (auricle)* and a lower, more muscular, ventricle. The very
muscular left ventricle pumps oxygenated blood (Figs. 237 to 241)
through the aorta (artery) to all parts of the body (except lungs). From
all parts of the body (except lungs) blood is carried back to the right
atrium through a series of veins. From the right atrium the blood passes
through the right atrioventricular valve (tricuspid valve) into the right
ventricle from which it is pumped through the pulmonary arteries to the
lungs where it is oxygenated. The blood is returned from the lungs by
pulmonary veins (two right and two left) to the left atrium, from which
it passes through the left atrioventricular valve (bicuspid valve) into the
left ventricle. The portion of the system which supplies the body is
called the systemic circulation and the part which carries blood to the
lungs to be oxygenated is the pulmonary circulation. These, however,
are all one complete circulation unit.

*The terms atrium and auricle are sometimes used synonymously, as are auriculoventricular
and atrioventricular, although there are minor differences. Atria is the plural of atrium.

478 Animal Biology

The heart Is enclosed by a double-walled membranous sac known as
the pericardium whose surfaces are kept moist by a secretion of serum.
for lubricating" purposes (Figs. 237 to 239). The walls of the atria and
ventricles consist of ( 1 ) an inner epithelial lining known as the endo-
cardium, (Gr. endo, within; cardium, heart), (2) a middle muscular
layer called the myocardium (Gr. myo, muscle), and (3) an outer, single
layer of mesothelial cells called the pericardium (Gr. peri, around). In
a heartbeat the contraction phase is called the systole, while the relaxa-
tion phase is called the diastole, and the two constitute a ''cardiac cycle/'

Aor+a

Superior
vena. caveL

Auricle op
Rl^ht eitrlum

Ri(4ht
QLtriunn

Ri(4ht
ventricle

Coronarq
arterij

Inferior
vena cava

PulmonarLj ar+erij

\-^»^ Auricle of lefi ««Ltrlum

'V ^ In-terven-trlcular

fi *^~ branch of left
I V coronary artertj

Lept ventricle

'■<'^;^

ii>>7^

^^'^^'^^ — Apex Of heart

Fig. 237. — Human heart, front view, showing some of the blood vessels. The
aorta (artery) carries blood from the left ventricle to all parts of the body (ex-
cept lungs). The pulmonary arteries carry blood from the right ventricle to the
lungs. The coronary arteries arise from the aorta to supply blood to the walls
of the heart. Both the superior vena cava (also known as the precaval vein) and
the inferior vena cava (known as the postcaval vein) return blood from the body
(except lungs) to the right atrium. The atrium has an outpouching called the
auricle because of its earlike shape. The pulmonary veins (two right and two
left) return oxygenated blood from the lungs to the left atrium. The blood from
the heart walls is returned by way of the coronary sinus (not shown) to the
right atrium. The opening between the right atrium and right v'cntricle is closed
by the right atrioventricular valve (tricuspid valve, because it has three cusps).
The left atrium and left ventricle are separated by the left atrioventricular valve
(mitral valve, has only two cusps). (From Francis, Knowlton, and Tuttle: Text-
book of Anatomy and Physiology, The C. V. Mosby Co.)

Biology of Man 479

When a heart beats 70 times per minute, a cardiac cycle requires less
than one second. During contraction the heart undergoes electrical
changes, the active cardiac muscle is electrically negative to an inactive
cardiac muscle. These action currents can be recorded by a special
instrument called the electrocardiograph. The record known as an
electrocardiogram shows a series of waves which are correlated with
heart actions.

Arteries (Figs. 237 to 241 ) are a series of vessels whose walls are rather
thick, contractile, and elastic. They consist of ( 1 ) an inner layer of
endothelial cells and elastic tissue, (2) a middle or intermediate layer
of muscle and elastic tissue, and (3) an external layer of elastic tissues.
Arteries carry blood away from the heart while veins carry blood back
toward the heart.

Aorta

Pulmonary arterij
AuLPicle Of

left atrium

Left

Pulmonarq veins

Breinch of lept
coronary art.

Left ^
ventricle

per'ior vena cava

RKjht pulmoneLrq
veins

Left atrium
Coronary sinus

Inferior vena cava
Ri^ht ventricle

Fig. 238. — Human heart, posterior (back) view. (Compare with Figs. 237 and
239.) (From Francis: Introduction to Human Anatomy, The C. V. Mosby
Co.)

Veins (Figs. 237 to 239) are a series of vessels whose structure re-
sembles that of arteries, being composed of three layers, but whose walls
are thinner and less elastic because of a poorly developed middle layer
and the presence of very little muscle and elastic tissue. Certain veins,
especially those of the lower extremities, have a series of semilunar valves
to prevent the backflow of blood. In general, the systemic veins accom-

480 Animal Biology

pany the systemic arteries, frequently having the same names as the
arteries. However, many systemic veins are distributed in two sets: (1)
deep and superficial veins and (2) special veins, called the portal system,
which carry the blood from the digestive tract back to the heart.

Three systemic veins return blood to the right atrium: (1) the coro-
nary sinus (vein) returns blood from the heart walls, (2) superior vena
cava (also called precaval vein) returns blood from the head, neck,

ARCH OF AORTA

SUPERIOR VFNA CAVA
INFERIOR VENA CAVA

PULMONARY
VALVE

RIGHT
AURICLE

TRICUSPID
VALVE

RIGHT
VENTRICLE

AORTA

PULMONARY
ARTERY

PULMONARY
VEIN

LEFT AURICLE

AORTIC VALVE

MITRAL VALVE

>LEFT VENTRICLE

CHORDA TENDINEAE

Fig. 239. — Human heart shown in longitudinal section. (From Haggard;
and His Body; Copyright, 1927, 1938, by Harper & Brothers.)

Man

thorax, and upper extremities, and (3) inferior vena cava (postcaval
vein) returns it from the abdomen, pelvis, and lower extremities. The
superior vena cava is formed by the union of the two innominate veins,
and it receives the azygos vein which drains the abdominal region. Each
innom,inate vein is formed by the subclavian vein and the internal jugular
vein (blood from brain, etc.). The external jugular veins (right and

Biology of Man 481

left) receive blood from the face and scalp (regions supplied by the ex-
ternal carotid artery) and empty into the subclavians just before sub-
clavian and internal jugular unite to form the innominate. The veins
of the upper extremity enter the subclavian vein. The deep veins of the
upper extremity accompany the corresponding arteries and have the
same names: axillary, brachial, radial, and ulnar veins. The superficial
veins of the upper extremity are (1) cephalic, (2) basilic, and (3)
median. All arise from the dorsal part of the hand: the cephalic runs

"Veins from uppcp.
part of Body

lA/mpf»atic5 -

Thoracic duct

^upcriop vena cava-t- /- /'^v^'^^

'Pulmonary artery -j —

"Ri^fit aupiclc
Infepiop vena cava-

1Si<^ht vcntpiclc
I^actcab —

Mcpalic vein,

Vcias from lower
part of Body

ApIcpIcs to uppe^
papt of Body

Pulmonapy vein

L^mpBaticj

- Left ycntpicle

ArtcpiGS to lov/Gf»
pari of Body

Fig. 240. — Diagram of circulation in a mammal. Only the general courses of
circulation are shown diagrammatically. Arrows show the direction of blood
flow. Oxygenated blood is shown in black; venous blood in white. The lym-
phatics are the black irregular lines. (See Figs. 237-239 and 241.) (From Mc-
Clendon and Pettibone: Physiological Chemistry, The C. V. Mosby Go.)

482 Animal Biology

DIVISIONS AND BRANCHES OF THE HTTWAN AORTA

R.& L. CORONARY ARTERIES (to heart wall muscles)

R. SUBCLAVIAN ^ R. AXILLARY ^ R. BRACHIAL ,^R. RADIAL

(under clavicle) (armpit) (upper arm)""^:^R.rLNAR

\r.coh

^(in

irMOMINATE ^yR. EXTERNAL CAROTID ( face, scalp, etc. )

*" ~,comoN CAR0TID<;;;_

neck) ^-^R. INTERNAL CAROTID (brain, eye, etc . )

syL. INTERNAL CAROTID ( brain, eye , etc . )
L. COMMON CPlBOTIIX:^

^^L. EXTERNAL CAROTID ( face , scalp, etc . )

^>rL. RADIAL (thumb side,f©rearm)

L. SUBCLAVIAN >L. AXILLARY > L. BRACHIAL CIlTl^L.nLNAR

INTERCOSTALS (9 pr, to intercostal muscles , etc . )

BRONCHIALS (lung tissue, etc.)

ESOPHAGEALS( 4-5 pr . to esophagus)

SUPERIOR PHRENIC (diaphragm)

INFERIOR PHRENIC (diaphragm and abdominal v;ells)

^^.^^CASTRIC (stomach)
HEPATIC:— —>GASTP0rU0DENAL ( stomach, duodenum, pancreas)
( 11 ver)^"-^ CYSTIC (gall bladder)

CELIAC •_

'splenic ( spleen, stomach, pane re as )

L. GASTRIC ( stomach, esophagus, liver)

SUPERIOR MESENTERIC (small intestine , cecum, ascending & descending colon)

LUMBARS (4 pr . to abdominal walls)

RENALS (1 pr.tc kidneys)

SPEPKATIC or OVARIAN (1 pr. to gonads)

INFERIOR MESENTERIC (to descending colon, rectum, etc . )

.^.HYPOGASTRIC (pelvic viscera, bladder, buttocks , etc. )

p . comoN

ILIAC "~^R. EXTERNAL ^^R. ANTERIOR TIBIAL

ILIAC ^R. FEMORAL ^R . POPLITEAL-v^^

(thigh) (under knee )^^R. POSTERIOR TIBIAL

=,L« HYPOGASTRIC
L.COMWON

ILIAC '-^L. EXTERNAL JfL. ANTERIOR TIBIAL

ILIAC ^ L. FEMORAL >L. POPLITEAL

^L. POSTERIOR TIBIAL

Fig. 241. — Divisions and branches of the human aorta (artery) which arises
from the left ventricle of the heart. Most of the more important branches are
given somewhat in the order of their origin. The coronary arteries arise from the
ascending part of the aorta; the innominate, left common carotid and left sub-
clavian from the aortic arch; the next four from the thoracic aorta; the last
group from the abdominal aorta. R, right; L, left. Also listed are the regions
in which the arteries travel or the tissues and organs to which they supply blood.

Biology of Man 483

along the lateral surface of the arm and empties into the axillary; the
basilic runs along the inner surface and empties into the axillary; the
median runs between the other two and connects them.

The inferior vena cava is formed by the union of the right and left
common iliac veins (at about the level of the fifth lumbar vertebra) and
accompanies the aorta along the posterior abdominal and thoracic wall,
receiving such veins as the renal (kidneys), ovarian or spermatic (go-
nads), hepatic (from liver), lumbar (back), phrenic, intercostals (be-
tween ribs, etc. ) . The deep veins of the lower extremity follow the
arteries. The two superficial veins of the lower extremity are ( 1 ) the
great saphenous vein which arises in the medial side of the foot, passes
along the medial side of the leg, and empties into the femoral vein and
(2) the small saphenous which arises in the lateral side of foot and
empties into the popliteal vein. The veins which return the blood from
the digestive organs constitute the portal system which detours the blood
through the liver and then into the inferior vena cava. This blood is
changed in several ways by the liver to prepare it for entrance into the
general systemic circulation.

Capillaries are thin-walled vessels which form a network connecting
the arteries and veins. The walls are a single layer of flat endothelial
cells. The capillaries are so numerous that one can hardly touch any
part of the body without touching capillaries. Through them the ex-
change of materials takes place because of their thin walls and the slow
movement of the blood within. An average capillary is about 8 microns
in diameter. Compare this with the diameter of a red blood corpuscle.

Functions of the Blood System

(1) Respiratory — transporting oxygen to the tissues and carbon di-
oxide from them; (2) excretory — carrying waste materials from the tis-
sues to the organs of excretion; (3) nut/itive — transporting sugars, amino
acids, fats, minerals, and vitamins from the digestive system to the body
tissues; (4) regulatory — transporting water to and from various organs
so that the water content may be fairly constant, equalizing body tem-
perature by carrying water throughout the body and giving it off from
the vessels near the surface, distributing foods to the endocrine organs
(ductless glands) and transporting secretions (hormones) produced by
them; (5) protective — defending the body by means of the phagocytic
action of certain white blood corpuscles, and the circulation of specific
antibodies (antitoxins, etc.) ; (6) the maintenance of the proper acid-
alkaline reaction of the various parts of the body.

484 Animal Biology

Blood

Blood is a liquid tissue, sometimes classified with the connective tis-
sues, sometimes separately. It consists of clear, straw-colored plasma in
which are suspended the red blood corpuscles (erythrocytes), the various
types of white blood corpuscles (leucocytes), and the blood platelets,
the latter assisting in blood clot formation. Blood forms about one-
thirteenth of the total body weight and in an average man totals about
6 liters (over 6 quarts) . Arterial blood is bright red, while venous blood
is dark red, depending upon the amount of oxygen present. Blood is
somewhat viscous and slightly heavier than water. Blood is slightly alka-
line (pH of 7.35).

Erythrocytes (e -rith' ro site) (Gr. erythros, red; kytos, cell) constitute
about 50 per cent of the volume of blood. When mature they are with-
out a nucleus and consist of a supporting framework known as the
stroma (Gr. stroma, bedding) and hemoglobin (he mo -glo' bin) (Gr.
haima, blood; globos, sphere). Hemoglobin consists of a protein and
an iron-containing compound, the latter being responsible for the chemi-
cal affinity for oxygen. When hemoglobin carries oxygen, it is known as
oxyhemoglobin and liberates its contained oxygen where needed. Anemia
(an e' me ah) (Gr. an, deficient; aima, blood) is a condition in which
there is a decrease in the number of erythrocytes or in the amount of
hemoglobin or in both. These conditions may occur from impaired
blood formation or increased destruction of erythrocytes or both. When
blood escapes from an injured blood vessel, it is known as a hemorrhage
(hem'oraj) (L. haemorrhagia, blood, to break). The following corre-
lated measures are taken when a hemorrhage occurs : ( 1 ) clotting of
blood at the site of the injury, (2) decrease in the general blood pres-
sure, (3) contraction of the small vessels of the skin, muscles, and intes-
tines in order to supply the vital parts of the body, (4) increase the
blood volume by the contraction of the spleen which normally contains
a large quantity of blood, and (5) passage of water and salts from the
tissues into the capillaries because of increased osmotic pressure.

Leucocytes (lu'kosite) (Gr. leukos, white; kytos, cell) because of
their amoeboid movements are able to escape from the blood vessels and
penetrate into the body tissues. Leucocytes may be classified as ( 1 )
granulocytes (granular leucocytes) with distinguishing granules in the
cytoplasm and (2) agranulocytes (nongranular leucocytes) without
granules in the cytoplasm. Because of the variations in the lobes of the
nuclei of the granulocytes, the latter are sometimes referred to as poly-

Biology of Man 485

morphonuclear leucocytes (poll mor fo -nu' klear) (Gr. poly, many;
morphe, form; L. nucleus, kernel or nucleus). They act as phagocytes
(fag' o site) (Gr. phagein, to eat; kytos, cell) by engulfing bacteria, cells
fragments, and foreign materials. The granulocytes are classified in
three groups according to the type of granules in their cytoplasm : ( 1 )
eosinophils (e o -sin' o fil) (Gr. eos, dawn; philein, to love), which stain
readily by eosin (acid) stains; (2) neutrophils (nu'trofil) (L. neuter,
neither; Gr. philein, to love), which stain by neutral dyes; (3) basophils
(ba' so fil) (Gr. basis, base; philein, to love), which stain well with basic
stains.

The agranulocytes lack cytoplasmic granules and are classified in two
groups: (1) lymphocytes (lim'fosite) (L. lympha, lymph or water; Gr.
kytos, cell) and (2) monocytes (mon'osite) (Gr. monos, alone; kytos,
cell), both being formed in the lymphoid tissue. It is thought that

Human Blood

RED BLOOD CORPUSCLES
( ERYTHROCYTES )

white blood
corpuscles

(leucocytes)

BLOOD platelets

Nucleus

No nucleus when ma-
ture; nucleus when
immature

Always nucleated
(various kinds)

None

Shape

Flat, biconcave disks

Variable

Oval, biconvex disks

Motile

Amoeboid movement

Diameter

7.7 microns

8 to 15 microns

(depending on tvoe)

3 microns (average)

Hemo-
globin

Present (in mature
stage only)

None

Number

4,500,000 (women)
and 5,000,000 (men)
per cubic millimeter

5,000 to 9,000 per
cubic millimeter

250,000 per cubic
millimeter

Where
formed

In adult — red bone
marrow (of sternum,
ribs, vertebrae, cer-
tain parts of femur,
humerus and cranial
bones)

In embryo — bone mar-
row and liver

In red bone marrow
and lymphoid tissue
(depending on type)

Bone marrow

Where
lost

Liver and spleen

Liver and lumen of
intestine

Disintegrate rapidly
which may explain
variations in num-
ber

Length
of life

Short (10 to 100 days)

Unknown

Functions

Carry oxygen and aid
in transportation of
carbon dioxide

Protect against bac-
teria, cell fragments
and foreign particles,
repair tissues

Clotting of blood

486 Animal Biology

lymphocytes contribute to the repair of wounds by connective tissue for-
mation and give origin to the monocytes. A summary of the various
types of blood corpuscles and blood platelets is given in tables so they
may be compared and contrasted more easily. A decrease in the number
of leucocytes is called leucopenia (lu ko -pe' ne ah) (Gr. leukos, white;
penes, poor) and an increase is leucocytosis (lu ko si -to' sis) (Gr. kytos,
cell).

Summary of Leucocytes

TYPE

GRANULOCYTES

1. Neutrophils

2. Eosinophils
(Acidophils)

3. Basophils

AGRANULOCYTES

1. Lymphocytes

2. Monocytes

PER CENT
OF TOTAL

LEUCO-
CYTE

COUNT

65-75

2-5

0.5

20-25

3-8

DIAM-
ETER
IN
MI-
CRONS

10-12

CHARACTERISTICS

Fine light blue cytoplasmic granules, 3 to
5 lobed nucleus

Bright red cytoplasmic granules (Wright's
blood stain), nucleus with 2 lobes

Large, dark purplish-blue cytoplasmic
granules (Wright's stain), irregular
nucleus, often S-shaped

Thin layer of nongranular, robin's-egg
blue cytoplasm (Wright's stain), large
bright purple nucleus

hick layer of nongranular cytoplasm,
large horseshoe- or kidney-shaped, pur-
ole nucleus (Wrierht's stain)

Clotting (Coagulation) of Human Blood

The chemical process which blood undergoes when it clots is quite
complicated. Several theories have been proposed to explain the proc-
ess. A brief summary will illustrate the more important stages.

Blood

Body I

Tissues Platelets

(by disintegration)

(Injured)

Plasma

Vitamin K

(in iver)

Calcium

Fibrinogen

Thromboplastin + Prothrombin + Calcium — ^ Thrombin

(Cephalin) Thrombin + Fibrinogen — > Fibrin

Biology of Man 487

Thrombin (throm'bin) (Gr. thromhos, clot) as such does not exist in
significant amount in unshed blood or it might start the formation of a
clot in normal, circulating blood, but the thrombin is thought to exist
as inactive prothrombin (Gr. pro, before). In normally circulating
blood it is thought that heparin (hep'arin) (Gr. hepar, liver) formed
in the liver is combined with cephalin (thromboplastin) (sef alin) (Gr.
kephalos, head). Consequently, the lack of cephalin prevents the form-
ing of thrombin from prothrombin; hence there is no clotting in normal
circulating blood. When hemorrhage occurs (tissue injury and destruc-
tion of blood platelets), more cephalin is formed than can combine with
the heparin. The excess cephalin combines with the prothrombin and
calcium salts to form thrombin. The latter combines with a soluble
protein of the blood plasma known as fibrinogen (fi -brin' o jen) (L.
fibra, band; Gr. genos, to produce) to form the fibrin (network of in-
soluble, contractile threads). Fibrin collects blood corpuscles and other
available materials to form the clot. Vitamin K seems to be necessary
for the formation (in the liver) of the prothrombin which is normally
present in the plasma and has a life duration of only a few days. Vita-
min K must have bile from the liver in order to be absorbed in the
intestine and transported to the liver for the formation of prothrombin.
Vitamin K may be ingested as such or may be manufactured from foods
in the intestine. The formation of a clot within a blood vessel which is
not severed is called a thrombus (Gr. thrombos, clot). This may be due
to injury of the vessel wall from a blow or from toxins of bacteria which
injure the blood platelets. If a part of a thrombus circulates in the
vessels, it is called an embolus (em' bolus) (Gr. embolos, wedge). If
the embolus should block circulation to a vital part, serious consequences
may result.

Structure and Functions of Human Lymph

The composition of the lymph is similar to that of the blood plasma.
It ranges from colorless to yellowish color, has an alkaline reaction,
contains no blood platelets, clots slowly and not firmly, has a higher
percentage of waste materials than blood, contains a lower percentage
of nutrient materials than blood, may contain a few red blood corpuscles
(erythrocytes), and contains lymphocytes (white blood corpuscles).

The lymph is derived from ( 1 ) the blood plasma by filtration through
the thin walls of the capillaries and (2) secretions of the endothelial
cells which line the numerous capillaries.

488 Animal Biology

The functions of human lymph may be summarized as follows: (1)
It bathes all parts of the body not reached directly by the blood, thus
supplying foods, oxygen, etc., and receiving carbon dioxide and wastes.
There is a continuous interchange between the blood plasma and the
lymph through the processes of osmosis and diffusion. (2) It aids in
the fight against foreign materials, such as bacteria and protozoa. (3)
It helps to equalize body temperature. (4) It helps to regulate the
acid-alkaline balance of the various parts of the body. (5) It helps to

R. INT JUGULAR V.
R. SUBCLAVIAN V.

L. INT. JUGULAR V.
THORACIC DUCT
. SUBCLAVIAN V.

INNOMINATE

SUP.
VENA CAVA

THORACIC OUCT

RECEPTACULUM
CHYLI

LYMPH NODES

LACTEALS

INTE5TINC

MESENTERY

Fig. 242. — Lymph svstein and parts of certain veins of the upper part of the
body. Lymph from the abdominal organs and lower limbs flows into the tho-
racic duct which empties into the left subclavian vein. The lymphatics from the
left arm, and the left sides of the thorax, neck, and head also empty into the tho-
racic duct. Lymph from the right arm and the right sides of the thorax, neck,
and head flows into the right subclavian vein. (From Zoethout and Tuttle:
Textbook of Physiology, The C. V. Mosby Go.)

collect and transport fatigue products which are the result of cellular
activity. (6) It probably aids in transporting enzymes and other secre-
tions to various body parts (Figs. 240 and 242).

Human lymph may be found in various places and consequently may
have a variety of functions. The principal locations are (1) in the

Biology of Man 489

lymph ducts and their enlargements, the lymph nodes, (2) in tissue
spaces (tissue sinuses) or cavities in various tissues, (3) in the pleural
cavity (around the lungs), (4) in the pericardial cavity (around the
heart), (5) in the peritoneal cavity (abdominal cavity), (6) in the peri-
neural cavities (spaces between the various linings of the brain and
spinal cord), and (7) in the lacteals or lymphatics which originate in
the small fingerlike villi of the intestine. Fats are absorbed from the
intestine by the lacteals and eventually placed in the blood stream.

Human Blood Groups

The various types of human blood are classified as (1) Groups A, B,
AB, and O, (2) Groups M and N, and (3) Rh positive and Rh negative.
These are considered later in this chapter under Inheritance of Human
Traits.

VI. RESPIRATION IN MAN

Respiration may be defined as the supplying of oxygen to all cells of
the body and the removal of carbon dioxide from them. Breathmg may
be defined as the rhythmic inhalation of air into the lungs and the
exhalation of carbon dioxide and other gases from them (Fig. 244).
The composition of inhaled (inspired) air and of exhaled (expired)
air is:

inhaled air exhaled air

(per cent) (per cent)

Oxygen 20.96 15.8

Carbon Dioxide 0.04 4.0

Nitrogen 79.00 80.2

Respiration is controlled by the respiratory center of that portion of
the brain called the medulla oblongata (Fig. 247), whose activity is in-
fluenced by nerve impulses over afferent nerves leading to it and by
chemicals which influence the center either directly or reflexly. During
inhalation the size of the thorax (Fig. 243) is increased by contraction
of the respiratory muscles, thereby decreasing the pressure within the
lungs and allowing the greater pressure of the external air to force it
into the lungs until the pressures are equalized. During exhalation the
size of the thorax is decreased by relaxation of the respiratory muscles,
thus forcing out a certain quantity of the air from the lungs and allowing
a certain amount to remain. In adults, during rest, the normal rate of
respiration varies from 12 to 20 per minute, although these figures may
vary with different individuals. A certain amount of respiration takes

490 Animal Biology

Right common
carotid artery.

Subclavian
arteries.

Innominate
artery.

Arch of aorta.

Right lung.

Superior vena
cava.

Right auricle.

Larynx.

— Trachea.

Subclavian
arteries.

Left lung.

Pulmonary
artery.

Heart.

Coronary
artery.

Fig. 243.- — Organs of the human thoracic cavity. (From Turner: Personal and
Community Hygiene, The C. \' . Mosby Co.; after Ingals.)

CARTaAGE")

cartilageJ

RIGHT LUMG

CARTlLAGmOUS RlflGS

ROnCMUS

UARYMK

BROrtCHIOLE

i^C^AlR SAC 5

Fig. 244. — Human respiratory system shown in section. The walls of the air
sacs are dilated to form alveoli whose thin walls are covered with a network of
capillaries for the exchange of gases. (From Zoethout and Tuttle: Textbook of
Physiology, The C. V. Mosby Co. ; after Dalton.)

Biology of Man 491

place through the integument (skin) (Fig. 228) which has been pre-
viously described. However, it is estimated that the total inner surface
of the lungs is about 90 square meters or more than one hundred times
the total skin area of the body. The vital capacity of the average adult
lungs represents the maximum volume which can be exchanged in a
single respiration. This is about 4,000 c.c. (eight pints), although it
varies with different individuals and conditions. The following phe-
nomena occur in the lungs : ( 1 ) loss of about 5 per cent of the oxygen
from the inhaled air, (2) gain of about 4 per cent of carbon dioxide,
(3) gain of about 1 per cent of nitrogen, (4) saturation of the expired
air with moisture (about 1 pint daily), (5) warming the expired air to
nearly that of the blood (98.6° F.), thereby losing body heat, (6) trans-
fer of oxygen and carbon dioxide through the thin-walled air sacs of
the lungs (Figs. 234, 235, 243, and 244).

Respiration involves ( 1 ) the exchange of gases between the respiratory
membrane and the capillaries of the pulmonary circulation within the
lungs, known as external respiration and (2) the exchange of gases
between the capillaries of the systemic circulation and the body tissue
known as internal respiration.

The respiratory system is composed of the nose, pharynx, larynx (voice
box or "Adam's apple"), trachea (windpipe), bronchi, and lungs (Figs.
234, 235, 243 and, 244). The nose is divided by a partition (septum)
to form two wedge-shaped cavities which are lined by a highly vascular,
mucous membrane, the upper layer of which is ciliated. Sinuses in the
bones are associated with the nasal cavities so that inflammations may
spread to the sinuses easily. The lateral surface of each nasal cavity
has three light, spongy, bony projections called conchae to make the
upper part of the nasal passages very narrow. The nose has the follow-
ing functions: (1) to act as a sounding board for the voice (organ of
phonation), (2) to give warmth and rnoisture to the inhaled air, (3) to
remove dust and other foreign materials by hair, cilia, and mucus (se-
creted by goblet cells), and (4) to detect odors by means of the olfactory
nerve endings in the upper passages.

The pharynx is a common cavity (Fig. 234) which connects the nasal
cavities with the larynx as well as the mouth with the esophagus. Be-
cause of this dual function it is impossible to inhale air and swallow
food at the same time.

The larynx is a cartilaginous box which forms the prominence in the
midline of the front part of the neck. Within the laryngeal cavity are
two folds of mucous membrane extending from front to back but not

492 Animal Biology

quite meeting in the middle. Embedded in the edges of these folds are
fibrous and elastic ligaments which constitute the true vocal folds (vocal
cords), because they function in voice production as air passes between
them. Above the vocal folds are two smaller folds which do not aid in
voice production but protect the larynx during swallowing, help keep
the true vocal folds moist, and assist in holding the breath. They are
called the false vocal cords. The opening between the true vocal folds
is the glottis. The size of the glottis and the tension of the vocal folds
regulate the tone produced. The glottis is protected above by a leaf-
shaped fibrocartilage called the epiglottis.

The trachea is a membranous tube about four inches long located in
front of the esophagus. The walls are strengthened by sixteen to twenty
cartilaginous, C-shaped structures. It extends from the lower end of the
larynx to the two branches, each of which is known as a bronchus (plural,
bronchi). Each bronchus divides and subdivides, the smallest branches
being the bronchioles. Each bronchiole terminates in a series of saclike
air cells (alveoli). The thin-walled alveoli are surrounded by thin-walled
capillaries through which the exchange of gases occurs.

The two lu?igs are cone shaped and lie in the thorax (Figs. 235 and
243), being separated by the thick mediastinum which contains the heart,
larger blood vessels, trachea, etc. The left lung is smaller and longer
than the right because the heart occupies part of this space. Each lung
is enclosed in a serous sac called the pleura, which consists of an outer
layer, or parietal pleura, which adheres closely to the diaphragm and the
walls of the thorax, and a visceral pleura which covers the lungs. The
two pleurae are separated by a thin layer of serum to reduce friction.
Inflammation of the pleura is called pleurisy.

VII. EXCRETION OF WASTES

The excretion of human wastes may be considered as the elimination
from the body of the undesirable products of metabolism and other activi-
ties and includes liquids, gases, and solids (soluble and insoluble). The
elimination of indigestible materials which have served no purpose might
be considered as egestion.

Excretory organs and the waste materials eliminated may be sum-
marized on page 493.

The pair of bean-shaped kidneys, located at the back of the abdominal
cavity, one on each side of the vertebral column, select wastes from the
blood brought to them and pass them through the ureters to the urinary

Biology of Man 493

PRIMARY

SECONDARY

Kidneys (Fig. 245)

Water, soluble salts

Carbon dioxide, heat

Lungs (Fig. 244)

Carbon dioxide (12 cubic
feet daily)

Water (250 c.c. daily), heat

Skin (Fig, 228)

Water, salts, carbon dioxide,
heat

Dead skin, nails, etc.

Alimentary canal (Fig.

Solids, secretions

Water, carbon dioxide and

236)

other gases, salts, heat

Liver (Fig. 236)

Bilirubin formed from hemo-
globin of blood and ex-
creted by the intestine;
collect end-products of
protein metabolism and
convert them into urea.

etc., to be excreted by
kidneys

bladder where wastes are stored (Fig. 245). Each kidney consists of an
outer cortical substance (cortex) and an inner medullary substance (me-
dulla). When examined microscopically, the cortex contains numerous

Renal v:iil^

kidney

Aorta-

||1_ }»Ascer)d'm(^ vena cava

BJadder

Bowman's capsule

Urethra

Loop of Heri}e

rab«?_

Fig. 245. — Human urinary system. One kidney has been dissected to show
the internal structures. At the right, the details of the blood vessels and the col-
lecting tubes are shown. The latter empty the urine into the enlarged end of the
ureter which transports it to the bladder. The outer portion of the kidney is the
cortical region (cortex) and the inner portion, which contains the numerous glo-
meruli and tubes, is known as the medullary region.

494 Animal Biology

globelike reiial (Malpighian) corpuscles, each of which is composed of
(1) a coiled mass of thin-walled capillaries arising from the reiial arteries,
each mass being called a glomerulus, and (2) a thin double-walled en-
closing glomerular capsule ( Boivm,an s capsule) which is the beginning
of a renal tubule (Fig. 245). The convoluted renal tubules travel irregu-
larly and empty into the straighter collecting tubes which in turn pass
the urine into the basinlike pelvis of the kidney from which it goes out
through the ureter (Fig. 245). The blood from the glomeruli eventually
passes from the kidney through the renal veins into the ascending vena
cava. When examined microscopically, the medulla consists of cone-
shaped renal pyramids whose apices are known as renal papillae. The
collecting tubes empty at the apices of the papillae, which vary from eight
to eighteen in number.

The glomeruli extract the wastes from the blood, thus helping" to main-
tain the normal composition of the blood. The kidneys selectively ex-
tract almost all the protein waste, most of the salts not required by the
blood, and about half of the excess water. They also extract foreign sub-
stances such as toxins. The quantity of urine secreted in twenty-four
hours varies, but the normal average for a healthy adult is 1,200 to 1,500
c.c.

The contractions of the muscles in the walls of the ureters cause the
urine to pass toward the muscular bladder located in the pelvic cavity.
The bladder normally holds about one pint, and the contraction of its
three layers of muscles forces the urine to the exterior through the tubu-
lar urethra.

VIII. COORDINATION IN MAN AND
SENSORY EQUIPMENT

All living protoplasm is necessarily irritable or subject to stimulation.
A stimulus is any external or internal substance, material, or condition
which affects a cell or group of cells, thereby setting up a change known
as a response. General types of stimuli are chemical, electrical, thermal,
mechanical, radiant, and osmotic. General types of responses are move-
ment, secretion, thermal, chemical, electrical, and photic. The respon-
sive mechanisms of man are complex and varied. The three steps in-
volved are as follows: (1) a special structure called a receptor must be
stimulated; (2) some method of conduction of the effects of stimulation
to (3) a specialized structure called an effector which must respond in
some way. Receptors in man are frequently specialized epithelial cells

Biology of Man 495

in close association with the conductors. The following is a brief sum-
mary of the receptors of man:

1. Chemoreceptors (receptors sensitive to chemicals)

(a) Taste buds on the tongue are clusters of specialized epithelial
cells (Fig. 11) closely associated with nerves leading to the
brain (Figs. 246 and 247).

(b) Ends of sensory nerves in the nasal epithelium (Fig. 11) receive
the stimuli of odors, thus giving us a sense of smell.

2. Mechanoreceptors (receptors sensitive to mechanical stimuli)
a) Tactile (touch) receptors (Meissne/s corpuscles) over much

of the body, but especially beneath the epidermis on the hands
and within the digestive tract (hunger) .

Choroid plexua
Of ^

third
ventricle

Pineal ^land—-

Cerebral
aqueduct
Arbor vi.ta.e

Foarth ventricle
Cerebellum

Corpus
callosum

.Third
ventricle

Stalk op
hqpophqsis

NDl^actori^ bulb
Pons

Fig. 246. — Human brain in sagittal section, showing the medial aspect of the
left half. The convoluted cerebrum (cerebral hemisphere) is shown above the
corpus callosum and the spinal cord below the pons. (From Francis: Fundamen-
tals of Anatomy, The C. V. Mosby Co.)

(b) Auditory (hearing) receptors which are vibrating "hair cells"
located in the cochlea of the inner ear (Fig. 250) . Sound waves
enter the external ear and vibrate the tympanic membrane
which transmits the vibrations along the bones of the middle
ear (hammer, anvil, and stirrup bones). From the latter a
fluid in th^ cochlea (resembHng a snail shell) carries the vibra-
tions to the "hair cells" which in turn set up action currents to
be conducted over th^ auditory (acoustic) nerve to the tem-
poral lobe of the brain (Fig. 247) .

496 Animal Biology

(c) Receptors for equilibrium located in the inner ear (Fig. 250).
The semicircular canals, which are hollow and hairlined, con-
tain fluid. Three canals in each inner ear are all at rie^ht ans^les
to one another in three different planes. Movement of the fluid
stimulates the hairs, giving a sensation of movement. The sac-
cule and utricle arc hollow or^i^ans lined with sensitive hairs and
contain solid granules of calcium carbonate called otoliths.

LOnCITUOItlAL FISSURE

FROMTAL LOBE

OPTIC CHIASMA

TEMPOR
LOBE

STALK OF
HYPOPHYSI

OPTIC
TRACT-

CER
PEDUMCL

MAMMILL
BODY

POfIS

PYRAMID

CEREBELLUM

MED
OBLOMGATA

$PmAL CORD
OCCIPITAL LOBE

I. OLFACTORY

2. OPTIC

3 OCULOMOTOR

4. TROCHLEAR

5(TRIGEMIt1AL MOTOR
(.TRIGEMItlAL SEnSORY

6. ABDUCENT

7 FACIAL

IflTERMEDIATE
6 ACOUSTIC

9. GLOSSOPHARYtlGEAL

10. VAGUS

I. SPIMAL ACCESSORY

2. HYPOGLOSSAL

Fig. 247. — Human brain, from undcrsurface, with parts labeled and the twelve
cranial nerves listed on the right. (From Zoethout and Tuttle: Textbook of
Physiology, The C. V. Mosby Co.; after Morat.)

Head movements cause the latter to stimulate the hairs, giving
a sensation of position.
(d) Proprioceptors (L. propricta, property, condition), peripheral
receptors of the afferent nerves in muscles, tendons, joints, which
assist in the complex coordinated movements in locomotion and
posture (kinesthetic sense).

Biology of Man 497

Photoreceptors (receptors sensitive to light)
In the human eye (Figs. 248 and 249) hght waves pass through the
transparent cornea, through the aqueous humor, and the pupil
(opening in the colored iris), striking the lens. The latter changes
its shape, thereby focusing the light and producing an image on the
rods and cones (sensitive cells) of the retina. This starts a photo-
chemical change in the photosensitive visual purple located in the
cells of the retina. This change induces action currents in the optic
nerve which carries them to the brain (Fig. 247) .

-«jn/j rectus niu^'cle

Sclera.- - -y^.

Choroid---/
Reitna /-

ConjuncttVcL
/

chamber

VA // Posterior
chuuiber

x,y Ctlictrij body

■'In f. rectus muscle

Fig. 248.- — Human eyeball in vertical section shown diagrammatically. The
anterior and posterior chambers contain aqueous humor; the vitreous body is a
transparent jellylike substance; the circular opening in the iris is the pupil; the
ciliary body is composed of bundles of smooth muscles to control the lens; the
inner layer (retina) is composed of light-sensitive nerve cells. (From Francis:
Introduction to Human Anatomy, The C. V. Mosby Co.)

4. Thermoreceptors (receptors sensitive to heat)

These are located in the skin in various parts of the body.

5. Osmotic receptors (thirst) located in the mouth and throat

6. Pain receptors — free nerve endings of sensory nerves located in various

parts of the body.

The effectors in man are mainly glandular (for secretion) and me-
chanical (for movements). Secretions are produced by the protoplasm
of cells from the food materials brought to them. In man there may be
isolated secretory cells or groups of secretory cells associated together to

498 Animal Biology

form a secretory organ known as a gland. Glands may emit their secre-
tions through permanent channels, as in the case of the salivary glands,
or distribute them throughout the body by means of the blood stream and
tissue fluids. The latter type of gland is called a ductless (endocrine)

gland.

These are considered in detail later in this chapter.

Superior rectus /A.
' Medial rectus A/I.
1 / _...=:..^rr.??ii'-l>' _pauey

Sup. oblique M'

Lid

/ Eyelash

Iris

Lateral

rectus M.

Eyelash

Lid

Lateral rectus AL \ "^^r^H^;^' ^)f j'^1 _ _ /nf. obi ique M.
Inferior rectus M.

Fig. 249. — Human eye muscles and optic nerve. Observe that the muscles are
in pairs but that the superior oblique runs through a pulley and is longer than
the inferior oblique.

semicircuTar
canals

pharynx

Fig. 250. — Human ear, in section, shown diagrammatically. The car bones
are malleus (hammer), incus (anvil), and stapes (stirrup). (By permission from
General Zoology by Storer. Copyright, 1943. McGraw-Hill Book Company, Inc.)

The contraction of a muscle is accompanied by electrical, mechanical,
and thermal changes. Contraction may be caused by nerve impulses or
by chemical substances. When a muscle is stimulated there is a short
latent period of about .01 of a second, followed by a period of contraction
of about .04 of a second, then a period of relaxation (lengthening) of

Biology of Man 499

about .05 of a second. The contraction is brought about by energy re-
leased in the use of foods. Part of the energy associated with muscular
activity is heat energy which explains the increase in temperature when
muscles are active. Certain metabolic products, designated as fatigue
substances, result in muscle fatigue. If a minimum supply of oxygen is
present, muscles fatigue sooner if stimulated repeatedly. Recovery from
fatigue results from the use or elimination of fatigue substances and the
replenishment of the food supply, if this is necessary.

+ + + + + + + + +
A + ^

RESTING NERVE FIBER

+ + + +

Oepolarized reg

• f + + +

+ + + + + + + + +

K/. L/JJjy/jyyyy^^^j^y/yyy/yyjy,yy^,,^^yy^,,j/

( I
« I

/^+ + + + + + +

t^-

yyyyyy'yyyyyjy >/^-</^ ^^^^y^^yyyy ji

a:".:

/^+ + + + +

■t<- —

yyyyyyyyyyyy jjj/j/jjj

)

hijjjjj,jjj,i

•S-^

JjyyjyjyJJ

)

— ^

Wj//,rjft,,jitjJj„,,,,i,,l>l,,

Fig. 251. — Membrane theory of nerve impulse transmission shown diagram-
matically. A, Resting nerve, showing the polarized membrane (positive charges
on the outside and negative charges on the inside) ; B, nerve conducting an im-
pulse, showing, from left to right, the partially repolarized region behind the
impulse, the depolarized region where the impulse is located, and the polarized
region ahead of the impulse ; C, passage of the impulse along the nerve shown in
successive stages. (From Hunter and Hunter: College Zoology, W. B. Saunders
Company.)

500 Animal Biology

The conductors in man are (1) the nervous system^ composed of the
brain and cranial nerves, spinal cord and spinal nerves, autonomic nerves
(Figs. 16, 17, 246, and 247) and (2) the blood stream (Figs. 237, 240,
and 241) and the tissue fluids. The activities of various organs may be
aflfected by chemical substances produced in other tissues and organs and
carried by the blood, lymph, or body fluids. This is chemical coordina-
tion, and the substances, designated as hormones, are produced by duct-
less (endocrine) glands discussed later in this chapter.

Since much of the coordination of the many organs, tissues, and sys-
tems of the human body is due to the activities of the nervous system
and its so-called nerve impulses, the nature and characteristics of the
latter must be understood in order to appreciate the marvels of coordina-
tion of the various parts of the body.

Some of the more important characteristics of nerve impulses are as
follows: (1) They are electrochemical phenomena (Fig. 251) in which
a stimulus originates electrical changes in one part of a nerve fiber which
in turn institutes similar electrical changes in adjacent parts of the fiber
as the impulse travels along. According to the polarized membrane
theory of nerve im,pulse, the semipermeable membrane surrounding each
nerve fiber permits certain ions (charged chemical particles) to penetrate
it but prevents others from doing so. Through normal metabolic activi-
ties of the nerve, the membrane is polarized (charged) by having an extra
number of positive ions on its outer surface and an equal number of nega-
tive ions on its inner surface. The positive and negative ions do not neu-
tralize each other normally because the membrane is impermeable to
them. However, when stimulated at a certain point, the membrane is
depolarized (loses the excess positive ions) and its permeability is in-
creased so that the ions from an adjacent, nonactivated region pass
through this depolarized region to neutralize each other. This results
in depolarization (probably because of chemical actions) of this adja-
cent region, making it permeable to the movement of the ions from the
next region, and so the impulse moves along the surface of the nerve fiber
by a series of depolarizations (Fig. 251 ) . After a period of time, a nerve
over which an impulse has traveled becomes repolarizcd again with its
positive ions on the outer surface of the membrane and negative ions on
its inner surface. (2) After a nerve fiber has conducted an impulse, it
undergoes certain chemical and physical changes ("recovery") over a
definite period of time (0.001 to 0.005 second) and then it can transmit
another impulse. The interval between consecutive impulse transmissions
is known as the refractory period. (3) When a nerve fiber transmits an

Biology of Man 501

impulse, it uses more oxygen, gives off more carbon dioxide and heat,
and expends more energy than when it is not transmitting impulses, which
suggests the oxidative nature of the phenomenon. (4) Normally the
rate of travel of a nerve impulse is independent of the intensity and
nature of the stimulus, providing the stimulus is of a certain minimum
intensity; in other words, stronger stimuli do not cause impulses to travel
faster, because the energy for im.pulse conduction comes from the nerve
and not the stimulus. This is known as the all-or-none law which implies
that a stimulus of sufficient intensity results in an impulse independent
of the strength or nature of the stimulus. In other words, stimuli result
in an impulse — or they do not. The rate of travel of a nerve impulse
may be dependent on the state of the nerve fiber, because certain drugs
may retard or even prevent impulse transmissions. Advantage is taken
of this in "blocking off" and preventing the transmission of certain im-
pulses by the use of certain drugs. The speed of nerve impulses is much
slower than the speed of electricity; hence they are not electric currents
even though certain electrical phenomena may be associated with them.
Injured or dead nerves are capable of conducting electrical currents, but
they cannot transmit nerve impulses. The rate of impulse travel over a
given nerve is the same whether the stimulus be chemical, heat, touch,
electrical, etc. (5) It is thought that all types of nerve cells (sensory,
motor, etc.) conduct impulses in a similar way and that the end result
depends on the nature of the specific structure to which the impulses
travel; impulses traveling from the ear to a certain part of the brain
result is a sensation of sound; proper impulses traveling to muscles result
in movements, etc. (6) Although impulses may be initiated anywhere
along a nerve, they usually originate at one end only and travel toward
the opposite end; that is, from the dendrite toward the axon. (7) Nerve
fibers do not seem to fatigue so long as a sufficient supply of oxygen is
present. (8) Neurons (nerve cells) consist of one or more dentrites, one
or more axons, and a cell body with its nucleus. Adjacent neurons do
not quite contact each other, and the small area between them is called
a synapse (sin' aps) (Gr. synapsis, union). It has been proved experi-
mentally that in certain instances an impulse travels across the synapse
from the tip of the axon of one neuron to the dendrite of an adjacent
neuron because of a chemical secretion known as a neurohumor, pro-
duced by the tip of the axon. Because this neurohumor is produced by
the axon and stimulates the adjacent dendrite, the impulse travels from
the axon of one neuron to the dendrite of another neuron and not the
reverse because dendrites are unable to secrete this substance. In cer-

502 Animal Biology

tain synapses a much simpler type of impulse transmission may take place
than what has been described. The rate of impulse transmission through
a synapse is slower than along a nerve under ordinary conditions. In
case the tip of an axon is adjacent to a gland or muscle, the neurohumor
stimulates and causes a secretion, or a movement, accordingly. In the
case of impulse transmission from nerve to muscle the chemical is spe-
cifically known as acetylcholine. The chemical known as synipathin be-
tween a nerve and the heart results in speeding up the latter. The ex-
planation for a lack of continuous impulse transmissions through a
synapse is based on the presence of an enzyme called cholinesterase which
oxidizes (destroys) the acetylcholine, thus preventing a constant flow of
impulses through a synapse. Impulses travel through when acetylcholine
is present but do not when the latter has been destroyed by the cholin-
esterase. The natural resistance offered by synapses may be modified
by nerve impulses. In some cases one impulse strengthens another and
is known as reinforcement, while in other instances one impulse may
cancel the effect of another which is called inhibition. Impulses may
cross a synapse if reinforced by others or may not cross if they are in-
hibited. This complex reinforcement-inhibition relationship may explain
many of the phenomena of the nervous system.

The human hrain (Figs. 246 and 247) consists of (1) cerebrum, (2)
cerebellum, (3) midbrain, (4) medulla oblongata, and (5) pons varolii.

Central
nervous
system

Autonomic
nervous
system

Summary of the Human Nervous System

'Cerebrum, which is large, ovoidal, convoluted, and made of

two hemispheres with five lobes
Cerebellum, which is smaller, oval, nonconvoluted but with
smaller furrows (sulci)

Midbrain, which is short and connects the cerebellum with
Brain ■{ the pons varolii

Medulla oblongata, which is pyramid shaped and continues
^ with the spinal cord

Pons varolii, which is in front of the cerebellum between the

midbrain and medulla oblongata and which connects the

parts of the brain (Fig. 247)

Cranial nerves (12 pairs) and their end organs (Fig. 247)

Spinal cord for reflexes and pathways to and from the higher nervous

centers (Fig. 247)

^Spinal nerves (31 pairs) and their end organs

Sympathetic, which has centers, ganglia, and plexuses in the cervical,
thoracic, and lumbar regions of the spinal cord

Parasympathetic, which consists of the centers and ganglia of the
cranial and sacral parts of the autonomic system

Enteric, which consists of the part of the autonomic system associated
with the walls of the alimentary tract

Biology of Man 503

The cerebrum, which is the largest and most prominent part of the brain,
is divided into the right and left cerebral hemispheres. Each hemisphere
is divided by sulci into five distinct areas known as lobes (frontal, parietal,
temporal, occipital lobes, and the insula, the latter not visible from the
surface). The outer layer of the cerebrum, known as the cortex, has
numerous foldlike convolutions which greatly increase the surface area.
Certain functions are localized in specific regions of the cerebral cortex
as illustrated by the following: motor area, sensory areas (heat, cold,
pain, touch, light pressure, muscle sense), auditory area, visual area,
olfactory area (taste and smell), and speech area. Beneath the gray cor-
tex of the cerebrum is a mass of nervous tissue known as white matter.

Spinal Nerves of Man

Cervical (neck) 8 pairs

Thoracic (thorax) 12 pairs

Lumbar (back) 5 pairs

Sacral (pelvis) 5 pairs

Coccygeal (tail) 1 pair

31 pairs

The brain contains cavities (ventricles) as follows: fl) two lateral
ventricles, one in each cerebral hemisphere; (2) the third ventricle be-
hind the lateral ventricles and connected with each by an opening called
the foramen of Monro; the fourth ventricle in front of the cerebellum
and behind the pons and medulla, being connected with the third ven-
tricle by a small canal called the aqueduct of Sylvius. The coverings of
the brain are called meninges and are the same as for the spinal cord
(dura mater, outer; arachnoid, middle layer; pia mater, inner). Thin
layers of fluid separate the various layers.

Functions of the cerebrum in addition to those already mentioned are
as follows: it governs all our mental activities (reason, will, memory,
intelligence, higher feelings, and emotions) ; it is the seat of consciousness,
interpreter of sensations, originator of voluntary acts; it is a control on
many reflex acts which originate as involuntary (weeping, laughing,
defecation, micturition, etc.).

The cerebellum (Figs. 246 and 247) lies at the base or posterior part
of the brain. The outer, cerebellar cortex is made of gray matter, which
is not convoluted but is traversed by numerous furrows (sulci). All
functions of the cerebellum are below the level of consciousness, the
main function being the reflex control of skeletal muscle activities.

The midbraiii connects the cerebral hemispheres with the cerebellum
and pons. Two pairs of round elevations, known as the corpora quad-

504 Animal Biology

rigemina, act as centers for auditory and visual reflexes. Important path-
ways to and from other parts of the brain pass through the midbrain.

The pons (Figs. 246 and 247) Hes in front of the cerebellum and above
the medulla. Its fibers connect the two halves of the cerebellum and join
the medulla with the midbrain.

The medulla oblongata (Figs. 246 and 247) lies between the pons and
the spinal cord, being much like the latter structurally. The fourth
ventricle of the brain is located within the medulla and connects with
the central canal of the cord. The medulla contains such vital centers
as cardiac, respiratory, and vasoconstrictor centers, the latter for the con-
trol of arterial pressure.

The twelve pairs of cranial nerves (Fig. 247) may be summarized as
follows :

1. Olfactory — sense of smell

2. Optic — sense of sight

3. Oculomotor — control of following eye muscles: ciliary, inferior
oblique, superior, inferior, and internal (medial) recti, sphincter of the
iris of eye

4. Trochlear (pathetic) — superior oblique muscle of eye

5. Trigeminal — sensory to the head, motor for the muscles of mastica-
tion

6. Abducent — external (lateral) rectus of the eye

7. Facial — motor to the face and scalp; sensory to the tongue, secre-
tory to the submaxillary and sublingual (salivary) glands of the mouth

8. Acoustic (auditory) — to cochlear part of the ear for hearing, to
vestibular part of the ear for equilibrium

9. Glossopharyngeal — -motor to pharynx; sensory to tongue, mucous
membranes of pharynx, tonsils, Eustachian tube, tympanic cavity of the
ear; secretory to the parotid gland (salivary) of mouth.

10. Vagus (pneumogastric) — sensory to larynx, trachea, lungs, esopha-
gus, stomach, small intestine, part of large intestine; motor for respira-
tion, heart action, digestion (inhibits heart action) ; secretory for gastric
and pancreatic glands,

11. Accessory — the cranial part to the pharyngeal and superior laryn-
geal branches of vagus; the spinal part to the trapezius (of back) and
sternocleidomastoid (neck) muscles

12. Hypoglossal — motor to tongue

The sensory nerves of the skin transmit sensations of pressure, pain,
heat, and cold from the specific sense organs to the proper parts of the

Biology of Man 505

central nervous system to be interpreted (Fig. 246) . Special sense organs
in the muscles, called muscle spindles, originate the so-called muscle sense
to tell the degree of contraction or the general condition of the muscles.

The human taste buds are the end organs of nerve filaments arising
from the trigeminal, facial, and glossopharyngeal nerves (cranial nerves).
The taste organs are located chiefly on the tongue, but also on the palate,
epiglottis, and even vocal folds (Fig. 234). The human auditory ap-
paratus (Fig. 250) consists of (1) an external ear with its auditory canal
with a membranous tympanum (eardrum) at its inner end; (2) the
middle ear with its Eustachian tube connecting it with the pharynx to
equalize air pressure; the middle ear bones — ham,mer or malleus) (L.
malleus, hammer), anvil or incus (L. incus, anvil), and the stirrup or
stapes (L. stapes, stirrup) ; the two openings of the middle ear into the
inner ear, which are known as the fenestra vestibuli (ovalis) and the
fenestra cochleae (rotunda) ; (3) the internal ear with its vestibule, its
snail-shell-like cochlea, and the three semicircular canals; the last serve
the purpose of equilibrium; (4) the auditory or acoustic nerve, leading
from the internal ear to the central nervous system.

The human visual apparatus (Fig. 248) consists of (1) the eyeballs
with their six muscles for eye movement (the superior and inferior recti
muscles, the external and internal recti, the superior and inferior oblique
muscles) (Fig. 249), (2) the lacrimal apparatus to keep the eye moist
and protect it, (3) the conjunctiva or mucous lining of the paired eyelids
internally, (4) the eyebrows for protection; (5) the complicated appa-
ratus of lens, aqueous humor (in anterior chamber), vitreous body, iris,
pupil, cornea, and the sensitive retina, choroid coat, the sclera, etc., (6)
the optic nerve, which transmits the stimuli recorded by the retina to the
visual centers of the brain where the sensation of sight is really located.

The human olfactory apparatus consists of a fine network of olfactory
nerves spread over the irregular surfaces of the superior nasal conchae
and upper nasal septum (Fig. 234). These nerves terminate in olfactory
cells, each with six to eight hairlike processes. The latter are affected by
small particles of solids or gases in solution. The olfactory nerve carries
the impulses to the olfactory center of the brain (Figs. 246 and 247).

The spinal cord consists of a central canal surrounded by a central
core of gray m,atter which is surrounded by white matter. The gray
matter in cross section resembles the letter H, the two forward projections
being called anterior colum.ns and the two backward projections, the
posterior columns. The spinal cord serves as a center for spinal reflexes

506 Animal Biology

and as pathways to and from the brain. The white matter of the cord
has ( 1 ) long ascending tracts to transmit afferent impulses from the spinal
nerves to the brain and (2) long descending tracts to transmit efferent
impulses from the motor centers of the brain to the anterior columns of
the cord to control muscular movements.

The autonomic nervous system consists of ( 1 ) the sympathetic (tho-
racolumbar) which has centers, ganglia, and plexus in the cervical, tho-
racic, and lumbar regions of the spinal cord, (2) the parasympathetic
(craniosacral) which consists of centers and ganglia of the cranial and
sacral parts of the autonomic system, and ( 3 ) the enteric which consists
of the part of the autonomic system associated with the walls of the
alimentary tract. The autonomic nervous system innervates smooth
muscles, cardiac muscles, and glands. The autonomic system is a highly
important functional portion of the entire nervous system and not a self-
controlling, independent, segregated unit, as the word autonomic might
imply. In fact, the autonomic is one of the most essential parts of our
vital nervous system.

IX. ENDOCRINE (DUCTLESS GLAND) SYSTEM OF MAN

The structure and functions of various organs in the human body are
also affected by substances produced in other organs and transmitted
primarily by the blood. This chemical coordination is brought about by
specific chemical substances known as hormones (hor' mon) (Gr. hor-
maein, to excite). These hormones are manufactured in certain organs
from ingredients brought to them by the blood and carried away without
the benefit of ducts. The more important ductless glands and their hor-
mones and functions are given in summaries.

Endocrine glands (en'dokrin) (Gr. endon, within; krinein, to sep-
arate) and their secretions which contain the specific hormones are in-
fluenced by such factors as ( 1 ) the quantity and quality of foods brought
to them by the blood, (2) the action of hormones from other endocrine
glands, and (3) the action of certain parts of the nervous system such as
the hypothalamus of the brain, the sympathetic nervous system, etc.
Endocrine glands were studied separately, but recent work has shown
the great interdependence of many of them, and this new approach has
been profitable in getting a more correct picture of them. Regulating
substances in invertebrate animals are probably present, but their roles
and distribution are not well known. For example, it is probable that

Biology of Man 507

sex hormones may be present in certain annelids and Crustacea. Color-
influencing hormones which affect pigment cells have been studied experi-
mentally in Crustacea. Some endocrine glands, such as testes, ovaries,
and pancreas, may function as both ductless and duct glands. Some
endocrine glands, such as the pituitary, thyroid, parathyroids, and
adrenals, function only as ductless glands. Several of them produce a
number of hormones with more or less specific functions, which compli-
cates the problem of investigating them.

P\nQa\

-V Pituitary

Parathyroids^

.Thyroid

Thymus

Liver \—m^

—ifcomacb
.-Spleen

-y^drcnalj
-Pancreas
_ htestinQ

Ovaries

Testes

Fig. 252. — Approximate locations of endocrine (ductless) glands of human being.

The location and brief descriptions of some of the human endocrine
glands are as follows:

1. Pituitary (Hypophysis). — Small (1 cm. diameter), reddish-gray;
located at center of the base of the brain; composed of an anterior lobe,
intermediate portion, and a posterior lobe which is connected with the
hypothalamus of the brain; in certain animals the two lobes are sep-
arate (Fig. 252).

2. Thyroid. — A pair of shield-shaped glands connected by an isthmus
and located in front of the trachea, just below the larynx; present in all
vertebrates; thyroxin is an amino acid containing iodine.

508 Animal Biology

3. Parathyroids. — Usually four small compact masses of cells closely
associated with the thyroid but which differ from the latter structurally
and functionally.

4. Adrenals (Suprarenals). — One soft, cup-shaped gland covering the
upper part of each kidney; composed of an outer, pale pink cortex and
a dark inner medulla, which differ as to embryologic origin, structure,
and functions; the two parts are separate in certain lower vertebrates.

Fig. 253. — Cretin, 19 years of age, showing dwarfism, deficient bone develop-
ment, thickened lips, thick pasty skin, etc. (From Bard: Macleod's Physiology
in Modern Medicine, The C. V. Mosby Co.)

5. Pancreas. — This organ secretes digestive juices which are carried
away by ducts, but certain clusters of cells (islands of Langerhans) are
without a duct and secrete endocrine hormones; it is flat and irregular
and lies in the curvature between the stomach and duodenum; weighs

Biology of Man 509

about 3 ounces; insulin was extracted from pancreas by the Canadians,
Banting and Best, in 1922 and has been used successfully in the treat-
ment of sugar diabetes, which would otherwise be fatal because of the
accumulation of toxic materials and constant loss of weight.

6. Testes. — Two ovoid bodies suspended in the scrotum; the seminif-
erous tubules produce sperm; the interstitial cells between the tubules
secrete the endocrine hormones; castration (removal of testes) results in
the lack of development of secondary sexual characters; such a man
(eunuch) has a hairless face, high-pitched voice, and a tendency to
obesity; castration is frequently used on domestic animals; it is doubtful
if the administration of testicular hormones is of benefit in attempts at
rejuvenation.

7. Ovaries. — Two bean-shaped organs (1^ inches long) attached
to the abdominal cavity near the uterus; the outer layer of germinal
epithelium produces eggs which are placed in internal follicles; each
month one (or more) follicle with its egg fills with fluid, comes to the
surface, and ruptures, thus releasing the egg into the oviduct; if after
ovulation the egg unites with a sperm, fertilization results; the ruptured
follicle fills with yellowish cells which constitute the corpus luteum
(corpus, body; luteum, yellow) ; the latter is absorbed in two weeks if
fertilization did not occur, but it enlarges and remains throughout the
period of pregnancy.

8. Placenta. — This organ attaches the developing embryo to the wall
of the uterus and supplies it with nourishment; during pregnancy a hor-
mone similar to the luteinizing hormone of the pituitary is produced, and
its presence in the urine can be used for testing early pregnancy when
injected into nonpregnant, female animals such as rabbits, rats, mice,
etc.

9. Stomach. — Certain cells of the lining of the stomach secrete a hor-
mone which stimulates the stomach to form digestive enzymes.

10. Duodenum (First Part of Small Intestine). — Certain cells produce
several kinds of endocrine hormones.

1 1 . Thymus. — A fairly large gland of children in the upper part of
the chest which regresses after puberty; no specific hormone has been
isolated but it is thought to be associated with juvenile growth.

12. Pineal (Epiphysis). — One small, cone-shaped body located be-
tween the cerebral hemispheres dorsal to the pituitary; no specific hor-
mone but it is thought to be associated with growth.

510 Animal Biology

Summary of Endocrine (Ductless) Glands

ENDOCRINE
GLAND

HORMONES AND FUNCTIONS

PITUITARY

(pi -tu' i ta ry)
(L. pituita,
phlegm) ("mas-
ter gland" or
"director gland")

ANTERIOR LOBE

1. Growth-promoting (somatotropic, phyrone). — Regu-
lates growth; deficiency in children results in dwarfs or
midgets (usually well developed physically and men-
tally) ; excess secretion results in giants; oversecretion
in adults results in acromegaly (enlarged facial fea-
tures with long, broad jaws, and enlarged cheek bones,
large barrel chest, enlarged joints of feet and hands)

2. Diabetogenic (anti-insulin hormone) — Increases blood
sugar (effects opposite to those of insulin)

3. Ketogenic (fat metabolism hormone) — Controls fat
metabolism and increases fat in liver

4. Thyrotropic — Stimulates thyroid gland

5. Adrenotropic (adrenocorticotropic or ACTH) — Stim-
ulates cortex of adrenals to function normally

6. Pancreotropic — Stimulates pancreas

7. Parathyrotropic — Stimulates parathyroids

8. Prolactin (lactogenic) — Necessary for lactation (milk
production) by mammary glands

9. Follicle-stimulating (F. S. H., Gonadotropic) — Con-
trols growth of egg-bearing follicle in the female
ovary; formation of sperm in seminiferous tubules of
male testes

10. Luteinizing (L. H.) — Necessary for forming corpus
luteum by ruptering follicle and liberating the egg and
for forming male sex hormone by interstitial cells of
testes

POSTERIOR LOBE

Pituitrin which probably contains the following hormones:

1. Pitressin (pressor hortnone) — Increases blood pressure
by contracting muscles of smaller arteries

2. Pitocin (Oxytocic) — Influences contraction of smooth
muscles of uterus, particularly during childbirth

3. Gastrotropic — Controls secretions of stoinach possibly
by altering blood supply

4. Galactogenic — Increase milk flow possibly by acting on
smooth muscles of mammary glands

5. Antidiuretic — Diminishes quantity of urine possibly by
increased reabsorption of water from kidney tubules

INTERMEDIATE LOBE
1. Intermedin — May affect metabolism in man; intensifies
skin color of lower vertebrates by affecting color-bearing
chromatophores

Biology of Man 511

Summary of Endocrine (Ductless) Glands — Cont'd

ENDOCRINE
GLAND

HORMONES AND FUNCTIONS

THYROID

(thi'-roid) (Gr.
thyreos, shield;
eidos, resemble)

. PARATHY-
ROIDS

(para -thi' roid)
(Gr. para, beside;
thyroid)

ADRENALS

(ad -re' nal) (L.
ad, to; renes, kid-
ney)
SUPRARENALS

5. PANCREAS

(pan' kreas)
(Gr. pan, all;
kreas, flesh)

Thyroxin (thyroglobulin) — Controls rate of basal metab-
olism and normal body growth
A. HYPERTHYROIDISM (OVERACTIVITY OF
NORMAL-SIZED GLAND OR INCREASED
GLAND)
1. Exophthabnic Goiter — thyroid may be enlarged with
such symptoms as increased heartbeat, nervousness and
restlessness, often protruding eyeballs, increased heat
production and perspiration, increased blood pressure,
muscular weakness, and tremors
B. HYPOTHYROIDISM (UNDERACTIVITY)

1. Simple goiter — thyroid may be enlarged (not always)
and thyroxin deficient because of lack of iodine; symp-
toms may resemble somewhat those of mild myxedema

2. Myxedema — Deficiency of thyroxin in adult may result
in lowered metabolism and heat production, slow pulse,
physical and mental lethargy; appetite usually normal
with tendency to obesity; dry, waxy, puffy skin because
of increased mucus beneath it; dry hair usually falls
out.

3. Cretinism — Insufficient hormone during early life may
result in improper development, physically, mentally,
and sexually.

1. Parathormone (parathyrin) — regulates calcium and
phosphorus metabolism; proper amount necessary for
normal bone development; too little parathormone
lowers blood calcium and increases irritability of nerves
and muscles; too much withdraws calcium from bones
(soft bones) ; complete removal of parathyroids results
in tetany or quick death (tremors and convulsions due
to increased irritability of muscles and nerves because
of lack of calcium)

CORTEX (OUTER LAYER)

1. Cortin (probably several hormones? ) — Influences
growth excretion, sugar metabolism, water balance,
sodium, potassium, and chloride balance, normal sexual
functioning; cortin deficiency in man may cause Addi-
son's disease (bronzed skin, decreased heart action and
blood pressure, muscular weakness, digestive upsets)
MEDULLA (INNER PORTION)

1. Adrenalin (adrenin, epinephrine) — Increases glucose
(sugar) of blood, heart rate, and blood pressure; in
emotional stress the increased secretion may result in
increased blood pressure and heart action, increased
glucose production by the liver, increased saliva secre-
tion, dilation of eye pupil, increased rate of blood co-
agulation, paleness of skin because arteries in it decrease
in size

Produced by the Islands of Langerhans:

1. Insulin — Regulates glucose (sugar) metabolism and
decreases blood sugar; deficiency causes sugar diabetes
(excess sugar in blood and urine)

2. Lipocaic — Regulates fat metabolism in liver

512 Animal Biology

Summary of Endocrine (Ductless) Glands — Cont'd

ENDOCRINE
GLAND

HORMONES AND FUNCTIONS

6. TESTES

(tes'tes) (L.
testis J testicle)

Produced by interstitial cells of testes:

1. Testosterone — Controls development of secondary sex-
ual traits (hair growth on face and body; affects voice;
develops size of pelvis; controls muscular development) ;
may influence sex behavior

2. Androsterone (androgen) — Influences development of
secondary sexual traits

7. OVARIES

(o'vari) (L.
ovarium, ovary)

PRODUCED BY FOLLICLE

1. Estrone (estrin, theelin) — Controls development of sec-
ondary sexual traits; growth of pubic hair; broadening
of pelvis; dev^elopment of uterus and vagina; change
of voice; initiates development of mammary glands;
controls onset of menstrual cycle.

PRODUCED BY CORPUS LUTEUM

1. Progesterone (progestin, corporin, lutin) — Influences
increased development of mammary glands, uterus and
placenta during pregnancy; regulates menstrual cycle;
prevents menstruation and formation of more follicles
during pregnancy; sensitizes uterus wall for implanting
fertihzed egg on it

2. Relaxin — -Relaxes the pelvic ligaments during labor of
childbirth (parturition)

8. PLACENTA

(pla -sen' ta)
(L. placenta,
flat cake)

1. Estrogen — Influences development of secondary sexual
female traits (eflfects similar to those of estrone)

2. Emmenin — May stimulate estrone production in ovary

3. APL (anterior pituitary-like) — Influences ovaries; may
influence development of fetal sex organs, especially
descent of testes from abdomen to scrotum

9. STOMACH
(stum' ak) (Gr.
stomachos, gullet)

1. Gastrin — Stimulates certain stomach cells to secrete
gastric juice for digestion

10. DUODENUM
(of small intes-
tine) (duo-de'-
num) (L. duo-
deni, twelve)

1. Secretin — stimulates pancreas to secrete pancreatic juice
for digestion

2. Enterocrinin — stimulates cells of duodenum to secrete
intestinal juice (succus entericus)

3. Enterogasterone — diminishes movements of stomach
under influence of fats

4. Cholecystokinin — Causes gall bladder to empty into in-
testine

11. THYMUS

(thi'mus) (Gr.
thymos, thymus)

No specific hormone has been isolated, but it is suggested
that it may retard sexual development in early life;
may produce lymphocytes

12. PINEAL or
EPIPHYSIS
(pin' e al)
(e -pif i sis)
(L. pineus, pine
cone) (Gr. epi,
upon ; phyein, to
errow )

No specific hormone has been isolated but it is thought
that growth may be influenced by it

13. LIVER

(A.S. lifer, liver)

An unknown hormone may stimulate the bone marrow to
produce erythrocytes (as in anemia)

Biology of Man 513

13. Liver. — Composed of four lobes located just beneath the dia-
phragm; an unknown hormone may stimulate the bone marrow to form
erythrocytes.

The great complexity and interdependence of the various parts of the
endocrine system may be observed from the following summary in which
some of the more important functions are given with some of the par-
ticipating hormones listed:

Digestion — Gastrin (stomach) ; secretin, enterocrinin, enterogasterone, cholecys-
tokinin (intestine); gastroscopic, pancreotropic (pituitary)

Sugar metabolism — Insulin (pancreas) ; adrenalin, cortin (adrenals) ; diabetogenic
(pituitary)

Fat metabolism — Ketogenic (pituitary) ; lipocaic (pancreas)

Calcium and phosphorus metabolism — Parathormone (parathyroids)

Sodium and potassium metabolism — Cortin (adrenal)

General metabolism — Thyroxin (thyroid) ; cortin (adrenal)

Excretion — Cortin (adrenal) ; antidiuretic (pituitary)

Growth regulation — Thyroxin (thyroid) ; growth-promoting (pituitary) ; cortin
(adrenal) ; possibly thymus and pineal?

Sexual characters and reproduction — Testosterone, androsterone (testes) ; estrone,
progesterone, relaxin (ovaries) ; follicle-stimulating, luteinizing, prolactin,
galactogenic (pituitary) ; estrogen, emmenin, anterior pituitary-like (placenta) ;
cortin (adrenals)

X. HUMAN REPRODUCTION AND DEVELOPMENT

The stages in human reproduction and development are somewhat
similar to those of other higher vertebrates but, as might be expected,
there are differences depending upon the species (Figs. 363 to 366).
Many of the early stages of various vertebrates are so similar that it is
difficult to distinguish them (Fig. 363). The stages in the embryologic
development of a frog and of man are described somewhat in detail in
Chapter 24.

The human male reproductive system (Fig. 254) consists of (1) a
pair of testes suspended in the scrotum, (2) numerous vasa efferentia
which lead into a single, highly convoluted collecting tubule, the two con-
stituting the epididymis which is attached to each testis, (3) the pair
of vasa deferentia (singular, vas deferens) or sperm ducts which lead
from the collecting tubules to the pair of saclike seminal vesicles, just
behind the bladder; (4) the small prostate gland surrounding the urethra
and ejaculatory ducts, (5) the ejaculatory ducts leading from the semi-
nal vesicles to the single tubular urethra which leads to the outside, and
(6) the pair of small Cow per' s glands posterior to the urethra and con-
nected to it by a pair of small ducts.

514 Animal Biology

The testes contain many seminiferous tubules which produce sperm
(spermatozoa) by a proHferation of the spermatogonia cells (Fig. 351)
which line the tubules. The number of sperm discharged at one time
may be about two hundred million suspended in a small amount of
seminal fluid (semen). The latter is secreted by the seminiferous tubules,
epididymis, vas deferens, and primarily by the prostate and Cowper's
gland. The sperm is extremely small and has a globular head with a
nucleus, a neck, and a slender tail of cytoplasm (Fig. 223) .

Ureters

.Bladder

Fig. 254. — Reproductive organs of human (male)

diagrammatic.

Seminal vesicle

Prostate gland
Cowper's gland

Vas deferens
Urethra

Epididymis

Teistis

Scrotum
Side view and somewhat

The human female reproductive system (Fig. 255) consists of (1) the
pair of oval ovaries in the lower abdominal cavity and (2) the pair of
Fallopian tubes (oviducts) the anterior ends of w^hich are funnel shaped
and lie near the ovary; the anterior opening of the tubes is the ostium
(infundibulum) which picks up the ovum (egg) (Fig. 223) produced
and liberated by the ovary; the Fallopian tubes carry the ovum to the
pouchlike uterus in which the embryo develops; (3) the vagina which
connects the uterus with the exterior. The walls of the uterus contain
smooth muscles which contract vigorously under certain conditions, such
as childbirth. The inner lining of the uterus, called the endometrium,

Biology of Man 515

is a heavy, mucous, glandular layer to which the fertilized ovum may
adhere. The uterus is well supplied with blood vessels for the nourish-
ment of the future embryo.

With the onset of sexual maturity (puberty) the female begins to ovu-
late (produce and mature an ovum in the ovary). The production and
maturation of the ovum are illustrated in Fig. 351. The ovum is ripened
within the ovary and released into the Fallopian tube where it may be
fertilized by a male sperm, or die if not fertilized. The sperm have been
deposited in the vagina during copulation and have moved up the Fallo-
pian tubes. Each developing ovum in the ovary is contained within a

Tube

Ovary

Round
ligament

Fundus

Ovary

Uterine
tube

Ovarian
artery

broad
llgameul

Vagina

Uterine
cavity

Ureter

Uterine
artery

Fig. 255. — Human female reproductive organs showing the uterus, ovaries, and
associated organs. The left half shows posterior (back) view and right half a
diagrammatic section. The ovary reveals several internal follicles in which the
ova (eggs) are formed. The uterine tube is also called the Fallopian tube.
The outer, funnel-shaped end of the Fallopian tube (near the ovaries) opens into
the body cavity. The round and broad ligaments give the tubes and ovaries sup-
port. (From Pitzman: Fundamentals of Human Anatomy).

Graafian follicle which in later stages of its development occupies
a position near the surface of the ovary, appearing there as a small bump.
In fact, an ovary may possess several Graafian follicles in various stages
of development at the same time. When the ovum is mature, the follicle
ruptures the wall of the ovary and deposits the ovum in the coelom (body
cavity) from which it passes into the Fallopian tube. Most of the Gra-

516 Animal Biology

afian follicle cells remaining in the ovary organize themselves into a yel-
lowish ductless gland called the corpus luteum (L. luteolus, yellowish),
which is described in a summary of endocrine glands earlier in this chap-
ter. If the ovum is not fertilized, the corpus luteum degenerates. The
human ovum is very small (0.15 mm. in diameter) because of a minimum
of food (yolk). Consequently, the developing embryo must have nour-
ishment from the mother. The ovum while in the upper part of the
Fallopian tube produces a small, nonfertilizable polar body (polocyte)
(Fig. 351) and a second polar body after fertilization. Ovulation occurs
at regular periodic intervals and the series of interrelated phenomena,
including the preparation of the uterus for the implantation of the fer-
tilized ovum, is called the estrous cycle. The estrous cycle in the human
female occurs more or less within twenty-eight days but may be altered
by mental shocks, psychic disturbances, worry, physical illness, climatic
changes, etc. If fertilization does not occur, the superficial mucous layer
of the uterus is shed and accompanied by rupturing of blood vessels (hem-
orrhage). This ends in menstruation in which tissues and blood leave
the uterus through the vagina.

A study of the development of a human being will reveal (as in many
other animals) numerous vestigial (rudimentary) organs which are re-
duced in size and are without appreciable use at present, although they
may have been larger and functional in the past. Many of them seem
to be in the process of disappearing, having served their period of useful-
ness. Over one hundred vestis:ial structures and ors^ans occur in the
human body, among the more common being ( 1 ) vermiform appendix,
(2) special muscles to move the ears, (3) lobe at the bottom of the ear,
(4) point ("Darwin's point") at inner curled ridge of the upper margin
of the ear, (5) whitish nictitating membrane (third eyelid) in inner angle
of the eye, (6) third molars ("wisdom teeth"), (7) hair on body, (8)
special patterns or arrangements of hair on various parts of the body,
(9) small muscles to erect body hair, (10) mammary glands in male,
(11) segmented muscles of abdominal wall, (12) caudal (tail) vertebrae
called the coccyx. Many of the vestigial structures of man have their
homologous structures in related lower organisms in which cases they
are functional. This is evidence that organisms have changed struc-
turally and functionally; in other words, have evolved.

XI. DISEASES OF MAN

Disease may be defined as an abnormal or pathologic condition of any
part of the body or mind. Diseases may be classified as (1) infectious, or

Biology of Man 517

those due to the presence of living organisms or their products, and (2)
noninfectious (organic), or those due to a variety of causes other than
living organisms. Infectious diseases may be classed as ( 1 ) communica-
ble, or those transmitted naturally from one person to another and (2)
none om,m,unic able , or those not contracted from another infected in-
dividual. Hence, pneumonia, tuberculosis, etc., are infectious, com-
municable diseases, while tetanus (lockjaw) is an infectious, noncom-
municable disease. Sometimes the less desirable term, contagious, is
applied to infectious diseases which are transmitted by direct contact
("catching"). Satisfactory progress has been made in this country
against the infectious diseases, as is shown by the mortality (death) and
morbidity (sick) rates. The noninfectious diseases include a wide variety
of abnormal conditions of body and mind caused by an even greater
variety of causes. Some of them such as pellagra, scurvy, etc. (discussed
elsewhere) are grouped as vitamin deficiency diseases; others are due to
chemical poisons; still others (sunstroke, concussions, frostbite, lacera-
tions, etc.) are due to physical agents; and still others, such as Bright's
disease (kidneys), cerebral hemorrhage, various types of heart diseases,
psychosis, and imbecility, are due to derangement of tissues. Upon the
basis of speed, diseases may be classed as (1) acute (sudden onset and a
short period of rather severe illness with subsequent recovery or death)
and (2) chronic (Gr. chronos, time) (gradual onset of symptoms and
prolonged illness) .

The various types of living organisms which may cause infectious dis-
eases in man are bacteria, yeasts, molds, pathogenic protozoa, parasitic
worms, ticks, mites, etc. Before an infection can occur, certain condi-
tions must be fulfilled : ( 1 ) the living organisms must enter the body
in sufficient numbers, (2) they must enter the body through the right
channels, (3) they must maintain themselves in sufficient numbers to
cause the disease, (4) the body being entered must be susceptible to the
actions of the living organisms, and. (5) the invading organisms must
be sufficiently virulent or potent to produce the disease.

Numerous discussions and examples of infectious diseases caused by
bacteria, yeasts, molds, pathogenic protozoa, parasitic worms, viruses,
etc., are given in various parts of this book, to which the reader should
refer.

Since earliest times man has been afflicted by diseases and has theorized
as to their causes. The follov\'ing, by no means a complete list, will suf-
fice: (1) Demonic theory — the earliest primitive peoples believed that
disease was due to evil spirits or demons. Consequently, they tried to

518 Animal Biology

prevent, treat, and cure diseases by scaring the demons by terrifying
noises, using vile-tasting or -smelling medicines, by exorcising the demon,
by wearing charms, etc. (2) Humoral theory of Hippocrates (460-395
B.C.) in which the body was thought to consist of four humors: blood,
phlegm, black bile, and yellow bile. Disease was thought to ensue if too
much or too little of one or another were present. Bloodletting was a
common curative procedure. (3) Pythogenic theory of Murchison in
which this Englishman, of about one hundred years ago, contended that
diseases were due to dirt and filth. (4) Germ theory in which diseases
were considered to be caused by minute organisms. Many individuals
contributed their bit to this theory as the following will show: Leeuwen-
hoek (1632-1723) studied microorganisms with his crude microscope;
Fracastorius, in 1546, suggested that infectious diseases were due to a
living contagion; Plenciz, in 1764, theorized that each disease was caused
by a specific microbe; Davaine, in 1850, proved that anthrax of cattle
was due to rodlike organisms; Pasteur, in 1865, showed that the silk-
worm disease (pebrine) was due to protozoa; the German country doctor,
Robert Koch (1843-1910), perfected many techniques in bacteriology
and proved that the cause of tuberculosis is a bacterium, known today as
Mycobacterium, tuberculosis.

The mere presence of microorganisms in air, food, milk, and water is
not sufficient to produce a disease in all instances. As stated above, cer-
tain conditions must be fulfilled before an infectious disease will develop.
Among the most important deterrents to disease production in man are
the various body defenses, as the following will show :

1. Defenses (First line). — Skin — acting as a mechanical barrier; nose
— mucus collecting the organisms, cilia moving them toward the exterior,
the enzyme lysozyme destroying bacteria, sneezing, coughing; eyes —
washing organisms away mechanically by tears which also contain the
enzyme lysozyme; m,outh — mucous membrane acting as a mechanical
barrier; stomach — acid of gastric juice; intestine — mucous membrane
acting as a mechanical barrier, antagonistic action of other organisms
within the intestine; urethra — action of urine.

2. Defenses (Second line). — (1) The production of inflammations in
which many of the organisms which have penetrated the deeper tissues
are trapped and destroyed (inflammations are usually characterized by
redness and swelling due to increased supplies of blood; temperature,
due to increased metabolic activity in the area; pain, due to the ab-
normal activities; pus formation in later stages due to the destruction of
microorganisms and tissues) ; (2) phagocytic action of certain white blood

Biology of Man 519

corpuscles in which the phagocytic cells engulf and destroy microorgan-
isms in the various body tissues, in the blood stream, in lymph nodes, and
in the phagocytic cells which line the capillaries of the liver and spleen.

3. Defenses (Third line). — Other defensive reactions of the body
which depend upon previous or present contact with the infectious or-
ganisms are known as immu7iologic reactions. When infectious organ-
isms or their poisons penetrate to the deeper tissues, the body may be
stimulated to produce a series of substances which have the ability to
destroy or inactivate the organisms and to neutralize their toxic products.
These reactions are concerned with ridding the body of foreign proteins
which have been brought in by the invading organisms or through some
channel which is an unnatural method of entrance for that protein.
These reactions manifest themselves only under certain conditions and
only as a specific response to a specific protein. These reactions can, in
a general way, be illustrated by the introduction of egg proteins or simi-
lar foreign proteins. If egg protein is introduced into the digestive tract
it is digested and used in the natural building of protein substances in
the body. However, if this egg protein is injected directly into the blood
system, or in some other unnatural manner, the egg protein stimulates
the body to form a specific substance which will react specifically with
the egg protein. These specific substances appear in the blood stream
and are known as antibodies. The proteins which stimulate their for-
mation by the body are called antigens. For example, the foreign pro-
tein material of diphtheria toxin serves as the antigen to stimulate the
body to produce the specific antibody known as diphtheria antitoxin.
When the latter contacts diphtheria toxin, it neutralizes it, thus defend-
ing the body.

Some of the more common antibodies may be described briefly as
follows :

1. Antitoxins, which are substances which neutralize specific toxins
in an animal body or even in a test tube. They are formed only in an
animal body in direct response to toxins produced by bacteria, plants,
or animals; they are protein in nature and are aflPected by heat; they are
specific in their action; i.e., diphtheria antitoxin reacts only with diph-
theria toxin, and not with the toxins of tetanus, scarlet fever, gas gan-
grene, etc.

2. Agglutinins, which are antibodies that agglutinate (clump) the
specific organisms which acted as antigens in their formation in a body.
The agglutination may occur in the body (hence, defend it) or outside
where it can be used for identifying specific organisms, for diagnosis of

520 Animal Biology

certain diseases, etc. For example, if the blood serum of an animal im-
munized against typhoid organisms is mixed with a suspension of typhoid
organisms, the latter are agglutinated. The blood serum from a person
who has recovered from typhoid will likewise agglutinate typhoid organ-
isms but not other organisms even though they are closely related to
them.

3. Precipitins^ which are antibodies with the power to precipitate
(settle out) foreign proteins against which they have been formed. After
precipitation the foreign proteins may be phagocytized in the body. Be-
cause precipitins are so specific, they are utilized in identifying specific
proteins of various organisms and in establishing the parentage of oflF-
spring in certain medicolegal cases.

4. Bacteriolysins, which are antibodies which kill and dissolve the spe-
cific organisms which have stimulated the body cells to produce them.
Immune blood sera containing these specific antibodies are commonly
called antibacterial sera rather than antitoxin sera.

5. Opsonins, meaning "to prepare food for," which are antibodies
which prepare bacteria so that they are more readily destroyed by the
phagocytes. The numerous opsonins are specific and act on only one
species of organism. The measurement of the opsonin content of blood
serum is known as the opsonic index.

6. Antiaggressins — many bacteria secrete substances called aggressins
which repel or kill leucocytes. The body responds by forming an anti-
aggressin to neutralize the aggressin thus protecting the leucocytes.

7. Complement and amboceptor — normal blood serum contains a sub-
stance called complement; immune serum contains other substances
called amboceptors, which are specific for the antigen which has stimu-
lated the body to form them. The two substances together aid in the
destruction of invading pathogenic bacteria.

A phenomenon closely allied to antibody formation is known as hyper-
sensitivity, which is a state of a body which shows increased reaction to
a subsequent introduction of substances which provoked little or no
reaction when first introduced. Excessive and severe hypersensitivity in
animals and man is designated as anaphylaxis (meaning, "against pro-
tection," in contrast to prophylaxis which means "protection" or "pre-
vention"). Allergy (Fig. 256) ("altered reaction") is applied to milder
types of hypersensitivities in man. Some of the more common types
of allergies are ( 1 ) those due to inhaling such protein antigens as pollens
and dusts from animal hair, causing hay fevers, and certain types of
asthma, (2) those due to ingesting certain foods, such as milk, straw-

Biology of Man 521

Fig. 256. — Forty-eight causes of allergic reactions. (Courtesy of Lederle Labora-
tories.)

522 Animal Biology

berries, clams, eggs, sauerkraut, or certain drugs, (3) those due to con-
tacting the skin with wool, silk, feathers, etc. About 10 per cent of our
population suffers from some type of allergy which may be characterized
by such symptoms as gastrointestinal disturbances, respiratory disturb-
ances, skin eruptions, and even migraine headaches. Nonprotein allergies
may be Illustrated by formaldehyde, Iodine, aspirin, and certain sulfon-
amide drugs.

Immunity in general may be considered as (1) natural or (2) acquired.
Natural immunity Is an Innate characteristic w^hlch Is determined genet-
ically and does not depend upon the reactions of the body when in con-
tact with an Infectious organism. It may be influenced by malnutrition,
fatigue, decreased temperature, certain anatomic structures, and certain
physiologic reactions and varies with the individual. Man and cattle
are naturally Immune to hog cholera. Acquired immunity is not Inherent
in the protoplasm of that species but must be acquired either actively or
passively. Immunity may be acquired actively by (1) having the dis-
ease, (2) being exposed repeatedly to quantities of the germ which are
not sufficient to produce the disease, (3) being treated by the products of
organisms. Immunity may be acquired passively by the administration
of immune sera which contain the proper antibodies that the patient has
had no part in actively producing. An advantage of passive immuniza-
tion Is the speed of protection, while its disadvantage is that it lasts only
a short time.

XII. INHERITANCE OF HUMAN TRAITS

Much Information regarding the inheritance of certain human traits
has been secured in recent years by a study of lower animals as well as
by the scientific study of human families. From these studies it is ap-
parent that many human traits are inherited according to Mendel's laws
just as are many of the traits of other animals and plants. Heredity of
plants and animals. Including man, is considered In Chapter 34. It will
be noted that some traits are not Inherited as simple Mendellan traits
but are due to sex-linked, blended, or multiple-gene Inheritances. One
of the most valuable methods of studvlns^ human inheritance is the scien-
tific assembling of accurate data In the form of "family trees" (Figs.
352 to 356). The correct interpretation of these data has contributed
much to our knowledge of the methods of inheritance of specific human
traits. Much is still unknown about certain traits, but additional Infor-
mation is constantly being added. Some of the difficulties encountered

Biology of Man 523

in the scientific study of human inheritance are: (1) the impossibility
of securing complete and reliable data over a sufficient number of gen-
erations, (2) the great difficulty of securing reliable and complete data
for all members of the family being studied, (3) the impossibility of the
scientific observer to collect all the data firsthand and the frequent un-
reliability of data supplied by others who are insufficiently trained in
heredity, (4) the small size of many families which does not always give
a complete picture of the particular inheritance being studied, (5) the
inability to cross or breed experimentally as has been done so profitably
in lower organisms, and (6) the great length of time required for, let
us say, three consecutive generations to display what they have inherited.
In spite of these difficulties, much progress has been, and is being, made.
This explains why it is unknown whether certain traits are inherited and
why there is still a difference of opinion as to the exact method of in-
heritance of certain human traits.

It is known that there is a continuity of germ plasm (Figs. 350 and
351) connecting the individuals of all generations, and through which
traits are transmitted to future generations. Body cells (somatic cells)
with their traits develop from these germ cells with their germ plasm.
The development of human traits depends upon the presence of specific
genes within the chromatin materials of the germ plasm and the develop-
ment of these genes in the proper environments as the body grows. Pos-
sibly the cytoplasm of these cells plays a greater role in inheritance than
we have surmised in the past. Human heredity studies have usually
concerned themselves with the more obvious traits (such as eye color,
hair color, hair consistency, skin color), or certain abnormal traits (such
as webbed toes, psychosis, etc. ) , but in all probability the more common
traits (such as stomach, liver, intestines, etc) also have a structural and
functional inheritance. Is it not possible that there is a typical Smith-
family- type of stomach or a Jones-faniily-type of intestine? Because
they have been considered to be of secondary importance such traits have
not been generally studied. Infectious diseases are not believed to be
inherited, as such, because the transmission of the causal agents for
such diseases in the germ plasm would seriously affect or prevent the
formation of the offspring. However, predisposing tendencies for cer-
tain diseases may be transmitted. Certain conditions have erroneously
been thought to be inherited, when, as a matter of fact, they have been
acquired by the offspring before or after birth.

The average person is interested primarily in whether a certain hu-
man trait is inherited and how. Many human traits are considered in

524 Animal Biology

Chapter 34 (Heredity-Genetics) (Figs. 347 and 352 to 356). The reader
is warned not to jump at erroneous conclusions in his attempt to inter-
pret the inheritance of some of his own traits or those of famihes with
which he is more or less familiar. Careful interpretations by experienced
geneticists should be followed rather than depending upon our own
limited knowledge.

Some of the most important data in human heredity are concerned
with the inheritance of specific blood groups. It is known that blood
from certain individuals when mixed frequently results in an agglutina-
tion (clumping) of the red blood corpuscles. Four types of human blood
are known as Groups A, B, AB, and O. Agglutination occurs when
certain groups are mixed and not when others are mixed. Agglutination
of human blood depends upon the presence of ( 1 ) the specific substance
known as the agglutinogen (a type of antigen) in the red blood corpus-
cles and (2) the specific substance known as the agglutinin (a type of
antibody) in the blood plasma. Both of these are necessary for a blood to
agglutinate, so naturally both cannot occur in the same person or his
blood would agglutinate in his blood vessels. The two inheritable ag-
glutinogens are known as A and B in man. Hence the following human
blood groups are possible: An individual of group A has agglutinogen
A in his red blood corpuscles; group B has agglutinogen B; group AB has
both agglutinogens A and B; group O has neither agglutinogen. Which-
ever agglutinogen an individual has in his red blood corpuscles, the cor-
responding agglutinin (antibody) is absent in his blood plasma. When
an agglutinogen is absent in his erythrocytes, the corresponding agglutinin
is present in his plasma. A summary of the blood groups, their agglutino-
gens, agglutinins, etc., is given in the following table:

Human Blood Groups

MAY

PER CENT OF THE

AGGLUTIXOGEN

AGGLUTININ

RECEIVE

WHITE POPULATION OF

(antigen) in

(antibody)

BLOOD

MAY GIVE

THE UNITED STATES

BLOOD

RED BLOOD

IN BLOOD

FROM

BLOOD TO

REPRESENTED BY EACH

GROUP

CORPUSCLES

PLASMA

GROUP

BLOOD GROUP

None

a and b

O, A, B,
AB

O, A

A, AB

B, AB

O, B

A and B

None

O, A, B,
AB

Persons of type O are often called "universal donors" because their blood
may be given safely without agglutination to any other person; persons of

Biology of Man 525

type AB are known as "universal recipients" because they can receive
blood from any type.

Additional agglutinogens, known as M and N, have been found in
human erythrocytes, but no corresponding agglutinins are reported.
These M and N agglutinogens are inherited independently of the pre-
vious groups and are useful in identifying bloods but need not be con-
sidered in blood transfusions.

A third type of agglutinogen is known as the Rh factor because it
was first discovered in the blood of the Rhesus monkey. The erythro-
cytes in about 85 per cent of the white people contain Rh agglutinogen;
hence such persons are Rh positive; the remaining 15 per cent are Rh
negative. Under normal conditions no agglutinin (antibody) is present
in the blood plasma to react with the Rh agglutinogen. However, if
an Rh-negative (Rh— ) person receives Rh-positive (Rh+) blood by
transfusion, there will be formed in the plasma of the recipient some
Rh-positive agglutinins (anti-Rh-positive antibodies). When this re-
cepient receives a second quantity of Rh-positive blood, the previously
formed Rh-positive agglutinins will react with the Rh-positive agglutino-
gens (of second transfusion) with serious reactions. The Rh-positive
agglutinogen was at first thought to be inherited as a dominant factor,
but recent studies suggest that instead of just two types (Rh-positive and
Rh-negative) there are eight or more alleles which may result in many
genetically different combinations.

In human pregnancies, a Rh-negative mother and a Rh-positive fa-
ther may have a Rh-positive offspring (inherited from its father). The
Rh-positive factor of the embryo while in the mother may pass by blood
through the placenta to stimulate the mother to produce Rh-positive
agglutinins (antibodies). If the same two parents conceive a second
child, the mother may pass some of her Rh-positive factor through the
placenta to this second Rh-positive child and the reactions may cause
destruction of erythrocytes in the latter. If extreme, the embryo may
die prenatally (anemia) or it may die postnatally, but if not serious the
infant may recover.

The inheritance of the type of blood (O, A, B, or AB) is due to a series
of alleles (genes) : allele A produces agglutinogen A; allele A^ produces
agglutinogen B; allele a produces no agglutinogen, and the latter is re-
cessive to the other two. Neither gene A nor A^ is dominant to the other.
When both A and A^ are present, an individual of the AB group results.
Blood types are inherited specifically and do not change; hence, blood
tests may be used in certain cases of disputed parentage. These blood

526 Animal Biology

tests cannot prove that a certain man is the father of that particular oflf-
spring but only whether he could be the father. This means that a cer-
tain offspring might have been produced by any one of a number of in-
dividuals belonging to certain different blood groups. In other instances
a certain child with a specific blood group could not have been produced
by certain individuals of other definite blood groups. Information se-
cured from types of blood is helpful in ascertaining certain racial and
national information as well as in certain legal cases.

XIII. IMPROVEMENT OF THE HUMAN RACE— EUGENICS

The human race has only recently become interested in the scientific
improvement of the members of which it is composed, in spite of the
fact that men have for a long time attempted to create and maintain
better and better types of plants and other animals. The individual
member can be improved by bettering their environment, thereby per-
mitting that which they have inherited (physically and mentally) to
develop as far as possible. If all members of the race develop what they
have inherited to a maximum, the race as a whole is benefited. How-
ever, it must be clearly understood that such benefits are purely tempo-
rary and do not improve the hereditary genes or factors of the indi-
viduals when these genes are transmitted to future generations. In
other words, this temporary improvement in developed characteristics
does not take the place of real improvement of the heredity mechanism.
Man has attempted to improve the human race by preventing those with
extremely undesirable mental or physical traits from propagating their
kind. One procedure has been the segregation in institutions of those
with undesirable traits, but the trouble has been that there are more
afflicted than can be accommodated in our present institutions. Pres-
sure has also been applied to release individuals who are lightly afflicted
but who are potentially undesirable from a heredity standpoint. In some
cases the afflicted have been protected in institutions until they are ma-
ture. They are then released to propogate their kind. Add to this the
fact that the rate of reproduction of mentally deficient couples is about
twice that of couples with high mentality.

Another procedure now legalized in many states is sterilization of cer-
tain classes of defectives of both sexes in such a way that reproduction
of defective offspring is impossible, though the normal sexual relations
of the married state are in no way affected. In each sex the method is
simply to cut the ducts leading from the sex organs so that sex cells can-

Biology of Man 527

not pass. Careful and scientific study of the results of legalized and con-
trolled sterilization in various states has indicated favorable progress.
Wars of the past which have claimed many of our best youths have robbed
us of countless good prospective parents of future offspring. It is also
known that the number of children produced by parents possessing in-
ferior traits is far greater than the number produced by superior parents.
In a short time the entire race will be affected by this rapid increase in
the less desirable traits. Every possible measure should be taken to in-
crease the birth rate among the better endowed families rather than let
it continue to decrease as at present. Every possible measure should be
taken to reduce as far as possible the birth rate of undesirable parents.
More of the better types of offspring, fewer of the poorer types, together
with the best of environments (educational, religious, home, recreational,
occupational, etc.) in which the inherited materials can develop, will
improve mankind.

QUESTIONS AND TOPICS

1. List the systems of the human body with the important general functions of
each.

2. Explain the phenomenon of cellular differentiation and its effects in the hu-
man body.

3. Explain why the human skin is sometimes spoken of as "the jack of all
trades." Describe the anatomy of the skin layers and the functions of each.

4. Explain the origin of (1) teeth, (2) nails, (3) sebaceous glands, and (4)
hair.

5. Explain why there are more men afflicted with inheritable baldness than
women.

6. Describe the process of heat production, distribution, equalization, and elimi-
nation in the human body.

7. Contrast human and frog skins, giving differences in structure and functions.

8. Describe each of the embryologic origins of bones, with an example of each.

9. Compare and contrast the three types of muscle tissues in as many ways as
possible from a structural and functional standpoint.

10. List several methods used in naming skeletal muscles.

11. Define the following terms as applied to muscles: origin, insertion, voluntary,
involuntary, abductor, adductor, striated, and nonstriated (smooth).

12. Explain in detail the physiologic process of digestion of various foods in man.

13. Explain why all substances in nature are not desirable for human foods.

14. Explain specifically why we cannot inhale air and swallow food at the same
time.

15. List the properties, common sources, and effects produced by each of the more
common vitamins.

16. List the chemical formula for each vitamin, commenting on the similarity or
dissimilarity of the various formulae. What does this mean ?

528 Animal Biology

17. Beginning at a certain point, trace the complete human circulation (naming
all structures in proper sequence) back to the starting point.

18. Contrast in as many ways as possible from a structural and functional stand-
point (1) arteries, (2) veins, (3) capillaries, and (4) lymph vessels.

19. Classify human blood corpuscles, giving the anatomy and physiology of each.

20. Explain in detail the theory regarding the clotting of human blood.

21. Describe in detail (1) external respiration and (2) internal respiration.

22. Classify human wastes, telling specifically how and where each is eliminated.

23. Explain coordination in man by (1) nervous system and (2) chemical sub-
stances.

24. Describe the structure and function of ( 1 ) the various kinds of receptors,
(2) the various kinds of effectors, and (3) the different types of conductors.

25. Explain in detail the theory regarding the initiation and conduction of nerve
impulses.

26. List the more important structural and functional characteristics of the parts
of the human nervous system.

27. Describe the structure and important functions of each endocrine gland.

28. Explain the process of human reproduction, including the formation of sperm
and egg and the stages of embryologic development.

29. List several vestigial structures in man and give their significance.

30. Classify human diseases and describe the various body defenses against infec-
tious diseases.

31. Briefly describe some of the earlier theories of human diseases.

32. Give characteristics and functions of the important antibodies in man.

33. Explain the method of inheritance of such human traits as the instructor may
suggest.

34. If you know the blood group of each of your parents, give all the possible
blood group types in your family.

35. Discuss each of the methods for human race improvement, including the effec-
tiveness of each method.

SELECTED REFERENCES

Amberson and Smith: Outline of Physiology, F. S. Crofts & Co.

Anthony: Textbook of Anatomy and Physiology, The C. V. Mosby Co.

Best and Taylor: The Living Body, Henry Holt & Co., Inc.

Carlson and Johnson: The Machinery of the Human Body, University of Chi-
cago Press.

Clendening: The Human Body, Alfred A. Knopf, Inc.

Cowdry: Human Biology and Racial Welfare, Paul B. Hoeber, Inc.

Davenport: How We Came by Our Bodies, Henry Holt & Co., Inc.

Dorsey: Why We Behave Like Human Beings, Harper & Brothers.

Edwards: Concise Anatomy, The Blakiston Co.

Francis and Knowlton: Textbook of Anatomy and Physiology, The C. V. Mosby
Co.

Gerard: The Body Functions, John Wiley & Sons, Inc.

Gruenberg and Bingham: Biology and Man, Ginn & Co.

Guyer: Speaking of Man, Harper & Brothers.

Hance: The Machines We Are, Thomas Y. Crowell Co.

Herrick: The Brains of Rats and Men, University of Chicago Press.

Hoskins: The Tides of Life— The Endocrine Glands, W. W. Norton & Co., Inc.

Kahn: Man: In Structure and Function (2 vols.), Alfred A. Knopf, Inc.

Biology of Man 529

Kimber, Gray, and Stackpole: Textbook of Anatomy and Physiology, The Mac-

millan Co.
Marshall: Introduction to Human Anatomy, W. B. Saunders Co.
Millard and King: Human Anatomy and Physiology, W. B. Saunders Co.
Newman: The Nature of the World and Man, University of Chicago Press.
Scheer: Comparative Physiology, John Wiley & Sons^ Inc.
Sherman and Lanford: Essentials of Nutrition, The Macmillan Co.
Sherman and Smith: The Vitamins, American Chemical Society.
Stanford : Man and the Livdng World, The Macmillan Co.
Turner: Endocrinology, W. B. Saunders Co.

Williams: Textbook of Anatomy and Physiology, W. B. Saunders Co.
Youmans: Nutritional Deficiencies, J. B. Lippincott Co.
Zoethout and Tuttle: Textbook of Physiology, The C. V, Mosby Co,

Chapter 26

ECONOMIC IMPORTANCE OF ANIMALS

Naturally, not all the animals of economic importance, nor the eco-
nomic importance of all the animals listed, can be given in a short chap-
ter. Economic importance is considered from the beneficial as well as
the detrimental standpoints. Additional information along these lines
may be found in the chapter on Applied Biology. The following exam-
ples are representative, but more detailed accounts should be read if
these are not sufficient for the particular needs of the reader.

PHYLUM 1— PROTOZOA (SINGLE-CELLED ANIMALS)

Certain Protozoa which bear shells (class Sarcodina, order Foraminif-
era) leave a deposit of chalk after their death. The limestone pyramids
of Egypt contain numerous, large Foraminifera. Other Foraminifera
are useful in determining the proper places to drill oil wells. Foraminif-
era (Fig. 257) are of great geologic importance because they are common
fossils from the Silurian rocks (395 million years ago) down to the pres-
ent (Figs. 320 to 322).

Certain marine, fossilized types of Protozoa (class Sarcodina, order
Radiolaria) are found in chalk, flint, slate, and deep-sea deposits. The
siliceous skeletons of certain Radiolarians aid in the formation of flint.

Protozoa of various kinds may impart unpleasant odors, tastes, and
colors to waters. For example, Bursaria (class Infusoria) produces a
''salt marsh" odor in water (Fig. 258) ; Uroglena (class Mastigophora)
produces a yellow color and a "codfishy" odor (Fig. 259) ; Peridinium
(class Mastigophora) turns the sea water along the coasts of California
and Australia a reddish color; Dinohryon (class Mastigophora), a colonial
form, produces a "fishy," seaweed odor (Fig. 260) ; Synura uvella (class,
Mastigophora) produces a bitter, spicy taste (like ripe cucumbers) and
an "oily" odor in water (Fig. 261) ; Noctiluca (class Mastigophora) may
be quite common in sea water, giving a reddish-brown color or a green-
ish-blue phosphoroscence at night.

530

Economic Importance of Animals 531

A number of Protozoa produce a variety of human diseases, of which
the following are typical and representative: Balantidium coli (class In-
fusoria) (Fig. 262) produces intestinal ulcers and a type of dysentery.

^^^^^^^^HIj^B' •«.J^^^_^v^^l^K ^^^^.T^^^^H^V

fimg

B^^Mfi8i^y^5^

fe* ^

S 2^ w

i*.^^

^kiriR^v "Ci

1 &> ^

^"^-^i ' M

*^i'-*^-^

*mt0am^ ^

Fig. 257. — Various species of Foraminifera of the class Sarcodina (phylum
Protozoa). (Courtesy of Victor Animatograph Corporation.)

Peristome

— Cilia

uM:)f— Nucleus

Flagella

Matrix- — -Mil

_ YaaJo\&

Fig. 258.

Fig. 259.
gophora).

Fig. 258. Fig. 259.

-Bursaria truncatella of the class Infusoria, phylum Protozoa.
-Spherical colony of the protozoan Uroglena americana (class Masti-

532 Animal Biology

Trypanosoma gambiense (class Mastigophora) (Fig. 263) produces
African sleeping sickness; Giardia intestinalis produces a type of diarrhea.
In the class Sarcodina, Endamoeba histolytica (Fig. 264) produces
amoebic dysentery and ulcers and E?idamoeba gingivalis is associated with
Pyorrhea alveolaris. In the class Sporozoa, Plasmodium vivax produces
tertian malarial fever with a characteristic chill every forty-eight hours

¥\acje]]a
^ody she]]

Chromatophores- _
Spines

FJageUa-

Fig. 260.

Fig. 261.

Fig. 260. — Branched colony of Dinohryon sertularia, a protozoan of the class
Mastigophora. Note the flagella of unequal length.

Fig. 261. — Spherical colony of Synura uvella, a protozoan of the class Masti-
gophora. Note the flagella of unequal length; the chromatophores are paired color
bands; spines are bristles on the body of each individual.

Pcriftome

-food

-Macleus

Contractile vacuole

Cilia

Fig. 262. — Balantidium coli, a protozoan of the class Infusoria, is associated with

a type of diarrhea.

and for which quinine is specific treatment; Plasmodium malariae (Fig.
176} produces quartan malarial fever with its attacks of malaria at inter-
vals of three days; Plasmodium falciparum produces estivoautumnal ma-
larial fever (tropical malaria) with chills daily or at irregular intervals.

Fig. 263. — Trypanosoma gamhiense, a protozoan of the class Mastigophora, is
the cause of tropical sleeping sickness as found in central and western Africa.
Observe the dark nucleus and the flagellum on the protozoa as they lie between
the blood corpuscles. (Copyright by General Biological Supply House, Inc.,
Chicago. )

NUCLEUS
PSEUDOPODIUM

VEGETATIVE STAGE

NUCLEI

ENCYSTED STAGE

Fig. 264. — Endamoeha histolytica of the class Sarcodina is the cause of human
amoebic dysentery. The vegetative stage frequently ingests red blood corpuscles.
(From Parker and Clarke: Introduction to Animal Biology, The C. V. Mosby
Co.)

534 Animal Biology

Certain diseases of animals other than man are produced by Protozoa.
The following are typical and representative: Opalina (class Infusoria)
is responsible for a parasitic condition in the intestine of frogs (Fig. 265) .
In the class Mastigophora, Histomonas meleagidis produces ''black-head"
of turkeys; Trypanosoma hrucei (Fig. 266) is carried by the tsetse fly

Ci/ia

_/VucI<?as

■IZ.ir

Fig. 265.

Fig. 266.

Fig. 265. — Opalina ranarum, a protozoan of the class Infusoria, is parasitic in
frogs, worms, and mollusks.

Fig. 266. — Trypanosoma hrucei of the class Mastigophora causes the deadly
Nagana disease of various animals in Africa. This parasite is transmitted by the
tsetse fly {Glossina sp.) (Copyright by General Biological Supply House, Inc.,
Chicago.)

Fig. 267. — Babesia bigemina, a protozoan of the class Sporozoa, causes Texas fever
in cattle. Four stages in red blood corpuscles are shown.

(Glossina morsitans) and causes the tsetse fly disease of cattle; Trypano-
soma evansi produces a disease known as surra in cattle and horses;
Trypaiiosoma equiperdum is responsible for the disease called dourine in
horses. In the class Sporozoa, Monocystis parasitizes the seminal vesicles
of the earthworm (Fig. 77) ; Coccidia produces red dysentery in calves;
Babesia bigemina (Fig. 267) causes Texas cattle fever; Nosema bombycis

Economic Importance of Animals 535

produces the silkworm disease (pebrine) ; Pseudospora volvocis is a para-
site on another protozoan animal, l^olvox.

Certain flagellated Protozoa (class, Mastigophora) live symbiotically
in the intestines of wood-feeding termites ("white ants"). The Protozoa
receive protection, in turn digesting the woody materials for use by the
termites. Enzymes produced in the bodies of the Protozoa make the wood
particles in the intestine of the termites available for the latter. The
mutual benefit is classed as a case of symbiosis. Cristispira (class Mas-
tigophora) frequently is found in oysters and clams. Certain ciliated
Protozoa (class Infusoria) destroy bacteria in sewage disposal plants.
This phenomenon is taken advantage of in the necessary destruction of
sewage.

Certain types of Protozoa, especially in water, furnish foods for other
animals. Protozoa are well adapted for laboratory experimentation for
such studies of life processes, characteristics of living protoplasm, cell
studies, and the efTects of physical and chemical agents on living proto-
plasm, as well as many others. Many Protozoa are at present unknown,
and many of those which have been studied are of unproved economic
importance. Undoubtedly, future work will place many more in their
proper places in the economies of Nature.

PHYLUM 2— PORIFERA (SPONGES)

Sponges furnish protection for both plant and animal organisms. They
are not used as foods because of the presence of skeletal spicules, strong
odors and tastes, poisonous ferments, and an extremely small amount of
stored food material in their bodies. Boring sponges (Cliona) bore the
shells of oysters and other mollusks for protection rather than for food.
The siliceous sponges and certain Protozoa (order Radiolaria) initiate
the process of flint formation. It is stated that beds of flint may be made
from a mass of sponge skeletons within fifty years.

Fresh-water sponges (Fig. 86) frequently attach themselves to water
pipes, reservoirs, water filtration equipment, and, together with other
miscellaneous forms of life, form a feltlike mass which interferes with the
water system.

Sponges may starve oysters and other shelled mollusks by attaching
themselves to the shells and taking the food from the mollusks, and they
may interfere with other forms of life in their vicinity by using the oxygen
in the water.

536 Animal Biology

Fossil sponges, similar to present-day forms, have been found chiefly in
chalk and flint formations from the Cambrian period (550 million years
ago) to the present.

The glass fibers of the glass sponges (Fig. 85) were formerly used in
making ''glass wool" which was used for filtering clumps of bacteria and
in the manufacture of toys and ornaments. This type of wool is now
made by melting glass and forcing it through small pores and rapidly
cooling the fine fibers.

The commercial uses of sponges are too well known to require much
elaboration. The annual value of the sponge industry is approximated
at $2,000,000, while that of Florida alone approximates $700,000. Ro-
man soldiers were said to have used sponges as drinking utensils many
years ago.

The United States Department of Agriculture states that sponge spic-
ules in the marsh soils of Florida wear away the shoes of men and the
hoofs of animals in a short time in the attempts to reclaim such lands.

PHYLUM 3— COELENTERATA (HYDRA, CORALS,
SEA ANEMONE, SEA CUCUMBER)

Hydra is slightly beneficial in that it captures mosquito larvae and
other insects, but it is detrimental in that it also captures Crustacea and
worms which might profitably have been used as food by higher animals.
Hydra has been observed actually to destroy young fishes in fish hatch-
eries. Hydra has been frequently used in experiments in grafting and
regeneration.

Coelenterates, in general, are not commonly used as food by man but
are eagerly devoured by fishes (Figs. 88 to 95). Sea anemones are used
by Italians for food, in which case they are sold under the name of
"Ogliole" (Fig. 95).

Coral reefs and islands may be formed by the limestone secretions of
innumerable corals (Fig. 96) which structurally somewhat resemble the
sea anemone. Such coral reefs may serve as protection or prove to be
treacherous hazards in ocean travel. The Great Barrier Reef extends
parallel to the northern coast of Queensland for over 1,000 miles and
at a distance varying from 10 to 100 miles from the shore. Many of the
islands of the Pacific are more or less of coral origin. Certain types of
corals are used in the manufacture of jewelry or for ornamental pur-
poses. The finest varieties of the rose pink coral cost about $500 per
ounce. Pale pink Japanese coral necklaces are frequently valued at
$5,000.

Economic Importance of Animals 537

PHYLUM 4— CTENOPHORA (COMB JELLIES OR
SEA WALNUTS) (Fig. 97)

Ctenophores are found in warm and temperate seas where they eat
fish eggs, the larvae of Crustacea, oysters^, and other mollusks. Ctenoph-
ores are eaten by some marine animals. In the dark, they produce
and emit a luminescent light from beneath their comb plates. Because
of this phenomenon they are a source of much interest to the nocturnal
visitor to the seashore.

PHYLUM 5— PLATYHELMINTHES (FLATWORMS)

The adults and larvae of tapeworms found in the alimentary canals of
man and other animals interfere seriously with the digestion and ab-
sorption of foods (Figs. 182, 183, and 268). The larvae of certain dog
tapeworms (Echinococcus granulosus) may form large vesicles or blad-
derlike structures in man. These structures are known as hydatids or
hydatid cysts which may rupture with serious or fatal results. The larvae
of the dog tapeworm (Multiceps multiceps) (Fig. 268) cause "staggers"
or "gid" in sheep by lodging in the brain or spinal cord. Cattle, deer,
and goats also may be affected. The broad fish tapeworm (Diphyl-
lobothrium latum) may cause severe anemia in man. This form is trans-
mitted by improperly cooked fish. In general, the tapeworms (class,
Cestoda) are internal parasites usually present in the alimentary tract
and requiring an invertebrate or another vertebrate animal as their
secondary host.

There are many parasitic flatworms in mammals, birds, and fishes,
although there is little danger of contracting disease if the meats are well
cooked. All flatworms of the class Trematoda are parasitic either in or
on the bodies of invertebrate or vertebrate animals. Fossils of flatworms
are commonly encountered, although thiey occur from the Pennsylvanian
epoch (255 million years ago) down to modern times (Figs. 320 to 322).

Planaria (Figs. 177 to 179) are used frequently in experiments in re-
generation (Fig. 28) and grafting, for which they seem to be particularly
qualified. Dr. C. M. Child, of the University of Chicago, experimented
with Planaria and as a result elaborated his important Theory of Axiate
Organization of Animals. According to this theory, there is in all animals
a gradient of metabolic activity located along an imaginary axis. The
most active end of the gradient exercises a functional dominance over all
other lower regions. Planaria was used to illustrate a principle, which
in all probability will also apply to many, if not all, other animals.

538 Animal Biology

Liver flukes (Figs. 180 and 181) frequently live in the bile ducts of
the liver of sheep^ pigs, cows, etc., and occasionally in man. This para-
sitism causes the organs to rot or become otherwise aflfected. The sheep
liver fluke (Fasciola hepatic a) (Figs. 180, 181, and 374) spends part of
its life history in the soil, on grass, and also in the body of a certain
species of snail of the genus Lyrnnaea, which acts as a secondary host for
the liver fluke.

Hoohs

.Juckcf

Brain

}nvaqinaied
^ jcolex _

Coenuras ,xsr-

Fig. 268. — Gid tapeworm [Multiceps multiceps) causes "staggers" or "gid" in
sheep by lodging in the nerv^ous system. A, Anterior region of adult; B, portion of
brain with a cyst. Such a cyst with several scoleces is known as a coenurus.

PHYLUM 6— NEMATHELMINTHES (ROUNDWORMS)

The number of parasitic roundworms is probably small in comparison
with the number living freely in water and soil. Dr. N. A. Cobb esti-
mates that the upper foot of arable soil contains thousands of miflions
per acre, where they constitute very important biologic and mechanical
factors. Cobb also estimates that there are many thousands of species
of roundworms which infest vertebrate animals, besides manv thousands
which infest such invertebrates as insects, worms, and Crustacea. Round-
worms are universally distributed, being present in the cold waters of the
Antarctic, in hot springs, in the depths of the sea, and at high mountain
altitudes. Geologically, the roundworms range from the Upper Pale-
ozoic era (250-330 million years ago) to the present (Figs. 320 to 322).

Ascaris (Fig. 184) is a genus of roundworms which is parasitic in the
intestines of frogs, hogs, calves, man, etc. Ascaris lumbricoides infests
the small intestine of the hog; the stomach, causing nausea; the pancreas,

Economic Importance of Animals 539

causing jaundice; the lungs, causing "thumps." This species is sometimes
called the human roundworm.

Trichinosis is a human disease (also affecting pigs and rats) which
is produced by a certain order of roundworms (Trichinelloidea) when
they are eaten in inadequately cooked meat from infested pigs. These
worms are commonly called the "porkworm" (Fig. 100).

Elephantiasis is a human disease in which the limbs and other regions
of the body swell to enormous size. This condition is caused by certain
roundworms known as Filaria worms (order Filarioidea) (Fig. 101).

The hookworm disease is produced by a roundworm, Necator ameri-
canus (Fig. 99). Shiftlessness, loss of blood, anemia, a depraved appetite
for dirt, paper, and plaster are common symptoms. Probably 2,000,000
human beings are afflicted, especially in warmer climates. The hook-
worm larvae enter through the skin of the body, especially the feet.
Placing shoes on the feet of all persons will prevent the spread of this
very important disease.

The human pinworm (Enterohius vermicularis) is a small, white
roundworm, the female of which is 10 mm. long and the male about
3 mm. long. It is still a debated question as to the relationship between
the larvae and eggs of the pinworm and appendicitis.

Gapes is a disease of poultry and game birds which is caused by the
parasitic roundworm or "gapeworm" (Syngamus trachea). The round-
worm, Dictophyme renale, infests the kidneys of dogs, cattle, horses, and
man. The females of the species may be over three feet long.

Heterodera (Caconema) radicicola attacks the roots of such plants
as potato, tomato, lettuce, turnips, and weeds, the irritation producing
the characteristic swelling known as root knot or root gall.

The "vinegar eel" (Turhatrix [Anguillula] aceti) (Fig. 98) lives in
vinegar and other sour materials. It is frequently used in experimenta-
tion.

PHYLUM 7— ROTIFERA OR TROCHELMINTHES
(ROTIFERS) (Fig. 102)

Rotifers serve as food for higher forms of life. Certain Rotifers para-
sitize the intestine and coelom of worms as well as certain Crustacea
(phylum, Arthropoda) . Rotifers are frequently used in experiments on
bisexual and parthenogenetic development. Rotifers, in certain stages

540 Animal Biology

at least, are very resistant to freezing temperatures and dryness, thus
initiating new food supplies for higher animals after such climatic condi-
tions have passed.

PHYLUM 8— ECHINODERMATA (STARFISH, SEA URCHIN,
SAND DOLLAR, ETC.)

The spines of echinoderms in general are a menace to those who fre-
quent the seashores for bathing. The spines of sea urchins are used as
slate pencils in certain regions of the world (Fig. 108) .

Starfishes and other echinoderms are frequently used in experiments in
artificial parthenogenesis, autotomy, embryology, and regeneration (Figs.
28 and 104 to 107). Starfishes forcibly open great numbers of oysters
and clams and use them for food (Fig. 328). The remains of starfishes
are frequently used as fertilizer. The eggs of starfishes and sea urchins
are used for food. Dried sea cucumbers (class Holothurioidea) , known
as "trepang" or "beche-de-mer," are used for food in southern China,
Queensland, and the South Pacific islands.

Geologically, the echinoderms are present from the Pennsylvanian epoch
(255 million years ago) of the Paleozoic era down to the present (Figs.
320 to 322). Huge masses of limestone are frequently found to be com-
posed of the remains of fossilized feather stars (Fig. 112) .

PHYLUM 9— ANNELIDA (SEGMENTED WORMS)

Earthworms serve as food for higher animals, and probably even for
certain tribes of savages (Figs. 185 to 190). By burrowing through the
soil, they permit air and moisture to penetrate to the roots of plants.
They rarely attack living plants. The "castings" of earthworms bring
the more fertile portions of the soil in contact with the less fertile, thus
resulting in a general mixing of it. Charles Darwin estimated that more
than eighteen tons of earthy castings may be carried to the surface in a
year on one acre of ground by 50,000 earthworms. Earthworms also
help to destroy dead plant materials and change them into available
and usable types for future living plants. Earthworms have been used
experimentally in studies of regeneration and grafting. They may acci-
dentally act as intermediate hosts in the transmission of the roundworm
or gapeworm (Syngamus trachea). This parasite need not pass through
the earthworm as a host in all cases.

Certain marine, fresh-water, or terrestrial forms possessing setae (class
Chaetopoda) have been found as fossils from the Cambrian period (550

Economic Importance of Anim,als 541

million years ago) down to the present. These forms are among the
earliest in geologic records (Figs. 320 to 322).

The "sandworm" or "clamworm" of the genus Nereis is used as food
by marine animals (Fig. 113),

Leeches (class Hirudinea) (Fig. 114) are parasitic annelids which
infest both vertebrate and invertebrate animals. They have been used
as food by certain peoples. Medicinal leeches (Fig. 114) are used to
draw blood in such conditions as "black eyes" and after contusions.
Leeches produce a substance (hirudin) which prevents the clotting of
blood. This enables the leech to secure blood as food after once attach-
ing itself to its host. Leeches, because of their soft construction, have
left no geologic records.

PHYLUM 10— MOLLUSC A (OYSTERS, CLAMS, SQUIDS,
SNAILS, DEVILFISH, OCTOPUS)

Geologically, the Mollusca are found from the Cambrian period (550
million years ago) to the present time (Figs. 320 to 322). Clams and
mussels were especially abundant in the Cretaceous (chalk) period in
America.

Certain types of mollusk shells have been used as money in certain
communities. Certain shells are used in button manufacture and are
ground for chicken feed or used as fertilizer. Molluscan shells have been
and are still being used as ornaments in a great variety of ways. The
shells also may be used for road-building purposes. The "window-
glass" shell of Placuna placenta (class Pelecypoda) is used as a window
pane in certain parts of the tropics.

In the embryologic development of the fresh-water mussels, the so-
called Glochidium stage attaches itself to the gills and fins of fishes, thus
ensuring its distribution. Mollusca are especially suited for studies of
growth because the shell is added and extended by the mantle as the
animal grows. Oysters, scallops, clams, and mussels are used as food by
man. Oysters and other Mollusca may be a means of transmitting ty-
phoid fever and other diseases unless they are properly grown and trans-
ported. Rigid inspection has reduced this possibility to a great extent.
Sometimes snails may attack the eggs of fishes in nests, others may de-
stroy plants and vegetables, and still others may act as intermediate
hosts to various parasites, transferring them to other animals.

Pearls are manufactured by pearl oysters, mussels, and clams by an
accumulation of "nacre" or "mother-of-pearl" laid down in layers around

542 Animal Biology

such foreign substances as grains of sand, fragments of tissues, bits of
shell, eggs, worms, small Crustacea, and similar objects {Figs. 118, 120,
and 121). In some instances foreign bodies are artificially introduced
into the bodies of the mollusks and the layers of mother-of-pearl are
added in concentric lavers bv the mollusk. Should we consider this an
artificial or natural method of pearl formation?

The internal shell of the cuttlefish (class Cephalopoda) is sold as cuttle
bone. This is used for food for birds and is porous and made largely
of lime. Cuttlefishes or Sepias furnish the ingredients for sepia ink,
which is used in art. India ink is made from the ink bags of fossil cut-
tlefishes. Ground cuttle bone is called "pounce" and is used by drafts-
men to prevent blotting and used in medicine as an antacid.

The devilfish or Octopus (Fig. 124) sometimes attacks man, although
not as frequently as once supposed. This type of mollusk is used for hu-
man food.

Snails are of medical and sanitary importance because they act as hosts
to larval flatworms which may eventually become parasitic for higher
vertebrate animals, including man. The European land snail (Helix
pomatia) (Figs. 116, 117, and 119) is imported in large numbers for
food and laboratory purposes. The snail is a great source of food in
certain European countries, taking much the same status as the oyster in
this country. In spite of many attempts at introduction, it has never
pleased the palates of the American populace.

The giant land slug (class Gastropoda) is used by Indians of South
America to manufacture the so-called "bird lime" to capture humming-
birds.

The boring snail (Natica) destroys other mollusks by boring into their
shells and eating them. The borer (Pholas) (class Pelecypoda), because
of its filelike shell, is able to bore through concrete and rocks, thus being
of importance to shipping industries. The wood-boring shipworm
(Teredo navalis) (class Pelecypoda) is able to destroy the wood of ships,
wharves, and piles unless protected by concrete or creosote (Fig. 122).
They have been known to bore for a distance of more than two feet.
Chitons (class Amphineura) are used for bait and human food (Fig. 115).

The squid (class Cephalopoda) is used for food. Squid oil is used by
the Chinese as medicine and is used elsewhere for lubrication purposes
(Fig. 123). The so-called "pen" is a thin, internal, chitinous shell em-
bedded along the dorsal side. The ink sac discharges an inky secretion
into the water to confuse enemies.

Economic Importance of Animals 543

PHYLUM 1 1— ARTHROPOD A (CRAYFISH, LOBSTER,
CENTIPEDE, MILLIPEDE, INSECTS, TICKS, MITES,
SPIDERS, ETC.)

The arthropods are so numerous and of so many varieties that a short
discussion of their economic importance is quite difficult. The more
representative examples of each of the classes of arthropods will be
discussed.

Class Crustacea

Crayfishes (Figs. 128, 129, 130, and 307) and lobsters are used as
food by man and other animals. There are two distinct genera of cray-
fishes in the United States: the genus Cambarus east of the Rocky
Mountains and Astacus west of the Rockies.

The materials which crayfishes use as food vary greatly. Probably
the materials most abundant and convenient are most frequently used
by them for foods. The following have been used as sources of food
by different species of crayfishes at various times: dead fish, clams,
adult and larval insects, frogs, eggs of salamanders, toads, and frogs,
eggs and adults of other crayfishes, dead leaves, such vegetable matter
as young bean plants, young corn, potatoes, onions, buckwheat, and
many other young plants.

The materials which lobsters use as food might be listed as follows:
long-neck clams, hard-shell clams, conchs, dead and living fishes, eel-
grass, etc.

The enemies of the crayfish include man, certain fishes (especially the
black bass), many birds (such as the eagle and kingfisher), certain water
snakes, common box turtle, and the larger salamanders.

The crayfish acts as a scavenger, thus cleaning many pools and
streams which otherwise might retain their contained materials. They
also injure dikes, dams, reservoirs, and levees by burrowing in them.
Rather discouraging and unsuccessful methods for their extermination
include drainage of the infested areas, scattering of unslaked lime over
the infested area, pouring carbon bisulfide into their burrows.

Crayfishes have been used extensively for laboratory studies in neu-
rology, homology (Fig. 307), reactions and behavior, and habits and
activities. They may eventually take the place of our diminishing sup-
ply of lobsters as a source of food.

Certain Crustacea, such as Daphnia (Fig. 134), Copcpods, and many
other similar types, are a great source of foods for fishes and other

544 Animal Biology

aquatic life at certain periods of their life history. Many Crustacea
(subclass Copepoda) (Fig. 127) are fish parasites.

Barnacles are degenerate Crustacea (subclass Cirripedia) which en-
crust the bottoms and sides of ships, wharves, and piles, and are an
annoyance to bathers, while other species act as parasites (Fig. 133).

The "sow bugs" or "wood lice" (subclass Malacostraca; order Isop-
oda) are grayish Crustacea found in dark, moist places, usually under
boards and rocks. They breathe by means of abdominal gills and feed
on decaying vegetable matter, although they may attack living plants
(Fig. 126).

Several species of shrimp (subclass Malacostraca; order Decapoda)
are found along our coasts and are widely used for human food.

Several species of crab (subclass Malacostraca; order Decapoda) such
as the blue crab or soft-shell crab, the painted crab, the rock crab and
the oyster crab are commonly used for human food (Fig. 132).

In general, the Crustacea are most cosmopolitan in their geographic
distribution, thus ensuring their existence and consequently being either
detrimental or beneficial. They also produce large numbers of offspring,
which naturally affects their economic importance. Several deep-sea
Crustacea are phosphorescent and many have brilliant colors.

Class Diplopoda and Class Chilopoda

Very few of the millipedes (Fig. 135) are of economic importance.
The common house centipede feeds on bedbugs, flies, and cockroaches
(Fig. 135, C) . It is not very poisonous to man. The venom of the large
tropical centipedes may be fatal to man and other animals.

Class Arachnoidea

The "red spider," which is a mite, attacks nearly two hundred dif-
ferent plants, especially in greenhouses (Fig. 270).

The follicle mite (Demodex folliculorum) produces "blackheads" in
man and other mammals by entering the hair follicles. The itch mite
parasitizes the skin. The so-called chigger (the young of the harvest
mite) burrows into the skin of man and other mammals, causing a
severe irritation (Fig. 269). The common tick transmits the organisms
which cause the disease of African relapsing fever (Fig. 138). Ticks
and mites are rather small, being external or ectoparasites in many
instances. Some forms burrow beneath the skin, causing rather severe
irritations, while others merely suck blood from the host. Some types
are able to transmit the causes of diseases from one host to another. An

Fig. 269. — The "chigger" or harvest mite {Tromhicula sp.) of the class Arach-
noidea, highly magnified. The immature stage,. A, burrows in the skin and has
only three pairs of legs. The adult mite, B, has the typical four pairs of legs;
hence, it is not a true insect. (From Chittenden: Harvest Mites, or "Chiggers,"
U. S. Department of Agriculture; courtesy of Bureau of Entomology and Plant
Quarantine.)

Fig. 270. — The red spider (Tetranychus sp.) of the class Arachnoidea. This
adult female mite is greatly enlarged. (From McGregor: The Red Spider on Cot-
ton. U. S. Department of Agriculture; courtesy of Department of Entomology and
Plant Quarantine.)

"^B^'iW *■

Fig. 271. — For legend, see opposite page.

Economic Importance of Animals 547

example of this is the cattle tick which is able to transmit the cause of
Texas fever, the loss from which amounts to over $100,000,000 annually
in the United States.

The daddy longlegs or "harvestmen" (Fig. 138) feed on living insects
and are thus of economic importance. Many of us as children have
asked these interesting animals this question: "Which direction shall I
go to hunt the cows?" We watched carefully to see which of the eight
legs was moved. This was supposed to be the direction of our bovine
search. Naturally and invariably, they had not been good herd masters
for their leg movements always led us in the wrong direction.

The black widow spider is quite poisonous and is said to have caused
a number of deaths. The web of certain spiders is used in the manu-
facture of certain scientific instruments. Gomstock states that the
tarantula or "banana spider" is not capable of seriously injuring man.
If this is true, undoubtedly many fingers have been needlessly ampu-
tated and many hours of anxiety wasted.

•The horseshoe crab or king crab (Limulus) of our Atlantic Coast
feeds on worms and is used as hog feed and fertilizer (Fig. 136).

Class Insecta or Hexapoda

The economic importance of insects is so great and varied that only
a few representative examples can be given. For a more complete dis-
cussion, textbooks in entomology and governmental publications are
suggested for references.

General Usefulness of Beneficial Insects. — Tannic acid, secured from
certain galls produced on plants by insects, is used for tanning animal
skins for leather or fur. Many galls (Fig. 271) produced by insects
contain ingredients for dyes and inks. Most of the common fruits,
vegetables, and many ornamental plants are pollinated by insects. In
order for clover seed to develop from clover flowers, the latter must be
visited by some insect, usually some kind of bee. It has been observed
that the production of fruits and seeds is materially increased if there is
a hive of bees near by. This is quite profitable because the bees collect
the nectar from the flowers and make it into honey, and in collecting

Fig. 271. — Several species of common galls produced on plants by insects of the
order Hymenoptera. 1. Blackberry seed gall [Diastrophus cuscutaeformis) ; 2.
knot gall {Diastrophus nebulosus) ; 3, mealy rose gall (Rhodites ignotus) ; 4, oak
bullet gall {Holcapsis globulas) ; 5, mossy rose gall {Rhodites rosae). From
Viereck: Insects of Connecticut, State Geological and Natural History Survey,
Bulletin 22.)

548 Animal Biology

nectar and pollen from various flowers they carry pollen from one flower
to another, thus ensuring the pollination necessary for fruit and seed
formation. Certain insects act as scavengers by destroying dead animals
and plants. Others bury dung and carcasses. All of these cause these
dead materials to be reverted to the soil where they can be utilized
again by future plants.

Certain insects also serve as food for other animals which are valu-
able for us. Many game and song birds depend for the most part on
insects for their natural diet. Many of our fishes use aquatic insects
as foods. The large numbers of May flics which occur in fresh water
at certain periods of the year are used in great quantities for this pur-
pose. Racoons, skunks, and other wild, fur-bearing animals eat insects.

In many parts of the world such insects as crickets, grasshoppers,
beetles, termites, aquatic bugs, bee larvae and pupae, and caterpillars
are used as food by the more primitive races of men.

Insects promote soil fertility and improve soil conditions by serving
as fertilizer and by burrowing throughout its layers, thus permitting air
and moisture to penetrate to the roots of plants. Insects also destroy
great numbers of weeds which might be harmful or at least take the
nourishment away from more desirable plants. In this way insects are
beneficial to man in helping him keep weeds somewhat under control.

Insects also have certain aesthetic values, because their colors, shapes,
and patterns serve as models for decorators, artists, and milliners. The
highly colored types are used for such ornaments as pins, necklaces,
jewelry, and trays. They serve as subject matter and inspiration for
poetry. The Oriental peoples train certain types of crickets for sport
purposes. Fleas are trained for performances in flea circuses, not only
for amusement but for financial reasons. Last but not least, insects
aff'ord much diversion and entertainment for the many amateurs who
collect and studv them.

Many types of insects are beneficial to man because they destroy
other injurious types by capturing and devouring them. Many kinds
live as parasites in or on the bodies of other more harmful types.

Scientific investigations of great value to man have been based on the
study of insects. A study of the fruit fly or banana fly (Drosophila)
has aided man materially in his study of heredity (Fig. 332). The
psychology and behavior of higher animals frequently have been illumi-
nated by a study of the simple tropisms and reactions of insects.

A study of coloration in insects undoubtedly has influenced the science
of camouflage. It is a possibility that insect coloration may have sug-
gested the idea of artificial camouflage in the beginning.

Economic Importance of Animals 549

Injurious or Detrimental Insects in General. — The insects of this
group might be considered from the following viewpoints: (1) those
which annoy and attack man and other animals, (2) those which attack
and injure plants and crops, and (3) those which destroy and diminish
the values of man's commodities.

Insects may attack man in such ways as the following: They may
live in or on the body as internal or external parasites. They may serve
as secondary hosts for certain disease-producing organisms which with-
out the insect could not exist for any period of time. Some species may
inject poisons into the body by means of stingers, nettling hairs, or
mouth parts. Others may influence the tastes and odors of foods be-
cause of repulsive odors and secretions which they produce.

Insects may injure plants and crops in a great variety of ways. The
examples given will at least give some idea of the methods in which
this can be accompHshed. They may attack the underground stems
and roots; they may suck the vital sap; they may chew and destroy the
flowers, bark, stems, and foliage; they may bore in stems, leaves, and
fruits; they may construct damaging nests and shelters in various plants;
they may deposit eggs in or on some part of the plant which will later
develop into destructive forms; they may transport other injurious
insects to new plants and establish them there at the expense of the
latter; they may inject disease-producing organisms, such as bacteria,
Protozoa, and fungi, into plant tissues; they may destroy parts of plants,
particularly the leaves, which will prevent or hinder the normal process
of photosynthesis. If this is done, normal growth and other plant activi-
ties may be highly impaired.

Insects may destroy and diminish the value of man's commodities,
such as foods, clothing, books, furniture, papers, drugs, bridges, houses,
lumber, collections of plants, and animals in museums. The above may
be accomplished in many ways, as can be shown by the following
examples: Insects may increase the expense and labor for sorting, pack-
ing, transporting, and preserving foods. Certain kinds, such as termites
(Fig. 283), may destroy wooden houses, bridges, and similar articles.
Clothes moths (Fig. 301) may destroy large quantities of clothing and
upholstered furniture. Carpet beetles may destroy rugs,, carpets, and
similar objects. Papers may be destroyed by such insects as the silver-
fishes (Fig. 273). Foods may be contaminated by insect secretions,
excretions, eggs, etc., even though the food may not be eaten by the
insects themselves. Certain species of powder-post beetles (order Co-
leoptera), known as lead cable borers, eat holes through leaden cover-
ings of aerial telephone cables, causing short circuits (Fig. 272).

550 Animal Biology

Economic Importance of Representatives of the Orders of Insects. —

Order 1 — Thysanura: The common silverfish, or bristletail, Uves on
starchy materials and such things as book bindings, wall paper paste,
and starched clothing. They are particularly common in dark, moist
places (Fig. 273).

Order 2 — Collembola: The springtails (Figs. 204 and 274) are com-
mon under stones and decaying leaves and w^ood, etc., where they live
on decaying materials. Sometimes certain kinds known as snow "fleas"
(Fig. 203) are abundant on the surface of snow, where they appear as
tiny black specks which spring away because of a special springlike struc-
ture on the ventral side of the abdomen. They may be a pest in maple
sugar camps by collecting in large numbers in the collected sap.

Fig. 272. — Lead-cable borer {Scohicia declivis) of the order Coleoptera, show-
ing an adult, A, and larva, B. (From Burke, Hartman, and Snyder: The Lead-
Cable Borer or "Short-Circut Beetle" in California, U. S. Department of Agricul-
ture; courtesy of Department of Entomology and Plant Quarantine.)

Order 3 — Ephemerida: The larvae and adult May flies (lake flies)
(Fig. 275) are a source of food for fish. The larvae develop in water
for one to three years, depending on the species. Especially during their
emergence periods in the summer, their collection in large numbers and
their decomposition around lights and on bathing beaches are great
sources of annoyance. The adults cannot harm man because of the
absence of stings and well-developed mouth parts.

Order 4 — Odonata: The dragonflies ("darning needles") (Figs. 205
and 276) as adults and larvae are enemies of mosquitoes during the day,

Economic Importance of Animals 551

although many of the mosquitoes are active after dark. The adults and
larvae of dragonflies and damselflies (Fig. 277) serve as food for aquatic
and terrestrial animals.

Order 5 — Plecoptera: The stonefly larvae (Fig. 278) live in running
water under stones and serve as food for fish and other aquatic animals.

Order 6 — Mallophaga: The biting bird lice (Fig. 279) eat the hair,
epidermal scales, and feathers of mammals and birds. Their sharp
claws produce irritations and bleeding which causes the host much an-
noyance and may even lead to infections. Birds often resort to dust
baths in their attempt to combat the lice.

r.'

/'^

■^

V,..,

^-^#*'

--.

, -.^- ^ ■*-

i
t

t-^-.-y-f..

Fig. 273.

Fig. 274.

Fig. 273. — Silverfish or fish moth {Lepisma saccharina) of the order Thysanura.
Dorsal view and much enlarged. (From Back: Silverfish, U. S. Department of
Agriculture, courtesy of Department of Entomology and Plant Quarantine.)

Fig. 274. — Springtail {Isotomurus palusiris) of the order Collemhola (much en-
larged). (From Folsom: Nearctic Collemhola or Springtails, of the Family Isoto-
midae, U. S. National Museum, Smithsonian Institution.)

552 Animal Biology

Fig. 275. — An adult Mayfly or lakefly of the order Ephemerida. Observe dif-
ferences in fore- and hind-wings, and the long slender, many-jointed "tails" at the
tip of the abdomen. The adult takes no food and lives a very short time, while
the larva (naiad) with its abdominal tracheal gills develops in the water from one
to three years (depending on the species).

ODONATA

EPHEMERIDA

TR/CHOPTERA

PLECOPTERA

Fig. 276. — Representative insects of the orders Odonata, Ephemerida, Trichop-
tera, and Plecoptera. Immature stages in the water: adults above. (From
Krecker: General Zoology, published by Henry Holt and Company, after Pearse.)

Economic Importance of Animals 553

Order 7 — Anoplura: These true lice are wingless parasites which
suck juices from man and other mammals. The three common species
which attack man (Fig. 280) are the head louse, the body louse, and
the crab louse. The rat louse, dog louse, and hog louse attack other
mammals. The true lice differ from the Mallophaga in having piercing-
sucking mouth parts.

srxis?'

Fig. 277.

Fig. 278.

Fig. 277. — An adult damsel fly of the order Odonata. Note the position of the
two pairs of wings when the insect is at rest.

Fig. 278. — Stone fly (adult) of the order Plecoptera. Note the pair of tail
filaments at the tip of the abdomen and the resting position of the wings. . In
well-aerated water, the flat larva clings to stones; hence, the name stone fly. The
larvae make excellent fish bait.

Fig. 279. — Biting bird* louse {Menopon pallidum) of the order Mallophaga.
A parasite from a chicken, much enlarged. (From Bishopp and Wood: Mites
and Lice on Poultry, U. S. Department of Agriculture; courtesy of the Department
of Entomology and Plant Quarantine.)

554 Animal Biology

Order 8 — Orthoptera: Extracts from the bodies of cockroaches (Fig.
281) are used to a certain extent for medicinal purposes. The four
species of cockroaches in the United States attack foods, bedbugs, silver-
fishes, and other cockroaches. The "praying mantis" (Fig. 329) consumes
other insects as food. The "walking sticks" feed on the foliage of trees
and plants; they resemble the twigs that surround them in general shape,
making them difficult to detect. The locusts or short-horned grass-
hoppers (Figs. 191 to 193) devour many kinds of vegetation and, when
they migrate in swarms, may destroy all living plants in their paths.

Fig. 280. — Parasitic mites (class Arachnoidea) and lice (class Insecta, order
Anoplura) . A, Human itch mite (Sarcoptes scahiei) , female from ventral surface;
B, male of mite shown in A, from ventral surface; C, body louse or "cootie"
{Pediculus corporis) ; D, head louse (Pediculus capitis) ; E, crab louse (Phthirius
pubis). (From Turner: Personal and Community Health. The C. V. Mosby
Co.)

Economic Importance of Animals 555

Certain species are used as food by savages and Orientals. The green-
ish katydids feed on leaves and tender plants, while they occasionally
attack other insects. Their characteristic chirping in the evening is a
source of amusement and joy unless it should become excessive and
disharmonic. The long-horned or meadow grasshoppers consume large
quantities of vegetation of the fields, including grains and grasses.
Grasshoppers may destroy entire fields of crops, particularly in the
West and South. The house cricket (Fig. 282) or true cricket produces
the characteristic chirping and feeds principally on plants, although
they may attack clothing. The mole cricket burrows in the ground and
attacks plants, especially potatoes. The striped tree cricket attacks
berry plants, grapevines, and other plants.

Fig. 281. Fig. 282.

Fig. 281. — A common household cockroach of the order Orthoptera.
Fig. 282. — A common cricket of the order Orthoptera (class Insecta).

Order 9 — Isoptera: The termites (Fig. 283) are social insects living
in colonies. Originally they were abundant only in the tropics, but in re-
cent years they have become a serious pest in the United States where
they greatly damage structures which are made of wood. They live in
dark places and may not be noticed by the untrained except during their
so-called swarming periods. At other times they are usually unnoticed,
which may lead one to believe they are not present. They may build
earthen tunnels and pass through them out of sight. The colonies of
certain species are underground in order to secure moisture and to pre-
vent freezing in cold weather. They usually destroy only the inner parts
of woods and rarely come to the surface, thus betraying their presence
and great destruction. Sometimes, only the outer shell of a wooden

556 Animal Biology

Q.uetjn

Alates (Male and female
wirx^ed reproducfcives)

SupplGmcntary/ Reproductive SoMier-

worher

^A/ymph

Fig. 283. — Castes and life history of termites {Reticulitermes sp.) of the order

Isoptera.

Fig. 284.

Fi?. 285.

Fig. 284. — Bark louse (winged) of the order Corrodentia. (From Kellogg:
American Insects, Henry Holt and Co.)

Fig. 285. — Book louse of the order Corrodentia (much enlarged). (From Back
and Cotton: Stored-Grain Pests, U. S. Department of Agriculture; courtesy of
Department of Entomology and Plant Quarantine.)

Economic Importance of Animals 557

structure is all that remains. They may attack books, and at times
even living plants. Qualified experts should be consulted if their pres-
ence is suspected.

Order 10 — Corrodentia: The winged bark lice (Fig. 284) live on the
various parts of higher plants, on lichens, etc. The wingless book lice
(Fig. 285) devour paper, book bindings, etc.

Order 11 — Thysanoptera: Several species of thrips are pests on such
plants as wheat, oats, onions, grasses, and fruits (Fig. 286). Because of
their small size, they are able to pass through window screens and may
be quite annoying at times.

Fig. 286. — The thrips are small insects with long fringe on the wings, and be-
long to the order Thysanoptera. Much enlarged. (Copyright by General Biologi-
cal Supply House, Inc., Chicago.)

Order 12 — Hemiptera: The aquatic and terrestrial true bugs are
included in this order. The chinch bug (Fig. 287) does great damage
to corn and wheat crops. The squash bugs attack garden vegetables,
especially squash and pumpkin. Bedbugs (Fig. 288) attack human
beings by sucking blood and thereby cause certain diseased conditions.
The assassin bugs attack other insects, such as the bedbug. At times

558 Animal Biology

they attack man. Are they to be considered man's friend or enemy?
The leaf bugs consume large quantities of plant foliage and flowers.
The giant water bugs are enemies of small fishes, tadpoles, and other
insects. The harlequin cabbage bug is a serious pest of various garden
plants, such as cabbage, Brussels sprouts, and others.

Fig. 287. — Chinch bug {Blissus leucopterus) of the order Hemiptera. Adult of
long-winged form, much enlarged. (From VVebster: The Chinch Bug, U. S.
Department of Agriculture; courtesy of Department of Entomology and Plant
Quarantine.)

Fig. 288. — Mature bedbug (Cimex lectularius) of the order Hemiptera, much
enlarged. (From Back: Bedbugs, U. S. Department of Agriculture; courtesy of
Department of Entomology and Plant Quarantine.)

Order 13 — Homoptera: Cochineal and crimson lake dyes or pigments
are made from the bodies of certain scale insects found particularly on
cactus plants. Shellac is a secretion from the glands on the backs of
certain scale insects found particularly in India (Fig. 289). Such scale
insects as the San Jose scale (Fig. 290), oyster shell scale, cottony
cushion scale^ and many others attack a great variety of plants, thus

Economic Importance of Animals 559

producing very extensive damage. The leaf hoppers are difficult to
control, for they attack many types of plants. The rose leaf hopper is
a typical form which is very destructive of rose plants. Aphids (plant
lice) are small, very prolific Homoptera which attack a great variety of
vegetation. Some of the more common forms are the grape Phylloxera,
which causes decay by puncturing the roots of grapevines; the apple

Fig. 289. — The lac insect (Tachardia lacca) of the order Homoptera. A, Piece
of twig encrusted with lac; at right the wormhke lac insects are shown in their
cells; B, young lac insect, greatly enlarged; C, body of an adult female lac insect
freed from its resinous secretions. (Modified from Green: Coccidae of Ceylon,
from Metcalf and Flint: Fundamentals of Insect Life, The McGraw-Hill Book
Co., Inc.)

grain Aphid, which attacks the buds of apple trees, pear trees, haw-
thorn trees, as well as grasses and grains in warmer weather; the woolly
apple Aphid, which (Fig. 291) attacks the roots and branches of apple
trees. The cicadas are incorrectly called locusts. The 17-year cicada

560 Animal Biology

(Fig. 292) spends over sixteen years of its life history as a larva in the
soil. During the seventeenth year, the adult emerges and deposits eggs
in the branches of trees, particularly fruit trees. The branches fall to
the ground, where the eggs hatch into larvae, there to remain for an-
other sixteen years. The destruction of the branches of trees by the
egg-depositing process is very great. Sometimes all of the smaller
branches are so badly punctured that they drop to the ground or at

Fig. 290. — San Jose scale of the order Homoptera. A, Adult wingless female,
ventral view, showing very long sucking setae; B, bark of tree showing young
larvae and scales in various stages of development. The adult male, C, is winged.
All much enlarged. (From Marlatt: The San Jose or Chinese Scale, U. S.
Department of ^Agriculture ; courtesy of Department of Entomology and Plant
Quarantine.)

least die on the tree. All these branches should be removed and burned
to destroy the eggs. The common cicada or harvest fly does damage
by eating vegetation, although not to such an extent as the periodical
17-year cicada.

Economic Importance of Animals 561

Order 14 — Dermaptera: Earwigs (Fig. 293) feed on flowers and
fruits at night but are rare in the United States. They are said to have
damaged the eardrums of human beings by their pincerlike structures
at the tip of the abdomen.

Fig. 291. — Woolly apple Aphid (Eriosoma lanigera) of the order Homoptera.
a. Agamic female; h, larval aphid; c, pupa; d, winged female with the antenna
enlarged above. All are greatly enlarged and with, the customary woolly, waxy
excretion removed. (From Marlatt: The Woolly Aphis of the Apple, U. S. De-
partment of Agriculture; courtesy Department of Entomology and Plant Quar-
antine. )

Fig. 292. — The periodical cicada {Tibicina septendecim) of the order Homop-
tera. a, Adult; b, adult, side view; c, shed pupal skin. (From Marlatt: The
Periodical Cicada in 1911, U. S. Department of Agriculture; courtesy of De-
partment of Entomology and Plant Quarantine.)

562 Animal Biology

Fig.

293. — Photograph of an earwig of the order (Dermaptera) (Euplexoptera)
(Copyright by General Biological Supply House, Inc., Chicago.)

Larva
(Hcllgrammifcc)

Adult male

Fig. 294. — Dobson fly or horned corydalis (Corydalis cornuta) of the order
Neuroptera. Observe the pair of large hornlike mandibles extending forward on
the adult male; in the female they are much smaller. Note the short, hairlike
tufts of tracheal gills on the abdomen of the larva which lives in water.

Economic Importance of Animals 563

Order 15 — Neuroptera: The larva (hellgrammite) of the Dobson fly
is used as fish bait (Fig. 294). The larva of the lacewing fly (Aphis
lion) destroys plant lice (Aphids) by sucking blood. The larvae of ant
lions ("doodlebugs") wait at the bottom of a pit made in sand, dirt, or
decayed wood, where they capture and destroy many types of insects.

Order 16 — Coleoptera: The dried bodies of a certain European blis-
ter beetle known as "Spanish fly" are used as a source of cantharidin,
which is used for medicinal purposes. The larvae of click beetles, com-
monly known as "wire worms," cause extensive damage in plants. The
metallic wood-boring beetles injure shade, forest, and fruit trees by bor-
ing in them. Some of the so-called checkered beetles destroy some of
the larvae of wood-boring insects. The so-called death-watch beetles
damage wood greatly by boring in it. The light-producing secretion
(luciferin) of fireflies (beetles) is used for illumination and is a source
for study in the attempt to duplicate this material in the laboratory.

Fig. 295. — Tiger beetle of the order Coleoptera. Note the light markings on the

wings.

This material gives off light with a minimum of heat. The tiger beetles
(Fig. 295), both in the adult and larval stages, destroy large numbers
of other harmful insects. Most of the ground beetles (Fig. 296) are
predacious and attack such insects as leaf-eating insects, canker worms,
cutworms, and the so-called tent caterpillars. The carnivorous water
beetles attack numerous aquatic insects, including the mosquito. The
ladybird beetles or "lady bugs" (Fig. 297) are predacious in both adult
and larval stages, when they attack detrimental scale insects and plant
Aphids in particular. They are consequently of great importance and
the various species should be protected so that they may continue their
useful habit. The Mexican bean beetle is rapidly becoming a serious
pest of garden products. When bean plants are all destroyed, they do
not hesitate to attack other plants. A certain species of powder-post

564 Animal Biology

beetle, known as the lead cable borer, makes holes in the lead coverings
of telephone cables, thus causing short circuits and interruptions in
service. The carpet beetles destroy large quantities of carpets, clothing,
rugs, and feathers. The so-called buffalo moth (beetle) also destroys
carpets, woolen fabrics, furs, and feathers. The saw-toothed grain

Ti^er Beetle Ground Beetle (Tizry
Cicindcla. Ca^rAbus vinc+us CaJosomat

aoraAlia .scruTaior

PredaceouaDivin^ y^^^ . Burrowing

Beetle- IV'acua -Hydrophaur ^ Beetle *

^k,.,M ^ "■' * \ necrophorua

^. Peach Borer, ^'^c'^^^a^^ (- ^^ *" Leptinota«V'l(D-linea-ta
Dicerca divaricate. ^ "" "Faaaalus cornuiua «>v /

Eyed Ela-ter
AI&U.S oculactua

lady Beetie . ,

Cocci neila S-noiAta June Bee-tl

Acorn Weevil
B&l&ninua

Oune, Deetle
Fhyliopha^<

Bcin Veevil Kound-headed Borer
ruchua obtecfua oAperda Candida.

Bruc

Fig. 296. — Common beetles of the order Coleoptera. (Copyright by General

Biological Supply House, Inc., Chicago.)

Fig. 297. — Two-spotted ladybird beetle {Adalia bipunctata) of the order Cole-
optera. a, Larva; b, mouth parts of larva; c, claw of larva; d, pupa; e, adult; /,
antenna of adult (all enlarged). (From Quaintance: The Aphides Aflecting the
Apple, U. S. Department of Agriculture; courtesy of Department of Entomology
and Plant Quarantine.)

Economic Importance of Animals 565

beetles are quite destructive of stored grains. The bean weevil (beetle)
larva attacks bean and pea seeds, rendering them useless for planting
or food purposes. The adult June beetle is a household annoyance in
early summer, besides eating plant foliage. The larvae or white grubs
do great damage to lawns and underground vegetation. The elm leaf
beetle destroys large numbers of elm and other trees. The Colorado
potato beetle destroys potato plants and other garden vegetation. This
beetle migrated into Colorado from Mexico and has since spread to the
East and West. The blister beetles, when dried and pulverized, produce
a blister when applied to the human skin. The mealworm beetle is used
as food for pet birds. It is quite common in grocery stores, flour mills,
and granaries. The leaf-chafing beetles feed on the pollen, flowers, and
leaves of plants. The Japanese beetle has been very destructive to
plants, especially grasses, since its appearance in New Jersey in 1916
and its subsequent spread to other parts of the country. The bark
beetles produce a damage of over $100,000,000 annually to forest trees
in the United States. Many species of the so-called long-horned beetles
are very destructive of shade, fruit, and forest trees. Some of the more
common species are the maple tree borer and the apple tree borer. The
cotton boll weevil causes millions of dollars' damage to cotton crops in
the South. The scavenger beetles are quite beneficial because they bury
or eat decaying materials, thus reverting them back to the soil where
they can be used by future plants. This cleaning activity also rids the
surface of the earth of them where they might be annoying if allowed
to accumulate. What would be the condition of the earth if all the
animals and plants of the past were still lying on the ground?

Order 17 — Mecoptera: Both the larvae and adults of the scorpion
flies (Fig. 298) are carnivorous and feed on numerous smaller insects.

Order 18 — Trichoptera: The caddice flies (Fig. 299) are of no great
economic importance. The aquatic larvae build characteristic protec-
tive cases of small rock, sand, leaves, and grass. The cases of each
species are characteristic of that species. How do these supposedly
stupid, aquatic larvae know what type of case pattern to build in order
to display their characteristic racial coat of arms?

Order 19 — Lepidoptera: The saliva of the silkworm (Fig. 300) pro-
duces the true silk of commerce. The larva of silkworms spins a cocoon
of a single, continuous strand over 1,000 feet in length. This thread
must be unravelled and woven together with others in order to make a
single silk thread. Is it difficult to see what makes true silk cloth

566 Animal Biology

more expensive when one considers the great amount of material needed
to make a single yard of it? The larvae of the army worms (certain
moth larvae) migrate from field to field in armylike fashion and destroy
large quantities of living plants, such as wheat, corn, oats, timothy, and
other grasses. The larvae of the codling moth bore into the blossoms
of the apple, eventually eating the core and seeds of the apple. Losses

Fig. 298. — Scorpion fly of the order Mecoptera (class Insecta). Note the scorpion-
like tip of the abdomen; hence, the name scorpion fly.

Larva-

Fig. 299. — Caddice fly of the order Trichoptera. Adult and larva (in a case)

from such attacks of the codling moth amount to more than $12,000,000
annually. The larvae, or caterpillars, of the cabbage butterfly destroy
the heart and leaves of large quantities of cabbage. The larvae of one
type of gossamer-winged butterflies known as the harvester are car-
nivorous eating woolly Aphids. They are consequently of value to fruit
growers. We wish the harvesters successful and prosperous lives. The

Economic Importance of Anim,als 567

larvae of the clothes moths (Fig. 301) produce great damage to furs and
woolen clothing. There are two distinct kinds which may be distin-
guished by the kind of web which the larva builds in the cloth. The
larvae of the European corn borer (Fig. 302) cause great damage to
corn and a great variety of other plants. They attack and reside in such

Cocoon

J? (k worm moth

Fig. 300. — Silkworm (Bombyx mori) , an insect of the order Lepidoptera. The
larva or silkworm is shown feeding on a leaf. The pupa is shown with part of
the cocoon removed. Note the silk threads on the cocoon.

Fig. 301. — The case-bearing clothes moth {Tinea pellionella) of the order Lepi-
doptera (enlarged). Adult moth (above); larva (lower right); larva partially
concealed in its portable case (lower left). The indistinct dark spots on the buff-
colored forewings distinguish the adult from the adult webbing clothes moth, the
wings of which are uniformly buff-colored. (From Back: Clothes Moths, U. S.
Department of Agriculture; courtesy of Department of Entomology and Plant
Quarantine.)

568 Animal Biology

a great variety of plants that it is difficult ever to destroy all of them in
a certain locality. The Mediterranean flour moth is a very common
and injurious pest, especially in flour mills. The cotton worm and the
cotton boll worm cause millions of dollars' damage annually to cotton.
The various types of tussock moths attack numerous forest, shade, and
fruit trees. The larvae of the grain moth bore into the grain of corn,
wheat, and rye. The larvae of the black swallow-tail butterfly eat
celery and parsley.

licT^^

Pupa

Ecjqs

/VIqIg moth

Larva

Fig. 302. — European corn borer [Pyrausta nubilalis) of the order Lepidoptera.
The larva is the true borer in corn stalks and many other plants. The larva de-
velops into the pupa, which in turn develops into the adult moth. The eggs laid
by the female develop into the larvae.

Order 20 — Diptera: The tachina flies are valuable enemies of leaf-
eating beetles, locusts, and caterpillars, particiilarly those of the army
worm. The common housefly, besides transmitting disease germs, such
as typhoid and tuberculosis, carries the eggs of several species of para-
sitic flatworms. They also destroy foods by depositing their eggs in
them. The horseflies attack horses, cattle, and human beings. The
flesh flies and blow flies deposit eggs in meats. The eggs under proper
conditions develop into maggots (larvae) which feed on the meat, thus
rendering it unfit for use. The bee flies resemble true bees somewhat.
Their larvae eat young grasshoppers, wasps, and bees, while the adults
feed on the nectar of flowers. The banana flies (one of the fruit flies)
are of great value for experimental studies in heredity. The adult flower

Economic Importance of Animals 569

Fig. 303. — Life history and mouth parts of mosquitoes of the order Diptera.
A, Malarial mosquito {Anopheles) ; B, common mosquito (Culex). 1, Eggs; 2,
larva; 3, pupa; 4, larva in resting position; 5, adult in resting position (contrast
the two species) ; 6, adult male; 7, mouth parts of male; 8, adult female; 9, mouth
parts of female, a, Antenna; b, thorax; c, abdomen; d, siphon; e, a,nal segment;
/, gills; g, compound eye; h, clypeus; i, maxillary palpus; ;, proboscis; k, labella;
/, labrum epipharynx; m, hypopharynx; n, mandible; o, maxilla. (Copyright by
General Biological Supply House, Inc., Chicago.)

570 Animal Biology

flies live on pollen and nectar of flowers, while the larvae eat plant
materials and other insects. The larvae of the ox-warble flies cause over
$100,000,000 damage annually by ruining the hides of cattle by boring
through the skin. The adult black flics are well-known pests because of
their blood-sucking habits. Every hunter, fisherman, and out-of-door
man has certainly been sufficiently annoyed to remember them well.
Mosquitoes (Fig. 303) of the genus Aedes transmit the virus of yellow
fever. Those of the genus Anopheles transmit the protozoa which cause
human malaria (Fig. 176). Only the females of these two species are
capable of carrying the germs because they suck blood, while the male

Fig. 304. — Dog and cat flea {Ctenocephalus canis) of the order Siphonaptera.
a. Egg; h, larva in cocoon; c, pupa; d, adult; e, mouth parts of adult from side;
f, antenna; g, labium (lower lip) from below {h, c, and d, much enlarged; a, e,
f, and g, more enlarged). (From Howard: House Fleas, U. S. Department of
Agriculture; courtesy of Department of Entomology and Plant Quarantine.)

probably feeds on the nectar of flowers. The females suck up the disease
germs from the blood of the patient ill with the disease. The germs
undergo part of their life cycle in the body of the insect and at the
proper time are injected into a susceptible person bitten by the germ-
carrying mosquito. The Hessian fly (one of the so-called gall gnats)
produces over $10,000,000 loss annually to the wheat crop in the United
States. The gall gnats deposit eggs in plant tissues. The eggs hatch into
larvae which irritate the plant so that the latter produces abnormal,
swollen enlargements known as galls (Fig. 271). Different types of galls

Economic Importance of Animals 571

on different kinds of plants are produced by specific kinds of insects.
The crane flies resemble large mosquitoes, and the midges resemble small
mosquitoes, for which they are both commonly mistaken.

Order 21 — Siphonaptera: Fleas live among the feathers of birds and
the hair of wild or domestic mammals. The human flea and the chigoe
are important enemies of man. The latter burrows in the skin and is
not the common chigger which is a mite belonging to the class Arach-
noidea. The dog and cat flea is quite common and attacks dogs, cats,
and human beings (Fig. 304). They most frequently breed in the dirt
and filth, although they have recently been encountered in large quan-
tities in the grass and weeds out of doors. The rat flea transmits the
bacterium which causes bubonic plague from rats and ground squirrels
to man. The larvae of fleas feed on decaying plant and animal matter
so these should be destroyed in our attempt to eliminate the adult fleas.

s?fe

adult male

pupa

Fig. 305. — Development of the black ant (Monomorium sp.) of the order Hymen-
opt era. (Copyright by General Biological Supply House, Inc., Chicago.)

Order 22 — Hymenopetra: Honeybees (Figs. 195 to 200) collect
nectar from flowers which is changed chemically, dehydrated, and made
into honey which is sealed in the wax "cells" of the honeycomb. Honey-
bees also pollinate certain types of .flowers which they visit. Beeswax
is secreted by glands on the underside of the abdomen. Bees have been
studied extensively as representatives of social life among the animals.
The so-called mud-daubing wasps construct nests of mud and catch
other insects which are placed in these nests for food for the young
wasps after they hatch. Other species of wasps excavate tunnels in the
earth or dig cavities in wood. Yellow jackets build nests consisting of
a series of combs surrounded by a paperlike covering. Bumblebees live
in colonies in the summer and assist in pollination of clovers for seed
production. Ants (Fig. 305) are colonial insects whose social life has
been studied extensively. A colony, as in the case of social bees and
wasps, contains different types of individuals (workers, males, female

572 Animal Biology

[queen]). The workers may be modified as soldiers or as small or large
workers. Ants usually live in terrestrial tunnels, in hollow cavities in
wood and plants, or in mounds in the ground. The leaf-cutting ant
carries pieces of leaves into the nest where other workers make them
into balls in which they cultivate and regulate a growth of fungus (a
lower type of plant). In this way white masses of food are produced
and stored for the colony. The carpenter ant builds its nest in the dead
wood of trees and buildings, thus impairing their usefulness. The corn
louse ant carefully uses and protects a very detrimental plant Aphid
which attacks the roots of corn plants. In this way the Aphid is some-
what protected. The common red and black ants are common house-
hold pests which cause untold annoyance. They destroy large quanti-
ties of foods, grasses, and lawns.

Fig. 306. — An adult ichneumon wasp of the order Hymenoptera. Note the
long ovipositor by means of which eggs are frequently laid in the larvae of other
insects and in which the eggs develop parasitically.

The "gall flies" (Hymenoptera) possess long ovipositors by means of
which eggs are deposited in plant tissues. The plant is thus stimulated
to develop abnormal, enlarged growths known as galls (Fig. 271). The
gall naturally protects the young gall fly. The ichneumon wasps or
flies (Fig. 306) are parasitic Hymenoptera which attack many injurious
insects, such as tussock moths, cabbage butterflies, tent caterpillars, and
corn borers.

PHYLUM 12— CHORDATA (LAMPREYS, SHARKS, FISHES,
FROGS, REPTILES, BIRDS, AND MAMMALS)

This phylum of animals contains such a variety of types that it is
difficult to discuss the economic importance of its members without
taking each class by itself. The following examples of each class will
suffice to give a representative idea of the group as a whole.

Economic Importance of Animals 573

Class Cyclostomata (Cyclostomes)

The lampreys ("round mouths") feed on blood, mucus, and internal
organs of fishes and crustaceans which they attack with their rasping
mouth (Fig. 143). The flesh of certain lampreys is used as food.

Class Elasmobranchii (Sharks)

Several species of dogfish sharks destroy lobsters and fishes. Oil and
fertilizers are manufactured from sharks. The skin of the dogfish shark
is used as leather and shagreen. The teeth of sharks are used as
weapons by certain people (Fig. 144).

Class Pisces (True Fishes)

Fishes (Figs. 145 to 147) furnish an important article of food. Cod-
liver oil and halibut-liver oil are valued because of their high vitamin
contents. Caviar is prepared from the salted roe of the sturgeons. Fish
scales are used for ornamental purposes. The swim bladder of codfishes
is used in the making of isinglass. Fishes are frequently used as ferti-
lizer, the early settlers of this country many times placing a fish with the
seeds they planted.

Class Amphibia (Frogs and Toads)

Frogs are used extensively as food, the breeding of large specimens
for human consumption having become quite a business in itself. Frogs
and toads destroy large numbers of harmful insects. Frogs are used
extensively for laboratory studies in dissection and physiology.

Class Reptilia (Reptiles)

Reptiles are frequently of considerable benefit because they kill large
numbers of obnoxious insects and other pests. Turtles and tortoises are
used as food. Certain lizards (Iguana of tropical America) are used as
food. The skins of crocodiles and certain snakes are used for manufac-
turing bags, boots, and cases. Tortoise shell, especially that from the
horny covering of the carapace of the Hawk's bill turtle, is used in
manufacturing combs and similar articles. There are only a few species
of poisonous snakes in the United States, while the venomous types of
the tropics cause a larger number of human deaths than any other
group of tropical animals. The oils of the boa, rattlesnake, and copper-
head are used for medicinal purposes. Musk, leather, and oils are
secured from alligators (Figs. 151 to 153).

574 Animal Biology

Class Aves (Birds) (Fig. 154)

Plumes and feathers are used for millinery purposes. Feathers are
also used in manufacturing pillows. The flesh and eggs of domestic
and game birds are used as food. Poultry products are valued at mil-
lions of dollars annually in the United States. Excretions and ejecta of
certain species of birds are known as guano, which is used as fertilizer
because of its high content of nitrogen and phosphoric acid. Game
birds are a source of a great amount of sport. The equipment necessary
for hunting them requires quite an expenditure of money when the en-
tire country is taken into consideration. Certain birds are beneficial
by destroying injurious animals, such as field mice, rabbits, ground
squirrels, and insects, as well as the seeds of weeds. Other birds are
detrimental because they destroy valuable animals as well as important
plant and grains in large numbers.

Class Mammalia (Mammals) (Fig. 156)

The relations of mammals in general to man are so complex and
varied that only a general account and a few suggestions can be given.
More detailed books are suggested for reference studies.

Domestic animals are used extensively and for a variety of purposes.
Cattle supply milk, meat, skins, hair, and hoofs. The cattle industry is
one of the most important animal industries in this country. Sheep
supply meat and wool for the manufacture of woolen garments. Goats
serve as draft animals and as a source of meat and milk. Camels serve
as draft animals and supply hair for the manufacture of fabrics and
brushes. The llama is used for transportation in South America. The
elephant is used for transportation and general labor. It supplies us
with ivory. The dogs serve a great variety of purposes from the useful
to the ridiculous. The dog was probably one of the first animals to be
domesticated. Could man have selected a more faithful companion and
ser\^ant?

Leather is made by "tanning" the hides of a number of animals, par-
ticularlv those of cattle. Manv animals are utilized in the manufacture
of fertilizers. The horns and hoofs of animals are used in making glue.
The skins of such animals as the otter, mink, weasel, marten, badger,
wolverine, muskrat, skunk, fox, lynx, raccoon, and rabbit are used as
sources of the various kinds of furs.

The destructive habits of such animals as rats, mice, and rabbits are
well known and need not be discussed.

Economic Importance of Animals 575
QUESTIONS AND TOPICS

1. What do we mean by the phrase economic importance?

2. (1) Summarize the economic importance of the representatives of each
phylum of animals. (2) Which phylum, if any, contains animals of great-
est economic importance ? Why do you say so ?

3. Discuss the ways in which biology may be of value to us in everyday life.

4. In what ways may a knowledge of biology be valuable to students of medi-
cine? To students of dentistry? To students of pharmacy? To students
of agriculture and horticulture ?

5. Are all the beneficial forms of life found in one phylum? Are all the detri-
mental forms ?

6. Must an animal or plant be beneficial or detrimental to man in order to be
of economic importance ? Explain your answer.

7. List as many departments of our national government as you can in which
the economically important animals and plants are studied and the results
of such studies disseminated and practically applied in your community.

8. What department of your state government is interested in the economic
importance of animals and plants ? Tell what it has done in your com-
munity in this connection.

9. Why does the federal government inspect plants and animals imported into
this country?

10. List the general purposes of the National Association of Audubon Societies,
1974 Broadway, New York, N. Y.

11. List as many organizations as possible which are interested in out-of-door
life. What does each attempt to accomplish ?

12. Give a report on the nearest Federal or State fish hatchery, telling what is
done there and what effect its work has on the average citizen.

13. Can you think of any animals or plants which might be improved? How?

14. List several new varieties of animals and plants which have recently been
originated. Tell how each new kind was produced and why.

SELECTED REFERENCES*

Metcalf: Textbook of Economic Zoology, Lea & Febiger.
Reese: Economic Zoology, P. Blakiston's Son & Co.

*Also consult various textbooks on zoology, entomology, etc., references to which are made in
various parts of the text.

Chapter 27

HOMOLOGY; ANALOGY; AUTOTOMY;
REGENERATION; MORPHOGENESIS

HOMOLOGY (ho-moroji) (Gr. homos, same; logos, discourse)

Homologous organs or structures are those which are jundamentally
sim.ilar in structure and in embryologic developm,ent, having their origin
in a common ancestral type. The arms of man, the forelegs of cats, the
wings of birds, etc., are structurally homologous and morphologically
similar in spite of their apparent differences upon casual observation. If
they are compared carefully and in detail, they will be observed to be
quite alike. In this case, two homologous bones, one small and the
other large, may make the over-all picture of the two appendages ap-
pear to be more different than they are fundamentally.

Several appendages on the same organism may show homology be-
cause of their similar embryologic origin and development as well as
their similar structure in the adult. For example, the pairs of appen-
dages on a crayfish or lobster (Figs. 128-130, 307) show homology, and
since the appendages form a consecutive series, it may be called serial
homology. The apparently different appendages of the crayfish have
evidently developed from a fundamental type and in the adult are con-
structed along fundamentally similar lines, even though some of them
perform different functions.

Likewise, the legs of different insects are structurally homologous (Fig.
308) since they are composed of fundamentally the same units, some of
which may vary in size or shape, which makes the legs of different insects
appear more different than they actually are.

Homologous structures or organs may have similar functions (for
example, the legs of man and the hindlegs of cats, dogs, horses, etc.) or
they may have different functions (for example, the arms of man and
the wings of birds). A study of homology teaches that certain struc-
tures may be more closely related embryologically and structurally than
a casual observation of them might reveal.

576

Homology 577

Fig. 307. — Crayfish appendages (Cambarus sp.) to show homology. Appendages
are numbered from I to XIX j removed from the left side and drawn to scale.
Appendages XIV and XV are drawn from both male and female crayfishes. 1,
Protopodite; 2, endopodite; 3, exopodite; 4, epipodite; 5, epipodite with gill fila-
ments; 6, gill with gill filaments; 7, chitinous threads. Appendage I is the anten-
nule (first antenna) ; II, the antenna; III, mandible for chewing; IV- V, first and
second maxillae; VI-VIII, first, second, and third maxillipeds; IX-XIII, walking
legs; XIV-XVIII, swimmerets; XIX, uropod (sixth swimmeret). (See Fig. 128.)

578 Animal Biology

Certain corresponding parts on diflferent plants appear to have origi-
nated from the same part of some common ancestor and to be struc-
turally similar. Such are known as homologous structures. For example,
the stamens and carpels of a flowering plant may be considered, in gen-
eral, to be homologous with the scalelike sporophylls (spore-bearing
leaves) of pine cones and the sporophylls of ferns. Pollen sacs and
ovules may be considered homologous with sporangia.

.^U—

L Temar ^^

Tibia

Coxa

Jfrochanten-

...Mh

Tibial J pur
__T(arja5

Wasp

Fig. 308. — Legs of insects, showing similarity of structure in different species.

ANALOGY (a -naV o ji) (Gr. analogia, proportion)

Analogous organs or structures are similar in junction hut are not re-
lated genetically and do not have a similar embryologic origin or mor-
phologic structure. For example, the wings of bats and butterflies are
analogous because they are used for flying, but they are not homologous.

AUTOTOMY (o-tot'omi) (Gr. autos, self; tone, cutting)

Certain organisms such as sea cucumbers, starfishes, crayfishes, lobsters,
etc., have the natural ability to sever (self amputate) a structure or organ
at a definite, predetermined point or area. This phenomenon is called
autotomy. In the crayfish and lobster there is a definite breaking point,
varying with the appendage, and a new one similar to the lost one
develops from the remaining portion. In certain crustaceans the ap-
pendage is flexed by muscles until it breaks at its breaking point. After
the appendage is thrown off, a protective membrane is formed at the
site of the injury to prevent hemorrhage until regeneration is accom-
plished.

Regeneration 579

If an arm of a starfish is injured, it is usually cast off near its base,
and the arm with part of its central disk will regenerate a new starfish.
The lost arm on the original starfish will also be regenerated (Fig. 28).
Sea cucumbers (Fig. Ill) when irritated may cast out their respiratory
apparatus, and part, or all, of their intestine; in both cases the lost
parts may be efficiently regenerated. Autotomy is an advantage since
the wound heals more efficiently at the breaking point or area than if
the injury had occurred elsewhere. The idea seems to be that it is
more desirable to sacrifice an easily replaceable part than to jeopardize
the total organism. Autotomy without the subsequent regeneration
would not be very practical.

REGENERATION (re jen e -ra' shun) (L. re, again; generare, to
beget)

This phenomenon consists of the replacement or renewal of an organ
or structure which has been lost or injured, whether by autotomy or
otherwise (Fig. 28). Certain structures appear to be more easily re-
generated than others. In fact, certain ones are never regenerated if
once lost. Regeneration is common in such organisms as protozoa,
sponges. Hydra, earthworms, planarians, starfishes, sea cucumbers, cray-
fishes, lobsters, etc. Usually a renewed structure resembles the lost one,
but this is not always true. For example, the removal of a nonfunc-
tional, degenerate eye from a so-called "blind" crayfish may result in
the regeneration of a functional, antenna-like tactile organ. The rate
of regeneration is influenced by such factors as the age of the organism,
the extent of the injury, the specific tissue or organ involved, etc.

In protozoa, during reproduction, two entirely complete individuals
may be formed from the two halves which have been divided by fission
(Figs. 162 and 169) . In many sponges, if the individual is cut into pieces,
each piece will regenerate a norma] animal. Bath sponges, if cut into
pieces of about two cubic inches, will regenerate a sponge about six
times this size in about two months. When certain species of sponges
are broken up and strained through fine cloth so as to dissociate the
cells, the latter will again fuse together and eventually form a sponge
with its typical skeleton, pores, canals, etc.

Hydra (Fig. 28) may be cut into pieces and each part will regenerate
an entire animal. The part with the tentacles produces a new indi-
vidual. If split lengthwise into two or four parts, each part forms a
normal individual. A hydra with two "heads" with tentacles can be
produced by the splitting and separation of that region. Even pieces of

580 Animal Biology

hydra too small to regenerate themselves may fuse together and the
mass then form a new hydra. Parts of one hydra may easily be grafted
upon another.

If a planarian flatworm (Dugesia) is cut into two pieces, the anterior
part will regenerate a posterior portion, while the posterior part will
regenerate a new head. A middle piece may regenerate both head and
posterior end. The head may regenerate another head, in rare instances.

A posterior end of an earthworm may regenerate an anterior end
(Fig. 28). An anterior piece regenerates a posterior part. A posterior
end under certain conditions may regenerate another posterior end
which results in the eventual death of the individual. Pieces from sev-
eral worms may be united (grafted) to form a longer worm.

In higher and more complex organisms the process of regeneration is
more or less limited if not lacking entirely. In general, the less spe-
cialized tissues and structures have greater powers along this line than
the more specialized structures. In man, such tissues as blood, bone,
skin, etc., are replaced, while other tissues and organs are not.

Certain tissues which are injured or lost may be regenerated by the
active tissues of a plant. The process is dependent upon (1) the quan-
tity and quality of the auxins (plant hormones) present which initiate
and control the growth, (2) an adequate supply of water, (3) a suffi-
cient amount of energy and building materials supplied by such foods
as carbohydrates and proteins, (4) the particular type and age of the
tissue involved, etc. In general, the natural, inherent process of regen-
eration in plants starts with the forming of a protective layer over the
injury and called a callus (ka'lus) (L. callium, hard skin). The latter
develops meristematic tissues from which the proper parts are regener-
ated. Roots may be regenerated on such stems as coleus, geraniums,
willows, roses, etc. Roots may be regenerated on the leaves of begonias,
African violets, etc. Stems may be formed from roots, and roots from
roots. Regeneration is frequently taken advantage of in the commercial
propagation of plants from cuttings. The latter phenomena are mate-
rially assisted through the use of certain plant hormones, which are con-
sidered in greater detail elsewhere in the text.

MORPHOGENESIS (mor fo -jen' e sis) (Gr. morphe, form; genesis,
origin)

This phenomenon includes the origin, differentiation, and develop-
ment of specific structures, organs, or parts of organisms. In normal
embryologic development of cells, tissues, organs, etc., of an organism,

Morphogenesis 581

as well as in the regeneration of lost parts, there must be an inherent
blueprint which is followed if the structure is to develop typically. Of
what docs this blueprint or master plan consist? Since all living or-
ganisms, according to the cell principle, are composed of cells, it would
be surmised that cells form the basis for this origin and development.
Evidence is available that this is true, but a cell is a complex structural
unit composed of many integrated, component parts. Which parts
specifically guide this remarkable phenomenon of living organisms?
Experimental evidence, at least in certain organisms, suggests that the
cytoplasm as well as the nucleus may play an important role in this con-
nection. Experiments on the eggs of certain echinoderms suggest that
cytoplasm from which all formal, organized nuclear material has been
separated is capable of originating and developing the embryo up to a
certain stage. Probably, beyond this stage the nuclear materials (genes,
etc.) take over and influence the specific traits which develop. It is
known that genes are units capable of self-duplication within the living
cells, although their multiplication outside the living cell has not been
observed to date. Since genes are known determiners of hereditary traits
and are capable of multiplication in living cells, we have an explanation
for the development of similar cells during the process of cell division.

However, a multicellular organism which arose from a single cell
(zygote) is composed of thousands of cells, but the cells are not, and
cannot, all be alike. Certain kinds must be differentiated (developed
differently) so that the various types of tissues and organs may be
formed. What forces control this differentiation? What changes occur
in the organization of the protoplasm whereby different structures may
arise from what was originally the same material? At present, scientists
do not know the complete answer to this question. However, by the
application of the scientific method in the study of these problems, bit
by bit additional information is being secured. It is known that the
abilities of a cell or tissue during emBryologic development are influenced
by (1) the inherent, intrinsic abilities of that cell or tissue and (2) the
environmental forces around it.

By careful, scientific studies of the development of frog embryos, the
embryologist Spemann found that each of the cells (of the two-celled
stage) when completely separated by a fine hair loop would develop into
a normal, although small, tadpole. What does this mean? Simply
that each separated cell of the original pair is capable of forming a com-
plete, diminutive individual whose genes are necessarily like those of
its mechanically divorced partner. If the two cells had not been arti-

582 Animal Biology

ficially separated, they would have collaborated to form the two sides
of a complete individual. In other scientifically performed experiments
it appears that stimulating chemical substances are produced which in-
fluence the development of structures in certain places, when and where
such specific substances are formed. These specific chemical substances
have been moved experimentally from one part of an animal to another
part of the same animal with the subsequent development of a rather
typical structure in the newly stimulated region. The stimulating influ-
ence may even be transplanted successfully to another animal. This
suggests that not only genes are at work but the latter are influenced by
environmental, chemical substances. Possibly the production of the
specific chemical substances is influenced by the action of specific genes.
It is to be expected that the type and amount of the development of a
particular structure or ability will be influenced by such factors as ( 1 )
the specific genes involved, (2) the quality and quantity of the specific
chemical substances available at that particular region, (3) the suscepti-
bility of the particular tissue or organ involved, (4) the age of the or-
ganism itself, etc. Undoubtedly, enzymes, hormones, vitamins, and
similar substances influence the specific type of development in an area
where such substances are available in the proper quantity. It is known
that these substances are usually specific; that is, they are capable of
stimulating specific actions in certain places. In other words, the spe-
cific chemical stimulator must be present in the proper area in the proper
amount, and the tissues, or organ, must be susceptible to its influence
before a reaction can take place. Abnormalities of either tissue or
stimulator may bring about abnormal reactions, or possibly none at all.
A point to be borne in mind is that various forces are necessary to initi-
ate and maintain a particular development, but there is also an equally
important phenomenon of discontinuing development at the proper time.
For example, the necessary factors must be present in order to develop
a finger embryologically, but there must also be a cessation of develop-
ment when the finger has reached normality. Undoubtedly, modifica-
tions of such factors are responsible for certain abnormal anomalies
(a-nom'ali) (Gr. anomalos, uneven). With the incidence of old age
and its attendant atrophy of certain structures (and functions), we
encounter other problems, probably the opposite of the morphogenic
development type. Other closely related problems are those associated
with the death of tissues and organisms as a whole. Causes and eflPects
of death are still unknown, and much scientific work must still be done
in this field.

Morphogenesis 583

Normal morphogenesis occurs when the correct balance between spe-
cific stimulators and susceptible structures is present. Occasionally, cer-
tain tissues will abnormally assume growths known as neoplasms (ne' o-
plazm) (Gr. neos, new; plasma, formation). If such a growth is harm-
ful or malignant, we commonly refer to it as a cancer or carcinoma (kar'-
sinomah) (Gr. karsinos, crab, cancer). We commonly use the word
tumor (tu'mor) (L. tumere, to swell) if the growth in general is harm-
less or nonpathologic. Sometimes a neoplasm may grow only at its
original site, but occasionally certain of the abnormal cells may circulate
to other areas by metastasis (me -tas' ta sis) (Gr. met a, change; stasis,
place) and initiate abnormal growths in new places.

Plants also possess morphogenesis whereby tissues and organs are dif-
ferentiated and developed. Quite different tissues and organs of plants
must originate differentially from what appears to be similar cells and
tissues. How can a plant develop such different structures from appar-
ently the same cells and tissues? As in animals, so plant morphogenesis
is influenced by the hereditary potentialities of the various species as well
as by the presence of specific substances. Not only are specific genes
involved, but plant hormones known as auxins (ok' sin) (Gr. auxein, to
increase) initiate and regulate many phases of plant growth and develop-
ment. Auxins are organic acids which are synthesized by the living
protoplasm in certain parts of plants. These auxins are specific, at least
to a certain degree, and may affect organs in which they are formed or
other tissues and organs to which they may be transferred. The latter
seems to be primarily polar; that is, they are transferred largely in one
direction. A more detailed consideration of auxins and their actions is
given elsewhere.

QUESTIONS AND TOPICS

1. Learn the correct pronunciation, spelling, and derivation of each new term
used in this chapter. Include as many typical examples of each as possible.

2. Contrast homology and analogy and give as many examples of each as pos-
sible.

3. Explain why it might be desirable or undesirable for living organisms to
possess autotomy generally and extensively.

4. What benefits have you derived from a study of homology, analogy, autot-
omy, regeneration, and morphogenesis ?

5. Explain why differentiation and growth are not necessarily synonymous.

6. Explain how each of the various factors may be influential in the process of
differentiation in morphogenesis.

7. What is the relationship between genes and environmental chemical sub-
stances in the determination of specific traits ?

584 Animal Biology

8. Explain the results of abnormal morphogenesis, including examples.

9. In this connection, propose a method for the prevention of cancer or at least
a scientific method for an investigation which might lead to its prevention.

10. Explain why it might be undesirable or desirable for living organisms to
possess a high degree of ability to regenerate all types of structures easily.
In considering this topic, bear in mind that Nature did not supply many of
the higher, more complex tissues with this ability.

SELECTED REFERENCES

Arey: Developmental Anatomy (Embryology), W. B. Saunders Co.

Demerec: Advances in Genetics, Academic Press, Inc.

Goldschmidt: Physiological Genetics, McGraw-Hill Book Co., Inc.

Huxley and DeBeer: Elements of Experimental Embryology, Cambridge Univer-
sity Press.

Maximow and Bloom: Textbook of Histology, W. B. Saunders Co.

Morgan: Embryology and Genetics, Columbia University Press.

Muller, Little, and Snyder: Genetics, Medicine and Man, Cornell University
Press.

Riley: Genetics and Cytogenetics, John Wiley & Sons, Inc.

Stern: Human Genetics, W. H. Freeman & Co.

Weiss: Principles of Development, Henry Holt & Co., Inc.

Wilson: The Cell in Development and Heredity, The Macmillan Co.

Chapter 28

EARLY MAN AND HIS RECORDS

HISTORY OF MANKIND AND HUMAN SOCIETY

Our knowledge of the gradual evolution of mankind from its early
ancestry has been obtained in the last hundred years from fossils of an-
cient human beings, from their habitations, weapons, tools, records
carved on stones, from sculpture and paintings. Early man probably
gathered wild plants, roots, fruits, and seeds for his various needs and
hunted wild animals for food, shelter, clothing, and crude implements.
Domestication of animals and the cultivation of plants by man occurred
many centuries ago. The cultivation of wheat and barley occurred in
Egypt between 5,000 and 4,000 e.g. Cattle for milk production and
horses for transportation probably were used in western Asia before 3,000
B.C. Sheep and asses were used by man in early Egypt. Early man
probably ate raw foods, as the use of fire is associated with the Peking
man. Today, the human being is the only living organism which utilizes
cooked foods for a greater or lesser part of his diet. The human race
is thought to have originated in Central Asia and to have migrated slowly
in various directions. Man is thought to have arrived in America from
Asia across Bering Strait, whose waters are shallow and sometimes solidly
frozen in winters. Before Columbus discovered America in 1492, two
great human cultures were present: the Incas in the Andes Mountains
of South America, whose culture rests on earlier cultures dating back
to before the Christian era, and the Mayas and Aztecs of Central Amer-
ica. The Mayas culture began before 3,000 B.C. None of these early
American civilizations had Old World domestic animals, except dogs,
but they had such New World plants as maize (corn), cotton, sweet po-
tatoes, beans, tomatoes, peppers, squashes, peanuts, etc. These early
accounts of ancient men are so interesting and extensive that the reader
is referred to the many excellent sources now available.

All records of man in the past suggest that he has been a social ani-
mal, parents and children living in groups rather instinctively. Because

585

586 Animal Biology

of this method of living, the young were somewhat protected, profits
from past experiences were made, surpluses could be accumulated and
shared, forces could be combined against enemies, and affections and
mutual regards developed. Several family groups combined to form a
larger tribe, and tribal groups formed a society, with its inherent benefits
and detriments. Naturally, individual and group antagonisms developed,
with their attendant consequences. The rise and fall of civilizations
have been, and are still, inseparable from the cultures of peoples; that
is, from the skillful attempts with which they have kept themselves physi-
cally and mentally well, happy, and well supplied with the essentials of
life and from the skillful uses that they have made (or should have
made) of their surpluses of time, energies, and material things. The
uses to which these surpluses are put are more important than the sur-
pluses themselves. The progress of human civilization is in the hands of
man himself.

EARLY MAN AND HIS RECORDS

Early man has left many interesting and valuable records (Fig. 309),
by means of which we are able to get an idea of his physical and mental
traits as well as his achievements and activities. In many instances
rather complete skeletons of early man have been preserved in the depths
of the earth's strata. These, together with his implements and tools,
form the basis for our knowledge of our remote ancestors. Early man
probably did not always bury his dead, so that extremely early records
do not date before the Pleistocene epoch (Figs. 320 to 322). The most
valuable records of early man date from the early Pleistocene epoch or
possibly the very late Pliocene epoch. Many records of early man have
been found, but the following are representative:

Java Ape-Man (Pithecanthropus erectus). — The skull cap, the left
femur, and the lower jaw with three teeth were found near Trinil in Java
in 1891 by Dr. Eugene Dubois. These remains are also known as the
"Trinil Man." It is thought that this type existed during the first glacial
age of the early Pleistocene epoch. His cranial capacity was about
950 c.c, which is approximately one-half that of an average modern
European, but half as much again as that of a large gorilla. His higher
psychic functions were limited because of the poorly developed frontal
regions of his brain. The centers of taste, touch, and vision were prob-
ably well dev-eloped. He may possibly have used speech of some type.
The skull cap was very thick and his forehead was low, receding, and with

Early Man and His Records 587

bo— H ^ oj

o<.s

588 Animal Biology

massive supraorbital ridges. His skull was narrow. His jaw projected
almost snoutlike. His average height was about 5 feet 7 inches. He
lived on land and seems to have been more similar to man than any ape.
He used sharpened sticks and stones for implements.

Peking Man ( Sinanthropus pekingensis). — Skulls, teeth, and brain
cases were found near Peking, China, in 1926 to 1928, by Dr. D. Black.
This type is supposed to have lived during the first interglacial age of
the early Pleistocene epoch. His cranial capacity was about 1,000 c.c;
hence his head was larger than that of Pithecanthropus. The brain case
shows the brain to be human but small and comparing rather favorably
with normal human brains of primitive men of today. Dubois thinks
that this type may probably have been a variant member of the Neander-
thal race, to be considered in a later paragraph. The walls of the skull
were thick. The forehead was low, receding, and possessed heavy su-
praorbital ridges. This early man used fire because charcoal and charred
remains of various materials have been found buried with his remains.
He used tools and implements of bone and stone, over two thousand
stone implements being present with the remains so far unearthed.

Piltdown Man or Dawn Man (Eoanthropus dawsoni). — Fragments
of a female brain case and half of a lower jaw were found in a gravel pit
in 1911 to 1913 by C. Dawson at Piltdown in southern England. This
type is thought to have existed during the first interglacial age of the
early Pleistocene epoch. His cranial capacity was about 1,300 c.c, which
was larger than either Pithecanthropus or Sinanthropus. His brain was
primitive and human with certain simian characteristics. The cranium
was unusually thick (0.4 inch). The jaw and teeth were apelike in some
respects and human in others. His forehead was apelike but without
prominent supraorbital ridges. He was probably more manlike than
Pithecanthropus or Sinanthropus. Crude flints deposited in the gravel
with his remains indicate a primitive culture. He was burly and knew
little about tools.

Heidelberg Man ( Palaenthropus [Homo] heidelbergensis ) . — The

lower jaw and teeth were found by Dr. O. Schoetensack near Heidel-
berg, Germany, in 1907. The Heidelberg man may have existed during
the third interglacial age of the early Pleistocene epoch. His cranial
capacity has not been accurately determined. The jaw was massive and
primitive with the teeth large and human. The mouth region projected
more than modern man but not as much as in the chimpanzee or gorilla.
The forehead was low with prominent supraorbital ridges. From the

Early Man and His Records 589

remains, he evidently used flints and may have used rudimentary speech.
His entire skeleton was massive, suggesting a powerful physique.

Neanderthal Man (Homo neanderthalensis ) . — The skull cap and
parts of the skeleton were found in 1856 by Dr. Fuhlrott in the Neander-
thal valley near Diisseldorf, Germany. This type is thought to have
existed during the third interglacial and third glacial ages of the Pleisto-
cene epoch. His cranial capacity was between 1,400 and 1,600 c.c. His
higher mental faculties were not highly developed. The anterior region
of his brain was not as highly developed or as large as in Homo sapiens.
Neanderthal man had a low, broad forehead with massive supraorbital
ridges. His eyes were large and round. His nose was broad. His knees
were bent and his head was held forward when he stood or walked.
His spinal column was slightly curved. All of this gave him a peculiar
slouching attitude. His skeleton was not over 5 feet 4 inches tall; usually
his average was less than 5 feet. His feet and hands were large and his
legs were longer than his arms. He had a receding chin. More than
fifty skeletons of this type of man have been found in England, Belgium,
Germany, France, Spain, Italy, Palestine, Syria, Arabia, Iraq, Rhodesia,
and China. This suggests a very wide distribution of this primitive race.
From their remains it is thought that they lived at the entrance to caves
rather than in them; that they used a language; that they used fire for
warmth and cooking; that they were great hunters and ate the bone
marrow of their captured animals; that they used implements of flint,
bone, and unpolished stone; that they believed in a hereafter because they
buried flint implements and foods with their dead. He probably clothed
his hairy body in the skins of animals.

Cro-Magnon Man or Modem Man (Homo sapiens). — Five skeletons
were found in the Cro-Magnon cave in Dordogne, France, in 1868. He
is thought to have been present during the fourth glacial or ice age of the
late Pleistocene epoch, even down to the recent epoch. His cranial
capacity was from 1,400 to 1,500 c.c, which is equal to, if not greater
than, that of the average European of today. The anterior part of the
brain was large and well developed, being equal to, if not greater than,
the average of today. The skull was large, long, and narrow. The
forehead was high with moderate supraorbital ridges. The face was
broad; the jaws, wide; the cheek bones, large; the eyes, large and far
apart; the spinal column had four distinct curves. The male averaged
6 feet 2 inches in height, which suggests a strong, athletic race. The
chin was well developed. In general, they were probably handsome peo-
ple comparing quite well with existing races. They lived in caves and

590 Animal Biology

rock shelters. They hunted and fished by means of skillfully made har-
poons and spears. Many implements and ornaments of bone have been
found. They developed an art in which they carved and made draw-
ings in oil. They developed primitive industries in which they used bone
more extensively than flint. All in all, the Cro-Magnon man is a good
ancestor of modern man from a physical as well as a mental standpoint.
In the distant future, when man shall unearth the remains of some of
us, what type of record will we have left, and for what will our civiliza-
tion be noted?

QUESTIONS AND TOPICS

1. List the various types of fossils and records which ancient man has left and
include the specific manner in which each has been preserved.

2. Give logical reasons why more records of ancient man have not been dis-
covered.

3. Make a table of the more representative types of ancient man, including the
outstanding characteristics of each.

4. Explain where and how records of ancient man are discovered. Are additional
records being found at the present time? Where? (Read articles on present-
day discoveries before answering these questions.)

5. What logical conclusions might you draw from a study of the sequence of
records left by ancient man?

6. Explain how we might determine the type of life which ancient men led.

7. Where in the world have the records been found? What does this mean?

8. What important changes seem to have taken place in the structure of man
as revealed by the remains available to date ?

9. What type of records do you think we today will leave for future generations,
and in the light of our present civilization what interpretations may be made
of them?

SELECTED REFERENCES

Andrews: On the Trail of Ancient Man, G. P. Putnam's Sons.

Andrews: Meet Your Ancestors, Viking Press, Inc.

Coon: The Races of Europe, The Macmillan Co.

Gates: Human Ancestry, Harvard University Press.

Gregory: Our Face From Fish to Man, G. P. Putnam's Sons.

Hooton: Un From the Ape, The Macmillan Co.

Howells: Mankind So Far, Doubleday, Doran & Co., Inc.

Macgowan: Early Man in the New World, The Macmillan Co.

Moir: Antiquity of Man in East Anglia, Cambridge University Press.

Osborn: Men of the Old Stone Age, Charles Scribner's Sons.

Romer: Man and the Vertebrates, University of Chicago Press.

Schmucker: Man's Life on Earth, The Chautauqua Press.

Shimer: Evolution of Man, Ginn and Co.

Weidenreich: Apes, Giants and Man, University of Chicago Press.

Wilder: Pedigree of the Human Race, Henry Holt & Co., Inc.

Yerkes: Almost Human, London, Jonathan Cape, Ltd.

Yerkes and Yerkes: The Great Apes, Yale University Press.

Part 3
GENERAL AND APPLIED BIOLOGY

Chapter 29

GEOGRAPHIC DISTRIBUTION OF ANIMALS

AND PLANTS— BIOGEOGRAPHY (ZOOGEOGRAPHY

AND PHYTOGEOGRAPHY)

The scientific study of the distribution of living organisms in space is
known as hiogeography. If the study pertains to animals the science is
called zoogeography; if it pertains to plants it is known as phytogeog-
raphy. In general the study of the geographic distribution of living or-
ganisms deals with larger areas or regions such as a country or continent,
while the ecologic study of those same organisms would be made in a
more or less limited area, such as a field, pond, or river. Ecology is con-
sidered elsewhere in another chapter.

I. WHY STUDY GEOGRAPHIC DISTRIBUTION?

Zoogeography may profitably be studied for the following reasons : ( 1 )
To see that each species of animal is rather definitely restricted to certain
regions of the world or to certain limited areas of a certain environment.
The entire world has been divided into seven major geographic regions
and each region has certain animals which are typical and representative
for that region (Fig. 310) . It is by a thorough study of geographic distri-
bution that the various principles of zoogeography can be properly learned
and interpreted. (2) To see, as a result of adaptation of a species of ani-
mals to a particular environment, that such a species is thus restricted
by its resulting morphology and physiology to those parts of the world in
which that particular type of environment exists. If animals change
because of adaptations, they must then select an environment which will
be satisfactory if they are to live successfully. All of this study attempts

591

592 General and Applied Biology

to ascertain and explain the various reasons for the particular distribu-
tion of various organisms. The eflfects of various environmental factors
on the morphologic, physiologic, and developmental characters of animals
also may be observed. Such a study of the interrelationships between
organisms and their various environmental factors is known as the science
of ecology. It will be observed also that a similar environment in two
different and widely separated places does not necessarily contain similar
animals. (3) To see that in the past the boundaries of sea and land have
changed repeatedly, in some instances erecting natural barriers, in others
providing favorable highways for dispersal. It will be seen also that two
widely separated present-day types may have had a common ancestor
in the past. The fossils of extinct North American camels were the an-
cestors of the present Old World camel and the llamas of South America.

II. TYPES OF GEOGRAPHIC DISTRIBUTION IN SPACE

There are two general types of geographic distribution of animals in
space. The first is the lateral or longitudinal distribution throughout
the various geographic regions of the world (Fig. 310). This type of

(AUSTRALIAN

«-v ^

Fig. 310. — Geographic regions of the world.

distribution is limited to the spread of animals over the face of the earth
in the various directions of the compass. The second is vertical distribu-
tion of animals throughout the various altitudes (Fig. 311). This type
of distribution emphasizes the differences in animal distribution on

Geographic Distribution of Animals and Plants 593

mountains, in valleys, in caves, and in the various depths of the sea.
Undoubtedly there are regions of animal distribution as we ascend from
the lowest depths of the ocean to the top of the highest mountains.

Fig. 311. — Diagram of the parallel distribution of organisms in longitude, .(4,
and altitude, such as mountains, B, 1, 2, Tropical and subtropical organisms;
3, deciduous trees; 4, evergreen trees; 5, limited varieties of such plants as mosses,
lichens, etc. ; a similar transition exists from the equator to the South Pole.

III. PRINCIPLES OF GEOGRAPHIC DISTRIBUTION

There are probably many principles of zoogeography, but the more im-
portant will be discussed only rather briefly in such a work as this. The
principle of dispersion illustrates the fact that animals naturally tend to
migrate or disperse from their birthplace. This is necessary because more
offspring are usually produced than ^normally can be accommodated in
that particular habitat. This so-called reproductive pressure tends to
overpopulation. The latter leads to dispersal in an attempt to remedy
these conditions. It is also known that offspring and parents cannot har-
moniously occupy the same area because they all possess inherently the
attitudes of survival of the fittest and the struggle for existence. Parents
frequently destroy, or at least actively compete with, the offspring which
they have produced.

The problem of overpopulation may be overcome in one of the follow-
ing ways, or in a combination of several of them : ( 1 ) There can be a

594 General and Applied Biology •

migration of a number of individuals from the overcrowded area. (2)
There can be an extermination of a number of individuals by parents,
brothers, sisters, or other species. (3) There can be a natural death for
a sufficient number so that a balance again can be realized. (4) The
problem of overpopulation may also be regulated by a reduction in the
number of offspring produced. This is a factor which cannot easily be
controlled, especially among the lower animals. (5) A different type of
food can be utilized if the struggle should develop around this very im-
portant factor.

The principle of definite habitats shows that the home or habitat of a
particular species is determined by such physical factors as the following:
( 1 ) The quantity and quality of foods. The herbivorous animals, such
as deers, must be near suitable vegetation. The carnivorous animals,
such as tigers and lions, must live near a source of suitable flesh foods.
The omnivorous animals, such as man, can usually be more widely dis-
tributed, although they must also be distributed so as to get the proper
types of both vegetable and animal foods. (2) The quantity and quality
of water also affect the selection of a habitat by a particular species. A
certain amount of water is essential for all animals because their bodies
are made of 50 to 95 per cent water. Many forms in dry climates prevent
excessive evaporation by some type of thick covering. Many species
found under rocks are not always there in order to shun light but for
moisture and protection. The depth, salinity, and hydrogen-ion concen-
tration of the water also are important factors in influencing the selection
of the proper habitat. (3) The quantity and quality of the air are also
influential in determining the habitat selected by a certain species of ani-
mal. This is particularly true for terrestrial forms, although the avail-
ability of air in the water also affects the aquatic types. (4) The quantity
and quality of light, including sunshine, is a factor which is influential
in the distribution of many animals. Some types shun light for protec-
tion and for reduction of heat produced in their bodies. Others actually
require certain amounts of light for their various normal metabolic activ-
ities, (5) The presence or absence of an optimum temperature may be
a determinative influence in animal distribution. It is well known that
animals will tend to seek the temperature for which they are particu-
larly fitted. Many animals living in tropical regions pass the summer in
a condition of aestivation or semitorpid condition of semiactivity. Cer-
tain animals living in colder climates pass the winter in various ways:
(1) Hibernation, or a period of inactivity in some protected location.
Such animals as frogs, turtles, snakes, the larvae and pupae of insects.

Geographic Distribution of Animals and Plants 595

hibernate. (2) Migration to warmer regions. Certain species of birds
migrate from the arctic regions to the tropics. The golden plover (bird)
illustrates such a migration. (3) Continued activity in their cold habi-
tats. If animals remain in the cold habitats in winter, they frequently in-
crease their fat layers as well as their coats of hair to help withstand the
attacks of the cold. They may also change their diets to include foods
which will produce greater amounts of heat. (4) Animals may die be-
cause of the extreme temperature. Many species naturally expect this
and have carefully taken the precaution of depositing their eggs so that
the developing offspring may take their places when more favorable
temperatures return.

The principle of harriers and highways is one of the most important
in animal dispersal. What may prove to be a barrier for one species may
serve as a favorable highway for another. Some of the more common
barriers are as follows : ( 1 ) There may be a lack of the proper quality
and quantity of foods along the route of migration. (2) Water may be
a barrier for terrestrial forms but may successfully be used by aquatic
types. The size, depth, temperature, acidity, and pressure in bodies of
water all may be important factors in dispersal of even aquatic animals.
The aridity and humidity of terrestrial environments may act as high-
ways or barriers, depending on the type of animal in question. Salt water
may be a barrier for fresh-water forms, and fresh water likewise may be
one for marine forms. Amphibia are rarely found in salt water. (3)
The various kinds of land may serve as barriers or highways, depending on
the type of land as well as the species of animal. For instance, tracts of
land may act as barriers for aquatic forms; forests may act as barriers
for open-country or prairie-inhabiting species; deserts and open country
may act as such for forest-inhabiting types. Mountains with their char-
acteristic temperatures, moisture, oxygen supply, and food supply may
act as barriers to many types in their attempt to migrate over them. (4)
The interference by other animals either through bodily struggles or com-
petition for foods may influence the dispersal of certain kinds of organ-
isms. (5) Winds, especially strong winds, tend to carry species of flying
habits in the direction of the wind blow. This may result in their migra-
tion into more favorable or less favorable habitats as the case may be.
(6) Temperature may prevent the dispersal of many animals, either by
its direct effect on the migrant or by its effect on the vegetation upon
which the migrant must depend for food and shelter. (7) The lack of
adaptive ability of the animal may result in its inability to adapt itself
quickly enough to new and changed environmental conditions. The

596 General and Applied Biology

result may be extermination or an attempt to continue its migration.
This is an illustration of what is frequently known as a biologic barrier.
Much of this adaptive ability is due to inherent, inherited properties of
the protoplasm of each particular animal.

The following methods of dispersal are rather common in the animal
world. ( 1 ) Driftwood may transport animals for great distances. Wil-
liam Beebe on his Arcturus voyage observed fifty-four species of marine
fisheSj worms, and crabs on one floating log. (2) Ships in their travels
from port to port may transport various types of organisms. How many
rats have had free transportation from one port to another can never
be known. (3) Water and floods may mechanically transport organisms,
drive them from their original habitats, or change the food supplies suf-
ficiently that dispersal will be necessary. The presence of desirable water
supplies for consumption during migration may determine the final and
future habitation. (4) Aquatic animals may transport other animals on
their bodies or within their bodies. The larvae of clams may be carried
on the gills and fins of fishes. Many aquatic parasites are dispersed by
aquatic organisms. (5) Terrestrial animals may transport other animals
on the exterior or interior of their bodies. Birds may carry eggs, larvae,
pupae, or adults of smaller animals, especially during migration. (6)
Winds may direct the course of certain animals or may blow objects to
which certain types are attached. (7) Glaciers may cause animal migra-
tions by actually transporting them or by changing the temperature or
food supply. (8) Man, either knowingly or unknowingly, aids in animal
dispersal through the means of automobiles, airplanes, boats, and trains.
A "horned toad" was transported from Texas to Springfield, Ohio, by a
circus train, although after its arrival it found the rigors of the city too
great. This was no fault of the method of migration. English sparrows
were transported from the East to the West in returning empty grain cars.
This method was successful for the rather friendly sparrow but would not
have been used by the more timid bluejay which would hesitate to fre-
quent the empty grain cars in the East.

The principle of discontinuous distribution is illustrated by the presence
of the same species of animal in two widely separated regions, in which
case it is usually concluded that the distribution of that species was once
continuous between the present regions. For example, the tapirs today
inhabit Central and South America, southern Asia, and the Malay archi-
pelago only. In the Pliocene epoch of the past (Figs. 320 to 322), tapirs
were distributed over nearly all of North America, Europe, and northern

Geographic Distribution of Animals and Plants 597

Asia. Today they are extinct except in those regions mentioned above.
There was a rather continuous distribution originally, but today they il-
lustrate discontinuous distribution.

The principle of vertical distribution states that the organisms of higher
elevations of mountains simulate those of the polar regions of the world.
As we progress downward in altitude, the forms simulate those which
would be found in travelling from the poles toward the equator. In
general, the temperate zones not only extend laterally north and south
of the equator but also vertically in parallel succession from the somewhat
tropical conditions at sea level to the somewhat frigid conditions at the
mountain peaks (Fig. 311).

IV. GEOGRAPHIC REGIONS OF THE WORLD

The world has been divided into seven regions (Fig. 310) each with
its different characteristics and peculiar, yet typical, fauna and flora.
Each of these seven regions will be briefly described.

1. Nearctic Region (Gr. neo, late or new; arctic). — This region in-
cludes North America down to the edge of the Mexican plateau, as well
as Greenland. Great groups of mammals are characteristic of this region.
Many types in this region are related to the Palaearctic region, although
they differ in minor details. Animals which are peculiar to this region
include the blue jays, rattlesnakes, raccoons, opossums, skunks, prairie
dogs, water dogs (Cryptobranchus is found in the Mississippi RiverVal-
ley), and the musk ox. The latter, which is peculiar to North America,
was until recently present in Siberia and originally lived in continental
Europe and England. What a difference in the distribution of the musk
ox in the past and present !

2. Palaearctic Region (Gr. palae, ancient; arctic). — This region in-
cludes Europe, Africa (north of the Tropic of Cancer), Asia (north of
the Himalayas), and Japan. Many types of mammals of this region are
closely related to those of the Nearctic region, differing in minor respects.
Many trees and plants are common to both regions. These two regions
are the most similar of all regions and are sometimes combined into one,
known as the Holarctic region (Gr. holo, whole; arctic). Animals com-
mon to both Nearctic and Palaearctic regions include beavers, deers,
hares, foxes, wildcats, and bears. Animals of the Palaearctic region in-
clude the nightingale, Megalobranchus (water dog of Japan which re-
sembles our own water dog), and the camel and dromedary of central
Asia and northern Africa.

598 General and Applied Biology

3. Neotropical Region (Gr. neo, new or recent; tropical) . — This region
includes Central America, Mexico, South America, and the West Indies.
The following types are present in this region : tapir,* sloth,f armadillo,!
wild pig (peccary),* llama,* marmoset,t flat-nosed monkeys, f tree ant-
eaters,! tree porcupine,f and many kinds of deer,* rats,* cats,* wolves,*
and rabbits.*

4. Ethiopian Region (Gr. aithiops, black face). — This region includes
Africa (south of the Sahara Desert), southern Arabia, and Madagascar
and adjacent islands. The following animals are characteristic of this
region, some of which are native only of this region: African elephant,
hippopotamus, rhinoceros (several species), zebra, giraffe, antelopes
(many species), lions, leopard, lemurs (found in Madagascar), gorilla,
chimpanzee, baboon, and secretary bird.

5. Oriental Region (L. orientalis, eastern).- — The region includes India
(south of the Himalayas), southern China, the Philippines, Siam, Burma,
Borneo, Java, and Sumatra. Animals of this region include the Indian
elephant, rhinoceros, Indian tapir, tigers, jungle fowls (ancestors of do-
mestic fowls), gibbons, orangutan (in Borneo and Sumatra), and the
cobra.

6. Australian Region. — This region includes Australia, New Zealand,
New Guinea, Tasmania, Papua, etc. This region has practically no
higher mammals. It is the home of the marsupial animals (animals with
pouches in which the young may be carried). It is still the home of the
so-called Monotremes or lowest types of mammals, such as the duckbill.
This region is one of the most peculiar in the world. Such animals as
the following are characteristic: the lizardlike Rhyncocephalia of New
Zealand, certain wingless birds of New Zealand, the Australian kangaroo
with its closest relative the opossum in America, and certain character-
istic birds, snakes, and lizards.

7. Polynesian Region (Gr. poly, many; islands). — This region includes
the oceanic islands of the tropical Pacific, such as the Hawaiian Islands,
Samoa, Society Islands, and Fiji Islands. This region is sometimes in-
cluded with the Australian. The islands were formed in many instances
by volcanic eruptions. Their shores are fringed with coral reefs. The
vegetation is often large and herbaceous, such as the palm and banana
trees. There are fewer types of living organisms than in the larger re-
gions, and consequently there is less competition. There are no land
mammals present except bats, and there are no amphibia on these islands.

*Types peculiar to South America now but have similar representatives in North America.
The llama has its nearest lelative, the camel, in the deserts of Asia.

fTypes peculiarly South American with practically no forms in North America except the
Canadian porcupine.

Geographic Distribution of Animals and Plants 599

V. REGIONS OF GEOGRAPHIC DISTRIBUTION OF
VEGETATION OF NORTH AMERICA

If a study were made of the geographic distribution of plants through-
out the worldj we would find that the world could be divided into geo-
graphic regions (just as for animals), each with its particular environ-
mental characteristics and peculiar flora. However, it may be just as

Fig. 312. — Vegetation areas of North America (the boundaries of the various

regions are given in a general way).

interesting and profitable to limit our study of phytogeography to North
America. It will be observed (Fig. 312) that the North American con-
tinent can be divided into various vegetation areas (geographic regions).
These areas are summarized in an accompanying table in which the gen-
eral environmental characteristics and the plants typically present in
each region are given. Observe that the environmental characteristics

600 General and Applied Biology

Regions of Vegetation of North America (See Fig. 312)

A. Tundras

a. Deserts

C. Grasslands

D. Forests
(a) Northern
evergreen

(b) Southern
evergreen

GENERAL CHARACTERISTICS

Fringes the northern limits of North
America from Labrador to Alaska
(north of latitude 55 to 60°)

Long cold winters

Limited moisture ; light snowfall

Air dry in winter

Strong winds

Short growing season because upper
limits of soil thaw slightly and
ground water is cold

Soil temperature low

Most of Arizona and Nevada; south

ern parts of New Mexico, Cali

fornia and Texas

lower California

Mexico
High evaporation of

plants due to intense heat and low

atmospheric moisture
Intense and generous sunlight
Small amount of rainfall
Winds fairly strong

peninsula of
and northern

moisture from

Extends from central Texas to Mani-
toba and along foothills of the
Rocky Mountains from New Mex-
ico to Alberta

Soil rich in humus overlying sand
and clay

Few trees probably because of
limited soil moisture and exces-
sive evaporation due to excessive
heat

Light annual rainfall

PLANTS TYPICALLY
PRESENT

Certain mosses
Certain lichens
Certain grasses
Certain sedges
Certain herbs
Certain low shrubs
Certain dwarf willows

From Atlantic to the Pacific Oceans
between the tundra on the north
and the Great Lakes on the south;
extends northwestward to Alaska

Sagebrush

Cacti with small, spine-
like leaves to protect
and prevent excess
evaporation

Yucca trees

Certain species of bunch
grasses

Few species of small
herbs

Various species of bunch

grasses
Various types of cacti
Various kinds of shrubs

Southeastern U. S. from Texas to

Florida and Virginia
Many low, rolling sandy plains
Many large swamps
Also high coastal plains farther from

the ocean

Cone-bearing trees as:

Spruce

Balsam fir

White pine, red or
Norway pine, jack
pine

Hemlock

Arbor vitae
Deciduous trees as:

Balsam poplar

Aspen

White birch

Long-leaf pine
Short-leaf pine
Water oaks
Bald cypress
Magnolia trees
Gum trees

Geographic Distribution of Animals and Plants 601

Regions of Vegetation of North America (See Fig. 312) — Cont'd

(d) Rocky

Mountain
forests

(e) Pacific Coast
forests

general characteristics

From central New York to Texas
and Louisiana; from Wisconsin to
Oklahoma

Along Rockies from southern Mexico
to Columbia (except coasts of Mex-
ico)

These mountains present such varia-
tions in elevations and climates
that a great variety of trees exists
here

No trees in altitudes higher than
10,000 feet, although there exist
low vegetation which resembles that
of the tundra

plants typically

PRESENT

White oak; black oak

Hickory trees

Chestnut trees

Walnut trees

Maple trees

Ash trees

Birch trees

Elm trees

Certain cone-bearing

trees as:

Short-leaf pine

White pine

Hemlock

Western yellow pine
Lodgepole pine
Douglas fir
Western hemlock
Western larch

Extend along the western slopes of
the mountains from California to
Alaska

( 1 ) Canadian-Alaska region

(2) Washington-Oregon region (mild
winters and heavy rainfall; very
luxuriant vegetation)

(3) California region

rSitka spruce
-{ Douglas fir
IWestern hemlock
Sitka spruce
Douglas fir
Western hemlock
^ Western white pine
Dense undergrowth of
ferns; shrubs; short,
deciduous birches,
I maples, and poplars
S Coast redwoods
' Sequoia trees

(f) Tropical
forests

Found in West Indies, Central Amer
ica, coasts of Mexico, southern tip
of Florida

Jungles present in many places, and
in certain regions they are so dense
overhead that limited light result?
in diminished vegetation around
the tall trees; upper parts of these
tall trees filled with masses of
ferns, mosses, lichens, tropical or-
rhids, and lianas

Various palms
Tropical orchids
Lianas (woody, climb-
ing vines)
Mangrove swamps.

602 General and Applied Biology

differ in tundras, deserts, grasslands, and forests. Naturally, we would
expect to find different types of vegetation in each region. If the dis-
tribution of forests is studied in detail, it is apparent that different types
of trees are distributed in various parts of the continent, depending upon
the influential characteristics of the environment peculiar to each of
these forest areas. Could we expect the same type of forest in the far
north as we find in the tropics? Attempt to list the environmental char-
acteristics of each vegetation area and then use them to explain the
distribution of the types of vegetation peculiar to each of these regions.
In doing so, you will begin to appreciate how Nature functions in limit-
ing certain kinds of vegetation to specific areas.

VI. GENERAL FACTORS INFLUENCING THE
DISTRIBUTION OF ORGANISMS

Only a few of the more common and important factors can be con-
sidered in such a brief discussion as this. ( 1 ) The connection of regions
by the formation of bridges, such as the isthmus of Panama during the
later Miocene epoch (7,000,000 years ago) (Fig. 320) permitted migra-
tions of organisms in both directions. North and South America were
not connected in the early Miocene epoch of the Ccnozoic era as is
shown by fossil records of the prevailing faunas in these regions. (2)
Disconnection of regions by the formation of channels or straits, such
as Bering Strait between Asia and North America, prevented migrations
of certain animals. Fossil records in both regions show that migrations
occurred in both directions across the former land bridge before the
present strait was formed. (3) Glaciers may cause a lateral as well as
a vertical migration because of changes in temperatures, food supplies,
and places of protection. (4) The flora (plant population) of a region
affects either directly or indirectly the animal population of that region
as far as food, shelter, and protection are concerned. (5) The presence
of belligerent, antagonistic species may influence the distribution of cer-
tain species of organisms. The first appearance of certain species in
definite centers of dispersal may make it possible or impossible for later
migrations. In this case, priority rights of possession are determinative
factors. (6) When organisms are isolated from the main stock of species,
divergence is promoted in proportion to the degree of isolation and the
length of time isolated. This is in part accomplished by preventing new
types from being eliminated by interbreeding with the old. Isolation is
thus a factor in the process of descent with changes. According to Jor-

Geographic Distribution of Animals and Plants 603

dan, species are present in specific habitats because (a) they are pre-
vented from migrating elsewhere because of barriers; (b) they have
been unable to maintain themselves in other habitats and thus have had
to move into this particular region because they were successful in doing
so in this type of habitat; (c) they have been so changed in their new
habitats that they now constitute a new species. The latter might ex-
plain certain origins of species in limited localities at least.

QUESTIONS AND TOPIC

1. Select ten animals from each of the seven regions of the world and give
reasons why each animal is distributed as it is.

2. Select ten animals of your immediate community, telling why each is dis-
tributed as it is.

3. What biologic environmental factors have been and are the most influential
in the distribution of the animals selected in the second question ?

4. With somewhat similar conditions in Brazil and Africa, why does the former
have the sloth, tapir, and New World monkeys, while the latter does not ?
Why does the latter have the elephant, chiinpanzee, and gorilla, while the
former does not ?

5. Why are the marsupials the prevailing mammals of Australia ?

6. In regions having similar environments, why do we often find an entirely
different fauna of animals ?

7. Why do we frequently find similar forms on the summits of two mountains
which are a great distance apart, while the bases of these same mountains
are inhabited by entirely different types ?

8. On mountain tops, why are the types frequently similar to those which live
in the polar regions of the world ?

9. Why is the fauna of the British Isles similar to that of the adjacent con-
tinent?

10. Explain the relationship between long periods of isolation and the develop-
ment of endemic species.

11. List the values derived from a study -of biogeography. What are the rela-
tionships between biogeography and geography?

12. Discuss fully the importance of each of the principles of geographic distri-
bution. Which are the most plausible ? Why ?

13. What does the parallel distribution of organisms in altitude and longitude
suggest? Give several examples of each.

14. Give the general characteristics and boundaries of each of the seven regions
into which the animal world is divided. What factors might prevent migra-
tion from one region to another ?

15. How might a certain condition act as a barrier to one type of animal and
at the same time act as a method of transportation to another type? Give
several examples.

604 General and Applied Biology

16. List animals which are rather generally distributed throughout our country.
Describe the methods of dispersal of such animals as the European corn
borer, Mexican bean beetle, the English sparrow, and other forms with which
you are familiar.

1 7. What is the effect of quarantine on the dispersal of organisms ?

18. What is the effect of better methods of transportation by man on the dis-
tribution of organisms ?

19. List ten plants distributed in a certain area, and tell specifically why they
are distributed there rather than elsewhere?

20. Give all the reasons you can for the particular distribution of such plants as
the instructor may suggest.

SELECTED REFERENCES

Braun-Blanquet: Plant Sociology, McGraw-Hill Book Co., Inc.

Cain: Foundations of Plant Geography, Harper and Brothers.

Campbell: Outline of Plant Geography, The Macmillan Co.

Clements and Shelford: Bioecology, John Wiley & Sons, Inc.

Daubenmire: Plants and Environment, John Wiley & Sons, Inc.

Jones: Economic Geography, The Macmillan Co.

Oosting: Study of Plant Communities, W. H Freeman & Co.

Sears: Deserts on the March, University of Oklahoma Press.

Wallace: The Geographical Distribution of Animals, London, The Macmillan Co.

Weaver and Clements: Plant Ecology, McGraw-Hill Book Co., Inc.

Wulff: Historical Plant Geography, Chronica Botanica Co.

Chapter 30

ANIMALS AND PLANTS OF THE PAST
AND THEIR RECORDS

I. RECORDS OF LIFE

A fossil may be defined as any trace, remains, or impression of a plant
or animal of past geologic ages. The science which deals with fossil
plants and animals is known as paleontology (Gr. palaios, ancient; onto,
being; logos, a study). Paleontology may be divided into two sciences:
the one dealing with fossil plants, known as paleobotany (Gr. palaios,
ancient; hotane, plant or pasture) and the other dealing with fossil ani-
mals, known as paleozoology (Gr. palaios, ancient; zoon, animal; logos, a
study). Much of our present knowledge about ancient life has been
gained by a very careful and accurate study of the records left by these
ancient organisms in the various strata of the earth (Fig. 313). The
rocks of the earth's surface are of two kinds according to their origin, sedi-
mentary and igneous. The sedimentary rocks, such as limestone, sand-
stone, shales, etc., may contain fossils and are formed by the transporta-
tion and deposition of small rock particles or by the precipitation of ma-
terials from solutions or by the secretions by certain organisms, as in the
case of limestones. Igneous rocks (L. igneus, fire), such as volcanic rocks
formed by consolidation of molten lava of volcanoes, are produced as the
result of heat and do not contain fossils. In the formation of sedimentary
rocks the oldest naturally occur at the bottom of a series of strata and the
youngest nearest the top. The most ancient fossils thus will be found in
the oldest rocks, while the most recent fossils will occur in the youngest
rocks.

II. NATURE AND KINDS OF FOSSILS

The following are ways in which animals and plants of the past (Figs.
313 to 319) have left their records: (1) by actual preservation of the
original material of the organism intact, (2) by preservation of the
skeletal structures practically unchanged, (3) by natural molds or in-
crustations, (4) by petrifaction, (5) by carbonization, and (6) by leav-
ing trails and imprints (impressions).

605

606 General and Applied Biology

Actual preservation of the original material of the organism intact may
take place by freezing and preserving in ice or soil (Fig. 314). This is
not a common method, but an excellent example is the frozen mammoth
discovered in Siberia a few years ago. Even plants of the same period
were refrigerated with the mammoth. The complete remains of organ-
isms may be enclosed in rocks as illustrated by a leaf of a plant. The
remains of animals and plants may be preserved more or less intact in
tar, amber, or oil-impregnated soils (Fig. 316). Amber is a yellowish

Fig. 313. — Fossils of invertebrate animals with the geologic period in which
each type was found (see Figs. 320-322). I, Protozoa, Foraminifera {Fusulina
secalica), Pennsylvanian epoch; II, Porifera, sponge {Astraeospongia meniscus),
Silurian Period; III, Porifera "Astylospongia" {Carpomanon stellatim-sulcatum) ,
Silurian Period; IV, Coelenterata, horn coral {Zaphrentis prolifica) , Devonian
Period; V, Coelenterata, coral (Acervularia davidsoni) , Devonian Period; VI,
Coelenterata, honeycomb coral {Favor sites sp.), Devonian Period; VII, Echino-
dermata, sea bud or Blastoid {Pentremites sp.), Mississippian epoch; VIII, Echino-
dermata, stem or stalk of a Crinoid, Mississippian epoch; IX, Echinodermata
(Epiaster whitii) , Cretaceous Period; X, Brachiopoda, Brachiopod {Cyclothyris
difformis) , Cretaceous Period; XI, Brachiopoda, Brachiopod (Rafinesquina
alternata) , Ordovician Period; XII, Brachiopoda, Brachiopod (Spirifer pennatus) ,
Devonian Period: XIII, Mollusca, Pelecypod {Glycimeris subovata) , Miocene
epoch; XIV, Mollusca, Gastropod (Bembexia sulcomarginata) , Devonian Period;
XV, Mollusca, Gastropod {Solutilites sayanus) , Eocene epoch; XVI, Arthropoda,
Trilobite {Calymene niagarense) , Silurian Period.

Animals and Plants of Past and Their Records 607

fossilized plant resin (pine tree) which was originally soft and captured
the animal or plant intact. Later, the more volatile materials of the resin
disappeared, leaving the hard amber with its imprisoned organism. Cer-
tain organisms may leave their remains more or less intact by being
mired in quicksands or swamps.

When the skeletal structure is preserved practically unchanged, it re-
mains almost in its original condition, except that it has lost most, if
not all, of its organic material. In this method of fossilization, only the
skeleton remains, while in the method described above, the skeleton and

Fig. 314. — Beresovka mammoth {Elephas primigenius) discovered frozen in the
soil in Beresovka, Siberia, 800 miles west of Bering Strait and 60 miles north of
the Arctic Circle. Clotted blood, unswallowed grass, as well as the entire specimen
were quite well preserved by refrigeration. The specimen is shown as it appears in
the Petrograd Museum. (From Lull: Organic Evolution. By permission of The
Macmillan Company, publishers.)

all Other structures as well are preserved. The author has found several
skeletons of ancient mastodons, more or less well preserved, in soils of
central and southwestern Ohio. In some instances the skeletal remains
may have added such chemicals as carbonate of lime, which makes them
more compact and heavier than the original. In other instances the
skell-like skeletons of ancient animals have become more porous and
somewhat lighter than they were originally.

608 General and Applied Biology

6Ck<kCHioeAuAus

Fig. 315. — Three enormous dinosaurs (Gr. deinos, terrible; sauros, lizard),
extinct reptiles of the past. Diplodocus was over eighty feet long and weighed
forty tons; Brontosaurus was over sixty-five feet long; Brachiosaurus was about
eighty feet long. (From Atwood: A Concise Comparative Anatomy, The C. V.
Mosby Co.)

Fig. 316. — Pleistocene tar pool near Los Angeles, Calif., with entrapped ani-
mals. The elephant and wolves are caught while the saber-toothed tiger is about
to suffer the same fate. (From Cleland: Physical and Historical Geology, pub-
lished by the American Book Company.)

Animals and Plants of Past and Their Records 609

Fig. 317. — Specimens showing a natural mold, A, of the interior of an animal
from which the shell has disappeared ; B, the original shell of a similar speci-
men. (From Cleland: Physical and Historical Geology, published by the Amer-
ican Book Company.)

Fig. 318. — Trilobite, an extinct, fossil marine arthropod of the Ordovician
period (see Figs. 320-322). Dorsal (left) and ventral views show the restored
appendages. Trilobites (Gr. tri, three; lobos, lobes) had flattened, oval bodies
composed of head, thorax, and abdomen; on the dorsal side the body is divided
lengthwise by furrows into 3 lobes (one median and two lateral). They possess
one pair of delicate antennae; their gills are attached to thoracic appendages; they
have numerous, delicate, biramous appendages. (From Cleland: Physical and
Historical Geology, published by the American Book Company.)

610 General and Applied Biology

In natural molds or incrustations (Fio;, 317) neither the minute struc-
tures nor the materials of the original organism are preserved but merely
the general outlines of form and shape are recorded. Animals or plants
may be enclosed by incrustations of calcium carbonate or silica which
harden around the buried organism before it decays. The organic ma-
terials of the former organism eventually are removed by decay and a
percolation of dissolving waters. The cavity which eventually remains
retains the general form and shape of the original organism. In some

Fig. 319. — Passenger piegon {Ectopistes migratorius) which was once extremely
abundant but is now extinct. (Copyright by General Biological Supply House,
Inc., Chicago.)

instances the skeleton has disappeared entirely, leaving only the mold of
it as a record. The shells of certain mollusks may have been covered
with sediment while the soft parts decayed. The interior then may have
been filled with the same sediment. Acidified waters then may have dis-
solved the limy shell, leaving only the molds of the exterior and interior.
Sometimes the shell is removed, and the space left between the external
and internal molds is filled with mineral matters carried in by percolat-

Animals and Plants of Past and Their Records 611

ing waters. In this manner the form of the original skeleton is preserved
but not its natural structure.

In petrifaction, more or less of the original materials of the organism
have undergone a certain amount of mineralization. In this case, the
plant or animal materials have decayed in waters which contained large
amounts of lime, silica, iron oxides, iron pyrites, or other dissolved sub-
stances. These chemicals replaced the original materials of the organ-
ism, sometimes faithfully retaining the original shape, size, and even
minute details of structure of the former organism. Usually, the older
the fossil in time, the greater the degree of mineralization. The harder
parts of an organism are most frequently preserved. Shells, teeth, tusks,
bones, and the harder, woody parts of plants are most frequently petrified
by mineralization. We may find petrified wood which shows the minute
structures just as they existed in the living trees but in which the walls of
the cells are formed of the mineral silicon instead of the original cellulose.
In this process, as each particle of cellulose disappeared, its place was
accurately taken by a particle of silicon, thus retaining the minute details.

Carbonization of the original materials usually takes place in animals
which possess chitinous skeletons. This also occurs in some plants. In
this case, the organism loses oxygen and nitrogen, thus increasing the
relative percentage of carbon. Even when plant materials are carbon-
ized, they may afford valuable information regarding their original struc-
ture.

Trails and impressions (imprints) are the "fossils of living organisms,"
while other records are of dead organism. Many animals may leave their
trails and imprints, but only vertebrate animals with feet can leave foot-
prints. In all cases the records must be left in soft materials which later
become hardened and preserved. Trails and imprints, although forming
no part of the organism itself, nevertheless are considered as fossils. One
of the most common of impressions is that made by a leaf in soft mud
which later hardens and retains the impression. If the material in which
the plant or animal impression is made turns to rock, the result is a fos-
sil. This type of fossil usually does not give much information concerning
the internal structures but much concerning the shape and form of the
organism as a whole or of its parts.

III. CONDITIONS FOR FOSSIL FORMATION

In order for fossils to be properly formed, there must be a rather
rapid burial of the original organism in a locality suitable for fossil
formation. This burial usually is accomplished by water-borne sediment.
Organisms with hard parts are more likely to fossilize than softer ones.

612 General and Applied Biology

Hence, the simpler, softer organisms are rarely fossilized. This explains
the absence of many fossils of the earliest plants. The organism must
also remain intact a sufficient length of time to permit the fossilization
process to take place. The original organism must be sufficiently heavy
to settle to the bottom to be eventually covered rather than float on the
water. Air must be excluded in order to prevent the oxidation of the
organism as well as to prevent bacterial decay before the fossil is formed.
During and after formation, the fossil must withstand such natural
conditions as the elevation and sinking of the earth's strata, pressure and
heat, the erosion processes within the strata, and the slow circulation of
waters, especially acidulated waters, through the fossil. Because there
are few places on land where materials are being extensively deposited,
terrestrial plants and animals have little chance of becoming fossilized
unless they are placed in water and eventually covered. The majority
of land plants and animals after death will be quickly decomposed on
the surface of the earth, thus leaving no extensive records. However,
if covered with large quantities of volcanic ashes or lava, sand or dust,
earth through landslides or earthquakes, or calcareous materials from
calcareous springs, even terrestrial plants and animals may be fossilized
to a limited extent. If the structures of an animal or plant are thin,
fragile, easily broken, easily dissolved, and easily decayed, there may
be little opportunity to form a fossil.

IV. SIGNIFICANCE OF FOSSILS

Fossils of certain types may indicate the boundaries and extent of
former waters and lands. Fossils also may suggest the types of organ-
isms of the past and their probable relationships with modern forms.
The character of the fossils included in certain strata of the earth gives
clues as to their geologic ages and when those particular sediments which
formed these strata were laid down. Hence, certain animal and plant
fossils are known as index fossils because through them it is possible to
determine particular geologic ages and periods. Certain fossils also dem-
onstrate that life has not existed without changes in the past because
of the revelations of records of past animals and plants.

Fossils may give evidences of geographic distribution of organisms of
the past and may show where land connections once existed but are no
longer present. The Bering Strait between Asia and Alaska is about 35
miles wide and has a maximum depth of 200 feet. Studies of the fossils
on these two continents show undoubtedly that they were once connected
by land which sank beneath the water. It has been suggested that there

Animals and Plants of Past and Their Records 613

is little land today which has not at some time been below the level of the
sea, sometimes repeatedly. This explains why we may find fossils of
former marine organisms even on high mountains today. Records of
past animals and plants frequently suggest certain climatic conditions,
such as moisture and temperature, which have existed at certain periods
in the earth's history. Certain types of fossilized plants present in cer-
tain strata give us a good idea of the type of vegetation and necessary
climatic conditions at the time when such plants were placed in these
forming strata.

The study of fossil animals and plants is important because they often
include the ancestors of modern species. In addition, the data secured
from such fossils often explain relationships of present animals and
plants. In some instances the ancient types serve to connect groups of
organisms which today seem to have no direct connections. A study of
fossil animals and plants also reveals that the race history (phylogeny)
can be accurately traced. A study of the stratigraphic successions of
fossil animals and plants gives much information in regard to the pro-
gressive developments of these animals and plants of the past, as well as
suggests present and future progressive developmental tendencies. This
study naturally would be much easier and more complete if unbroken
and perfect records of fossil organisms could be procured. This is not
possible so that these data must be interpreted accordingly.

Many interesting facts about ancient plants have been ascertained
from a study of their fossil records in geologic rocks of the past. One
reason for studying plant fossils is to secure a complete picture of the
relationships between living organisms of today and their ancestors.
The earliest known plants were very simply constructed. Age by age,
more and more complex types appeared as shown by the study of the
proper strata of the earth (Fig. 320). Before the Paleozoic era the
only plants of which we find good records are the bacteria and blue-
green algae. The most ancient land plants were the ancient spore plants
from the Devonian period of the Paleozoic era. During the succeeding
Carboniferous period there appeared large, complex, treelike ferns. The
earliest seed plants (the seed ferns) occurred during the late Devonian
and early Carboniferous periods. These primitive ferns belonged to
the gymnosperms and became extinct in the Mesozoic era. Angiosperms
are first found in the Cretaceous period of the Mesozoic era. They were
dominant in this period and have retained this position ever since.

A knowledge of fossil plants is necessary for an understanding of the
classification of plants. Formerly, the classification of plants was based
on living forms, but as the knowledge of fossil plants increased, the clas-

Geologic Time Chart

ERA

PERIOD

EPOCH

DURATION
IN YEARS

DOMINANT
LIFE

Cenozoic
(Gr. kainos,

Quaternary

Recent or Post-
glacial

10,000

Man
IMammals

recent; soe,
life)

Glacial or Pleis-
tocene

(Gr. pleistos, most;
kainos, recent)

1,000,000

Birds
Modern
insects
Flowering

Tertiary

Pliocene

(Gr. pleion, more;
kainos, recent)

6,000,000

plants

Miocene

(Gr. melon, less;
kainos, recent)

12,000,000

Oligocene
(Gr. oligos, little;
kainos, recent)

16,000,000

Eocene

(Gr. eos, dawn;
kainos, recent)

20,000,000

Paleocene

(Gr. palaios, an-
cient; kainos,
recent)

5,000,000

Mesozoic
(Gr. mesos,

Cretaceous

(L. creta, chalk)

65,000,000

Reptiles

middle; zoe,
life)

Jurassic (fine de-
velopments in
Jura mountains)

35,000,000

Angiosperms

Triassic (threefold
development in
Germany)

35,000,000

Paleozoic
(Gr. palaios,
ancient; zoe.

Permian (exten-
sive in Perm,
Russia)

25,000,000

Amphibia

life)

Carboniferous
(carbon or coal-
bearing rocks)

Upper or Pennsyl-
vanian (well de-
veloped in Penn-
sylvania)

40,000,000

Seed ferns
and giant
spore plants

Lower or Mississip-
pian (well de-
veloped in Missis-
sippi River Valley)

45,000,000

Gymnosperms

Devonian (com-
mon at Devon,
England)

50,000,000

Fishes

Ancient spore
plants

Silurian (Silures,
ancient tribe in
Wales)

40,000,000

Algae

Ordovician (Ordo-
vici, ancient tribe
in Wales)

85,000,000

Invertebrates

Cambrian (Latin
for Wales)

70,000,000

Algae

Proterozoic
(Gr. pro-
teros, early;
zoe, life)

Upper Precam-
brian

550,000,000

Primitive
multicellu-
lar organ-
isms

Archeozoic.
(Gr. arche,
beginning;
zoe, life)

Lower Precam-
brian

650,000,000

Unicellular
organisms,
including
bacteria

Fig. 320. — Divisions of geologic time with most important parts described. (Com-
pare with Figs. 321 and 322.) (From various sources.)

Animals and Plants of Past and Their Records 615

sification was made more accurate and complete by incorporating the
data contributed by paleobotany. Many large groups of plants of the
past, although they have disappeared completely, have thrown much
light on the relationships of living plants through their fossil records.
Other large groups of plants which were originally dominant have dimin-
ished in numbers and importance until they are represented by a limited
number of types today. However, they too have contributed to a more
accurate classification of present-day plants.

A study of the fossil remains of ancient plants also reveals certain
climatic conditions which prevailed at the time such plants existed. In
other words, the presence of large numbers of plants at a certain period
precludes a certain type of climate in order that such plants might fluor-
ish. Such studies reveal luxuriant vegetation in regions which are at
present more or less devoid of that type of plant. In general, the climate
throughout a great part of geologic time is thought to have been much
more uniform than at present. It is thought to have been quite mild,
somewhat like present tropical climates, and with an abundance of
moisture.

A study of paleontology also reveals certain geographic conditions of
the past. Regions of the world now united originally may have been
widely separated by barriers. Regions once connected are now widely
separated. For example, mountains may have arisen or large land areas
may have been submerged beneath the water. It is thought that much
of the land area of today at some time in the past may have been below
the surface of the sea. This is concluded by the type of fossils found in
the earth's strata. Such natural phenomena as floods, glaciers, volcanic
eruptions, and earthquakes have aflfected plant distribution in the past.
A change in the quantity and quality of the atmosphere, water, food, or
soil in the past undoubtedly influenced the distribution of plants. The
greater and more extensive the changes in this connection, the greater
the effects on plants. All of these factors have in the past been quite
influential in determining plant growth and distribution.

A study of the fossil records of plants reveals that there has been a
development from the simple to the complex and that the more com-
plex flowering plants appear late in geologic history. In other words,
throughout geologic time there has been a continued succession of plants.
With each era and period, more complex and highly evolved plants be-
come dominant, only to be superseded later by newer and more compli-
cated groups. An accurate study of the plants of the past and present
enables us to reconstruct much of the history of the plant world (Fig.
320).

Cenozoic and Mesozoic Eras

t-H

EPOCH

S-i

■»->

Recent

Pleistocene

O
N

• r-l

Pliocene

Miocene

Oligocene

Eocene

Paleocene

O
o

^-5

I»

"fc.

CHARACTERISTICS OF THE TIMES
AND VARIOUS TYPES

Civilized man, modern mammals,
modern birds, modern insects

Periodic glaciation, elevation of

continents
Primitive man, modern mollusks,

extinction of great mammals

Elevation of continents; develop-
ment of Pre-man, rise of mod-
ern insects, decline of various
mammals

Maximum numbers of mammals

Rise of higher mammals

Vanishing of primitive mammals

Rise of primitive mammals

Climates quite mild ; large de-
posits of chalk due to forami-
nifera (Protozoa) ; very spe-
cialized reptiles followed by
extinction of giant reptiles;
birdlike reptiles, toothed birds,
bony fishes, rise of snakes,
crocodiles, turtles, extinction
of ammonites (Mollusca with
coiled, chambered shells)

Giant reptiles (dinosaurs, ich-
thyosaurs, pterodactyls) ; rise
of birds; clams and snails
dominant ; bony fishes, butter-
flies; decline of brachiopods;
abundant ammonites (Mollusca
Avith coiled, chambered shells)

Rise of dinosaurs, primitive mam-
mals, bony fishes; amphibia
and mollusks

REPRESENTATIVE LIFE

Fig. 321. — Description of the periods and epochs of the Cenozoic and Mesozoic
Eras of geologic time. Representatives of life during these times are shown at the
right. (Not drawn to scale.) (Compare with Pig. 320.)

Paleozoic, Proterozoic, and Archeozoic Eras

EPOCH

«H

• I-H
PI

Upper or
Pennsyl-
vanian

Lower or
Mississip-
pian

•f— (
m

• rH

^H f-

o pQ

l^i

P s

• fH

^H >H

0) pQ

^ a

9 ee

^^ s

CHARACTERISTICS OF THE TIMES
AND VARIOUS TYPES

Periodic glaciation; elevation of
continents ; several climatic
changes; aridity pronounced

Rise of land vertebrates and mod-
ern insects; rise of ammonites
(Mollusca with coiled, cham-
bered shells)

Coal-forming plants common;
earliest reptiles, amphibia, fishes ;
mollusks, arthropods (crayfishes,
beetles, cockroaches, centipedes,
spiders), echinoderms

Coal-forming plants common
Amphibia, fishes, mollusks, cri-
noids (coelenterates)

Rise of amphibia, crabs, and
snails; bony fishes, brachiopods;
Mayflies; abundant mollusks;
decline of trilobites

Many parts of the world very
arid; rise of air-breathing ani-
mals (as insects, scorpions, etc.)

Abundant corals (coelenterates),
armored fishes, mollusks, bra-
chiopods, decline of trilobites

Rise of land plants, rise of fishes
(cartilaginous and sharklike),
rise of corals (coelenterates),
brachiopods, trilobites

Only invertebrate animals present ;
segmented worms, mollusks; rise
of brachiopods, echinoderms,
jellyfishes, sponges, corals ;
abundant trilobites

Rise of primitive, multicellular
invertebrate animals; very few,
imperfect fossils; traces of
marine algae, bacteria, shelled-
protozoa, coelenterates, seg-
mented worms, sponges, and
trilobites

Rise of simple, primitive, unicel-
lular types; large deposits of
limestone, graphite, and iron
ores of unicellular origin; no
fossils remain, if any w^ere ever
formed

REPRESENTATIVE LIFE

■^ ^^Il2:z23sas^

Fig. 322. — Description of the periods and epochs of the Paleozoic, Proterozoic,
and Archeozoic Eras of geologic time. Representatives of life during these times
are shown at the right. (Not drawn to scale.) (Compare with Fig. 320.)

618 General and Applied Biology

Fossils of certain characteristics are included in certain strata of the
earth and give clues as to the geologic age of these strata. This is im-
portant in knowing when those particular sediments which formed these
strata were laid down. Hence, certain plant and animal fossils are
known as index fossils because through them it is possible to determine
particular geologic eras and periods. Fossils also demonstrate that life
has not existed without changes in the past because of the revelations of
the records of past plants and animals.

V. GEOLOGIC TIME CHART

Because of the extensive studies of the strata of the earth, geologists
have divided the earth's history into eras (Figs. 320 to 322). Each era
has been divided into periods and the periods subdivided into epochs.
Each of these eras, periods, and epochs has specific characteristics and
definite ages and durations, as well as certain types of life which were
dominant during that particular time. The most recent fossils are found
in the upper strata, and the more ancient are successively arranged be-
low, with the most ancient at the bottom. We find the fossil remains of
plant and animal organisms distributed in this order in the strata of the
earth.

The reader is probably wondering how the relative and actual lengths
of the eras and periods have been calculated. This can be accomplished
in two ways. The age can be approximated by the thickness of the sedi-
mentary rocks formed during each period. It is known that a definite
time is required to form a certain thickness of sedimentary rock of a cer-
tain type. From these data it can be estimated how long it would re-
quire a certain thickness to be formed. Another method of ascertaining
the age of various strata is by the radioactive disintegration method.
The radioactive elements, uranium and thorium, disintegrate sponta-
neously at constant, determined rates with the formation of lead. The
age of a uranium mineral thus can be calculated from the proportions
of uranium and the lead it contains. Determinations of the uranium-
lead content of the oldest rocks suggest that the age of the earth is ap-
proximately 2,000,000,000 years. An accurate analysis of minerals re-
veals the fact that the Paleozoic era began over 500,000,000 years ago.
Figures secured by this method correspond with similar figures secured
by estimating the amount of time required for such sedimentary rocks
to be formed. The characteristics of the various periods of the Cenozoic,
Mesozoic, Paleozoic, Proterozoic, and Archeozoic eras, as well as domi-
nant organisms of each era, are shown in Figs. 320 to 322.

Animals and Plants of Past and Their Records 619
QUESTIONS AND TOPICS

1. Give your own definition of a fossil.

2. Where have you found fossils, and what was their probable method of for-
mation?

3. Of what importance in everyday life is a knowledge of animals and plants of
the past and their records?

4. List several reasons why certain softer types of animals and plants have left
no fossil records.

5. How are we able to estimate the age of the earth by a scientific study of the
fossils in the successive strata of the earth?

6. Define index fossils and explain their values.

7. Do geologic records reveal a progressive change in life in the past? Give
several specific examples from the animal and plant fields to prove or dis-
prove this statement.

8. What conclusions do you draw from a careful study of the Geologic Time
Charts? Upon what evidence do you base these conclusions?

9. If the older, earlier forms of life are found in the lower earth strata, and the
more recent life in the upper strata, what effects might glaciers, earthquakes,
and volcanic eruptions have on the proper interpretation of the data secured
from areas so affected?

10. How have the various estimates of the age of the earth been made? How
accurate are these estimates?

11. What is the estimated age of the earth from the Lower Precambrian Period
down to the present?

12. What percentage of the total age of the earth represents the time which
human beings have inhabited the earth?

13. As you remember specimens of petrified wood you may have seen, what were
its characteristics? Do these characteristics conform to those described in the
process of petrifaction?

SELECTED REFERENCES

Andrews: Ancient Plants and the World They Live In, Comstock PubHshing Co.,
Inc.

Arnold: An Introduction to Paleobotany, McGraw-Hill Book Co., Inc.

Darrah: Textbook of Paleobotany, D. Appleton-Century Co., Inc.

Eames: Morphology of Vascular Plants, McGraw-Hill Book Co., Inc.

Huxley: Evolution, The Modern Synthesis, Harper & Brothers.

Lucas: Animals of the Past, New York, American Museum of Natural History
(Handbook No. 4).

Lull: Organic Evolution, The Macmillan Co.

Raymond: Prehistoric Life, Harvard University Press.

Schuchert and Dunbar: Textbook of Geology (part 2), John Wiley & Sons, Inc.

Seward: Links With the Past in the Plant World, Cambridge University Press.

Smith: Cryptogamic Botany (vol. 2): Bryophytes and Pteridophytes, McGraw-
Hill Book Co., Inc.

Thomas: Paleobotany and the Origin of Aneriosperms, Botanical Rev^ 2: 397-
418, 1936.

Chapter 31

AN ECOLOGIC STUDY OF LIVING ORGANISMS-
PLANTS AND ANIMALS

Ecology (e-kol'oji) (Gr. oikos, household; logos, discourse) is that
part of biology which deals with the interrelationships between living
organisms and their environment. Usually an ecologic study is made of
a rather limited area, while a study of a larger area is usually considered
as geographic distribution (biogeography) . The term bionomics (bio-
nom'iks) (Gr. hios, life; nomos, law) is used in place of ecology at times.
The factors which influence the interrelationships between living organ-
isms and their environment are numerous and quite complex. Some of
the most interesting and valuable results of a course in biology may be
derived from a study of the ecologic relationships of living plants and
animals. Consequently, the following outline for such a study is discussed
in some detail so that the student may secure an idea of the complexity
of such a study and procedures which might be followed in making it.

I. ECOLOGY OF LIVING ORGANISMS
(PLANT AND ANIMALS)

Ecology may be defined as a scientific study of the interrelationships
or interactions of living organisms and their environments. The ecology
of an individual organism may be studied, or the ecology of a group of
organisms of the same species may be included in such a study. On the
other hand, a group of organisms (plant or animal) of two or more dif-
ferent species may be studied ecologically. Hence, the type of ecologic
study which is made will be determined by the results we expect to
secure.

In general, ecology concerns itself, inore or less, with local or limited
conditions, while biogeography deals with the wider faunal and floral
relations and distributions. Biogeography, which is divided into phyto-
geography (plant geography) and zoogeography (animal geography)
will be considered in another chapter. Hence, we might study the

620

Ecologic Study of Living Organisms 621

A. Heredity

B. Envdronment <

1. Physical
factors

Chemical
factors

Biologic
factors

Human
factors

'1. The specific genes (factors) of the organism being studied.

2. The inherited abilities and reactions of the organism.

3. Mutations and the production of new types of organisms.

4. Inheritance of specific structures by an organism.
^5. Rates of metabolism of the organism.

Temperature
Light
Wind
Gravity

Alternate recurrence of day and night
Physical makeup of the soil
g. Slope of soil as affecting the drainage
and exposure to light and heat
Pressure

Currents of air and water
Presence or absence of natural barriers
Presence or absence of natural methods
of dispersal

Quantity and quality (chemical com-
position) of the soil
Quantity and quality of water (mois-
ture)

Quantity and quality of the atmosphere
(oxygen, carbon dioxide, etc.)
Quantity and quality of usable foods
Ease and efficiency with which waste
materials can be removed from around
the organism

Competition between different kinds of
animals (or plants) or even the same
kinds of animals (or plants), for foods,
light, moisture, space, etc.

b. Competition between sexes (animals)

c. Dependence of certain types of plants
on insects for pollination

d. Mutual help, such as symbiosis, com-
mensalism

e. Parasitism, saprophytism, predacious-
ness

Dissemination and destruction of plants
and their seeds by animals
Plants contributing usable foods and
oxygen

-Plants detrimental to certain animals
Plants affording shelter, protection, and
concealment for animals

'a. Animal and plant quarantine regula-
tions
b. Transportation of animals or plants by
automobiles, trains, ships, airplanes, etc.
Usefulness and domestication of certain
types of animals or plants not only
influence their distribution, but also the
distribution of other organisms around
them

Detrimental animals and plants are de-
stroyed at the hands of man which per-
mits other types to take their place

a.
b.
c.
d.
e.
f.

h.
i.

J-
k.

d.
e.

■<

h.
i.

622 General and Applied Biology

ecology of a pool or square foot of soil and the biogeography (geographic
distribution) of a continent or a certain country.

In making an ecologic study of a particular plant or animal (or groups
of them), the specific heredity of the organisms involved, as well as all
the environmental factors, must be taken into consideration. A brief,
rather incomplete outline is given, which might be followed in such a
study. When this outline is somewhat elaborated, the general problems
of ecology, as well as the interdependence of hereditary and environ-
mental factors, can be rather easily observed.

A. Heredity

1. The Specific Genes of the Organism Being Studied Ecologically. —

Since hereditary genes (determiners) in the cells of an animal or plant
determine to a great extent what the organism is going to be, its struc-
tures, its general abilities, its abilities to use certain foods, and its neces-
sity to develop in a certain type of environment, it can be seen why
heredity must be included in any study of the ecology of that particular
organism. The genes of heredity also determine to a great extent the
ability of a particular organism to develop variations by means of which
it can attempt to fit into its environment, especially if the environment
should vary from time to time. The inheritance of the ability to move
around or be stationary also influences the ecology of any organism.
These, as well as many other inherited factors, determine to a great
extent the limits of distribution of a particular organism and conse-
quently its ecologic relationships as well. When environments are
changed from their normal, the organism living in them may attempt to
vary itself sufficiently to continue living in the changed environment; it
may, if possible, move to a more favorable environment, or it may die
because it cannot accommodate itself to the changed conditions. Each
living organism probably has an optimum environment in which it lives
most successfully, although in many instances life can continue in changed
environments, provided the changes are not too excessive. Animals and
plants which do not possess the inherited abilities to vary sufficiently to
meet changed environmental conditions have less opportunity of survival
under such conditions.

Certain organisms, such as the common dandelion, are so constituted
as to be able to live in a great variety of environments, in many types of
soils, in the lowlands and on high elevations. Cranberry plants grow
naturally in acid bogs and will not grow in neutral or alkaline soils.

Ecologic Study of Living Organisms 623

Cacti grow best in arid soils and will not grow in poorly aerated, wet
soils. Citrus fruits and palms of the tropics will not grow in habitats
with freezing temperatures. Because of the hereditary factors in the
grain of corn, a corn plant will be a corn plant, but the specific way in
which it develops will be determined by many environmental factors
which influence its growth. The common earthworm might be abun-
dant in a moist soil well supplied with humus and organic food, while
it might be very scarce, or entirely absent in a dry, sandy, abrasive soil
with little or no available food.

2. The Inherited Abilities and Reactions of the Organism Being
Studied. — All animals start their life by inheriting certain capacities to
develop in a particular way. If the environment is not of the type to
permit that development, the animal may move elsewhere, it may at-
tempt to alter its environment, it may develop abnormally by remaining
in such adverse environment, or it may be killed by such adverse en-
vironment. In some animals development must take place in a rather
uniform environment in which conditions change very slightly. In other
animals development must take place in an environment in which con-
ditions are constantly changing in a very definite order. It is easily seen
that one type of animal described above cannot well develop in the other
environment and vice versa.

An example of inherited abilities and reactions which have influenced
the ecologic relationships and distribution is that of the EngUsh sparrow.
If this common bird had not possessed in many successive generations a
tendency to be unafraid, its distribution today would be quite different
than it is. Because of its inherited lack of timidity, the sparrow has had
protection and a generous supply of foods most of the time. In fact,
the sparrow has followed man and has taken advantage of all of its
opportunities. Not being afraid, the sparrows are said to have entered
the empty grain cars in the East and, after the doors of the cars were
closed, have rather contentedly "hitch-hiked" their way to the West.
Their inherited lack of temerity aided them no doubt in their distribu-
tion. Would one have expected such birds as blue jays, with entirely
different inherited reactions, to have been transported easily and quickly
across the continent? What happened to the West after the rapid in-
flux of these birds from an ecologic standpoint? The inherited ability
of sparrows to build their nests anywhere and from all kinds of materials
also influences their ecology, while other birds require nesting sites and
nesting materials of more specific qualities.

624 General and Applied Biology

Each living plant has inherent tendencies to respond to certain stimuli
in certain specific ways. For instance, a certain species of plant responds
in a definite way to moisture, light, x-rays, cosmic rays, temperature,
gravity, etc. These inherent abilities to react in a definite manner in no
small measure determine how and where this species will be distributed
and the characteristics which such species will possess.

3. Mutations and New Types of Organism. — Plants and animals which
have been accustomed to a certain habitat may mutate rather abruptly
and spontaneously. Such resulting mutants may be of such a variety
that they will require an entirely different environment from that of
their parents, so that the former will have to develop in the new habitats
or be exterminated.

Natural crossing of plants, or animals, may result in offspring which
are so different from their parents that the offspring may have to de-
velop in a different kind of environment. In this case, as in the one
mentioned above, an entirely new ecologic relationship may be instituted
and consequently the distribution will be affected.

4. The Inheritance of Specific Structures by Organisms Being Studied.

— Such inherited structures as the gills of a fish or a crayfish naturally
limit their distribution to water, while the lungs of men, birds, rabbits,
and turtles necessitate their living on land. The sucking type of mouth
part of certain insects makes it necessary that they suck their nourish-
ment from certain hosts, while the chewing type of mouth part of other
insects determines their distribution on hosts of other types. Snails, in
order to build their characteristic calcareous shells, cannot live in acid
waters in which there is no lime. Certain insects, such as the common
"walking stick" (order Orthoptera), because of their resemblance to a
twig, are usually found in bushes where they are protected by their in-
herited morphology. These same insects distributed artificially on
smooth surfaces are easily exposed and thus exterminated. Many moths
and butterflies, because of their inherited structures and colorations, are
found in certain environments because they are afforded protection
there which they would not enjoy if they were distributed in an entirely
diff"erent environment. Certain animals inherit definite color patterns
by means of which they are partially hidden and protected by one type
of environment. If moved to another type of environment, these same
animals are easily detected and exterminated. These, as well as many
other illustrations, show the importance of inherited structures which
influence the ecologic relationships of the animals possessing them.

Ecologic Study of Living Organisms 625

Certain plant seeds through inheritance are suppHed with definite struc-
tures, by means of which they are disseminated. Claws, hooks, spirals,
etc., may help such structures in being transported by animals, insects,
birds, and the wind. The inheritance of certain structures for purposes
of controlling the process of transpiration naturally will determine the
distribution of such plants in various environments. The method of car-
ing for transpiration on the part of cactus plants is such that they are
able to exist in arid habitats, while plants which have not inherited such
mechanisms cannot exist under such conditions. Hence, the distribu-
tion of these opposite types is somewhat predetermined.

The root systems of certain plants are such that they cannot possibly
supply the necessary materials and provide the necessary anchorage and
support in certain types of soils. In other words, certain types of roots
make it necessary that such a plant be distributed in soils for which such
roots are fitted.

Certain combinations of genes in plants sometimes result in a lack
of development of chlorophyll. Naturally, such plants cannot long exist
and the result is that the distribution is affected.

5. The Rates of Metabolism of the Organism Being Studied Ecolog-
ically.— Animals usually inherit certain rather definite, normal rates of
metabolism. Certain factors of the environment are conducive to this
normal rate, while other factors are not. To be successful, the animal
must find that environment in which its particular rate of metabolism
may be developed properly. If it cannot find such an environment, or
because of an inherited lack of ability cannot locomote to better regions,
it may die because of an abnormally induced rate of metabolism. This
may prove to be a large factor in the ecologic relationship of that animal.

B. Environment

1. Physical Factors. —

(a) Temperature: Most animals have an optimum temperature at
which their metabolic processes react best and at which they live most
successfully. They also have a minimum and a maximum below and
above which they will not live. Hence, animals will tend to select, as
far as possible, those temperatures in which they can best exist. Freez-
ing of water in which animals live affects them in the following ways:
(1) some become hard and inactive during the frozen period; (2) oth-
ers escape the freezing by burrowing deep in the mud; (3) others die
under such conditions, but only after they have made the necessary

626 General and Applied Biology

provision to carry on the race by producing protected or resistant eggs.
Such factors as these naturally affect the ecologic relationships of ani-
mals under these conditions. A covering of ice on a body of water not
only affects the animals directly but also indirectly by altering the oxy-
gen and food supply. This explains why many animals come to holes
cut in the ice. Many fishes can be caught in this manner through holes
in the ice.

It is a well-known fact that all types of plants cannot exist in the same
temperature. Since temperatures vary in different environments, a
plant must be placed in its required thermal environment or be killed be-
cause of this ill-adjustment.

(b) Light: Certain animal protoplasms are so constructed as to be
unable to tolerate excess light, while others require large quantities to
exist. In fact, some species seem to require the stimulation given by light
in order to carry on many of their metabolic processes efficiently. Light
naturally acts as an important factor in animal distribution directly.
Indirectly, animals are affected by the presence of plants which require
light for their existence. In other words, certain animals depend upon
plants for food, protection, and oxygen. In turn, these plants depend
upon the proper amount of light. Hence, animals are indirectly and
directly influenced by the quantity and quality of light. Certain types
of animals move around only in daylight (diurnal), while others do so
only at night (nocturnal). In this case the presence or absence of light
is a factor in the ecologic relationships of such animals.

Certain plants require a maximum of light, some require a medium
amount, while still others require a minimum, or possibly none at all
(such as mushrooms, bacteria) . Plants will successfully locate them-
selves in the proper quantity and quality of light which suits their par-
ticular and specific requirements.

(c) Wind: The direction and velocity of the wind undoubtedly are
very decided factors in the dispersal of certain animals. Very strong
wind mav also affect the water in which animals live so that it mav be
a factor in the distribution of such aquatic forms. The wind may affect
them in various ways. It may cause injury to them directly. It may
stir up the sediment in water so that animals may be influenced by it.
The action of the wind also may influence the oxygen content of the air
or of the water in which they live and thus be a factor in their distribu-
tion. Winds also may affect the temperature and moisture content of
an environment and thus may directly influence animals or plant dis-

Ecologic Study of Living Organisms 627

trlbution upon which animals may be dependent. Very strong and con-
stant winds may cause certain animals to change their habitats and seek
a more quiet environment. Wind afTects the ecologic relationships of
plants in such ways as pollination (transfer of pollen from male part of
the plant to the female part), in helping to disperse the seeds of many
varieties, and in supplying movements of plants (can it be called exer-
cise?) which may be necessary for the development of such plants.
Winds might also aid in the distribution of oxygen, carbon dioxide, and
obnoxious gases which in various ways might influence plant activities.

(d) Gravity: Unless land animals have special mechanisms by means
of which they can counteract gravity, the heavier ones will be distributed
at or near the surface. If animals move away from the surface, they
do so in opposition to the force of gravity. Hence, the heavier animals
are usually found at a lower level than the lighter ones. In water cer-
tain animals seem to be very little affected by gravity, for they are found
at various depths. Other animals seem to live only near the surface,
while others live on or near the bottom. Undoubtedly, other factors,
besides gravity may influence these distributions of animals in various
depths of the water. The force of gravity affects all plants either posi-
tively or negatively, sending stems and leaves upward and roots down-
ward. Gravity in all probability affects aquatic organisms and some-
what determines their vertical distribution, depending on the specific
gravity or density of the organisms in question.

(e) Alternate Recurrence of Day and Night: It is well known that
the distribution of animals is quite different in daylight than at night.
For instance, certain insects are to be observed only in the daytime
(diurnal), while others are found more abundantly at night (nocturnal).

There are many other factors besides the presence or absence of light
which influence animal distributions as just described. The temperature
is usually lower at night. This, in addition to more moisture at night,
may cause certain animals to be seen at such times. This is particularly
true for those types which have no special equipment to prevent the
rapid evaporation of moisture from their surface. The stimulating effect
of sunlight also may influence the distribution of certain types of animals.

(f) Physical Make-Up of the Soil: Some soils do not possess specific
foods which are very essential to the growth of certain plants, because
these foods are not in a form which these plants can utilize. Some kinds
of soils are too hard for certain organisms and others are too loose or
yielding for others. Certain animals require certain types of soil for

628 General and Applied Biology

iood, burrowing, protection, etc. Plants requiring a specified amount
of moisture may not be able to get it from one soil but are able to do so
from some other soil. One plant requires a soil of a certain consistency
to give it its necessary anchorage, while the requirements of another
plant may be entirely different. The aeration of the soil is also deter-
mined to a great extent by its physical make-up. All of these and other
similar factors help to determine the ecologic relationships.

(g) The Slope of the Soil: The slope of the soil and its exposure
naturally determine the quantity and quality of light and heat. Some
plants require a minimum of light and heat and hence would not find
conditions ideal on a slope which is exposed to the hot sun of the after-
noon. The opposite slope might be much more favorable for such plants.
The slope of the soil also aflfects the drainage and this may also be an
important factor in the distribution of certain kinds of plants. In all
probability animal distributions are also affected by the environmental
conditions of the slope of the soil. The slope may be conducive to erosion
which may aflfect plant and animal distributions.

(h) Pressure: Pressure may be considered from the following stand-
points: air, water, and soil. Naturally, the type of environment in which
an animal lives will determine which of these pressures will influence
its distribution. Air pressure is 15 pounds per square inch at sea level
and decreases uniformly as one ascends from sea level to the higher
regions. In high elevations the air pressure becomes too low to permit
normal respiration in certain animals. This is a very salient factor in
determining certain animal distributions.

Water pressure increases as one descends from the surface. Water
pressure in the ocean is equal to the depth in feet multiplied by 0.434.
Thus, at 200 feet depth, the water pressure per square inch is approxi-
mately 87 pounds. This pressure naturally determines the vertical dis-
tribution in deeper bodies of water because not all animals are so con-
structed as to withstand such enormous pressures. The rapidity of
movement or the quietness of the waters also influences directly or indi-
rectly the ecologic relationships of animals living in them. Soil pres-
sures also vary according to the depth and physical construction of the
soil. The pressure in soils is in some instances so great as to prevent the
locomotion of certain types of animals through them. The porosity of
the soil, its oxygen and moisture contents, and its food content are addi-
tional factors which might influence the distribution of living animals
in it.

Ecologic Study of Living Organisms 629

(i) Currents of Water and Air: Water and air currents in any one
direction have a tendency to be a hindrance to locomotion of organisms,
even for those equipped to swim or fly. Continuous strong winds have
a tendency to move animals out of one area into another in the direc-
tion of the air currents. Strong water currents also have a similar eflfect.
Water currents have a tendency to carry nonmotile types in the direc-
tion of the flow of water. Only those animals particularly constructed
are able to counteract the water currents effectively. The "streamline"
construction of many aquatic forms is beneficial to them for locomotion
purposes and may be a great factor in their distribution.

(j) Presence or Absence of Natural Barriers: All types of living or-
ganisms have certain kinds of environments which are conducive to their
dispersal. Any natural hindrances to dispersal are known as natural
barriers. Something which may be a barrier to dispersal for one species
may be a natural method of dispersal for another species. Water may
be a natural method of dispersal for fishes, but it may prove to be a
natural barrier for terrestrial forms unless the water is not too deep or
extensive. Mountains may be natural barriers for certain types of ani-
mals, even if they are normally terrestrial forms. In this case, altitude,
snow, ice, lack of proper vegetation for foods, shelter, home sites, etc.,
may be influential factors. Plants of certain types, when absent from
certain regions, may serve as barriers to animal dispersal because those
animals depend upon such vegetation for foods, shelter, home sites, etc.
Earthquakes and volcanic activities may be barriers to the dispersal of
certain types of animals and plants. Floods may be barriers to certain
forms, while they may be used as methods of dispersal by others.
Whether a certain condition serves as a means of dispersal or as a bar-
rier depends upon the structural and physiologic properties of the par-
ticular organism in question. Heavy seeds, which cannot be easily car-
ried by animals or the wind, may have difficulty in passing over a moun-
tain or a large body of water. Lighter seeds may not be affected by
these same barriers. The swiftly moving parts of a stream may be a
barrier to the dispersal of the inhabitants of a quiet body of water be-
cause the environmental factors of the swift stream are different from
those of the quiet area.

(k) Presence or Absence of Natural Methods of Dispersal ("High-
ways"): Most types of animals and plants have particular methods by
means of which they are dispersed. The seeds of the dandelion are so
constructed that they are easily carried by the wind. Sometimes when

630 General and Applied Biology

the most desirable method of dispersal is lacking, an alternative method
may be used. If all usable types of dispersal are lacking, that particu-
lar animal or plant may be limited in its distribution. If certain types
of vegetation depend upon inoisture for dispersal, they may not be dis-
tributed during periods of extreme dryness. Certain types of seeds (burs,
etc.) which depend upon animals for their distribution may have little
or no distribution if animals are absent. The seeds of certain plants
may be distributed widely through the feces of birds. If birds are absent,
these plants must depend on alternative methods or not be dispersed at
all.

2. Chemical Factors. —

(a) Quantity and Quality of the Soil: The quantity and quality of
the soil affect not only animals living in the soil but also the aquatic
forms living in the water which necessarily comes in contact with the
soil. Certain soils, because of their high acidity, are not ideal for cer-
tain organisms, while alkaline or even neutral soils may be. Un-
doubtedly, the hydrogen-ion concentration (pH) of the soil is a vital
factor in the ecology of many animals. The hydrogen-ion concentration
of waters also is influential in determining their ecologic reactions. Cer-
tain chemical elements may either permit certain organisms to live in
that particular soil or cause them to select other habitats, depending
upon the quantity and quality of the chemical present. The quality and
quantity of the soil also determine the kind of vegetation growing on it.
Because certain types of vegetation are required as food, protection, and
concealment by certain forms of animals, the characteristics of the soil
may indirectly influence the ecology of the animals in that area. In ad-
dition to this, some plants supply moisture, oxygen, and homes for ani-
mals, and in this manner influence animal distribution.

Earthworms do not abound in sandy soils because such soils contain
very little dead plant material to be used as food. The sand also irritates
the worm as it burrows through it and tends to roll into the tunnels made
by such worms, thus interfering with their movements and necessary
oxygen supply. The moisture content of sandy soils also may be a fac-
tor in earthworm distribution in them. Other types of soils which possess
a supply of available food, which are less irritable, and which retain the
tunnels efficiently are more frequently used as habitats by earthworms.

Insects, turtles, and snakes deposit their eggs in soils of certain tex-
tures, temperatures, and moisture content. Decided variations from

Ecologic Study of Living Organisms 631

these desirable characteristics will influence the ecology of such animals.
Some types of soils are unfit for making burrows and nests so that rab-
bits, gophers, skunks, and similar forms may distribute themselves
where they may find habitats to their liking. Each plant requires an
adequate amount of soil of the proper quality (chemical composition)
to meet its specific requirements. In some instances the requirements
are quite definite and specific. In such cases plants will not be found in
soils which do not satisfy their peculiar needs. Cranberry plants will
grow only in acid soils and not in alkaline. Certain weeds can be elimi-
nated by merely altering the acid-base reaction of the soil. Dandelions
evidently are not so specific in their requirements, for we find them
growing in a great variety of soil environments.

(b) Quantity and Quality of Water (Moisture): All living organ-
isms require water for various purposes, although the quantity which
is sufficient for one type may be excessive for another. Protective sub-
stances and structures may prevent excessive evaporation and thus per-
mit an organism to live in less than the normal requirement of moisture
after it has once secured its normal supply. The presence in water of
salts which are more or less ionized determines the acidity or alkalinity
of that water. Some organisms apparently are not aflfected by the
acid or base content (hydrogen-ion content), while others require ah
environment with a rather definite reaction. Hydrogen-ion concentra-
tion of 7 is known as neutral; that above 7, as alkaline; that below 7, as
acid. When animals which normally live in a certain hydrogen-ion
concentration are artificially transferred to an entirely different con-
centration, the animals may attempt to move out of the latter or they
may be killed. Certain animals are constructed with hard, nonporous
coverings, oils, or mucus in order to prevent excessive evaporation of
moisture. In arid regions one would expect to find such characteristics
in animals.

. The transparency of the water permits the entrance of light which
not only affects the animal directly but also affects the growth of plants
upon which those animals depend for food, oxygen, and protection.
The depth of the water, its suspended materials, and its rapidity are
also factors in animal ecology. The pollution of waters with wastes and
obnoxious materials is a decided factor in the ecology of certain ani-
mals, while the same conditions apparently do not affect others. Cer-
tain industrial wastes are responsible for the elimination of fishes, snails,
clams, and Crustacea from certain streams. This waste not only influ-
ences these types of animals but also the many other organisms which

632 General and Applied Biology

are associated with them. By eliminating large groups of organisms ol
certain types, the entire floral and faunal relationship of that area may
be affected, and thus indirectly the ecology of many forms of life may
be influenced. The elimination of one individual from a particular area
may not have a great effect, but the wholesale removal of all members
of a particular species may have far-reaching effects. In other words,
there must be a reorganization of that area in order that life may con-
tinue efficiently and harmoniously.

Terrestrial and aquatic plants require water of a certain quantity
and quality for their particular needs. Aquatic plants usually require
much more than the average terrestrial type. The plants which grow
in arid areas require much less moisture. It can be easily seen that an
exchange of these various types of plants, as far as this type of environ-
mental factor is concerned, mav have detrimental results. Within cer-
tain limits the water conditions may be varied for a particular plant,
but beyond that the plant will refuse to develop.

(c) Oxygen, Carbon Dioxide, and Obnoxious Gases: All living or-
ganisms require oxygen of a certain quantity. If this amount is insuffi-
cient for a certain animal, it may become extinct, or, if possible, may
locomote to an area in which the oxygen supply is satisfactory. Oxygen
is necessary for the oxidation of foods, and thus a sufficient quantity in
an environment is an important factor in animal ecology. Carbon
dioxide, if present in large quantities, is not conducive to animal life.
The excess of this gas may be instrumental in the distribution of many
types of animals, both terrestrial and aquatic. Obnoxious gases, either
naturally or artificially produced, may result in a redistribution of or-
ganisms in that particular area. In fact, certain such gases are pro-
duced artificially to combat many undesirable animal types, such as
insects, rats, moles, and gophers.

All green plants require a certain quantity of carbon dioxide to meet
their needs for the process of photosynthesis. If the supply is insuffi-
cient, this very essential process cannot take place. If the oxygen supply
is limited, a plant may be unable to oxidize its protoplasmic substances
properly and thus be unable to liberate a sufficient amount of necessary
energy to supply its particular demands. Obnoxious gases of various
types may interfere with respiration, transpiration, and photosynthesis
and thus indirectly be a very important factor in the ecology of the
plants involved. Plants which do not possess chlorophyll (bacteria,
mushrooms, etc.) quite naturally would require an entirely different
atmosphere and consequently would be distributed accordingly.

Ecologic Study of Living Organisms 633

(d) Quantity and Quality of Usable Foods: All animals require
foods of animal or plant origin. Some types require specific foods of
definite qualities. If such foods are lacking, the animal may die, or the
lack may cause it to move, if possible, to a locality in which desirable
foods are present. Other types of animals are not so specific in their
food requirements and can exist on a great variety. The latter types
of organisms are not so easily affected by the scarcity of any particular
kind of food. Animals may be classified according to the types of foods
utilized. Organisms depending upon animals for food are known as
carnivorous (flesh-eating) ; those depending upon plants, as herbivorous
(plant-eating) ; those which utilize both animal and plant foods, as
omnivorous (all-eating). Animals of one of the above types may be
compelled to change their habitat because of the quality and quantity
of the particular foods they require in that community.

All living plants require foods of one type or another. In some in-
stances their requirements are very specific and in others they are more
general. If an area has a limited amount of food of a specific quality
and plants require this kind of food in large quantities, it is quite evi-
dent that plant distribution will be affected accordingly. In some
instances the foods present are in a form which is not usable. This fact
also will be of importance in the determination of dispersal of plants.

(e) Ease and Efficiency of Waste Elimination: The ease with which
detrimental wastes can be successfully removed from the environment
of an animal no doubt affects its ecology. Since wastes, if allowed to
accumulate, are detrimental to living protoplasm, it is necessary that
the animal live in a habitat in which they can be quickly removed as
they are formed. If a certain environment cannot accomplish this suc-
cessfully for an animal, the animal will attempt to find a more favor-
able habitat. Thus, wastes may be a factor in animal ecology. The
removal of wastes from a plant may be a minor factor in its ecology,
but together with other minor factors may be quite influential. Under
normal conditions, wastes are rather effectively removed from plants,
but in case they are not they could be partially responsible for some of
their peculiar behaviors.

3. Biologic Factors. —

(a) Competition for Food, Light, Moisture, Space: If too many ani-
mals with the same food requirements are present in an area with
limited quantities of usable foods, there will be a stiiiggle between them

634 General and Applied Biology

for that food. The result will be either the migration of certain of
them in order to get suitable foods or the death of a certain number of
the competitors. Since all animals require foods, it is easily seen that
this struggle for them is one of the greatest ecologic factors in the animal
kingdom. This migration in search of food may upset the natural
balance of the new community in which the migrants locate.

Competition between plants of different species or even between
plants of the same species rather closely resembles the struggle for
existence in the animal world. Apparently nature sanctions this natural
phenomenon in order to permit the fit to survive and exterminate the
unfit. Such a struggle for foods, light, moisture, space, or position
naturally will affect all of them in a minor or major way with its result-
ing ecologic effects.

(b) Competition Between Sexes: In the process of propagating the
race, certain animals may travel long distances for the opposite sex. In
other instances the competition of several members of one sex for a
limited number of animals of the opposite sex may lead to dispersal or
extermination. Since the urge to continue the individual as well as the
race is a strong one, it can readily be seen that such a factor might be
a very great one in determining the distribution of a particular species.

(c) Dependence of Certain Plants on Insects for Pollination: Certain
plants require insects to carry pollen from the male reproductive organs
to the female. In some instances a specific insect is required if extensive
pollination is to occur. Bees are quite essential for this purpose in
clovers. If bees are absent, the clover will bear a minimum of seed
and hence will present an entirely different ecologic picture than if bees
were present in sufficient numbers. Hives of bees are frequently to be
seen in orchards and in clover fields for this purpose. Of course, such
sources of nectar for making honey are also items not to be overlooked.
Other plants do not depend upon insects for their pollination, so that
the problem is quite different from the one presented above.

(d) Distribution Affected by Mutual Help, Such as Symbiosis and
Commensalism: Sometimes organisms are distributed in certain areas
because of the help which they give or receive from organisms of a dif-
ferent species. If this help were not available, there would be an entirely
different distribution of the species in question. Symbiosis pertains to the
rather intimate association of two different species of organisms with a
mutual benefit to both. For instance, the termites ("white ants") are
able to digest wood because they harbor in their digestive tracts certain

Ecologic Study of Living Organisms 635

flagellated protozoan animals which prepare the wood for absorption
by the termites. In turn for their labors, the Protozoa are given pro-
tection by the termites. This mutual benefit results in a distribution of
both the termites and their Protozoa in such a way that would not be
possible if symbiosis did not exist. In a similar manner, certain green
algae (plants) live symbiotically in the body of certain species of Hydra
(animal). The green algae manufacture food through the process of
photosynthesis in addition to giving oxygen to the Hydra. The latter
gives protection and carbon dioxide to the algae. This symbiotic rela-
tionship between these two species of plant and animal causes a dis-
tribution of both of them that would not exist if symbiosis were not
practiced. In the construction of the plants, known as lichens, the
green, chlorophyll-bearing algae live symbiotically with the colorless
fungi. In this case, two different species of plants live together so as to
be mutually beneficial.

Commensalism literally means "eating at a common table," although,
in a more general application, it means the association of two species
of organisms, in which one species benefits and the other at least is not
harmed. The sea anemone (Fig. 95) may attach itself to the shell of a
crab, giving some protection to the crab in return for its food which the
crab shares with it. The sea anemones are distributed by the crabs as
the latter move from place to place. The various interrelationships of
various living plants and animals are considered in more detail in other
chapters.

(e) Distribution Affected by Parasitism, Saprophytism, and Preda-
ciousness: These types of association of living organisms also influence
the ecologic relationships of the organisms in question. Parasitism is
the association of two organisms of different species in which the one,
known as the parasite, lives at the expense of the other, known as the
host. If the parasite lives within the host, it is known as an endopara-
site, such as the liver fluke which lives in the body of a snail or sheep
or the parasitic tapeworms or roundworms which live within the bodies
of other animals. Various species of roundworms may be parasites
within the bodies of plants. If the parasite lives externally on its host,
it is known as an ectoparasite. Examples of ectoparasites are lice which
live externally on the skins of dogs, cats, and men, the biting lice living
on the surface of birds, plant lice (aphids) living on the surface of
plants, certain fungi (plants) which cause "athlete's foot" living para-
sitically on the body of man. Some species of fungi live parasitically

636 General and Applied Biology

on or in the bodies of other plants. The disease of corn, called corn
smut, is due to a parasitic fungus (class Basidiomycetes). The wheat
rust is produced by a fungus parasite which also spends part of its life
cycle on the common barberry (shrub). All of these illustrate the ways
in which the ecologic relationships of these parasites and their hosts are
influenced.

Saprophytes are those organisms which live on dead organic mate-
rials. Frequently, saprophytic plants or animals require rather specific
types of dead materials for their existence so that their ecology is in-
fluenced.

Predaciousness, although somewhat similar to parasitism, differs in
that the "host" is destroyed rather quickly, while in parasitism it may
be destroyed only after a long period of time. Cats are predacious on
mice and robins on earthworms. In each instance the distribution of
each species is influenced by the presence of the other.

(f) Dissemination and Destruction of Plants or Their Seeds by Ani-
mals: Seeds or plants themselves may be widely distributed by insects
and other animals by having the seeds carried in the digestive tract, on
the external surfaces, or by mud on the feet. Many types of useful
and detrimental plants and their seeds are destroyed by animals which
eat them for food, use them for making nests, parasitize them, or in
some other way interfere with their normal habits.

(g) Plants Contributing Usable Foods and Oxygen; The ecologic
relationship between living plants and living animals is quite well known.
It usually results in the green plant giving oxygen and food to animals,
while the latter give carbon dioxide and waste materials which are use-
ful to the plant.

(h) Plants Detrimental to Certain Animals: Certain types of plants
may be detrimental to animals and in that way aff^ect not only the dis-
tribution of the animals but also the distribution of the plants. Detri-
mental plants may be classed as either poisonous or predacious. The
former may produce poisons which may affect animals and thus influ-
ence their distribution. The latter, or predacious plants (Fig. 330),
actually capture and destroy animals. Examples of such predacious
plants are Venus's-flytrap [Dionaea muscipula) , the sundew [Drosera
sp.), various pitcher plants (Sarracenia sp., Nepenthes sp., DarUngtonia
sp.), and the bladderwort (Utricularia sp.). In Venus's-flytrap the two
halves of each leaf blade have long stout teeth and three sensitive hairs.

Ecologic Study of Living Organisms 637

When the latter are stimulated by an insect, the two halves of the leaf
fold quickly together. The soft parts of the insect are actually digested
by digestive juices secreted by the glandlike hairs on the leaf. In the
sundews the flat leaf is covered with long, radiating, glandular hairs
covered at their tips with a sticky secretion which contains a digestive
enzyme capable of digesting insects lighting on the hairs. In the pitcher
plants the leaves form urnlike pitchers which are partly filled with liquid
in which the insects are captured and digested.

The bladderwort is a rootless, submerged water plant which bears
numerous small bladderlike structures on its branches. Each bladder
has one opening to the outside, closed by a valvelike trap opening in-
ward. Small aquatic animals entering these traps are prevented from
escaping and are used as food. In all these cases of predacious plants
the ecologic distribution of the captured animals is affected.

(i) Plants Affording Shelter, Protection, and Concealment for Ani-
mals: Many animals live in certain places because they receive pro-
tection and shelter from particular plants. Without these plants they
would be subjected to the ravages of nature and would be exterminated,
or at least be distributed elsewhere. A little investigation will reveal
many instances where animals are distributed in certain areas because
of the presence of plants. Where do we find more animals, in a sandy
area with limited vegetation or in an area with abundant plant life?
List as many reasons as you possibly can for this phenomenon.

4. Human Factors. —

(a) Animal and Plant Quarantine Regulations: Quarantine regula-
tions enforced by the government prevent, to a great extent, the import-
ing of many varieties of animals and plants which otherwise would be
brought to us from foreign countries in large numbers. Many of these
types, if imported, would be very destructive of plants and other ani-
mals. In addition, these unwelcome immigrants would upset the natural
balance or equilibrium of the present flora and fauna. This change in
the equilibrium would necessarily affect the ecologic relationships of
many other types of living organisms either directly or indirectly. In
spite of this vigilance, many undesirable animals and plants are im-
ported either secretly or knowingly. It is suggested that the organisms
responsible for the destruction of large numbers of our elm trees (Ameri-
can elm disease) were brought in from Europe. If this parasite could
have been prevented from entering, we could have saved many of our

638 General and Applied Biology

beautiful elm trees and by so doing could have saved large quantities of
money. The destruction of large numbers of elms is not only a direct
loss, but their absence also affects the ecologic relationships of other
plants and animals which are present in the area in which they are
destroyed. If there were no quarantine and everybody were permitted
to import all types of vegetation, many detrimental, diseased, and para-
sitic plants as well as parasitized plants, would quickly make their ap-
pearance in this country. This would greatly add to our already enor-
mous problems of economic botany.

(b) Transportation of Animals and Plants by Automobiles, Trains,
Ships, and Airplanes: Only a little time need be spent on the highways
or wharves to see how animals and plants are easily transported long
distances by any of a number of methods. Not only are these truly
methods of dispersal, but after animals or plants have been suddenly
imported into new regions, their presence quite decidedly influences
the former population to such an extent that an entirely new ecologic
relationship will exist. These methods of dispersal are man's inventions
and an animal or the seeds of plants may be quickly transported a
great distance in a short time.

(c) Usefulness and Domestication of Animals and Plants: The very
rapid changes in natural vegetation due to man's activities undoubtedly
influence the distribution of numerous animals dependent on or asso-
ciated with a vegetation of that type. The clearing of a land of its
trees has a decided effect on the animal population of that area. The
introduction of new species of wild or domesticated plants also directly
or indirectly affects the animal distribution within that area. Man not
only has taken domestic animals with him as he has gone over the
earth's surface, but these animals also have taken their parasites with
them. This has resulted in a necessary redistribution of the population
into which the newcomers were taken. In general, it may be concluded
that what may appear to be a small, insignificant factor may in the
end prove to be a very influential one as far as ecology is concerned.
The destruction of a few apparently useless animals may have a great
effect in nature's balance, just as the introduction of a few apparently
harmless varieties may cause an ecologic readjustment.

Domestication of useful plants has resulted in their being protected
and cultivated, and hence their wide distribution has been ensured.
The cultivation of domestic plants has a tendency to influence many

Ecologic Study of Living Organisms 639

wild types directly and indirectly. Many wild types are destroyed as
weeds because they interfere with the normal development of domestic
types. Many wild types influence the development of domestic types;
an example is the destruction of corn plants by the European corn borer
which may spend part of its life cycle in a great variety of weeds and
other types of plants. Hence, the number of wild types which sur-
round a field of corn and which harbor corn borers affects the domestic
corn plants. The relationship between the barberry bushes and the rust
of wheat is another example. A great variety of new types ot plants
have been "artificially" produced because they possess certain qualities
which are beneficial for foods, shelter, fuel, or industry. The production
and cultivation of many of these new species naturally affect the ecology
of other plants in their vicinity.

(d) Destruction of Detrimental Animals and Plants by Man: This
type of destruction not only affects the animals and plants being de-
stroyed, but their absence affects many others indirectly by giving them
more food, light, space, and moisture. The destruction of one kind of
plant may cause animals which were dependent upon it to turn to some
other type of plant and thus affect it. The destruction of certain plants
may expose others to sunlight, heat, winds, etc., to which they were
not accustomed. This will present a new ecologic factor for the re-
maining plants.

II. TYPICAL ENVIRONMENTS AND THEIR FAUNA
AND FLORA

The following summary of a few typical environments and the types
of organisms usually found in such environments will illustrate many
points in the study of ecology. Environments for convenience will be
divided as follows:

A. Water or aquatic

1. Rapid streams

2. Pools

3. Ponds

4. Lakes

B. Land or terrestrial

1. Open fields

2. Deserts

3. Tundras

4. Forests

640 General and Applied Biology

Water or Aquatic

AQUATIC

CHARACTERISTICS OF
ENVIRGXMEXT

TYPICAL ANIMALS
PRESENT

Rapid streams

Rapid flow of water

Usually a hard, firm, clean bottom

Usually many loose rocks with crevices

between them for protection
Usually shallow, and hence plenty of

light and oxygen from the surface
Difficult for swimming animals
Usually a minimum of vegetation

May fly larvae
Stone fly larvae
Caddis fly larvae
Horsefly larvae
Midge larvae
Fishes, such as darters
Snails (unless water is
too acid)

Pools (more
quiet part of
streams)

Slow flow of water

Usually a soft, yielding bottom of mud

or sand useful for burrowing
Crevices, if present, are soon filled with

quickly settling silt
Certain types of vegetation common

Dragon fly larvae
Damsel fly larvae
Midge larvae (blood

worms )
Clams

Various types of com-
mon fishes, water
snakes, and water
turtles

Ponds

Slow flow of water
Usually a soft, yielding bottom
Certain types of vegetations which sup-
ply food, oxygen, etc., are quite com-
mon

Midge larvae
Dragon fly larvae
Damsel fly larvae
Caddis fly larvae
Crustacea
Leeches
Clams

Water snails

Fishes, water snakes, and
water turtles

Lakes

Lakes are longer, wider, and deeper

than ponds
Wave action depends on many conditions
Bottom may be sand, gravel, mud, loose
rocks, or solid ; these different types
of bottoms influence the type of life
to be found on each; constantly mov-
ing gravel or sand is not desirable for
sessile animals; sand interferes with
respiration of animals with gills;
vegetation is limited because of sand
movement and limited nourishment

The types of animals
vary greatly, depend-
ing on the great va-
riety of conditions
encountered in such
large bodies of water
as lakes

Ecologic Study of Living Organisms 641

Land or Terrestrial

CHARACTERISTICS OF

TYPICAL ANIMALS

TERRESTRIAL

ENVIRONMENT

PRESENT

Open fields

Temperatures usually severe in both

Beetles

summer and winter

Grasshoppers

Wind action great

Leafhoppers

Light intense

Certain types of spiders

Moisture evaporation high

Certain types of snakes

Very few places for protection except

Certain types of mice

in the ground and in the limited vege-

Certain types of birds

tation

Toads

Bees (if flowers are
present)

Deserts

Temperatures severe in summer and

Beetles

winter

Grasshoppers

Wind action great

Leafhoppers

Light intense

Certain spiders

High evaporation of moisture due to in-

Certain snakes

tense heat and low atmospheric mois-

Certain birds

ture

Horned toads

Vegetation limited to sagebrush, cacti,

yucca trees, bunch-grasses, etc.

Tundras

Winter long and cold, only upper limits

Very few animals can

of soil thaw

withstand the ravages

Air in winter is dry

of this polar and semi-

Often strong winds

polar area

Relatively light snowfall

Water of ground is cold

Plant growth season short

Vegetation consists of mosses, lichens.

certain grasses, herbs, and shrubs

Forests

Temperatures usually more moderate

Bees

than surrounding areas

Crickets

Wind action reduced

Cockroaches

Protection from light, heat, wind, and

Millipedes

moisture evaporation

Centipedes

The type of forest will determine to a

Certain spiders

great extent the type of vegetation,

Certain grasshoppers

and this in turn will greatly influence

Katydids

the distribution of animals

Tree toads
Numerous birds, etc.

642 General and Applied Biology

o
o

oi
O

o
o

NUMBER AND TYPES

OF ANIMALS PER

SQUARE FOOT

Midge larvae (50)
Snails

(Goniobasis) ( 4)
Round worm ( 1 )
Caddis fly larva ( 1 )

Caddis fly larva (36)
Midge larvae (27)
Hydra (15)
Snails

Goniobasis) ( 9)
Caddis fly pupae ( 6)
May fly larva ( 1 )

Caddis fly larvae (35)
Snails

(Goniobasis) ( 8)
Midge larvae ( 4)
May fly larva ( 1 )

Snails

(Lymnea) (25)
Midge larvae ( 4)

u
o
>-

z
<

Q
O

Very little sediment to

interfere with animal

respiration
No aquatic plants for

food or to supply O2
Shallowness permitted

light and O2 from

surface

Slight sediment

Great masses of green
algae to supply food,
O2 and protection

Slight sediment
Few plants for food,
O2, or protection

No sediment

Surface was covered
with vegetation
which was actively
emitting O2

ATTACHMENT
AND SHELTER

Strongly at-
tached

No shelter

No plants for
protection

Fairly strongly
attached to all
surfaces of
rocks

Algae (plant)
very abundant

Fairly strong
and uniform
attachment

Few plants

•

Shght attach-
ment

Numerous plants
(diatoms, des-
mids, algae)

GENERAL
CHARACTERISTICS

Bottom of smooth,
solid limestone

Strong wave action ;
no crevices in the
bottom

Numerous, irregular

rocks of various

sizes
Medium wave action;

back wave action

pronounced
Many large crevices

Smooth, solid lime-
stone bottom with
occasional, free ir-
regular rocks; sur-
face wave action
strong

Few crevices

Solid, smooth lime-
stone bottom ; no
free rocks; no great
disturbance by
waves

TEM-
PERA-
TURE

U
0

0
1—1

DEPTH

OF
W^ATER

1—1

t£>

LOCATION

STATION

S-i

C/3

6 ft. from
shoreline

12 ft. from
shoreline

Inland pool
with connec-
tion with
lake; 4 ft.
inland from
lake

STA-
TION
NUM-
BER

c
c

«3

3
C/3

CO
CM

Ecologic Study of Living Organisms 643

III. ECOLOGY OF A PORTION OF A LAKE SHORE

As an example of an ecologic study of a limited area, let us use a
portion of a shore of a fresh-water lake. Four stations designated as A,
B, C, and D are shown in Figs. 323 and 324. A thorough study of the
environmental conditions and total numbers of animals found in each
station (Fig. 323) will illustrate the problems of ecology. Note the dif-
ferences in the environmental conditions and populations of Stations A,
B, and C. Contrast these with Station D, which is a small, shallow
pool located several feet from the lake but connected with it when wave
action in the lake is particularly strong. A square foot of the bottom
was studied carefully in each station. How can you account for such
variations in the numbers and types of organisms in these stations?
List as many factors as you can which you think might be responsible
for such distributions.

5hrab5>
Qrass-

Lake

Fig. 324.

-Diagram showing the location of Stations A, B, C, and D of an ecologic
study of a fresh-water lake (see Fig. 323.)

A very good method of studying ecology is to select some desirable
area, either land or water, and make a careful and detailed study of it
yourself. You will also find quite a seasonal change in the animal and
plant population of each area when studied at different times of the
year.

IV. ECOLOGIC STUDY OF A PORTION OF YOUR CAMPUS

In order to understand the principles of ecology and the many fac-
tors involved in determining the distribution of living organisms, it is
suggested that you study a small portion of your campus , following the

644 General and Applied Biology

outline given earlier in this chapter. You may study the ccologic rela-
tions of all the living plants and animals in a certain well-defined area,
or you may attempt to ascertain the influence of all the factors (heredi-
tary, chemical, physical, and human) on the distribution of one par-
ticular species. Be very accurate in your observations, records, and
interpretations of your data.

QUESTIONS AND TOPICS

1. Select several different types of environments (upon consultation with the
instructor) and make an ecologic study of the animals and plants in each area
studied. Make use of the outline as presented in the chapter, adding or
omitting as may be necessary for your particular problems. Record the data
carefully after you hav^e made the scientific observations. Make proper inter-
pretations of your data and formulate conclusions which can be drawn logically
from the data collected.

2. How can a knowledge of ecology be beneficial in the successful cultivation of
vegetables and flowers? Give specific explanations.

3. How can a knowledge of ecology be beneficial in the proper care and opera-
tions of an out-of-door pool? Of an aquarium? Of a terrarium?

4. List some probable factors which might influence migrations of certain species
of animals.

5. Study some maps which show the annual rainfall for the United States and
interpret the distribution of certain types of plants in the light of this infor-
mation.

6. Explain why cotton is primarily a southern crop. Give specific reasons.

7. Give reasons for the limitation of the cultivation of corn to certain regions of
the United States. Do the same thing for wheat.

8. Secure data on the areas where citrus fruits are grown in the United States
and attempt to explain why.

9. Explain how the distribution of certain types of plants might influence the
distribution of certain t^qaes of animals and vice versa.

10. List all the benefits which might be derived from a scientific ecologic study of
living organisms. How might you make practical applications of this infor-
mation in the future?

SELECTED REFERENCES

Allee: Animal Aggregations, University of Chicago Press.

Allee: Social Life of Animals, W. W. Norton & Co., Inc.

Allee, Emerson, Park, Park, and Schmidt: Animal Ecology, W. B. Saunders Co.

Bates: The Nature of Natural History, Charles Scribner's Son.

Braun-Blanquet: Plant Sociology, McGraw-Hill Book Co., Inc.

Chapman: Animal Ecology: With Special Reference to Insects, McGraw-Hill

Book Co., Inc.
Clements and Shelford: Bioecology, John Wiley & Sons, Inc.

Coker, Juday, Osburn, and Welch: Problems of Lake Biology, The Science Press.
Daubenmire: Plants and Environment, John Wiley & Sons, Inc.
Elton: Ecology of Animals, John Wiley & Sons, Inc.

Ecologic Study of Living Organisms 645

Fasset: Manual of Aquatic Plants, McGraw-Hill Book Co., Inc.

Gates: Field Manual of Plant Ecology, McGraw-Hill Book Co., Inc.

King and Pessels: Working With Nature, Harper & Brothers.

McDougall: Plant Ecology, Lea & Febiger.

Morgan: Field Book of Ponds and Streams, G. P. Putnam's Sons.

Muenscher: Aquatic Plants, Comstock Publishing Co., Inc.

Needham and Needham: Guide to the Study of Fresh-Water Biology, Comstock

Publishing Co., Inc.
Costing: Plant Communities, W. H. Freeman & Co.
Pearse: Animal Ecology, McGraw-Hill Book Co., Inc.
Ward and Whipple: Fresh Water Biology, John Wiley & Sons, Inc.
Weaver and Clements: Plant Ecology, McGraw-Hill Book Co., Inc.
Welch: Limnology, McGraw-Hill Book Co., Inc.
ZoBell: Marine Microbiology, Chronica Botanica Co.

Chapter 32

UNITY AND INTERDEPENDENCE
IN THE LIVING WORLD

L UNITY IN THE LIVING WORLD

The term unity can be applied in a variety of ways in the animal and
plant kingdoms. In such a brief space as can be devoted to this very
important biologic principle, the following kinds of unity will be con-
sidered: (A) unity within each living organism, (B) similarity of struc-
tures and functions between closely related species of organisms, and,
to a lesser degree, even in distantly related species, (C) unity and co-
operation between various types of living organisms of similar or dif-
ferent species, (D) biologic communities (associations) and successions
of plants and animals, and (E) dependence of all living animals and
most plants on photosynthesis.

A. Unity Within Each Living Organism

L Unity Within the Individual Cell.^ — One would easily surmise that
there must be unity and harmony within the protoplasm of each living
cell if that cell is to perform its various functions effectively and effi-
ciently. When this unity ceases, the cell becomes abnormal, the degree
of abnormality determining whether that cell will alter its structures
and functions or whether it will eventually die. The foundation of unity
and order, in the individual cell as well as in the living organism as a
whole, is the "inherent ability of living protoplasm to transmit dynamic
changes and impulses from one point to another within that proto-
plasm." This phenomenon results in all parts of a living organism
knowing what is going on in other near-by or distant regions and acting
accordingly. The living protoplasm also has the ability to "properly
integrate and harmonize these various dynamic waves of excitation so
that more or less complete harmony and cooperation results." It has
been suggested that individual cells have certain regions ("poles")
which are the controlling points for the activities of that particular cell.

646

Unity and Interdependence in. Living World 647

Such a construction might well be called cell polarity. One of these
so-called poles has a higher rate of metabolic activity than the remain-
der of the protoplasm and consequently assumes the necessary and
desirable control of the cell as a whole.

2. Unity Between the Various Cells of Each Tissue. — We have sug-
gested how unity and correlation might occur within an individual cell.
This would be worth very little in a complex, multicellular organism
if each cell did as it pleased. There must be unity and cooperation
between the various cells of each tissue of a living organism if life proc-
esses are to be accomplished efficiently. The explanation suggested for
the unity within a single cell might be extended and elaborated so that
cooperation between various cells might be accomplished. Electrical
phenomena, chemicals, and impulses of the nervous system probably
integrate to a great extent the various cells of a tissue so that real har-
mony and cooperation exist. Electricity within cells and the electrical
phenomena associated with nerve impulses suggest probable causes of
integration. Various chemicals pass more or less freely from one cell
to another, hence playing an important role in unity between cells. The
chemical secretions in the ductless (endocrine) glands of higher animals
will illustrate this process of coordination. (See discussion of ductless
glands.) It has been demonstrated in certain cells that there are minute
strands which extend from one cell to another, .and evidently through
such structures coordination might also be secured. All that has been
said up to this point has dealt with the proper coordination of cells.
There are times when certain cells, or certain parts of cells, must be
subordinated, because all units cannot have the same degree of activity.
This subordination of certain parts is just as important as the coordina-
tion process and is probably accomplished in much the same way.

3. Unity Between the Various Tissues of Each Organ. — An organ is
an assemblage of different tissues, all of which work for a common pur-
pose (perform a common function). Even though the various tissues
of a certain organ are closely associated in the construction of that
organ, there must be a specific integrating influence or force in order
to make these various tissues function together as a unit. This is ac-
complished in much the same way as in individual cells and tissues,
except on a larger scale.

4. Unity Between the Various Organs of Each System. — If each sys-
tem of a living organism is to function normally and efficiently, there
must be unity between the various organs which compose that particu-
lar system. The higher types of organisms with their greater numbers

648 General and Applied Biology

of cells and their more numerous tissues and organs must necessarily
have a more complicated nervous system than lower organisms in order
to ensure the proper coordination. Chemical and physical factors
probably play important roles in this respect. Could the digestive sys-
tem of an organism function properly if all the organs of that system
worked independently? How would one organ know what to do if it
were not properly notified what is expected of it? Another evidence
that all organs are closely related and associated is shown by the fact
that effects of illness in one part of a system are frequently relayed to
other parts of that system or even other systems so that the unity of
the organism as a whole may be again regained. In other words, "sym-
pathy" is expressed between the various units of a living organism.
This is quite essential. In some instances when defects or abnormalities
arise in a certain region, organs in some distant part of the animal
may take on extra responsibilities until the defect is remedied. If the
abnormality is not properly remedied, dissension may spread; over-
worked tissues cease to carry their double burdens and still greater con-
sequences result. In other words, a living organism is as healthy as its
weakest part.

5. Unity Between the Various Systems of a Living Organism. — From
what has been said abo\e, it is quite evident that every living organism
must have the proper coordination and subordination of its various sys-
tems if efficiency is to result. A slight abnormality starting in a certain
tissue, unless corrected, may spread to other tissues, to organs, and to
systems, and eventually the organism as a whole may be affected. This
may appear to be a mistake in construction on the part of Nature, but
in reality it is a blessing in disguise, for without these consequences little
might be attempted to care for minor disturbances. Consequently, it
becomes highly desirable and essential to correct defects so that they do
not spread.

B. Similarity of Structures and Functions Between Closely Related
Species of Organisms

Students who are just beginning their study of biology will probably
have some difficulty in realizing the great number of similarities between
various apparently unrelated organisms. We have a great tendency to
observe one or two differences when comparing two organisms and not
to notice a greater number of similarities which are observ^ed only after
detailed study. As you study the structures, functions, and reactions of
various types of living organisms, you will observe many more similari-

Unity and Interdependence in Living World 649

ties than you at first surmised. These many similarities among living
organisms reveal a certain close relationship, which in turn proves a
certain degree of unity or uniformity among all living organisms. If a
study of the entire animal or plant kingdom were to be made, and the
similarities of the various species noted, one would have to conclude
that there is a certain degree of unity in the animal and plant kingdoms.

C. Unity and Cooperation Between Various Types of Living Organ-
isms

As we look about us in the living world and note the great struggles,
animosities, battles, and antagonisms, it is difficult to realize that there
are many, if any, instances in which there is real cooperation. However,
a little investigation will reveal that this is true. In spite of all the
struggles in the living v/orld, none of them arc so great as to disrupt life
in any great region or cause any great catastrophes. After all, there
must be, and is, more unity and harmony than discord among living
organisms or they would quickly exterminate each other, which would
result in ultimate and widespread ruin. In spite of the many hatreds
and struggles throughout the living world, there are many attempts at
cooperation, which in the final analysis seems to be a clue to a successful
living and accomplishment. When will man with all his powers and
abilities learn this one fact and place it into actual use? It is quite true
that a certain amount of struggle and competition is necessary to bring
out and develop the best in organisms, but these carried too far and
made unnecessarily vicious tend to hinder development and progress
and may ultim.ately lead to destruction. How does this link up with
the condition of mankind over the world today? Is there not a great
lesson to be learned from this great biologic principle in the conduct of
human affairs?

When one studies the living organisms as a group, there is apparent
a great degree of unity and cooperation not only between members of
the same species, but also among members of different species. In fact,
this spirit of cooperation exists not only between animals of diflferent
species but between various species of animals and a great variety of
plants. Undoubtedly, there are many examples of the latter phenome-
non, but none will better illustrate the point than the so-called cycles in
Nature. The following typical cycles (Fig. 325) will be considered:
nitrogen, carbon, and oxygen cycles.

1 . Nitrogen Cycle. — Nitrogen is one of the essential elements of which
living protoplasm is composed, being particularly essential in the con-

650 General and Applied Biology

struction of proteins. Briefly stated, the following steps may be ob-
served in a typical nitrogen cycle starting with the utilization of the
free nitrogen of the atmosphere: (1) Free nitrogen of the atmosphere

PROTEINS

o
a>

(D
ct
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CO
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UREA

AMMONIA (NH3)

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ANIMALS

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CARBOHYDRATES

Fig. 325. — Nitrogen, oxygen, and carbon cycles in nature.

is utilized by certain species of bacteria ( Rhizohium sp.) living sym-
biotically in the roots of leguminous plants (as clover, alfalfa, peas, etc.)
to form nitrates (containing NO3) which are usable by plants to build

Unity and Interdependence in Living World 651

plant materials. Because of the irritating presence of these bacteria
in the roots of such plants, the latter are stimulated to form enlarged
nodules on their roots. The nitrogen-fixing organisms are in these
nodules. (2) Free nitrogen is also changed to nitrates by other bacteria
hving in the soil (genus Azotohacter and genus Clostridium). (3)
Other plants may secure their nitrates by bacterial decomposition of ani-
mal products (such as urea) and other nitrogenous materials. Certain
bacteria (ammonifying bacteria) act on nitrogenous compounds chang-
ing them into ammonia (NH3) through a process known as ammonifi-
cation. (4) Other bacteria {Nitrosomonas sp. and Nitrosococcus sp.)
oxidize the ammonia into nitrites (containing NO2). (5) Still other
types of bacteria (Nitrohacter sp.) oxidize the nitrites into nitrates. This
whole process of transforming ammonia into nitrites and the latter into
nitrates is called nitrification. The nitrates so formed are usable by
plants. ThuSj the two sources of nitrates for plants are: (a) the fixation
of free nitrogen from the atmosphere and (b) the production of nitrates
from ammonia by the process of nitrification.

When plants die, their complex nitrogenous compounds are reduced
by bacterial action to ammonia, which can be used in the process of
nitrification. When animals die, their complex nitrogenous compounds
are also reduced by bacterial action to such simple compounds as ure.a,
which can be converted into ammonia, to be used as a starting point in
the nitrification process. Plants and animals both depend on these
chemical compounds for their food materials, the animals depending
upon the plants for at least part of their nitrogen supply from which
to build proteins. As has been shown above, the roots of certain plants
also contribute to the available supply of nitrates to be used by plants.
Animals in turn use plant nitrates for their various needs.

There are still other types of bacteria which convert nitrates to nitrites,
oxides of nitrogen, and free nitrogen — a reverse process which removes
nitrogen from the soil. This process is known as denitrification.

2. Carbon Cycle. — Carbon is also an essential constituent of both
plant and animal protoplasms. The stages in the carbon cycle may be
briefly summarized. The carbon dioxide of the atmosphere comes from
the respiration of animals, from the burning of wood, coal, oil, and gas,
from various manufacturing processes, and from volcanoes (Fig. 325).
Green plants which contain chlorophyll are able to combine the carbon
dioxide with water in the presence of sunlight to form plant carbo-
hydrates such as sugars, starches, and cellulose. This process is known
as photosynthesis. Plants utilize the materials produced by photosyn-

652 General and Applied Biology

thesis to manufacture more complicated plant proteins and fats. Ani-
mals use these carbon materials of plants with which to build even more
complicated animal carbon compounds.

When plants and anim.als die, their carbon compounds are reduced
into simpler carbon materials which can eventually be used again by
living plants. Earthworms, certain insects, and such plants as bacteria
and molds aid in restoring this carbon material to the soil where it can
again be utilized.

3. Oxygen Cycle. — Oxygen is also an essential constituent of proto-
plasm (Fig. 325). It not only goes into the make-up of the protoplasm,
but it is used in the process of oxidation, in which the oxygen combines
with a substance so as to liberate the energy which originally held the
units of the substance together. Oxygen is liberated and carbon dioxide
is taken in by green plants during the active process of photosynthesis.
Some of the oxygen is retained by the plant and used for building or
oxidation purposes. Animals require oxygen for respiration. This oxy-
gen oxidizes the foods of the animal with the release of energy and the
formation of carbon dioxide which can be utilized again by chlorophyll-
bearing plants. Hence, there is a mutual exchange and interdependence
between animals and plants as far as oxygen is concerned. This ex-
change of oxygen and carbon dioxide also occurs between animals and
plants in an aquarium, out-of-door pool, or any other body of water.

D. Biologic Communities (Associations) and Successions of Plants and
Animals

Very few, if any, organisms live alone (Fig. 326). In many instances,
groups of the same or different species are associated in a community
in which there may be unity, disunity, helpfulness, interdependence, or
destruction, depending on the many factors or conditions under which
they are living. A certain association of organisms m.ay live in harmony
in one community with its particular environments, while the same asso-
ciation of organisms in another community might not live harmoniously
because of certain environmental factors which differ from those in the
first community. There is not one, all-important factor which is re-
sponsible for the distribution and successful living of animals and plants
in any community. In making a scientific study of the reasons why
certain organisms live as they do, we must take into account the he-
redity of those organisms, as well as such environmental influences as
chemical, physical, and biologic factors in the surroundings. Even hu-
man factors may be quite influential as will be observed when these are

Unity and Interdependence in Living World 653

considered in detail in another chapter. Frequently, we classify living
organisms into different communities because of their habitats (where
they live). Animals that live on land are terrestrial (Gr. terra, land);
those that live in water are aquatic (L. aqua, water) ; and those that live
in water and on land are amphibious (Gr. amphi, both; hios, life).
Plants may be classed as water plants or hydrophytes (Gr. hydro, water;
phyton, plant) ; land plants or terraphytes; desert plants or xerophytes
(Gr. xeros, dry; phyton, plant) ; plants requiring moderate moisture are
mesophytes (Gr. mesos, moderate or middle; phyton, plant). Living
plants and animals may be divided into such communities as seashores,
fresh waters, forests, grasslands, deserts, etc.

Fig. 326. — Balance in Nature as rev^ealed by a diagram showing the food inter-
relationships in a hypothetical prairie community. All living things depend on
other living things for various things, including food. The arrows point toward
the organism which uses the other organism as a source of food. (Redrawn and
modified from Shelford ; from Potter: Textbook of Zoology, The C. V. Mosby Co.)

Animal and plant communities are never constant or static but are
continually changing. These changes in individuals, or in the com-
munity as a whole, are the attempts on the part of living organisms to
adjust themselves successfully to their changing, nonliving, and living
environments. The introduction, naturally or artificially, of new species

654 General and Applied Biology

may require a complete readjustment in a certain community. In fact,
these constant changes in the living world communities result in what
is called a succession of living organisms. When environmental factors
change sufficiently, the plants and animals which originally lived there
may be destroyed and their places taken by other types. Such a sequence
of plant and animal replacements is a succession which may occur natu-
rally or be brought about, at least in part, by artificial means. For
example, a fresh-water pond may have a certain type of animal and
plant population. When this pond dries, the resulting changes in the
environmental factors may result in a succession somewhat as follows:
animals and plants which require a great amount of water will be gradu-
ally replaced by those whose water requirements are not so great; as
the pond develops into a swamp, plants and animals typical of swamps
will succeed; herbaceous plants will appear, to be followed by various
types of shrubs, and eventually a succession of trees which will range
from poplars to oaks and hickories to beech and maples. Even the ap-
pearance of these trees show a typical succession of species, each follow-
ing the other as the proper environmental factors present themselves.
The same phenomenon of succession is to be noticed in the replacement
of plants and animals in an original forest community which was burned.
As diflferent plants succeed one another as environments change, so the
animal population will also undergo a succession in that area. Certain
types of animals requiring specific kinds of plants for protection and food
cannot reappear in the burned area until the proper plants have reap-
peared in the plant succession. These and many other similar phe-
nomena prove the unity and interdependence in the living world.

E. Dependence of All Living Animals and Most Plants on Photosyn-
thesis

All plants and animals require foods of some type or another. Since
animals and plants without chlorophyll cannot manufacture food, it is
apparent that in the final analysis all life depends, directly or indirectly,
upon the photosynthetic process for food. It is true that certain ani-
mals eat other animals, but somewhere in the continuous chain of food
supply the animal was dependent upon plants for food. Even the plants
without chlorophyll, such as fungi, bacteria, etc., must depend, directly
or indirectly, upon the process of photosynthesis for their source of food.
Bacteria mav live on an animal which has eaten another animal, but
probably the latter had consumed food which was manufactured by the

Unity and Interdependence in Living World 655

process of photosynthesis. Photosynthesis not only supplies many of the
foods but also materials used for shelters, clothing, fuels, etc. Refer to
the detailed discussion of photosynthesis elsewhere in the text.

II. WEB OF LIFE AND BALANCE IN NATURE

All life in the world is so interdependent and closely related that it
may be viewed as a web (Fig. 326) composed of various individuals and
species of animals and plants which are more or less intimately associ-
ated together into a living unit. This web or unity of life may be con-
stantly changing from time to time as far as the individuals who com-
pose it are concerned, yet there seems to be more or less of a constancy
in any given area. Probably no living organism lives unto itself alone,
but each organism affects other living organisms and in turn is affected
by one or more organisms. The more we study biologic phenomena,
the more we realize and appreciate the interdependence of all living
things. In any particular area of life, each organism contributes some-
thing, either large or small, to the total life of that area. In the web
there may appear many struggles and antagonisms among the inhabi-
tants, but in spite of them there actually exists a balance in Nature —
all these struggles somehow counteract and balance each other so that
the number of species in a given area remains about the same. If one
group of organisms in a locality is eliminated, another group may take
its place or the remaining organisms may expand sufficiently to fill the
vacancy which was created.

All living organisms may be considered as links in a chain, all con-
tributing their part so that the chain is an endless one. For example,
certain bacteria of the soil change free nitrogen of the air into nitrates
which help to build plant tissues. The latter are eaten by animals
which may be consumed by other animals. Even if the latter die, their
bodies are decomposed by other species of bacteria and molds, thus
returning the ingredients to the soil where they are again available for
future generations of plants. '

III. PLANT AND ANIMAL MIGRATIONS (DISPERSAL)

Because of a lack of means of locomotion, most plants are not sub-
ject to the true migrations found in many animals such as birds, fishes,
mammals, etc. However, plants do disperse by slow, gradual spreading
by means of seeds, spores, or vegetative (propagative) units, such as
parts of stems, roots, etc.

656 General and Applied Biology

Animal migrations may take place ( 1 ) in order to meet the emergency
of overpopulation in any particular area, (2) in order to ensure a better
quantity and quality of food for themselves or their offspring, (3) in
order to find more suitable environment in which to develop their off-
spring, or (4) in order to escape certain types of climate which are not
highly satisfactory for their well-being.

The salmon (male and female adults) migrate from the ocean up the
Yukon and Columbia rivers, possibly for distances up to two thousand
miles. In the fresh water of these rivers, the adults spawn and then
die. The young salmon migrate from these fresh waters to the salt
water of the ocean where they mature and spend several years. Even-
tually, som.e of these adults again migrate up the rivers to spawn.

In the case of eels, the young are born in the salt water of the ocean
and they migrate up fresh-water rivers, sometimes journeying over three
thousand miles. After a few years, they return to salt water and breed,
eventually dying, because adult eels do not return to fresh waters.

In the case of such mammals as fur-bearing seals, great herds of adult
males and females migrate each spring to islands in the Bering Sea
where they remain from about May 1 to September 1. During this
time their young are produced. Great herds of the young seals migrate
from these islands to other regions of the North, while other herds
migrate long distances to cold regions of the South. Since seals are
valuable because of their fur, they are protected by laws in many coun-
tries. The "bachelors" (three-year-olds) are caught for their fur.

We are familiar with the seasonal migrations of certain species of
birds. A unique migration is illustrated by the Arctic tern which breeds
in northern North America and migrates across the Atlantic Ocean to
Europe, southward past Africa to the Antarctic, returning by a circui-
tous route to cross the Atlantic again to the northern habitat. The dis-
tance between their summer and winter habitats is over 10,000 miles,
thus making a journey of over 20,000 miles each year.

QUESTIONS AND TOPICS

1. Attempt to give from your own observations as many illustrations as possible
of (1) unity between various species of living organisms, (2) plant and ani-
mal antagonisms, resulting in a struggle for existence and a survival of the
fittest, (3) plant and animal successions, and (4) Web of Life or Balance
in Nature.

2. From your studies would you say that a living organism can live a life of com-
plete isolation? Give reasons why you say so.

Unity and Interdependence in Living World 657

3. From your studies would you say that unity or disunity predominates in the
hving world? Think carefully before answering this question, and give spe-
cific reasons why you say so.

4. What happens when there is more disunity than unity?

5. Do you think that the phenomenon of interdependence in Nature is deliberate
or a mere coincidence? Give reasons why you say so.

6. Does a study of the interdependence among lower forms of life throw any
light upon the problems encountered in human conduct? Explain.

7. List several ways in which you might improve human conduct with specific
suggestions for attaining that goal.

8. Explain the importance of the nitrogen, oxygen, and carbon cycles in Nature.

9. Discuss biologic communities (associations) and successions of plants and
animals.

10. Explain the dependence of living animals and plants ultimately upon photo-
synthesis, either directly or indirectly.

11. Explain the causes and effects of animal migrations and plant dispersals.
Explain in detail how certain animals have migrated or certain plants have
dispersed. Be specific and include examples.

12. List all the reasons for migrations or dispersals that you can. Do these same
reasons apply to human migrations? Explain.

SELECTED REFERENCES*

Gamow: The Birth and Death of the Sun, Viking Press, Inc.

Sanderson: Mystery of Migration, Saturday Evening Post, July 15, 1944.

^See also additional references in other chapters.

Chapter 33

PARASITISM AND PATHOGENESIS; SYMBIOSIS;
COMMENSALISM; GREGARIOUSNESS AND
COMMUNAL LIFE; PREDACIOUSNESS;
INSECTIVOROUS PLANTS; EPIPHYTISM;
SAPROPHYTISM

There are many kinds of biotic relationships in the living world, ex-
tending from the more or less dependence of living organisms on each
other to the more or less independence, or even antagonism, in other
organisms. These relationships may exist between different species of
animals, different species of plants, or between animals and plants. The
following brief descriptions of some of these relationships are representa-
tive:

I. PARASITISM AND PATHOGENESIS

In parasitism (par' a sit izm) (Gr. para, beside; sitos, food) an organ-
ism known as the parasite lives on, or within, and at the expense of, an-
other living organism known as the host. In this condition the host may
not be killed immediately (contrast with predaciousness and insectivorous
plants). When the parasite lives on the outside of the body of the host
it is an ectoparasite (Gr. ektos, outside) ; when it lives within the body of
the host, it is an endoparasite (Gr. endo, within). In parasitism the host
is harmed while the parasite benefits.

When the effects of parasitism on the host result in discernible, ab-
normal characteristics (symptoms), we may consider the condition as
disease-production, or pathogenesis (path o -jen' e sis) (Gr. pathos, dis-
ease or suffering; genesis, origin). In some cases the distinction between
parasitism and pathogenesis may be slight, but when actual, discernible
disease-production results, we may consider it as pathogenesis and the
parasite which causes the disease as a pathogen.

658

Parasitism and Pathogenesis 659

fc>"

A. Plants Pathogenic for Animals

Bacteria (Fig. 34) may cause such diseases of man as typhoid fever,
tuberculosis, leprosy, botulism (a type of food poisoning), undulant fever
(brucellosis), boils, diphtheria, pneumonia, scarlet fever, gonorrhea, men-
ingitis, whooping cough, tetanus (lock jaw), and many others. Bacteria
produce diseases in many ways by the production of injurious substances
which may tend to overcome the defenses of the body to infections or
which may destroy tissues or impair their normal capacities to function
properly. Certain bacteria produce a substance by which red blood cor-
puscles are broken down by the process of hemolysis (he -mol' i sis) (Gr.
hiama, blood; lysis, loosing). Certain bacteria (staphylococci, strepto-
cocci, pneumococci) produce substances known as leucocidins (luko-
si'din) {leucocyte; L. caedere, to kill) which destroy leucocytes (white
blood corpuscles). Certain organisms (certain streptococci) dissolve
blood clots. In certain staphylococcic infections thrombi (blood clots in
vessels) are formed. Certain types of bacteria (including staphylococci,
streptococci, pneumococci, and the rod-shaped, anaerobic bacteria asso-
ciated with gas gangrene) produce a substance which affects the per-
meability of tissues so that materials will readily diflfuse into surrounding
tissues. Sometimes organisms block the blood vessels to produce damage
either directly or indirectly. Bacteria may also influence disease produc-
tion by the use of oxygen, and by the formation of acids, gases, and other
detrimental products of metabolism. In some diseases the bacteria pro-
duce bacterial toxins ("poisons") which are water-soluble proteins and
are extremely potent. Compared with some of them, the poison strych-
nine is rather mild.

Bacteria may produce in other animals such diseases as Bang's disease
(contagious abortion or brucellosis) in cattle and other animals, tubercu-
losis in cattle, hogs, and other animals, tularemia ("rabbit fever") in
rabbits and other similar animals, "lumpy jaw" in cattle, plague in rats
and other animals, "black leg" in cattle, "limber neck" (botulism) in
chickens, chicken cholera, glanders in horses, sheep, and goats, and an-
thrax ("wool sorter's disease") in sheep, horses, goats, etc.

Fungi may produce in man such diseases (Fig. 74) as actinomycosis,
ringworm of various types, including "athlete's foot," aspergillosis (caused
by certain species of Aspergillus) , maduromycosis (madura foot), coc-
cidioidomycosis (valley fever), etc.

660 General and Applied Biology

Yeasts mav cause such diseases in man as North American blasto-
mycosis (Gilchrist's disease)^ moniliasis (thrush), European blastomyco-
sis, etc.

Higher plants such as poison ivy, poison oak, deadly nightshade, loco-
weed, water hemlock, etc., are poisonous for man and other animals.
The pollen of certain plants (ragweeds, grasses, roses, oaks, etc.) may
produce allergies (Fig. 256) of various types and consequences in suscep-
tible human beinos.

B. Plants Pathogenic for Plants

Bacteria may cause such diseases in plants as wilt diseases of tomatoes,
potatoes, melons, cucumbers, corn, etc., soft rot of carrot, cabbage, cu-
cumber, celery, etc., bacterial blight of beans, fire blight of pears and
apples, crown galls of apple, grape, raspberry, alfalfa, etc., bacterial blight
of walnut, canker of citrus, and many others.

Higher fungi may cause such diseases in plants as rusts and smuts
(Figs. 66 and 67) of such cereal grains as corn, wheat, barley, etc., downy
mildew of grapes, chestnut blight, potato blight, Dutch elm disease, apple
scab, bitter rot of apple, brown rot of peaches, peach-leaf curl, "damping
off" disease of seedling plants, ergot of rye, barley, and wheat, black knot
of cherry and plum, leaf spot of strawberry, black spot of roses, and many
others. It should be noted that the disease of elms known as phloem
necrosis is due to a virus and is not to be mistaken for the Dutch elm dis-
ease produced by a fungus.

Certain flowering plants such as dodder and mistletoe may parasitize
other species of plants and produce damages which may often cause the
death of the host.

C. Animals Pathogenic for Animals

Protozoa may produce such diseases in man as syphilis, amoebic dysen-
tery, African sleeping sickness, various types of malarial fevers, tropical
ulcers, kala-azar, and many others. Protozoa may cause diseases in other
animals such as chicken septicemia, surra in horses and other animals,
nagana in cattle, and many others.

Worms may cause such diseases in man as sheep liver fluke disease
[Fasciola hepatica), Chinese liver fluke disease {Clinorchis sinensis),
blood fluke diseases (Schistosoma japojiicum, S. mansoni, S. haemato-
bium), Oriental lung fluke disease (Paragonimus ivesterm,ani), tapeworm
diseases {Taenia solium, T. saginata) , human ascaris disease [Ascaris

Parasitism arid Pathogenesis 661

lumhricoides) , human pinworm disease {Enterobius vermicularis) , hook-
worm diseases [Necator americanus and Ancylostoma duodenale) ^
ground itch {Ancylostoma hraziliense) , elephantiasis [Wuchereria [Fi-
larial bancrojti) , loa loa disease of the eye {Loa loa) , Trichinosis or
pork roundworm disease {Trichinella spiralis) , human whipworm disease
{Trichuris trichiura) , and many others.

Worms may cause liver rot of sheep, cattle, and hogs (Fasciola he-
patica). Chinese liver flukes may be found in monkeys, cats, dogs, and
snails [Clinorchis sinensis) . Blood flukes may be found in monkeys, dogs,
cats, pigs, cattle, and sheep (Schistosoma sp.) and lung flukes in dogs,
cats, pigs, tigers, and snails [Paragonimus) . Tapeworms may spend their
immature stages in the pig, cattle, rabbit, mouse, lice, fleas, fish, sheep,
monkeys, cat, dog, etc. "Gid" or "staggers" of sheep is caused by the im-
mature stages of the tapeworm (Multiceps) . Horse pinworm disease
(Oxyuris equi) may be quite common. "Gapes" of birds is caused by the
bird gapeworm {Syngamus trachea). The pork roundworm (Trichi-
nella) may inhabit the pig, cat, dog, rat, etc.

The immature stages of certain mollusks, known as glochidia (glo-
kid' i a) (Gr. glochis, arrow-point; idium, diminutive), may attach them-
selves to the gills and fins of fish where they may cause diseased condi-
tions. Lice and fleas may attack man, dogs, cats, rats, and many other
animals, on which they may produce ill effects. Insects may parasitize
other insects and even eventually destroy the host. An ichneumon wasp
lays eggs in the cocoon of the tent caterpillar, the latter being aff"ected by
the developing larval stage of the ichneumon. The eggs of the tachina
fly may develop into a larval stage in the army worm; insects of the hy-
menoptera type may parasitize boll worms, army worms, plant lice
aphids), etc.

D. Animals Pathogenic for Plants

Roundworms (nematodes) may attack the roots, stems, or leaves and
produce nematode diseases in such plants as wheat, rye, cotton, tomato,
clpver, sugar beets, tobacco, peony, begonia, and many other higher
plants; the immature stages of the Oriental intestinal fluke {Fasciolopsis)
may be present in fresh- water plants; the immature stages of the Chinese
liver fluke {Clinorchis) may be present in freshwater plants; the round-
worm {Heterodera [Caconema] radicicola) may affect the potato, to-
mato, lettuce, trees, weeds, and many other plants.

662 General and Applied Biology

Insects not only transmit plant diseases but as a result of their chewing,
sucking, boring, and egg-laying activities are responsible for many serious
consequences in the tissues of higher plants. Enlargements known as
galls on leaves, stems, etc., are common examples. Bark lice, mealy bugs,
various scale insects, etc., cause a great variety of serious diseases in
plants.

The various causes and effects of the different diseases of plants and
animals cannot be discussed in detail here, but the reader is referred
to other sources for those in \vhich there is a particular interest.

II. SYMBIOSIS

In some instances, in the living world there is more than mere living
together in harmony, for there is more or less of a mutual helpfulness
between certain living organisms. A condition in which two species of
organisms (known as symhionts) live together with mutual benefit to
both is known as symbiosis (simbi -o' sis) (Gr. sym, together; hios, life).
In some cases this association is so complete that there is organic unity
in which each type of organism contributes something to the other with
which it is living. In the so-called green Hydra there live small green
algae (plants) which photosynthesize food by combining water and car-
bon dioxide, the latter being given off by the Hydra. The foods and the
by-product (oxygen) of photosynthesis may be used by the Hydra. In
a group of plants known as lichens {W ken) (Gr. leichen, liverwort)
(Fig. 327) there is a close relationship between the green, chlorophyll-
bearing algae and the nonchlorophyll-bearing fungi of which lichens are
composed. The algae supply foods for the fungi, while the latter give
protection, supply water, etc.

Termites feed on cellulose of wood but are unable to digest it. Certain
flagellated protozoa within their intestine render the cellulose digestible
for both. These protozoa cannot exist outside the termite intestine. Cer-
tain types of ants protect certain species of aphids (plant lice) and in
return use as food the sweet "honey milk" produced by the latter. The
so-called green paramecium {P. bursaria) has within its endoplasm the
unicellular, green alga (Chlorella vulgaris). The alga uses the wastes
of the Paramecium and gives food and oxygen in return. Certain sponges
and green algae possess a relationship similar to that described above.

The Portuguese man-of-war, a coelenterate, possesses long tentacles
among which live certain species of fish. The nematocysts of the tentacles
protect the fish, and the latter share some of the foods which they cap-
ture with the Portuguese man-of-war.

Symbiosis 663

The hermit crab may live in an empty mollusk shell upon which are
placed various types of hydroid coelenterates. The stinging cells (nema-
tocysts) of the latter protect the crab, while the sessile coelenterates are
advantageously carried from place to place by the crab and secure some
foods captured by the crab.

Fig. 327. — Types of lichens which are plants composed of algae (blue-green or
green) and fungi (chiefly Ascomycetes, infrequently Basidiomycetes). The three
principal types of lichens are (1) foliose (flat, often leaflike bodies), (2) crustose
(hard, often granular crusts on bark or rocks), and (3) jruticose (branched struc-
tures which may be erect or hanging).

The so-called spider crab carries a species of sponge on its back which
protects it through concealment and its disagreeable qualities. The ses-
sile sponge is carried from place to place by the crab.

664 General and Applied Biology

In certain higher plants, especially trees, a close relationship may exist
between the mycelium of certain fungi and the roots. This association
does not seem to harm the tree, and the mycelium may form an encircling
mantle around the finer roots, causins; them to enlars:e and become much
branched. This close association of fungus and roots is known spe-
cifically as mycorrhiza (mi ko -ri' za) (Gr. mykos, fungus; rhizos, root),
in which both plants derive mutual benefit ; the fungi may prepare nitrog-
enous foods for the roots and receive food from the roots in return.

Certain types of nitrogen-fixing bacteria live in the small swellings
(nodules) on the roots of leguminous plants such as clovers, alfalfa,
beans, soybeans, etc. These specific bacteria take free nitrogen from the
atmosphere and convert it into certain nitrogen compounds, which are
changed by other bacteria eventually into usable nitrates. The nitrogen-
fixing bacteria secure food and protection from the plant, while the lat-
ter profits from the foods formed by the bacteria. The nitrogen-fixing
bacteria (Fig. 325) which are present in the root nodules of plants are
refen^ed to as symbiotic nitrogen-fixing bacteria to diflferentiate them
from other bacteria which can accomplish a similar phenomenon, but the
latter bacteria live free in the soils. The latter phenomenon is known as
7ionsymbiotic nitrogen-fixation.

III. COMMENSALISM

An association of members of two or more species of organisms in
which one (commensal) is benefited but not injured while the other
(host) is neither benefited nor injured, but both using the same supply
of food, is known as com.mensalism (kom -en' sal izm) (L. com, together;
mensa, table, or food). In this type of association there is not quite the
close relationship of organisms as found in symbiosis. A special type of
tropical fish known as the shark sucker (Remora) attaches itself by means
of a sucker to the body of sharks, turtles, whales, etc. Part of the food
captured by the animal host is used by the Remora. In this case the host
does not appear to receive any benefit from the association. Certain small
birds, such as one of the grackles, may build nests near the nests of larger
birds, such as a fish-eating osprey, thus securing protection. The so-
called "rudder fish" secures shelter and protection from the stinging
tentacles of large jellyfish but apparently gives nothing in return, but
both may eat of the same food. Protozoa, yeasts, and fungi may live in
the digestive tract of man and other animals, doing neither harm nor good
but using some of the common food and receiving protection from the
host.

Gregariousness and Communal Life 665

IV. GREGARIOUSNESS AND COMMUNAL LIFE

In gregariousness (gre -ga' ri us nes) (L. grex, flock) certain animals
may associate with each other for protection, for securing foods, or pos-
sibly for reproduction purposes (which may be incidental in certain
cases). The herding of herbaceous mammals, the flocking of birds, the
schooling of fish are common examples. Dogs and wolves often hunt in
packs, thereby attacking larger animals than they probably would if in-
dividuals did the hunting. The reasons for gregarious habits are not al-
ways known, and they are not always based on sex, because in certain
schools of fish only one sex is present. In the latter case foods are pos-
sibly a controlling factor which brings about the association of the fish,
and mass movements are the result of imitation of a so-called "leader."
Herds of large mammals also display group or mass movements because
of the leadership of one individual, usually a large or old male. The
various social groups might be classified as ( 1 ) those in which there is
division of labor among the various distinct castes, as in the bees, ants,
termites, etc., (2) those groups of animals which react more or less as a
unit, such as a family group of mammals, and (3) those which show a
social toleration of similar individuals in a certain area, such as schools
of fish, flocks of birds, etc.

Gregariousness may involve diff'erent species and may be due to the
presence of certain desirable conditions for their existence such as shelter,
food, moisture, nesting materials, etc. If organisms of the same species
associate together, a communal society may result. In higher types of
animals the gregarious habit may be the result of a desire for companion-
ship or a feeling of safety in numbers. In the latter case alarms may be
given by individuals, thereby giving warning to others of impending
dans:ers.

Among lower animals the best examples of communal life are shown
by the insects. Castes and well-developed divisions of labor are present
in honeybees, social wasps, ants, and termites. Possibly associations might
be considered as temporary groupings dependent upon environmental
factors, while communal societies are held together and the conducts of
the members influenced by the so-called social instincts. Possibly asso-
ciations and societies have much in common, but they are also different
because in the latter there is greater complexity and a variety of behaviors
of the diff'erent members. Frequently in a group there is one leader, who
is usually the strongest or most experienced. This one is followed by other
members, and the leader may have acquired the position of leader through

666 General and Applied Biology

a process of destroying one or more less experienced or weaker adver-
saries. Much is unknown about the communal life of animals, and the
reader is referred to additional references in this important field. After
Charles Darwin proposed his doctrine of the survival of the fittest, it
was maintained that all living animals and plants struggle for their exist-
ence. If this be true, then the success or failure of individuals or groups
may be influenced to a greater or lesser extent by their inherent abilities
of survival commensurate with the specific environmental factors present
in the area in which they live. Cooperation between individuals is ob-
served in the care of young by most mammals, the protection of wounded
and sick by many higher animals, the protection of the herd by the male
deer, the sharing of foods in such animals as apes and man, and the pro-
tection of members of a family against enemies, etc.

V. PREDACIOUSNESS

Predatism or predaciousness (pre -da' shus nes) (L. praeda, prey or
booty) is a condition in which one animal captures and preys on another
living organism, usually using it for food. Predatism is characteristic of
those animals which we term predatory which kill animals and devour
them for food. These predatory habits may be exhibited by a great num-

Fig. 328. — Starfish attacking an oyster. Note the tube feet on the underside of
the starfish arms. (Courtesy of The American Museum of Natural History.)

Predaciousness 667

ber of animals whose methods of capturing and devouring their prey
may vary greatly. Amoeba, Paramecium, and other protozoa may cap-
ture a variety of living organisms for food. Hydra and other coelenterates
may devour aquatic organisms. The Portuguese man-of-war (Fig. 93)

Fig. 329. — Praying mantis, a predacious insect of the order Orthoptera.

may prey on fish and crustaceans. Planarlans may feed on mollusks,
arthropods, etc.; squids capture fish; starfish capture oysters and other
animals (Fig. 328) ; dragonflles (Fig. 205) may destroy flies and mos-
quitoes; certain Insects (praying mantis [Fig. 329], ground beetles, lady-
bird beetles [Fig. 297] aphis lions, etc.) may destroy other insects, many

668 General and Applied Biology

of which may be detrimental. Fish may devour worms, crustaceans, in-
sects, etc.; frogs may capture worms, insects; snakes may destroy frogs,
birds, etc.; owls may kill rabbits, mice, etc.; chicken hawks may kill chick-
ens, etc.; cats may destroy rats, mice, birds, etc. Harmful predacious
mammals include wolves and cougars which kill sheep, cattle, horses,
and big game; dogs and cats may be beneficial predators when they de-
stroy harmful animals such as rats, mice, etc.

VI. INSECTIVOROUS PLANTS

The so-called insectivorous plants (in sek -tiv' or us) (L. insectus, cut
into or insect; vox are, to devour) possess special structures, usually modi-
fied leaves or parts of leaves, whereby they are able to trap and devour
insects for part of their food (Fig. 330). The specialized structures se-
crete enzymes for the digestion of the insects, and the latter are absorbed

PITCHER PLANT
S&rracenift

SUNDEW

Drosera

VENUS'S-rLYTRAF
Dionaee

lUTTXRWORT^

Pinguicula

Fig. 330. — Insectivorous plants. In the pitcher plant the pitcherlike leaves are
filled with water in which insects drown and are digested. In the sundew the
leaves are supplied with sticky hairs for capturing insects. In the bladderwort
(Utricularia) numerous "bladder traps" capture aquatic animals, and one is
shown enlarged. In Venus's-flytrap the two halves of the leaves act like a spring-
trap to capture insects. The sticky leaves of the perennial butterwort capture
insects. (Copyright by General Biological Supply House, Inc., Chicago.)

by the plant. The so-called "pitcher plants" [Sarracenia) common in
bogs possess a pitcherlike device which is filled with water and in which
insects drown. Escape is prevented by inwardly directed spines and the
digested insects are absorbed. In Venus's flytrap (Dionaea) the special-
ized leaves possess a row of "teeth" on the outer margin of each half
of the leaf blade. On the upper surface, in the center of each half, are
sensitive "hairs" which when stimulated by an insect cause the two halves
to spring together to entrap the insect. Digestion by enzymes somewhat
resembles that in the pitcher plant. In the common sundew {Drosera)

Epiphytism 669

the somewhat circular leaves are covered with long glandular hairs
("tentacles") which secrete a sticky substance to capture insects. The
tentacles bend toward the center to form a trap in which the enzymes
digest the insect. There are approximately two hundred species of
chlorophyll-bearing, angiospermous plants which are insectivorous or
carnivorous. They photosynthesize their foods but supplement with cer-
tain essential elements by the digestion of insects. If the correct ingredi-
ents are present in the soil, they need not ingest the animal foods. In the
so-called bladderwort plants, present in ponds and lakes, there are tiny
"bladder traps" on the submerged stems. Each bladder has a one-way
trap door through which aquatic animals enter and in which they are
digested. The leaves of Venus's flytrap and certain pitcher plants are
able to digest such foods as hard-boiled ^gg, meat, etc.

VII. EPIPHYTISM

Epiphytes (ep'ifite) (Gr. epi, upon; phyton, plant) are plants which
use other plants, poles, trees, wires, etc., for support but do not derive
nourishment from the other plant; hence they are not parasitic. Epi-
phytes are primarily autotrophic (o to -trof ik) (Gr. auto, self; trephein,
to nourish) which means they photosynthesize their food and do not get
it from plants on which they may happen to be attached. They secure
carbon dioxide and water from the atmosphere and moisture and nu-
trients from debris in crevices in which they may be anchored. Ordi-
narily, epiphytes take no sustenance from the plant on which they are
attached, but they may injure the plant by shading the leaves, by break-
ing limbs because of excessive weight, etc.

Certain algae may be epiphytes on other plants. The green alga Proto-
coccus may grow epiphytically on the bark of trees. Certain brown algae
and marine red algae may grow on other algae as epiphytes. Certain
species of algae even grow among the hair of the three-toed sloth. Cer-
tain species of lichens, mosses, ferns, and tropical orchids and certain
members of the pineapple family may be epiphytes. "Spanish moss"
{Tillandsia) of the South is an epiphyte which is a rootless, flowering
plant of the pineapple family and which hangs in great masses from
trees, poles, and wires (Fig. 331) . Often the growth is so enormous that
the tree is killed, even though the "moss" is not parasitic. The flexible
internal filaments of Spanish "moss" are being used for commercial pur-
poses.

670 General and Applied Biology

Fig. 331. — Spanish "Moss" (not a true moss), a flowering, epiphytic plant of
the pineapple family which hangs in great masses from trees, poles, and wires in
the South.

Saprophytism 671

VIII. SAPROPHYTISM

A saprophyte (sap'rofite) (Gr. sapros, dead; phyton, plant) Is an
organism which secretes enzymes capable of utilizing (absorbing) as foods
such dead organic materials as carbohydrates, proteins, etc. Saprophytism
differs from other similar phenomena in that two living organisms are
not involved but one living organism and a dead substance which may
have been part of a living organism originally. The enzymatic actions
bring about chemical changes in the dead, organic materials. When the
latter involves carbohydrates and is usually associated with the produc-
tion of gas, it is called fermentation (L. jermentum, ferment or yeast) ;
when it involves proteins and is manifested by the production of foul
odors, it is called putrefaction (L. putrere, rotten; facio, to make).

Plants without chlorophyll cannot photosynthesize foods so must ab-
sorb them from outside sources, which involves the presence of a certain
amount of necessary moisture. Many bacteria absorb foods from dead,
organic substances and are called saprophytic bacteria in contrast with
parasitic or pathogenic bacteria. Slime molds may grow on decaying
plant materials, rotting woods, and leaf molds; hence, they live sapro-
phytically. Certain species of molds (fungi) may live on the dead organic
materials of plants or animals or in humus-containing soils. Saprophytic
fungi usually live wherever they encounter a suitable supply of organic
matter, oxygen, water, and warmth. Rhizopus nigricans (Fig. 36) and
similar molds are common saprophytes on moist bread, overripe fruits,
foodstuffs, animal dung, etc. Yeasts may live in sugar solutions by utiliz-
ing an enzyme, zymase, which they secrete. Alcohol is formed in the
process, with the liberation of carbon dioxide. The blue and green molds
(Penicillium and Aspergillus) grow on fruits, foodstuffs, tobacco, leather,
fabrics, nuts, and other organic materials in damp places. Mushrooms
and related fungi live saprophytically^ in soils, on dead leaves, dung,
dead wood, and bark and similar organic materials. Shelf fungi (bracket
fungi) are common on dead wood, although parasitic species may kill
living trees.

Saprophytism is not as common in higher plants as it is in lower, non-
chlorophyll-bearing fungi. The Indian pipe {Monotropa) is a flowering
plant that lacks chlorophyll which may obtain food from decaying leaf
mold by the aid of fungi which inhabit its underground basal portion.
In some instances it may be partially parasitic on the roots of living
plants.

672 General and Applied Biology
QUESTIONS AND TOPICS

1. Learn the correct pronunciation, derivation, and true meaning of each new
term used in this chapter,

2. Add from your own experience any additional examples for each biotic phe-
nomenon described in this chapter, being very careful to check so that it is
placed in the proper category.

3. Discuss the probable origin of parasitism in the living world.

4. Give probable reasons why there are so many types of pathogenic organisms.

5. Discuss gregariousness and communal life, giving examples from your own
observations.

6. What are the benefits of successful and efficient communal life?

7. What attributes are common to colonies of honeybees, ants, and human
beings?

8. Discuss the uniqueness of predaciousness, insectivorous plants, and epiphytes.

9. Discuss plant and animal antagonisms, including the probable origin for such
behavior and its consequences.

10, In the light of your present knowledge, discuss the human family, a colony
of people, and possible communal life for entire countries and the world at
large,

SELECTED REFERENCES*

Allee: The Social Life of Animals, W. W. Norton & Co., Inc.
Alverdes: Social Life in the Animal World, Harcourt, Brace and Co., Inc.
Chandler: Animal Parasites and Human Disease, John Wiley & Sons, Inc,
Conant et al. : Manual of Clinical Mycology, W. B. Saunders Co.
Darwin: Insectivorous Plants, London, John Murray.
Dodge: Medical Mycology, The C. V. Mosby Co.

Ewing: Manual of External Parasites, Charles C Thomas, Publisher.
Faust: Human Helminthology, Lea & Febiger.

Harshberger: Mycology and Plant Pathology, P. Blakiston's Son & Co.
Henrici and Ordal: The Biology of Bacteria (Microbiology), D. C. Heath & Co.
Lloyd : Carnivorous Plants, Chronica Botanica Co.

Sweetman: Parasitic and Predacious Insects, Comstock Publishing Co., Inc.
Wheeler: The Social Insects; Their Origin and Evolution, Harcourt, Brace and
Co,, Inc,

* Additional references in the chapter on Fungi, p. 184.

Chapter 34
HEREDITY— GENETICS

1. Definitions and Methods of Studying Genetics. — Genetics (je-net'
iks) (Gr. genesis, descent) is the science of heredity (L. her edit as, heir-
ship) in which this branch of biology attempts to discover how hereditary
materials are transmitted through succeeding generations of plants and
animals and, as a consequence, how similarities and differences develop
from these hereditary materials subject to the influences of various inter-
nal and external environmental conditions.

In general, genetics may be studied (1) by the experimental crossing
method in which organisms of known genetic composition are crossed
and the results interpreted, (2) by the cytogenetic method which is a
study of those structures and functions of cells responsible for the trans-
mission and development of hereditary traits, and (3) by the pedigree
method whereby the differences and similarities of individuals in large
populations are properly recorded and scientifically analyzed. Much
valuable information regarding the inheritance of certain human traits
has been secured by this method. Sometimes a combination of all three
methods is used in an attempt to solve certain problems in genetics. In
some instances, the hereditary mechanism is subjected to physical influ-
ences, such as x-rays, atomic radiations, etc., or chemicals, such as
colchicine, and the results on the inheritance observed.

2. Chromosomes, Polyploidy, and Mitosis. — Chromosomes carry a
linear series of genes or determiners by^ means of which hereditary mate-
rials are borne from parents to offspring and through which the expres-
sion of traits is controlled (Figs. 334 and 335). Chromosomes within
the nucleus are always closely related and dependent upon the cyto-
plasm which surrounds the nucleus, either for their normal activities or
for the normal and proper development and expression of their inherent
hereditary factors. Chromosomes occur in even numbers (in pairs) in
most organisms. Species which apparently are closely related may differ
widely with respect to the number of their chromosomes, while species
of unquestionably remote relationship may have an identical number of
them in each of their cells (see accompanying table).

673

674 General and Applied Biology

Chromosomes in Various Animals and Plants*

NUMBER OF
CHROMOSOMES

PER BODY OR
SOMATIC CELL

Animal

Hydra fusca (phylum, Coelenterata) 12
Campanularia (phylum, Coelenterata) 20
Horse roundworin (Ascaris megalocephala) (Nemathelminthes) 4
Human roundworm (Ascaris lumbricoides) (Nemathelminthes) 48
Earthworm (Lumbricus sp.) (phylum, Annelida) 32
Leech (Nephelis sp.) (phylum, Annelida) 16
Snail (Helix sp.) (phylum, Mollusca) 48
Water flea (Cyclops sp. ) (phylum, Arthropoda) 4
Brine shrimp (Artemia sp.) (phylum, Arthropoda) 168
Crayfish (Cambarus virulus) (phylum, Arthropoda) 200
Crayfish (Cambarus immunis) (phylum, Arthropoda) 208
Fruit fly (Drosophila sp.) (phylum, Arthropoda) 8
Cabbage butterfly (Pieris sp.) (phylum, Artl^ropoda) 30
Housefly (Musca sp.) (phylum, Arthropoda) 12
Mosquito (Anopheles sp.) (phylum, Arthropoda) 6
Cockroach (Periplaneta sp.) (phylum, Arthropoda) 34
Gypsy moth (Lymantria sp.) (phylum, Arthropoda) 62
Frog (Rana sp. (subphylum, Vertebrata) 26
Salamander (subphylum, Vertebrata) 24
Pigeon (Columba sp. ) (subphylum, Vertebrata) 16
Opossum (Didelphys sp.) (subphylum, Vertebrata) 22
Hedgehog (subphylum, Vertebrata) 48
Armadillo (subphylum, Vertebrata) 60
Rabbit (Lepus sp.) (subphylum, Vertebrata) 44
Dog (Canis sp.) (subphylum., Vertebrata) 78
Horse (Equus sp.) (subphylum, Vertebrata) 60
Cat (Felis domesticus) (subphylum, Vertebrata) 38
House mouse (subphylum, Vertebrata) 40
Monkey (Rhesus macacus) (subphylum, Vertebrata) 48
Man (Homo sapiens) (subphylum, Vertebrata) 48

Plants

Green alga (Spirogyra sp.) (phylum, Thallophyta) 24
Ascus or Sac fungus (Pyronema sp.) (phylum, Thallophyta) 24
Rockweed (Fucus sp. ) (phylum, Thallophyta) 64
Peat moss (Sphagnum sp.) (phylum, Bryophyta) 40
Pine tree (Pinus sp.) (Gymnosperm) 24
Yew tree (Taxus sp.) (Gymnosperm) 16
Fir tree (Abies sp.) (Gymnosperm) 32
Pea (Pisum sp.) (Angiosperm) 14
Currant (Ribes sp.) (Angiosperm) 16
Chinese Primrose (Primula sinensis) (Angiosperm) 18
Tomato (Lycopersicum esculentum) (Angiosperm) 24
Black nightshade (Solanum nigrun) (Angiosperm) 72
Corn (Zea mays) (Angiosperm) 20
Sedge or shear grass (Carex aquatilis) (Angiosperm) 74
Onion (Allium cepa) (Angiosperm) 16
Lily (Lilium sp.) (Angiosperm) 24
Hawk's beard (Crepis virens) (Composite Family) (Angiosperm) 6

*For a list of chromosomes for approximately 1,000 species, see the Journal of Morpholoey
34: 1-67, 1920.

Heredity — Genetics 675

The evidence that inheritance is due to chromatin may be shown by
the following facts: (1) Of all the parts of a cell, the chromatin is the
most constant portion through all the changes of the cell. This sug-
gests the chromatin as the probable carrier of hereditary factors. (2)
The chromosome complex is maintained throughout the process of cell
division (mitosis). At this time the mechanism for the transmission of
hereditary factors from one cell to its daughter cells must be present

AUTOSOMES

SEX CHROMOSOMES

FEMALE

^m^-x

MALE

mm^-x

^ V

Fig. 332. — Chromosomes of the fruit fly (Drosophila sp.), showing pairings,
sizes, and shapes in the male and female (diagrammatic). In the female thenr
are three pairs of autosomes and a pair of straight X chromosomes. In the male
there are three pairs of autosomes and one straight X chromosome and a hook
shaped Y chromosome.

>tO>IO»ll

(CfCKOUiMjc*

Fig. 333. — The chromosomes of man. A, Spermatogonium (of the male) dur-
ing division, drawn so that the chromosomes do not overlap; B, the twenty-four
pairs of chromosomes from a somatic (body) cell. (From Lindsey: A Textbook
of Genetics. By permission of The Macmillan Company, publishers.)

and functional; otherwise there could be no such transfer. (3) There
is a close correlation between abnormal inheritance and abnormal
chromatin behavior. (4) There is a close relationship between chromo-
somes and the determination and development of sex, the latter being
a hereditary character. The fact that the number of chromosomes is

676 General and Applied Biology

equal, or nearly so, in both sexes of most organisms ensures an equal
opportunity of inheritance from each parent. It is worth noting that
the cytoplasm of most sex cells is much greater in volume in the female
sex cell. If heredity were fundamentally dependent upon the cytoplasm,
there would not be the necessary equal opportunity suggested above.
The role played by the chromosomes during the process of reduction-
division, when sex cells are formed, also suggests their value in heredity.
(5) The entire field of Mendelian heredity and its modern interpreta-
tions and modifications all tend to prove the chromosome theory of
inheritance.

Fig. 334. — Giant chromosomes as photographed from the salivary gland of the
fruit fly (Drosophila melanogaster) . (Copyright by General Biological Supply
House, Inc., Chicago.)

Chromosome Polyploidy (Increase in the Number of Chromosomes):

Under ordinary conditions, chromosomes do not change their normal
number. However, in some instances, changes take place naturally or
can be induced by artificial methods. One of the earliest examples of
natural change in chromosomes was giv^n by the Dutch botanist, Hugo
de Vries (1895), in which he discovered the origin of a new species of

Heredity — Genetics 677

primrose (Oenothera gigas) from the common primrose (Oenothera
Lamar ckiana). The new species appeared suddenly and possessed a
double number of chromosomes in the nuclei, and this double number
of chromosomes remained constant afterward. De Vries had no expla-
nation for this phenomenon, but in recent years it has been discovered
that it may take place naturally or can be induced by certain chemicals,
by such physical influences as x-rays, high or low temperatures, or cen-
trifuging, or by removing the growing tip of a plant. The most striking
results have been obtained by using a drug called colchicine (koF ki sin)
which is an alkaloid poison (C22H25O6N) extracted from the seeds of
the plant called meadow saffron. Colchicine is almost a specific for in-
ducing the doubling of chromosomes without cell division in plants. If
a 1 per cent solution is applied to the growing buds or tips of plants,
cells are formed with the double number of chromosomes. Frequently

n :■

■..Vc>:.Ci|i?)fV<»

„.^ ^o <:>-*-<xi»-

^l>-

>— 00

oO<^<x:> —

Y'lg. 335. — Chromosome from the salivary gland of the larva of a black fly
(Simulium sp.), an insect of the order Diptera (camera lucida drawing). The
longitudinal threadlike bands are called chromonemata, consisting of a linear
series of granules, the chromomeres, which have a specific arrangement of group-
ing. ^ is a semidiagrammatic representation of the types of chromomeres and
the ways in which they are connected. At a in the main figure there are two
rows of dotlike chromomeres associated in pairs. The band at h is composed of
fifteen or sixteen vesiculated chromomeres closely packed together; c-h are other
groupings of chromomeres along the chromonemata of the chromosome. (From
Painter and Griffen: Chromosomes of Simulium, Genetics 22: 616, 1937.)

redoubling as many as three times takes place. The colchicine inhibits
cell division while chromosome division continues as usual. This change
is permanent because cells with doubled chromosome numbers continue
to divide to form tissues, seeds, and embryos, all with double numbers of
chromosomes.

The ease with which many plants may be artificially induced to double
their chromosome number may explain the frequency of its occurrence
in Nature. Miintzing concludes that more than half of the species of
flowering plants, including many of our economically important plants,
which have been studied have doubled or redoubled chromosomes. For
example, different species of wheat with 14, 28, and 42 chromosomes are

678 General and Applied Biology

known; also chrysanthemum species with 18, 36, 54, 72, and 90 chromo-
somes. The regularity of these series of numbers (multiples of a lower
number) suggests the origin of new species by doubling the chromosomes
or by adding a single set such as found in a sperm or egg. Individuals
with three or more single sets of chromosomes in their body cells are
known as polyploids, and the condition is known as polyploidy.

In animals such series of chromosome numbers are encountered less
frequently than in plants, and polyploidy has rarely been induced in ani-
mals by artificial methods. One explanation is that higher animals have
their sexes separate, while most plants are monecious (hermaphroditic).
If the sexes are separate, the doubling of chromosome numbers can
occur only in case it takes place in males and females which subsequently
cross. In addition, the doubling of chromosomes may lead to irregularity
in the distribution of the sex chromosomes (X and Y chromosomes)
which may cause sterility. In animals, new species probably originate by
the slower method of gradual divergence by the accumulation of gene
differences rather than by chromosome doubling.

Plants which have doubled numbers of chromosomes usually are larger,
have thicker stems, thicker, broader leaves, darker green color, larger
flowers and seeds; they develop more slowly, take longer to mature, and
are often more hardy than the original plants. Many new plant types
have been produced which are superior economically because of their
doubled chromosomes. Tomatoes with doubled chromosomes have been
produced; they contain about twice the usual quantity of vitamin C.

Chromosomes (Figs. 332-335) and their genes play important roles
during the process of mitosis whereby the determiners for future traits
are accurately duplicated during the division of cells. If genes were not
accurately duplicated during mitosis, the resulting daughter cells might
not possess their necessary hereditary materials from which future traits
could be developed. Much valuable information regarding the internal
structure of chromosomes has been secured by a study of the stained
cells during mitosis.

During the so-called resting stage of a cell the chromatin is in the
form of long thin, granular threads (chromatin strands) which even-
tually will shorten and thicken to become chromosomes^ the number,
size, and shape of which are specific for each species of plant or animal.
During the prophase stage of mitosis each chromosome appears to pos-
sess a pair of thin, fiberlike (often coiled) chromonemata (kromo-ne'-
ma ta) (Gr. chroma, color; nema, thread) or gene strings. Each
chromonema contains a specialized region known as the centromere (sen'-

Heredity — Genetics 679

tro mer) (Gr. kentron, center; meros, part) or kinetochore — the point
for attachment to the spindle fiber when chromosomes migrate along the
latter. As prophase progresses, the chromonemata thicken, uncoil, and
acquire an accumulation of the matrix which surrounds them. The two
threadlike chromonemata and their matrix in each prophase chromo-
some are called chromatids. In later prophase the two chromatids of
each chromosome appear to be identical and lie next to each other. The
two centromeres lie in close contact. After the chromosomes are ar-
ranged on the equator, the two chromatids of each chromosome repel
each other, possibly through some electrical process between the two
centromeres. This action results in the migration of the daughter chro-
mosomes toward opposite poles. Attached to each chromonema in a
linear series are numerous, beadlike granular chromomeres (kro' mo mer)
(Gr. chroma, color; meros, part) of various sizes and different distances
apart. The chromomeres occur in different sizes and arrangements
which are constant and characteristic for each chromosome. In other
words, each chromosome has its unique arrangement of chromomeres of
specific sizes which characterize it. It may have a series of large, small,
or medium-sized chromomeres arranged along the chromonema, and
this arrangement is specific for that particular chromosome. In studies
of the giant chromosomes of the salivary glands of fly larvae of various
species the chromosomes appear like a cylinder with larger numbers of
characteristic crosshands or disks. Comparable to the differences in sizes
of chromomeres and distances between them, these bands may be thin
or thick, far apart or close together, all of this so characteristic and con-
stant for each chromosome of a set that each band can be indentified
and numbered. Are these bands the hereditary entities known as genes
(Gr. genos, descent) or are these bands associated with genes? Evidence
is inconclusive, although it is known that at least certain bands are asso-
ciated with more than one gene.

3. Chromosomal Aberrations. — Normally the number of chromosomes
in the somatic (body) cells of animals and the sporophyte generation of
plants is double or diploid (2N), while it is single or haploid (N) in
gametes, spores, and the gametophyte generation of plants, but there are
exceptions. For example, the endosperm (stored food) of angiosperm
seeds normally and regularly contains a triple (triploid) number (3N).
In addition to the ploidy condition previously described, there are nu-
merous chromosomal aberrations such as those which involve pieces of
chromosomes, entire chromosomes, or entire sets of chromosomes
(genomes) .

680 General and Applied Biology

In chromosomal deficiency a segment of a chromosome is missing,
while in chromosomal duplication an extra segment is present. The
duplicated segment may be inserted within a chromosome or it may be
attached to the exterior. Because of chromosomal aberrations, the genes
within the invohed chromosome can produce disturbed genetic phe-
nomena and ratios. In inversion a chromosome segment becomes in-
verted in position (changed end for end), and this may occur spon-
taneously and naturally or may be produced by various types of irradia-
tions. If a portion of one chromosome is transferred to another position
on the same chromosome or to another chromosome by a process that is
not normal crossing over (to be discussed later), this aberration is called
translocation. Commonly a segment of one chromosome may become
exchanged for a segment of a nonhomologous chromosome (not one of
the pair) .

When aberrations of entire chromosomes are considered, there may be
one or more entire chromosomes missins^ or one or more extra chromo-
somes present. In either case the genes involved may have effects of
greater or lesser importance, depending on the type of involvement.
These phenomena appear to originate from an irregular cell division so
that two homologous chromosomes (members of a pair) become included
in one daughter nucleus instead of one to each daughter nucleus. This
abnormal behavior in which homologous chromosomes fail to separate
normally is called nondisjunction. This phenomenon usually occurs at
meiosis (maturation of germ cells) but may occur during mitosis. Many
plants and some animals have been found which differ from the normal
diploid set of chromosomes, some having only one set (haploid), while
others possess three or more sets (polyploidy). All of these phenomena
may have a corresponding effect on the traits which may develop.

4. Genes and Genie Action. — Genes are thought to be minute, in-
visible, molecules of highly specific giant nucleoproteins with enzymatic
or catalytic properties capable of influencing structural, functional, and
developmental processes in cells and consequently in organisms which
are composed of these cells (Figs. 334 and 335).

They are thought to act as autocatalysts, because they generate or
increase their own substance prior to each mitosis (cell division). In
other words, each gene reproduces itself during mitosis, thus forming
two genes which are identical. One of each pair of genes is placed in
each new daughter cell. The characteristics of adult organisms are
inherited from their parents through the medium of one or more specific
genes for each trait in each of the gametes (sex cells). Each gene has

Heredity — Genetics 681

a definite location in a particular chromosome. The various genes are
arranged in a linear series within the chromosome. The position of a
gene in the chromosome bears no relation to the location of the result-
ing characteristic developed in the body of the organism. For example,
the genes for the determination of characteristics of the anterior end of
an organism are not necessarily all located at one end of a chromosome,
nor are all the genes for the traits of the posterior part of an organism
located in the opposite end of the chromosome. They are, however,
scattered promiscuously, yet specifically, throughout the chromosome.

Each zygote (fertilized egg) contains two genes for each hereditary
character, one coming from each parent. This does not mean that the
two are necessarily identical, although they may be. Thus, all body
cells arising by mitosis from this zygote have duplicate genes for each
specific hereditary character (Figs. 335, 350, and 351).

Genes recently have been photographed so that their form, at least,
has been somewhat demonstrated. The size of certain genes is thought
to approximate the size of a large organic molecule with a maximum
dimension of about 40,000 millimicrons.*

A great majority of genes are stable and usually very resistant to en-
vironmental influences. X-rays and similar radiations are known causes
of changes in genes. A few genes apparently are unstable, being changed
frequently under ordinary conditions.

Over 1,000 genes have been determined so far in the chromosomes of
the fruit fly {Drosophila melanogaster) (Fig, 332) and about 400 in
corn. Undoubtedly, the twenty-four pairs of human chromosomes con-
tain even greater numbers of genes. The total number of human heredi-
tary characters has never been stated or even approximated.

The cells of an organism before maturation of the germ cells retain
the duplicate set of chromosomes and genes. During maturation, those
chromosomes which carry equivalent genes (hence, homologous chromo-
somes) unite temporarily in pairs. Later, during reduction division, one
of each pair of chromosomes (and hence, one of each pair of genes) goes
to each of the two new daughter cells. Therefore, each resulting gamete
or sex cell has only a single set of chromosomes (and genes). Thus,
when two sex cells are united during fertilization, the resulting cell
(zygote) again has its duplicate supply, one of each pair having been
contributed by each parent.

Since chromosomes are usually found in pairs in typical organisms
(Figs. 332 and 333), genes must also be present in pairs. The pairs of

*1 milllcrom is one-thousandth part of a micron, and a micron is one-thousandth part of a
millimeter.

682 General and Applied Biology

chromosomes and genes are known as homologues or homologous chro-
mosomes. In each homologous chromosme there is a gene at a particu-
lar place or locus which affects a certain trait, although in some traits
several genes may be required. Two genes at the same locus on homolo-
gous chromosomes but producing somewhat different effects on the indi-
vidual are called alleles or allelomorphs (al-el') (Gr. allelon, one an-
other). For example, tall and dwarf traits in peas are due to alleles
located at the same locus in homolooous chromosomes. When one allele

(gene) expresses itself to the exclusion of its "partner" allele, the former
is called a dominant gene and the trait is known as a dominant trait.
The allele whose effect is not visibly expressed is called a recessive gene,
and the trait is known as a recessive trait. An organism having two
identical genes at one locus is homozygous for that gene or is said to
possess homozygous genes. When an organism possesses a dominant
allele (gene) and a recessive allele (gene) at the same time, it is hetero-
zygous for that gene or is said to possess heterozygous genes. For ex-
ample, TT and tt are homozygous, while Tt is heterozygous (T repre-
sents tall; t represents dwarf pea plants) .

It is known that genes in the nucleus of cells control cellular metabo-
lism, the synthesis of various biochemical compounds, and the inherit-
ance of certain traits. How do these genes act? How can the genes
(contributed by both parents) in the fertilized ^gg determine the various
structures and functions of the embryo and eventually the adult? As a
matter of fact, the nucleus with its genes and the surrounding cytoplasm
constitute a complex system or unit whose interactions are responsible
for the phenomena suggested. It is not well known how these reactions
function but it is theorized that the genes in the nucleus interact with
certain specific substances also in the nucleus to form the products of
genie action. The latter products may interact with other newly formed
products in a sort of chain reaction so that numerous products may be
formed in the nucleus. It is thought that eventually some of the origi-
nal gene products as well as some of the newly formed gene products
pass into the cytoplasm. In the latter, the various gene products may
react still further with each other or with certain products of the cyto-
plasm. It is probable that some of the cytoplasmic products may dif-
fuse back into the nucleus so that the entire process is one in which the
great numbers of genes interact in a great variety of ways to lay the
basis for cellular phenomena.

The fertilized egg by repeated mitoses develops into a multicellular
embryo whose cells quite early show slight inequalities, some being

Heredity — Genetics 683

slightly larger than the others. Internally the composition of the cyto-
plasm may differ in the two sides of the cells, and there may be more
yolk granules in one side (lower) than in the other (upper). Hence,
there are two types of cells (smaller, upper ones, and larger, lower ones)
with the cytoplasm differing between the two poles of the cells. This is
known as differentiation of the cytoplasmic contents of cells, and this
phenomenon may lead to additional differentiations within cells and
between certain adjacent cells. Hence, the identical genes in the nuclei
of the various cells are surrounded by different cytoplasms as well as
different gene-products and nongenic contents within the different nuclei.
The organization and differentiation of an embryo depend upon genie
actions in cells as well as the interactions between cells and between the
various regions of the embryo and its surroundings.

How does genie action produce the traits or characteristics displayed
by living organisms? A trait in a developing or fully developed organ-
ism may be any observable structure or function such as a biochemical
property, a structure or function of a cell, tissue, or organ, a mental
characteristic, etc. It is to be expected that no simple connection exists
between genes and most observable, developed traits, but usually there
may be several steps in sequence in the process. Most traits arise
through complex interactions of numerous genes as well as interactions
between genes and cytoplasmic influences, so that a single gene may
often influence the development of more than one trait. The statement
that a trait may depend on the interactions of several genes may seem
to contradict the statement that a certain gene is responsible for a trait.
A single gene, by being part of this network of developmental inter-
actions, then may be indirectly responsible for the eventual development
of a particular trait which is to say that a particular gene may not
directly develop that trait but does so in an indirect manner. In other
words, that particular trait might not have developed specifically as it
did if that "one" gene had not been associated in the complex network
of gene interactions. If "another" gene had been present instead of the
"one," the resulting interactions might have been quite different and
the trait developed might have also been quite different. The particular
way in which genie and nongenic actions take place in a network of
interactions might well be influenced by the presence of a single gene
of a specific type.

5. Mendel's Experiments and Laws. — Gregor Mendel, a monk in
Austria, in 1864 gave the first scientific interpretation of the heredity
mechanism through his experimental crossings of pea plants in the gar-

684 General and Applied Biology

den of his monastery. Mendel was not a professional geneticist but his
training in mathematics directed him to record accurately the exact
numbers of the thousands of individuals of the various types produced
by his experimental crosses. His scientific interpretations of his recorded
data led to his famous laws and ratios. His work laid the foundation
for scientific, experimental crossing in genetics. Although his laws do
not explain all types of inheritance, wherever his laws do apply they are
as valid today as at the time of their discovery. He was fortunate in
having selected organisms which possessed clear-cut, alternative traits,
each controlled by a single pair of genes; otherwise he might not have
made his discoveries. If he had not discovered these phenomena in
heredity, they would ultimately have been formulated in 1900 by three
other scientists: De Vries in Holland, Correns in Germany, and von
Tschermak in Austria. However, Mendel died before his great contri-
butions were accepted and understood. He had published his results,
so the credit belongs to him — not to the three workers just mentioned.
Their contribution, which is highly important in science, was that their
work substantiated Mendel's earlier but unaccepted work.

From the many traits of peas, Mendel selected the following seven
pairs of alternative ("diflferent") characteristics:

DOMINANT

RECESSIVE

Plant height

Tall

Dwarf

Form of ripe seeds

Round

Wrinkled

Color of stored endosperm

Yellow

Green

Color of seed coat

Gray-brown

White

Color of unripe pod

Green

Yellow

Form of ripe pod

Smooth

Constricted

Position of flowers

Axial

Terminal

By cross fertilization he experimentally crossed two pea plants, one of
which had one of the traits and the other plant the alternative trait.
The resulting hybrids, which resembled one or the other parent, were
then crossed with each other. In the hybrid, Mendel recognized the
trait which expressed itself as the dominant, while the one which was
latent and did not express itself he called the recessive. When he crossed
the hybrids, the dominant and recessive traits reappeared in a definite
ratio of approximately 3 dominants to 1 recessive. This ratio based on
outward appearance is called the phenotype ratio. The latter may be
resolved into a genotype ratio which is based on different genetic com-
positions of the various individuals (refer to later consideration in this
chapter) .

Heredity — Genetics 685

From a scientific interpretation of the data, Mendel formulated the
following principles known as Mendel's Laws or Mendelism.

(1) Law of Unit Characters: The inheritance of a pair of characters
occurs as a unit and independently of any other pairs of characters.

(2) Law of Segregation: Each pair of genes for a character segregate
(separate) during the formation and maturation (gametogenesis) of
gametes, so that no gamete has more than one gene from each pair.
Each pair of genes undergoes this assortment independently of every
other pair.

(3) Law of Dominance (Complete): When a gene and its alternative
gene are both present at the same time in an individual, the one which
expresses itself is called the dominant, while the one which is latent and
unexpressed is the recessive. An individual displaying a dominant char-
acter may do so because of the presence of two dominant genes (TT)
and be homozygous or because of the presence of one dominant and one
recessive gene (Tt) and be heterozygous. For a recessive character to be
expressed the genes must be homozygous (tt). In this type of inherit-
ance the dominant completely masks the recessive.

Common Illustrations of Dominance and Recessiveness

dominant

recessive

Cattle

Short legs

Long legs

Cattle

Hornlessness

Horns present

Guinea pigs

Short hair

Long hair

Guinea pigs

Rough (rosetted) coat

Smooth coat

Guinea pigs

Colored hair

White or albino hair

Horses

Gray hair

Other colors of hair

Horses

Trotting

Pacing

Rabbits

Short hair

Long hair

Rabbits

Black hair

White hair

Poultry

Extra toes

Normal number of toes

Poultry

Feathered shank

Bare shank

Poultry

Rose comb (as in Wyandottes)

Single comb (as in Leghorns)

Fruit fly

Red eyes

White eyes

Fruit fly

Ebony colored body

Gray colored body

Fruit fly

Long wing

Vestigial wing

Fruit fly

Straight hairs or spines

Forked hairs or spines

Peas

Tall plant

Short or dwarf plant

Peas

Smooth seed

Wrinkled seed

Peas

Green pod

Yellow pod

Peas

Colored flowers

White flowers

Peas

Flowers axial (arranged along

Flowers terminal (arranged in

axis or stem)

bunches at top of stem)

Peas

Yellow seed coat

Green seed coat

Barley

Beardlessness

Beardedness

Sunflower

Branched habit

Unbranched

Tomato

Tall vine

Dwarf or short vine

Summer squash

Disk-shaped squash

Sphereshaped squash

686 General and Applied Biology

6. Monohybrid, Dihybrid, and Trihybrid Crosses. — Monohybrid
crosses are those in which only one pair of differentiating characters
are considered, dihybrid are those in which two pairs are considered,
and trihybrid are those in which three pairs of different genes are in-
volved.

By using the guinea pig and the following characters with their sym-
bols, the different crosses suggested above may be illustrated.

B, black hair
b, white hair
R, rough hair
r, smooth hair
S, short hair
s, long hair

When the dominant (ex-
pressed by the capital
letter) is present, it
expresses itself, even
though the opposite or
recessive be present.

Monohybrid Cross (Guinea Pig)
Parents (P)
Gametes produced
Offspring (Fi)
Gametes for both sperms and eggs

Black (BB) X White (bb)

i i

B b

\ ^

Black (Bb)

B b

Sperm

Offspring (F2) shown by the

Punnet square or checkerboard

g
g
s

BB
Bb

Thus we have produced 1 BB (black) 2 Bb
(black) and 1 bb (white) or a ratio of
3 black to 1 white. This is a phenotype
ratio of 3:1 for a monohybrid cross.

BLACK-SMOOTH

BbRr

BLACK-ROUCH

WHITE-ROUGH

BLACK-ROUGH

o ay

BLACK-ROUGH BLACK-SMOOTH

WHITE-ROUGH

WHITE-SMOOTH

Fig. 336. — Dihybrid cross in guinea pigs when parents (P) are crossed. All

of the Fi generation are black-rough. When the latter are intercrossed, the F2

generation is produced as shown. The genes for the P and Fi generations are
shown.

Heredity — Genetics 687

DiHYBRiD Cross (Guinea Pig) (See Fig. 336)

Parents (P)

Gametes produced

Offspring (Fi)

Gametes in equal numbers in

both sperms and eggs
Offspring (F2) (shown by the

Punnet square)

Black-smooth (BBrr)

X White-rough (bbRR)

Black-rough (BbRr)

i i i i

BR Br bR br

Sperms

BR
BR

BR
Br

Br bR

Br
BR

Br
Br

Br
bR

bR
BR

br
BR

bR
Br

br
Br

bR
bR

br
bR

br
br

From the above squares there are the following:
9 black-rough
3 black-smooth
3 white-rough
1 white-smooth

This is the phenotypic ratio of 9-3-3-1 for a di-
hybrid cross in the F2 generation, when the
above parents are used.

Parents (P)

Gametes produced
Offspring (Fi)

Trihybrid Cross (Guinea Pig)

Black-short-smooth
(BBSSrr)

BSr

X White-long-rough
(bbssRR)

bsR

Gametes (equal numbers
of each kind in both
sperms and eggs)

Offspring (F2)

Black-short-rough

(BbSsRr)

BSR BSr BsR Bsr bSR bSr bsR bsr

By the Punnet square as in the monohybrid
and dihybrid crosses there will be:
27 black-short-rough
9 black-short-smooth
9 black-long-rough
9 white-short-rough
3 black-long-smooth
3 white-short-smooth
3 white-short-smooth
3 white-long-rough
1 white-long-smooth

Thus a typical F2 trihybrid, phenotype ratio is 27-9-9-9-3-3-3-1. By means of
the Punnet square or checkerboard, it is apparent that all of the 27 which ap-

688 General and Applied Biology

pear black-short-rough are not aHke as far as their gene content is concerned.
When we group together all those whose gene content is the same, we have the
so-called genotype ratio (based on the gene content).

A very useful method in determining the number and difTerent types of gametes
(sex cells) produced by a particular organism is known as the bracket method.
In the case of the trihybrid cross of guinea pigs considered above, the Fi off-
spring, which is black-short-rough and with genes (BbSsRr), the gametes may
be ascertained by the use of the bracket as shown in Fig. 337.

BbSsRr

(Parent genes)

hil"

— BSR
BSr

I P.— -BsR

Bsr

r R— .bSR

bSr

{I::

--bsR
bsr

Fig. 337. — The so-called bracket method of determining the number and types
of gametes (sex cells) produced by a parent containing the genes BbSsRr.

By using a plant, such as the pea, and the following characters with their sym-
bols, the different crosses (monohybrid, dihybrid, trihybrid) may be illustrated:

T, tall plant
t, dwarf plant
R, round seed
r, wrinkled seed
Y, yellow seed
y, green seed

When the dominant (ex-
pressed by the capital
letter) is present, it
expresses itself even
though the opposite or
recessive is present.

Monohybrid Cross (Pea)

Parents (P)

Gametes produced

Offspring (Fi)

Gametes for both male and female

Offspring (Fz) shown by the Punnet
square or checkerboard

Tall (TT) X Dwarf (tt)

I i

T t

\ ^

Tall (Tt)

T t

Male
gametes

Female

T
TT

J' T

Thus we have produced 1 TT (tall), 2 Tt (tall), and 1 tt (dwarf), or a ratio
of 3 tall to 1 dwarf. This is a phenotype ratio of 3:1 for a monohybrid cross.

Heredity — Genetics 689

PARENTS >

Round-yellow
(RRYY)

OFFSPRING (Fj)

Wrinkled- green
(rryy)

(F^)^

Q /
> S

M
W

Round-yellow
(RrYy)

Fig. 338. — Dihybrid cross of peas showing gene content of each individual. The
genes for the various members of each generation are shown. When two similai
Fi individuals are crossed, the results are shown in the checkerboard (F2).

690 General and Applied Biology

Parents (P)
Gametes produced

Offspring (Fi)

Gametes for both male and female

DiHYBRiD Cross (Pea) (See Fig. 338)

Round-yellow (RRYY) X Wrinkled-green (rryy)

RY ry

\ /

Round-yellow (RrYy)

^ i i ^

RY Ry rY ry

Offspring (Fz) when (Fi) are

intercrossed or self-pollinated
(shown by the Punnet square)

Male Gametes ^

Female

gametes

RY
RY

Ry
RY

rY
RY

ry
RY

RY
Ry

Ry
Rv

rY
Ry

. ry

RY
rY

rY
rY

ry
rY

ry
ry

From the above squares it is seen that the following offspring are secured;

9 round-yellow
3 round-green
3 wrinkled-yellow
1 wrinkled-green

This is the phenotype ratio
of 9-3-3-1 for a dihy-
brid cross in the F- gen-
eration.

Parents (P)

Gametes produced
Offspring (Fi)

Trihybrid Cross (Pea)

Tall-yellow-round X Dwarf-green-wrinkled
(TTYYRR) (ttyyrr)

i i

TYR tyr

\ >/

Tall-yellow-round

(TtYyRr)

Gametes for both male and female TYR TYr TyR Tyr tYR tYr tyR tyr

Offspring (Fo) by the Punnet square as in the monohybrid and dihybrid crosses,
there will be produced in the F2 generation the following:

27 tall-yellow-round

9 tall-green-round

9 tall-yellow-wrinkled

9 dwarf-yellow-round

3 tall-green-wrinkled

3 dwarf-green-round

3 dwarf-yellow-wrinkled

1 dwarf-green-wrinkled

This is a typical F2 trihy-
brid, phenotype ratio of
27-9-9-9-3-3-3-1 when
such individuals as Fi
are used as parents.

7. Incomplete Dominance. — From studies just made it was noted that
when opposite members of a pair of genes were present, one or the other

Heredity — Genetics 691

White 1 1 rr

\f RedwRR

Pink II Rr

Pink rl Rr

White

Fig. 339. — Incomplete dominance when a homozygous white-flowered four-
o'clock (Mirabilis jalapa) is crossed with a homozygous red-flowered four-o'clock.
The somatic condition is shown by the flower colors; the letters show the genes
involved. When two pinks of the Fi generation are crossed the results are shown
in the Fz.

Black

OO
White-Splashed

• o

Wbite-5pla5hed

Blue/\nda\(js'ian

Black

Fig. 340. — Incomplete dominance in blue Andalusian fowls. When a black
fowl is crossed with white-splashed-with-blue, all the Fi generation will be blue
Andalusian. When the latter are interbred, there are produced one-fourth white-
splashed-with-blue, one-half blue Andalusians, and one-fourth black in the F2 gen-
eration. When the white-splashed-with-blue of the Fs are interbred, only white-
splashed-with-blue are produced. When the blue Andalusians of the Fi are
crossed, they produce offspring like those resulting from the Fi. When the black
of the Fi are crossed with each other, only blacks are produced. The black dots
and circles show the factors involved in each individual.

692 General and Applied Biology

completely dominated. In so-called incomplete dominance the Fi does
not resemble either parent exactly for the trait in question, neither gene
of the pair completely dominating the other. An example is the four-
o'clock flower (Fig. 339) in which homozygous white is crossed with
homozygous red and the Fi is pink. The genetic content and ratios are
shown. Note that the phenotype ratio in the F2 is identical with the
genotype ratio. Incomplete dominance, with one pair of genes, is illus-
trated by the blue Andalusian fowl (Fig. 340). The Fi shows incom-
plete dominance by being neither black nor white but an intermediate
shade called ''blue," which is always heterozygous. When two blue fowls
are crossed, the offspring show a ratio of 1 white : 2 blue : 1 black. When
a blue and black are crossed, the ratio is 1 black: 1 blue; when a blue
and a white are crossed, the ratio is 1 white: 1 blue.

8. Multiple Genes and Interaction of Genes. — There are many traits
which are determined by more than one pair of genes and the specific
methods of inheritance vary, but the following may give a general idea
of some of these genetic phenomena. When a quantitative character
(one with various degrees of trait expression) is the result of several,
duplicate, cumulative genes, such genes are known as multiple genes
(multiple factors). The hair color in wild rabbits is the result of no
less than thirteen pairs of different genes located in various chromosomes.
Some of these genes are recessive, but a majority in this case are domi-
nants.

Another example of multiple genes (more than one pair for a trait) is
the production of skin color in which Negroes differ from whites in two
pairs of genes. These two pairs of genes interact cumulatively and show
incomplete dominance. Explanation: Negro, AABB; dark mulatto,
AABb or AaBB; medium mulatto, AaBb, AAbb, or aaBB; light mulatto,
Aabb or aaBb; white, aabb. Using these gene symbols, if a pure Negro
(AABB) and a pure white (aabb) are crossed, the Fi offspring are
medium mulatto (AaBb) . Another crossing may be shown as follows:

Parents Medium mulatto (male) X Medium mulatto (female)

(AAbb) (AaBb)

i ^ 4. i \

Gametes Ab AB Ab aB ab

Fi 1 dark mulatto (AABb), 2 medium mulattoes (AAbb) (AaBb),

1 light mulatto (Aabb).

When three pairs of cumulative genes interact and possess incomplete
dominance, there result various degrees of trait expression. For example.

Heredity — Genetics 693

Nilsson-Ehle found three pairs of genes in certain strains of red
wheat. Deepest red is represented by R1R1R2R2R3R3 and white wheat
by ririr2r2r3r3. The more genes represented by the capital letters in
any individual^ the darker the red. This may be shown by the following:

Parents Deepest red wheat X White wheat

(R1R1R2R2R3R3) N^ (ririr2r2r3r3)

Fi Medium red wheat

(RiriR2r2R3r3)

When two of the Fi are crossed, the F2 ratio is:

1 deepest red (6 red genes)

6 very deep red (5 red genes)
15 deep red (4 red genes)
20 medium red (3 red genes)
15 pale red (2 red genes)

6 very pale red (1 red gene)

1 white (no red genes)

When two dominant genes located in diflferent pairs of chromosomes
interact and supplement each other to produce an altogether new pheno-
type, such are called supplementary genes. In the combs of chickens,
pea-comb is represented by at least one P and rr, rose-comb by pp and
at least one R, single-comb by pprr, walnut-comb by at least one P and
at least one R. The following cross shows a homozygous rose-comb
crossed with a homozygous pea-comb with the genetic contents and
ratios :

Parents

Gametes
Fi

When two walnut-combed chickens of the Fi are crossed, the F2 shows:

9 walnut-combed (at least one P and at least one R)

3 pea-combed (at least one P and rr)

3 rose-combed (pp and at least one R)

1 single-combed (pprr)

This shows not only a new type in the Fi, but, when intercrossed, a still dif-
ferent type, namely, single-comb (pprr), is produced.

When two dominant genes located in different pairs of chromosomes
interact and complement each other (both present to produce a visible
effect), such are called complementary genes. When two pure strains
of white sweet peas are crossed, they produce only purple-flowered peas
in the Fi. Purple flowers are represented by at least one C and at least

Rose-comb X

Pea-comb

(pp RR)

(PP rr)

Walnut-comb

PpRr

694 General mid Applied Biology

one P. White flowers are represented by at least one C and pp, by cc
and at least one P, and by ccpp. This may be shown as follows:

Parents

White-flowered pea

(CCpp)

(ccPP)

Purple-flowered pea
(CcPp)

When the Fi are crossed, the F2 ratio is:

F2 9 purple (at least one C and at least one P)

3 white (at least one C and pp)
3 white (cc and at least one P)
1 white (cc and pp)

This phenotype ratio is 9 purple:? white.

9. Lethel Genes. — When lethal genes (le' thai) (L. letum, death) are
present they may kill the organism containing them or at least prevent
the individual from attaining normal maturity (Fig. 341), Lethal genes
are known in mice, fruit flies, human beings, in certain plants, etc. In

GAMETE

1
J

DIES

Fig. 341. — Inheritance of lethal, sex-linked factor in the fruit fly (Drosophila
sp.) and its effect on the sex ratio. /, The lethal factor; L, its normal, nonlethal
allele; P, parents (squares are males; circle are females); Fi, the first filial
generation in which one-half of the males fail to develop, giving the sex ratio
of two females to one male. Note that both parents (P) are normal but that the
female carries the lethal factor which she later contributes to one-half of her sons,
who consequently never develop.

Heredity — Genetics 695

];)lants, lethal genes may prevent the development of chlorophyll so the
young plant is unable to photosynthesize food. Lethal genes may arise
naturally, or they may be induced by irradiations by x-rays, radium, etc.
About 80 per cent of all mutations induced by radiations are lethals.
Possibly many of the lethal mutations may actually result from some type
of chromosomal aberration, although some are true gene mutations.
Some lethals have been discovered which are dominant, while others
behave as recessives.

10. Mutations. — A mutation (mu -ta' shun) (L. mutare, to change)
is an inheritable trait which appears suddenly not as a result of environ-
mental influences, but has originated spontaneously in the hereditary
mechanism; hence, it may be transmitted to future ofTspring. Morgan,
in 1910, discovered the sudden appearance of a white-eyed mutant in a
stock of true-breeding red-eyed fruit fly, Drosophila melanogaster. When
the white-eyed mutant was crossed with red-eyed flies, the white-eye trait
was inherited as a recessive gene in the X chromosome. Hundreds of
plants and animals have mutated with greater or lesser frequency. Muta-
tions may aff'ect any part of an animal or plant or any of their functions.
They may occur periodically and frequently and be unobserved in
Nature. The same mutation may arise simultaneously in diff^erent indi-
viduals. A mutation results in a new trait which is inheritable, and, if
sufficiently extensive, may result in a new type or even a new species of
that organism. Mutations may occur naturally, although some may be
induced by irradiations such as x-rays, radium, etc. About 80 per cent
of all induced mutations are lethal. In general, mutations are usually
changes for the worse, although a few may be valuable. Some of our
important plants and animals have arisen as mutants which possessed
desirable traits. In the broad sense, changes in traits are the result of
(1) actual, sudden change in a gene (gene mutation), (2) changes in
the number of chromosomes or from (:hromosomal aberrations (anomo-
zygous mutations), or (3) recombinations of previous genes in an en-
tirely new arrangement for that particular organism (recombination).
In a strict sense, the term mutation is reserved for those inheritable
traits which arise abruptly from changes in a gene. If an organism
mutates in a certain manner, it may now possess a trait which will
benefit it in the future, or it may mutate in such a way as to possess
undesirable traits which will interfere with its normal existence.

11. Linkage and Crossing Over. — Genes are considered to be asso-
ciated with each other in a linear order within chromosomes. All the
many genes in each chromosome tend to be inherited as a group and

696 General arid Applied Biology

C A

D D

C A

B D

Fig. 342. — Diagram showing the crossing ov^er of genes from one homologous
chromosome to the other during synapsis. Observe the exchange of the genes A-C
and B-D. Crossing over may occur at more than one point in much the same
raianner as shown. (From Potter: Textbook of Zoology, The C. V. Mosby Co.)

I(X)

KY)

-■XELLOW BODY
-WHITE EYE
-RUBY EYE

— rCOT WING
— TAN BODY

--DUSKY WINO
--SABLE BODY

SMALL WING

-CLEFT WINO
__ BOBBED HAIR
--MALE FERTILITY t

i ^LONG BRISTLES t

'^-- ROUGHOID EYE

--A-MALE FERTILITY T

/--STAR BYE
./-■-GULL WINO
"STREAK BODY

-/—JAMMED WING

-BLACK BODY
-PURPLE EYE

-V — VESTIGIAL WING
A — FRINGED WING

-LETHAL
--SPECK BODY

-DIVERGENT WING

-SEPIA EYE
/—HAIRY BODY

SCARLET EYE
-MAROON EYE

^\-i- SPINELESS HAIR

\- -EBONY BODY
A--WHITE OCELLI

-\ — ROUGH EYE
-CLARET EYE

BENT WING
7 EYELESS

:^-7 MINUTE HAIRS

Fig. 343. — Chromosome map of the fruit fiy (Drosophila sp.), showing the
locations (loci) of some of the genes in the autosomes (11, III, IV) and in the sex
chromosomes {I, X) and (/, Y). The name applied to the gene is given to the
right of its locus, and the distances between them are approximate.

Heredity — Genetics 697

are said to be linked. This linkage force keeps the genes in proper as-
sociation. It is known that during meiosis (reduction divisions during
gametogenesis) the homologous pairs of chromosomes separate as units,
one of each pair passing to each gamete. Linkage between genes is
usually not complete. During the process of synapsis (temporary fusion
of homologous chromosomes), associated with gametogenesis (discussed
later in this chapter), the homologous chromosomes often mutually ex-
change segments and their contained genes. This mutual exchange is

PARENTS

FEMALE

MALE

GAMETES

Fig. 344. — Inheritance of sex in the fruit fly (Drosophila sp.), shown somewhat
diagrammatically. Observe that in both male and female there are two pairs each
of chromosomes known as II, III, IV. In the female there is an additional pair
known as the X chromosomes. In the male there is an additional X chromosome
and a Y chromosome. When gametes are produced, there is a separation of the
members of each pair. When offspring are formed, the males have the three pairs
of chromosomes in addition to an X and a Y chromosome, while the females
have an additional pair of X chromosomes instead. Note the two kinds of male
gametes. (From Parker and Clarke: Introduction to Animal Biology, The C.
V. Mosby Co.)

698 General and Applied Biology

called crossing over (Fig. 342). The controlling mechanism is unknown,
but the greater the distance between the two loci and any two given
genes, the greater the chance that crossing over will take place between
them. Likewise, the smaller the distance between the loci of any two
genes, the less the chance that crossing over will occur. New combina-
tions of linked genes within the pair of chromosomes involved result
from the crossing-over process.

From data secured from crossing-over experiments it is possible to
locate approximately the genes (loci of genes) within the chromosome.
Such an approximate location of genes is called a chromosome map (Fig.
343 ) . The approximate locations of genes are determined experimen-
tally by recording the percentage of crossing over between them. Let us
take a theoretical example. If the experiments show that in a certain
chromosome crossing over between its genes A and B occurs 8 per cent
of the time, then these two genes are considered to be eight "units" of
distance apart in that chromosome. If crossing over between genes B
and C occurs 3 per cent of the time, they are three "units" apart. This
could be interpreted as meaning that the sequence is A: : : : : : :B: :C.
However, G might be between A and B. If the genes A and C cross
over 5 per cent of the time, then the sequence is A: : : :C: :B. In a simi-
lar manner other genes may be located within this chromosome.

Linkage and crossing over have been observed in many types of plants
and animals, including human beings.

12. Sex Determination and the Sex Ratio. — From scientific cytologic
studies of the fruit flv it has been found that each somatic cell contains
three pairs of chromosomes known as autosomes and one pair of sex
chromosomes (Fig. 344). The female has three pairs of autosomes and
a pair of sex chromosomes called X chromosomes, while the male has
three pairs of autosomes and one X chromosome and one Y chromosome.
When female gametes (sex cells) are produced, each contains three
autosomes and one X chromosome. When male gametes are produced,
one type contains three autosomes and one X chromosome, while the
other type contains three autosomes and one Y chromosome. Since the
two types of male gametes are produced in equal numbers and each type
is thought to have somewhat equal chances for fertilizing an egg, the
ratio of male and female offspring is approximately 50:50.

It is known that somatic cells of human beings contain twenty-three
pairs of autosomes and a pair of sex chromosomes as described for the
fruit fly. The distribution of sex chromosomes in man is similar to that
in the fruit fly.

Heredity — Genetics 699

The method of producing gametes and of fertihzation, as well as the
production of the sex of the offspring, is also similar. Sex is deter-
mined at the time of fertilization. If an egg is fertilized by an "X
sperm," the zygote will develop into a female, while an egg fertilized by
a "Y sperm" leads to an XY zygote which develops into a male. After
fertilization, mitosis provides every cell of the developing embryo and
the ultimate adult with the original chromosome constitution.

This explanation seems quite simple and sufficient, but it is only the
basis for solving the problem of sex determination and its attendant
phenomena. Many of these are too complicated to be considered in
detail here, but the following may suggest some of the complications.
A human XX zygote or XY zygote develops in a short time into an
embryo which is structurally neither male nor female, or rather is both
male and female, because the embryonic gonads consist of two parts — a
characteristic ovary-like portion, and a characteristic testis-like part.
Likewise, a pair of male and a pair of female internal sexual ducts are
present in each early, "neutral" embryo. Even the embryonic parts
which later develop into external genitalia of either sex are present.
After this neutral stage has been reached, the specific genetic sex consti-
tution of the embryo begins to differentiate visibly. In the embryo with
XX cells the neutral embryonic gonads develop into ovaries, while the
embryo with XY cells develops testes. Likewise, the proper types of
internal sexual ducts and external genitalia are developed if things de-
velop normally. It happens at times that parts of both male and female
reproductive systems are present in certain adults who are known as
hermaphrodites or intersexes.

In newborn children, sexual differentiation is not yet complete. Sec-
ondary sexual traits (differences apart from actual sex organs) develop
during puberty and include differences in larynx and voice, differences
in pelvic developments, breasts, hair growth, etc., which are influenced
by specific hormones produced by the male and female sex organs.

13. Sex-Linked Traits. — Besides assisting in the determination of the
sex, the sex chromosomes also possess genes for the determination of
other traits, which, because of the location of the genes in the sex chro-
mosome, are known as sex-linked traits. Two types of sex-linked inherit-
ance are possible, depending upon whether the sex-linked genes are in
the X chromosome or Y chromosome. Certain genes are known which
are always associated with the Y chromosome, while others are associated
with X chromosomes. Other genes have been found in males which
cross over from the X to the Y chromosome, or vice versa. Very few

700 General and Applied Biology

human traits show absolute Y Hnkage (do not appear in females and are
not transmitted to them). An example is the so-called "porcupine man"
trait (bristly, scaly skin) which appears in males only. Another possible
Y-linked inheritance is a special type of web toe (web skin between
second and third toes). It is known that a diflferent web toe condition
exists which is present in both males and females, with a preponderance

Fig. 345. — Sex-linked inheritance in the fruit fly (Drosophila sp.). The red-
eyed male (upper right) and the white-eyed female (upper left) are crossed to
produce the male and female of the Fi generation. The factor {W) for red eyes
is carried in the X chromosome of the male, while the curved male Y chromosome
does not carry an eye-color factor. The factor {w) for white eyes is carried in
the X chromosome of the female. When members of the Fi generation are crossed,
the four kinds of the Fo generation are produced (lower group). Note that a
male has a larger tip of black on his abdomen than the female. Contrast these
results with those in Fig. 346. (From Morgan: Evolution and Genetics, Prince-
ton University Press.)

Heredity — Genetics 701

in the former, however. Sex linkage has been observed in fishes, poultry,
silkworms, plants, fruit flies, man, etc.

In the fruit fly (Drosophilia) the gametes are heterozygous in the males
and homozygous in the females. White eyes are sex-linked characters
which are recessive to the normal red eyes.

Fig. 346. — Sex-linked inheritance in the fruit fly (Drosophila sp.J. The white-
eyed male (upper right) and the red-eyed female (upper left) are crossed to pro-
duce the male and female of the Fi generation. The factor (W) for red eyes is
carried in the X chromosomes of the female. The factor (w) for white eyes is
carried in the X chromosome of the male. The curved male Y chromosome does
not carry an eye-color factor. When the members of the Fi generation are crossed,
the members of the Fo generation are produced, as shown in the lower line. Note
that a male has a larger tip of black on his abdomen than the female. Contrast
these results with those in Fig. 345. (From Morgan: Evolution and Genetics,
Princeton University Press.)

702 General and Applied Biology

When a white-eyed female is crossed with a red-eye male, the Fi
males are white eyed and the females are red eyed. In the F2 generation
one-half of the individuals of each sex are white eyed and one-half are
red eyed (Fig. 345).

In the reciprocal cross in which a red-eyed female is crossed with a
white-eyed male, all the offspring (both male and female) of the Fi
generation are red eyed. All the females of the Fo generation are also
red eyed. One-half of the males of the F2 generation are red eyed, while
the other half are white eyed. (Fig. 346.)

Color blind

Normal

Color blind

Normal

Normal Color blind

<m>-i

r<^

2DC

<^<®><®><e> <^

9 9 c? d" 9

XX x^ xy 2sy X2?

Fig. 347. — Inheritance of color blindness in man. On the left a color-blind
man marries a normal woman. None of the children are color blind, but the
defect is transmitted through the daughters to half of their sons. Color-blind per-
sons and the chromosomes carrying the gene for color blindness are shown in white.
On the right a normal man marries a color-blind woman, and all the sons are
color blind, while the daughters are normal but carry a color-blind gene. In the
second generation (on the right) from the type of mating shown in the diagram,
half of the daughters and half of the sons will be color blind. Contrast the
results of the two pedigrees and observe the effects of a sex-linked trait. (From
Turner: Personal and Community Health, The C. V. Mosby Co.)

Human color blindness, or the inability to distinguish red from green,
is usually transmitted from a color-blind mother to all of her sons but
to none of her daus^hters. From a color-blind father it is transmitted
through his daughters (who are normal as far as color blindness is con-
cerned) to one-half of his grandsons (Fig. 347). When both parents
are color blind, all the offspring are color blind. Another human sex-
linked trait is hemophilia, a condition characterized by inability to form
blood clots.

Heredity — Genetics 703

14. Sex-Influenced Traits. — Sex-influenced traits are sometimes cafled
sex-modified or sex-controUed traits. Such traits are inherited by genes
which are not present in the sex chromosomes (they are autosomal genes)
but which are influenced or modified by the sex of the organism. These
influences are due in part, at least, to the sex hormones of the male and
female gonads and are responsible for differences in the expression of the
traits in the two sexes, even though the genes may be the same in both.

Pattern baldness in human beings is sex influenced, being affected by
the sex hormones. There are more bald males than females because only
one gene for baldness is required in men, while two genes are required in
women. For example, BB causes baldness in both men and women; bb
causes no pattern baldness in either sex; however, Bb causes baldness in
men but not in women. The same genes (Bb) produce different effects
in the two sexes, depending upon the influence of the sex hormones.

The horns of certain types of sheep are phenotypically different in males
than in females. The genes HH produce horns regardless of sex; hh is
hornless in either sex; however, Hh produces horns in males, but the
same genes produce a hornless female. Hence, Hh expresses itself dif-
ferently in the two sexes, so is sex influenced. A similar condition exists
in the production of mahogany spots and red spots in Ayrshire cattle.

15. Inbreeding and Outbreeding. — When closely related individuals are
crossed, we call it inbreeding, and when unrelated strains or individuals
are crossed, it is known as outbreeding. There seems to be much misin-
formation regarding these phenomena. It is commonly thought that
inbreeding is harmful and leads to the production of undesirable ab-
normalities of various kinds. Inbreeding in itself may not be harmful,
but it depends on what is inbred. If the parents have undesirable traits,
inbreeding naturally will transmit them, and the chances that both par-
ents may possess undesirable traits is greater because of their close heredi-
tary relationship. Crossing less closely^ related individuals might prevent
the expression of some of the undesirable traits.

On the other hand, commercial breeders use inbreeding constantly to
improve and retain their strains of horses, cattle, dogs, chickens, wheat,
fruits, etc., in which cases they capitalize on the good traits possessed by
both parents even though they may be closely related. In fact, closely
related individuals may be desirable parents providing they possess de-
sirable traits (genes). If any stock of plant or animal has undesirable
recessive traits, inbreeding may cause some of them to appear, while any
stock of plant or animal having desirable traits will transmit them, or
may even result in improvements. Many plants (beans, peas, wheat,

704 General and Applied Biology

FIRST YEAR

OETASSELEO

INBRED PLANT ^ INBRED PLANT

A B
S/^ ■

■, INBRED PLANT " ^ INBRED PLANT
C D

SECOND YEAR

"\^

Fig. 348. — Diagram of the method of crossing inbred corn plants and the
resulting single-cross to produce double-cross hybrid seed. The four plants, A, B,
C, D, are inbred for several generations. Then strain A is crossed with strain B
{A furnishes pollen and B is detasseled). Strains C and D are crossed similarly.
Then the product of these two single-cross lines are crossed to produce the double-
cross seed used in commercial plantings. (From Richey, F. D.: The What and
How of Hybrid Corn, Farmers' Bulletin No. 1744, U. S. Department of Agri-
culture.)

Heredity — Genetics 705

oats, etc.) and some animals normally reproduce entirely or largely by
self-fertilization, which is a type of inbreeding. On the other hand, such
a plant as corn is normally cross fertilized. When a vigorous, desirable
strain of corn is repeatedly inbred by self-fertilization, the quality, yield,
and vigor decline for several generations. It is commonly known that
inbreeding in certain human families results in highly undesirable con-
sequences. If a huyian family has recessive genes for undesirable traits
and if they are not expressed normally because of dominant genes, then
inbreeding of closely related persons will tend to produce offspring who
are homozygous for the undesirable recessive defects. Inbreeding in such
a family is undesirable.

Outbreeding frequently results in offspring which are better than either
parent, a phenomenon known as hybrid vigor or heterosis. This vigor
may manifest itself in various ways in different animals and plants. In
corn increased vigor may result in larger ears, greater number of grains
per row, greater height of the plant, etc. Much of the corn grown in
the United States is a special hybrid developed by crossing four different
inbred strains of corn (Fig. 348). This will be considered in greater
detail in a later part of this chapter. Hybrid vigor is a common
phenomenon in many types of plants and animals. When a horse and
donkey are crossed, the resulting hybrid mule is strong, sturdy, and more
vigorous than either parent.

16. Genetic Improvements of Plants and Animals. — Many plants and
animals have been produced as a result of some type or other of genetic
improvement. Man has merely taken advantage of the natural genetic
phenomena possessed by these organisms and has somewhat controlled
and directed them so as to result in a better type. The number of geneti-
cally improved organisms is so extensive and the methods employed so
varied that only a few examples can be given. Probably one of the more
valuable and recent contributions is the production of hybrid corn; the
method employed is given briefly.

Corn is normally cross-pollinated. When self-pollinated (selfed) for
at least seven successive generations, the corn plants become progressively
less productive and smaller. Eventually when two such self-pollinated
corn plants are crossed, the resulting hybrid is more productive and
larger than the ancestors. The procedure, in brief, is as follows: (a)
Inbreeding (self-pollination) for at least seven successive generations in
order to produce homozygous strains; (b) Two such homozygous strains
which possess traits desired in commercial strains are then cross pol-
linated to produce the Fi hybrids known as single-cross hybrids. How-

706 General and Applied Biology

ever, such seeds are usually not sold because the yield is usually low and
grains are of variable size; (c) Two single-cross hybrids, produced from
different homozygous strains, are now crossed, producing double-cross
hybrids, which produce higher yields of uniformly large seeds (Fig.
348).

Original Corn Plant Original Corn Plant Original Corn Plant Original Corn Plant

Self-pollinated Self-pollinated Self-pollinated , Self-pollinated

(inbred) for seven (inbred) for seven (inbred) for seven (inbred) for seven

generations generations generations generations

Inbred Strain
A

Inbred Strain
B

Inbred Strain
C

Inbred Strain
D

(Furnishes Pollen) (Detasseled)

\ /

Single-Cross Hybrid

(AXB)

(Detasseled) (Furnishes pollen)

Single-Cross Hybrid

(CXD)

(Detasseled)

Double-Cross Hybrid

(AXB) (CXD)

(Furnishes pollen)

Seed for Commercial Planting (Fig. 348)

Other genetic improvements in plants include fiber length in cotton,
sugar content of melons, yellow color of peaches, resistance to diseases
in plants (wheat rust, corn blight, oats smut, tomato wilt, etc.), resist-
ance of plants to pests (melon aphids, wheat Hessian fly, grape phyl-
loxera, etc.), seedless grapes, improved tobacco plants, etc.

The genetic improvements in animals are extensive as shown by the
dev^elopment of poultry resistant to white diarrhea {Salmonella pul-
lorum) , resistance to abortion in rabbits, increased egg production by
developing earlier maturity in fowls, the production of platinum (silver-
blu) minks, hornless (polled) cattle, increased butterfat in milk, im-
proved qualities in race horses, better meat qualities in turkeys, improve-
ments in various breeds of dogs and cats, etc. (Fig. 349).

17. Production and Maturation of Germ Cells. — Since a great amount
of the process of germ cell production, maturation, and fertilization deals
with the various phases of inheritance, it is discussed in this chapter.

Weismanns theory of the continuity of germ plasm, states that the germ
plasm is transmitted from one generation to the next, or even many fu-
ture generations, in a continuous and uninterrupted manner. The body
cells (somatoplasm) arise from the germ plasm at the proper time and
become specialized for their various bodily functions. Body cells thus
can arise from germ plasm, but germ cells or germ plasm cannot arise

Fig. 349. — Inheritance in collie dogs. A, Normal tan and black collie with
genes (vv) ; B, blue merle collie with genes (Vv) ; C, merle collie with defective
hearing and eyesight and genes (VV). The homozygous (VV) merle spotted
collies have defective sight and hearing, while in the heterozygous (Vv) condition
some ill eflfects are shown. The latter usually have such pale blue eyes as to be
wall-eyed, with a coat of intermediate blue merle. (After Mitchell. Reprinted
from United States Department of Agriculture Yearbook, Heredity in the Dog.)

708 General and Applied Biology

from body cells or somatoplasm. The continuity of type is thus main-
tained through a continuous lineage of germ plasm and germ cells from
generation to generation (Fig. 350).

From the above statements, it is apparent that the germ plasm pre-
sents an unbroken descent from generation to generation. The history
of this important process is known as the germ plasm cycle and may be
divided into the following arbitrarily chosen periods or stages:

(a) The definite differentiation and segregation in the embryo of
one or more primordial germ cells, which are the first cells set aside for
the development of future sex cells (Fig. 351 ) .

'• I #-2. 3. -i

s • • '■

7.---## ##

mi^. u fim

fo/oloio mm %4 Ao/oip^

/ V

II.

/3. /2 ^^

.f ft ft 9;

If.

Fig. 350. — Continuity of germ plasm and the origin of somatoplasm. The germ
plasm is represented by black and the somatoplasm by white. 1, Sperm from
mother's father; 2, egg from mother's mother; 3, sperm from father's father; 4,
egg from father's mother; 5, zygote (fertilized egg) from which mother developed;
6, zygote (fertilized egg) from which father developed; 7, two cells arising from
the zygote by cell division; 8, numerous cell divisions of body cells (somatoplasm),
which have arisen from the germ plasm originally; 9, numerous cell divisions of
the germ cells (germ plasm) which have arisen from previous germ plasm; 10,
egg produced by the mother; //, sperm produced by the father; 12, zygote (fer-
tilized egg) of the offspring from which two cells develop by cell division; 13,
germ cells (germ plasm) arising originally from the germ plasm of the zygote;
14-, body cells (somatoplasm) arising originally from the germ plasm of the zygote.

Heredity — -Genetics 709

(b) A period of multiplication of the primordial germ cells^ during
which they increase in number.

(c) A period of rest, with no division or mitosis of the primordial germ
cells, but a gathering into one or two groups to form the primordia or
forerunners of the gonads (testes or ovaries) .

(d) A second period of mitosis or multiplication which results in the
formation of large numbers of spermatogonia (in male animals) and
oogonia (in females). The stages in the embryologic development of
man and the frog are given in an earlier chapter.

(e) Certain spermatogonia differentiate into nutritive or Sertoli cells,
while other spermatogonia remain undifferentiated; in the female certain
oogonia remain undifferentiated or germinal, while other oogonia dif-
ferentiate into nurse cells.

(f) Then follows a period of growth without mitosis in which the
spermatogonia and oogonia grow to form, respectively, the primary
spermatocytes and primary oocytes. In this stage the homologous
chromosomes unite (appose) during the process of synapsis (union of
homologous chromosomes), and crossing-over of chromatin materials (in-
cluding genes) may take place.

(g) Next, there is a period of maturation in which the number of
chromosomes is reduced to one-half the number ordinarily found in body
cells or the soma cells of that particular species. . Cells with a reduced
number of chromosomes are now called secondary spermatocytes and sec-
ondary oocytes. In the formation of the secondary oocyte there is an un-
equal division of the cell, producing one normal cell and a smaller, abor-
tive, nonfunctional cell called the polocyte or polar body. Such a special-
ized type of two consecutive mitoses is called meiosis (reduction division)
in which the sperm, or ovum, receives only a haploid (monoploid or
simplex) number of chromosomes instead of the diploid (double) number
usually present in cells.

(h) In the next stage the secondary spermatocytes produce a num-
ber of spermatids, which are the forerunners of the future male sex cells
or sperm. The secondary oocyte again divides by unequal division in this
stage, producing a normal cell and a small polocyte. The polocyte of
the previous stage has divided equally into two abortive, nonfunctional
polocytes. We thus have three polocytes and one normal, functional egg
arising from each of the original primary oocytes.

(i) In the next step there is a transformation of spermatids into male

sperm.

{']) The eog or ovum produced by the secondary oocyte can now be
fertilized by the sperm. In this process the hereditary factors or genes

710 General and Applied Biology

/ \

rema/c

/ \

y \.

Fig. 351. — For legend, see opposite page.

Heredity — Genetics 711

carried in the chromosomes of the sperm are united or fused with the
genes carried by the egg. In fact, fertilization is this fusion to a very
great extent. It will be noted that each sex cell (sperm and egg) has
contributed equal numbers of chromosomes to the resulting fertilized
cell, known as the zygote. Thus each parent has an equal opportunity
of contributing characteristics to the offspring, although this does not
mean that each parent does contribute equally, merely the opportunity
to do so. The number of chromosomes in the zygote is again normal.

(k) The zygote or the first cell of the new individual is really old mate-
rial, but it is starting out on its journey primarily as an individual.

The zygote divides by mitosis, giving equal halves of each chromosome
(also gene) to the two resulting cells. Hence, the inheritance of each
of these two cells is the same as that of the previous cell, or zygote.

Mitosis of these two cells, as well as future cells, continues until there
is a rather solid mass of similar cells (similar as far a hereditary factors).
Such a mass of cells is known as the morula stage.

(1) The cells of the morula, after a certain length of time, arrange
themselves in the form of a hollow sphere which is known as the hlastula
stage. The cells of this stage continue to divide by mitosis, thus increas-
ing the size of the hollow structure. Naturally, this process cannot con-
tinue indefinitely, or we will have an animal which will be an enormous
hollow ball, the wall of which will be only one cell in thickness.

(m) By a more rapid rate of cell division or mitosis at a certain point
in the blastula, there is eventually an accumulation of cells at that point.
These numerous cells usually push inwardly or invaginate, thus forming
a structure which resembles a hollow ball, one side of which has been
partly pushed in. Such an invaginated stage is known as the gastrula
stage.

Fig. 351. — Germ plasm cycle. (The normal number of chromosomes in the
body or somatic cells is considered to be four, or two pairs.) A, Primordial germ
cells of both male and female ; B, spermatogonia of male and oogonia of female ;
C, primary spermatocyte; D, primary oocyte; E, secondary spermatocyte; F, sec-
ondary oocyte; G, polar body or polocyte; H, spermatid; I, egg or ovum; /,
sperm; K, entrance of the sperm into the egg during the fertilization process; L,
zygote or first cell of the new individual in which the nuclear walls of both sperm
and ovum disappear, and their contents tend to fuse; note the flagellum of the
sperm left just outside the ovum wall; M-R, various stages in mitosis in which two
cells are eventually formed, each with equal chromosomes; S, four-cell stage; T,
morula or many-cell stage; U, blastula, or hollow-sphere stage ( half -section ) ; F,
early gastrula stage (half-section view) ; W, later gastrula stage in which the
three primary germ layers, the ectoderm, mesoderm, and entoderm, are shown;
the mesoderm gives rise to primordial germ cells of the next generation.

712 General and Applied Biology

The outer layer of cells of the gastrula is known as the ectoderm layer;
the inner layer, the entoderm layer; and a middle layer, formed by both
of the other layers, the mesoderm layer.

All these cells have received a portion of the original inherited mate-
rials which they will continue to pass on to future cells as they are formed.
Thus, we see how an organism retains what it inherited at fertilization.

Various types of tissues arise from the three layers described above.
Naturally, at some stage there will be set aside the first cell, or primordial
germ cell, which will later develop into sex organs which in turn will
produce sex cells. Thus, the cycle is completed. The reproductive or-
gans arise from the mesoderm layer.

This cycle shows the continuity of life and the immortality of the germ
plasm. The somatoplasm or body plasm which develops from the germ
plasm is temporary and is mortal or dies.

18. Inheritance or Noninheritance of Acquired Characters. — Acquired
characters are those responses or structural modifications acquired by an
organism in its attempt to adjust itself to the various factors of the en-
vironment which surround it. Because most of the acquired characters
affect only the body plasm (somatoplasm), it is considered that they are
usually not inheritable, although some experimental evidence seems to
point to the opposite view, at least in a few instances. Probably the cor-
rect conclusion is that most acquired characters are not inherited while
a few may be. This does not mean that environment has no effect, be-
cause it is known that the development of even inherited characters of
any individual organism depends upon the proper environment in which
the inherited genes may develop properly. In other words, both nature
and nurture are necessary for development.

19. Human Inheritance. —

Why Study Human Inheritance? A study of human heredity gives
us an insight into the question of how and why we, as individuals, have
come to be what we are and how and why we act as we do, through the
interaction of various external and internal environmental factors and
our inherited materials. We also may observe that human inheritance
follows the same laws of heredity that pertain to other organisms. We
may become familiar with the methods of race improvement; with the
main applications of heredity and environment in our dealings with
various sociologic, educational, and legal problems of our daily life.
Through a knowledge of human heredity, we may have a more sympa-

Heredity — Genetics 713

thetic understanding of human behavior, inheritances of diseases, and
temperaments. Human inheritance is also considered in the chapter,
Biology of Man.

Methods of Studying Human Inheritance: The following methods
may be more or less successfully used in our study of human inheritance:
(1) A study of genealogic records collected by families, public institu-
tions, or scientific observers. (2) Selective mating which corresponds to
experimental crossing in lower organisms. Certainly many defectives
should never be permitted to pass these defects to their offspring. The
latter will be personally handicapped and will in turn transmit them to
their offspring. This is costly for human society at large. Undoubtedly,
a wise selection of a prospective husband or wife can never be regretted
from the standpoint of heredity. It is from studies of selected marriages
that much of our information of human heredity has been secured. (3)
Cytogenetic methods, in which a study of the cellular construction of
the heredity mechanism of human beings is made, which should prove
profitable. However, many obstacles prevent as much progress in this
direction as might be desired.

Difficulties Encountered In Studying Human Heredity: The study of
human heredity is quite difficult and complicated. This is true because:
( 1 ) The length of human life, especially the time required for individuals
to reach maturity, is quite long, so that a single observer, at best, can
see or study only three or four generations during his lifetime. This is
a handicap because one of the necessities for the successful study of any
heredity problem is the availability of a large number of successive gen-
erations. (2) Some individuals are reluctant to be studied. Frequently
inaccuracies are recorded by observers because the persons who volunteer
the information either willfully or unknowingly give the wrong informa-
tion or impressions. (3) There is a lack of scientific and accurate rec-
ords of human characters, if any record has been kept at all. Often,
only the defects or particularly outstanding characters are Hsted or
recorded. Certain individuals will give inaccurate information to "cover
something up," or will give a type of information which will tend to
make their family appear much better than it really is. Unless the ob-
server can collect all his data personally, this is a severe handicap. (4)
Many phases of human heredity are much more complicated than they
are in lower organisms. With our present limited knowledge of heredity
in general, we are unable to make great progress in the field of compli-
cated human heredity. (5) The lack of definite description and defini-
tion of human traits, such as mentahty, insanity, musical abilities, genius,

714 General and Applied Biology

Inheritance of Human Traits

dominant

RECESSIVE

Hair

Dark

Blond

Nonred

Red

Curly (incomplete dominance)

Straight

Abundant body hair

Little body hair

Baldness (Sex influenced)

Normal

White forelock

Normal

"Dog-faced" (excess embryonic hair

Normal

remains)

Skin and Teeth

Piebald (spotted pigmentation of
skin and hair)

Normal

Pigmented skin, hair, and eyes

Albinism

Black (multiple factors; incomplete

White skin »

dominance)

Dry scaly skin (ichthyosis)

Normal

Freckles

Normal

Absence of tooth enamel

Normal

Absence of sweat glands

Eyes

Brown

Gray or blue

Hazel or green

Gray or blue

Pigmented eye color

Albino (nonpigmented)

Cataract (congenital)

Normal

Glaucoma

Normal

Astigmatism

Normal

Far sightedness

Normal

Near sightedness

Normal

Color blindness (sex-linked)

Normal

Night blindness (congenital, defec-

Normal

•

tive twilight vision)

Large eyes

Small eyes

Long eyelashes

Short eyelashes

Ears and Nose

Free ear lobe

Attached

Broad nostrils

Narrow nostrils

High narrow bridge

Low broad bridge

Curved nose ("Roman")

Straight nose

General

Short stature (multiple factors)

Tall

Midget

Normal

Dwarfism (short limbs)

Normal

Polydactyly (more than five digits on

Normal

hands and feet)

Brachydactyly (short digits)

Normal

Syndactyly (skin [web] between toes

Normal

or fingers)

"Lobster claw" (split hand or foot)

Normal

High blood pressure (certain types)

Normal

Anemia (certain inheritable types)

Normal

Hemophilia (sex linked)

Blood groups A, B (multiple factors)

Blood group O

Blood groups (Rh factor) (multiple

Normal

factors)

Resistance to tuberculosis

Susceptibility

Allergies (tendency)

Normal

Diabetes mellitus

Normal

Heredity — Genetics 715

Inheritance of Human Traits — Cont'd

Nervous System

Normal

Schizophrenia (dementia
praecox) (multiple
genes)

Normal

Juvenile idiocy (amau-
rotic) (nervous system
degeneration)

Maniac-depressive insanity (multiple

Normal

genes)

Normal

Microcephaly (small-
headed idiot)

Paralysis agitans (involuntary move-

Normal

ment of hands, etc.)

Huntington's chorea (involuntary

Normal

twitching of head, arms, legs, etc.)

Normal

Epilepsy (inheritable
types) (multiple
genes)

Normal

Deaf-mutism

Sick headache (migraine)

Normal

health, etc., has prevented our study of them in heredity. In other
words, definite unit characters must be w^orked out so that we know^
their limits, variations, normalities, and abnormalities.

Human Pedigrees or Family Trees: Much of our information regard-
ing human inheritance has been secured by the accurate collection of
data and their proper evaluation and interpretation. A most desirable
method of recording such data is in the form of a family tree or pedigree,
several of which are shown in Figs. 352 to 356. In order for such a study
to be of value, there must be a rather large number of individuals in the
families, and there must be several generations. Every member of each
family must be recorded accurately and none can be omitted, because
if one is omitted it may be just the one who would throw most light upon
the inheritance of that particular trait. The investigator must not guess
in any case, since the guess may be wrong and consequently the final
result inaccurate.

20. Eugenics and the Future. — Eugenics (u-jen'iks) (Gr. eu well;
genos, birth) attempts to impro\e the human race through scientific
genetic measures. Race improvement may be brought about by attempt-
ing to prevent the hereditary transmission of undesirable traits or causing
the transmission of desirable traits from generation to generation. Im-
provement of certain environmental conditions whereby that which is
inherited may develop to the maximum of its inherent abilities may also
prove beneficial, although this does not alter the genie composition of
the individuals involved. No matter what the approach may be, there

716 General and Applied Biology

is no substitute for good inheritance. The two parts to the solution of
the problem of racial improvement are ( 1 ) the best possible inheritance
(2) and the best possible environment in which specific inheritances can
develop to their maximum.

The problems of preventing racial degeneration, let alone the question
of racial improvements, are more numerous and extensive than can be
treated here. With differences in birth rates between those with un-
desirable qualities and those classified as desirable, it becomes a major
problem if we are even to maintain our present level of racial develop-
ment.

III

€

•

1. *

Fig. 352. — Pedigree of webbed toes (zygodactyly). Black symbols indicate
persons possessing the trait. Squares represent males; circles, females. /, II, III,
IV represent four generations. Note that Individual Ilh was married twice.

Hj#

3 ^-^y

€MJ^.

Fig. 353. — Pedigree of diabetes. Black symbols indicate persons having the trait.
Squares represent male; circles, female. I, II, III represent three generations.

Some of the methods of eugenics which might be employed profitably
are as follows: (1) An attempt to increase the number of offspring of
parents who possess higher types of mental and physical traits. (2) The
prevention of those with certain types of undesirable traits from propa-
gating their kind by the rather simple process of sterilization. This is
practiced to a greater or lesser extent in about thirty states and in many
countries. An alternative to sterilization is complete segregation during

Heredity — Genetics 111

III

Fig. 354. — Pedigree of deafness (otosclerosis). Black symbols indicate persons
having the trait. Squares represent males; circles, females. I, II, III, IV repre-
sent four generations.

\\\

♦■■Qfl

UtKJ,

,i,6.6t a

Fig. 355. — Pedigree of insanity (an inheritable type). Black symbols indicate
persons having the trait. Squares represent males; circles, females. /, //, ///,
IV represent four generations.

IV
V

[^'S6

Fig. 356. — Pedigree of twinning. One or both twins died at birth in each case.
Squares represent males; circles, females. /, //, ///, IV, V, represent five genera-
tions. D represents death in infancy.

718 General and Applied Biology

the period of procreation. Surveys show that sterilization is satisfactory
to those sterilized and to society in general, and the cost is much less
than the more expensive care and treatment of great numbers, either in
or outside of institutions. (3) By methods of birth control, or the spac-
ing of the birth of children and the regulation of their number com-
mensurate with the abilities of the parents to care and train them prop-
erly. (4) By methods of contraception whereby fertilization may be
prevented, although this method will probably be of least benefit to those
groups who need it most — morons, imbeciles, idiots, etc. About 5 per
cent of the people of the United States have an inteUigence quotient
(I.Q.) of 70 or less. It is up to the people of our country to decide what
action is to be taken, but whatever action is taken should be in the light
of scientific knowledge so that the results will be what are expected
and desirable.

QUESTIONS AND TOPICS

1. Define genetics in your own words.

2. Discuss each of the methods used in the study of genetics. For what particu-
lar type of investigation is each method fitted?

3. Which method is best fitted for the study of human genetics? Discuss the
reasons why certain methods cannot be used practically in human genetics.

4. Discuss reasons why the study of human genetics apparently has not reached
the high level that has been attained in genetic studies of plants and lower
animals.

5. What is the relationship between the study of genetics and a study of varia-
tions? What is the relationship between genetics and the general principles
of evolution? How can genetics assist in solving problems in these two fields?

6. In what ways can hybridization of animals and plants be of practical value?
List several specific examples to prove your points.

7. Discuss the properties of genes and genie action.

8. Discuss multiple genes and the interaction of genes, describing each type and
giving an example of each.

9. Describe chromosomes, giving their outstanding characters. Do closely related
animals or plants necessarily have identical or similar numbers of chromosomes?
Give examples to prove your point.

10. Giv^e all the evidence you can for believing that inheritance of detailed struc-
tures is due to chromatin rather than to other parts of the cell.

11. State and illustrate the laws of Mendelism.

12. Define (1) hybrid, (2) heterozygous, (3) homozygous, (4) dominant, (5)
recessive, (6) phenotypc ratio, (7) genotype ratio, (8) allele.

13. Explain what is meant by a monohybrid cross; by a dihybrid; by a trihybrid.

14. What is the value of the Punnet square or checkerboard in determining
heredity?

Heredity — Genetics 7l9

15. Why do parents have duplicate genes for each specific character? From what
source has each been received ? Why, in the production of sex cells or gametes
by parents, is it necessary to separate or segregate the allelomorphic genes?
What happens when they are not segregated?

16. List reasons why it is desirable for each parent to contribute a gene for each
character.

17. Do parents contribute equally to their offspring or do they merely have equal
opportunity to contribute? Explain your statement.

18. Explain the difference between incomplete dominance and complete domi-
nance.

19. Explain the phenomena of linkage and crossing-over. What are the results
which follow each of these phenomena?

20. Contrast sex-linked and sex-influenced characters. Give several illustrations
of each.

21. Discuss and give examples of the different types of chromosomal aberrations.

22. What are the chief causes of mutations? What are their chief characteristics?
What benefits might be derived from mutations ?

23. Explain how sex is determined. What has this to do with heredity?

24. Explain Weismann's theory of the continuity of germ plasm. Of what impor-
tance is this in heredity? Explain the origin of somatoplasm.

25. Explain all the more important stages in the production and maturation of
germ cells. How does this affect heredity? Define meiosis and contrast with
normal mitosis. Of what importance is synapsis in genetics ?

26. List several human traits, telling which is dominant and which is recessive.

27. Problems in heredity:

Work the following problems in guinea pig inheritance using the following
symbols: B, black hair; b, white hair; R, rough coat of hair; r, smooth coat of
hair; S, short hair; s, long hair.

(a) Work out the entire monohybrid cross in the following by using the proper
symbols. Carry through to the F2 generation in each case: (1) Homozygous
rough X homozygous rough; (2) homozygous rough X smooth; (3) hetero-
zygous rough X heterozygous rough; (4) heterozygous rough X smooth.

(b) Work out the entire dihybrid cross through the F2 generation using the cor-
rect symbols in the following : ( 1 ) Homozygous black-rough X homozygous
black-rough; (2) homozygous black-rough X white-smooth; (3) heterozygous
black-rough X heterozygous black-rough; (4) white-smooth X white-smooth.

(c) Work out the entire trihybrid cross through the F2 generation using the correct
symbols in: (1) BbRrSs X BbRrSs; (2) BBRRSS X bbrrss; (3) BbRRSs X
bbRrSs; (4) bbrrSs X bbRrss; (5) bbrrss X bbrrss.

Work out the following problems in the inheritance in peas, using the following
symbols: T, tall plant, t, dwarf plant; Y, yellow seed; y, green seed; R, round,
smooth seed; r, wrinkled seed.

(a) Work the following monohybrid crosses as above: (1) Homozygous tall X
dwarf; (2) heterozygous tall X heterozygous tall.

(b) Work out the following dihybrid crosses as above: (1) Homozygous tall-
round X dwarf -wrinkled ; (2) heterozygous tall-round X heterozygous tall-
round; (3) homozygous tall-round X heterozygous tall-round.

720 General and Applied Biology
SELECTED REFERENCES

Altenburg: Genetics, Henry Holt & Co., Inc.

Bauer, Fischer, and Lentz: Human Heredity, The Macmillan Co.

Beadle: Science in Progress, Yale University Press.

Beadle: The Genes of Men and Molds, Scient. Am. 179: 30-38, 1948.

Beadle: Genes and the Chemistry of the Organism, Am. Scient. 34: 31-53, 1946.

Burch and Pendell: Human Breeding and Surviv^al, Penguin Books.

Burlingame: Heredity and Social Problems McGraw-Hill Book Co., Inc.

Colin: Elements of Genetics, P. Blakiston's Son & Co.

Dunn and Dobzhansky: Heredity, Race and Society, Penguin Books.

Fasten: Genetics and Eugenics, Ginn and Co.

Goldschmidt: Physiological Genetics, McGraw-Hill Book Co., Inc.

Hunt: Some Biological Aspects of War, Galton Publishing Co.

Holmes: The Eugenic Predicament, Harcourt, Brace and Co., Inc.

Holmes: Human Genetics and Its Social Import, McGraw-Hill Book Co., Inc.

Lindsey: Textbook of Genetics, The Macmillan Co.

Mohr: Heredity and Disease, W. W. Norton & Co., Inc.

Osborn: Preface to Eugenics, Harper & Brothers.

Popenoe and Johnson: Applied Eugenics, The Macmillan Co.

Rife: Dice of Destiny, Long's College Book Co.

Riley: Gentics and Cytogenetics, John Wiley & Sons, Inc.

Ruggles-Gates: Heredity in Man, The Macmillan Co.

Scheinfeld: You and Heredity, Frederick A. Stokes Co.

Shull: Heredity, McGraw-Hill Book Co., Inc.

Sinnott, Dunn, and Dobzhansky: Principles of Genetics, McGraw-Hill Book Co.,

Inc.
Snyder: Principles of Heredity, D. C. Heath & Co .
Stern: Principles of Human Genetics, W. H. Freeman & Co.
Waddington: Introduction to Modern Genetics, The Macmillan Co.
Walter: Genetics, The Macmillan Co.

Chapter 35

VARIATIONS AND ADAPTATIONS
IN ANIMALS AND PLANTS

Variations (L. variare, to change) are diflferences, both structural and
functional, which exist between offspring of the same parents or in in-
dividuals of the same species. Variation also may be considered as the
process of changing from one organic condition to another. The ability
to vary is an inherent property of living organisms by means of which
they attempt to live more or less successfully in their changing environ-
ment.

Adaptations (L. ad, to; aptere, to fit) are the result of structural or
functional changes on the part of an organism whereby it attempts to
adjust itself, directly or indirectly, to the influences of the environment
in order to live more or less successfully. The powers of adaptation are
the result of the inherent responsive ability (irritability) of living sub-
stance to stimuli. Since environment is changing constantly, a living
organism must have a corresponding ability to change in order to attempt
to adapt itself to these environmental changes.

IMPORTANCE OF VARIATIONS

Variations make it possible for individual organisms to differ from
each other and thus express their individualities. Educational, cultural,
or sociologic progress is due to the inherent abilities of living organisms
to vary. Differences in variations are due to (1) a difference in the
hereditary materials with which the organism starts its life, (2) the
effects of different environmental factors, external and internal, upon
these original hereditary materials, and (3) the interaction of the above
factors.

Variations are of great importance in our studies of heredity. The
causes, limitations, heritability, and effects of variations must be fully
understood in order to draw correct conclusions in the study of heredity.
It can be readily seen that ignorance of variations might lead to the

721

722 General and Applied Biology

conclusion that a particular character is being inherited when in reality
it is merely a natural, normal variation. By taking advantage of varia-
tions, improvements in races of organisms can be made. New varieties are
often the result of the proper selection and development of variations.
A study of variations reveals that all life is constantly changing. As
often stated, the most invariable thing in nature is variability. The suc-
cessful plant or animal is the one which successfully can take advantage
of its numerous variations.

CLASSIFICATION OF VARIATIONS

According to Their Heritability. — Somatic modifications or acquired
characters are not thought to be inheritable, except in a few instances.
Somatic modifications are structural and functional adjustments of the
bodies (soma) of individuals to differences in environment, either dur-
ing or after their embryologic development. Examples of somatic modi-
fications are muscular changes, calloused hands, tanned skins, acquired
information, and acquired injuries to animals and plants.

Combinations result from the combining of the hereditary characters
of two different races or strains, with the production of nothing distinctly
new but a mere combining of the old characters. Certain types of com-
binations are inheritable. For instance, the angora coat of a mother
guinea pig might be combined with the black color of the father to pro-
duce a combination of angora and black in the offspring.

Mutations or hereditary variations are always inherently inheritable
if they are to be classed as mutations. They are variations resulting from
spontaneous chemical changes in the chromatin of the cells or an ab-
normal number of chromosomes or their contained genes. (For a more
detailed discussion of mutations, see the chapter on Heredity.) An
example of a mutation is the production of a fruit fly with a narrow,
elongated eye (called bar eye) from a normal, oval-eyed form.

According to Their Nature. — Morphologic or structural variations
(Fig. 357) are usually differences in size, shape, color, or number of
structures.

Physiologic or functional variations are usually differences in such
things as vitality, nutrition, productivity, or secretions. These variations
are usually a necessary corollary of morphologic variation.

Psychologic variations are variable expressions of the nervous system
or the inherent sensitivity of living protoplasm. Such things as responses,
dispositions, and mental abilities are well-known variations in this field.

Variations and Adaptations in Animals and Plants 723

Ecologic variations result from a fixed relation to environment. Varia-
tions brought about by environment might be illustrated as follows:
Members of the same species of an organism differ or vary when they
live under entirely different environmental conditions. The same species
of plant will appear quite differently when grown in high altitudes and
when grown at sea level.

£l

I I

22 24 26 28 30

23 25 27 29

mllllmetera In diameter

Fig. 357. — Diagram to show variations in snails. The diameters were measured
of 100 land snail shells collected from an area with uniform environment. The
diameters varied from 22 to 30 mm. The number of individuals of each diameter
is represented by the upright blocks. Observe that these variations so plotted
form a curve.

According to Gradations. — Continuous variations or fluctuations are
common variations which occur in individuals with identical heredity;
they grade one into another so as to make an unbroken, graded series
from one extreme to the other. Examples of continuous variations are

724 General and Applied Biology

heights of human beings (Fig. 358), lengths of appendages, weights of
individuals, sizes of leaves, heights of trees of the same species.

Discontinuous variations or mutations are the result of certain char-
acteristics, appearing abruptly in an individual, which are so distinctly
variable that they do not fit into the graded series of the main body.
(Mutations are more fully considered in the chapter on Heredity.)

According to Their Direction. — Orthogenetic or determinate variations
follow such a sequence that there is a straight development along specific
and logical lines toward a definite goal. An example of this type is the
ancestry of the horse (Figs. 359 and 360) in which the five- toed ancestor
developed into the four-toed, then into the three-toed, and finally into
the one-toed persent-day form.

76. 7a: n 73. 72. II. 70. 69. 68. 67. 66. 6i: 6f. 63i 62. 6/. 60. 5t SQ^ S7.

HEIGHT IN INCHES

Fig. 358. — Distribution curves showing heights of college men and women includ-
ing all ages; (— — — ) represents the men; ( ) represents the women.

Fortuitous or indeterminate variations fluctuate back and forth about
a mean, apparently always within the same limits, generation after gen-
eration. For instance, the leaves of a tree may be larger one season than
another and may continue to vary back and forth several generations,
but they never fluctuate far from the mean size for leaves of a plant of
that particular species. Such variations are caused by ( 1 ) recombinations

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726 General and Applied Biology

of one or more minor hereditary factors, (2) fluctuations in environment,
or (3) the interaction of the above two causes.

According to Their Utility. — Variations may be such that they are
harmful, indifferent, or useful to the organism possessing them. The
utiHty is determined not only by the degree of variation but also by the
type of environment in which the organism is asked to use that type of
variation. What is useful in one environment might be harmful in
another.

WrJst

Wrist-

Fig. 360. — Comparative stages in the elevation of the horse's foot to the tip of
the middle toe, as shown by the human hand. (Courtesy of The American
Museum of Natural History.)

CAUSES OF VARIATIONS

The origins of variations are known as ( 1 ) germinal if they arise in-
ternally in the germ plasm, and (2) somatic if they arise in the soma-
toplasm (body plasm) due to external environmental causes, either dur-
ing embryologic development or in adult life.

Charles Darwin considered variations as "axiomatic" or self-evident
and thus needed no explanation. Lamarck regarded the causes of varia-
tions as being ( 1 ) intrinsic or physiologic, in which case the organism put
forth an internal eflfort or response to successfully adapt itself to its
particular surroundings or (2) extrinsic or external, in which the ex-
ternal environmental factors produced or caused the variations. In the

Variations and Adaptations in Animals and Plants 727

above two cases, one cannot consider either one by itself, but in all prob-
ability the two working together would explain the causes of variations
in a majority of cases. However, at one time the major or originating
force might be external, while at another it might be internal. August
Weismann believed that the causes of variations, at least the heritable
ones, were inborn or intrinsic in the germ plasm. He suggested that sex-
ual reproduction was for the purpose of mingling two strains of germ
plasm, thereby doubling the possibilities of variations. Bateson sug-
gested the futility of attempting to guess at the causes of variations,
especially in the light of our present profound ignorance in this direction.

RESULTS OF VARIATIONS

Reflection will suggest many and varied results of variations. A few
of the more important effects might be listed as follows: (1) Improve-
ment of a race of animals and plants is possible by taking advantage of
variations within them. (2) Through variations, individualities of or-
ganisms can be expressed. (3) With variations always present it is
difficult to maintain pure lines or standard types. (4) The presence of
variations provides for the diversification of species so that at least some
of the individuals may be better fitted to cope with their environments,
especially should the latter change, as they constantly are doing. Since,
environments are always varying, it is necessary that organisms vary also
in order efficiently and harmoniously to fit into their environments. (5)
Variations furnish valuable materials for the study of genetics. Without
variations, the science of genetics would be much simpler and more easily
understood. (6) Variations produce the "spice of life," for without
them all organisms would produce such similarities that there would be
few changes and all things always would be the same. (7) Education is
based on variations. Without the possibility or ability of producing
variations, attempts at education would be unnecessary and impossible.
Through this process, the hereditary materials of an individual are sub-
jected to the educational or environmental stimuli, thus bringing out and
retaining such varieties of abilities as distinguish us one from another.
Would it be desirable to have all individuals of equal ability, even though
that ability might be high? Can two individuals really be equal?

ADAPTATIONS

Adaptations might be considered to be the result of those variations
which are advantageous and enable an organism to live more success-
fully in its environment and in its struggle for existence (Fig. 361).

728 General and Applied Biology

Adaptations may be internal (structure and activities of internal organs,
tissues, etc.) or external (external phenomena), just as variations may
be internal or external. The adaptive modifications in living organisms
are apparently unlimited as we study the great variety of plants and
animals. For example, the specific types of wings, legs, mouth parts,
antennae, digestive tract, respiratory system, metamorphosis, etc., are
among the most conspicuous adaptations of the numerous kinds of in-
sects to fit them into various environments. Through adaptations, cer-
tain plants have become able to live in the arid regions of the desert

UERON

GULL

Fig. 361. — Adaptations of the bills of birds, showing variations in structure
for different uses. The generalized bill of the Grebe is for eating seeds; spoonbill
and duck, for straining mud; the heron, for catching fish; whippoorwill, for
catching insects; hawk, for tearing flesh; petrel, for catching Crustacea; gull, for
devouring refuse. (From Atwood, A Concise Comparative Anatomy, The C. V.
Mosby Co.)

Variations and Adaptations in Animals and Plants. 729

(cacti) and some are able to live in swampy areas (cattails, etc.), while
others are able to live in the frigid regions of the poles or on mountain
tops (certain mosses, shrubby plants, etc.). An organism may be ren-
dered unfit for a particular environment because of the presence of
certain variations and their attendant adaptations, while that same
organism with its same traits might fit perfectly into a different environ-
ment. Successful living depends upon the mutual fitting in of inherent
abilities and the surrounding environment. An adaptation may be
regarded as the result of developmental changes resulting from inherita-
ble variations, with the retention of those which are advantageous. Un-
desirable variations may have resulted in the destruction of other or-
ganisms through the "struggle for existence" in the process of natural
selection.

Motile organisms may be able to move into an environment which may
prove to be more satisfactory for their particular abilities. The assump-
tion is that the degree of adaptability to an environment or the ability
to seek and find a more desirable environment commensurate with its
abilities is an influential factor in the successful struggle for existence.

Adaptations may be divergent (L. diver gere, to incline away) or con-
vergent (L. convergere, to incline together). In divergence (adaptive
radiation), species of living organisms that are somewhat closely related
tend to radiate in various directions into diflferent environments and be-
come modified accordingly. From the standpoint of locomotion, the
various species of mammals have become adapted to live on land (walk-
ing and jumping), in the ground (digging), in water (swimming), in
trees (hanging), and in the air (flying). In co7ivergence (parallelism),
species of organisms belonging to different orders, families, etc., tend to
become adapted to the same type of environment by means of similar
modifications. For example, the wings of bats and flying squirrels are
adapted for flying, the forelimbs of badgers and ant eaters for digging,
the forelimbs of seals and porpoises for swimming, the limbs of sloths
and gibbons for hanging, etc. In convergent (parallel) evolution there
is a development of similar traits or features along similar lines among
unrelated, or distantly related, groups of organisms. An example of con-
vergent evolution among members of widely separated (distantly related)
families of plants growing in similar environments is the development in
desert-inhabiting cacti, spurge, live-for-ever, etc., of such similar char-
acters as reduction or complete absence of leaves, formation of heavy
layers of protective cutin, production of spines, and development of water
storas^e tissues.

730 .General and Applied Biology

Some of the most striking adaptations in animals are the various colors
and patterns which characterize certain species. Colors may be due to
roughs reflecting, physical structures which scatter (diffuse) light into its
various colored rays, or they may be due to the deflection of rays of light
from the straight paths as they pass obliquely from one medium to an-
other through the process of refraction. Hence, the physical structure
of the bodies of insects, the scales of fish, the feathers of birds, etc., are
responsible for many bright colors. Other colors in animals are due to
chemical pigments which frequently are in special cells called chromato-
phores (kro' ma to for) (Gr. chroma, color; phoreo, to bear) . The latter
contain pigments such as black, brown, yellow, orange, red, etc., which
vary with the species and may even change size and shape in individual
organisms, thereby altering the coloration (Fig. 209). In general, the
coloration of an or2:anism which blends with its environment renders it
more or less inconspicuous in that particular habitat, while the same
coloration in a different habitat may make it conspicuous. The colora-
tions in animals may serve such natural purposes as protection (conceal-
ment) or aggression, warning or signaling, assisting in courtship and selec-
tion of mates, etc. Certain species seem to change colors rather quickly
to more or less blend with the environment, as shown by the changing
colors of certain fish, chameleons, etc. Others change colors with the
seasons (seasonal coloration), thereby securing protection or being sup-
plied with characters which conceal them for aggressive purposes. The
weasel and ptarmigan (bird) change to white in the autumn and to dark
colors in the spring.

Some organisms are so constructed as to resemble other organisms or
even nonliving objects [protective resemblance) , thereby being protected
somewhat. The walking stick (an insect, order Orthoptera) structurally
resembles a dead twig. The underside of the wings of the "deadleaf"
butterfly [Kallima) of India resembles a dead leaf when folded at rest.
The caterpillars of certain insects also resemble sticks. The viceroy but-
terfly [Basilar chia) greatly resembles the disagreeably tasting Monarch
butterfly [Danaus) so the former may be somewhat immune from attack
by birds. Such a phenomenon involving a model and mimic is called
mimicry. Some animals may not use their colorations or special struc-
tures for protection but for aggression. This seems to be true for tigers,
lions, tree frogs, praying mantes, etc., in which they may blend into their
surroundings, thus permitting them to approach their prey more easily.

Variations and Adaptations in Animals and Plants 731
QUESTIONS AND TOPICS

1. Define variations and give examples you have observed.

2. List and discuss the values of variations in Nature. What would happen in the
living world if nothing changed ?

3. Classify variations in several different ways with examples of each type.

4. Discuss each of the various causes of variations.

5. Discuss the results of variations in the plant and animal worlds.

6. What do the various fossils of such animals as the horse found in successive
periods in the earth's strata prove ?

7. How might mutations explain the origin of certain new species or types of
plants or animals ?

8. Explain the statement that "mutations are the hope and the despair of plant
and animal breeders."

9. Describe specifically how you might produce variations in certain plants and
animals.

10. What is the relationship between variations of the inheritable type and descent
with change (evolution) ?

11. Define adaptations and give examples you have observed.

12. Contrast divergence (adaptive radiation) and convergence (parallelism),
giving examples of each.

13. Discuss coloration as to causes and the uses to which it may be put, including
examples of each type of coloration.

14. Explain protective resemblance, giving examples which you may have ob-
served.

15. Explain seasonal coloration, including some examples you may have observed.

SELECTED REFERENCES

Allee: Animal Aggregations, University of Chicago Press.

Allee et al.: Principles of Animal Ecology, W. B. Saunders Co.

Child: Individuality in Organisms, University of Chicago Press.

Cott: Adaptive Coloration in Animals, Oxford University Press.

Daubenmire: Plants and Environment, John Wiley & Sons, Inc.

Oosting: The Study of Plant Communities, W. H. Freeman & Co.

Sears: Life and Environment, Columbia University Press.

Thayer: Concealing Coloration in the Animal Kingdom, The Macmillan Co.

Chapter 36

LIVING ORGANISMS— THEIR ORIGIN, CONTINUITY,
DEVELOPMENT, AND DESCENT WITH CHANGE

I. ORIGIN OF LIFE

A. Abiogenesis (Spontaneous Generation)

A majority of scientists up to the seventeenth century beHeved in
abiogenesis, which stated that Hving things, especially the lower types,
arose spontaneously from nonliving substances. Such beliefs as the fol-
lowing were common: Field mice were thought to arise spontaneously
from the mud of the Nile River. Aristotle (384-322 b.c.) believed that
eels (fishes) arose spontaneously from nonliving materials. Kircher
stated that he actually saw animals arise through the action of water
on the stems of plants. Von Helmont (1577-1644), a Flemish physician,
believed that house mice were generated from pieces of cheese placed in
bundles of rags. Flies were thought to arise spontaneously from dirt,
manure, and decaying meats. Anaximander (611-547 B.C.) thought that
air imparted life to all living things.

Reasons Why Abiogenesis Was Believed. — Abiogenesis, or sponta-
neous generation of things, was believed because the complex life cycles
of many of the animals and plants were not understood at that time.
Many microscopic stages of certain living organisms were not seen or
escaped methods of observation, because the microscope had not been
sufficiently perfected to observe accurately. This lack of accurate knowl-
edge formed a natural setting for such a theory as abiogenesis. Experi-
mental methods of attacking such problems were not yet developed.
Scientists attempted to prove by hearsay, supposition, or discussion rather
than by experimental investigation. Rather than prove by exact evi-
dence, they would attempt to prove by more or less logical reasoning.

Needham, in 1749, believed he had demonstrated the spontaneous
origin of minute living organisms in infusions which he had boiled and
sealed in flasks. By boiling he thought he had killed all living matter

732

Living Organisms 733

from which living organisms could arise later. The living organisms
which later arose in his flasks probably arose from living materials which
had not been killed by boiling.

B. Biogenesis (Life From Life)

Spallanzani (1729-1799) stated that Needham's results were incon-
clusive because they were obtained by insufficient sterilization of the in-
fusions in the flasks. The chemists also entered the controversy by stat-
ing that free oxygen which is an essential material for life processes was
excluded by Spallanzani in his experiments, thus preventing the possi-
bility of spontaneous generation. To answer the latter point, various
investigators during the first half of the last century showed that thor-
oughly sterilized infusions never developed living organisms even when
sterile air was admitted. The air was sterilized by heating or by passage
through acids in order to remove the suspended "dust particles" on
which living substances were attached.

Francisco Redi (1626-1698), an Italian scientist, by a simple experi-
ment of protecting decaying meat from contamination by flies, demon-
strated that the maggots of these flies did not arise spontaneously from
the meat, but that they developed from living eggs deposited by living
flies. Redi's results definitely formulated the theory that "life must arise
from living organisms" and cannot arise spontaneously from nonliving
sources.

Louis Pasteur (1822-1895), by means of a special type of flask, con-
vincingly proved that the source of life, which so rapidly appeared in
infusions exposed to the air, was the air itself, or rather the life existing
in the air. It was thus contended that much of the dust of the air was
made up of microorganisms in a dormant condition ready to become
actively alive when suitable environmental conditions, such as moisture,
temperature, and food, were encountered. He stated that such organ-
isms were the causes of certain chemical changes, fermentations, putre-
factions, and certain diseases. Pasteur thus laid a rather accurate foun-
dation for the germ theory of diseases and many chemical activities.

XL ORIGIN OF LIFE ON THE EARTH

Geologists and astronomers tell us that the condition of the earth at
one time was such that life could not exist but that life was finally estab-
lished hundreds of millions of years ago and has existed continuously
since.

734 General and Applied Biology

Theories for the Origin of Life on the Earth

1 . Cosmozoa Theory. — This theory suggests that, because of the com-
plexity of hving matter and the cstabhshment of biogenesis, hfe came to
the earth from some other part of the universe. It was assumed that
certain heavenly bodies of the universe have always been the abode of
life and that life in a latent state was carried to the earth from them by
small particles of those planets on which it existed at that time. This
does not explain the real origin of life at its very beginning. This theory
is based on two unproved assumptions: (1) that life exists or has
existed elsewhere in the universe and (2) that life can be maintained
during the interstellar voyage to the earth.

We have proof that certain present-day organisms under the influence
of unfavorable environments can resist dryness, heat, cold, etc., although
this does not prove that their remote ancestors may have had similar
or greater properties of this type. These would be necessary to resist
in transit such factors as the effects of light waves, extremely low tem-
peratures, absence of water vapor in cosmic space, radiations, etc.

2. Pfliiger's Theory. — Pfliiger assumed that the earth was originally
a superheated, incandescent mass from which arose a combination of
carbon and nitrogen atoms to form cyanogen (CN). This union can
occur only at high temperatures and takes up a large amount of energy
in the form of heat which contributes energy to the organic protein com-
pounds of which living substances (protoplasm) are composed.

3. Moore's Theory. — Moore suggests that life arose under suitable
conditions from the inorganic elements of a cooling earth by a process
of continuous complexification; that is, matter in general will tend to
assume more and more complex forms in labile equilibrium. He sug-
gests that the process of complexification is inherent in all matter and
that, when a sufficiently complex stage is once reached in this evolution-
ary process, life invariably will be an attribute. Atoms, molecules,
oxides, carbonates, colloids, and then living organisms arise as a result
of these successive operations. This theory attempts to bridge the gap
between nonliving and living substances.

4. Allen's Theory. — Allen suggests that at a time when the physical
conditions of the earth were much as they are now some reactions as
the following occurred: Energy coming from the sun was absorbed by
the iron in damp earth or water and acted on certain raw materials in
such a way as to dissociate and rearrange the atoms. This interaction
between the nitrogen, carbon, hydrogen, oxygen, and sulfur resulted in

Living Organisms 735

their accumulation in the water or damp earth. Later, still further
actions followed because of the lability of the nitrogen compounds until
poorly organized, diflfuse substances were formed which still later
changed into living protoplasm.

5. Troland's Theory. — At some moment in the earth's history a small
quantity of a certain autocatalytic enzyme spontaneously appeared in
the warm ocean waters. It then combined with a drop of rather inactive
oily liquid, thereby increasing its rate of activity and size until the drop
became split into smaller globules, giving rise to a substance having the
power of continued and indefinite growth.

6. Osborn's Theory. — Osborn assumes that the air, water, and earth
had all the necessary chemical elements and that they arranged them-
selves into water, nitrates, and carbon dioxide at a temperature between
6° and 89° C, long before sunlight could penetrate the various vapors
of the atmosphere. He suggests that these materials so formed captured
and transformed the electric energy of the chemical elements constitut-
ing living protoplasm and this property probably later developed only
in the presence of heat energy from the sun or earth. First, there was
a grouping of the several "life elements," and then by mutual attraction
their arrangement in a state of colloidal suspension, with numerous
actions and reactions, until an organic, living organism was formed which
was distinct from the various other aggregations of the nonliving or in-
organic matter previously brought together and held by forces of gravity.

7. Transcendental Theory (Creation). — This religious answer sug-
gests that life was created by an agent working outside the realms of
matter and science.

III. CONTINUITY OF LIFE

If, as we now believe, all life arises and has arisen from preexisting
life (biogenesis), then the stream of life is continuous from the beginning
of life to the present time (Figs. 350 and 351 ) . The Hfe of an individual
organism is merely one Hnk in the endless chain extending from the dis-
tant past to the future. After a study of the metamorphosis and life
cycles of various animals and plants, we see that life transferred to the
offspring by one or more parents is carried by that offspring through its
various stages of development to maturity, when it in turn will pass life
on to its offspring. This is possible because of the continuity of living
substance between parents and their offspring (Chapter 34). Reproduc-
tion is for the purpose of continuing the life of a particular species after

736 General and Applied Biology

it is once started. The germ cell cycle is considered in Chapter 34. Two
of the more important phases of the process (Fig. 351) are (1) the pro-
duction of germ cells and (2) the maturation of the germ cells.

IV. DEVELOPMENT OF LIVING ORGANISMS

Development may be defined as the bringing to the fore what is al-
ready present but latent in an organism. The amount and type of devel-
opment of a particular organism depend on ( 1 ) its particular inheritance
and (2) the external and internal environmental factors which surround
it and in which it must develop. All living organisms are affected by
such factors as the quantity and quality of the food, amount of water
available, quantity and quality of light, the improper elimination of their
waste materials, their type of activity, the presence or absence of vita-
mins, enzymes, etc.

V. DESCENT OF ORGANISMS WITH CHANGE
(EVOLUTION)

A. Evidences of Descent With Change

Evidences of descent with change have been secured from such sciences
as (1) paleontology (science of fossil remains), (2) taxonomy (classifica-
tion), (3) comparative embryology, (4) comparative anatomy, (5) com-
parative physiology, (6) biogeography (geographic distribution), and
(7) genetics and variations.

1. Evidences From Paleontology. — Geologists can determine, in most
cases with remarkable accuracy, the chronologic succession in time of
the various strata composing the earth. The fossils of these various
strata testify to the order of appearance and disappearance of various
types of animals and plants on the earth, the more recent appearing
nearer the surface.

Two examples of descent with change may be cited. (1) Birds seem
to have evolved gradually from a rcptilelike ancestor, because, in spite
of superficial dissimilarities (such as the scaly-skinned, cold-blooded rep-
tile and the feathered, warm-blooded bird), there are many fundamental
structural and functional similarites not only between adult reptiles and
birds but also between their embryonic stages. Fossil remains of a rep-
tilelike bird (Archaeopteryx) show a connecting link between reptiles and
birds as they are known today (Fig. 362). (2) The horse also has de-
veloped to its present status through a series of successive changes. These

Living Organisms 737

developmental changes through which the ancestors of our modern horse
are believed to have gone are shown in the evolution of the horse (Figs.
359 and 360).

2. Evidences From Taxonomy (Classification). — A comparative study
of the various species of animals and plants reveals a very great simi-
larity; in fact, so great that it is difficult to decide where one species with

Fig. 362. — The Archaeopteryx, A, a reptilelike bird of the Upper Jurassic
period compared with the pigeon (Columha livia), B. (From Lull: Organic
Evolution. By permission of The Macmillan Company, publishers.)

its variations ends and another species with its variations begins. The
intergrades (divergent individuals with a certain species) frequently are
very similar functionally and structurally to those of a closely related
species. When we attempt to classify similar types of organisms, we see
clearly the close anatomic and physiologic relationships between many
of them. What is the explanation for these similarities? Are living

738 General and Applied Biology

m .

111

Tortoises

ill '

Fig. 363. — Parallelism in development of vertebrate animals. The upper row
shows very similar stages of the eight different species of embryos; the middle
row shows the different species becoming somewhat distinct; the lower row shows

Livins. Organisms 739

ife -^. /#/ \h :/,' Z.J, ij ^/ M ;v /J

% f %.y- O H

v>:--

■^ ..r^'r^

-Q .

IDC

still greater differentiation in the various species. Note the gill slits, metameres
and external tails in the early stages of all types. (From Romanes: Darwin and
After Darwin, published by the Open Court PubHshing Company.)

740 General and Applied Biology

things constantly changing? What things in your experience do not
change? Does it decrease the glory and magnitude of Nature to have
living things constantly evolving or changing according to definite, con-
trollable laws? Would it increase our respect for the marvels and mag-
nificence of Nature by having living things which would be static and
unchanging? Could we make progress or educate ourselves if living
protoplasm did not have the ability to change and evolve? What would

AURICLES

VENTRICLES

Fishes

One; receives blood returning
through v^eins from entire
body

One; receives blood from
auricle and pumps it through
gills on its way to all parts
of the body

Amphibia

(frogs, toads,
etc.)

Two separate; left receives
blood from veins from lung :
right receives blood from
veins from all parts of body

One; receives blood from both
auricles and pumps the mix-
ture through arteries to all
parts of the body

Reptiles (lower
types; lizards,
snakes,
turtles)

Two separate; left receives
blood from veins from lungs;
right receives blood from
veins from all parts of the
body

Two partially separated; right
receives blood from right
auricle; left receives from
left auricle ; blood from the
two auricles is mixed in the
partially separated ventricles
and pumped to all parts of
the body

Reptiles (higher
types; alli-
gators, croco-
diles, etc.)

Two separate; left receives
blood from veins from lungs ;
right receives blood from
veins from all parts of the
body

Two completely separated;
right receives blood from
right auricle ; left receives
blood from left auricle

Birds (adults)

Two separate; left receives
blood from veins from lungs;
right receives blood from
veins from all parts of the
body

Two completely separated;
right receives blood from
right auricle ; left from left
auricle ; left ventricle pumps
blood to all parts of body ;
right ventricle, to lungs

Mammals
(adults)

Two separate; left receiv^es
blood from veins from lungs ;
right receives blood from
veins from all parts of the
body

Two completely separated;
right and left have sam.e
functions as in birds

Fig. 364. — Chambers of the hearts of vertebrates.

be the state of affairs if all things remained constant? Is it not logical
and desirable to believe that all living things constantly change more or
less and that such changes are controlled by certain natural laws? The
answers to these questions will prov^e beneficial in laying the foundation
for proper study of the descent of organisms with change.

3. Evidences From Comparative Embryology. — A comparative study
of the embryologic stages through which animals pass reveals a wide-

Living Organisms 741

Carotid Artery — --,

Duct of
Cuvier

Afferent Branchial
Arteries

Truncus Arteriosus
— Bulbus Arteriosus

Sinus Venosus-

Sinus Venosus

-Hepatic Vein

Precaval Veins £^

arotld A.

Systemic Arch
— ^Pulmonary A.

Pulmonairy V,

Postcaval Vein

Innominate A.

Aorta

Innominate A.

Aorta— — ??

Precaval Veins

Postcaval Veln-

\ \ Hepatic V.
\ Postcaval V.

Left Subclavian A;
Left Carotid A, \

Pulmonary
Arteries
and Veins

R.and L, Precaval Veins Innominate A

R. Pulmonary Artery —

Precaval Vein —
(Superior Vena Cava)

Postcaval Vein

(Inferior Vena Cava)

■ Aortic Arch,

Left Pulmonary A.

|-Right Pulmonary Veins
} Left Pulmonary Veins

Fig. 365. — Hearts and blood vessels of vertebrates (somewhat diagrammatic).
A, Fish (Pisces): B, frog (Amphibia); C, turtle (Reptilia) ; D, pigeon (Aves) ;
E, man (Mammalia). Arrows show direction of blood flow. A (within heart)
shows the auricle; V (within heart) shows the ventricle; R, right; L, left. A
(outside heart) shows an artery; V (outside heart) shows a vein. The terms
auricle and atrium (plural, atria) are sometimes used interchangeably.

742 General and Applied Biology

spread general correspondence of the developmental stages in higher
forms with the existing adult stages of lower forms. The history of the
embryologic development of an individual frequently corresponds in a
general and broad way to the history of the development of the race as
a whole (Fig. 363). In other words^ the development of the individual
recapitulates the ancestral descent of the race; ontogeny repeats phylog-
eny. Read further in regard to ontogeny, phylogeny, and recapitula-
tion (biogenetic) theory.

A study of the embryologic development of the heart of a bird or mam-
mal shows that the various stages through which its development occurs
really succeed each other in the same general way from the two-cham-
bered to a four-chambered condition, as is shown when we pass from the
lower vertebrates, such as the fishes, up through the amphibia, reptiles,
and birds to mammals (Figs. 364 and 365) .

A similar comparative study of the brains (Fig. 366), reproductive
systems, skeletal systems, and digestive systems of these various vertebrates
shows a similar condition in which the organs of the higher animals dur-
ing their development pass through stages which correspond in general
with the larval or adult condition of similar organs in the lower forms.
Thus, the knowledge of the anatomy of an animal gives a broad and gen-
eral idea as to its type of embryologic development.

These similarities of lower and higher types of organisms found by
embryologic studies suggest a similar inheritance as a basis and probably
an actual blood relationship between them. The only other alternative
is that the same "blueprint" with slight modifications and alterations
was used in the process of specially and individually creating each of the
various species.

4. Evidences From Comparative Anatomy. —

a. From Gross Comparative Anatomy: A detailed comparative study
of the anatomy of apparently different types of animals reveals a multi-
tude of similarities which really overbalance the more visible dissimilari-
ties which they possess. For instance, the differences possessed by the
five classes of vertebrates are relatively slight when compared with the
many basic and fundamental resemblances which they all possess to more
or less degree.

The forelimbs of the frog, lizard, bird, horse, and man, for example,
are constructed on the same general structural plan and arise in a simi-
lar way embryologically. They are thus said to be homologous struc-

Aving Organisms 743

744 General and Applied Biology

tures, and such differences or variations as exist are principally the result
of the absence of some minor part or the transformation of a certain part,
depending on disuse or specific use to which that part has been put.
Nearly all the bones, muscles, nerves, and blood vessels are constructed
and arranged in a homologous manner in the forelimbs of the entire
group from the lower types or frogs to the higher types or man. The
same thing is true for the hindlimbs, digestive systems, reproductive sys-
tems, and circulatory systems of this series.

b. From Vestigial Structures: Man has approximately one hundred
useless or harmful structures which are also represented in lower types,
in which case the same kind of structure may be very useful. What is
the explanation of the presence of such useless or harmful structures in
certain animals if they have not had their origin in some common an-
cestor? Why should they have been specifically placed in animals in
which they are useless? Is it not logical to believe that they have evolved
differently in different animals?

Illustrations of vestigial structures in man are quite numerous, but the
following are most commonly cited as being representative: (1) The
vermiform appendix is a remnant of an organ which is useful in certain
herbivorous (plant-eating) animals. The appendix may have had a
specific function in man many generations ago, although no specific
function can be stated for it at present. (2) The third eyelid in the
inner angle of the human eye corresponds to the nictitating membrane
or lid which moves laterally across the eye in such lower animals as the
frog, bird, and dog. (3) Muscles of the external ear are useless for man
but are used by lower animals to turn the ear in the proper direction to
acquire the sound waves more accurately. (4) The terminal vertebrae
(coccyx) are of no value to man, but they are the foundation for the
external tail in lower animals. It is interesting to note that the early em-
bryos of man (Fig. 363) possess an external tail which is useless and
which is discarded before the adult stages are reached. Only occasionally
does the external tail persist in the adult man. (5) The lobe of the ear
is of no practical benefit to man, although it may have had some func-
tion in the past. (6) The point of the ear, known as Darwin's point,
on the edge of the upper roll or margin of the human ear, corresponds
to the tip of the ear of animals who hold their ears upright. What is
the value of this vestigial structure? Why should it have been placed
there specifically if there is not some type of relationship?

Living Organisms 745

Illustrations of vestigial structures in other animals are numerous as
the following will illustrate: (1) The splint bones of the legs of the horse
are remnants of original toes. (2) The poison glands of certain snakes
are modified, specialized salivary glands which have evidently developed
from the latter through the many stages of descent with change. (3)
The gill slits of the embryos (Fig. 363) of higher vertebrates all dis-
appear except one pair which develop as the Eustachian tubes connecting
the pharynx and the middle ear. (4) The milk glands of mammals are
merely modified and specialized sweat glands of the skin. In all prob-
ability the various stages of the descent with change brought about this
modification. (5) Certain snakes bear small, useless hindlimbs which
structurally resemble those of other animals in which they are useful.

5. Evidences From Comparative Physiology. — Since functions and
structures are interdependent, one would expect to find fundamental
physiologic similarities in organisms with structural similarities. The
following examples will be sufficient to illustrate the point: (1) The
bloods of closely related organisms are more nearly alike chemically and
physiologically than the bloods of the more distantly related types. (2)
The hormones of the excretions of closely related organisms are quite
similar and in many instances interchangeable. The insulin of the pan-
creas of the sheep may be used for an insulin deficiency in man. (3) The
crystal structures of bloods of similar organisms are more nearly alike
than the crystalline structures in bloods of more dissimilar or unrelated
organisms. In general, common properties persist in bloods of closely
related types, and variations are greatest in distantly related forms.

6. Evidences From Biogeography (Geographic Distribution). — Cer-
tain organisms have been observed actually to undergo distinct and spe-
cific changes (descent with change) when placed in environments differ-
ent from their relatives.

All the embryos produced by a single female aquatic snail were divided
equally into two groups: one group was permitted to develop in the acid
waters of a harbor and the other group in the alkaline waters of the open
lake. Some time later, the developing offspring were compared. The
results were so striking and significant that had the facts not been known,
one would have stated that there was no relationship between the groups.
Those developing in the acid waters had very thin, semitransparent
shells; those in the alkaline water had large, heavy, crusty shells. Is this
not suggestive of what happens in other living organisms all the time?
May forms originally closely related develop along entirely different

746 General and Applied Biology

lines, depending on one or more differing envii^onniental factors? Is this
not illustrative of "descent with change" ?

In fact, when similar animals or plants having identical inheritance
are placed in widely different environments, the development is quite
different and characteristic for each. Even human identical twins in
whom the inheritance is considered as nearly identical as is possible,
when placed in different environments develop into somewhat different
types.

7. Evidences From Heredity and Variations. — The scientific study
of heredity and variations has shown through indisputable facts and data
that organisms are constantly changing. What is this so-called "descent
with change" but an evolving which is fundamental and inherent in all
life, regardless of where we may care to place the origin, the responsi-
bility, and control of this evolving process?

If there were no change during descent, what would be the possibility
for progress? Is it more remarkable to have created a world, the living
contents of which are immutably constant and static, or to have one in
which life has the abilities of constantly changing according to natural
laws? Since our environmental factors are constantly changing, is it
not necessary that our living organisms have the ability constantly to
vary in order that they may keep step with the environment in which
they are to live, develop, and struggle for their existence?

B. Theories of Descent With Change

1. Lamarck's Theory of Acquired Characters (1809). — Lamarck at-
tempted to explain differences in individuals by suggesting that through
disuse or use for specific purposes certain parts of an organism were
under- or overdeveloped and that such differences were later inherited
by future offspring. The first part is true — use and disuse modify struc-
tures and functions — but even today we have no conclusive evidence
that such or similar modifications of the body or somatic cells are in-
heritable.

2. Darwin's Theory of Natural Selection as a Factor in the Origin of
Species (1859). — Darwin observed that animals produce larger numbers
of offspring than can naturally and normally exist in any given locality
but that the total numbers of that particular species remain more or less
constant or stationary.

Because of their morphologic and functional differences (or varia-
tions due to descent with change), there ensues between these offspring

Living Organisms 747

a "struggle for existence" and a consequent "survival of the fittest."
This permits a "natural selection" of the best to survive, and thus the
race as a whole is changed or benefited. If there were no natural selec-
tion or survival of the fittest through the various individual struggles for
existence, there would be present many of the weaker types from which
future populations might arise. In other words, the stronger win nat-
urally in their struggle with the less fit. This is a factor in the explana-
tion of the characteristics of a group of animals.

3. Elmer's Theory of Orthogenesis (1898). — The theory of ortho-
genesis (or definitely directed evolution) suggested that the evolution
of organisms has followed a perfectly predetermined direction or path-
way; that complex organisms arose through a series of directed and or-
derly sequences from simpler forms, much in the same way that a com-
plex adult develops from the egg through a series of predetermined
stages. This theory is on the border line of a vitalistic or supernatural
interpretation of the directive physicochemical factors which cause evo-
lution. According to this theory, certain types of variations are naturally
destined to arise, and hence determine the course of evolution not merely
at random but along a definite or straight line. This theory attempts
to explain the origin of many characters which arise spontaneously with-
out visible or apparent causes.

4. De Vries' Theory of Mutations (1901). — De Vries suggested that
the production of sudden mutations results in the appearance of pro-
found changes and differences between parents and offspring, thereby
producing new species. Natural selection operates to eliminate or retain
such organisms which have mutated. Undoubtedly some species have
arisen through mutation, as shown by tailless dogs and cats, the short-
legged breed of sheep (Ancon sheep) descended by mutation from a
long-legged ram, the hornless Hereford cattle descended from a single
calf born in Kansas in 1889.

5. Weismann's Theories of the Continuity of Germ Plasm and the
Noninheritance of Acquired Characters. — One essential feature of Weis-
mann's doctrine is that the germ plasm (germinal material) is con-
tinuous or forms a direct path from one generation to the next and is
not derived from the soma or body plasm. Because of experimental evi-
dence, he maintained that characters acquired by the body plasm were
not inheritable. He suggested that only germinal variations which might
arise as a result of new combinations in the germ cells (independent of
environment) were inheritable. He recognized the almost limitless num-

748 General and Applied Biology

ber of combinations possible when the germ cells of parents fuse during
fertilization. This, together with natural selection, he held to be suf-
ficient to determine which characters might arise and perish or persist
and consequently be transmitted to future ofTspring.

6. Theory of Hybridization. — This theory attempts to explain how
evolution might occur by the appearance of characters that are new
by a combination of genes of organisms of the same species or more
rarely of organisms of different species. Hybridization between animals
of different species rarely occurs, although an example of such a new
type is the infertile mule produced by crossing a horse and an ass.

QUESTIONS AND TOPICS

1. (1) Explain why abiogenesis was a common belief in the past. (2) Explain
when and how abiogenesis was finally disproved.

2. Explain in detail each of the theories of the origin of life on the earth. Which
one, if any, seems most plausible ? Why do you say so ?

3. Explain the phrase "continuity of life." How does this influence inheritance ?

4. From your observations, do you believe organisms descend with change, or, in
other words, evolve? Is there anything wrong in such belief? Why? To
what source or sources must we look for the causes and control of such a
phenomenon? Would it be desirable to have a static, unchanging world?

5. Discuss all the evidences from the seven biologic sciences which attempt to
explain descent with change. Which, if any, contributes the most logical
evidences?

6. What would you infer from observing the parallelism in the development of
vertebrate animals?

7. ( 1 ) What does a comparative study of the hearts of vertebrates suggest to
you? (2) What does a comparative study of vertebrate brains suggest?

8. Explain two of the great theories of descent with change.

9. What is the relation of genetics to the general principle of evolution?

10. Define Darwinism and Lamarckism. Do their theories necessarily hold true
today? Why do yon or do you not believe in Darwinism today?

SELECTED REFERENCES

Andrews: This Amazing Planet, G. P. Putnam's Sons.

Clark: The New Evolution, Zoogenesis, Williams & Wilkins Co.

Conklin: The Direction of Human Evolution, Charles Scribner's Sons.

Darwin: Origin of Species by Means of Natural Selection, London, John Murray.

Dobzhansky: Genetics and the Origin of Species, Columbia University Press.

Florkin: Biochemical Evolution, Academic Press, Inc.

Gamow: Biography of the Earth, Pelican Mentor Books.

Haldane: The Causes of Evolution, Longmans, Green & Co.

Hooton: Up From the Apes, The Macmillan Co.

Huxley: Evolution, the Modern Synthesis, Harpers & Brothers.

Lindsey: Evolution and Genetics, The Macmillan Co.

Lull: Organic Evolution, The Macmillan Co.

Living Organisms 749

Mason: Creation By Evolution, The Macmillan Co.

Oparin: The Origin of Life, The Macmillan Co.

Osborn: From the Greeks to Darwin, The Macmillan Co.

Osborn: Men of the Old Stone Age, Charles Scribner's Sons.

Osborn: Origin and Evolution of Life Upon the Earth, Charles Scribner's Sons.

Parker: What Evolution Is, Harvard University Press.

Shimer: Evolution and Man, Ginn and Co.

Shull: Evolution, McGraw-Hill Book Co., Inc.

Simpson: Tempo and Mode in Evolution, Columbia University Press.

Waddington: How Animals Develop, W. W. Norton & Co., Inc.

Ward: Evolution for John Doe, Bobbs-Merrill Co.

Williams: The Human Frontier, Harcourt, Brace & Co., Inc.

Chapter 37

BIOCHEMICAL AND BIOPHYSICAL PHENOMENA

Many of the scientific explanations for various biologic phenomena
come from a knowledge of chemistry and physics. In fact, a complete
understanding of the structures and functions of plants and animals
must be made from the chemical and physical standpoints. The progress
in the fields of chemistry and physics and their contributions to biology
have become so extensive that such sciences as biochemistry and bio-
physics are essential in the explanations of the phenomena of living or-
ganisms. Numerous biochemical and biophysical phenomena have been
considered throughout the text, but it seems desirable to give additional
explanations for some which have been described previously as well as
to discuss others which have not been considered in great detail.

Chemical and Physical Properties of Living Protoplasm

These properties of living protoplasm have been considered previously,
and in order to lay a proper background for considering other phe-
nomena it is desirable that a review be made of them. The chemical
construction of living protoplasm is influenced by the chemicals avail-
able from foods, but the actual composition of specific materials and
their complex associations within it are determined by certain natural
laws. Some of these laws must be understood in order to explain the
structures and living process in plants and animals. A few of the more
important are considered and possibly additional reading of selected ref-
erences will be highly desirable in certain instances.

Atoms and Molecules

The universe is composed of two fundamental components called
energy and matter. Under certain conditions these two may be inter-
converted. To the average person energy and matter may seem to be
unrelated, but Einstein's equation suggests a close relationship: E =
mc^ (E = energy; m = mass; c = the velocity of light, which is con-

750

Biochemical and Biophysical Phenomena 751

stant). Usually we think of energy as the ability to produce a change
or motion in matter (ability to perform work) and matter as anything
which occupies space and has weight. Energy may take the form of
heat, light, electricity, or motion. Potential energy is the ability to per-
form work because of the position (of atoms, molecules, or larger bodies),
while kinetic energy is the energy of movement. A stationary ball at
the top of an inclined plane has potential energy, but it displays kinetic
energy as it rolls (motion) down the incline. Stored energy in foods is
potential energy because of the position of atoms in the food molecules,
but chemical digestion of the food results in changing the potential
energy into heat, light, electricity, or energy of movement. According
to the law of the conservation of energy, it cannot be created or destroyed
but only transformed into another form. There are many examples of
this law in the living and nonliving world.

All matter, whether it be solid, liquid, or gas, is composed of atoms.
The properties of atoms and molecules are considered elsewhere and
should be reviewed.

Electrolytic Dissociation

Electrolytes (e -lek' tro lite) (Gr. elektron, amber or electricity; lutos.,
soluble) are substances which in solution are able to conduct electric cur-
rents, while those which do not are known as nonelectrolytes. For in-
stance, sodium hydroxide (NaOH) in solution has positively charged
Na ions and negatively charged OH ions. The Na atom acquires this
positive charge because it loses an electron, while the OH atom acquires
a negative charge because it gains an electron. Atoms charged in this
way are called ions. Compounds which dissociate or ionize in such a
manner are electrolytes. In general, inorganic compounds exhibit ioni-
zation to a greater extent than organic compounds. Acids, bases, and
salts are good electrolytes, while alcohols and sugars are not. Ordinary
salt (NaCl) dissociates or ionizes into a positively charged sodium ion
(Na+) and a negatively charged chlorine ion (C1-). The base, sodium
hydroxide (NaOH), dissociates in water into a positive sodium ion
(Na+) and the negative hydroxyl ion (OH-). The hydroxyl ions give
the alkaline or basic properties to the solution. In water, hydrochloric
acid (HCl) dissociates into positive hydrogen ions (H+) and negative
chlorine ions (CI—). The hydrogen ions give the acid properties to an
acid. The numbers of hydrogen ions in a solution are an index of its
acidity, and the hydrogen-ion concentration is expressed by the symbol

752 General and Applied Biology

pH. Distilled water has a pH of 7.0 or neutrality. Acids extend in pH
from 0 to 7, while bases (alkalies) extend in the scale from 7 upward.

Protoplasm is a mixture of electrolytes. The acids, bases, and salts
of the protoplasm are dissociated into ions. These substances confer
charges on any surfaces on which they accumulate. Colloidal particles,
each bearing a minute charge, may be changed as chemical reactions
take place in the protoplasm or as ionizing substances are introduced
from the outside. The effects on colloidal particles of the protoplasm
by organic and inorganic substances brought to the protoplasm may ex-
plain the reasons for the invariable variations in all living protoplasm.
The hydrogen ion acts as a catalyzer by hastening hydrolysis (double
decomposition involving water) in the digestion of foods. The pH of
human blood is slightly alkaline (about 7.4), which is of great impor-
tance in counteracting the acidity of other tissues. The body tissues,
by constantly giving carbon dioxide to the blood, produce carbonic acid
which causes only a very slight change in pH of the blood because of
the buffer action of the carbonates, phosphates, and proteins in the
blood. The carbonic acid also stimulates the respiratory centers of the
nervous system to increase respiration to eliminate the excess carbon
dioxide.

Permeability of Membranes and Osmotic Pressure

Permeability may be defined as the property of a membrane or parti-
tion that determines its penetrability. The permeability of a membrane
depends on (1) the size of the pores of the membrane, (2) the size of
the particles of the substance attempting to pass through that mem-
brane, and (3) the solubility of the substance in the membrane. A mem-
brane may be permeable to small molecules but impermeable to large
molecules (Fig. 367). Another membrane may be permeable to ions
but impermeable to even the smaller molecules. The boundary of cells
consists of fatty substances and other aqueous materials which influence
its solubility properties, which in turn, at least partially, determine its
permeability. Living membranes, such as the plasma membrane of cells,
which have a selective permeability are known as semipermeable mem-
branes. Living membranes usually permit the passage of small molecules
and certain ions, while larger molecules, like protein molecules, and
colloidal particles are restrained. Diflferent cells vary in the permeability
of their boundaries. The cells of the lining of the lung allow certain
gases to pass, while the cells of the intestine permit certain other sub-
stances to pass. Each has its specific type of permeability, and the

Biochemical and Biophysical Phenomena 753

plasma membrane of each individual cell plays an important role in
regulating the activities of the protoplasm within that cell.

The force exerted by the pressure of moving molecules in a solution
against a membrane is known as osmotic pressure. The passage of a sub-
stance through a semipermeable membrane is known as osmosis. The
measurable force within living cells is considerable and usually keeps the
cell membrane distended.

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Fig. 367. — Demonstration of osmosis in which the test-tube shaped semipermea-
ble membrane separates sugar solution and water. The pores of the membrane
are of a size that permit the passage of water molecules but not sugar molecules.
Hence, the passage of water is sufficient to cause it to rise in the upright tube.
Water molecules pass in either direction, but they pass faster into the tube than out
of it because of the greater concentration of water molecules on the outside. The
liquid will rise in the upright tube until it reaches a level at which its hydrostatic
pressure, due to its weight, is equal to the osmotic pressure produced by the sugar
solution. (From Roe: Principles of Chemistry, The C. V. Mosby Co.)

A solution with greater concentration (less water) than the proto-
plasm, and which draws water from the protoplasm of the cell, is known
as a hypertonic solution. In this case, water will pass out of the cell
in an attempt to equalize the pressure. Under such circumstances (loss
of water), animal cells will tend to shrink as a whole because of their
delicate cell membrane, while the protoplasm of plant cells shrinks away

754 General and Applied Biology

from the rather rigid, resistant cell wall. Such shrinking of protoplasm
from the cell wall or membrane during the loss of water is called plas-
molysis (Gr. plasma, form; lysis^ loose). A solution with less concentra-
tion (more water) than the protoplasm, and which places water into the
protoplasm of the cell, is known as a hypotonic solution. In this case
the addition of water to the protoplasm causes a condition known as
turgor (L. turgeo, to swell). If carried to extreme, the cell may be
destroyed. A solution which has the same concentration as the proto-
plasm and which neither withdraws nor adds water to the cell is known
as an isotonic solution. In this case pressures are equal on both sides of
the cell membrane and there is no shrinking or swelling. There can be
no passage of materials to or from a cell under such conditions. It is
quite clear that hypertonic and hypotonic solutions around a cell deter-
mine the passage of materials out of the cell and into the cell. The
securing of foods and the elimination of wastes probably are accom-
plished in this way.

Diffusion and Conduction

Diffusion may be defined as the movement of two kinds of molecules
in a solution, gas, or solid whereby the molecules of each kind tend to
be uniformly distributed in all parts of the substance. Molecules always
pass from a region of high concentration to a region of lower concen-
tration. The molecules of a gas may diffuse through another gas or
through a liquid. One liquid may diffuse through another. A solid
may dissolve and then diffuse through a liquid. A crystal of copper
sulfate in water will go into solution and then diffuse through the water
until there is a uniform distribution of copper sulfate molecules. In this
manner, by diffusion, the molecules of gases, liquids and solids taken in
through the cell membranes are made available to the protoplasm of
the entire cell.

The firmness or solidity of matter is determined by the distance
which the molecules can travel without colliding with another molecule.
In liquids the molecules are attracted and usually cannot escape from
each other because of cohesive force. The application of heat over-
comes this cohesion and the molecules escape in the vapor. Some liquids
are very volatile and vaporize easily on contact with air. Gas molecules
have no cohesion and can move freely throughout another gas.

Materials may be conducted from one cell to its neighbors, or they
may be conducted great distances. In the latter case they may be
rather quickly transported by the transporting system of the organism

Biochemical and Biophysical Phenomena 755

or by the slow process of passage from cell to cell. The phenomenon of
conduction is very essential to ensure efficient distribution of materials
to those regions where they are required or from those regions where
they are not desired. Without molecular movements in the diffusion of
substances from one part of a cell to another, the protoplasm would
soon become lifeless.

Surface Tension

Surface tension may be defined as the greater tension or attraction
between molecules on the surface of a liquid than between those beneath.
All molecules of a substance exert an enormous attraction for each other.
This property is called cohesion. In the deeper portions of a volume of
liquid each molecule is attracted by adjacent molecules with equal force
in all directions. However, on the surface of the liquid, the liquid
molecules are attracted downward by the lower molecules of the liquid
and attracted upward by the molecules of the gases of the air. The
attraction of the liquid molecules for each other is greater than the at-
traction of the gas molecules for the liquid molecules. Hence, the
attraction forces on the surface molecules of the liquid are unequal.
Equilibrium is attained only when the surface is made as small as pos-.
sible by reducing the number of liquid molecules on the surface. This
produces a tendency for the surface to occupy the least amount of space.
When a droplet of oil is immersed in water, the former will assume a
spherical shape, and the boundary, known as the interface, between the
oil and water is in a state of tension and therefore represents an equi-
librium between forces. This tendency for surfaces to contract because
of tension is known as surface tension. Naturally, surface tension differs
widely among various materials.

Any substance which reduces surface tension has a tendency to ac-
cumulate at the surface. When ether is added to water, the ether
molecules accumulate in greater numbers at the surface of the water
than elsewhere in the water. The amount of potential energy at the
surface of an ether-water mixture is much less than at the surface of
pure water. If the area of the surface of a substance is reduced, there is a
release of energy. Surface tension in living protoplasm is constantly being
reduced by the presence of fats. In protoplasm the energy relation of the
interfaces (boundaries) between the colloidal particles and their suspend-
ing medium is constantly changing. In the living process new compounds
are constantly formed, and different sorts of molecules appear and dis-

756 General and Applied Biology

appear, so that the interfaces are also constantly changing. This con-
stant change in surface tension at these interfaces is closely related with
many of the phenomena of living protoplasm.

Energy

Energy may be defined as the ability to produce change or do work.
Energy, which may be in the form of electromagnetic waves, is the unit
of the universe because the various types of matter are thought to be
merely different forms of energy. The power to do work or produce
change is a property of living protoplasm. Energy, which is involved in
all changes constantly taking place in living protoplasm, is ordinarily
measured by the amount of work or change performed. A great variety
of energies are known, the following being the more common: electrical,
chemical, radiant, mechanical, and heat. Energies may be divided into
potential and kinetic. Potential energy is the stored energy possessed by
a substance because of its position or condition. Coal and wood before
they are burned possess potential energy. Carbohydrates before they are
digested also possess potential energy. Kinetic energy is action energy,
or energy possessed by virtue of motion. Kinetic energy may become
potential, and potential energy may become kinetic. Energy required to
form a molecule of substance becomes inactive potential energy when
stored in that molecule, but it is converted into active kinetic energy
when the molecule is broken down. Energy cannot be created anew or
decreased, but, when a quantity of a certain type disappears, an exactly
equal quantity appears in some other forms.

All chemical reactions involve changes in energy distribution. Certain
chemical reactions require some form of energy, usually heat, while others
release energy in some form. When a sugar is built, energy is required;
when it is catabolized, energy is released. The construction and cata-
bolizing of other foods reveal a similar phenomenon. Both types of
reactions, those which require and those which release energy, occur in
living protoplasm. Much of the energy for heat production, muscular
action, and similar activities is the result of oxidizing foods containing
potential energies. Energy is used in joining chemical compounds to-
gether, and chemical energy is produced by the transformation of foods
containing these chemical compounds. The living protoplasm of both
animals and plants is composed of compounds so arranged as constantly
to transform potential to kinetic or other energies. This constant trans-
formation of energy requires a constant supply of potential energy in
order to exhibit the continual changes and perform work. The ultimate

Biochemical and Biophysical Phenomena 757

source of the energy of our foods produced by green chlorophyll-bearing
plants is the sun (see Radiant Energy). The energy value of a food is
measured by a unit called a calorie, which is the amount of heat required
to raise the temperature of 1 Gm. of water 1° G. One gram of fat
produces about 9 calories of heat; 1 Gm. of carbohydrate, about 4 calo-
ries; 1 Gm. of protein, about 4 calories.

Radiant Energy

Radiant energy is the energy possessed by the sun's rays. When the
electromagnetic waves of sunlight are passed through a prism, there is
produced a spectrum (L. spectrum, vision) of various wave lengths and
colors. These waves of different lengths (Fig. 368) are capable of dif-
ferent types of work and of producing a variety of phenomena. The
longer, visible waves at the red end of the visible spectrum grade through
the orange, yellow, green, and blue to the shorter, visible violet rays at

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units (A). One Angstrom unit (A) is one ten-billionth of a meter (0.000,000,-
000,1). Roentgen rays extend from 2 A to 12A; unexplored rays and x-rays from
12A to 500 A; infra-red rays extend from 8,000 A to 3, 100,000 A; unexplored rays,
31 X 105 to 160 X 105 A; radio rays, from 160 x 10^ to 120,000,000 x 10^ A.

the opposite end of the spectrum. At each end of the visible spectrum
there are no visible wave lengths or colors, but rays continue indefinitely
to become longer and longer beyond the red end, and shorter and shorter
beyond the violet end. The waves at the red end are heat rays, as are
those, known as infrared rays, just beyond the red. Those waves just
beyond the violet end are the 'mvisihle,\ltraviolet waves. Certain waves
of the visible spectrum, as well as those of the violet end, show certain
chemical activities (Fig. 368).

The chlorophyll of green plants in the presence of red, blue, and
ultraviolet waves photosynthesizes carbohydrates from carbon dioxide
and water. These waves of radiant energy split off the oxygen from the
carbon dioxide molecule, this permitting the free carbon to unite with
the water to form a carbohydrate. The free oxygen passes off into the
atmosphere. The carbohydrate can be ( 1 ) oxidized for metabolic pur-
poses, (2) stored for future use, and (3) combined with salts, especially

758 General and Applied Biology

those containing nitrogen, to form proteins. When sugars are stored,
they are changed by enzymes through a process of dehydration (loss of
water) to form starch. For example, glucose (G6H12O6), a sugar,
through the process of dehydration (loss of H2O) is changed to starch
(C6Hio05)x, where x is a very large number. The chloroplasts con-
taining the green chlorophyll are especially concentrated in the chlor-
enchyma cells of the palisade layer of plant leaves where a maximum of
light is available (Fig. 60). Iron is not a constituent of chlorophyll,
but it must be present in the presence of light in order for chlorophyll
to be formed. The visible green color of chlorophyll is due to the ab-
sorption of certain light rays (Fig. 368) in the red, blue, and violet
regions, with the transmission to our eyes of the remaining rays which
give us the characteristic leaf-green color. The absorption of these
specific rays by the chlorophyll explains the ability of green plants to
manufacture foods. Certain lower plants as the blue-green, the brown,
and the red algae, as well as such higher plants as the coleus and red
cabbage, possess other pigments which may mask the chlorophyll, which
is nevertheless present in them. These phenomena are considered in
greater detail in other chapters.

Plant and Animal Colorations

The ability quickly to change color and shades in animals in response
to external stimuli is usually confined to reptiles, amphibia, fishes, Crus-
tacea, and cephalopod Mollusca. Pigments are produced by cells known
as chromatophores, which may function as single cells or as groups of
cells (Fig. 209). In fishes the chromatophores are rather large and star
shaped, and with a small central disk with repeatedly subdividing
branches which radiate from the center. The four types of chromoto-
phores which have been most extensively studied are: (1) Melanophores
(Or. melan, black; phoros, to bear), containing the black pigment
melanin. The granules of melanin can be dispersed in cells by ether or
dilute solutions of sodium chloride and can be aggregated by adrenalin
or potassium chloride. (2) Xanthophores (Gr. xanthos, yellow; phoros,
to bear) containing the yellow carotinoid pigment xanthophyll. The
amount of xanthophyll in certain fishes, at least, depends upon the type
of plant food. (3) Erythrophores (Gr. erythros, red; phoros, to bear),
containing the red carotinoid pioment. (4) Guanophores, containing
white crystals of guanin.

In each type of chromatophore an external stimulus causes a move-
ment of the pigment within the cell. When a fish becomes paler, the

Biochemical and Biophysical Phenomena 759

melanin pigment granules move centripetally and concentrate in a small
area in the center of the cell. When that fish becomes darker, the
melanin pigments move centrifugally and fill the branches of each cell
to increase the blackness of the skin. This transition from one shade to
another may occur in a few minutes. The other chromatophores un-
dergo similar phenomena. Stimuli which produce changes as described
above usually include chemical, mechanical, thermal, or photic. In
fishes the melanophores and xanthophores are controlled by the termi-
nation of different peripheral nerves of the autonomic nervous system
so as to function independently. Hormones in the secretions from duct-
less glands of the fish supplement this nervous control. In amphibia the
chromatophores (Fig. 209) are controlled by the secretions in the blood
produced by the hypophysis (ductless gland). In reptiles the chroma-
tophores arc controlled directly by the nervous system supplemented by
the secretion of the medulla of the adrenal gland (ductless gland).
When a fish is placed on a yellow background, it assumes a quite dif-
ferent color from a similar fish placed on a gray background. The wave
lengths of the light reflected from these backgrounds are influential fac-
tors in this behavior. This light-reflecting capacity of the surroundings,
regardless of the degree of illumination, is the important factor. For
example, a dull black surface placed in direct sunlight causes a fish to
be black, while a white surface in diflfuse light causes it to be pale.
Recent research also suggests that fishes have a somewhat limited color
vision. Many of the colors of plants and plant pigments arc considered
in detail in another chapter.

Coloration in plants and animals may be due not only to the absorp-
tion of certain waves of light by pigments or other substances, but also
to the interference of light. A certain type of interference known as
refraction (L. re, back; frango, to bend) is caused by the bending of
rays of light as they come to our eyes with the result that a variety of
colors is produced. Another type of interference known as diffraction
(L. dis, apart; frango, to break or bend) is caused by the separation of
light into parts which produces a variety of color sensations on our eyes.
The metallic blue color of the tropical butterfly (Morpho sp.) is due to
the interference of light. The bright colors on the neck of a humming-
bird are due to interference, while those on the body are due to absorp-
tion of fight. Colorations due primarily to absorption are those of cer-
tain moths and butterflies, the skin pigments of vertebrates, the feathers
of many birds, and the hemoglobin of the red blood corpuscles.

760 General and Applied Biology

Not all the functions of colorations in plants and animals are known.
The complex color-producing mechanism of an animal renders that
animal less conspicuous and less likely to be destroyed because of its
''protective coloration." When pigments are located on or near the sur-
face, they are usually protective for the sensitive tissues beneath by ab-
sorbing certain light waves. Pigments which line the visceral cavity or
cover certain nerves of animals also may protect. Albinism (absence of
pigment) causes an organism to be very sensitive to light. Human albinos,
and even blonds, are more sensitive to light than darker-skinned persons.
People in the tropics are heavily pigmented, naturally, or acquire pro-
tective pigments in the form of heavy tan. "Freckles" in the human
skin are due to the increase in the pigments naturally present when
stimulated by light. The interesting and complicated phenomena of the
coloration of autumnal leaves have been considered in detail elsewhere.

Production and Use of Heat

When any kind of energy is released, there is an accompanying for-
mation of more or less heat. In some instances this heat may be used
to regulate chemical activities or control the body temperature, while in
others the heat is a waste product which is no longer of use to the or-
ganism. In the formation of certain chemical compounds, there is often
some heat produced. In some instances, such as the spontaneous com-
bustion of hay, the amount of heat produced is sufficiently great to start
a fire. In the destruction of chemical compounds, usually by oxidation,
there is liberated a certain quantity of heat. For example, the oxidation
of such foods as carbohydrates, fats, and proteins releases heat for use
by the living organism.

A living organism which generates large quantities of heat through
its activities is frequently not very efficient. In such cases much more
heat is liberated than is required by that organism. A plant is much
more efficient in this respect than animals generally are. Most of the
heat acquired by plants is absorbed from the surroundings, and much of
it is lost by transpiration. So-called cold-blooded animals attempt to
maintain a body temperature somewhat similar to that of their environ-
ment, while warm-blooded animals generate and conserve their heat so
as to maintain a rather constant temperature throughout life, regardless
of the environment. Animals lose heat (1) by conducting it to other
objects, (2) by radiating it, (3) by losing it through their feces and
urine, (4) by the process of evaporation from the lungs and the sweat
glands of the skin.

Biochemical and Biophysical Phenomena 761

All energy eventually tends to be resolved into heat which cannot be
resolved in turn into other energies. Consequently, the energy of the
sun is constantly required to replace that which has become a useless
waste. Animals to a limited extent, and green plants to a great extent,
depend on the sun for this supply of heat. From these green plants
this heat is transferred to animals. Kinetic energy usually produces
heat. For example, a moving body encounters more or less friction and
consequently causes a certain amount of heat to be produced. Potential
energy may possess large quantities of latent heat which must be liber-
ated in some manner or other before they are available.

Production and Reception of Sound

The vibration of some sounding body produces sound waves which
are borne to, and interpreted by, a specialized organ, such as the ear of
higher animals. The plants and lower animals do not produce sounds
in the accepted sense, although they may be affected by sound waves in
certain instances. In several higher animals sounds are produced and
interpreted in some manner. Almost every insect which has sound
receiving mechanisms also has sound producing (stridulating) organs.
In the common locust there are two types of stridulation. When at rest,
certain species draw the femoral joint of the hind leg across a specialized
vein of the wing cover to produce sound. When flying, they produce a
crackling sound by rubbing wings and wing covers together. Tympanic
membranes connected by nerves to the nervous system are assumed to
be auditory organs. The female mosquito produces a characteristic
sound by vibrating her wings 512 times per second. In male mosquitoes
the hairs on the antenna are auditory. The hairs are adjusted during
flight so that the two plumelike antennae are stimulated equally by the
wing sounds produced by the female, thus directing the male toward
the female. In the cicada the male has a pair of large, ridged, parch-
mentlike drumheads on the first abdominal segment beneath the wings.
The drumheads are vibrated by a pair of muscles. A pair of cavities
within the body act as resonators for the sounds produced. The female
cicada has no sound-producing or sound-receiving apparatus. In the
katydid the stridulating organs consist of a rough file and a scraper on
the wing covers. The sound-receiving apparatus consists of a series of
tympanic chambers with membranous tympana. The latter pick up the
sound vibrations (chirp) and transmit them to the nervous system. The
chambers intensify the sounds. The honeybee produces its humming
sound by moving its wings 190 times per second. The housefly produces

762 General and Applied Biology

its buzzing sound by completing 330 wing strokes per second. Many
insects, especially those with heavy, chitinous exoskeletons, possess spines
and hairs attached to nerves by means of which they recognize or "feel"
sound vibrations.

In lower fishes the ear is primarily affected by stimuli produced by
changes in the position of the fish. Hence, such fishes maintain a typical
position with respect to their surroundings. Well-developed vocal cords
and organs of hearing appear only in terrestrial vertebrates. Eardrums
and vocal cords are not present in fishes. Amphibia (frogs, toads) have
the simplest of vocal cords. It seems that the developments of sound-
production and sound-reception mechanisms go together and that they
are rather closely correlated. Male and female frogs (Rana pipiens)
produce different kinds of croaking sounds by forcing air back and forth
from the mouth cavity and lungs across their vocal cords. Frogs produce
a "pain scream" when caught, a "grunting" sound when satisfied, an
"alarm cry" to tell others to seek safety. In the ears of higher vertebrates
(Fig. 250) the semicircular canals function as an organ of equilibrium,
while the cochlea ("snail shell") receives sound waves and sends them
over the auditory nerve to the brain. The human vocal apparatus and
ears are described elsewhere.

Bioluminescence and Light

Bioluminescence may be defined as the phenomenon of light produc-
tion by living organisms apart from incandescence (light with heat).
Light may be defined as the form of radiant energy, the waves of which
act on the eye so as to render visible the object from which the light
comes. Light waves travel approximately 186,000 miles per second.
Bioluminescent light is known as cold light because only 1 per cent is
invisible heat rays. This is the most efficient light known. Luminous
cells of plants and animals secrete granules containing luciferin, which
glows in the presence of oxygen when activated by the enzyme lucijerase.
Luminescence is displayed by such animals as the firefly (beetle), the
glowworm, certain squids and fishes, certain jellyfishes and shrimp, cer-
tain species of Protozoa, etc. In the firefly, photogenic organs containing
localized masses of fatty substances produce a very efficient light by
oxidizing the fatty substances. The photogenic organs are well supplied
with oxygen by a copious supply of tracheal tubes. The greenish-yellow
light has few nonluminous rays. Its emission appears to be controlled by
the nervous system by regulating the oxygen supply. These photogenic
organs are associated with sexual attraction, the female generally produc-

Biochemical and Biophysical Phenomena 763

ing flashes of longer duration. In the luminous squids and fishes there are
luminous organs, perfect lenses, and reflectors to reflect the glow. In the
jellyfish {Pelagia noctiluca) the entire surface of the umbrella is covered
with glowing granules. In the minute protozoan {Noctiluca miliaris) the
luminous granules remain inside the cell. The shrimp emits the luminous
granules into the water. Among the plants, certain putrefactive bacteria
and special types of mushrooms emit a limited amount of luminescence.
Luminous bacteria are frequently found on fish and ham, where they
emit rather large quantities of light if the food and oxygen requirements
are satisfactory.

Light afTects animals in several ways. The protozoan, Euglena (Fig.
173), has a light-sensitive substance localized in a visible pink spot
(stigma) near the reservoir. This mechanism directs the Euglena into
the proper light for its metabolic activities. The earthworm has no
eyes, yet it moves away from light. This is due to the presence of light-
sensitive cells near the surface. The starfish locomotion is influenced by
light. Protozoa, Planaria, clams, snails, and certain Crustacea are also
influenced by it. The simple eyes of insects and spiders are influenced by
light intensities. The compound eye of arthropods is constructed like a
bundle of hollow tubes arranged in the form of a cone. The tubes are
isolated from each other by black pigment, and together they produce-
an upright but reduced image of the object being viewed. The outer
end of each tube contains a lens and a facet which is easily seen on the
surface of the compound eye. The inner ends of these tubes possess
light-sensitive materials connected with the nerves. These compound
eyes also give the organism an interpretation of movement of objects.
The eyes of vertebrates (Fig. 248) act somewhat like a camera. The
lens focuses and forms an image on the retina. A black pigment inside
the eyeball is present for the same reason as in a camera. The retina
consists of enormous numbers of nerve cells, each with a chemical mate-
rial which is temporarily changed by light. Each temporary image on
the retina produces chemical changes in the nerve cells varying with
the quantity of light on each cell. These chemical changes stimulate
other nerve cells which send impulses over the optic nerve to the brain.

In plants, leaves arrange themselves to get a maximum of light. Sun-
light supphes the energy for the chlorophyll of green plants to combine
carbon dioxide and water to form carbohydrates through the process of
photosynthesis. This process is described in detail in other parts of the
book. Parts of plants react to light in diff'erent ways. Stems bend
toward light, changing direction with the source of light. Roots bend

764 General and Applied Biology

away from light, while leaf stalks bend so that the leaves secure the
necessary amount of light. This bending is due to the unequal amount
of growth on opposite sides of the stem or root. Light, gravity, and
contacts may influence this unequal growth. Possibly, all living proto-
plasm is affected by light to a greater or lesser extent, depending upon
its degree of complexity.

Bioelectric Phenomena

Many recent experiments have tended to prove that a number of
biologic phenomena are associated with electricity. When an acid col-
loid is separated from an alkaline colloid by a semipermeable, dielectric
membrane or film, there is formed an electric cell within which an elec-
tric potential exists between the acid-positive nucleus and the alkaline-
negative cytoplasm. The thin lipoid films surrounding the nucleus and
cytoplasm ofTer definite resistance to positive hydrogen ions, while in
death this resistance is lowered. The maintenance of the acid-alkali
balance between the nucleus and cytoplasm of cells (the electric poten-
tial) is essential to life and furnishes the energy of the living processes.
The reduction of it to equilibrium (zero) results in death. The vital
potential in cells is due to oxidation, and this oxidation in turn is gov-
erned by the electric potential acting as a physical catalyst within the
cell. Hence, we have the source and a controlling factor of the elec-
trical phenomena associated with cells. Because of its high rate of
oxidation, the comparatively acid nucleus supplies vital force in the
form of electrical energy. Because of its higher electric potential (ten-
sion), the nucleus sends interrupted currents toward the cytoplasm, the
currents following each other in rapid succession. As the electric poten-
tial of the nucleus increases, the current breaks through the nuclear
membrane; the potential of the nucleus then falls and the current stops
momentarily; oxidation immediately restores the potential in the nucleus
with another discharge into the cytoplasm, which explains the inter-
rupted currents passing from the positive nucleus to the negative cyto-
plasm as well as the accumulated charges on the surface of the mem-
branes. The nuclear membrane and the plasma membrane are both
lipoid films, semipermeable, exquisitely thin, and with high dielectric
(nonconductive) capacities. The thinner this lipoid film, the higher the
electric charge or capacity.

Water is an important catalyst and has an extremely high dielectric
constant. Water holds an infinite variety of substances in solution and

Biochemical and Biophysical Phenomena 765

suspension in protoplasm. Many of these substances are easily ionized
to initiate the electrical phenomena of living materials. Electrolytic
solutions and colloids make up a bulk of protoplasm and are especially
adapted to electrochemical processes. Carbohydrates are important
sources of hydrogen ions which are released by oxidation. These hy-
drogen ions permeate all living matter and are of great significance in
the electrical phenomena displayed by living protoplasm.

Just as the parts of the cell are positive and negative, so there are
certain tissues and organs w^hich are positive and negative. The so-
called positive tissues are made of cells which possess greater oxidative
capacities (hence, higher temperatures) and higher electrical potentials
than the so-called negative tissues. The brain is a positive organ and
the liver is considered as a negative according to recent experimental
evidence. Consequently, the brain and liver may be considered as work-
ing together. The electric conductivity of the brain and liver varies in
opposite directions. The removal of one quite naturally aflfects the
other. The removal of the liver (negative pole) causes the brain (posi-
tive pole) to lose its potential and cease to function. When the circuit
between the brain and liver is broken, the lipoid membranes, the inter-
facial surfaces between colloids, and the interfaces in proteins no longer
receive electrical charges upon which their structures and functions
depend. Coagulation and death result. Minor electric circuits, similar
to that described above, carry on the activities of muscles, nerves, glands,
and similar tissues. If a battery works continuously by keeping its cir-
cuit closed, its plates are polarized, which means that the difference in
potential is diminished or disappears. Hence, the battery is exhausted.
In a similar manner, continued use of cells and organs without a period
of rest will lead to exhaustion and probable death. If the work period
(passage of electric current) is short, as in a single heartbeat, the
degree of polarization is quite small. The smaller the degree of polari-
zation, the shorter the time required for depolarization through rest.
Salivary glands, the stomach, and intestines have alternate periods of
work (polarization) and rest (depolarization). The theory regarding
the transmission of nerve impulses has been considered earlier in the text.

In order to operate efficiently a bipolar organism through the main-
tenance of an optimum difference of electrical potential, the following
are essential: (1) to have an abundant water supply, (2) to have an
abundant oxygen supply, (3) to maintain the semipermeability of the
lipoid membranes of the cells, (4) to maintain an optimum temperature,

766 General and Applied Biology

(5) to ensure sufficiently long and frequent periods of rest for depolari-
zation purposes, and (6) to maintain the integrity of the poles of the
organism.

In the light of the discussion above, there would appear to be greater
or lesser quantities of electricity in all animals. In the fishes of certain
species there are modified muscle cells which are arranged in series to
serve as electric organs. In such organs the electricity is produced,
stored, and discharged into the surrounding water for offensive and
defensive purposes. In these electric organs the positive pole of one cell
is arranged against the negative pole of the next, so that the voltage
produced is determined by the number of cells arranged in the series.

Burdon-Sanderson in 1882 and Waller in 1913 demonstrated that such
motor plants as the sensitive plant and Venus's-fly trap display electric
variations during their specific response to stimuli. These electric action
currents are also known as "blaze" currents and are accompanied by a
temporary increase in the permeability of the plasma membranes of the
cells. Bose in 1907 stated that electrical phenomena attend the activi-
ties of plants.

Enzymes

An enzyme (Gr. enzymos, ferment) may be defined as a complex,
organic, catalytically active substance produced by living protoplasm, the
action of which is independent of the life processes of the protoplasm.
An enzyme is a chemical colloid, usually proteinlike, although the chemi-
cal formula has been determined for only a few of them. The numer-
ous enzymes act as catalyzers (activators) in chemical reactions but ap-
parently are not used up in the reactions. Enzymes play important roles
in the life processes of all cells, including the bacteria as well as the cells
of higher organisms. They were formerly called ferments which explains
their being named enzymes. Enzymes are usually named by adding the
suffix -ase to the name of the substance acted upon. For example, mal-
tase acts on maltose, lactase on lactose, and protease on proteins. The
total number of enzymes is as great as the number of different chemical
substances that are acted upon. The substance acted on by an enzyme
is called the substrate. The product formed by the action of the enzyme
on the substrate is unstable because the enzyme is released unchanged, to
be used over and over again. However, the amount of substrate which
may be affected is not infinite as is true of a catalyst. By doubling the
quantity of an enzyme, we reduce the time required for a reaction by

Biochemical and Biophysical Phenomena 767

approximately one-half, because each particle of enzyme repeats the
same type of work over and over. Enzymes are specific in their action,
each one causing a specific chemical change upon one substrate. Only
a small quantity of an enzyme is required to produce a specific reaction.
Many enzymes are produced in an inactive condition, known as pro-
enzymes, which are changed into an active condition by such activators
as acids, alkalis,, or electrolytes. The number of different enzymes pro-
duced by the protoplasm of even one cell is probably quite large because
the variety of reactions in such a cell is quite great. Enzymes are indis-
pensable for all metabolic activities. Only a few of the more common
enzymes with their functions will suffice to illustrate their general distri-
bution. The various stages in the process of food digestion are depend-
ent upon specific enzymes. The ripening and over-ripening of fruits are
due to specific enzymes. Autolytic enzymes normally present in animal
tissues sometimes cause the spoilage of meats in storage. Certain enzymes
are responsible for specific effects in the preparation of foods, such as
bread, butter, cheese, sauerkraut, etc. Industrially, enzymes are used in
manufacturing alcohol, acetic acid, and lactic acid, etc. Enzymes in the
liver change glucose into glycogen which is stored in the liver. Another
enzyme changes unusable glycogen into usuable glucose again. The
enzyme luciferase oxidizes luciferin, which is the photogenic material in
certain animals, such as the firefly.

Plant and Animal Hormones, Including the Ductless (Endocrine)
Gland Secretions

A hormone (Gr. hormao, to excite) is a chemical substance which in-
creases activity, while a chalone (Gr. chalinas, to curb) diminishes or re-
tards activity. Hormones differ from enzymes in that they take part in
the reaction and are consequently used up. In this case they must be
replaced. Hormones are produced in one part of the body and carried
to other parts of the body where they produce specific structural or
functional changes. Since these secretions do not travel in special ducts
to their ultimate destination, they are known as ductless gland secre-
tions. They are also known as endocrine secretions (Gr. endon, within;
krino, separate). They are summarized in the chapter on Biology of
Man.

The activities and characteristics of animal hormones have been known
for some time, but only recently have data been secured for plant hor-
mones. Growth hormones in plants are normally found in all rapidly

768 General and Applied Biology

growing regions of the tip of roots and stems from which they are trans-
ferred to the growing areas to promote cell elongation and possibly
mitosis. When plants are stimulated by light coming from one direction,
the o-rowth hormones flow down the shaded side and decrease on the
lighted side. Thus the growth is hastened on the shaded side and
retarded on the lighted side. The light displaces the specific hormone
toward the shaded side but does not enter into its formation. It is sug-
gested that light changes the electrical potential, the shaded side being
the positive side electrically. Since these growth hormones are acid, they
would be displaced toward the positive (shaded) side. The respective
growth of stems toward light and of roots away from light may be ex-
plained at least partially on this basis.

Certain hormones in plants conduct stimuli from one part of a plant
to another. This is known as the hormone theory of conduction. These
hormones are of great importance in the correlation phenomena in plants.
Plant hormones might be defined as chemical substances naturally pro-
duced in minute quantities in certain regions of the plant and either
stored or transported to other regions to regulate the growth, develop-
ment, or reactions of that organism. The tropic responses of plants to
light and gravity are definitely associated with specific hormones. Sev-
eral diflferent plant hormones have been isolated, such as auxin A, auxin
B, and heteroauxin. These are considered in detail in another chapter.
Another plant hormone, traumatin (Gr. trauma, wound), seems to initi-
ate and influence healing of plant wounds. Plant hormones are trans-
ported (1) by diflfusion, (2) by protoplasmic streaming, (3) by plant
circulatory systems if they are present, and (4) by electrical phenomena
by which they are moved toward a positively charged area because of
changes in electrical potential within the plant. A plant hormone
(indole-3-acetic acid) produces a tumorlike growth in certain plant tis-
sues. In spite of the fact that plant hormones can be isolated from
plants, we have no chemical test which provides a simple and efficient
means of qualitative and quantitative detection of minute amounts of
them in living plants. However, certain physiologic methods are now
used to determine their concentration.

Many data have been collected in connection with hormones in higher
animals. Hormonelike substances are present at the nerve endings of
nerve fibers in vertebrates, where they may transfer impulses from nerve
endings across synapses to responding tissues. Recent data associate hor-
mones with the conduction of impulses in nerves. Recent experiments

Biochemical and Biophysical Phenomena 769

have demonstrated the presence of organic hormones In such inverte-
brate animals as insects, worms, crustaceans, cephalopods, etc. It is be-
lieved that invertebrates produce certain hormones, many of which
resemble those of the vertebrate animals, whose functions approximate
those of higher animals.

Vitamins

The definite chemical composition of certain vitamins is now fairly
well established. Certain vitamins are rather unstable, especially when
subjected to heat, oxygen, or light. Vitamins may be present in all
living protoplasm in minute amounts, but in larger quantities they are

Fig. 369. — Effect of vitamin A on the growth of young white rats. These two
rats, from the same htter, received the same food except that the one on the left
had its allowance of vitamin A reduced. (Courtesy of Parke, Davis and Co.)

Fig. 370. — Xerophthalmia, an eye disease caused by a dietary deficiency of
vitamin A. The eye becomes dry and a layer of horny tissue forms upon the
cornea. (From Harris: Vitamins in Theory and Practice, 1935. Courtesy of the
Cambridge University Press and The Macmillan Company.)

770 General and Applied Biology '

present principally in certain plants and plant products. Animals and
animal products may have certain types in rather large amounts. The
chief source of vitamins for animals is plants. DifTerent plant and ani-
mal foods vary in the types and quantities of vitamins present, some
being rich in certain vitamins and poor in others. Although their spe-
cific method of action is unknown, minute amounts of them probably
act much like enzymes or catalyzers.

Fig. 371. — Polyneuritis, a dietary disease of animals due to vitamin Bi de-
ficiency. Above is a pigeon with a characteristic symptom, while below is the
same pigeon a few hours after administration of vitamin Bi. The disease result-
ing from this dietary deficiency in man is called beriberi. (From Plimmer:
Vitamins and the Choice of Food, Longmans, Green & Co.)

The first important experiments in search of vitamins were made by
Lunin, in 1888, in Switzerland. He fed mice synthetic foodstuffs iso-
lated, or prepared, in the laboratory by chemical methods. This diet
contained proteins, fats, carbohydrates, and inorganic salts in the quan-
tities which Lunin thought were present in milk. When fed on this

Biochemical and Biophysical Phenomena 771

diet, the mice died. However, when milk was added to the prepared
diet, the animals lived. Lunin concluded that milk contained an un-
known substance which must be present in a diet to maintain life.

In 1913, McCollum and Davis and Osborne and Mendel independ-
ently announced results of experiments showing that there is a sub-
stance in butterfat which promotes the growth and well-being of rats.
Thus was discovered a fat-soluble dietary substance which is essential
for satisfactory animal nutrition. The substance was first known as

Fig. 372. — Pellagra, which means "skin seizure," is a dietary disease of man
caused by the deficiency of nicotinic acid (niacin) (of the vitamin B complex).
Skin lesions are characteristic of pellagra, in addition to diarrhea, anemia, and
lesions in the central nervous system producing mental confusion, dementia, and
mania. (From Stitt: Diagnostics and Treatment of Tropical Diseases. Courtesy
of P. Blakiston's Son & Co.)

772 General and Applied Biology

"fat-soluble A" factor and is now called vitamin A (Fig. 369). A char-
acteristic function of vitamin A is the maintenance of a normal con-
dition of the eyes. A dietary deficiency of vitamin A produces a con-
dition known as night blindness (inability to see well in dim light).
Further deficiency of vitamin A results in a severe disease called xeroph-
thalmia (Fig. 370) which will result in real blindness if the diet is not
corrected.

A dietary deficiency of vitamin Bi causes a loss of appetite, diminished
digestive secretions, muscular atrophy, lesions in the central nervous sys-
tem, and finally paralysis. This disease in man is called beriberi, and in
other animals polyneuritis (Fig. 371) .

A dietary deficiency of nicotinic acid (niacin) (of the vitamin B com-
plex) causes pellagra ("skin seizure") in man, with characteristic
skin lesions (Fig. 372), diarrhea, anemia, and lesions of the central nerv-
ous system which result in confusion, dementia, and mania. Pellagra
is quite common in southern United States. A similar dietary disease
called "black tongue" occurs in dogs. For a summary of the more com-
mon vitamins, consult the chapter on the Biology of Man.

Toxins, Split Proteins, Antibodies, and Hypersensitiveness (Allergies)

Real toxins are proteinlike substances of unknown chemical composi-
tion produced by the metabolic activities of the living protoplasm of
certain bacteria. Split proteins are produced by the decomposition
(probably enzymatic) of nonliving proteins or by the death and subse-
quent decomposition of any kind of bacterial cell. Real toxins stimu-
late the tissues of animal bodies to form specific chemical substances
known as antibodies (antitoxins) which act specifically on the toxins in
question. Split proteins do not excite the formation of antibodies, al-
though they may institute a type of tolerance with no definite immunity.
Toxins are specific in that they have a chemical affinity for certain cells
or tissues on which they produce specific eflfects. Toxins are usually
quite injurious. One-millionth of a cubic centimeter of botulism toxin
kills a guinea pig weighing 250 grams in a rather short time. Such
bacteria as diphtheria, tetanus, botulism, and gas gangrene organisms
produce true toxins. Bacterial toxins prevent body cells from using
foods in a normal manner, or they may destroy the cells because of the
irritating eff'ects of chemical constituents of the toxin. Toxins do not
attack tissues as readily when the latter are well nourished, not over-
worked, and subjected to normal temperatures. A protein may be a
perfectly good material, but, when split into smaller particles of pro-
teins, the latter may become quite poisonous.

Biochemical and Biophysical Phenomena 773

Antibodies are specific chemical substances produced by animal tis-
sues when stimulated by specific proteins. For example^ diphtheria anti-
toxins are produced by a horse when injected with diphtheria toxin.
These diphtheria antitoxins when introduced into a patient act only on
diphtheria toxins and not on any other type of toxin, even though it
may be present. Antibodies may be formed in several places but espe-
cially in the bone marrow, lymph glands, and spleen. Antibodies do not
act directly on bacterial cells. Certain white blood corpuscles, known
as phagocytes (Gr. phagein, to eat), actually ingest bacteria and destroy
them. This occurs when a sufficient amount of a substance known as
an opsonin is present (Gr. opsonin, to prepare for). The chemical com-
position of opsonins is unknown. Various antibodies are also considered
in the chapter on Biology of Man.

The phenomenon of hypersensitiveness (increased sensitiveness) is
probably quite common in living organisms. Most, if not all, of these
phenomena are hypersensitiveness on the part of animal protoplasms to
protein materials. Their chemical compositions are not exactly known.
The susceptibility of an individual to a certain protein material depends
on the permeability of the cell membranes of his body to these protein
materials. One person may have a type of cell membrane which pre-
vents the entrance of a particular protein substance, while another indi-
vidual may have cell membranes which permit their entrance. The
former would be immune from attacks by that type of substance but
might readily be attacked by a different protein material. It is well
known that certain foreign proteins when taken into the body in certain
states may create a characteristic reaction. These protein materials
may be simple proteins which occur naturally, such as plant pollens, or
they may be simple proteins which have been produced by the incom-
plete digestion of more complex proteins. Our reactions to eggs, milk,
strawberries, and similar foods may be of the latter class. Several terms
have been applied to such phenomena. Anaphylaxis is applied to acute
conditions of hypersensitivity. Allergy (Fig. 256) is applied to the less
fatal hypersensitive reactions in man.

QUESTIONS AND TOPICS

1. Discuss the specific interrelationships of biology, chemistry, and physics, in-
cluding several examples in detail.

2. Define each of the terms Hsted in this chapter.

3. State the law of the conservation of energy.

4. Explain the roles of electrolytes in living protoplasm.

5. Discuss the permeability of membranes and osmotic pressure as they pertain
in living protoplasm.

774 General and Applied Biology

6. Contrast and give examples of each: hypertonic and hypotonic solutions,
turgor and plasmolysis, potential and kinetic energy, melanophore, xantho-
phore, erythrophore, and guanophore, refraction and diffraction, luciferin and
luciferase, hormone, vitamin, and enzyme, toxin and antitoxin, phagocytes and
opsonins, anaphylaxis and allergy.

7. Explain the structure and functions of atoms as they pertain to certain phe-
nomena in living organs, including specific examples to prove your points.

8. Review the physical and chemical properties of living protoplasm (discussed
in earlier chapters).

9. Explain each of the various types of energy transformations encountered in liv-
ing animals and plants.

10. Explain the electrical phenomena present in living organism, including the
probable causes and effects of each.

11. Discuss the statement that "the ultimate source of energy of living organisms
is the sun," including examples to prove your contentions.

12. Discuss the causes and effects of colorations in plants and animals, including
examples of each type.

13. Discuss the production and the effects of light in the living world.

14. Outline an experiment whereby you would attempt to discover the way in
which bioluminescence is produced by a particular living organism.

15. List as many specific enzymes as possible in plants and animals, including
their origin, functions, etc.

16. Make a list of the vitamins, including sources, functions, etc., of each.

17. Discuss hormones in ( 1 ) plants, (2) invertebrate animals, and (3) vertebrate
animals. (Read additional references.)

SELECTED REFERENCES

Avery: Hormones and Horticulture, McGraw-Hill Book Co., Inc.

Barrows: Biological Actions of Sex Hormon'es, Cambridge University Press.

Beutner: Physical Chemistry of Living Tissues and Life Processes, Williams &
Wilkins Co.

Boysen-Jensen: Growth Hormones in Plants, McGraw-Hill Book Co., Inc.

Brown: Hormones in Crustaceans, Academic Press, Inc.

Cott: Adaptive Coloration in Animals, Oxford University Press.

Davson and Danielli: The Permeability of Natural Membranes, The Macmillan
Co.

Eddy: Vitaminology, Williams & Wilkins Co.

Gaynor: Pocket Encyclopedia of Atomic Energy, Philosophical Library, Pub-
lishers,

Hanstrom: Hormones in Invertebrates, Oxford University Press.

Harrow: Textbook of Biochemistry, W. B. Saunders Co.

Harvey: Living Light, Princeton University Press.

Hoskins: The Tides of Life, the Endocrine Glands, W. W. Norton & Co., Inc.

Howard-Jones: Applied Biophysics, Chemical Publishing Co.

Lotka: Elements of Physical Biology, Williams & Wilkins Co.

Meyer and .\nderson: Plant Physiology, D. Van Nostrand Co., Inc.

Mitchell: Textbook of Biochemistry, McGraw-Hill Book Co., Inc.

Scharrer: Hormones in Insects, Academic Press.

Schmidt and Allen: Fundamentals of Biochemistry, McGraw-Hill Book Co., Inc.

Selye: Textbook of Endocrinology, L'niversity of Montreal Press.

Sherman and Smith: The Vitamins, American Chemical Society.

Solomon: Why Smash Atoms? Harvard L'niversity Press.

Stuhlman: Introduction to Biophysics, John Wiley & Sons, Inc.

Turner: Endocrinology, W. B. Saunders Co.

Chapter 38
APPLIED BIOLOGY

After reading as far as this chapter, the reader undoubtedly will see
for himself many of the numerous applications of biology in the various
fields of endeavor. To cover this important topic properly would require
much more space than can be devoted in one short chapter. It must
suffice to point out only a few of the ways in which an application of
biology has been made in the world about us. The majority of the appli-
cations will be left to the reader who with some reflection and investiga-
tion can easily add to the list. For more detailed discussions of certain
phases of applications, the reader is directed to additional references, as
well as such chapters as The Economic Importance of Animals and The
Economic Importance of Plants.

I. BIOLOGY AND ITS RELATION TO AGRICULTURE
AND HYDROPONICS

For many years man has utilized the animals and plants he has found
in Nature, and in some instances he has improved and domesticated them
so that they might better serve his needs. His earlier attempts in this
connection were necessarily somewhat crude and unscientific. With the
advent of scientific biology, he has made more successful progress, so
that today the securing of most of our foods, fuels, clothing, shelter,
furniture, and raw materials for many industries are in some way or an-
other directly or indirectly influenced and made possible by what we
have found through a study of biology.

Agriculture rests upon the knowledge of the structure, functions, in-
heritance, and development of domesticated plants and animals and of
the great variety of environmental factors by which they are beneficially
or detrimentally affected. Biology in no small measure has contributed
to each of these phases and consequently has helped to make agricul-
ture what it is today.

Biology, together with other sciences, has given practical and basic
methods in many other fields. The improvement of the qualities of

775

776 General and Applied Biology

plants and animals by the proper selection of seeds and parents has made
possible better offspring. The production of new kinds of animals and
plants has been possible by crossing or hybridization which has been
based upon the knowledge of heredity. The increase in the quantities
of animals and plants has been made possible as the result of biologic
investigation. Methods of controlling many parasites of plants and ani-
mals have been evolved by biologic investigation. Many improvements
in the proper cultivation and care of soils have also had their biologic
foundation and origin. Biology has also contributed in the prevention
and treatment of many plant and animal diseases. Plant and animal
foods have also been more perfectly preserved and more efficiently trans-
ported. Biology and chemistry have made it possible to use more com-
pletely and efficiently the by-products of animal and plant products
which originally were wastefuUy discarded.

Hydroponics (hi dro -pon' iks) (Gr. hydor, water; ponos, exertion) is
a procedure in which plants are grown in solution cultures or sand cul-
tures. The solutions used in hydroponics must have the essential elements
required for the specific plants and in proper proportions. If, however,
the nutrient requirements of plants are to be ascertained experimentally,
the solutions may be made accordingly. Much of the information secured
regarding the relative importance of various elements for plant growth
has been secured through experiments with solution and sand cultures.
Commercially, the process of hydroponics has been used successfully but
on a large, scale would be expensive and might not warrant the extra
efforts and expense required. The elements which have been proved to
have some physiologic importance in green plants include magnesium,
nitrogen, sulfur, phosphorus, calcium, potassium, iron, boron, manganese,
zinc, and copper. The importance of various amounts of these essential
elements and the effects of their deficiencies are too extensive to be con-
sidered here. The reader is referred to texts on botany, plant physiol-
ogy, etc. "Water farming" or aquiculture when performed experi-
mentally has given much \aluable information as to plant requirements.
Biology has made many valuable contributions in fish propogation, oyster
cultivation, etc.

II. BIOLOGY AND ITS RELATION TO FOODS,
CLOTHING, FURNITURE, AND FUELS

Most of our foods, clothing, shelter, and fuels and much of our wealth
are all directly or indirectly influenced in some way by the proper and
effective application of a knowledge of biology. Most of our foods are

Applied Biology 111

either plant or animal in 'origin. We eat plants and animals, the latter
depending on plants or other animals for their foods. The production,
transportation, proper preparation, and efficient use of foods have all
been materially affected by increased knowledge of biology. Through
animal experimentation, the vitamin content and chemical composition
of foods have been determined and their uses evaluated. More detailed
information in this connection will be found in the chapters on economic
importance of plants and animals.

Many of our articles of clothing originate directly or indirectly from
plant or animal sources. The following typical examples will show the
validity of such a statement: (1) true silk from the silkworm, (2) cot-
ton from the cotton plant, (3) wool from the sheep and other animals,
(4) linen from flax plants, (5) furs from rabbits, skunks, opossums, foxes,
goats, muskrats, beavers, raccoons, (6) leather from prepared skins of
the cow, horse, pig, alligator, and other animals; (7) straw from the
stalks of wheat, rye, oats, and barley, (8) felt from the wool, fur, and
hair of animals, and (9) rubber from the juice of the rubber tree.

Many of the materials for the construction of our furniture are of
plant or animal origin: (1) wood from plants, (2) willow furniture
from willow trees, (3) glue from the skins and hoofs of animals, (4)
leather from the prepared skins of various animals, (5) excelsior from
shredded wood, (6) paper from straw, bark, wood, and other fibers of
plants, (7) shellac from the resinous materials secreted by certain scale
insects, and (8) stains, varnish, and paint, at least in part, secured from
various plant materials.

Unless we stop to reflect carefully and conscientiously, we do not
realize how many of our fuels are closely related to plants which were
formerly alive. The following brief suggestion in each instance will
suffice. Coal is really formed from plant materials for the most part.
Vegetation and stored solar energy, buried in the swamps of long ago,
have undergone many changes so that coal of one kind or another has
been formed. Wood is plant tissue which was once alive. It forms one
of our most valuable fuels. Natural gas is the product of biologic decom-
position of plant and animal remains of the past. This has probably
taken place under great pressures within the deeper strata of the earth.
Peat is one of the intermediate stages in the formation of coal and is
utilized in localities where coal is not readily available. Petroleum is
also formed by the decomposition of materials which to a great extent
were of animal and plant origin. Gasoline is secured by refining petro-

778 General and Applied Biology

leum. Paper is made from straw, bark, wood, and other fibrous plant
materials. Coke is manufactured from certain kinds of coal by heating
in the absence of oxygen. For a more complete consideration of this
phase of resources, see chapter on the Economic Importance of Plants.

III. BIOLOGY AND ITS RELATION TO
HUMAN WELFARE

A. Medicine and Health

In few fields have the contributions of biology been greater than in
medicine and health. Courses in biology have given training for large
numbers of premedical students who have had the qualifications later
to enter the medical profession. Through animal experimentation, many
of the fundamental and basic truths of behavior, health, diseases, and
similar phenomena have been ascertained, with their subsequent appli-
cation in the field of medicine and public health. An experimental study
of animal reactions and behavior has suggested methods to be employed
in attacking the problem of individual and group behavior in man.

Many of the medicines used today are of plant or animal origin. In
addition, the efficiency and proper use of medicines have been deter-
mined largely through animal experimentation. Much of our knowledge
of foods, their correct use, their composition, their preservation, their
transportation, as well as diseases which they cause or transmit, are all
dependent upon certain biologic facts. The parasites of plants, animals,
and man have been studied in detail, and the information acquired has
been used successfully in making our environment a better place in which
to live. Many of the life cycles of parasites have been carefully studied
and this knowledge applied to the elimination of many of them. Re-
search in the fields of bacteriology and protozoology has contributed
many facts which, when practically applied, have resulted in lower
morbidity and mortality rates among living organisms. Heredity has
made a great contribution in explaining how we have come to be what
we are, how certain abnormalities arise, and how we may eliminate some
of the undesirable traits by the proper application of the knowledge
gained through the study of heredity.

Many of the improvements in our environment have been suggested
and influenced by what we have learned by biologic investigations. The
proper treatment of sewage, the purification of water, the inspection and
refrigeration of foods, the rigid inspection of oysters and other shell foods
for possible contaminations are only a few of the contributions in this

Applied Biology 779

direction. The studies of lower forms of the Hfe have shown us the many
frailties and shortcomings of the human race. This information in a
measure may prepare us for what we see when we observe many of the
behaviors and reactions of human beings. We come to appreciate that
man cannot be expected to be perfect, and we are disappointed that he
does not take full advantage of all his wonderful abilities and opportuni-
ties. Through our studies of biology we modify the attitudes and philos-
ophies of our daily lives. Science has affected us not only in material
ways but in mental and philosophic ways as well.

The science of endocrinology, by studying the ductless glands of cer-
tain animals, has pointed out the fundamental and basic principles to be
followed in the effective application of this field in human beings. Much
more in this field will have to be learned and a great amount of it will
be accomplished by first experimenting on other animals. A detailed
consideration of the endocrine glands is given in a summary in the chap-
ter on Biology of Man. Our studies of disease-producing (pathogenic)
bacteria, yeasts, molds, and Protozoa have given many methods of dis-
ease prevention, treatment, and cure. The extensive progress made in
bacteriology in the last few years has made it possible to reduce the
morbidity and mortality rates for many of our infectious diseases in this
country. Much more remains to be done, and much is being done daily
to alleviate the many human ailments and sufTerings due to these micro-
organisms. What we as individuals owe in health and happiness to the
hundreds who have scientifically investigated diseases in the past is be-
yond our imagination. Many of our human diseases are being success-
fully treated or prevented through the use of antibiotics which are the
products of certain lower plants, particularly fungi. Additional anti-
biotics are being discovered, and improved methods of production and
administration are recent contributions.

B. Biology and Wealth

Ordinarily, people do not associate biology and biologic products with
the wealth of this country. A few data will illustrate very definitely the
enormous contribution of biologic products to our national wealth. Over
a ten-year period the corn grown in the United States averages over
$1,500,000,000 annually. Over a similar ten-year period, the cotton was
valued at about $1,000,000,000 annually, while the wheat was valued at
about $635,000,000. Cotton is not grown in this country north of the
thirty-seventh parallel. In 1926 the South cultivated 44,608,000 acres

780 General and Applied Biology

of cotton from which were produced 17,755,570 bales. From the cotton
fibers of this yield were received $1,121,185,000, and from the cotton
seed, $172,131,000. When a cotton planter takes 1,250 pounds of seed
cotton to the ginnery, it is converted into one bale (500 pounds) of cot-
ton lint or fiber and 750 pounds of cotton seed. The value of all meat-
producing animals in the United States in 1928 was estimated to be
approximately $3,000,000,000. The value of the woUen and worsted
products in this country is slightly less than $1,000,000,000 each year.
The. fish industries are also extensive and their products are quite valu-
able. The salmon caught on our western coast are estimated to be
worth about $50,000,000 annually, while the codfishes are valued at more
than $30,000,000 per year. According to recent data, the total value
of all farm properties in this country is over $57,000,000,000. If we add
to the above list such products as rubber, lumber, hay, fruits, fuels, foods,
clothing, and other products, the totals become enormous. In each of
them biology plays a very important role in the cultivation, preparation,
or use of them.

Biology makes a great contribution in the production of wealth, but
it also makes an appreciable contribution to the methods of preventing
unnecessary loss in many fields of human endeavor. Nearly the entire
country is infested with rats which carry diseases causing untold dam-
ages. Rats destroy property valued at $200,000,000 each year. Metcalf
and Flint estimate that the loss caused bv insects in 1924 in the United
States was over $1,500,000,000. The science of entomology through
the study of insects has supplied us with information which, if efficiently
applied, would materially reduce this enormous and unnecessary loss.
Losses due to termites are increasing rapidly, and their extermination
has been suggested by procedures which have come as the result of ex-
tensive experimentation in this field. Fisher estimates that the disease
tuberculosis annually costs this country between $500,000,000 and $1,-
000,000,000 because of deaths, sickness, loss of work, inefficiency, main-
tenance of sanatoriums, hospitals, and similar projects. Much experi-
mental work in connection with this one disease has resulted in a decided
reduction of the loss due to its ravages. Most of our infectious diseases
have been attacked by bacteriologists, and satisfactory progress has been
made in many of them, so that today we can live longer and happier
lives as the result of their many investigations. How much this field of
bacteriology has contributed directly and indirectly to our wealth is
beyond human computation.

Applied Biology 781

C. Water Supplies and Sewage Disposal

Water is an important substance of all living organisms, and many of
the activities necessary for their existence are dependent upon the proper
quantity and quality of water. The chemical reactions of digestion,
growth, and reproduction are dependent upon water, and the enzymes
which aid in these processes act in aqueous solutions. Water is essential
in the elimination of wastes, regulation of body temperatures, main-
tenance of proper consistency of blood, lymph, etc. Water is one of the
best solvents for animals and plants as the following suggests: it dissolves
soil particles and chemicals for plant use and it dissolves acids, alkalis,
salts, gases and many other materials which have an endless variety of
uses in the living organism.

The value of water has been recognized by peoples of all times because
they have tended to settle where the supply has been of the proper quan-
tity and quality. In the past the quantity and quality were not always
the problem which they now are because of greater use of water and
greater centers of population, together with increased industrialization.
Today in many areas the "water problem" has become acute. Primitive
peoples used water for drinking, for preparing food, and a small amount
for washing and for their primitive handicrafts. As populations increased
and urban industrialization developed, the amount of water required was
greatly increased. Today, in some communities, we find water sanita-
tion so inadequate that people actually consume their own sewage or
that of the neighbor in order to get a sufficient supply. The per capita
daily consumption of water in our cities is about 100 gallons, although it
runs as high as 250 gallons in certain cities. European cities average
only about 50 gallons, with a few using as much as 100 gallons daily.
Such factors as the following influence the amount of water consumed:
the cost of the water, the number and types of industries, the chemical
and physical properties of the water, the amount used in cleaning streets,
the number of fires which firemen must put out, whether the water is
sold by meter or not, the number of leaky fixtures and pipes, the temper-
ature and humidity of the climate, the amount used in watering lawns
and gardens, etc.

Water comes to the earth in rain or snow; some is used by animals
and plants and some evaporates, while the remainder collects on the sur-
face of the earth or penetrates into the subsurface of the earth. Two
sources of water are: surface (rivers, lakes, reservoirs, etc.) and subsur-
face or ground (wells, underground rivers and lakes, etc.). Waters may
be classified as: (1) potable water, which is safe from the standpoint

782 General and Applied Biology

of health and is desirable from an odor, taste, or appearance standpoint,
(2) polluted water, which contains substances not necessarily harmful
but of such a character as to offend the senses of sight, taste, or smell
(pollution usually refers to such physical characteristics as unpleasant
tastes and odors, undesirable color, excessive turbidity, etc.), (3) con-
taminated waters, which contain substances harmful to health (patho-
genic microorganisms, inorganic or organic poisons, etc.), and (4) pure
waters, which are chemically and physically pure; such waters do not
exist naturally but can be secured by distillation.

Waters may become polluted and contaminated by picking up all
manner of materials in suspension and solution. They may acquire
silt by passing through fertile lands; they may be hard by incorporating
chemicals as they flow through limestone; they may have undesirable
tastes and odors by contacting decaying plant and animal matters; they
may be rendered undesirable by industrial wastes, wastes from oil wells,
seepage from mines, domestic sewage, etc. From a sanitary standpoint,
human excrements play the most important role in the contamination of
water.

Waters may be purified by (1) filtration through sand filters, with or
without previous coagulation induced by the use of chemicals which
precipitate undesirable materials, (2) disinfection by the use of certain
chemicals, usually chlorine, (3) some kind of water softening process,
or (4) a combination of the above processes. The specific method used
to purify is determined by the quality of the raw water and the quality
of the water expected after treatment. If water contains little dissolved
or suspended matter, chemical disinfection may be sufficient; if it is soft
but contains suspended matter and microorganisms, filtration and chlo-
rination may be necessary; if it contains such dissolved salts as those of
calcium or magnesium, it may be necessary to soften it by one means or
another.

Two types of sand filtrations are used for removing pollution from
waters: (1) slow sand filtrations and (2) rapid sand filtrations. The
former have been used extensively in Europe since 1830 but have not been
satisfactory in the United States. Slow sand filters were made of con-
crete, covered about one acre each, and were filled with sand to a depth
of one to four feet. Bacteria and other microorganisms are removed by
mechanical filtration and also by their destruction in the gelatinous,
zoogleal mass which covers the filter surface after it has operated for a
few days. Criticisms of the slow sand filter include the following: (1)
even if operated at full capacity the rate of purification is only two to

Applied Biology 783

three million gallons per acre; (2) it is not efficient if water contains large
amounts of suspended materials because the surface soon becomes coated,
thus interfering with the delivery of sufficient, desirable water; (3) it is
expensive, especially if large quantities of water are required, because
large areas of expensive land are required to build sufficient filters.

Rapid sand filters, introduced into the United States about 1890, are
extensively used in modern water purification plants. The process, in
brief, is as follows: (1) screen the raw water to keep out sticks, leaves,
animals, etc.; (2) mix the water with flocculating chemicals, such as
aluminum sulfate or iron sulfate, and allow the suspended floe to settle
out in settling tanks; (3) pass the clarified supernatant water through
rapid sand filter beds; (4) disinfect the water by means of chemicals,
usually liquefied chlorine gas.

In recent times the contamination of water supplies by sewage has
become a major problem because of increased centers of population and
industrialization in cities, because of the increased demand for more
water for homes and industries, and because of the greater difficulty in
efficiently disposing of large quantities of sewage. Sewage may be con-
sidered as the used water supply to which have been added (1) human
excrements (urine, feces), water used for bathing, washing, etc., (2)
industrial wastes from laundries, creameries, breweries, chemical plants,
slaughterhouses, tanneries, and many other similar industries, and (3)
water from streets, sidewalks, etc.

Sewage may be disposed of (1) by dilution, (2) by irrigation, or (3)
by stabilization of the sewage through bacterial actions. In the process
of disposition by dilution the sewage is placed in a body of water suffi-
ciently large to render the sewage more or less harmless. This old
method is inexpensive, and if the body of water is large enough to dilute
the sewage properly, and if the body of water is not to be used for other
purposes, it is reasonably satisfactory. Sewage disposal by irrigation or
by running raw sewage over land is not commonly used in the United
States. The stabilization of sewage by the actions of various bacteria
is based upon the fact that organic and inorganic substances in sewage
are excellent foods for bacteria. When bacteria use these substances,
they oxidize them more or less completely, forming new substances with
less energy and lower molecular weights. When most of the energy of
sewage is consumed, bacteria no longer grow rapidly and the sewage is
stabilized. The specific method for the bacterial treatment of sewage
depends upon many factors, such as the quality of the sewage, the quan-
tity to be disposed, the nature of the body of water or soil into which
the treated sewage is allowed to run, etc.

IV. DISEASES CAUSED OR TRANSMITTED BY ANIMALS*

A. Human Diseases

1. Protozoan Diseases

(a) Class Sarcodina

( 1 ) Amoebic dysen-
tery {Endamoe-
ba histolytica)
(Fig. 264)

(b) Class Mastigophora
[Flagellates)

(2) African sleeping
sickness (Gam-
bian) {Trypan-
osoma gam-
hiense) (Fig.
263)

(3) African sleeping
sickness (Rho-
desian) {T.
rhodesiense)

(4) Chaga's Disease
(7\ cruzi)

Kala-azar
{Leishmania
donovani)
Oriental sore
(L. tropica)

(7) Cutaneous
leishmaniasis
(L. hraziliensis)

(8) Flagellate diar-
rhea {Giardia
lamblia)

(9) Tertian malaria
{Plasmodium
vivax) (Fig.
176)

(10) Quartan malaria
{P. malariae)
(Fig. 176)

(11) Estiv'oautumnal
or subtertian
malaria {P.
falciparum)

(12) Diarrhea
{Isospora
hominis)

(d) Class Infusoria
[Ciliates)

(13) Diarrhea and
ulcers {Balan-
tidium coli)
(Fig. 262)

Transmitted by contaminated foods, water, flies;
may cause ulcerations of the intestine, abscesses
of liver, lungs, and brain; 10 per cent of world
population infected, many being carriers.

Transmitted by tsetse fly {Glossina) ; causes en-
larged glands, emaciation, weakened limbs,
coma, and eventually death ; present in Africa,
Europe, and tropics; from 1896-1906 over 500,-
000 died in Congo region

Similar to above ; common in Africa

Common in South and Central America; carriers
may be present in Southwestern United States;
causes dangerous swellings in muscles, heart, and
nervous system

Widely distributed in Asia; blood-inhabiting; at-
tacks lining of blood vessels and certain white
blood cells

Present in Near and Far East; one attack of this
cutaneous leishmaniasis immunizes against fur-
ther attacks

Occurs in South and Central America; parasite
resembles L. tropica morphologically.

May be the cause of a type of human diarrhea;
present in 10 per cent of population

Transmitted by female Anopheles mosquito (Fig.
303); parasites attack blood corpuscles; alter-
nate periods of fevers and chills every 48 hours;
more common type in temperate zone; less
serious

As above except that attacks occur every 72 hours;
not as common as other types

As above except for daily attacks, with more or
less constant fever; more common in tropics;
more serious type

Burrows in the intestinal wall causing diarrhea;
common in various regions of the Pacific in
World War II

Human beings may become infected by swallow-
ing resistant cysts (from pig feces) which con-
taminate drinks and foods; in some persons the
intestinal wall is ulcerated, producing diarrhea
and often killing the host

*Other diseases are considered elsewhere in other chapters; tlie list given here is incomplete
and descriptions are brief — merely to serve as a guide.

Applied Biology 785

A. Human Diseases — Cont'd

2. Human Diseases

Caused By Worms

' (a) Flatworms (Platy-

helminthes)

( 1 ) Pork tapeworm
(Taenia solium)
(Fig. 182)

(2) Beef tapeworm
(T. saginata)

(3) Chinese liver
fluke {Clinorchis

■sinensis)

Transrhitted by eating infested, improperly cooked
pork; common wherever such pork is eaten

Transmitted by eating infested, improperly cooked
beef; common wherever such beef is eaten (Fig.
183)

Lives in man in the Orient; transmitted by eating
improperly cooked, parasitized fish (Fig. 373)

Fig. 373. — Chinese liver fluke {Clinorchis sinensis) photographed, showing the
internal organs of an adult. Contrast with the sheep liver fluke (Fasciola
hepatica). (Figs. 180, 181 and 374), (Copyright by General Biological Supply
House, Inc., Chicago.)

(b) Roundworms
(Nemathelmin-
thes)

(4) Trichinosis or
pork roundworm

(Trichinella
spiralis)
(Fig. 100)

(5) New world
hookworm
{Necator
americanus)
(Fig. 99)

(6) Elephantiasis
{Wuchereria
{Filarial
hancrofti)
(Fig. 101)

(7) Human ascaris
{Ascaris
lumhricoides)
(Fig. 184)

Transmitted by eating infested, improperly cooked
pork; larvae may pass from human intestine into
muscles and lymphatic system

Transmitted through skin from infested soils; para-
sites may be present in human blood, lungs, in-
testines, etc.; causes shiftlessness and anemia
(loss of blood through intestine) ; common in
South

Transmitted by night-flying (nocturnal) mos-
quitoes from blood in skin of patient to next
person; in daytime the larval parasites (1/100
inch long) live in deeper human tissues (lungs,
larger arteries, etc.) ; parasites enter human
lymphatic system, obstructing the flow of lymph,
causing typically enlarged limbs, etc.

Eggs and larvae carried to human mouth by in-
fested foods, water, or soil; the larvae in the
human intestine migrate through the blood and
lymphatic system to liver, lungs, and heart and
eventually back to the intestine

786 General and Applied Biology

A. Human Diseases — Cont'd

3. Human Diseases

Caused by Arthropods
(a) "Chiggers"
(Trombicula
irritans)
(Fig. 269)

(b) Human lice

{Pediculus hu-
manis) and other
species (Fig. 280)

B. Diseases of Animals
Other Than Human

1. Protozoan Diseases

(a) Class Mastigophora
(Flagellates)

( 1 ) Dourine of
horses, etc.
{Trypanosoma
equiperdum)
(see Fig. 266)

(2) Nagana fever
{T. brucei)
(Fig. 266)

(3) Surra disease
{T. evansi)

(b) Class Sporozoa

(4) Silkworm dis-
ease or pebrine
{Nosema bom-

' bysis )

(5) Texas fever of
cattle
(Babesia
bigejnina)
(Fig. 267)

Diseases of Animals
Caused by Worms
(a) Flatworms (Platy-
helminthes)
( 1 ) Liver rot of

sheep {Fasciola
hepatica) (Figs.

The immature stages of this mite (class Arach-
noidea) have 3 pairs of legs, while the adult has
4 pairs; mites are transmitted from the soil and
vegetation to human skin where their claws
cause irritation; they are reddish in color ("red-
bugs"), just visible to the naked eye, and suck
blood with piercing-sucking mouth parts; adults
do not attack man but attack insects

Transmitted from person to person and by flies,
bedding, clothing, etc.; there are sev-eral vari-
eties of human lice each with its particular point
of attack and structure; sucking blood and
scratching by claws cause irritations; may trans-
mit other diseases

Transferred directly from host to host; usually a
chronic disease of horses, dogs, rabbits, etc., of
the United States, Canada, and parts of Europe
in which paralysis results in death in a few
months

Transferred by tsetse fly (Glossina) ; causes fever
in various African domestic mammals

Probably transmitted by tabanid flies; disease of
horses, mules, cattle, and camels of India

Transmitted by spores in the various stages of the
life cycle of the silkworm; within the silkworm
(Bombyx mori) the spores develop and invade
all body tissues, eventually killing the host; this
disease must not be confused with a bacterial
disease of the silkworm

Transmitted by cattle tick (Boophilus) ; present in
southern United States, parts of Europe, and
Africa; characterized by destruction of red blood
corpuscles, enlarged spleen, and aff"ected liver;
in acute stage the parasites usually appear as
pairs of pear-shaped bodies in the blood cor-
puscles

180, 181, 374)

(2) Tapeworm of
dogs, etc.

Transmitted by the snail (Lymnaea) ; not as com-
mon in this country as in Europe; very compli-
cated life cycle which is described elsewhere in
other chapters; also present in cattle, pigs, and
occasionally in man

Transmitted from dogs and other carnivorous ani-
mals to pigs, sheep, and man; the larvae, known

Applied Biology 787

&W BC^^o)

Fig. 374. — Life history of the sheep Hver fluke (Fasciola hepatica). A, Adult in
the sheep liver; B, egg passed from the body of the sheep; C, developing embryo
in the water; D, ciliated embryo (miracidium) in the water and ready to enter
the body of a snail; E and F, sporocyst containing rediae; G, redia containing
daughter rediae; H, redia of the second generation containing cercaria; I, cercaria
with tail; J, cercaria in water; K, cercaria encysted on grass; L, cercaria liberated
from cyst after ingestion by sheep; M, young fluke in sheep liver. Enlargements
of the various stages are indicated. (Reproduced by permission from Introduction
to Human Parasitology, eighth edition, by A. C. Chandler, published by John
Wiley & Sons, Inc., 1949.)

788 General and Applied Biology

B. Diseases of Animals Other Than Human — Cont'd

{Echinococcus
granulosus)

(3) "Staggers" or
gid tapeworm of
sheep

{Multiceps
multiceps)
(Fig. 268)

(b) Roundworms

(Nemathelminthes )

(4) Roundworm of
horses {Stron-
gylus vulgaris)
(compare Figs.
99 to 101)

(5) Dog ascarid
(Toxocara
canis)

(6) "Gapes" of
poultry and
game birds
{Syngamus
trachea)

(various species)
(Fig. 114)

3. Diseases of Animals
Caused by Mollusks
(a) "Blackheads" or
black cysts of fish
(larv^al stage or
glochidium of
mussels)

4. Diseases of Animals
Caused by Arthropods

as hydatid cysts, may reach the size of a child's
head and contain thousands of daughter cysts,
each of which may give origin to a new worm;
may be quite serious in severe cases; widespread
in distribution; called hydatid disease in man
The larva, known as a coenurus (se -nu' rus) (Gr.
koinos, common; oura, tail), contains several
scoleces in each cyst, and, lodged in the brain
of ruminant animals, causes "staggers" or "gid";
may be transmitted from dogs or other animals

Ingested larvae from feces of horses encyst in the
colon or cecum of the horse where sucking of
blood results in anemia; world-wide distribution,
especially in warmer countries

Dogs become infected by swallowing eggs, espe-
cially young puppies; an acquired immunity
results in the elimination of the worms in a few
months; larvae migrate through the body of the
dog much in the manner of Ascaris in man

Infestation occurs by ingesting larvae from feces
or materials coughed up by infested birds; larvae
travel through the esophagus, lungs, and trachea,
where they attach and forms capsules, produc-
ing the characteristic "gapes"; abscesses may
form; slender, red, adults in the trachea may
produce eggs which develop into larvae; com-
mon in fowls and wild birds; may affect hu-
man beings in the tropics

The fresh-water leech (Macrobdella) sucks blood
from man, frogs, fish, and cattle; the horse
leech {Haemopis) parasitizes horses, snails,
worms, etc., and lives in mud near fresh-water;
the medicinal leech {Hirudo medicinalis) sucks
blood from many types of vertebrate animals;
blood clotting is prevented by a special secre-
tion; may suck blood up to three times its own
weight and require several months to digest

The eggs of mussels develop into bivalved, larval
glochidia which are cast into the water where
they clamp their jaws into the gills, fins, and
body of fish; the fish forms a black cyst around
the glochidium; eventually the cyst ruptures to
liberate the developing larva and it begins its
free-living existence as a young adult mussel

The diseases of animals and plants produced by
members of the arthropod phylum and the dis-
eases transmitted by members of this group are
so numerous that the reader is referred to the
chapter on the Economic Importance of Ani-
mals (phylum Arthropoda) or to textbooks of
entomology

Applied Biology 789

V. DISEASES PRODLICED BY PLANTS

No attempt can be made to discuss fully the diseases which are pro-
duced by plants. Approximately 200 diseases of animals and man are
produced by bacteria, while many others are produced by pathogenic
yeasts and molds. Approximately 200 diseases of plants may be caused
by pathogenic bacteria. In general, the majority of infectious diseases
of man in this country are caused by bacteria rather than by protozoa.
This is true because climatic conditions prevent many of the protozoa
from existing in this area. The bacterial diseases of animals are con-
sidered elsewhere, but if further information is desired, the reader is
referred to the many textbooks in bacteriology. Besides the many bac-
terial diseases of living organisms, there are several produced by yeasts.
Included in this group are thrush (parasitic stomatitis), a disease of the
mouth, and blastomycetic dermatitis, which is an infection of the skin.
Certain types of fungi produce such typical disorders as dermatomycoses
of the skin; ringworm, a skin disease produced by at least two varieties of
fungi; sporotrichosis, a disease of the skin characterized by multiple ab-
scesses; "lumpy jaw" or "wooden tongue" of cattle; actinomycotic in-
fections of man.

The problems of toxins, antibodies, split proteins, allergies, and
hypersensitiveness are considered in more detail in other chapters. In
addition to the large number of diseases of plants and animals produced
by bacteria, yeasts, and fungi, there are certain higher plants, such as
poison ivy, poison sumac, nightshade, and similar forms, which are harm-
ful to man. Some of these must be taken internally to produce harm,
while mere contact with others will produce characteristic disorders.

VI. DISEASES CAUSED BY VIRUSES

Viruses are also known as "inframicrobes," "ultramicroscopic or filtra-
ble viruses," "microplasms," etc. A brief summary of some of the char-
acteristics of viruses are as follows: (1) they are assumed to be protein
in nature^ because all other living things are, and because they can serve
as antigens, and, according to present data, only proteins, or things com-
bined with proteins, can stimulate the production of antibodies; (2) some,
but by no means all, have been crystallized which differentiates some of
them from other infective agents; (3) they are regarded by some investi-
gators as a form of life in which one molecule, or aggregation of mole-
cules, of the living protoplasm composes a unit just as a cell forms a unit
of higher life, thus giving these chemical molecules the ability to repro-

790 General and Applied Biology

duce themselves; (4) in their resistance to chemical and physical agents,
they are intermediate between the resistant bacterial spores and the non-
spore-bearing baciUi; (5) the different viruses vary in size, some being
about 10 millimicrons and others as large as 200 millimicrons (a milli-
micron is one-thousandth of a micron, and a micron is one-millionth
part of a meter) ; (6) viruses cannot he grown in a strictly artificial
culture medium, but they must be grown parasitically in a cell for which
they are more or less specific; (7) they are invisible when using an ordi-
nary high-powered optical microscope employing ordinary visible light,
because the smallest particle visible under these conditions is about 0.2
micron in diameter, but they can be photographed with an electron
microscope; (8) they pass through filters of certain types and under cer-
tain conditions; (9) certain viruses produce animal diseases, such as
smallpox, measles, etc., and plant mosaic diseases, which are highly in-
fectious; (10) immunity to virus diseases in animals appears in general
to be rather permanent, as smallpox, chicken pox, mumps, etc. ; (11)
pathogenic viruses usually attack one set of tissues, the two most char-
acteristic tissues attacked being the skin (by dermotropic viruses) and the
nervous system (by neurotropic viruses); (12) viruses also tend to vary
(mutate) as a result of which some of them may change their disease-
producing capacity; in fact, new virus diseases in plants are appearing
continually; (13) according to one theory, viruses are nonliving chemical
substances, possibly autocatalytic enzymes, or "wild genes," because they
are protein, progagate themselves, etc.

The following are some of the more common diseases caused by patho-
genic viruses:

Smallpox (variola)

Cowpox (vaccinia)

Chicken pox (varicella)

Mumps

Foot and mouth disease (cattle and man)

Common colds and influenza

Yellow fever

Dengue fever ("breakbone fever")

Pappataci fever (three-day fever)

Infantile paralysis (poliomyelitis)

Rabies (hydrophobia)

Epidemic encephalitis
Warts (various types; some infectious)
Trachoma ("granulated eyelids")
Hog cholera

Parrot fever (psittacosis)
Dog distemper
Herpes zoster (shingles)
Herpes labialis ("cold sores")
Herpes febrilis ("fever blisters")
Mosaic disease of plants (tomato, po-
tato, tobacco)

QIESTIONS AND TOPICS

1. Describe the beginnings of agriculture in the distant past. What were the
first attempts at plant cultivation and animal breeding?

2. Discuss the dependence of man upon the soil, both in the past and at the
present time.

Applied Biology 791

3. List the ways in which biology contributes to the advancement of agriculture.

4. List several ways in which biology may be of importance in hydroponics, in-
cluding specific techniques used.

5. Explain the relationship between agriculture and the nitrogen, oxygen, and
carbon cycles discussed in a previous chapter.

6. Give a brief resume of animal diseases produced by bacteria. Of plant dis-
eases produced by bacteria.

7. Give a short resume of animal diseases produced by protozoa.

8. List all the ways in which biology may be directly or indirectly related to
human affairs.

9. Explain the relationship between biology and (1) medicine, (2) dentistry,
(3) pharmacy, (4) nursing, (5) industry, (6) forestry, (7) horticulture, (8)
floriculture, (9) landscape gardening, (10) out-of-door pools, (11) fruit
culture, (12) appreciation of nature, and (13) the formulation of a philosophy
of living.

10. List the more common characteristics of viruses and some diseases supposedly
caused by them.

SELECTED REFERENCES*

Burnet: Virus as an Organism, Harvard University Press.

Fernald and Kinsey: Edible Wild Plants of Eastern North America, Idlewild

Press.
Hill: Economic Botany, McGraw-Hill Book Co., Inc.
Howard: The Insect Menace, D. Appleton-Century Co., Inc.
Muenscher: Poisonous Plants of the United States, The Macmillan Co.
Reese: Outlines of Economic Zoology, P. Blakiston's Son & Co.
Smith: Plant Viruses, John Wiley & Sons, Inc.

*Also see references on bacteria, yeasts, molds, protozoa, flatvvorms, roundworms, entomol-
ogy, etc.

Chapter 39

CONSERVATION OF NATURAL RESOURCES

The constructive program to be followed in the conservation of our
natural resources will be in great part biologic. There are many in-
stances where there are shortages because of man's extravagance and
shortsightedness. No matter how adept man becomes in producing
substitutes artificially, there are instances where natural resources can-
not be supplanted. Natural resources must also be conserved and re-
stored from the standpoint of beauty and aesthetics. With greater lei-
sure, man is going to have more time with which to enjoy Nature and
the great out-of-doors. Proper conservation and provisions must be
made to meet the ever-increasing demands in this direction. The bio-
logic reclaiming of nonproductive lands also will be an important fac-
tor in supplying us with sufficient products for our various daily needs.
One of the greatest of natural resources of a nation is the health of the
individuals composing that nation. Biology in its various medical and
health phases can make a great contribution toward our future physical
and mental well-being.

Natural resources may be classified as (1) irreplaceable, or those
which, once used or destroyed, cannot be replaced, such as coal, oil, nat-
ural gas, and minerals and (2) replaceable, or those which are used or
destroyed but may be replaced if the proper conservation measures are
employed (forests, soils, water, fishes, wild life). Greater and greater
demands by homes, industries, wars, etc., have used great quantities of
our irreplaceable natural resources so that the supply will be exhausted
eventually. In some instances, substitutes may be found, but in most
cases these will not be sufficient. Mineral resources in addition to those
essential for industries are necessary for plant growth and the main-
tenance of health of all living things. Irreplaceable resources must be
used carefully and conserved properly to ensure future needs. In most
instances the replaceable resources will not replace themselves on their
own initiative but will do so only when man institutes and follows cer-

792

Conservation of Natural Resources 793

tain conservation measures. In order better to understand the problems
of conservation and the necessary remedial measures, the following re-
sources are considered briefly.

Destruction and Conservation of Forests. — Unless forests are con-
served, they will soon be unable to supply us with the necessities of life.
In years past when a smaller population required less forest and the per
capita supply was much greater, the problem was not so important. In
addition to the extensive cutting of forests, they have been destroyed by
the following: (1) Fires caused by lightning, careless campers, hunters
and vacationists. Ninety per cent of the 200,000 forest fires in the United
States each year are caused by man and the loss totals millions of dollars.

''ix^,r£frvA,'^<.

Fig. 375. — One careless act can burn a forest. Forest fires like this may travel
at tremendous speeds and burn millions of small and large trees^ destroy much wild
life, and start soil erosion. About 200,000 foYest fires occur annually in the United
States, and most of them are started by careless smokers, hunters, campers, fisher-
men, trash burners, etc. "Let Each Person Help to Keep America Green" is a
good slogan for everybody. (American Forest Products Industries, Inc.)

Forests may require over fifty years to be replaced and in the meantime
erosion of the soil may have started. Fires may kill trees or merely irt-
jure them, destroy plants, leaves and soil, deprive birds of nesting sites,
and deprive other animals of desirable protection; fires may injure trees
or their young seedlings so that they are subject to destructive bacterial
and fungal diseases. (2) Improper cutting of trees, which includes the
cutting of small, immature trees; the destruction or injury of young trees

794 General and Applied Biology

during cutting operations; the nonreplacement of trees cut, by new, young
trees. (3) Animals, which destroy young trees, seedHngs, seeds; by using
forests for grazing purposes, particularly if the forest is burned over for
grazing purposes.

Forest conservation measures include: (1) Replanting burned-over
areas. (2) Replanting forests which have been cut. (3) Removal of
undesirable trees and vegetation to permit better growth of desirable
varieties. (4) Prevention of forest tree diseases. (5) Providing basic
protection for all forests, qualifying for cooperative Federal-state protec-
tion under the Clarke-McNary Act. (6) Education of careless hunters,
campers, etc. If the following rules are followed faithfully, many forest
fires can be prevented: (a) Hold and pinch all matches until they are
cold; (b) crush out cigarette, cigar, and pipe ashes (use a rock or ash
tray); (c) drown all camp fires, stir and drown again; (d) learn and
obey laws about burning grass, brush, trash, etc.; (7) Building more fire
lookout posts and patrol stations. (8) Discontinuance of practice of burn-
ing-over forests for grazing purposes. (9) Wiser and more economical
use of timber. (10) Selection of better species of trees for particular
areas so that better qualities can be raised in a shorter time.

Loss and Conservation of Soils. — Soils are lost by ( 1 ) wind erosion
and (2) water erosion. Soils may be blown away because there is in-
sufficient surface vegetation to hold the soil particles. In a similar man-
ner, water currents may wash away great quantities of soil. It is esti-
mated that forty tons of soil per acre are washed away from land with a
2 per cent slope during one rainy season. Recent dust storms have re-
moved large amounts of soil for hundreds of miles, causing not only the
loss of soil where it is needed, but placing it where It Is not desired. The
removal of trees, grasses, and other vegetation has resulted in water and
wind erosion, with the loss of the water-retaining humus as well as min-
erals essential for plant growth. Soil washed into streams interferes with
plant and animal life there in addition to filling up rivers, lakes, and
ponds, thus rendering them useless. This silt will quickly fill a body of
water behind a dam, so that the original purposes of the dam are de-
feated. Soil erosion also Interferes with the water supply of cities, for
much effort is required to remove these soil particles from the water
supply. Many streams are polluted because of soil particles which inter-
fere with the normal growth and dc\elopment of plants and animals
normally inhabiting them.

Soil conservation measures include ( 1 ) the reestablishment of the
proper types of vegetation (trees, grasses, crops, etc.) to hold the soil par-

Conservation of Natural Resources 795

tides, (2) the building of level spaces, known as terraces, on lands whose
slope is great enough to permit erosion, (3) the correct type of contour
plowing and the practice of strip cropping to reduce erosion to a mini-
mum, (4) the establishment of permanent grasslands by planting the
proper types of grasses in a soil supplied with the proper fertilizing in-
gredients to ensure growth, (5) the establishment of permanent wood-
lands where other crops are not feasible, (6) the building of dams across
streams and gullies, and (7) the increase in fertility of the soil, either by
natural or artificial methods, so as to promote greater plant growth. In
brief, there should be no barren soils, but each soil should promote the
type of vegetation for which it is best fitted.

Loss and Conservation of Water. — As we look at the ocean or a large
lake we may wonder if it is necessary to conserve water. There may be
about as much water now as there has ever been, but it is not located
in the right places. Soils must contain a certain amount of water to en-
sure our water supplies and the proper plant growth. Any factors which
permit the rapid loss of water from the soil must be corrected if we are
to have sufficient supplies. Larger quantities of water are now being
used in homes and industries than formerly and this has aggravated the
problem still more. The greater use of water has reduced the "natural
water level" of the soil and this, in turn, diminishes the amount of plant
growth. Diminished plant growth results in greater loss of water, so that
the cycle is complete.

Another important factor influencing the quantity and quality of avail-
able, usable water is the pollution of our water supplies with wastes from
oil wells, coal mines, various industries, and sewage. Sometimes a suf-
ficient supply may be available, but it is unsatisfactory for the purposes
desired. Many streams have been altered so that their waters "run off"
too quickly to permit their retention by the soils. Vegetation on their
banks has been removed, thus permitting more water to enter the streams
quickly. The presence of wastes, silt, etc., the lowering of the natural
water level, the consequent changes in animal and plant foods, and the
destruction of natural feeding and breeding areas are among the in-
fluential factors responsible for the diminished supply of fishes and other
aquatic life in our waters.

Water conservation measures include (1) restoration of streams and
other bodies of water to their natural conditions as far as possible, (2)
prevention of unnecessary , pollution of water by wastes, (3) wiser and
more economical use of water, (4) replacement of the "vegetation
blanket" (trees, grasses, crops, etc.) on the soils in order to retain a

796 General and Applied Biology

maximum of moisture^ (5) the building of dams and dikes to conserve the
supply until needed, (6) employment of the correct types of plowing and
cultivating to retain a maximum of water in the soil, (7) reduction of
evaporation by a covering of vegetation, and (8) institution of a system of
flood preventions, thus alleviating the damages due to floods and also
conserving water for future uses.

Loss and Conservation of Animal and Plant Wild Life. — Many wild
animals and plants have been lost because of factors previously men-
tioned. Many species of wild flowers no longer exist because their nat-
ural habitats are no longer present. The removal of a forest results in a
destruction of wild plant and animal life which normally lives there.
Fishes, seals, deer, buffalo, birds, beavers, wild flowers will gradually
diminish, and probably disappear eventually, unless conservation meas-
ures are promptly instituted. It must be remembered that all living
things require more or less specific environments for their optimum
growth and development. When these are interfered with or destroyed,
the living organisms must perish if they are unable to adjust themselves
to another type of environment. The loss of each type of wild life con-
stitutes a unique problem in conservation, but the following general meas-
ures will illustrate: (1) regulation and control of fishing, hunting, collec-
tion of wild flowers, etc., (2) restoration of streams and other bodies of
water to their natural conditions as far as possible, (3) restoration of
forests, fields, and swamps so as to invite the growth of inhabitants
normally found there, (4) prevention of pollution of bodies of water by
industrial wastes, (5) prevention of destruction of plant and animal life
by the fumes from certain industries, (6) the building of bird sanctuaries,
providing nesting sites, proper foods, and protection, (7) protection of
such animals as fishes, seals, deer, pheasants, buffaloes, etc., by proper
hunting and fishing regulations, (8) the increase of state and national
parks and preserves in which the animals and plants have a natural
environment protected by laws, (9) prevention of the unnecessary de-
struction of wild life by the education of man as to the causes, results,
and remedial measures, (10) education of the public that picking wild
flowers, especially varieties which are scarce, will soon lead to their
extinction because each flower picked is the prospective parent for fu-
ture flowers, (11) increased support for the state and federal agencies for
the conservation of natural resources, (12) prevention of devastating
forest fires, and (13) the placing of big game in large forests where they
are protected by law.

Conservation of Natural Resources 797

Loss and Conservation of Minerals and Fuels. — Mineral resources in-
clude deposits in the earth which in crude or manufactured form are
of values in many phases of our personal and industrial life. They in-
clude ( 1 ) metals for building machinery, bridges, railroads, automobiles,
airplanes, etc., (2) building materials such as stone, cement, clays, etc.,
(3) mineral fuels such as coal, petroleum, and natural gas, (4) fertilizers
such as potash and phosphate, and (5) mineral products used in vari-
ous chemical and industrial processes. Mineral deposits have required
thousands of years to form and when once exhausted are not renewable.
Our country has great supplies of certain mineral resources but only
limited supplies of others, especially when the needs of our highly in-
dustrialized society are considered. Of the twenty-eight minerals of in-
dustrial importance, the United States possesses eleven in quantity suf-
ficient for normal needs. We are partially dependent on other countries
for eleven others, and wholely dependent for six (antimony, asbestos,
chromite, nickel, nitrates, tin) of which we have no deposits of commer-
cial value.

Mineral conservation measures include ( 1 ) more accurate data on the
demands on and the supplies of essential minerals, (2) utilization of
lower qualities of minerals (* 'marginal deposits") where possible, (3)
production of substitute materials from less essential minerals where these
are economically possible, (4) importation of certain scarce materials
to prevent exhaustion of domestic supplies during war and peace, (5)
utilization of more efficient methods of mining and processing essential
minerals, (6) more economical use of finished products made from essen-
tial minerals and an efficient system of reclaiming certain minerals from
worn-out or obsolete apparatus, and (7) more economical and efficient
use of our natural, mineral fuels such as coal, gas, and petroleum.

Conservation of Human Resources.-^^The greatest of all resources are
normal, healthy, and happy human beings. No nation can become,
or remain, great if its inhabitants are physically unfit or socially and
psychologically maladjusted. Other resources are unimportant if human
beings cannot properly enjoy and utilize them. To maintain itself, a
population must show more births than deaths over a period of time.
From a money standpoint, one of the greatest assets is that of healthy,
normal human beings. Of the total number of deaths in this country
each year, few are due to natural senility, but a large proportion are due
to causes which might be prevented if the proper conservation measures
were followed. Many times as many persons suffer from various diseases

798 General and Applied Biology

as die from them; therefore, the efficiency and happiness of men could
be greatly increased if the ravages of the various types of diseases and
accidents were controlled.

Human resources conservation measures include (1) reduction of the
rate of infant mortality, (2) control and prevention of communicable
diseases, (3) guarantee of pure foods and water in sufficient quantities
for the individual needs of each person, (4) proper elimination of sewage
and industrial wastes, (5) proper growth and inspection of foods so that
diseases may not be transmitted to man, (6) greater support to city,
county, state, and federal health agencies which are doing much to edu-
cate and control the general public in regard to physical and mental
health problems, (7) proper enforcement and acceptance of quarantine
regulations, (8) the institution of a program of physical activity to de-
velop and maintain a maximum of physical health for each person com-
mensurate with his inherited abilities, (9) the elimination of infectious
organisms, especially from crowded places, (10) the proper control of
"carriers" of disease germs so that they are unable to transmit them to
others, (11) better education of the public regarding the causes, transmis-
sion, prevention, treatment, and the effects of human diseases, (12) de-
crease in the occupational diseases through better working conditions and
a reduction of the number of deaths and injuries due to various types
of accidents, (13) better understanding of the dietary diseases due to
deficiencies of certain essential nutrients, (14) more rigid enforcement of
properly formulated pure food and drug laws, (15) more research in
the fields of bacteriology, protozoology, immunology, and public health,
and (16) the regulation of our individual lives so that we shall be able
to develop and maintain the maximum of physical and mental health of
which each of us is capable, considering the inherited materials with
which each has started existence.

QUESTIONS AND TOPICS

1. Define natural resources and conservation of natural resources.

2. Discuss the causes for the necessity of conservation and specific measures to be
used in the conservation of such natural resources as forests, soils, water, animal
and plant wild life, minerals and fuels, human beings.

3. Discuss the statement that "the United States is the richest nation in the
world," including such points on which we are strong or weak and how we
might improve our status in specific instances.

4. Why and how has the necessity for conservation changed in the last fifty years?

5. Explain how the great industrialization of our country has affected the neces-
sity for conservation.

Conservation of Natural Resources 799

6. Discuss the value of our twenty-eight National Parks and the many State Parks
in view of our increased leisure time.

7. Discuss the justification of including human resources in the total program of
conserving natural resources, including reasons why this problem has been
changed as a result of our ways of living in recent years.

8. Discuss the benefits and detriments of industrialization, greater periods of
leisure, concentration of populations in large cities (urbanization), increased
mechanization of homes, industries, methods of transportation, etc.

9. Discuss the probable status of human society if and when we shall have ex-
hausted many of the essential resources upon which we now seem so dependent.
Include the contrasting status of our forefathers who lived under quite differ-
ent conditions. Is it impossible for us to really exist if these conditions are
prevalent again?

SELECTED REFERENCES

Bennett: Elements of Soil Conservation, McGraw-Hill Book Co., Inc.

Gustafson: Soils and Soil Management, McGraw-Hill Book Co., Inc.

Gustafson, Guise, Hamilton, and Ries: Conservation in the United States, Com-

stock Publishing Co., Inc.
Jacks and Whyte: Vanishing Lands, Doubleday, Doran & Co., Inc.
Osborn: Our Plundered Planet, Little, Brown & Co.
Peattie: Cargoes and Harvests, D. Appleton & Co.
Sears: Deserts on the March, University of Oklahoma Press.
Smith: Conservation of Our National Resources, John Wiley & Sons, Inc.
Trippensee: Wildlife management, McGraw-Hill Book Co., Inc.
Vogt: Road to Survival, Wm. Sloane Associates.

Chapter 40

BIOLOGISTS AND THEIR WORK

HISTORY AND DEVELOPMENT OF BIOLOGY

The history and development of biology have passed through several
distinct periods. Agriculture, hunting, and husbandry of one kind or
another had their origins with prehistoric man. From a practical stand-
point, systems of medicine were in use at the very beginning of recorded
history more than 5,000 years ago. When the Greek and Roman civili-
zations were at their height, the foundations for natural science and
biology were laid. Particularly in Greece was the first systematic and
scientific work accomplished. After the Greek and Roman periods, there
was a decided decline during the Middle Ages, or so-called Dark Ages.
As will be observed from our discussion, there was a renaissance in
science which followed this long period of comparative inactivity. Dur-
ing the discouraging period of many years, the emphasis in scientific
work was based on the "opinions" of a few so-called "authorities." In-
vestigators made few attempts to prove things for themselves. The opin-
ions of the authorities were accepted without question. In fact, it was
on the border line of sacrilegiousness for an investigator to find out things
for himself. To evaluate the scientific attempts of those times properly,
we must judge and consider them in the light and spirit of that period
of history rather than compare them too drastically with modern at-
tempts. The following will give a few of the more important contribu-
tors to biologic development, the time during which they lived, their
nationalitv, and their individual contributions. More detailed informa-
tion will be found by reading the references given at the end of the
chapter.

Thales (624-548 b.c). — Theory that the ocean was the mother of all
life.

Anaximander (611-547 B.C.). — Theory that all creatures originated
from aquatic forms and were transformed into terrestrial forms.

800

Biologists and Their Work 801

Empedocles (495-435 e.g.). — Theory that living organisms were gen-
erated spontaneously from scattered materials by being attracted or re-
pelled by love or hate.

Hippocrates (460-370 e.g.). — Greek "Father of medicine." Made a
science of medicine.

Aristotle (384-322 e.g.). — Greek scientist and philosopher. "Father
of natural history." Studied the development, anatomy, physiology, and
classification of 500 animals. First used the inductive method of securing
facts and then based conclusions or principles on these facts.

Theophrastus (370-287 e.g.). — Greek student of Aristode. First scien-
tifically studied plants. Founded the science of botany and wrote a His-
tory of Plants. Named 500 species of plants.

Pliny the Elder (a.d. 23-79) . — Roman general, literary man, and scien-
tist. Compiled thirty-seven volumes of half-true, half-false natural his-
tory data from his predecessors.

Dioscorides (a.d. 40). — Greek physician. Studied medicinal plants.
Wrote De Materia Medica.

Galen (Claudius Galenus) (a.d. 130-200) — Roman. Greatest med-
ical anatomist of antiquity. Gave a standard for anatomy which stood
for fifteen centuries, without dissecting human bodies but by an analogy
with other animals.

Andreas Vesalius (a.d. 1514-1564). — Belgian, "Father of modern
dissective anatomy." Studied human anatomy by dissection. He per-
sonally dissected and did not permit the "barbers" to do this for his stu-
dents. By the age of 28 years he had written the Structure of the Hu-
man Body.

Konrad von Gesner (a.d. 1516-1565). — Swiss. Most learned natu-
ralist and zoologist of this period. Founded the first botanical garden
and first zoological museum.

Francis Bacon (1561-1626) . — English. Natural philosopher who broke
away from the trammels of contemporary scholasticism and deduced his
conclusions from facts.

William Harvey (1578-1657). — English. Founder of experimental
physiology. Observed and demonstrated the circulation of the blood in
1621. Revived experimental methods in zoology after the so-called Dark
Ages.

Francesco Redi (1628-1698) . — ItaHan. Overthrew the theory of spon-
taneous generation of insects by discovering their eggs and larvae.

Marcello Malpighi (1628-1694). — Italian. Related anatomy and
physiology to medicine. Studied tissues microscopically. Observed

802 General and Applied Biology

blood corpuscles and blood flow in capillaries. Started the study of
microscopic insect anatomy, particularly that of the silkworm. Studied
the anatomy of plants.

Antony van Leeuwenhoek (1632-1723). — Dutch. Philosopher nat-
ural historian, and student of microscopy. Studied many forms of mi-
croscopic plant and animal life. Discovered and described male germ
cells. Sent over 400 papers and letters to the Royal Society in London
and the French Academy of Sciences. Started the science of micro-
biology.

Jan Swammerdam (1637-1680). — Dutch. Great microscopic anato-
mist. Started the study of insect anatomy and life histories. Injected
blood vessels.

Robert Hooke (1635-1703). — English, Made numerous studies with
the compound microscope. Influenced the work of Grew in microscopy.
Discovered and described cells as "little boxes."

Nehemiah Grew (1641-1712). — English. Studied microscopic anat-
omy and plant physiology. His book, Anatomy of Vegetables, started
plant histology,

Bernard de Jussieu (1699-1777). — French. Laid the basis for our
present system of plant classification. Wrote Genera Plantarum.

Carolus Linnaeus (1707-1778). — Swedish. Originated binomial no-
menclature for naming organisms and a system of classification (taxon-
omy). He listed 4,437 different animals and plants. He originated uni-
form, latinized names and short descriptions which were more scientific
and accurate than the common names which previously had been used.

J. Gottlieb Koelreuter (1733-1806).- — German. Demonstrated sexes
in plants. Produced a plant hybrid by crossing two species of tobacco.

Jean-Baptiste Lamarck (1744-1829). — French. Suggested the theory
of the inheritance of acquired characteristics as an explanation of adap-
tations. He gave the first logical and complete theory of organic
evolution.

Constantine S. Rafinesque (1784-1840). — French-German. He came
to America in 1802. In 1815 he was professor of botany at Transylvania
College, Ky. He made a classificaiion of medical plants.

George Cuvier (1769-1832). — French. A zoologist who founded
modern comparative anatomy. Founded the science of vertebrate
paleontology (fossils). Originated the cataclysmic theory that there had
been numerous creations, each of which had been completely destroyed
and its place taken by newer forms.

Biologists and Their Work 803

't>

Karl von Baer (1792-1876). — Russian. Originated modern compara-
tive embryology.

Robert Brown (1773-1858). — Scotch. A physician who opened the
field of plant physiology and genetics. Discovered the importance of
plant cell nucleus.

Johannes Miiller (1801-1858). — German. He founded modern com-
parative anatomy, combined the knowledge of physics, chemistry, and
cytology (science of cells), and showed their proper relationships.

Matthias Schleiden (1804-1881). — German. A botanist who together
with Schwann formulated the cell principle in 1839.

Theodor Schwann (1810-1882). — German. A zoologist who with
Schleiden formulated the cell principle in 1839.

Louis Agassiz (1807-1873). — American. A great investigator and
teacher in zoology. Studied the development of animals and paleon-
tology. He was professor of zoology and geology at Harvard University
and founded the Museum of Comparative Zoology there.

Charles Darwin (1809-1882). — English. Formulated the theory of
natural selection (survival of fittest). Wrote Origin of Species in 1859.

Asa Gray (1810-1888). — American. First great botanist of America.
Improved the system of plant classification.

Gregor Mendel (1822-1884). — Austrian monk and scientist. Used
experimental method of studying heredity. Published Mendel's laws in
1865-1866.

Louis Pasteur (1822-1895). — French. Bacteriologist and chemist.
"Father of modern bacteriology." Proved that microorganisms cause
fermentation and decay. Proved relationship between bacteria and cer-
tain diseases.

Sir Francis Galton (1822-1911). — English. Formulated the laws of
filial regression and ancestral inheritance in heredity.

Alfred Russel Wallace (1823-1913).— English. Shared with Darwin
the credit for the theory of natural selection.

Thomas Henry Huxley (1825-1895). — English. Comparative anat-
omist and energetic defender of Darwin's theories.

Julius Sachs (1832-1897). — German. Proposed experimental methods
for the study of photosynthesis, respiration, and transportation in plants.

August Weismann (1834-1914). — German. Distinguished between
germ cells and somatic cells. Theory of continuity of germ plasm.
Identified chromatin material of nuclei as bearers of heredity.

804 General and Applied Biology

John Burroughs (1837-1921). — American. One of greatest of nat-
uralists, having written many books on the lives and habits of living
organisms.

Robert Koch (1843-1910). — German. Bacteriologist and physician.
Devised the plate method for obtaining pure cultures of bacteria. Proved
the relationship between bacteria and certain diseases (tuberculosis).

Carl Weigert (1845-1904). — German. Bacteriologist who first used
aniline dyes to study microorganisms.

Luther Burbank (1849-1926). — American. Improved many types of
domestic plants by crossing. Created several new varieties of plants.

HOW SCIENTISTS HAVE SOLVED PROBLEMS

There have always been and there always will be many problems of
various kinds to be solved. In fact, the solution of one problem fre-
quently creates other problems which require solution. Some of these
problems may be personal and some may seem insignificant, while others
may have far-reaching effects. The success of individuals, of groups, of
nations depends upon the correct solution of the many problems which
confront each. In order to become familiar with some of the problems
and their solutions, it may be profitable to read some of the accounts of
scientists in connection with the problems which they solved. The selec-
tion of the specific problems and their solutions may depend upon the
availability of the literature in which they are described, the particular
interests and qualifications of the students, and the specific reasons for
making such a study. The way in which an article is written must be
considered before it may be helpful, because sometimes the author does
not always clearly state the detailed steps followed in the solution of his
problem. The selection of specific references must be made with great
care, or the beginner may not derive the desired benefits from their
study. When reading a selected article, watch carefully for such steps
as the following: (1) accurate and clear statement of the problem, (2)
formulation of working hypotheses and methods of investigation, (3)
accurate collection and recording of data and facts, and (4) scientific
analysis and correct interpretation of data and facts, from which logical
conclusions are drawn. As stated above, certain articles, as written, may
not follow the steps suggested above, some steps being left out of the
printed report, even though they may have been utilized by the scientist
in his work. For purposes of brevity, some reports treat certain steps so
briefly that they are not easily recognized. When you read the reference,

Biologists and Their Work 805

do so very carefully, watching for the methods used in the solution of the
problem under consideration. After you have reread the reference
sufficiently, write a report, giving the contents under the proper head-
ings or steps listed above.

QUESTIONS AND TOPICS

1. Describe the conditions under which the science of biology originated.

2. Why does the "father of natural history" deserve that designation? Consider-
ing the conditions under which he worked, how do you evaluate his work?

3. Discuss the reasons why biology as a science did not originate earlier and why
progress was not more uniform and rapid.

4. Discuss several biologic theories proposed before the time of Christ.

5. Discuss the causes for the decline of biology after the so-called Greek period.

6. Discuss the reasons for the revival of science in the Middle Ages.

7. List the more important biologists of the past and include the contributions
which each made to the progress of the science.

8. What were the effects on biology of the invention and perfection .of the micro-
scope ? Be specific in your statements.

9. Why were the earlier biologists called natural philosophers? Is there still
philosophy in biology today? Explain your answer and give proof.

10. Are there greater biologists today than in times past? Why do you say so?
What makes a biologist great?

11. Was the lack of progress in biology of the past due primarily to a lack of
scientific equipment ? Why do you say so ?

12. In what directions do you expect the greatest advances in biology in the fu-
ture? Give reasons why you say so.

13. After you have read each of the assigned references which show how scientists
have solved problems, record all materials under the four headings suggested
in the chapter. Attempt to use the scientific method in the solution of as
many of the problems which you encounter as possible. If certain problems
do not seem to lend themselves to the use of the scientific method, is this due
to the fault of the method or to a probable incorrect use of the method?

14. Memorize the steps to be followed in the scientific solution of a problem and
use them in the solution of as many of the problems which you encounter as
possible.

15. When you have solved a problem, attempt to apply the conclusions in other
fields or problems as far as justifiable from the data at hand.

SELECTED REFERENCES*

Banting, Best, and Macleod: The Internal Secretion of the Pancreas, Am. J.

Physiol. 59: 479, 1922.
Bayliss and Starling: The Mechanism of Pancreatic Secretion, J. Physiol. 28:

325-359, 1902.
Dobell: Antony van Leeuwenhoek and His "Little Animals," Harcourt, Brace

and Co., Inc.

*Also see references to various chapters, especially Chapter I, and references supplied by the
instructor.

806 General and Applied Biology

Dubos: Louis Pasteur: Free Lance of Science, Little, Brown & Co.

Green: History of Botany, Oxford, Eng., Clarendon Press.

Hall: Source Book of Animal Biology, McGraw-Hill Book Co., Inc.

Howard: Luther Burbank: Victim of Hero Worship, Chronica Botanica Co.

Keynes: The Personality of William Harvey, Cambridge University Press.

Knobloch: Readings in Biological Science, Appleton-Century-Crofts, Inc.

Locy: Growth of Biology, Henry Holt & Co., Inc.

Locy: The Story of Biology, Garden City Publishing Co.

Loewi: Chemical Transmission of Nerve Impulses, Am. Scient. 33: 159-174, 1945.

Nordenskiold: History of Biology, Tudor Publishing Co.

Olmstead: Charles-Edward Brown-Sequard, Johns Hopkins University Press.

Pavlov: Lectures on Conditioned Reflexes, International Publishing Co.

Peattie: Green Laurels (Great Naturalists), Simon & Schuster, Inc.

Radl: History of Biological Theories, Oxford University Press.

Reed: Short History of the Plant Sciences, Chronica Botanica Co.

Sarton: Guide to the History of Science, Chronica Botanica Co.

Sears: Charles Darwin, Charles Scribner's Sons.

Sedgwick, Tyler, and Bigelow: A Short History of Science, The Macmillan Co.

Snyder: Biology in the Making, McGraw-Hill Book Co., Inc.

Vallery-Radot: The Life of Pasteur, Garden City Publishing Co.

Zinsser: Rats, Lice and History, Little, Brown & Co.

Parts

APPENDIX

I. IMPORTANT PREFIXES AND SUFFIXES USED IN BIOLOGY

The following list is by no means complete, but it will serve as a basis for
additional types. It will prove very useful if memorized with an example of
each type. The following abbreviations are used: Gr., from the Greek; L.,
from the Latin.

A- or An- (Gr., without or absent), apoda, without feet.

Ab- (L., away from or without), ahoral, away from the mouth.

Ad- (L., toward, upon, or equal), adrenal, upon the kidney; adductor, drawing

one part toward another.
-Ae (L.), plural ending of singular Latin nouns ending in A.
Aer- (Gr., air), aerobe, requiring free air.
Alb- (L., white), albino, without pigment.
Ambi- (L., both), ambidextrous, ability to use either hand.
Amphi- (Gr., on both sides), amphibia, living in water and on land.
Amy]- (L., starch), amylase, an enzyme changing starch to sugar.
Ana- (Gr., back or again), anabolism, building up process of metabolism.
Angio- (Gr., enclosed), angiosperm, protected or enclosed seeds.
Ante- (L., before in time or space), antedorsal, placed before the dorsal.
Anti- (Gr., opposed or opposite), antitoxin, opposed to or neutralizing a toxin.
Antr- (L., cavity), antrum, cavity in a bone.

Apo- (Gr., from or separate), apodema, extending from the body.
Aqua- (L., water), aquatic, living in water.
Arch- (Gr., early or chief), archenteron, early digestive tract or enteron; archeo-

zoic, earliest life.
Areol- (L., space), areolar, containing minute spaces.
Arthr- (Gr., joint), arthropoda, jointed appendages or feet.
Asco- (Gr., sac or bag), ascomycete, sac-bearing fungi.
-Ase, suffix designating an enzyme (zymase, protease).
Aster- (Gr., star), asteroidea, a class of echinoderms resembling stars.
Auto- (Gr., self), auto synthesis, self building-up.

Bacter- (Gr., rod), bacteria, rod-shaped.

Basi- (Gr., base), basidiospore, spore formed at the base of a basidium.

Bi- (L., double), bilateral, similar on both sides.

807

808 Appendix

Bio- (Gr., life), biology, science of life.

Blast- (Gr., bud or promotive), blastoderm, primitive germ layer.

Brachy- (Gr., short), brachydactyly, short digits.

Brevis (L., short), adductor brevis, a short adductor muscle.

Bryo- (Gr., moss), bryophyte, a plant of the phylum comprising the mosses.

Caec- (L., blind), caecum, blind pouch.

Calci- (L., lime), calcareous, containing lime.

Carp- (Gr., fruit), pericarp, around the fruit.

Cauda- (L., tail), caudal, tail.

Cav- (L., hollow), vena cava, hollow vein.

Ceno- (Gr., recent), cenozoic, recent life.

Centr- (L., centre), centrosome, center of activity during mitosis.

Cephalad (Gr., head), used adverbially, as toward the head or headward.

Chlor- (Gr., green), chlorophyll, green leaf.

Chond- (Gr., granular), mitochondria, small, granular parts of protoplasm..

Chondro- (Gr., cartilage), chondrocranium, part of the cranium developing from

cartilage.
Chrom- (Gr., color), chromatophore, color-bearing.
Cili- (L., eyelash), cilia, hairlike.

Circum- (L., around), circumesophageal, around the esophagus.
Cloaca (L., sewer), cloaca, outlet for excretions.
Cnido- (Gr., nettle), cnidoblast, nettle cell of certain animals.
Coel- (Gr., hollow), coelom, hollow body cavity.

Coeno- (Gr., common), coenosarc, common tissue in certain animals.
Coleo- (Gr., sheathed), sheathed insects, such as beetles.
Com- (L., together), commensalism, living together.
Con- (L., cone), conifer, cone-bearing tree; or (L., with), concretion, grow

together.
Cotyl- (Gr., cup-shaped), cotyledon, cup-shaped seed leaf.
Creta- (L., chalk), cretaceous, chalk period of geologic times.
Cyan- (Gr., blue), cyanophyta, blue-green algae.
Cyst (Gr., sac), cyst, a pouch or sac.
Cyt- (Gr., cell), cytology, branch of biology treating cell structure, function, etc.

De- (L., off), degenerate, to lose generative ability.

Dendr- (Gr., brush or tree), dendrite, treelike structure of nerve cell.

Derm- (Gr., skin), dermis, part of the skin.

Di- (Gr., twice), diploblastic, two germ layers; dicotyledon, two cotyledons.

Dis- (L., away), distal, away from.

Dors- (L., back), dorsal, pertaining to the back.

Dura- (L., tough), dura mater, tough outer covering of nervous system.

E- (L., without), egestion, to pass outside.

Ec- (Gr., house or environment), ecology, the habitats of an organism.

Appendix 809

Ecto- (Gr., outside), ectoderm, the outer layer of cells.

En- (Gr., in, or within), encyst, to cover with a membranous cyst.

Endo- or ento- (Gr., within) entoderm, inner layer of cells.

Eg- (Gr., dawn, or early), eocene, early geologic period.

Epi- (Gr., upon), epidermis, upon the dermis.

Equus- (L., horse), Equisetineae, the class to which the horsetails belong.

Eu- (Gr., good or well), eugenics, being well born from a hereditary standpoint.

Ex- (Gr., external), exoskeleton, external skeleton.

Extra- (L., beyond), extracellular, beyond or outside the cell.

Fer- (L., to bear), Porifera, pore-bearing sponges.
Fil- (L., thread), filiform, threadlike.
Flex- (L., bend), flexor muscles, bend joints.
Form- (L., shape), uniform, all one shape.

Gam- (Gr., marriage), gamete, a reproductive cell.

Gastr- (Gr., stomach), gastric, pertaining to the stomach.

Gen- (Gr., to produce), pathogenic, to produce disease.

Geo- (Gr., earth), geology, science of the earth.

Gest- (Gr., to bear or hold), ingest, to take in.

Glea- (Gr., jelly), mesoglea, the middle jellylike layer in certain animals.

Glyc- (Gr., sweet or carbohydrate), glycogen, animal starch.

Gone- (Gr., seed, or to reproduce), gonad, an organ of reproduction.

Gymn- (Gr., naked), gymnosperm, seeds not covered when being formed.

Haem- (Gr., blood), haemoglobin, a substance in the blood.

Hemi- (Gr., half), hemisphere, one-half of a sphere.

Hepat- (Gr., liver), hepatic, pertaining to the liver.

Hetero- (Gr., other or different), heterogeneous, formed differently.

Hex- (Gr., six), hexagonal, six-sided.

Homo- (Gr., same), homogeneous, similar.

Hyal- (Gr., glass), hyaline, glasslike cartilage.

Hydr- (Gr., water), dehydrate, to remov^e water.

Hymen- (Gr., membrane), hymenoptera, membranous wings.

Hyper- (Gr., above), hypersensitive, especially sensitive.

Hypo- (Gr., under), hypoglossal, under the tongue. '

In- (L., in, into, not, without), invaginate, to push in.
Infra- (L., below), infraorbital, below the orbit.
Inter- (L., between), intercellular, between cells.
Intr- (L., inside), intracellular, within a cell.
Is- (Gr., equal), isotherm, equal temperatures.

810 Appendix

Juga- (L., join), conjugate, a process of reproduction in which two animals are
joined.

Kata- (Gr., down or destroy), cataholism, tearing down or destroying.
Kine- (Gr,, kineo, more), kinetic, kinetic energy is energy of movement.

L
Labi- (L., lip), labium, a lip.
Lac- (L., milk), lactose, milk sugar.
Later- (L., side), lateral, to the side.

Lemma- (Gr., covering), neurilemma, covering of a nerve.
Lepi- (Gr., scale), lepidoptera, insects with scale wings.
Lip- (Gr., fatty), lipoid, a fatty substance.
Log- (Gr., study), zoology, study of animals.
Luci- (L., light), luciferin, a Jight-producing material.
Lysis- (Gr., destroy), bacteriolysis, a bacteria-destroying substance.

Macro- (Gr., large), macronucleus, large nucleus.

Mai- (Gr., mal, bad), malnutrition, bad nutrition.

Mega- (Gr., larger), megaspore, larger spore.

Mens- (L., table), commensalism, eating at a common source of food.

Mere- (Gr., part), micromere, small part.

Meso- (Gr., middle), mesoderm, middle cellular layer.

Meta- (Gr., after), metaphase, the later phases of mitosis.

Micro- (Gr., small), micronucleus, small nucleus.

Milli- (Gr., thousand), millipede, an animal with a "thousand" legs.

Mio- (Gr., less), miocene, less recent period in history.

Mito- (Gr., thread), mitosis, cell division with formation of threadlike structures.

Mono- (Gr., one), monograph, something written about one subject.

Morph- (Gr., form), morphology, study of form.

Multi- (L., many), multicolored, many colors.

Muta- (L., to change), mutation, an abrupt hereditary change.

Myco- (Gr., fungus), mycology, a study of fungi.

Myxo- (Gr., slime), myxomycophyta, slime molds.

Nema- (Gr., thread), nematocyst, a threadlike structure of coelenterates.
Neo- (Gr., young, or recent), neotropical, a recent region in the tropics.
Nephro- (Gr., kidney), nephridium, a kidney.
Nuc- (L., kernel, or center), nucleus, in the center of a cell.

Octo- (L., eight), octopus, an animal with eight appendages.
Oedo- (Gr., swollen), edema (oedema), a swollen condition.
-Oid (Gr., like), amoeboid, like an amoeba.

Appendix 811

Oligo- (Gr., few or little), oligotrichous, having few cilia. •

Oo- (Gr., egg), oogenesis, producing an egg.

Or- (L., mouth), oral, pertaining to the mouth.

Ortho- (Gr., straight), orthoptera, insects with straight wings.

Os- (Gr., bone), osseous, pertaining to bone.

Ovi- (L., e^g) , ovum, an egg.

Palaio- (Gr., ancient), paleontology, study of ancient life.

Para- (Gr., beside), parapodia, appendages beside others.

Path- (Gr., disease), pathogenic, disease-producing.

Ped- (L., feet), pedal, pertaining to the feet.

Peri- (Gr., around), peristome, around an opening or mouth.

Phaeo- (Gr., dark or brown), phaeophyta, brown algae.

Phage- (Gr., to eat), phagocyte, a cell which eats or destroys.

Phor- (Gr., to bear), sporophore, to bear spores.

Photo- (Gr., light), photosynthesis, building by means of light.

Phil- (Gr., loving), thermophil, heat loving.

Phyco- (Gr., alga, or seaweed), phycom.ycete, an algalike fungus.

Phyll- (Gr., leaf), mesophyll, middle part of a leaf.

Phyto- (Gr., plant), sporophyte, spore-bearing plant.

Plasm- (Gr., formed), ectoplasm, formed outside.

Plast- (Gr., living), chloroplast, a green body in certain living plants.

Platy- (Gr., flat), platyhelminthes, flatworms.

Plio- (Gr., more), pliocene, more recent period.

Poly- (Gr., many), polymorphous, many forms.

Post- (L., after), postnatal, after birth.

Pous- (Gr., foot), octopus, an animal with eight feet.

Pre- (L., before), prenatal, before birth.

Pro- (Gr., before), prostofnium, before the mouth.

Proto- (Gr., first or essential), protoplasm, an essential material.

Prox- (L., nearest), proximal, nearest.

Pseudo- (Gr., false), pseudopodia, false feet.

Ptero- (Gr., wing), diptera, two wings.

Re- (L., again, or back), regenerate, to form again.

Ren- (L., kidney), renal, pertaining to the kidney.

Rept- (L., creeping), reptile, creeping animals.

Retro- (L., backward), retrolingual, backward from the tongue.

Rhizo- (Gr., root), rhizopoda, rootlike appendage.

Rhodo- (Gr., red), Rhodophyta, red algae.

Roti- (L., wheel), rotifer, an animal with a wheel-like structure on its head.

Sarc- (Gr., flesh), ectosarc, outer flesh.

Schizo- (Gr., to divide), Schizomycophyta, fission fungi (bacteria)

812 Appendix

Scler- (Gr., hard), sclerotic, hard.

Sect- (L., to cut), dissect, to cut.

Semi- (L., half), semicircle, half of a circle.

Sept- (L., wall), septum, a partition.

Set- (L., bristle), seta, a bristlelike structure.

Sinu- (L., hollow), sinus, a hollow cavity.

Soma- (Gr., body), somatoplasm, protoplasm of the body.

Spor- (Gr., seed), spore, a structure for reproductive purposes.

Stoma- (Gr., opening), stoma, an opening, such as is found in leaves.

Sub- (Gr., under), submaxillary, under the maxilla.

Super- (L., over or above), superior, higher, upper, above.

Supra- (L., above), suprarenal, above the kidney.

Sym- (Gr., together), symbiosis, living together.

Syn- (Gr., together), synapsis, fusing together.

Teleo- (Gr., complete, or end), telophase, the end stage of mitosis.

Terato- (Gr., wonder), teratology, a study of wonders.

Tetra- (Gr., four), tetrapoda, four feet.

Thee- (Gr., case), spermatheca, sperm case.

Thermo- (Gr., heat), thermotropism, reaction to heat.

Thigmo- (Gr., contact), thigmotropism, reaction to contact.

Tom- (Gr., to cut), microtome, an instrument to cut small sections.

Toxic- (Gr., poison), toxin, a bacterial poison.

Trans- (Gr., across), transfer, to carry across.

Tri- (Gr., three), trilobed, three lobes.

Tricho- (Gr., hair), trichocyst, a hairlike structure.

Trop- (Gr., react), tropism, reaction to stimuli.

Ultra- (L., beyond), ultramicroscopic, beyond the microscope.
Uni- (L., one), unilateral, on one side.
Ur- (Gr., tail), anura, without a tail.

Vas- (L., vessel), vas deferens, a vessel to transmit male sex cells.
Ventr- (Gr., belly), ventral, pertaining to the lower or belly side.
Vit- (L., life), vital, essential to life.
Vorti- (L., to turn), vorticella, an animal which turns as it moves.

Zoo- (Gr., life or animal), zoology, study of animals.

Zyg- (Gr., to unite), zygote, the cell which results when male and female sex cells

unite.
Zym- (Gr., a ferment), zymase, enzymes which act on a certain carbohydrate to

produce carbon dioxide and water, or alcohol and carbon dioxide, etc.

Appendix 813

II. GLOSSARY, BIOLOGIC PRINCIPLES, AND THEORIES

One of the most important contributions which the science of biology can
make to the individual student is the imparting of a knowledge of the general
principles and theories which underlie living organisms and their varied activi-
ties. Many of the detailed structures and functions of living organisms may be
forgotten when the knowledge of the general principles will remain and con-
tinue to be a source of value and satisfaction. An attempt is made to summarize
briefly the more important principles and theories. In some instances, clarity
and completeness are sacrificed for the sake of necessary brevity. In cases where
the consideration is insufficient, the reader is directed to the proper part of the
text or to additional references.

The pronunciation, based on Webster's New International Dictionary, is given
and the syllable to be emphasized is marked by '. The derivations of the terms
are included not only for a better understanding of the term, but to enable the
student to use these derivations in an attempt to explain the meaning of other
words with which he may not be familiar. Those derived from Greek are desig-
nated by Gr., those from Latin by L., those from Anglo-Saxon by A.S., and those
from French by Fr,

Abdomen (ab-do'men) (L. abdomen, belly), the part of the animal, posterior to

the thorax.
Abductor (ab -duk' ter) (L. ab, away; duco, to lead), leading away from the

center or median line (contrast with adductor).
Abiogenesis (ab i o -jen' e sis) (Gr. a, not; bios, life; genesis, to create), the

former theory that all living matter arose spontaneously from nonliving

matter (same as spontaneous generation).
Aboral (ab -o' ral) (L. ab, from; os, mouth), opposite the mouth.
Abortion (a -bor' shun) (L. abortare, to miscarry), premature birth or incom-
pletely formed structure.
Absorption (ab -sorp' shun) (L. ab, away; sorbere, to suck or remove), the taking

up of substances or their passage through the walls of cells or vessels.
Acclimation (ak li -ma' shun) (L. ad, toward; klimat, region), the process of be-
coming accustomed or habituated to environmental conditions which are

not native.
Accommodation (a kom o -da' shun) (L. ad, to; commodus, fit), the ability of the

eye to adjust to objects near and far.
Accretion (a-kre'shun) (L. accrescere, to increase), increasing in size by adding

deposits to the surface (contrast with intussusception).
Acetabulum (as e -tab' u lum) (L. acetabulum, saucer-shaped), a cavity on each

side of the pelvic bone into which the femur fits.
Achromatic figure (a kro -mat' ik) (Gr. a, not; chroma, color), the nonstaining

part of the nucleus.
Acoelomate (a -se' lo mat) (Gr. a, without; koilos, hollow), without a hollow,

true, body cavity or coelom.
Acquired characters, modifications of structures or functions acquired by the

body plasm through the changes in environment or functions (contrast

with mutation).

814 Appendix

Acromegaly (ak ro -meg' a li) (Gr. akron, point; megas, large), a disease in
which the head, hands, and feet become enlarged, caused by overactivity
of the pituitary gland.

Actinic rays (ak-tin'ik) (Gr. aktis, beam or ray), the chemically active rays of
light.

Adaptation (ad ap -ta' shun) (L. ad, to; aptus, fit), the process of becoming
fitted to an environment or the mutual fitness of an organism to its internal
and external environments.

Adaptive radiation, the radiating or spreading in various directions of organ-
isms arising from the same generalized stock and the assuming of dif-
ferent characters by them because of their adaptation to different kinds of
environments encountered.

Adductor (a -duk' ter) (L. ad, to; duco, to lead), leading toward the center or
median line (contrast with abductor).

Adipose (ad' i pos) (L. adiposus, fatty), pertaining to fat.

Adrenal (ad -re' nal) (L. ad, near; renes, kidney), an endocrine (ductless) gland
near the kidney (same as suprarenal).

Adrenalin (ad -ren' a lin), a hormone secreted by the inner part or medulla of
the adrenals.

Aerobe (a'erob) (Gr. aer, air; bios, life), requiring free oxygen for living (con-
trast with anaerobe).

Aestivation (estivation) (es ti -va' shun) (L. aestas, summer), a semitorpid con-
dition of certain animals in summer.

Afferent (af er ent) (L. ad, to; ferro, to bear), conveying toward a center.

Agglutination (a gloo ti -na' shun) (L. agglutinans, gluing or clumping together),
the collection of cells in a liquid into clumps due to specific substances
known as agglutinins.

Agnostic (ag-nos'tik) (Gr. a, not; gnosco, to know), no convictions on a subject.

Albinism (al'binizm) (L. albus, white), the absence of normal pigments in the
hair, skin, and eyes of animals or the absence of normal chlorophyll in
plants which normally possess it.

Algae (al'ji) (L. alga, seaweed), simple, green, chlorophyll-bearing plants.

Alimentary (al i -men' ta ri) (L. alimentum food), pertaining to food and di-
gestion.

Allantois (a -Ian' to is) (Gr. alias, sausage), an embryonic membrane of higher
vertebrates for respiration.

Allelomorphs (alleles) (a -le' lo morf) (Gr. alleon, of one another; morphe,
form), genes similarly located in homologous chromosomes.

Allergy (al'erji) (Gr. alios, other; ergon, activity), a reaction to a foreign sub-
stance, especially protein.

Alternation of generations, see Metagenesis.

Alveolar (al -ve' o lar) (L. alveolus, small cavity), small cavity; foamlike.

Ambulacral (am bu -la' kral) (L. ambulacrum, covered way), regions in echino-
derms in which are located the ambulacral tube feet for locomotion.

Amino acid (a -me' no), organic acid containing the amino group (NH2) and
serving as building material for proteins.

Amitosis (ami -to' sis) (Gr. a, without; mitos, thread), cells dividing directly
without forming chromosomes, spindle, etc.

Appendix 815

Amnion (am' ni on) (Gr. amnos, lamb; the membrane around the embryo), thin
membranous sac enclosing the embryos of reptiles, birds, and mammals.

Amoeboid (a -me' boid) (Gr. amoibe, to change), resembling an Amoeba.

Amphiaster (am fi -as' ter) (Gr. amphi, both; aster, star), the figure formed in
dividing cells by the two asters and the spindle.

Amphibious (am -fib' i us) (Gr. amphi, both; bios, life), living both in water
and on land.

Amphiblastula (am fi -bias' tu la), free-swimming larval stage of sponges.

Amphimixis (am fi -mik' sis) (Gr. amphi, both; mixis, mingling), a union of
nuclear materials from two different cells, as in fertilization.

Amphoteric (am fo -ter' ik) (Gr. amphi, both), partaking of the nature of both,
as proteins have both acid and basic properties.

Ampulla (am-pul'a) (L. ampulla, flask), saclike structure of the ambulacral sys-
tem of starfishes.

Amylase (am' i las) (Gr. amylon, starch; «5^/enzyme), starch-splitting enzyme.

Amylopsin (am i -lop' sin) (Gr. amylon, starch), a starch-splitting enzyme of the
pancreatic juice.

Anabolism (an ab' o lizm) (Gr. anabole, to build), the building-up phase of me-
tabolism.

Anaerobe (an-a'erob) (Gr. an, without; aer, air), living without free oxygen
(contrast with aerobe).

Anal (a' nal) (Gr., anus, anus), pertaining to the anus.

Analogy (analogous) (a-nal'ogi) (Gr. ana, according to; logos, proportion),
organs structurally different which perform similar functions, as wings of
birds and butterflies.

Anaphase (an'afaz) (Gr. ana, up; phasis, appear), stage in mitosis in which
chromosomes move toward the poles of the cell.

Anaphylaxis (an a fi -lak' sis), the reaction to foreign protein material which has
a toxic effect and which may be due to increased sensitivity to the mate-
rial because of previous contact with it.

Anastomose (a -nas' to moz) (Gr. anastomosis, join), to join together into a net-
work such as blood vessels.

Anatomy (a-nat'omi) (Gr. ana, up; temno, to cut), structure of organs, espe-
cially as revealed by dissection.

Angiosperm (an' ji o spurm) (Gr. angio, covered; sperm, seed), plants with seeds
enclosed by carpels (contrast with Gymnosperm).

Animal pole, that part of a cell in which the protoplasm has the highest rate
of metabolism in contrast with the vegetal pole.

Anion (an' ion) (Gr. ana, up; ienai, to go), a negatively charged particle or ion
that travels to the positive anode during electrolysis.

Annelida (a-nel'ida) (L. annulus, ring), with ringlike segments as in the earth-
worm.

Annual (an' u al) (L. annus, year), plants which complete their life cycle and
die within one year.

Annular ring, ringlike structure in stems of higher plants which show seasonal
growth.

Antenna (an -ten' a) (Gr. ana, up; teino, stretch), jointed sensitive organ on the
head of insects, Crustacea, etc.

816 Appendix

Anterior (an -te' ri or) (L. anterior ^ front), or head end.

Anteroposterior differentiation, body with front (head) and hinder (tail) ends.

Anther (an' ther) (Gr. anthos, flower), pollen-producing part of a plant stamen.

Antheridia (an ther -id' i a), the male sexual organs that produce sperm in cer-
tain flowerless plants.

Antheridiophore (an ther -id' i o for) (Gr. antheridia; phoreo, to bear, antheridia-
bearing structure.

Anthocyanin (an tho cy' a nin) (Gr. anthos, flower; kyanos, blue), a coloring
matter of certain higher plants which impart a red or blue color.

Anthozoa (an tho -zo' a) (Gr. anthos, flower; zoa, animals), flowerlike coelenterate
animals, including corals, sea anemone, etc.

Anthropoid (an' thro poid) (Gr. anthropos, human), manlike organisms.

Anthropology (an thro -pol' o ji) (Gr. anthropos, human; logos, science), the
science of ancient man and his development.

Antibiotic (anti bi -ot' ik) (Gr. anti, against; bios, life), antagonism of one or-
ganism toward another; a drug, chiefly from bacteria and true fungi.

Antibody (an' ti bod i) (Gr. anti, against; A.S. bodig, body), a substance en-
gendered in an organism by the presence of a foreign material, especially
bacterial proteins; an antibody is specifically antagonistic to the antigen
or substance under the influence of which it was formed.

Antigen (an'tijen) (Gr. anti, against; gen, to form), a substance causing the
formation of an antibody.

Antimere (an' ti mere) (Gr. anti, opposed; meios, part), one of the parts of a
radially symmetrical animal, as the ray of a starfish.

Antitoxin (an ti -tok' sin) (Gr. anti, against; toxikon, poison), a specific defensive
substance in a body, either existing naturally or produced as a result of the
presence of a specific toxin which it tends to neutralize.

Aorta (a -or' ta) (Gr. aorta, raise), main artery arising from the heart.

Aortic arches, arteries arising from the ventral aorta and supplying the gill re-
gions of vertebrate animals.

Apical (ap' i kel) (L. apex, summit), apex, tip, or summit.

Apopyle (ap'opil) (Gr. ap, from; pyle, gate), an opening through which water
passes from the flagellated canals of sponges.

Apospory (a -pos' po ri) (Gr. apo, away; sporos, spore), the formation of a
gametophyte plant directly from sporophyte tissue rather than from a spore.

Appendix (ap-pen'dix) (L. ad, to; pendere, to hang), an outgrowth, such as the
vermiform appendix of man.

Apterous (ap' ter us) (Gr. a, without; ptera, wings), wingless.

Archegoniophore (ar ke -go' ni o for) (Gr. archegonos, first of a race; phoreo, to
bear), basal structure which bears the archegonium.

Archegonium (ar ke -go' ni um) (Gr. archegonos, first of a race), female, multicel-
lular sex organs in plants.

Archenteron (ar -ken' ter on), (Gr. archos, beginning; enter on, intestine), the
primitive digestive tract.

Archeology (ar ke -ol' o ji) (Gr. archos, beginning; logos, science), a study of
ancient peoples from their relics, equipments, etc.

Aristotle's lantern, the chewing apparatus of sea urchins.

Appendix 817

Artery (ar'teri) (Gr. arteria, artery), vessel conducting blood away from the

heart.
Arthropoda (ar -throp' o da) (Gr. arthron, jointed; pons, appendage), phylum of

animals with jointed appendages but without notochord or vertebral column.
Artificial parthenogenesis (par the no -jen' e sis) (Gr. parthenos, virgin; genesis,

orgin), the artificial activation of an egg to develop without fertilization

by a male sperm.
Artificial selection, the development of certain traits by artificially crossing se-
lected individuals.
Ascocarp (as'kokarp) (Gr. askos, sac; karpos, fruit), a structure which produces

saclike asci in sac fungi.
Ascomycetes (as ko mi -set' ez) (Gr. askus, sac; mycetes, fungi), higher fungi

whose spores are formed in saclike asci.
Ascospore (as' ko spor) (Gr. askus, sac; sporos, spore), a spore contained in a

saclike ascus.
Asexual (a -sek' shu al) (Gr. a, without; sexus, sex), reproduction without sex

cells.
Assimilation (as sim i -la' shun) (L. ad, to; similare, to make Hke), conversion

of digested food into living protoplasm.
Association areas, regions of the brain in which higher mental processes are

presumably affected.
Aster (as'ter) (Gr. aster, star), starlike figure of radiating lines about the cen-

trosome during certain stages of animal cell mitosis.
Asymmetry (a -sim' e tri) (Gr. a, not; symmetria, symmetry), without symmetry.
Atlas (at' las) (Gr. Atlas, name of a god whose pillars upheld the heavens), the

first or anterior vertebra of the neck.
Atom (at'um) (Gr. atomos, indivisible), structural unit of a molecule which

maintains its integrity in a chemical change; an atom enters into, and

issues from, a chemical reaction unchanged except for a loss or gain of

electrons.
Atomic theory, all matter is made of small units called atoms.
Atrophy (at'rofi) (Gr. a, not; trophe, nourishment), wasting away of an organ

or a part of it (contrast with Hypertrophy).
Attraction sphere (L. attr actus, draw to), structure which may aid in attracting

chromosomes toward the cell poles during mitosis.
Auditory (o' di to ri) (L. audire, to hear), pertaining to sound reception and

interpretation.
Autogamy (o -tog' a mi) (Gr. autos, self; gamos, marriage), nuclear reorganiza-
tion and self-fertilization within the same individual (example, Paramecia).
Autolysis (o-tol'isis) (Gr. autos, self; lysis, destroying), self-digestion of a tissue

or organ by enzymes formed by it.
Autonomic system (oto-nom'ik) (Gr. autos, self; nomos, law), a system of

nerves and ganglia regulating involuntary muscles, blood vessels, etc.,

and connected with the central nervous system by the cranial and spinal

nerves.
Autosome (o' to sum) (Gr. autos, self; soma, body), a regular chromosome as

distinguished from a sex chromosome,

818 Appendix

Autotomy (o -tot' o mi) (Gr. autos, self; tomos, cut off), self-mutilation of an
organism, as the loss of an appendage.

Autotrophisni (o to-trof izm) (Gr. autos, self; trophe, nourishment), capable of
self-nourishment by using chemical elements for food.

Autumnal coloration, colors produced in leaves by such pigments as antho-
cyanins, xanthophylls, carotenes, etc.

Auxin (ok' sin) (Gr. auxein, to increase), plant hormone influencing growth.

Auxospore (ox' o spor) (Gr. auxe, grow; sporos, spore), a reproductive cell in
diatoms, usually resulting from the fusion of two diatoms.

Avoiding reaction, a somewhat fixed, protective behavior induced by adverse
stimuli.

Axial gradient, an orderly arrangement of regions of different metabolic rates,
with the most active at the apical end and a decrease in this metabolic
rate as one goes toward the posterior end.

Axial skeleton (L. axis, axis), the main axis of the skeleton to which the ap-
pendages are attached.

Axis of polarity, an imaginary line extending from the anterior to the posterior
end of an organism; the pole known as the animal pole is at the anterior
end of the axis, while the pole with less activity, the vegetal, is at the pos-
terior end of the axis.

Axis of symmetry, double metabolic gradients which run from the middorsal (mid-
ventral in invertebrates) region laterally and ventrally (dorsally in inverte-
brates).

Axon (ak' son) (Gr. axon, axis), elongated process of a nerve cell for conducting
impulses away from the cell body (contrast with dendrite).

Azygos (az'igus) (Gr. a, without; zygon, yoke or mate), an unpaired muscle,
vessel or process such as the single azygos vein.

Backcross, a cross between an individual of the first filial generation (Fi) with
one of the parental types.

Bacteria (bak-ter'ia) (Gr. baktron, a stick), very small chlorophyll-less, single-
celled fungous plants, a number of which produce diseases, decay, fer-
mentation, and similar results, while others are beneficial.

Bacteriophage (bak -ter' i o faj) (Gr. baktron, bacteria; phagein, to eat), living
substance which destroys bacteria.

Barrier (bar' i er) (Fr. barriere, bar), any physical, chemical, or biologic object
which prevents natural migrations of organisms.

Basal metabolism, release of energy due to the oxidation of a definite quantity of
food.

Basidiomycetes (ba sid i o mi -se' tez) (Gr. basidium, base; mycetes, fungi), a
fungus which produces spores on a paddle-shaped base called a basidium.

Basidiospore, a spore produced on a basidium.

Behaviorism, the reaction of animals to their environment.

Biceps (bi' seps) (L. bis, two; caput, head), having two heads or origins, as biceps
muscle of the arm.

Biennial (bi -en' i al) (Gr. bi, two; annus, years), a plant which lasts two years
(seasons), producing only leaves the first season and flowers and seeds
the second.

Appendix 819

Bilateral symmetry, arrangement of parts on opposite sides of a certain plane

so that they are similar to each other.
Binary fission (bi' na ri; fish' un) (L. bini, two by two; fissura, to split), division

into two equal parts.
Binomial nomenclature, the scientific method of naming organisms by two Latin

or latinized words, the first the genus, the second the species.
Biochemistry, the chemical aspects of biologic phenomena.
Biogenesis (bi o -jen' e sis) (Gr. bios, life; genesis, origin), the law that all life

arises from preexisting living matter (contrast with Abiogenesis).
Biogenetic theory, each individual in its embryologic development (ontogeny)

repeats or recapitulates, in modified or abbreviated form, the stages in the

evolutionary development of that race (phylogeny). In other words,

ontogeny repeats phylogeny.

Phylogenetic Stages Ontogenetic Stages

(1) Single-celled animal (1) Egg (single cell )

(2) Solid mass of cells (2) Morula and blastula stage

(3) Two-layered animal (3) Gastrula (two layers)

(4) Three-layered animal (4) Three-layered embryo

Biogeography (bi o je -og' ra fi) (Gr. bios, life; geo, earth; graphein, to write),
geographic distributions of organisms in space {see Zoogeography and Phy-
togeography).

Biology (biol'o ji) (Gr. bios, life; logos, science), study of living things.

Bioluminescence (bi o lu mi -nes' ens) (L. luminis, light), light emission by living
organisms not directly attributable to heat that produces incandescence.

Bionomics (bi o -nom' iks) (Gr. bios, life; nomos, law), the relations of living
organisms to their environments {see Ecology).

Biophysics (bi o -fiz' iks) (Gr. bios, life; L. physica, natural), the physical aspects
of biologic phenomena.

Biparental (bi pa -rent' al) (Gr. bi, two), having a male and a female parent.

Biramous (bi-ra'mus) (Gr. bi, two; ramus, branch), having two branches.

Bisexual (bi -sex' shual) (Gr. bi, two; sexus, sex), possessing both male and female
sex organs.

Bivalent chromosomes (bi -va' lent; kro' mo som) (Gr. bi, two; valere, to have
power), two chromosomes, one from the male and the other from the fe-
male, united temporarily.

Bivium (biv' i um) (Gr. bi, two; via, way), one side of an echinoderm having two
rays.

Bladder worm (A.S. blaedere, bag), baglike stage of embryonic tapeworm.

Blastocoel (blas'tosel) (Gr. blastos, bud; koilos, hollow), hollow segmentation
cavity of the embryo.

Blastocyst (blastodermic vesicle) (bias' to sist) (Gr. blastos, bud or young; kystis,
sac), the hollow stage which follows the embryonic morula stage.

Blastoderm (bias' to durm) (Gr. blastos, young; derma, skin), a cellular mem-
brane formed by the division of the blastomeres.

Blastomere (bias' to mer) (Gr. blastos, young; meros, part), any cell formed by
mitosis of the egg.

Blastopore (blas'topor) (Gr. blastos, young; poros, pore), the pore of the blas-
tula stage.

820 Appendix

Blastostyle (bias' to stil) (Gr. blastos, young; stylos, pillar), the portion of a
hydroid, such as Obelia, which forms medusa buds.

Blastula (bias' tula) (Gr. blastos, young), spherical, hollow mass of cells result-
ing from the divisions of the egg.

Blood corpuscle, one of a number of types of bodies in blood for performing
certain functions.

Blood "islands," compact clusters of cells in the embryonic mesoderm for the
future development of an embryonic circulatory system.

Botany (bot' ani) (Gr. botania, a plant), study of plants.

Bowman's capsule, the enlarged end of a kidney tubule in which is found a mass
of thin-walled capillaries, known as a glomerulus.

Brachial (brak' i al) (L. brachius, arm), pertaining to the arm.

Branchial (brang' ki al) (Gr. branchia, gills), pertaining to gills.

Bronchus (brong' kus) (Gr. bronchos, windpipe), tube leading from trachea to the
lungs.

Brownian movement, the molecular movement of dispersed particles of a col-
loid, first described by Robert Brown.

Bryophyta (bri -of i ta) (Gr. bryon, moss; phyta, plants), phylum of plants in-
cluding mosses and liverworts.

Buccal (buk' al) (L. bucca, mouth), pertaining to the mouth.

Bud, an outgrowth which develops into a replica of the structure from which it
has arisen.

Caecum (se' kum) (L. caecus, blind), a blind pouch open. at one end.

Calcareous (kal -kar' e us) (L. calx, limy), limy composition.

Calciferous glands (kal -sif er us) (L. calx, limy; Gr. ferro, to bear), carrying

lime, as in earthworms.
Callus (kal' us) [Y,. callus, hard skin), tissue developed on wound surfaces of

plant.
Calorie (kal'ori) (L. calor, heat), a unit of heat measurement, usually the

amount of heat required to raise the temperature of 1 gram (1 c.c.) of

water 1° C.
Calyptra (ka -lip' tra) (Gr. kalyptra, covering), the archegonium of a moss or

liverwort distended or modified with the growth of the sporophyte. In

certain mosses it is carried to the top of the capsule to form a hood.
Calyx (ka'liks) (Gr. kylix, husk or cup), the outer whorl of floral leaves known

individually as sepals.
Cambium (kam'bium) (L. cambiore, change), the growing meristem tissue from

which the secondary phloem and xylem arise in roots and stems; located

between bark and wood.
Cambrian (from Cambria, Wales), earliest geologic period in which fossils are

found abundantly.
Camouflage (ka'moofiazg) (F. camoufler, to disguise), concealment by colors or

patterns to deceive.
Canaliculus (kan a -lik' u lus) (L. canaliculus, little vessel), small channels in bone

connecting the lacunae with one another or with the Haversian canals.

Appendix 821

Capillary (kap'ileri) (L. capillus, hair), minute blood vessels whose walls are
one cell thick and which connect arteries and veins.

Capillitium (cap il -esh' i um) (L. capillus, hair), delicate network in the spo-
rangia of slime molds (fungi).

Carbohydrate (kar bo -hi' drat) (L. carho, carbon; Gr. hydro, water), substances
composed of carbon, hydrogen, and oxygen, with the latter two usually
in the same ratio as in water (sugars, starch, etc.).

Carcinoma (kar sin -o' mah) (karkinos, crab, cancer), a malignant growth, cancer.

Cardiac (kar' di ak) (Gr. kardia, heart), pertaining to the heart.

Carnivorous (kar -niv' o rus) (L. carnis, flesh; vorare, to devour), flesh eating.

Carotene (kar' o teen) (Gr. karoton, carrot), a yellow-orange pigment of certain
higher plants.

Carotinoid, carotene pigments.

Carpal (kar' pal) (Gr. karpos, wrist), wristbone.

Carpel (kar' pel) (Gr. karpos, fruit), a floral organ which bears and encloses the
ovules.

Carpogonium (kar po -go' ni um) (Gr. karpos, fruit; gonos, offspring), female sex
structure of red algae.

Cartilage (kar' ti -lazg) (L. cartilago, gristle), elastic, flexible connective tissue.

Caste (kast) (L. castus, pure), a distinct type or form among a group of organ-
isms.

Castration (kas -tra' shun) (L. castrate, to castrate), removal of gonads (sex
organs) from animals or plants.

Catabolism (ka -tab' o lizm) (Gr. kata, down; holle, to throw), destructive phase
of metabolism.

Cataclysmic theory (kat a -kliz' mik) (L. cataclysmos, to inundate), the early
theory that the stratification of the earth, the formation of mountains, etc.,
were the result of a series of vast, violent disturbances which destroyed
all existing life, thus making necessary repeated, special creations to repopu-
late the earth.

Catalysis (ka -tal' i sis) (Gr. kata, down; lysein, to loose), the initiation or ac-
celeration of a chemical process by the presence of a substance (catalyst)
which itself does not enter into the reaction.

Cation (kat' ion) (Gr. kata, down; ion, going), a positively charged ion attracted
to the negative cathode during electrolysis (contrast with Anion).

Caudal (ko' dal) (L. cauda, tail), pertaining to the tail.

Cell (sel) (L. cella, small room), a small mass of protoplasm containing nuclear
materials and enclosed by an outer covering.

Cell law, the law which states that all plants and animals are made of one or
more cells.

Cell membrane, thin delicate membrane of a cell.

Cell wall, outer protective covering of certain cells.

Cellulose (sel' u losz) (L. cellula, little cell), an organic substance in plant cell
walls (a few animal cells such as the tunicates).

Cenozoic era (sen o -zo' ik) (Gr. kenos, recent; life), the most recent geologic
era which is characterized by mammals, birds, modern insects, etc.

Central nervous system, brain and spinal cord.

822 Appendix

Centriole (sen' tri ol) (L. centrum, center), small central granule of most centro-

somes.
Centrosome (central body) (sen' tro som) (L. centrum, center; soma, body), the

body enclosing the centriole and located in the center of the aster during

mitosis.
Centrosphere, see Centrosome.

Cephalic (se -fal' ik) (Gr. kephale, head), pertaining to the head.
Cephalization (sef al i -za' shun), development of larger head and brain in higher

animals.
Cephalochordata (sef a lo kor -da' ta) (Gr. kephale, head; chorde, chord), a sub-
phylum of the phylum Chordata in which the notochord is confined to

the temporary tail of the larva.
Cephalopoda (sef a -lop' o da) (Gr. kephale, head; pous, foot), certain moUusks

with muscular, sucker-bearing "arms" on the head region.
Cephalothorax (sef a lo -tho' raks) (Gr. kephale, head; thorax, chest), head fused

with the thorax.
Cercaria (ser -ka' ri a) (Gr. kerkos, tail), tailed larva of a fluke.
Cerebellum (ser e -bel' um) (L. dim. of cerebrum, brain), the part of a vertebrate

brain dorsal and anterior to the medulla.
Cerebrum (ser' e brum) (L. cerebrum, brain), anterior hemispheric part of a

vertebrate brain.
Cervical (sur' vi kal) (L. cervix, neck), pertaining to the neck.
Cestoda (ses -to' da) (Gr. kestos, girdle), a tapeworm.
Chaeta (ke' ta) (Gr. chaite, hair), spine or bristle.

Chalone (kal' on) (Gr. chalinos, depress), a hormone which depresses activity.
Chelicera (ke lis' era) (Gr. chele, claw; keras, horn), the most anterior pair of

appendages of the spider, scorpion, king crab.
Cheliped (ke'liped) (Gr. chele, claw; pous, foot), pincerlike appendage on the

thorax of crayfish and allies.
Chemosynthesis, manufacture of foods by certain bacteria which use energy

derived from chemical reactions such as the oxidation of ammonia, sulfur,

etc.
Chemotaxis (chemotropism) (kem o -tax' is; ke mot' ro pizm) (Gr. chemo, chemi-
cal or juice; taxis, reaction) (Gr. trophe, turning), the simple response

(either positive or negative) to chemical stimuli.
Chilopoda (ki -lop' o da) (Gr. cheilos, lip; pous, foot), centipedes.
Chitin (ki' tin) (Gr. chiton, covering), outer, horny covering of insects, Crus-
tacea, etc.
Chiton, a mollusk (class Amphineura) with a shell made of eight dorsal plates.
Chlamydospore (klam -id' o spor) (Gr. chlamys, mantle), a thick-walled, resting

spore in certain fungi.
Chloragogen cells (klo ra -gog' en) (Gr. kloros, green; ago, lead) cells on the outer

surface of the earthworm intestine.
Chlorophyta (klor -of i ta) (Gr. chloros, green; phyta, plants), green algae.
Chlorophyll (klo'rofil) (Gr. kloros, green; phyllon, leaf), the green pigment of

many plants.
Chlorophyllogen (klo ro -fil' o jen) (Gr. kloros, green; phyllon, leaf; gen, to form),

the plant material from which chlorophyll is formed.

Appendix 823

Chloroplast (Chloroplistid) (klo' ro plast) (Gr. kloros, green; plastos, mouded),

body containing chlorophyll.
Choanocyte (ko' a no sit) (Gr. choana, funnel; kytos, cell) {see Collar cell).
Chondriosonie (kon' dri o som) (Gr. chondros, cartilage; soma, body), feebly

refractive body in the protoplasm.
Chondroskeleton (kon dro -skel' e tun) (Gr. chondros, cartilage), cartilaginous

skeleton.
Chordata (kor-da'ta) (L. chorda, string or chord), animals having a temporary

or permanent dorsal skeletal notochord.
Chorion (ko' ri on) (Gr. chorion, membrane), outer membrane enveloping the

mammalian fetus and enclosing the amnion.
Choroid (ko' roid) (Gr. chorion, membrane; eidos, form), a vascular layer be-
tween the retina and the sclerotic layer of the eye.
Chromatid (kro'matid) (Gr. chroma, color), one of two threads and its matrix

in a chromosome.
Chromatin (kro'ma tin) (Gr. chroma, color), part of a nucleus which stains well.
Chromatophore (kro' mat o for) (Gr. chroma, color; phoreo, to bear), a colored

plastid or cell, as chloroplast.
Chromidia (kro -mid' i a) (Gr. chroma, color), small particles of chromatin out-
side the nucleus,
Chromomere (kro' mo mere) (Gr. chroma, color; meros, part), one of a linear

series of chromatin bodies in a chromosome.
Chromonemata (kro mo -nem' a ta) (Gr. chroma, color; nema, thread), threadlike

structures within the chromosome.
Chromosome (kro' mo som) (Gr. chroma, color; soma, body), deeply staining

bodies formed in the cell nucleus during mitosis; they carry the materials of

heredity.
Chrysophyta (cry -sof i ta) (Gr. chrysos, golden; phyta, plants), golden brown

algae, yellow-green algae, and diatoms.
Chyme (kim) (Gr. kymos, juice), semiliquid partially digested food in the stom-
ach.
Cilium (sir i um) (L. cilium, eyelash), hairlike, vibratile, cytoplasmic process on

certain cells, as certain protozoa, etc.
Cirrus (sir' us) (L. cirrus, a lock), hairlike structure on certain worms, insects,

etc.
Cleavage (klev'ij) (A.S. cleofan, to separate), division of the zygote into cells

known as blastomeres.
CHtellum (kli -tel' um) (L. clitellae, saddle), thickened area on certain annelids

to assist in reproduction.
Cloaca (klo-a'ka) (L. cloaca, sewer), common organ into which the intestine,

kidneys, and sex organs discharge their products.
Clone (klone) (Gr. klone, twig), all the asexual offspring of an individual which

are identical in regard to their gene content.
Cnidoblast (ni' do blast) (Gr. knide, nettle; hlastos, bud), sac-shaped stinging or

nettle cell with a permanent, long barbed thread and poisonous fluid as

in certain coelenterates.
Cnidocil (ni' do sil) (Gr. knide, nettle; L. cilium, eyelash), small, triggerlike

process for ejecting the thread from the cnidoblast.

824 Appendix

Coccus (kok' us) (Gr. kokkus, berry), spherical, unicellular organism.

Cochlea (kok' lea) (Gr. kochlias, snail), spirally coiled part of the inner ear,

containing receptors for hearing.
Cocoon (ko-koon') (L. concha, shell), the enclosed stage of certain insects in

which the pupa enters the cocoon and the adult emerges from it; e^g case

of spiders and earthworms.
Coelenterata (se lent er -a' ta) (Gr. koilos, hollow; enteron, digestive tract),

phylum of animals having a hollow digestive tract as Hydra, Obelia, etc.
Coelom (coelome) (se' lum) (Gr. koilos, hollow), a hollow true body cavity con-
taining organs.
Coelomization (se lom i -za' shun), presence of a true body cavity (coelom) be-
tween the body wall and the digestive tract formed from mesoderm.
Cohesion (ko -he' shun) (L. cohaerere, to stick), attraction whereby particles

(molecules) of a body are united throughout a mass (attract each other).
Cold-blooded, body temperature varies with the environment.
Coleoptera (ko le -op' tera) (Gr. coleos, sheath, ptera, wings), order of insects

with hard, chitinous wings, such as beetles and weevils.
Collar cell (choanocyte), cells with a collarlike structure on the surface as in

sponges.
Collembola (kol -em' bo la) (Gr. kolla, glue; embolon, rod), wingless insects such

as springtails.
Colloid (kol' oid) (Gr. kolla, glue), a finely divdded matter suspended or dispersed

through some continuous medium.
Columnar (kol -lum' nor) (L. column, column), column shaped.
Combination, an inherited variation due to the combining of genes from parents.
Combustion (L. combustio, burn), rapid oxidation of a chemical substance.
Commensalism (kom -men' sal izm) (L. com, with; mensa, table), an association

of members of two or more species (not truly parasitic) which live in, or

on, or with each other, usually partaking of the same food.
Commissure (kom'ishoor) (L. commisura, join together), a circle of nervous

tissue to connect various regions as in earthworms, snails, insects, etc.
Companion cell, one which usually accompanies seive tubes in phloem tissues of

plants.
Complementary factors, two or more dissimilar factors (genes) which interact

and complement to produce a particular trait.
Compound, a substance made of two or more elements in chemical union.
Compound eye, one made of numerous units called ommatidia, as in certain

arthropods.
Condyle (kon' dil) (Gr. kondylos, knuckle), rounded process for articulation of a

bone.
Congenital (kon -jen' i tal) (L. con, together; gigno, to bear), present at birth.
Conidia (ko -nid' i a) (Gr. konis, dust), small spores formed by constricting hyphae.
Conidiophore (ko -nid' i o for) (Gr. konis, dust; phoreo, to bear), structure which

bears conidiospores.
Conidiospore (conidium) (ko -nid' i o spor) (Gr. konis, dust; sporos, spore), spore

formed by constricting the tip of a hypha as in certain molds.
Conjugation (kon joo -ga' shun) (L. con, together; jugare, to join), temporary

union of two cells to exchange nuclear materials.

Appendix iB25

Connective tissues (kon -nek' tiv) (L. con, together; nectere, to bind), similar
cells for support and binding.

Conservation of energy, a law which states that the total energy content of the
universe is constant, that none is created, none is lost, but merely trans-
formed from one type to another {see Potential and Kinetic energy).

Continuity of germ plasm, germ plasm is continuous throughout all generations
and is not produced anew each time a new individual is produced.

Continuous variations, those in which varieties are merely plus or minus devia-
tions from the mode and which may be arranged serially in the form of a
simple curve.

Contractile vacuole (kon -trak' til; vak'uol) (L. con, together; trahere, to draw;
L. vaccus, empty), a hollow structure which alternately contracts and ex-
pands, as in amoeba, paramecium, etc,

Conus arteriosus (ko'nus; ar te ri -o' sus) (Gr. konus, cone shaped), cone-shaped
structure between the ventricle and arteries of certain animals.

Convergent adaptation, different organisms assuming similar forms because of
their adaptations to the same environmental medium.

Coordination, the harmonious working together of the various parts of an in-
dividual or of various individuals.

Copulation (kop u -la' shun) (L. copulare, to couple), sexual union.

Cork cambium, a ring of dividing cells, in woody plants, beneath the epidermis
which originates parenchyma on the inside and cork on the outside.

Cornea (kor'nea) (L. corneus, horny), transparent part of the sclerotic coat of
the eye that covers the iris and pupil.

Corolla (ko-rol'a) (L. corona, crown), all the flower petals taken together.

Corpus luteum (kor' pus lu' te um) (L. corpis, body; luteus, yellow), a yellowish
body developed from a Graafian follicle after extrusion of ovum.

Corpuscle (kor' pus 1) (L. corpusculum, little body), a small body, mass, or organ.

Cortex (kor' tecks) (L. corium, covering or bark), the outer covering.

Cortin (kor' tin) (L. cortex, covering), hormone from the cortex (covering) of
the adrenal glands.

Cotyledon (kot i -le' dun) (Gr. kotyledon, cup-shaped hollow), embryonic seed
leaf, usually having stored food,

Cowper's gland, small gland associated with the prostate gland and urethra of
male mammals.

Cranial nerves, those arising from the brain.

Cranium (kra' ni um) (Gr. cranios, brain case), the brain case.

Creatinine (kre -at' i nin) (Gr. kreas, flesh) nitrogenous substance in muscles,
urine, etc.

Cretinism (kre' tin izm) (L. christianus, human being), one who is physically and
mentally deficient due to deficient thyroid gland.

Crinoid (kri' noid) (Gr. krinon, lily; eidos, like), a lilylike animal of the phylum
echinodermata.

Criss-cross inheritance, paternal traits transmitted to daughters and maternal
traits to sons.

Cross fertilization, union of gametes (sex cells) produced by different individuals,
either animals or plants.

826 Appendix

Crossing over, rearrangement and crossing over of linked characters as a result of
exchange of genes between homologous chromosomes during synapsis.

Crustacea (krus -ta' she a) (L. crustaceus, shell or crust), a class of the phylum
Arthropoda characterized by a chitinous exoskeleton.

Cutaneous (ku -ta' ne us) (L, cutis, skin), pertaining to the skin.

Cuticle (ku' tik 1) (L. cutis, covering), transparent covering.

Cutin (ku' tin) (L. cutis, skin) waxy substance covering leaves to make the
cuticle impervious to water,

Cyanophyta (si an -of i ta) (Gr. kyanos, blue; phyta, plants), blue-green algae,

Cyclosis (si -klo' sis) (Gr. kyklosis, circulate), circulating movement of protoplasm
in a cell.

Cyst (sist) (Gr. kystis, sac), protective covering about an organism.

Cysticercus (sis ti -sur' kus) (Gr. kystis, sac; kerkos, tail), larval bladderworm
stage of certain tapeworms.

Cytogenic reproduction (si to -jen' ik) (Gr. kytos, cell; gen, to form), reproduc-
tion afifected by means of unicellular germ cells which grow and divide to
form a multicellular organism (contrast with Somatogenic reproduction).

Cytology (si -tol' o ji) (Gr. kytos, cell; logos, science), study of cells.

Cytolysin (si to -ly' sin) (Gr. kytos, cell; lysis, destroy), substance which destroys
cells.

Cytolytic, see Cytolysin.

Cytoplasm (si'toplazm) (Gr. kytos, cell; plasm, liquid), the portion of the proto-
plasm outside the nucleus.

Cytoplasmic inclusions, nonliving materials in the cytoplasm.

Cytotoxin (si to -tok' sin) (Gr. kytos, cell; toxicon, poison), substance having a
specific toxic efTcct on cells of certain types.

Dactyl (dak' til) (Gr. daktylos, finger), refers to finger.

Darwinism, theory of natural selection proposed by Charles Darwin; not synony-
mous with organic evolution.

Deciduous (de-sid'uus) (L. de, away; cadere, to fall), falling off at end of a
period of growth.

Dehydration (de hi -dra' shun) (Gr. de, from; hydros, water), extraction or re-
moval of water.

Deltoid (del' toid) (L. delta, triangle), triangular, like the deltoid muscle.

Dendrite (dendron) (den' drit) (Gr. dendron, tree), branched processes which
carry impulses toward the nerve cell (neuron) (contrast with Axon).

Denitrifying (de -ni' tri fy ing) (Gr. de, from; nitrogen) , break down of nitroge-
nous substances.

"De novo," a Latin phrase denoting an origin from no known source or from no
similar structure.

Dentine (den' teen) (L. dens, tooth), inner part of tooth.

Dermis (derma) (der' mis) (Gr. derma, skin), true skin underlying the epidermis
(same as corium).

Determinate cleavage, early divisions of an ^gg in which each blastomere can be
traced to some future tissue or organ and in which the original cells are
arranged along the various axes of the organism.

Appendix 827

Determiner, see Gene.

Dialysis (di-al'asis) (Gr. di, two; lysis, separating), separation of dissolved ma-
terials such as crystalloids from colloids by passage of former through a
semipermeable membrane; diffusion of certain substances in solution
through a membrane but not of other substances.

Diaphragm (di'afram) (Gr. diaphragma, partition), muscle separating thoracic
and abdominal cavities.

Diastase (di'astas) (Gr. dia, through; histanai, to set), enzyme which converts
starch into sugar.

Dichotomous (di -kot' o mus) (Gr. dicho, two; tome, divide), repeated forking
into two parts.

Dieclous (di-e'shus) (Gr. di, two; oikos, house), having male and female sex
organs in separate individuals (contrast with Monecious).

Differentiation (specialization), process of becoming structurally or functionally
unlike the original condition.

Diffraction (di -frak' shun) (L. diffractus, break), deflection of light waves when
passing through a narrow slit to form fringes of parallel light and dark-
colored bands.

Diffusion (di -fu' zhun) (L. diffusia, spread), passage of molecules of one sub-
stance among those of another from a region of greater concentration to
one of less concentration.

Digestion (di -jes' chun) (L. digestio, dissolve food), preparing food for absorp-
tion.

Dihybridization (di hy brid i -za' shun) (Gr. di, two; hyhrida, mongrel), produc-
ing an offspring from parents who differ with regard to two given char-
acters.

Dimorphism (di -mor' fizm) (Gr. di, two; morphe, form), two forms or types
belonging to one species, as males and females of same species but differing
from each other.

Diphyletic tree (dif i -let' ik) (Gr. diphy, twofold), schematic, treelike representa-
tion of the supposed ancestral relations of various animals and plants.

Diploblastic (dip lo -bias' tik) (Gr. diplos, two; blast os, germ), two germ layers
(ectoderm and entoderm).

Diploid (dip' loid) (Gr. diplos, two), double number of chromosomes found in
the sporophyte generation of plants and body cells of animals as contrasted
with single number in germ cells (contrast with Haploid).

Diplopoda (dip -lop' o da) (Gr. diploos, double; pous, foot), millipedes.

Diptera (dip' tura) (Gr. di, two; ptera, wings), insects with the two wings (one
pair) as flies, mosquitoes, gnats, etc.

Direct cell division, see Amitosis.

Discontinuous distribution, two species occurring in two or more widely sepa-
rated regions, suggesting that their distributions may at one time have
been continuous. Tapirs exist only in Malay and tropical America.

Discontinuous variation, see Mutation.

Distal (dis' tal) (L. dis, apart; stare, to stand), farthest from median line.

Divergence (adaptive radiation), somewhat closely related species radiate in vari-
ous directions into different environments and become modified (vary)
accordingly.

828 Appendix

Division of labor, distribution of functions among cells, organs, or individuals.
Dizygotic (di zi -got' ik) (Gr. di, two; zygon, yoke, pair), derived from two eggs

as in certain types of twins (contrast with Monozygotic).
Dominance (dominant character), one of a pair of alternative characters which

is always expressed when its gene is present and which appears to exclude

the other (recessive) character.
Dorsal (dor' sal) (L. dorsum, back), the back side of higher animals.
Dorsal aorta, chief artery arising from the heart to distribute blood to the body.
Dorsal horn (root), sensory root of a spinal nerve carrying impulses into the

spinal cord; ventral root carries impulses from the cord.
Dorso ventral differentiation, body with definite dorsal (back) and ventral (belly)

sides or regions.
Drosophila (dro -sof i la), the common fruit or banana fly; used extensively for

heredity experiments.
Ductless glands, see Endocrine glands.
Duodenum (duo-de'num) (L. duodeni, twelve), anterior part of small intestine,

twelv-e fingerwidths long.
Duplicate factors, different factors (genes) having identical but not cumulative

effects.

E
Ecdysis (ek'disis) (Gr. ek, out; dyein, to come), the losing or molting of an

outer structure as in the crayfish, insects, etc.
Echinodermata (e kin o -dur' ma ta) (Gr. echinos, spiny; dermos, covering), spiny-
covered animals, such as starfishes, sea urchins, sand dollars, etc.
Ecology (e-kol'oji) (Gr. oikos, home; logos, study), scientific study of living or-
ganisms and their living and nonliving environments.
Ectoderm (ek' to durm) (Gr. ektos, outside; derma, skin), outer layer of germ

cells.
Ectoparasitism (ek to -par' a sit -izm) (Gr. ektos, outside; para, beside; sitos, food),

parasites attached externally to the host.
Ectoplasm (ectosarc) (ek' to plazm) (Gr. ektos, outside; plasma, liquid), outer

layer of cell cytoplasm.
Efferent (ef er ent) (L. ex, out; ferro, to carry), convey away from.
Egest (e-jest') (L. ex, out; gerere, to carry) to throw out, usually indigestible

material.
Egg (ovum), the mature female sex cell of a plant or animal.
Elater (el'ater) (Gr. elater, driver), a springlike organ of various plants to

disperse spores.
Electrolyte (e -lek' tro lit) (Electric; Gr. lytos, dissolved), a substance, such as

salts, acids, and bases, which in solution dissociates into electrically charged

ions.
Electrolytic dissociation, breaking up of the molecules of electrolytes (acids, bases,

salts) into electrically charged positive and negative ions capable of con-
ducting an electric current.
Electron (e -lek' tron) (Gr. elektron, gleaming, sun), smallest part, or unit, of

negative electricity {see Nuclear electrons and Extranuclear electrons).
Element (el' e ment) (L. elementum, unit), a substance whose atoms are all the

same; over ninety elements are known.

Appendix 829

Elemental theory, the entire individual is explained as a result of the summation
of the activities and characteristics of its ultimate parts (contrast with
Organismal theory).

Elytra (el' i tra) (Gr. elytron, sheath), sheathlike wings of beetles.

Embryo (em' brio) (Gr. embryon, embryo), early stages of development of an
organism.

Embryology (em bri -ol' o ji) (Gr. embryon, embryo; logos, study), study of early
development of organisms.

Embryonic disc (embryonic shield), a cellular partition separating the amniotic
and yolk sac cavities of certain embryos from which the embryo proper
will form.

Embryophyta (em bri -of i ta) (Gr. embryon, embryo; phyta, plants), plants pro-
ducing a multicellular embryo.

Emulsion (e-mul'shun) (L. emulgere, to milk out), mixture of two liquids or
semisolids, neither of which is soluble in the other, with the result that one
is in the form of droplets suspended in the other.

Emulsoid, a suspension of the nature of an emulsion but with the dispersed phase
more finely divided. Cream is a system of fat droplets suspended in water.

Encystment (en -sist' ment) (Gr. en, in; kystis, sac), surrounded by a protective
coat.

Endocardium (en do kar' di um) (Gr. endon, within; kardium, heart), inner lin-
ing of the heart.

Endocrine (ductless) glands (en'dokrin) (Gr. endon, within; krinein, to sepa-
rate), ductless glands which produce internal secretions from materials
brought to them by blood and whose secretions are carried from them by
the blood.

Endoderm, see Entoderm.

Endometrium (en do -me' tri um) (Gr. endon, within; mefra, womb), a heavy,
mucous glandular layer of the uterus during pregnancy.

Endoparasite (en do -par' a sit) (Gr. endon, within; para, beside; sitos, food), an
internal parasite (lives within body of its host).

Endoplasm (en' do plazm) (Gr. endon, within; plasma, liquid), inner cytoplasm of
a cell.

Endopodite (en -dop' o dit) (Gr. endon, within; pons, appendage), inner of two
branches of a biramous appendage of a crustacean,

Endoskeleton, internal skeleton.

Endosperm (en'dospurm) (Gr. endon, within; sperma, seed), nutritive substances
within the seed coats but not a part of the embryo proper.

Endosteum (en -dos' te um) (Gr. endon, within; osteon, bone), internal lining of a
bone.

Endothelium (en -do -the' li um) (Gr. endon, within; thele, nipple), cells arising
from mesoderm and lining blood vessels and lymph spaces.

Enteric (en-ter'ik) (Gr. enteron, intestine), pertaining to digestion or digestive
tract.

Entoderm (en'todurm) (Gr. entos, within; derma, skin), inner germ layer (con-
trast with ectoderm).

Entomology (en to -mol' o ji) (Gr. entomon, insect; logos, study), science dealing
with insects.

830 Appendix

Entoparasite, see Endoparasite.

Enzyme (en' zim) (Gr. en, in; zyme, leaven), a ferment or organic catalyst se-
creted to bring about or hasten a reaction but which is not consumed in
the process.

Epicotyl (ep'ikotl) (Gr. epi, upon; kotyle, cotyledon), portion of the embryo
axis above the attachment of the cotyledons to form the young stem.

Epidermis (ep i -dur' mis) (Gr. epi, upon; derma, skin), outer layer of skin.

Epigenesis (ep i-jen' e sis) (Gr. epi, upon; genesis, origin), doctrine that develop-
ment proceeds from a relatively simple germinal substance, with complexity
arising through the interaction of the protoplasm and the environment
(contrast with Preformation).

Epiglottis (ep i -glot' is) (Gr. epi, upon; glotta, tongue), covering of the glottis
during swallowing.

Epimysium (ep i -miz' i um) (Gr. epi, upon; mys, muscle), covering of a muscle.

Epinephrine (adrenalin) (ep i -nef rin) (Gr. epi, upon; nephros, kidney), hor-
mone of the inner medulla of the adrenals, which are located on the kid-
neys.

Epiphyte (ep' i fite) (Gr. epi, upon; phyton, plant), a plant which is physically
supported by another plant or from poles, wires, etc.

Epithelium (ep i -the' li um) (Gr. epi, upon; thele, teat or nipple), membranes lin-
ing or covering a surface, including secreting glands.

Equatorial plate, middle or equator of the spindle during mitosis. ^

Erepsin (e -rep' sin) (L. eripere, to set free), protein-splitting enzyme of the
intestine.

Erythroblast (e -rith' ro blast) (Gr. erythros, red: hlastos, originate), cell from
which red blood cells (erythrocytes) develop.

Erythrocyte (e -rith' ro sit) (Gr. erythros, red; kytos, cell), red blood corpuscle.

Esophagus, see Oesophagus.

Estivation, see Aestivation.

Ethnology (eth-nol'oji) (Gr. ethnos, nation; logos, study), study of the charac-
teristics, distribution, and relationships of human races.

Eugenics (u-jen'iks) (Gr. eugenes, well born), science of race improvement
through heredity.

Eumycophyta (u mi -kof i ta) (Gr. eu, true; mykos, fungus; phyta, plants), true
fungi, as Phycomycetes, Ascomycetes, and Basidiomycetes.

Eustachian tube (u-sta'shun) (Eustachio, an Italian anatomist), tube connecting
pharynx and middle ear.

Evagination (e -vaj i -na' shun) (L. evageri, to go forth), outgrowing of a layer of
cells from a cavity.

Evolution (ev o -lu' shun) (L. evolvo, to unroll), theory that all living organisms
have undergone, and do undergo, gradual changes through successive gen-
erations; that all living organisms are constantly changing (evolving).

Excretion (eks -kre' shun) (Gr. ex, out; cernere, to separate), elimination of wastes.

Excurrent (eks -kur' ent) (Gr. ex, out; currens, to run), conducting away from a
cavity or organ.

Exhalant (eks -hal' ant) (Gr. ex, out: halare, to breathe), to conduct outward
from the interior.

Appendix 831

Exopodite (eks -op' o dit) (Gr, ex, out; pons, appendage), outer of two branches

of a biramous appendage of a crustacean.
Exoskeleton (ek so -skel' e ton) (Gr. exo, outside), outer skeleton.
Expiration (ek spi -ra' shun) (Gr. ex, out; spirare, to breathe), emitting air from

lungs.
Extensor (eks -ten' ser) (Gr. ex, out; tendere, to stretch), muscle to extend a limb

or part.
External receptor, sense organ on surface of an organism to receive stimulation.
External respiration, exchange of gases between blood and the outside through

lungs, skin, or gills.
Extra-embryonic coelom, one of the coeloms of the early embryo.
Extranuclear electrons, those outside the nucleus of the atom.
Eye spot, pigmented, light-sensitive area, as the stigma of Euglena.

Fi, Fo, F3, etc., abbreviations for the first, second, third filial generations in

heredity.
Factor, see Gene.
Facultative (fak' ul ta tiv) (L. facultas, faculty), the abiUty to change certain

methods of living to suit conditions.
Fallopian tube (fa -lo' pi an) (From Fallopius, a physician who died in 1562), the

oviduct in mammals.
Family (fam'ili) (L. familia, household), organisms of one group of an order.
Fascia (fash' i a) (L. fascia, band), bandlike covering of connective tissue.
Fat (A.S. faett, fat), adipose tissue, cells of which are filled with oil.
Fatty acid, one of a group of organic acids, such as acetic, butyric, oleic, stearic,

etc., which contains only one COOH (carboxyl) group.
Fauna (fo' na) (L. Faunus, god of the woods), animal life characteristic of a

given area.
Feces (fe' sez) (L. faeces, dregs), wastes or excrements.
Femur (fe'mer) (L. femur, thigh), thigh bone or the third segment of an insect

leg from the proximal (near) end.
Fermentation (fur men -ta' shun) (L. fermentum, ferment or leaven), change in

an organic substance caused by a ferment, as souring of milk.
Fertilization (fur til i -za' shun) (L. ferre, to produce), union of sperm and egg

in sexual reproduction.
Fetus (foetus) (fe' tus) (L. fetus, offspring),' the later embryo of a vertebrate

(after third month in human being).
Fibril (fi' bril) (L. fihrilla, small fiber), small, fibrous structure.
Fibrin (fi' brin) (L. fibra, band), an insoluble material in blood after clotting.
Fibrinogen (fi -brin' o jen) (L. fihra, thread; gignesthai, to form), a constituent

of blood that aids in fibrin formation.
Fibula (fib' u la) (L. fibula, buckle), outer, smaller bone of lower leg.
Filial (fil' i al) (L. filia, daughter; filius, son), one or more successive generations

after the parents.
Filial regression law, superior parents tend to have superior offspring but who

on the average are less superior than the parents; inferior parents tend

to have offspring who are also inferior, but less so than themselves.

832 Appendix

Fission (fish'un) (L. fissus, cleave), asexual division into two or more parts.

Flagellum (plural, flagella) (fla -jel' um) (L. fiagellum, whip), whiplike process
for locomotion.

Flame cell, an excretory cell with a bunch of cilia by means of which wastes are
expelled to the outside; the action of the cilia somewhat resembles a flick-
ering flame.

Flatworni, a member of the phylum Platyhelminthes.

Flavone (flavonol) (fla' von) (L. flavus, yellow), yellow pigment of certain
higher plants.

Flexor (flek' ser) (L. flexus, bend), rtiuscle to bend a joint.

Flora (flo' ra) (L. flos, flower), plants characteristic of a region or period (con-
trast with Fauna) .

Fluctuations, somatic variations which result from differences in environment or
functions and which are not inherited.

Fluke, a parasitic flatworm (phylum Platyhelminthes).

Fontanelle (fonta-nel') (Fr. fontanelle, little fountain), space between bones of
the cranium, covered with a membrane, through which blood flow pulsa-
tions show.

Foramen (fo-ra'men) (L. foramen, opening), an opening in a structure.

Foreign protein, one not common to an organism.

Fossil (fos'il) (L. fossilis, dug up), preserved record of ancient organism.

Fossilization, formation of records of ancient organism. ■'

Fragmentation, reproduction by isolating a part of an organism to form a new
individual.

Fraternal twins, those produced by fertilization of two different eggs which usu-
ally have different hereditary traits. Sometimes called nonidentical or
dizygotic twins.

Frond (frond) (L. frond, leafy branch), fern leaf.

Fructose (fruk' toz) (L. fructus, fruit), fruit sugar.

Fucoxanthin (fuk o -zan' thin) (L. fucus, seaweed; xanthos, yellow), yellowish-
brown pigment of brown algae.

Fundus (fun' dus) (L. fundus, base), base of an organ.

Fungus (fun' gus) (L. fungus, mushroom), lower chlorophyll-less plants.

Gall bladder, sac near the liver in which bile is stored.

Galvanotropism (gal va -not' ro prizm) (after the Italian, Galvani), response of
living organisms to electric currents.

Gametangium (ga me -tan' ji um) (Gr. gamos, gametes; angios, vessel), a gamete-
producing structure.

Gamete (gam' et) (Gr. gamos, marriage), mature male or female sex cell;

Gametogenesis (gam e to -jen' e sis) (gamete; genesis, origin) production and
maturation of gametes (sex cells).

Gametophyte ( ga -me' to fit ) {gamos, marriage; phyton, plant), plant producing
gametes (sex cells).

Ganglion (plural, Ganglia) (gang' lion) (Gr. ganglion, enlargement), an enlarge-
ment of a nerve which contains nerve cells and acts as a center of influ-
ence.

Appendix 833

Gastric (gas' trik) (Gr. gaster, stomach), pertaining to the stomach or to
digestion.

Gastrovascular (gas tro -vas' ku lar) (Gr. gaster, stomach; L. vasculum, vessel or
circulation) digestive-circulatory cavity as in Hydra.

Gastrulation (gas troo -la' shun) (Gr. gaster, digestive), the formation of the gas-
trula stage in embryonic development by an invagination (infolding)
process whereby the future digestive tract will be formed.

Gel (jel) (L. gelare, to stiffen), state of a colloidal system in which the external
phase is more solid than the internal phase (jellylike colloid).

Gelation (jel -a' shun) (L. gelare, to stiffen), the phenomenon of forming a gel.

Gemma (gem' a) (L. gemma, bud), small, green, asexual reproductive bodies
found in such plants as the Marchantia (Liverwort).

Gemmule (gem'ul) (L. gemma, bud), asexual reproductive body of several cells
found in certain sponges.

Gene (jen) (Gr. gen, to form), factor (determiner) in a chromosome which influ-
ences the development of a hereditary trait.

Genetics (je -net' iks) (Gr. genesis origin), science of trait transmission from par-
ents or other ancestors to offspring.

Genital (jen' i tal) (L. gignere, to beget), pertaining to reproduction.

Genotype (jen' o tip) (Gr. genos, race; typos, model), hereditary constitution of
an organism or a group of organisms based upon gene content (contrast
with Phenotype).

Genus (je' nus) (Gr. genos, race), somewhat similar organisms having one or more
species which are structurally or phylogenetically related.

Geographic distribution (biogeography), distribution of plants and animals in dif-
ferent geographic areas.

Geotropism ( je -ot' ro pizm) (Gr. ge, earth; trope, turning), reaction of organisms
to gravity.

Germ cell, male or female reproductive cell.

Germinal continuity (jurm' i nal) (Gr. germen, offspring), the unbroken, con-
tinuous stream of germ plasm from one generation to another.

Germinal variation, variation arising in a germ cell.

Germ layer, two or three embryonic cellular layers from which future adult tis-
sues and organs arise.

Germ plasm, material basis of inheritance found in germ cells (sex cells) and
transmitted by them to the cells of the offspring.

Germ theory of disease, certain types of diseases are caused by microorganisms.

Gestation (jes -ta' shun) (L. gestatio, to bear), carrying of young (normally in
the uterus) from conception to delivery (birth).

Gill, filamentous or platelike structure with blood vessels for respiration in water.

Gill book, specialized, booklike organ of respiration in certain Arachnida.

Gill slits, paired openings in vertebrates connecting the pharynx with the exterior
and permitting the exit of water (same as pharyngeal cleft).

Gizzard (giz' ard) (Fr. giser, gizzard), muscular grinding organ for digestion.

Gland (L. glans, nut), a cell or group of cells for secretion.

Glochidium (glo -kid' i um) (Gr. glochis, arrow point), bivalved larva of mollusks
which live parasitically, on a fish for a time.

834 Appendix

Glomerulus (glo -mer' u lus) (L. glomero, ball), ball-like mass of capillaries at
enlarged end of the kidney tubule of higher vertebrates (same as Mal-
pighian body).

Glottis (glot'is) (Gr. glotta, tongue), slitlike opening in the pharynx leading to
windpipe (trachea).

Glucose (glu' kos) (Gr. glykys) , grape sugar.

Glycogen (gli'kojen) (Gr. glykys, sweet), a starchlike carbohydrate stored in
the liver and other tissues and in certain algae and fungi.

Goiter (goi' ter) (L. guttur, throat), pathologic enlargement of the thyroid gland.

Golgi bodies (gol'je) (after Golgi, Italian physician), special bodies in cyto-
plasm of certain cells.

Gonad (gon' ad) (Gr. gonos, reproduction), a male or female sexual reproduc-
tive organ.

Gonidia (go -nid' i a) (Gr. gone, seed), asexual nonmotile reproductive cells.

Gonophore (gon' o for) (Gr. gonos, seed; phoreo, to bear), gonad-bearing struc-
ture.

Graafian follicle (graf i an; fol' i kl) (after de Graaf, Dutch physician; L. follis,
bag), small cavity in the ovary, especially of mammals, in which egg
develops. *

Grafting, transplanting an organ or tissue from one plant or animal to another.

Grana (gran' a) (L. granum, small grain), small particles of chlorophyll in chloro-
plasts.

Green gland, excretory organ of a crayfish.

Growth hormone, specific chemical substances in plants and animals (especially
higher animals) which influence, regulate, or control growth or other
activities.

Guanin (gwa'nin) (huano, dung), a white substance found in guano (excrement
of sea birds) and other animal substances.

Guard cell, specialized cell of the epidermis of leaves to regulate the size of the
stomata of leaves.

Gullet, see Oesophagus.

Gustatory (gus' ta to ri) (L. gustare, to taste), sense of taste.

Guttation (guta'shun) (L. gutta, drop), exudation of water drops from plants
(especially leaves) due to internal pressure.

Gymnosperm (gym' no spurm) (Gr. gymnos, naked, exposed; sperm, seed), a
plant whose seeds are not enclosed by carpels (contrast with Angiosperm).

Gynandromorph ( ji -nan' dro morf) (Gr. gyne, woman; aner, man; morphe,
form), an abnormal individual who has male characteristics in one part of
its body and female characteristics in another.

Habitat (hab' i tat) (L. habito, to dwell), usual or natural dwelling place.

Halteres (hal-te'rez) (Gr. halter, weight used in jumping), pair of capitate
bodies used as balancers during flight of insects in the order Diptera. They
represent the rudimentary posterior wings of these insects.

Haploid (hap'loid) (Gr. haplos, single; eidos, form), single or reduced number
of chromosomes in mature germ cells (gametes), or the gametophyte gen-
eration of plants, in contrast to the diploid number in body cells.

Appendix 835

Haversian canal (ha -vur' shan) (after Havers, an English physician of the Seven-
teenth Century), small canals in bone to conduct blood, etc.

Heliotropism (he li -ot' ro pizm) (Gr. helios, sun; trope, to turn), response to light.

Helminthology (hel min -thol' o ji) (Gr. helmins, worm; logos, study), study of
worms.

Hemiptera (he -mip' tur a) (Gr. hemi, half; ptera, wings), order of insects whose
front wings have their basal region hardened, while the tips are mem-
branous, as in true bugs,

Hemocoel (he'mosel) (Gr. haima, blood; koilos, hollow), special portion of the
coelom for blood circulation.

Hemoglobin (he mo -glo' bin) (Gr. haima, blood; L. globus, globe), reddish, oxy-
gen-carrying substance of red blood corpuscles.

Hemophilia (hemo-fil'ia) (Gr. haima, blood; philos, loving), a disease, usually
hereditary, with a tendency to excessive bleeding, even from slight wounds.

Hemorrhage (hem'orij) (Gr. haima, blood; rhegnymi, break), loss of blood from
broken blood vessel.

Hepatic (he -pat' ik) (Gr. he par, liver), pertaining to the liver.

Hepatic portal system, the double blood supply of the liver of vertebrates.

Herbaceous (hur -ba' shus) (L. herbaceous, grassy), plants without woody tissues.

Herbivorous (hur -biv' o rus) (L. herba, plant; vorare, to devour), plant-eating
organisms (contrast with Carnivorous).

Heredity (he -red' i ti) (L. hereditas, heir), transmission of physical and mental
traits from parent or other ancestor to offspring {see Genetics).

Hermaphrodite (hur-maf ro dit) (Gr. Hermes and Aphrodite) , having both male
and female reproductive organs in one individual (same as Monecious;
(contrast with Diecious).

Heterauxin (het er -ox' in) (Gr. hetero, different; auximos, promote growth), a
special hormone which affects plant growth.

Heterocyst (het' ero sist) (Gr. heteros, different; kystis, sac), clear cell in certain
algae which separate the filament into hormogonia.

Heterogamy (anisogamy) (het er -og' a mi) (Gr. heteros, other; gamos, mar-
riage), union of unlike gametes (sex cells) (contrast with Isogamy).

Heteronomous segmentation (het er -on' o mus) (Gr. heteros, different), dissimilar
segmentation or metamerism, such as in crayfish, etc. (contrast with
Homonomous).

Heterosis (het er -o' sis) (Gr. heteros, other), increased vigor due to crossing or
hybridization.

Heterospory (het er -os' po ri) (Gr. heteros, different; spora, spores), production
of unlike spores (contrast with Homospory).

Heterotrophic (het er o -trof ik) (Gr. heteros, different; trophe, food), organisms,
unable to manufacture their food; hence they are parasites or saprophytes
(contrast with Autotrophic).

Heterozygote (het er o -zi' got) (Gr. heteros, unlike; zygon, yoke), formed by
union of gametes that are unlike in their gene content (contrast with
Homozygote).

Hibernate (hi' ber nat) (L. hiberna, winter), torpor or dormancy of certain
organisms due to cold.

836 Appendix

Histogenesis (his to -jen' e sis) (Gr. histos, web, tissue; gen, to form), tissue for-
mation and development.

Histology (his-tol'oji) (Gr. histos, web, tissue; logos, study), study of tissues
and cells.

Holophytic (hoi o -fit' ik) (Gr. holos, whole; phyton, plant), plants that manu-
facture their own food (contrast with Holozoic).

Holozoic (holo-zo'ik) (Gr. holos, whole; zoon, animal), securing nourishment,
as in animals, by ingesting and digesting organic materials (contrast with
Holophytic).

Homologous chromosomes (ho -mol' o gus) (Gr. homos, same; logos, speech), a
pair of chromosomes, one from each parent, that have relatively similar
structure and gene values.

Homologous genes, genes similarly located in homologous chromosomes, con-
tributing to the same expression or a different expression of a trait.

Homology (ho-mol'oji) (Gr. homos, same; logos, study), parts or organs which
are similar structurally and which have originated embryologically in a
similar way; for example, the forelegs of a dog and frog show homology.

Homonomous segmentation (ho -mon' o mus) (Gr. homos, similar), similar seg-
ments (metameres) as in the earthworm (contrast with Heteronomous).

Homoptera (ho -mop' tur a) (Gr. homos, same; ptera, wings), order of insects
whose wings are similar and membranous throughout (contrast with
Hemiptera).

Homospory (ho -mos' po ri) (Gr. homo, same; spora, spore), production of like
spores (contrast with Heterospory).

Homozygote (ho mo -zi' got) (Gr. homo, same; zygon, yoke), union of gametes
that are alike in their gene content (contrast with Heterozygote) .

Hormogonia (hor mo -go' ni a) (Gr. hormos, chain; gonos, offspring), portions of
algal filaments able to form new individuals.

Hormone (hor' mon) (Gr. hormaein, to excite), a chemical substance secreted by
one organ and producing a specific effect in another.

Host (L. hostis, stranger), an organism in or on which a parasite lives.

Humerus (hu'merus) (L. humerus, shoulder), upper arm bone.

Hyaline (hi'alin) (L. hyalos, glass), clear or transparent as hyaline cartilage.

Hybrid (hi'brid) (L. hybrida, mongrel), a crossbred animal or plant; the off-
spring of two parents who differ in at least one trait.

Hydrogen-ion concentration (pH), the index of acidity due to the number of
positive hydrogen ions concentrated in a solution.

Hydroid (hi'droid) (Gr. hydra, water; cidos, like), resembling Hydra. ,

Hydrolysis (hi -drol' i sis) (Gr. hydor, water; lysis, destroy), destruction of a
chemical substance by the addition of the elements of water.

Hydroponics (hi dro -pon' iks) (Gr. hydro, water; ponus, exertion), growth of
plants in liquid culture media (soilless cultivation).

Hydrostatic (hi -dro -stat' ik) (Gr. hydor, water; L. statique, weigh), regulating
the specific gravity of an organism in relation to that of water, as the
air bladder of certain fish.

Hydrotropism (hi -drot' ro pizm) (Gr. hydor, water; trope, turning), response of
organisms to water.

Hydroxyl (hi -drox' il), the radical OH.

Appendix 837

Hymenoptera (hi men -op' tur a) (Gr. hymen, membrane; ptera, wings), order of
insects with membranous wings as bees, wasps, etc.

Hyoid (hi'oid) (Gr. hyoides, Y-shaped), bone or cartilage at base of tongue.

Hypersensitiveness (Gr. hyper, above), excessive sensitiveness to certain foreign
materials, especially proteins, because of peculiar permeability of mem-
branes.

Hypertonic (hi per -ton' ik) (Gr. hyper, above; tension), possessing greater os-
motic pressure than some related substance (contrast with Hypotonic).

Hypertrophy (hi -per' tro fi) (Gr. hyper, above; trophe, growth), excessive growth
or development (contrast with Atrophy).

Hypha (hi' fa) (pleural, hyphae) (Gr. hyphe, web), a threadlike element of the
mycelium of a fungus.

Hypnosis (hip -no' sis) (Gr. hypnos, sleep), type of artificially produced sleep in
which there are certain unusual activities, with the diminution or sus-
pension of others.

Hypocotyl (hi po -kot' il) (Gr. hypo, below; hotyle, cotyledon), portion of the
embryo axis below the attachment of cotyledons and forming the primary
root of the seedling.

Hypodermis (hi po -dur' mis) (Gr. hypo, below; derma, skin), cellular layer lying
below, and secreting, the cuticle of arthropods, annelids, and other in-
vertebrates.

Hypostome (hi'postom) (Gr. hypo, under; stoma, mouth), around or under the
mouth.

Hypotonic (hi po -ton' ik) (Gr. hypo, below; tension), possessing lesser osmotic
pressure than some other related substance (contrast with Hypertonic).

Identical twins, those produced by the division of a single, fertilized egg and
resulting in two separate individuals with identical hereditary traits.
(Same as monozygous twins; contrast with Dizygotic or nonidentical
twins.)

Ileum (il' e um) (L. ileum, groin), posterior or lower part of small intestine.

Ilium (il' i um) (L. ilium, flank), dorsal part of hip or pelvic bone.

Immunity (i -mu' ni ti) (L. im, not; munia, obligation), ability of an organism to
resist disease.

Inbreeding, mating or crossing closely related types of animals or plants.

Incisor (in -size' er) (L. incisis, cut), adapted for cutting.

Incomplete dominance, neither of two genie factors completely dominating the
other.

Indeterminate cleavage, segmentation of the egg in such a way that the pros-
pective fate of the individual cells is not easily traced, and consequently
there is very little specialization of the cells or blastomeres (contrast with
Determinate).

Indirect cell division, see Mitosis.

Individuality, in a living organism, consists of complex living protoplasm, some-
what limited in size, which possesses definite form, structure, chemico-
physical activities, and a certain degree of order, correlation, and sub-
ordination in order to bring about a unity of the whole.

838 Appendix

Incus (ing' kus) (L. incus, anvil), middle or anvil bone of the ear of certain

vertebrates.
Indusium (indu'sium) (L. indusium, cover), membranous cover of a fern sorus.
Infection (in -fek' shun) (L. in, in; facere, to make), invasion of tissues by patho-
genic organisms with a resulting pathologic condition.
Infundibulum (in fun -dib' u lum) (L. infundere, pour into), funnel-like outgrowth

from the ventral part of the diencephalon of. the brain (see Pituitary

gland).
Infusoria (in fu -sor' i a) (L. infusus, crowded in), class of Protozoa very common

in hay infusions, on plants in water, etc.
Ingest (in -jest') (L. ingestus, take in) take in food.

Inhalant (in -hal' ant) (L. in, in; halere, breathe), to draw in or inspire.
Inheritance, transmission of traits from one generation to another.
Inhibitor (in -hib' i ter) (L. in, in; haheo, to have), restrain or check.
Inner cell mass, the inner group of cells of the embryonic morula in contrast to

the outer layer or trophectoderm (trophoderm).
Innominate (in -nom' i nat) (L. in, not; nomen, name), nameless.
Inorganic (in or -gan' ik) (L. in, not; organic), not organic but pertaining to

nonliving.
Insecta (in -sek' ta) (L. insectus, cut into), class of Arthropoda to which insects

belong.
Insectivorous (in sek -tiv' or us) (L. insectus, insect; voro, to eat), insect eating.
Insertion (in -sur' shun) (L. insertus, join), place of attachment, as the more

movable end of a muscle (contrast with Origin).
Instinct (in' stingkt) (L. instinguere, to incite), subconscious fixed reflex act due

to a definite arrangement of an inherited pattern of nerve cells and tissues.
Insulin (in' su lin) (L. insula, island), hormone secreted by the islands of Langer-

hans of the pancreas. v

Integument (in -teg' u ment) (L. integumentum, covering), covering or investing

layer.
Intercellular (in ter -sel' u lar) (L. inter, between; cellula, cells), between cells.
Internal receptor, sense organ within the body.
Internal respiration, passage of oxygen from the blood into the protoplasm of

tissue cells (contrast with External respiration).
Internal secretion, see Hormone or Endocrine.
Internode (in' ter node) (L. inter, between; nodus, knot), space between two

joints.
Intestine (in -tes' tine) (L. intestinus, internal), part of the digestive tract be-
yond the stomach.
Intracellular (in tra -scl' u ler) (L. intra, within; cellula, cells), within cells (con-
trast with Intercellular).
Intussusception (in tus su -sep' shun) (L. intus, within; suscipere, take up), growth

by adding new materials within the living protoplasm (contrast with

Accretion).
Invaginate (in -vaj' i nat) (L. in, in; vagina, sheath), to fold in, as in the gastrula.
Invertebrate (in -vur' te brat) (L. in, not; vertehratus, vertebra), lower animals

without vertebrae or notochord (contrast with Vertebrate).

Appendix 839

Ionization, breaking up of solute molecules into electrically charged ions in the

process of solution.
Ions (i' ons) (Gr. ion, going), electrically charged particles into which molecules

may be split when in water.
Iris (i' ris) (L. iris, rainbow), colored part of eye.
Irritability (ir i ta -bil' i ti) (L. irrito, excite), ability to receive and respond to

external or internal stimuli.
Ischium (is' ki um) (Gr. ischion, hip), posterior and dorsal bone of the pelvic

girdle.
Islands of Langerhans, areas in the pancreas which secrete the hormone insulin.
Isogametes (i so ga -mete') (Gr. isos, equal; gamete), similar gametes (sex cells).
Isogamy (i-sog'ami), union of similar gametes (contrast with Heterogamy).
Isolation (is o la' shun) (L. isolate, island), to keep away from; in heredity the

prevention of interbreeding between certain organisms.
Isotonic solution (iso-ton'ik) (Gr. isos, equal; tonikos, tension), one with

osmotic pressure equal to that of protoplasm.

Jejunum (je -joo' num) (L. jejunus, empty), middle or second part of the small

intestine between the duodenum and ileum.
Jellyfish, group of jellylike coelenterates.
Jugular (jug' u lar) (L. jugulum, collarbone), pertaining to the neck, as jugular

vein in neck.

Kappa particle, a "killer" particle in a Paramecium.

Karyokinesis (kar i o ki -ne' sis) (Gr. karyon, nut; kiriein, to move), see Mitosis.

Karyolymph (kar'iolimf) (Gr. karyon, nut or nucleus; L. lympha, liquid),

liquid ground substance of the cell nucleus.
Karyosome (kar'iosom) (Gr. karyon, nut or nucleus; soma, body), nucleus-like

body in the cell nucleus as opposed to the nucleolus (plasmosome).
Keratin (ker' a tin) (Gr. keras, horny), insoluble substance, similar to chitin,

forming the basis for horns, hoofs, etc.
Kinetic energy (ki -net' ik) (Gr. kineo, move), possessed by virtue of motion such

as falling water, winds, etc. (contrast with Potential energy).
Krause's membrane, transverse membranes^ within striated, voluntary muscle.

Labial (la'bial) (L. labium, lip), pertaining to lip.

Labium (la' bi um) (L. labium, lip), lower lip of insects.

Labruni (la' brum) (L. labrum, lip), upper or anterior lip of insects, etc.

Lactase (lak' tase) (L. lac, milk; ase, enzyme), enzyme that changes lactose

(milk sugar) into dextrose and galactose.
Lacteals (lak' te al) (L. lacteus, milky), lymphatic vessels of small intestine to

convey the milky chyle from the intestine through the mesenteric glands

to the thoracic duct.
Lacuna (la -ku' na) (L. lacuna, cavity), cavity in which cells are located, as in

bone, cartilage, etc.

840 Appendix

Lamarckism (la -mark' izm), Lamarck's theory that acquired characters are

inherited.
Lamella (la-mel'a) (L. lamella, small plate), structure made by small plates,

as lamella of bone or layers of a cell wall.
Lanugo (la-nu'go) (L. lanugo, down), downy covering of fetus shed early in

life.
Larva (lar'va) (L. larva, mask), active, immature stage of development (con-
trast with Pupa).
Larynx (lar'inks) (Gr. larynx, larynx), enlarged anterior end of trachea (wind-
pipe) which contains the vocal folds; present in vertebrates except birds.
Legume (leg' yum) (L. lego, to gather), family of plants in which the seed

vessel is two-valved and having a linear arrangement of seeds, as beans,

alfalfa, peas.
Lepidoptera (lep i -dop' ter a) (Gr. lepis, scale; ptera, wings), order of insects

with scaly wings as moths, butterflies, etc.
Lethal factor (le'thal) (L. letum, death), genetic factor that brings premature

death to the individual.
Leucocyte (lu' ko sit) (Gr. leukos, white; kytos, cell), colorless blood corpuscle.
Leucoplast (id) (lu' ko plast) (Gr. leukos, white; plastos, formed), colorless

plastid.
Levator (le-va' ter) (L. lavare, to rise), a muscle to elevate a structure.
Lichen (li' ken) (Gr. leichen, lick), flat plant composed of a chlorophyll-bearing

alga and a fungus living together symbiotically.
Life cycle, various stages of development to maturity.
Ligament (lig'ament) (L. ligare, to bind), band of connective tissue to bind one

bone to another or a support for an organ.
Lignin (lig'nin) (L. lignum, wood), chemical substance related to cellulose, con-
stituting the essential part of woody tissue.
Linin (li' nin) (L. linum, thread), fine threadlike structure associated with the

chromatin of the nucleus.
Linkage, inheritance of traits in groups because their genes are near each other

(linked) in the same chromosome.
Lipase (li' pase) (Gr. lipos, fat), a fat-splitting enzyme.
Lipoid (li' poid), of fatty nature.
Locomotion (lo ko -mo' shun) (L. locos, place; motus, move), moving from one

place to another.
Lumbar (lum' ber) (L. lumbus, loin), pertaining to the loins (posterior to ribs).
Lumen (lu'men) (L. lumen, cavity), space within an organ or tube.
Lycopsida (lai -kop' si da) (Gr. \ykos, wolf; opsis, appearance), subphylum to

which the club mosses belong.
Lymph (limf) (L. lympha, liquid), the blood plasma and white blood corpuscles

which have passed from the circulatory vessels and which surround tissues

and cells.
Lysin (li' sin) (Gr. lysis, destroy), substance which destroys cells or tissues.

Macrogamete (mak ro ga met') Gr. makros, large; gamos, gamete), large female
gamete (sex cell) produced by an oiganism exhibiting heterogamy.

Appendix 841

Macromere (mak'romere) (Gr. makros, large; meros, part), large cells pro-
duced by embryonic cleavage in certain organisms.
Macronucleus (mak ro nu' kle us) (Gr. makros, large; L. nucleus, nucleus), the

larger nutritive nucleus of certain protozoa as distinguished from the

smaller reproductive micronucleus.
Macrophyll (mak'rofil) (Gr. makros, large; phyllon, leaf), large leaf (same as

Megaphyllous).
Macroscopic (mak ro -skop' ik) (Gr. makros, large; skopein, to see), visible to the

naked eye.
Macrospore (mak' ro spor) (Gr. makros, large; spora, spore), the larger spore

of a heterosporous plant.
Madreporite (mad' re po rit) (L. mater, mother; Gr. poros, porous), porous plate

leading to the water — vascular system of a starfish.
Malaria (ma -la' ri a) (L. mal, bad; aria, air), fever produced by Protozoa (class

Sporozoa), formerly thought due to "bad" air.
Malpighian (mal -pig' i an) (after Malpighi, of Pisa), malpighian corpuscle is a

body in a vertebrate kidney {see Bowman's capsule).
Mammal (mam'al) (L. mamma, breast), vertebrates having milk-giving breasts.
Mandible (man' di bl) (L. mandere, to chew), chewing jaw.
Mantle (man'tl) (L. mantellum, cloak), sheethke tissue in clams, oysters, snails

to secrete shell.
Marsupial (mar -sup' i al) (L. marsupium, pouch), mammals that carry young in

an abdominal pouch as opossum, kangaroo, etc.
Mastax (mas' taks) (Gr. mastax, mouth), crushing apparatus in rotifers.
Matrix (ma' triks) (L. ?nater, mother), noncellular material in which cells are

embedded, as in cartilage, bone, etc.
Maturation (mat u -ra' shun) (L. maturus, mature), m.aturing of sperm or eggs.
Maxilla (maks -il' a) (L. maxilla, jaw), a jaw, especially the upper in higher

animals.
Maxilliped (maks -il' i ped) (L. maxilla, jaw; pes, foot), an appendage modified

to serve as a masticatory organ and foot; the three pairs of appendages

of a crayfish thorax just posterior to the maxillae.
Mechanism (mechanistic view), theory (in contrast to Vitalism) that states that

life can be explained in terms of natural transformations of energy and

matter without the introduction of any immaterial or extranatural "vital

forces."
Medulla (me -dul' la) (L. medulla, marrow), inner portion of an organ as the

medulla of the kidney. Medulla oblongata is the posterior part of the

brain.
Medullary plate, groove, and tube, three successive stages in the embryologic

development of the central nervous system of vertebrates.
Medullary ray, pith ray that separates the vascular bundles in certain higher

plants.
Medullary sheath, covering of a medullated nerve fiber.
Medusa (me -du' sa) (Gr. medousa, one who rules), free-swimming hybroid

(jellyfish).

842 Appendix

Megagametophyte (meg a ga -me' to fite) (Gr. me gas, large; gamos, gametes;

phytcn, plant), fem.ale gametophyte resulting from the development of a

megaspore and producing female gametes (eggs).
Megasporangium (meg a spo -ran' ji um) (Gr. mega, large), a sporangium that

bears megaspores which develop into megagametophytes.
Megaspore (meg'aspor) (Gr. mega, large; spora, spore), a large spore produced

in a megasporangium.
Megasporophyll (meg a -spor' o fil), sporophyll which produces megaspores.
Meiosis (mi -o' sis) (Gr. meiosis, to make less) the preparation and maturation

(reduction division) of a sex cell for fertilization in which the chromosome

num.ber is reduced one-half.
Melanin (mel' a nin) (Gr. melas, black), blackish pigment.
Melanophore (mel' an o for) (Gr. melas, black; phoreo, to bear), chromatophore

that contains blackish pigment.
Mendelism (Mendel's laws), characters are inherited as units independently of

each other; genes separate (segregate) from one another and later recom-

bine in various ways in the germ cells; characters are in pairs (opposites),

one of which is dominant over the other or recessive one. These laws

were formulated by Gregor Mendel.
Meninges (me -nin' jez) (Gr. meninx, membrane), three membranous coverings of

the brain and spinal cord, outer dura mater, arachnoid, and inner pia

mater.
Meristem (mer' i stem) (Gr. merizein, to divide), undifferentiated tissue of grow-
ing plants composed of cells actively dividing.
Mesencephalon (midbrain) (mes en sef a Ion) (Gr. mesos, middle; kephale,

head), third region of vertebrate brain.
Mesenchyme (mes' eng kime) (Gr. mesos, middle; enchyma, infusion), middle,

cellular layer of embryos which forms connective tissues, blood vessels,

heart, etc.
Mesentery (mes'enteri) (Gr. mesos, middle; enteron, intestine), membrane to

invest and suspend internal organs such as the intestine.
Mesoderm (mes' o durm) (Gr. mesos, middle; derma, skin), middle germ layer of

cells which give rise to certain tissues and organs.
Mesogloea (meso-gle'a) (Gr. mesos, middle; gloios, glue), noncellular gelatinous

substance between ectoderm and entoderm of sponges and coelenterates.
Mesonephros (mes o -nef ros) (Gr. mesos, middle, nephros, kidney), vertebrate

kidney of animals from lamprey to amphibia inclusive.
Mesophyll (mes' o fil) (Gr. mesos, middle; phyllon, leaf), plant leaf tissues be-
tween upper and lower epidermis.
Mesophyte (mes' o fit) (Gr. mesos, middle; phyton, plant), plant requiring only

medium moisture.
Mesothelium (mes o -the' li um) (Gr. m.esos, middle; thelium, lining), lining of

the peritoneal cavity.
Mesothorax (mes o -thor' aks) (Gr. mesos, middle; thorax, chest) middle of three

thoracic segments of insects.
Metabolism (me -tab' o lizm) (Gr. metahole, change), sum of constructive (anab-

olism) and destructive (catabolism) phases of protoplasm.

Appendix 843

Metagenesis (met a -jen' e sis) (Gr. meta, over; genesis, origin), the alternation

of asexual and sexual generations in the life cycle of such animals as

Obelia and of several higher plants.
Metamere (met' a mere) (Gr. meta, over [repeat] ; meros, part), series of similar

parts (segments) of a body.
Metamerism (me -tam' er izm), displaying metameres.
Metamorphosis (met a -mor' fo sis) (Gr. metamorphosis, to transform), rather

abrupt change from one stage of embryonic development to another, as

from larval stage to pupa in insects.
Metaphase (met' a faz) (Gr. meta, between; phasis, to appear), a period in

mitosis between the prophase and anaphase stages.
Metaphysics (met a -fiz' iks) (Gr. meta, beyond; physics), aspects of science that

transcend the physical world.
Metaplasm (met' a plazm) (Gr. meta, beyond; plassein, to mold), nonliving

materials in living protoplasm.
Metathorax (met a -tho' raks) (Gr. meta, after; thorax, chest), posterior part of

insect thorax.
Metazoa (met a -zo' a) (Gr. meta, later; zoa, animals), higher, multicellular ani-
mals (contrast with unicellular Protozoa).
Microgamete (mi kro ga -met') (Gr. mikros, small; gamete), smaller of two

gametes formed by heterogamous organism.
Microgametophyte (mik ro ga -me' to fite) (Gr. mikros, small; gamos, gamete;

phyton, plant), male gametophyte resulting from the development of a

microspore.
Micron (mi' kron) (Gr. mikros, small), one-thousandth part of a millimeter; or

one twenty-five thousandth of an inch.
Micronucleus (mi kro -nu' kle us) (Gr. mikros, small; nucleus), smaller reproduc-
tive nucleus of certain Protozoa in contrast to the larger nutritive macro-
nucleus.
Microorganism (mi kro -or' gan izm) (Gr. mikros, small), microscopic organism

as a bacterium, protozoan, etc. ■
Micropyle (mi' kro pile) (Gr. mikros, small; pyle, gate), small opening.
Microspore (mi' kro spor) (Gr. mikros, small; spora, spore), minute spore which

grows into a male gametophyte; in seed plants it is the young pollen grain.
Microsporophyll (mi kro -spo' ro fil) (Gr. mikros, small; spora, spore; phyllon,

leaf), a sporophyll-bearing microsporangium (sporophyll which bears

microspores) .
Migration (mi -gra' shun) (L. migro, move), moving from one region to another.
Mimicry (mim' ik ri) (L. mimikos, imitate), resemblance for protective purposes.
Miracidium (mi ra -sid' i um) (Gr. meikakion, young), ciliated larval stage of a

fluke.
Mitochondria (mit o -kon' dri a) (Gr. mitos, thread; chondros, grit or grain),

somewhat regularly shaped bodies in cytoplasm.
Mitosis (mi -to' sis) (Gr. mitos, thread), indirect cell division characterized by

nuclear division with the formation of chromosomes, spindle, etc.
Modification, noninheritable variation in the somatoplasm due to environmental

causes.
Modifying factor, a gene which modifies others to bring about a changed trait.

844 Appendix

Mold (A.S. molde, earthy), saprophytic fungi.

Molecule (mol'ekul) (L. moles, mass), an aggregate of two or more atoms com-
bined chemically.

Mollusca (mol-lus'ka) (L. mollis, soft), soft-bodied animals such as clams,
snails, etc.

Molt (L. muture, to change), shedding of an outer covering.

Monecious (mo -ne' shus) (Gr. monos, one; oikos, household), both male and
female reproductive organs in the same individual (same as hermaphro-
ditic; contrast with Diecious).

Monohybrid (mon o -hi' brid) (Gr. monos, single; L. hybrida, mongrel), offspring
from parents who differ in one trait.

Monozygotic (mon o zi -got' ik) (Gr. monos, one; zeugon, yoke), two or more off-
spring formed from one zygote (fertilized egg).

Morphogenesis (mor fo -jen' e sis) (Gr. morphe, form; genesis, origin), origin and
development of form and structure in an organism.

Morphology (mor -fol' o ji) (Gr. morphe, form; logos, study), dealing with form
and structure of animals and plants.

Morula (mor' u la) (L. morum, berry), mass of cells, called blastomeres, formed
by cleavage of the egg in early development of many animals.

Motor fibers (L. moveo, move), nerve fibers whose impulses cause movement (in
muscles).

Mucous membrane (mu' kus) (L. mucus, slime), lining of alimentary tract and
respiratory system.

Multiple^ factors, two or more pairs of genes which have a similar or cumulative
effect.

Mutation (mu -ta' shun) (L. mutare, change) an abrupt inheritable germinal
variation.

Mutual symbionts (sim'bionts) (Gr. sym, with; bios, life), living together for
mutual benefit.

Mycelium (mi-se'lium) (Gr. mykes, mushroom), mass of filamentous hyphae of
all true fungi.

Myoblast (mi' o blast) (Gr. myo, muscle; blastos, bud), muscle-developing cell.

Myogenic theory (mi o -jen' ik) (Gr. myo, muscle; gene, origin), theory that the
rhythmic heartbeat is due to innate properties of heart muscles rather than
nerve impulses.

Myoneme (mi'onem) (Gr. friyo, muscle; nema, thread), contractile fiber of cer-
tain protozoa.

Myosin (mi' o sin) (Gr. myo, muscle), protein of muscle.

Myotome (mi'otom) (Gr. ?7iyo, muscle; tome, cut), muscle segments of the body
wall of embryonic higher chordates and of adult lower chordates.

Myxomycophyta (mix o my -kof i ta) (Gr. myxos, slime; mykos, fungus, phyta,
plants), the phylum of plants including slime molds.

Myxamoeba (miks a -me' ba) (Gr. myxa, slime; amoeba, change), swarm cell of
slime mold.

Nacreous (na'kreus) (L. nivcr^, mother-of-pearl), pearly.
Nares (na' res) (L. nare) , nost)ils.

Natural selection, Darwin's theory that the fittest individuals survive through
natural processes of struggle.

Appendix 845

Negative tropism (tro' pizm) (Gr. trope, turning), tendency to move away from

a stimulus.
Nemathelminthes (ne math el -min' thcz) (Gr. nema, round; helmins, worm),

roundworms.
Nematocyst (nem' a to sist) (Gr. yiema, thread; kystis, sac), permanent, stinging

thread thrust from a saclike cell as in Hydra.
Nematode (nem' a tod), class of roundworms.
Neoplasm (ne'oplazm) (Gr. neos, new; plasma, formation), newly added tissue,

generally pathologic.
Neoteny (pedogenesis) (ne-ot'oni) (Gr. neos, new; teinein, to stretch), re-
tention of larval traits throughout life, even being sexually mature in this

larval condition.
Nephritic (ne -frit' ik) (Gr. nephros, kidney), pertaining to the kidney.
Nephridium (ne -frid' i um) (Gr. nephros, kidney), tubular excretory organ of

lower animals as earthworms.
Nephrostome (nef'rostom) (Gr. nephros, kidney; stoma, opening), ciliated open-
ing of inner end of a nephridium.
Nerve (L. nervus, sinew), group of nerve fibers, end to end and side by side,

held together by special connective tissue called neuroglia.
Neural groove, tube, see Medullary groove, etc.
Neurilemma (nu ri -lem' a) (Gr. neuron, nerve; lemma, covering), membranous

covering of nerve.
Neuroblast (nu'ro blast) (Gr. neuron, nerve; blastos, origin), cell which embryo-

logically gives rise to nerve cells.
Neuroglia (nu-rog'lia) (Gr. neuron, nerve; glia, glue), special tissue to bind

and support nerve cells and fibers.
Neuromuscular, combining nervous and muscular functions.
Neuron (nu' ron) (Gr. neuron, nerve), unit of the nervous system composed of

dendrite, cyton, and axon.
Nissl's granules (Nis' 1) (after Nissl), present in nerve cell cytoplasm and asso-
ciated with its activity.
Nitrification (ni tri fi -ka' shun), preparation of nitrogenous materials for use by

organisms.
Nitrifying bacteria, those capable of changing ammonia into nitrites or nitrites

into usable nitrates.
Nitrogen-fixing bacteria, those capable of combining free nitrogen of the air

with oxygen, either in the nodules of the roots of leguminous plants (such

as clovers, peas, alfalfa, etc.) or by other species of bacteria that live

freely in the soil.
Nodes of Ranvier (ran-vya'), places on a nerve fiber where the membranous

covering (medullary sheath) is interrupted.
Nomenclature (no' men kla-tur) (Gr. nomen, name), system of naming objects

or organisms.
Nondisjunction (non dis jungk' shun), failure of homologous chromosomes to

separate after synapsis, both going to one cell.
Nonelectrolyte (non e -lek' tro lite), a substance such as sugar or alcohol which,

in solution, cannot be ionized and hence cannot conduct electric currents.
Notochord (no' to kord) (Gr. notos, back; chorde, string), rodlike structure in

the dorsal (back) side which is the forerunner of backbone.

846 Appendix

Nucellus (nu-sel'us) (L. nux, nut), the megasporangium of an ovule, locatec

inside the integument and enclosing the megagametophyte.
Nuclear electron, one within the nucleus of the atom.
Uucleolus (nu-kleolus) (L. dim. of nucleus), the somewhat spherical body

within the nucleus, probably of regulatory function (same as Plasmo-

some).
Nucleoplasm (nu' kle o plazm) (L. nux, nucleus; Gr. plasma, liquid), Hquid part

of the nucleus.
Nucleus (nu'kleus) (L. nucleus, kernel), specialized, central, organized structure

in most cells.
Nymph (nimf) (Gr. nymphe, bride), specific stage in metamorphosis of such

insects as the grasshopper.

Obligate (ob'ligate) (L. ob, about; ligo, bind), unable to change life habits to

suit varying conditions.
Occipital (ok -sip' i tal) (L. occiput, back of head), base of skull.
Ocellus (plural ocelli) (o -sel' us) (L. o cuius, eye), simple eye.
Octopus (ok' to pus) (Gr. okta, eight; pous, feet), a mollusk with eight feet

(arms) .
Oculomotor (ok u lo -mo' ter) (L. ocidus, eye; movere, to move), moving the eye.
Oesophagus (esophagus) (e-sof'agus) (Gr. oise, bear; phagein, to eat), tube

from pharynx to stomach.
Olfactory (ol -fak' to ri) (L. olere odor: facere, to make) pertaining to odors.
Ommatidium (om a -tid' i um) (Gr. omma, eye), unit of which compound eyes

are made, as in crayfish, certain insects.
"Oninis cellula a cellula," Virchow's dictum that all cells arise from cells.
Omnivorous (om -niv' o rus) (L. omnis, all; vovare, to eat), eating both plant

and animal tissues.
Ontogeny (on -toj' e ni) (Gr. on, being; genes, born), developmental life history

of an individual, including embryology, metamorphosis, and adolescence,

as distinguished from phylogeny (evolution of a race or group).
Oocyte (o'osit) (Gr. oon, egg; kytos, cell), female egg before maturation.
Oogamy (o -og' a mi) (Gr. oon, egg; gamos, marriage), union of nonmotile egg

and male gamete.
Oogenesis (o o -jen' e sis) (Gr.oon, egg; genesis, origin), formation of an egg

and its preparation for fertilization and development.
Oogonium (oo-go'nium) (Gr. oon, egg; gonos, offspring), primordial egg cell

before maturation; the one-celled female sex structure in certain thallo-

phytes and produces one or more eggs.
Operculum (o -pur' ku lum) (L. operculum, cover or lid), lidlike covering.
Opsonin (op' so nin) (Gr. opsonein, to cater), substance in the blood which aids

phagocytes to destroy bacteria.
Optic (op' tik) (Gr. optikos, sight), pertaining to sight or the eye.
Order (or' der) (L. ordo, order), methodical arrangement; group of closely allied

organisms all belonging to the same class.
Organ (or' gan) (Gr. organon, an implement), a group of different tissues all

performing a common function,

Appendix 847

Organelle (or gan -el' ), a special part of a single cell serving a specific function.

Organicism (or -gan' i sizm), a theory stressing the importance of the organiza-
tion of the entire living thing rather than the importance of the parts of
which that thing is composed.

Organism (or' gan izm) (Gr. organon, implement), an independent living being.

Organismal theory, a theory that an organism is a unit with its unity consist-
ing of centralized control of one dominant region over all subordinate
regions (contrast with Elemental theory).

Organogeny (or gan -og' a ni), formation and development of organs.

Orientation (o ri en -ta' shun) (L. orient, rise), change in location or position by
organs or their parts due to environmental influences; may also be applied
to an entire organism.

Orthogenesis (or tho -jen' e sis) (Gr. orthos, straight; genesis, descent), develop-
ment or evolution in a definite direction.

Orthoptera (or -thop' ter a) (Gr. orthos, straight; ptera, wings), order of insects,
such as grasshopper, whose wings meet in a straight line down the back.

Osculum (os'kulum) (L. osculum, little mouth), an excurrent opening as in a
sponge.

Osmosis (os-mo'sis) (Gr. osmos, pushing), diffusion of substances through a
semipermeable membrane.

Osmotic pressure, pressure exerted by substances in solution due to molecular
activity.

Osseous (os' e us) (L. os, bone), pertaining to bone.

Osteology (os te -ol' o ji), study of bones.

Ostium (os' ti um) (L. ostium, little opening), m.outhlike opening.

Otolith (o'tolith) (Gr. ous, ear; lithos, stone), a limy particle in the auditory
organ of certain animals.

Outbreeding, crossing of unrelated or distantly related individuals.

Ovary (o' va ri) (L. ovarium, ovary), female reproductive organ in which the egg
cells develop; the enlarged, basal part of a pistil (female) within which
seeds develop.

Oviduct (o'vidukt) (L. ovum, egg; ducere, to lead), tube to carry eggs from
ovary (to exterior).

Oviparous (o -vip' a rus) (L. ovum, egg; parere, bring forth), producing eggs
that hatch after being excluded from the body.

Ovipositor (o vi -poz' i ter) (L. ovum, egg; ponere, to place), specialized tip
of abdomen in certain insects for depositing eggs.

Ovoviviparous (o vo vi -vip' a rus) (Gr. ovum, egg; F. vivipare, produce), form-
ing eggs, with a well-developed covering, which develop within the body
of the parent.

Ovulation (o vu -la' shun) (L. ovum, egg), discharging mature eggs from the
ovary.

Ovule (ov' ule) (L. ovum, egg), structure consisting of a female gametophyte,
nucellus, and integuments, which, after fertilization, develops into a seed.

Oxidation (ox i -da' shun) (Gr. oxys, acid), combining oxygen with a substance.

Oxyhemoglobin (ok si he mo -glo' bin) (Gr. oxys, acid; haema, blood; L. globus,
globe), temporary union of oxygen with the hemoglobin of the blood.

848 Appendix

Paedogenesis (pedogenesis) (pe do -jen' e sis) (Gr. pais, child; genesis, origin),
reproduction by a larval or embryonic stage rather than by an adult.

Paleobotany (pa le o -bot' a ni) (Gr. palaios, old; botane, plants), science of
ancient plants.

Paleontology (pa le on -tol' o ji) (Gr. palaios, old; logos, study), science of plant
and animal life of the past geologic periods.

Paleozoology (pa le o zo ol' o ji) (Gr. palaios, old; zoa, animals; logos, study),
study of ancient animals.

Palisade layer (pal' i sade) (L. palus, stake), columnar cells with chloroplasts
in the mesophyll tissues of leaves, just below the upper epidermis.

Pancreas (pan' kre as) (Gr. pan, all; kreas, flesh), an accessory digestive gland.

Pangenesis (pan -jen' e sis) (Gr. pan, all; genesis, origin), Darwin's theory that
all body cells give rise to minute particles called pangenes which migrate
to the germ cells and impress their traits upon them (theory not accepted
today).

Parallelism {see Convergent adaptations or Variations).

Paramecin, a "killer" particle in a Paramecium.

Paramylum (par -am' i lum) (Gr. para, beside; amylon, starch), starchhke sub-
stance in certain protozoa.

Paraphyses (pa -raf i sez) (Gr. para, beside; physis, growth), sterile, hairlike
structures associated with sex structures in certain algae, fungi, mosses, etc.

Parapodium (par a -po' di um) (Gr. para, beside; pons, foot), paired processes on
the body segments of the sandworm (nereis) of the phylum annelida.

Parasite (par' a site) (Gr. para, beside; sitos, food), a plant or animal living in
or on another living organism ; livdng at its expense.

Parathyroid (par a -thi' roid) (Gr. para, beside), four small endocrine glands ad-
jacent to the thyroid.

Parenchyma (pa -reng' ki ma) (Gr. para, beside; en, in; chein, to pour), spongy
mesodermal tissues of lower animals or fundamental plant tissues as op-
posed to more highly differentiated plant tissues.

Parotid (pa -rot' id) (Gr. para, beside; otos, ear), salivary gland located below
the ear.

Parthenogenesis (par the no -jen' e sis) (Gr. parthenos, virgin; genesis, origin),
development of an egg without fertilization by a male sperm.

Pasteurization (pas ter i -za' shun) (after Pasteur), killing certain organisms by
heating a liquid to 142°-145° F. for thirty minutes (212° F. is boiling).

Patella (pa-tel'a) (L. patena, pan), kneecap.

Pathogenic (path o -jen' ik) (Gr. pathos, suffering; genesis, origin), disease-pro-
ducing.

Pathology (pa thol' o ji) (Gr. pathos, suffering or disease; logos, science), study
of diseased or abnormal conditions.

Pecten (pek' ten) (L. pecten, comb), comblike structure in certain insects.

Pectoral (pek' to ral) (L. pectus, breast), pertaining to chest or breast.

Pedal (ped' al) (L. pes, foot), pertaining to the foot.

Pedicelaria (ped i se -la' ri a) (L. pediculus, small foot), small, pincerlike struc-
tures on the surface of certain echinoderms such as the starfish.

Appendix 849

Pedogenesis, see Paedogenesis.

Pellicle (pel'ikl) (L. pellicula, small skin), thin layer as on certain cells.

Pelvis (pel' vis) (L. pelvis, basin), arrangement of bones to support abdominal
organs and for attachment of lower (hind) limbs.

Penis (pe' nis) (L. penis, penis), male organ of copulation.

Pentadactyl (pen ta -dak' til) (Gr. penta, five; daktylos, finger), five fingers or
digits.

Pepsin (pep' sin) (Gr. pepsis, digest), protein-digesting enzyme of the stomach.

Perennial (per-en'ial) (L. per, through; annus, year), plant living more than
two years (contrast with Annual and Biennial).

Perianth (per'ianth) (Gr. peri, around; anthos, flower), all the petals and
sepals of a flower taken collectively.

Pericardium (per i -kar' di um) (Gr. peri, around; kardia, heart), serous mem-
bane which encloses the heart.

Pericycle (per' i si kl) (Gr. peri, around; kyklos, circle), circle of plant tissue of
stems and roots between the cortex and stele.

Perimysium (peri -mizh' i um) (Gr. peri, around; mys, muscle), covering or bind-
ing muscle.

Periosteum (peri -os' te um) (Gr. peri, around; os, bone), membranous connective
tissue that covers bones.

Peripheral nervous system, that part of the nervous system composed of cranial and
spinal nerves (contrast with Central nervous system).

Peristalsis (per i -stal' sis) (Gr. peri, around; stallein, to arrange), wavelike con-
striction passing along a tube, due to muscular contraction, as in esopha-
gus, intestine, etc.

Peritoneum (per i to -ne' um) (Gr. peri, around; teinein, to stretch), membrane
which lines the coelom of vertebrates and covers the viscera of the coelom.

Permeable membrane, one which permits substances to pass.

Perspiration (per spi -ra' shun) (L. per, through; spiro, to breathe), watery ex-
cretion of perspiratory glands of skin.

Petal (pet' al) (Gr. petalon, leaf), one of the inner whorl of a flower, usually
colored; all petals taken collectively form the corolla.

Petiole (pet'iol) (L. petiolus, little stalk), slender support for the blade of a
foliage leaf.

Petrifaction (pet ri -fak' shun) (L. petra, rock), method of fossil formation in
which mineral matter takes the place of the original organic or living
matter during the disintegration of the organism.

Peyer's patches (after Swiss anatomist, Peyer), oval patches of lymphoid tissue
of the small intestine attacked by typhoid germs in man.

Phaeophyta (fe -of i ta) (Gr. phaeo, brown; phyta, plants), brown algae.

Phagocyte (fag' o site) (Gr. phagein, eat; kytos, cell), type of leucocyte which
engulfs foreign materials.

Phagocytosis (fag o si -to' sis), destruction of foreign materials by action of
phagocytes (white blood corpuscles).

Pharyngeal cleft, see Gill slit.

Pharynx (far' inks) (Gr. pharynx, pharynx), tube connecting mouth to esopha-
gus on the one hand and to the larynx on the other.

850 Appendix

Phenotype (fe' no tipe) (Gr. phaino, show; typos, impression), a type or kind
determined on the basis of visible traits as distinguished from genotype
(based on gene content).

Phloem (flo' em) (Gr. phloios, bark), food-conducting tissue of plants; phloem
and xylem together form a vascular bundle.

Photosynthesis (fo to -sin' the sis) (Gr. phos, Hght; synthesis, to build), produc-
tion of carbohydrates from water and carbon dioxide by means of chloro-
phyll in presence of light (to supply energy).

Phototaxis (fo to -tax' is) (Gr. phos, light; taxis, response), response to light.

Phototropism (fo -tot' ro pizm), see Phototaxis.

Phrenic (fren' ik) (Gr. phren, diaphragm), pertaining to the diaphragm.

Phycocyanin (fy co -si' a nin) (Gr. phycos, seaweed or alga; kyanos, blue), blue
pigment of the blue-green algae.

Phycoerythrin (fy co e -ryth' rin) (Gr. phycos, alga; erythros, red), red pigment
of red algae.

Phycomycetes (fi co mi -se' tez) (Gr. phycos, alga; mycetes, fungi), filamentous
(algalike) fungi.

Phylogeny (filoj'eni) (Gr. phylon, race; gen, descent), ancestral history of a
race or group as contrasted with ontogeny.

Phylum (fi' lum) (Gr. phylon, tribe), one of the main groups into which the ani-
mal and plant kingdoms are divided (plural, phyla).

Physiology (fizi-ol'oji) (Gr. phusis, nature; logos, study), study of functions.

Phytogeography (fi to ge -og' ra fi) (Gr. phytos, plant), geographic distribution
of plants ; same as Plant geography.

Phytopathology (fi to pa thol' o ji) (Gr. phyto, plant; pathos, diseased), study of
diseased or abnormal plants.

Pia mater (pi' a; ma' ter), inner of three coverings of brain and spinal cord.

Pigmentation of plants, various colors of plants produced by such specific pig-
ments as chlorophyll, xanthophyll, carotene, anthocyanins, and flavones of
higher plants and phycoerythrin, phycocyanin, fucoxanthin in algae, etc.

Pineal (pin'eal) (L. pinea, cone), small endocrine gland between the two cere-
bral hemispheres.

Pisces (pis' es) (L. piscis, fish), class of vertebrates to which fishes belong.

Pistil (pis' til) (L. pistilum, a pestle), the ovule-producing part of a flower, con-
sisting of one or more carpels.

Pith (A.S. pitha, pith), soft, spongy tissue in the center of the stems of certain
plants.

Pituitary (pi -tu' i ta ri) (L. pituita, phlegm), small, oval endocrine gland attached
to the infundibulum of the brain whose two lobes have entirely different
hormones."

Placenta (pla -sen' ta) (Gr. plakous, flat cake), flat vascular organ which aids in
nourishing the fetus in the uterus; or attachment of plant seeds.

Plankton (plangk' ton) (Gr. planktos, wandering), animal and plant life floating
in the water.

Plant geography, see Phytogeography.

Plasma (plaz'ma) (Gr. plasma, liquid), liquid part of the blood, lymph, or milk.

Plasmagene (plaz'majen) (Gr. plasma, form; genos, descent), a gene within
the cytoplasm in contrast to a nuclear gene; sometimes called a cytogene.

Appefidix 851

Plasma membrane, living semipermeable membrane covering the cytosome of
certain cells {see Cell membrane).

Plasmodesma (plaz mo -dez' ma) (Gr. plasma^ something formed; desma, bond)',
protoplasmic connection between cells (plural, plasmodesmata).

Plasmolysis (plaz -mol' i sis) (Gr. plasma, liquid; lysis, loosening), shrinking of
the cytoplasm in a living cell due to loss of water.

Plasmodium (plaz -mo' di um) (Gr. plasma, formed), naked, protoplasmic mass, as
in slime mold.

Plasmosome (plaz'mosom) (Gr. plasma, liquid; soma, body), body known as the
nucleolus within the liquid of the nucleus.

Plastid (plas'tid) (Grt plastes, to form), specialized protein body in a cell con-
cerned with producing a certain substance.

Platyhelminthes (plat i hel -min' thez) (Gr. platus, flat; helmins, worm), flat-
worms.

Plecoptera (pie -kop' ter a) (Gr. plekos, folded; ptera, wings), order of insects to
which the stone flies belong.

Pleura (ploor' a) (Gr. pleura, rib or side), membranous lining of thoracic cavity
of mammals and covering the lungs in the cavity.

Plexus (plek'sus) (L. plexus, interwoven), network of nerves or blood vessels.

Plumule (ploo'mul) (L. pluma, feather), primary bud of an embryo seed plant.

Poison (poy'sin) (L. poto, to drink), substance harmful to an organism.

Polar body, see Polocyte.

Polarity (po -lar' i ti) (Gr. polos, pivot), having two opposite poles with different
physiologic values. In an egg, there is usually a formative animal pole
and a nutritive vegetal pole.

Polar transportation, movement of plant hormones in young tissues in a basipetal
direction.

Polarized growth, development of younger plant tissues in length rather than
another direction due to specific plant hormones and certain environ-
mental conditions.

Polian vesicle (after the Italian, Poli), bulblike organ of the water vascular sys-
tem of certain echinoderms.

Pollen (pol' en) (L. pollen, fine flour), dustlike grains of material produced by
the male anthers of flowers.

Pollen tube, formed by a pollen grain and transports sperm to the eggs in ovules.
A pollen grain and its mature tube^ are the male microgametophyte.

Pollination (pol i -na' shun), application of male pollen to the female stigma, or
ovule, of a plant.

Polocyte (po' lo site) (Gr. polos, pole; kytos, cell), small cell separated from the
egg during maturation; function unknown; also called polar body.

Polygamy (po-lig'ami) (Gr. poly, many; gamos, marriage), more than one mate
at one time.

Polymorphism (poly -mor' fizm) (Gr. poly, many; morphe, form), more than two
types or castes of individuals in a colony or community which belong to
the same species and are derived from the same parents. The various
castes of honeybees, ants, termites, etc., are typical.

Polyp (pol' ip) (Gr. poly, many), sessile phase of the life history of certain
coelenterates.

852 Appendix

Porifera (po -rif era) (Gr. poros, pore; ferro, to bear), pore-bearing sponges.

Portal vein (port' al) (L. porta, gate), blood vessel carrying blood to the liver
from spleen, pancreas, digestive tract, etc.

Postcaval vein (post -ka' val) (L. post, after; cavus, hollow), inferior (posterior)'
vena cava carrying blood to the heart from posterior parts of the body.

Posterior (pos -te' ri or) (L. posterior, following), behind or opposite anterior
(head).

Potential energy (po -ten' shal) (L. potens, be able), stored energy possessed by
virtue of position or stresses, such as the stored energies of food, coal,
wood, etc. (contrast with Kinetic energy).

Precaval vein (pre -ka' val) (L. prae, before; cavus, hollow), anterior (superior)
vena cava carrying blood to the heart from the anterior parts of the body.

Precipitin (pre -sip' i tin) (L. praecipitare, precipitate), specific antibody devel-
oped in response to stimulation by a foreign protein and characterized by
causing a precipitation.

Predaceous (pre -da' shus) (L. Praeda, prey), outright killing of an animal, such
as owls killing (preying on) mice, etc.

Preformation (pre for -ma' shun) (L. prae, before), old theory that adults are
preformed (represented in miniature) in the germ cell (contrast with
Epigenesis).

Premaxilla (pre max -il' a) (L. prae, before; maxilla), in front of the maxilla or
upper jaw.

Prenatal (pre -na' tal) (L. prae, before; natalis, birth), before birth.

Primates (pri' mate) (L. primus, first), highest animals such as man, apes,
monkeys.

Primordial germ cell (pri -mor' di al) (L. primordium, origin), first cell set aside
in the embryo for future development of sex organs.

Proboscis (pro -bos' is) (Gr. proboskis, trunk), trunklike process.

Progestin (pro -gest' in), hormone of the corpus luteum (yellow body) of the ovary.

Proglottid (pro -glot' id) (Gr. pro, for; glotta, tongue), one of the sections or
individuals of the chain making up a cestode worm such as tapeworm.

Pronephros (pro -nef ros) (Gr. pro, before; nephros, kidney), first kidney struc-
ture to develop in a vertebrate.

Prophase (pro' faz) (Gr. pro, before; phasis, to appear), preparatory stage of
mitosis preceding the metaphase.

Prophylaxis (pro fy -lacks' is) (Gr. pro, before; phylasso, guard), preventive raieas-
ures in connection with diseases.

Prosopyle (pros' o pile) (Gr. proso, forward; pyle, gate), pores leading into flagel-
lated chambers from the incurrent canals in certain sponges.

Prostate (pros' tat) (Gr. pro, before; stare, stand), an accessory male reproduc-
tive gland near the urethra.

Prostomium (pro -stom' i um) (L. pro, before; stoma, mouth), portion of head
before the mouth.

Protective resemblance, protection of an organism due to the resemblance of it,
or some part of it, to its environment. This resemblance may be due to
structure, color, pattern, etc.

Protein (pro'tein) (Gr. protos, first), compound of carbon, hydrogen, oxygen,
and nitrogen, and frequently traces of phosphorus or sulfur.

Appendix 853

Prothallus (pro -thai' us) (Gr. pro, before; thallos, young part), the reduced pre-
thallus gametophyte of ferns and their alHes.

Prothorax (pro -thor' aks) {pro, before; thorax, chest), anterior segment of insect
thorax which bears first pair of legs.

Protista (pro -tis' ta) (Gr. protistos, first), single-celled plants and animals.

Proton (pro'ton) (Gr. protos, first), part of a nucleus of the atom, and with a
positive charge of electricity.

Protonema (pro to -ne' ma) (Gr. proto, first; nema, thread), first threadlike
growth from a spore in mosses.

Protoplasm (pro' to plazm) (Gr. protos, first; plasma, liquid), substance of which
all living organisms are composed.

Protopodite (pro -top' o dite) (Gr. protos, first; pons, foot), basal (proximal) seg-
ment of a typical crustacean appendage to which endopodite and exopodite
are attached.

Protozoan (pro to -zo' an) (Gr. protos, first; zoa, animals), simple, unicellular
animals.

Proventriculus (pro ven -trik' u lus) (Gr. pro, before; ventriculus, small stomach),
first part of a stomach in such animals as insects, birds, etc.

Proximal (prox' i mal) (L. proximus, near), nearest the main axis; opposed to
distal.

Pseudopodium (plural, pseudopodia) (su do -po' di um) (L. pseudo, false; pous,
feet), temporary protrusion of protoplasm from a cell, especially certain
protozoa like ameba, and serving for various functions but particularly
locomotion.

Psychical (si' kik al) (Gr. psyche, soul), pertaining to .the mind.

Psychology (si -kol' o ji) (Gr. psyche, mind; logos, study), study of the mind, etc.

Pteropsida (ter -op' si da) (Gr. pteris, fern; opsis, appearance), a subphylum to
which ferns, conifers, and flowering plants belong.

Ptomaine (to' mane) (Gr. ptoma, dead body), an organic base or alkaloid formed
by the action of putrefactive bacteria on nitrogenous matter. Some pto-
maines are poisonous but most are harmless.

Ptyalin (ty' a lin) (Gr. ptyalon, spittle), salivary enzyme changing starch to sugar.

Pubis (pu'bis) (L. pubes, adult), anterior part of the hip (pelvic) girdle.

Pulmonary (pul' mon a ri) (L. pulmo, lung), pertaining to the lung.

Pulsating vacuole, same as Contractile vacuole.

Punnet square, a checkerboard-like diagram for determining the results of a
cross in heredity.

Pupa (pu'pa) (L. pupa, baby), the quiet stage in the development of certain
insects occurring between the larval and adult stages; known as a cocoon in
moths and chrysalis in butterflies.

Pure line, a group of individuals arising from homozygous parents and having
identical genes.

Pylorus (pi-lo'rus) (Gr. pylorus, gate), opening between stomach and small in-
testine.

Pyrenoid (pi -re' noid) (Gr. pyren, fruit stone; eidos, resembling), plastid or cen-
ter for forming starch.

854 Appendix

Quadruped (quard' ru ped) (L. quattuor, four; pes, feet), four-footed animal.
Quard' ruplet, one of four offspring born at the same time.

Quaternary (qua' ter na ri), the last of the great fossil-bearing rocks (Pleis-
tocene).
Queen, the reproductive female in colonies of social insects.

Radial canal (L. radius, ray), canal radiating from a center as in starfish.

Radial synmietry, arrangement of similar parts around a central point like the
spokes of a wheel.

Radicle (rad' i cl) (Gr. radix, root), primary root of seedlings.

Radioactivity, a condition in which there is a partial disintegration of atoms, with
the shooting out from the atomic nucleus of alpha particles, electrons,
x-rays, etc.

Radioulna, fused radius and ulna bones of frog forearm.

Radius (ra' di us) (L. radius, rotate), rotating bone of forearm.

Radula (rad' u la) (L. radere, to scrape), scraping organ for mastication in
certain Mollusca as snails.

Recapitulation theory (re ka pit u -la' shun) (Gr. re, again; caput, head), the life
history of an individual repeats (recapitulates) in an abbreviated man-
ner the ancestral history of that race as a whole {see Biogenetic theory).

Receptor (re-sep'ter) (L. receptor, receiver), receiving sensory cell or organ.

Recessive characters, those traits which are not expressed, even though their
genes are present together with the gene for the opposite, allelomorphic
dominant.

Rectum (rek' tum) (L. rectus, straight), posterior part of intestine.

Red blood corpuscle, oxygen-carrying cell.

Redia (re'dia) (after Italian naturalist, Rcdi), the second type of larva found
in life cycle of flukes.

Reduction division, the division of chromosomes of maturing gametes in which
the normal, diploid, somatic number of chromosomes is reduced to the
haploid, single number.

Reflex action (L. re, back; fiectere, to return), automatic, involuntary response
of nervous and motor mechanisms to stimuli.

Refraction (re -frakt' shun) (L. re, back; frango, break), deflection of light waves
when passing obliquely from one medium to another with different re-
fractive indices.

Regeneration (re gen er -a' shun) (L. re, again; generare, to beget), ability to
replace a lost part or develop a new individual from a lost part.

Renal (re' nal) (L. renes, kidney), pertaining to kidney.

Renal portal system (L. renes, kidney; porta, gate), blood vessels (veins) carry-
ing impure blood from the posterior part of the body to the kidneys.
Oxygenated blood is carried to the kidneys by renal arteries. Fishes,
amphibia, and reptiles have this double blood supply for the kidneys, while
this system is vestigial in birds and absent in mammals.

Rennin (ren' nin) (A.S. rennan, run), milk-coagulating enzyme.

Appendix 855

Reproduction (re pro -duk' shun) (L. re, again; pro, forth; duco, to lead), pro-
duction of offspring.

Reptile (rep' til) (L. repere, to crawl), a class of vertebrates which ordinarily
crawl, as snakes, turtles, lizards, etc.

Respiration (res pi -ra' shun) (L. re, again; spiro, to breathe), exchange of oxy-
gen (entering) and carbon dioxide (leaving) in an organism.

Response, reaction to a stimulus, external or internal.

Resting cell, one not dividing by mitosis.

Reticular (re -tik' u lar) (L. reticulum, net), network of fibrils.

Reticular theory, that protoplasm is physically constructed of networks of fibrils.

Retina (ret'ina) (L. rete, net), hght-sensitive membrane of the eye to receive
images.

Reversion (re -ver' shun) (L. re, back; verto, to turn), return to an ancestral type
or condition.

Rhabdite (rab' dite) (Gr. rhabdos, rod), rodlike structure in epidermis of certain
fiatworms, probably for protection.

Rheotropism (re -ot' ro pizm) (Gr. rhein, flow; trope, respond), response to water
currents.

Rhizoid (ri' zoid) (Gr. rhiza, root; eidos, like), slender, rootlike filaments in cer-
tain lower plants which function as roots.

Rhizome (ri' zom) (Gr. rhiza, root), underground stem which has the appearance
of a root.

Rhodophyta (ro -dof i ta) (Gr. rhodon, red; phyta, plants), red algae.

Rodent (ro' dent) (L. rodere, to gnaw), gnawing animal such as rat.

Root cap, the extreme, protective tip of a root.

Root hair, fine hairlike extension of the epidermis of plant roots for absorption.

Rotifer (rot'ifer) (L. rota, wheel; ferro, to bear), small, multicellular, aquatic
animal with wheel-like organ of rotating cilia on the anterior end.

Rudimentary (roo di -men' ta ri) (L. rudis, immature), not fully developed.

Ruminant (roo'minant) (L. rumen, throat), animal which chews its cud, as a
cow.

S . '

Saliva (sa -li' va) (L. saliva, spittle), secretion of salivary glands.

Saprophyte (sap' ro fite) (Gr. sapros, rotten; phyton, plant), an organism living

on dead or decaying organic matter, particularly of plants.
Sarcolemma (sar ko -lem' ma) (Gr. sarx, flesh or muscle; lemma, covering), cover-
ing of a striated voluntary muscle cell.
Sarcoplasm (sar' co plazm) (Gr. sarx, muscle; plasma, liquid), the cytoplasm of

muscle cells exclusive of sarcostyles (fibrils).
Sarcostyles (sar' ko stile) (Gr. sarx, muscle; stylos, rod), fibrils in the cytoplasm

of voluntary, striated muscle cells.
Scapula (skap'ula) (L. scapula, shoulder blade), shoulder blade or dorsal part

of pectoral girdle,
Schizomycophyta (skiz o my -kof i ta) (Gr. schizo, fission; mykos, fungus; phyta,

plants), fission fungi or bacteria.
Sclerenchyma (skier -engk' i ma) (Gr. scler, hard; engchyma, poured in), plant

tissues whose cell walls are thickened for protection and support.

856 Appendix

Sclerotic (skle -rot' ik) (Gr. skleros, hard) , tough, outer coat of eyeball.
Scolex (sko'leks) (Gr. skolex, worm), enlarged anterior end of tapeworm.
Sebum (L. sebum, tallow), fatty secretion of the sebaceous glands of the skin.
Secondary sexual characters, structural, functional, or behavioral differences be-
tween two sexes other than those pertaining to the different sex organs

themselves.
Secretin (se -kre' tin) (L. secratio, secrete), intestinal hormone which activates the

pancreas.
Secretion (se kre' shun) (L. secretus, to separate), producing a substance by the

action of a gland or cell.
Sedentary (sed'enteri) (L. sedere, to sit), temporarily attached and not entirely

free moving.
Segmentation (seg men -ta' shun), i^^ Metamerism.
Segmentation cavity, hollow, central cavity (blastocoele) formed during early

cleavage of embryo.
Segregation law, passage of one member of each pair of allelomorphic genes to

different germ cells during maturation.
Selective absorption, absorption of certain substances and not others.
Self-fertilization, fertilization (fusion) of an egg by a sperm from the same indi-
vidual.
Semicircular canals (L. semi, half; circulus, circle), ear canals of vertebrates

devoted to sense of equilibrium.
Seminal receptacle (sem' i nal) (L. semen, seed fluid; recipere, to receive), organ

for storing sperm from opposite sex until needed for fertilization.
Seminal vesicle (sem' i nal) (L. semen, seed fluid; vesica, bladder), saclike organ

for storing sperm during spermatogenesis, as in earthworm.
Seminiferous tubule (sem i -nif er us) (L. semen, seed fluid; jerro, to carry;

tubules, small tube), tube to conduct seminal fluid of male.
Semipermeable, permitting passage of certain molecules but not others.
Sepal (se' pal) (L. separ, covering), one of the outer whorl of floral leaves which

taken as a group are known as the calyx.
Septum (plural septa) (sep' tum) (L. septum, partition), partition separating two

cavities.
Serial homology (ho-mol'oji) (Gr. homo, similar; logos, study), presence of

structures of similar origin and form on different segments of the same

animal.
Serous (se' rus) (L. serum., watery), clear, watery fluid.
Sertoli cells (ser-to'le), modified, supporting or nurse cells for forming sperm

in the testes.
Sessile (ses' il) (L. sedere, to sit), permanently attached and never free moving.
Seta (plural setae) (se' ta) (L. seta, bristle), bristelike structure.
Sex chromosomes, odd chromosomes (X and Y chromosomes) distinguished from

the regular chromosomes which aid in sex determination.
Sex-limited characters (sex-influenced), those traits influenced or modified by the

presence of a particular sex organ (and its secretion), such as beard and

voice of the male due to hormones from the male testes.
Sex-linked characters, those traits whose genes are located in the sex chromosome.

Appendix 857

Sexual dimorphism (dl -mor' fizm) (Gr. di, two; morphe, form), two forms or
types of a plant or animal due to their sex.

Sieve tube, elongated, fused, conducting cells of plant phloem which have per-
forated sieve plates at their ends.

Sigmoid (sig'moid) (Greek letter, sigma;. eidos, resemble), curved like the Greek
letter sigma.

Sinus venosus (si' nus ve -no' sus) (L. sinus, cavity; vena, vein), thin-walled cham-
ber in certain hearts into which main veins empty.

Smooth muscle, one whose cells are not striated.

Sol, a state of a colloidal system in which the external phase is more liquid than
the internal phase (contrast with Gel).

Solation (so -la' shun), phenomenon of forming a sol.

Soma (so' ma) (Gr. soma, body), entire body, exclusive of reproductive cells.

Somatogenic reproduction (so mat o -jen' ik) (Gr. soma, body; genesis, origin),
reproduction by division of a multicellular body by fission, budding, etc.
(contrast with Cytogenic reproduction).

Somatoplasm (so -mat' o plazm) (Gr. soma, body; plasma, liquid), protoplasm of
the body (somatic) cells.

Somite (so' mite), segment or metamere of an organism.

Sorus (sor' us) (Gr. sorus, heap), a heap of sporangia as on fern leaves.

Special creation, doctrine that each species of organism is specially created.

Species (spe'shes) (L. species, particular kind), individuals so similar that they
might appear to have originated from the same parents.

Sperm, see Spermatozoa.

Spermatheca (sperm a -thek' a) (Gr. sperma, sperm; theke, case), saclike struc-
ture of certain invertebrates for storing sperm.

Spermatia (spur -ma' she a) (Gr. sperma, seed), cells in rust fungi, produced in
spermagonia; also the male gamete of red algae.

Spermatid (sperm a -tid') (Gr. sperma, sperm), male cell arising by division from
a secondary spermatocyte and which later gives rise to a sperm.

Spermatocyte (sper -mat' o site) (Gr. sperm, sperm; kytos, cell), male germ cell
(arising from the spermatogonium) before it is mature.

Spermatogenesis (sper mat o -jen' e sis) (Gr. sperm, sperm; genesis, origin), for-
mation of mature sperm.

Spermatogonium (spur mat o -gon' i um) {Gr. gonos, offspring), primordial male
cell giving rise to the spermatocyte; flask-shaped structure in rust fungi,
producing spermatia.

Spermatozoa (spur ma to -zo' a) (Gr. sperma, sperm; zoa, animal), male sex cells
(sperm) .

Sphenopsida (sfen -op' si da) (Gr. sphen, wedge; opsis, appearance), subphylum
including horsetails.

Sphincter (sfingk' ter) (Gr. sphinggein, to bind tightly), circular muscle to close
an opening, as the stomach, bladder, anus, etc.

Spinal canal, canal in the spinal column containing the spinal cord.

Spinal column, bony structure enclosing spinal cord.

Spindle (A.S. spinnan, to spin), fibrous structure of nucleus associated with
chromosomes during mitosis.

858 Appendix

Spiracle (spir' a kl) (L. spiraculum, air hole), external opening of respiratory sys-
tem of insects.

Splanchnic (splangk' nik) (Gr. splanchnon, entrail), pertaining to internal, vis-
ceral organs.

Spleen (Gr. splen, spleen), ductless, vascular organ near the stomach.

Spongin (spun' jin) (Gr. spongos, sponge), horny material allied to silk, forming
skeletal fibers of certain sponges, especially commercial types.

Spongy tissue, plant mesophyll tissue with cells loosely arranged, with many in-
tercellular (air) spaces, and located beneath the lower leaf epidermis.

Spontaneous generation, see Abiogenesis.

Sporangium (spor -an' jium), structure containing spores.

Spore (Gr. sporos, seed or spore), cell with resistant covering and for reproductive
purposes; one or several may be produced at one time, depending on the
species.

Spore mother cell, a cell which by cell divisions produces usually four spores.

Sporophyll (spor' o fil) (Gr. spor a, spore; pyllon, leaf), a leaf that bears sporangia.

Sporophyte (spor'ofite) (Gr. spora, spore; phyta, plant), spore-bearing (asexual)
generation in plants exhibiting alteration of generations.

Sport, a mutant.

Squamous (skwa'mus) (L. .yq^Mawa, scale), flat, scalelike.

Stamen (sta'men) (L. sta, stand), pollen-bearing structure of a flower.

Statocyst (stat' o sist) (Gr. statos, stationary; kystos, sac), organ of equilibrium
as in medusae.

Steapsin (ste -ap' sin) (Gr. stear, tallow; pepsis, digest), a pancreatic enzyme able
to change fat to fatty acid and glycerin.

Stele (ste'le) (Gr. stele, post), central cylinder of united vascular bundles in the
root and stem of dicotyledonous seed plants.

Sterigma (Gr. sterigma, support), a stalk for bearing a basidiospore.

Sterile (ster' il) (L. sterilis, barren), infertile, free from all types of organisms.

Sternum (stur' num) (L. sternum, breast bone), breast bone.

Stigma (stig'ma) (L. stigma, a mark), upper part of pistil to receive pollen; or
same as eyespot.

Stimulus (stim'ulus) (L. stiryiulare, to incite), condition or substance which in-
duces a response.

Stoma (plural, stomata) (stom' a) (Gr. stoma, mouth), small opening as in
leaves.

Striated (stri' a ted) (L. stria, channel), marked by small channels, usually
parallel.

Strobilus (strob' i lus) (Gr. strohilos, twisted), cone-shaped group of sporophylls
in horsetails, conifers, etc.

Style (sti' 1) (Gr. stylos, pillar), stalk to support the stigma.

Subclavian (sub -kla' vi an) (L. sub, under; clavis, clavicle or collar bone), under
the collar bone.

Subcutaneous (sub ku -ta' ne us) (L. sub, under; cutis, skin), beneath the outer
skin.

Supplemental factors, genes which modify and supplement the ability of other
genes.

Suprarenal (supra -re' nal) (L. supra, above; ren, kidney), an endocrine (duct-
less) gland above each kidney (also called adrenal).

Appendix 859

Surface tension, greater tension (attraction) of the surface molecules of liquids

for each other than the attraction of molecules beneath the surface.
Suspension, particles not dissolved but suspended in a fluid.
Suture (su' tur) (L. suo, to sew), junction of two bones, usually an irregular,

serrated line.
Swimmerets, paired, branched appendages beneath the crayfish abdomen and just

posterior to the walking legs.
Symbiosis (sim bi -o' sis) (Gr. syn, together; bios, living), two different species of

organisms associated for mutual benefit.
Symmetry (sim' e tri) (Gr. syn, together; meton, measure), having similar parts

or regularity of form.
Sympathetic nervous system, see Autonomic system.
Synapse (sin'aps) (Gr. syn, together; hapto, unite), space between axon brush of

one nerve cell and dendrite of next nerve cell.
Synapsis (si -nap' sis) (Gr. synapsis, union), temporary conjunction of the pairs

of homologous chromosomes (from male and female parent) previous to

the maturation of germ cells.
Syncytium (sin -sit' i um) (Gr. syn, together; kytos, cell), undivided mass of pro-
toplasm with several nuclei, as in certain muscles, fungi, etc.
Synergid (si -nur' gid) (Gr. synergos, working together), two small cells near the

egg at the micropyle end of the embryo sac in an ovule.
Syngamy (sin' ga mi) (Gr. syn, together; gamos, marriage), union of male and

female gametes (sex cells) to form a zygote.

Tactile (tack' til) (L. tongere, touch), concerning stirnulation by contact.

Taenia (te'nia) (L. taenia, ribbon), tapeworm.

Tarsus (tar'sus) (Gr. tarsos, flat), ankle bone or the terminal segment of insect
leg.

Taxis (tack' sis) (Gr. taxis, arrangement), tropismal response involving movement
of the organism as a whole.

Taxonomy (taks -on' o mi) (Gr. taxis, arrangement; nomos, law), scientific classi-
fication of organisms.

Telegony (te-leg'oni) (Gr. telos, end; gonio, generation), the unproved theory
that mating of a female with a certain male will affect the future off-
spring of that female even when sh"e is mated to a different type of male.

Teleology (tel e -ol' o ji) (Gr. telos, end; logos, study), philosophical study of the
final purposes and causes of things which imply the existence of a design
in Nature.

Telophase (tel'ofaz) (Gr. telos, end; phais, appear), final stage in mitosis when
daughter cells are formed.

Tendon (ten' don) (L. tendo, stretch), connective tissue to connect muscle to bone.

Tentacle (ten'takl) (L. tento, touch), flexible appendage for movement, grasp-
ing, etc.

Terrestrial (ter -res' tri al) (Gr. terra, earth), pertaining to land.

Test (L. testa, shell), hard, outer shell of such animals as sea urchins.

Testis (tes' tis) (L. testis, Xcsiis) , male gonad for forming sperm.

Thalamencephalon (thai a men -sef a Ion) (Gr. thalamos, receptacle; engkephalon,
in brain), part of vertebrate brain derived from the embryonic forebrain.

860 Appendix

Thallophyta (thai -of i ta) (Gr. thallos, young shoot or branch; phyta, plant),

simple, thallus plants without true leaves, stems, or roots.
Thallus (thai' us) (L. thallos, a. shoot), simple, undifferentiated plant.
Thermotaxis (thur mo -tack' sis) (Gr. therme, heat; taxis, response), reaction to

heat or cold.
Thermotropism (thur -mot' ro pizm) (Gr. thertne, heat; trope, turn), see Thermo-
taxis.
Thigmotaxis (thig mo -tack' sis) (Gr. thigema, touch; taxis, arrangement), motile

response to contact or touch. ,

Thigmotropisni (thig -mot' ro pizm) (Gr. thigema, touch; trope, turn), response

to contact.
Thoracic (tho -ras' ik) (Gr. thorax, chest), pertaining to thorax (chest).
Threshold (thresh' old) (A.S. therscold, starting point), minimum amount of a

stimulus to get response.
Thrombin (thromb' in) (Gr. thrombos, clot), substance to aid blood clot formation.
Thymus (thy'mus) (Gr. thymos, thymus), ductless gland in the pharyngeal region

of vertebrates.
Thyroid (thy' roid) (Gr. thureos, shield; eidos, resemble), ductless gland in the

neck of vertebrates which regulates metabolism, growth, etc.
Thyroxin (thy -rok' sin), hormone produced by the thyroid.

Thysanura (thi sa -nu' ra) (Gr. thysanos, fringe; oura, tail), order of wingless in-
sects such as bristletails.
Tibia (tib'ia) (L. tibia, pipe), larger, inner bone of the lower leg of vertebrates.

The part between the femur and tarsus of an insect leg.
Tissue (tish' u) (Fr. tissu, woven), group, of similar cells performing a specific

function.
Toxin (tok' sin) (Gr. toxicon, poison), chemical substance of bacterial origin

which stimulates animal protoplasm to produce a specific antitoxin (against

toxin) .
Trachea (tra' ke a) (Gr. tracheia, windpipe), tube to carry air.
Tracheal tube (tra' ke al) (Gr. tracheia, tube), rather long tube of the plant

xylem composed of sev^eral hollow cells fused end to end.
Tracheid (tra'ke-id), single, hollow, enlongated plant cell with pitted walls (in

the xylem) to conduct materials.
Tracheole (tra'keol), small tracheal tube.
Tracheophyta (tre ke -of i ta) (Gr. tracheia, tube; phyta, plants), subphylum of

plants possessing vascular tissues.
Transformism (trans -form' izm) (L. trans, over; forma, form), the doctrine that

species may change to form new species, as opposed to special creation or

fixism.
Translocation (trans lo -ka' shun) (L. trans, beyond; locus, place), transfer of

soluble materials through the sieve tubes of the phloem of vascular plants;

the exchange of parts of chromosomes.
Transmutation (trans mu -ta' shun) (L. trans, over; mutare, change), ability of

genes to change their position, as in translocation from one chromosome to

a nonhomologous one.
Transpiration (trans pi -ra' shun) (L. trans, through; spiro, breathe), loss of

water from plants, especially from leaves.

Appendix 861

Trial-and-error, theory that living organisms find their way to favorable environ-
ments by continually avoiding less favorable ones.

Trichinella (tri ki -nel' la) (Gr. thrix, hair), small roundworm, sometimes parasitic
in pork, causing trichinosis in man.

Trichocyst (trik'osist) (Gr. thrix, thread; kystos, bag), organelle producing hair-
like fibers for offensive and defensiv^e purposes in such animals as Para-
mecium.

Tricuspid (tri -kus' pid) (L. tres, three; cuspis, point), three-pointed.

Trihybrid (tri -hy' brid) (L. tres, three; hyhridos, mongrel), offspring of parents
who differ with regard to three different traits.

Trilobite (tri' lo bite) (L. tres, three; lobos, lobes), type of extinct crustacean
with a trilobed body.

Triploblastic (trip lo -bias' tik) (Gr. triplax, triple; blastos, bud), three primary
germ layers (ectoderm, mesoderm, entoderm) from which all organs and
tissues arise.

Trochanter (tro -kan' ter) (Gr. trochanter, run), second segment of an insect's
leg.

Trophectoderm (Trophoderm) (trof -ek' to durm) (Gr. trophe, food; ecto, exter-
nal, derma, skin or layer), outer layer of cells of the embryonic morula
which later supplies nourishm.ent (contrast with Inner cell mass).

Trophozoite (trof o -zo' ite) (Gr. trephein, nourish; zoon, animal), sporozoan dur-
ing its growth stage.

Tropism (tro'pizm) (Gr. trope, turn), automatic response of living organism to
a stimulus.

Trypsin (trip' sin) (Gr. truein, rub down; pepsis, digest), protein-splitting enzyme
of the pancreas.

Tube foot (L. tuba, pipe), tubular organ of certain echinoderms (as starfish) for
locomotion, etc.

Turgor (tur' gor) (L. turgere, to swell), pressure within a cell because of absorp-
tion of water.
Twinning, production of two individuals at the same time.
Tympanum (tim' pan um) (L. tympanum, drum), eardrum.

Typhlosole (tif'losole) (Gr. typhlos, bhnd; solen, channel), median, dorsal fur-
row of earthworm intestine to increase absorption.

Ulna (ul' na) (L. ulna, elbow), bone which together with the radius forms the
forearm.

Umbilical cord (um-bil'ikl) (L. umbilicus, navel), cord composed of blood ves-
sels and connective tissues to connect fetus with the mother.

Umbilicus (im -bil' i kus) (L. umbilicus, navel), scar on the abdomen where the
umbilical cord was attached.

Uniformitarianism (uni form i -ta' ri an izm) (L. unus, one; forma, form), doc-
trine that past geologic processes were similar to those of the present (con-
trast with Catastrophism) .

Unit character, trait which is inherited independently and more or less as a unit.

862 Appendix

Unity of an organism, constant integration of various structural and physiologic
components of an organism so that it will be a unit, structurally and func-
tionally.

Urea (u-re'a) (Gr. ouron, urine), nitrogenous waste material of animal metab-
olism.

Ureter (u-re'ter) (Gr. oureter, ureter), tube carrying urine from kidneys to
bladder or to cloaca.

Urethra (u -re' thra) (Gr. ourethra, urethra), tube carrying urine for bladder to
outside.

Uriniferous tubules (u ri -nif er us), unit of urinary system of higher animals
consisting of coiled tubes and a capsule.

Urogenital (urinogenital) (u ro -gen' i tal) (Gr. oura, urine; gignesthai, to pro-
duce), the organs of both urinary and reproductive systems taken collec-
tively.

Uropod (u'ropod) (Gr. oura, tail; pons, appendage), modified swimmeret on
either side of the last abdominal segment of a crayfish.

Urostyle (u'ro stile) (Gr. oura, tail; style, pillar), last rodlike bone of frog spinal
column.

Uterus (u'terus) (L. uterus, belly, womb), enlarged part of oviduct; in female
mammals an organ for containing and nourishing the developing young
before birth.

Vaccine (vak' seen) (L. uacca, cow), the virus of cowpox administered to build
immunity against smallpox. The term is more generally applied, although
incorrectly, to many types of so-called "shots."

Vacuole (vak'uole)' (L. vaccum, empty), space for receiving something.

Vagina (va-ji'na) (L. vagina, sheath), in female mammals a tube leading from
the uterus to the exterior.

Variation (var i -a' shun) (L. variare, change), differences shown by individuals
of the same species, etc.

Vas deferens (plural, vasa deferentia) (vaz; def er ens) (L. vasa, vessel; de, down;
fero, to bear), tube to carry sperm to the exterior.

Vasa efferentia (vaza; ef er -en' sha) (L. vasa, vessel; ex, out; ferro, to bear),
tubes carrying sperm from testes to the vasa deferentia.

Vascular (vas' ku lar) (L. vasculum, little vessel), pertaining to vessels, usually
blood vessels.

Vascular bundle, structure composed of vessels (xylem and phloem) for conduct-
ing liquids in higher plants.

Vasomotor nerves (vas o -mot' er) (L. vasa, vessel; movere, to move), nerves con-
trolling the caliber of the arteries by the contraction and expansion of
muscles in their walls.

Vegetal pole (veg' e tal) (L. vegetare, enliven), pole of a cell where the rate of
metabolism is lower than that at the animal pole.

Vegetative reproduction, asexual reproduction by such methods as grafting, cut-
tings, fragmentation, etc.

Vein (L. vena, vein), vessel carrying blood toward the heart; vascular bundle of
a leaf.

Appendix 863

Ventral (ven' tral) (L. venter, belly), lower or belly side.

Ventricle (ven'trikal) (L. ventriculus, little belly), lower heavier chamber of

the heart from which blood is pumped out.
Vermiform appendix (ver' mi form) (L. vermis, worm; forma, form), slender

appendage of the large intestine where it joins the small intestine.
Vertebrate (vur' te brate) (L. vertebratus, backbone), animal having a vertebral

column.
Vestigial (ves -tij' i al) (L. vestigium, trace), rudimentary part of an organism

no longer functionally useful.
Villus (plural villi) (vil' us) (L. villus, hair), minute projection of small intestine

to increase absorption.
Virus (vi' rus) (L. virus, poison), living ultramicroscopic, virulent cause of certain

plant or animal diseases.
Viscera (vis' era) (L. viscera, internal organs), organs within a body cavity.
Viscosity (vis -cos' i ti) (L. viscosus, y'lscous) , tendency of certain liquids not to

flow easily due to internal friction (adherence of liquid particles to each

other).
Vitalism (vi' tal izm) (L. vita, life), the doctrine which attributes at least some

of the living phenomena to an interplay of nonmaterial forces other than

those prevailing in the lifeless world (contrast with Mechanistic view).
Vitamin (vi'tamin) (L. vita, life; amin, a chemical radicle, NH2), substance

which is essential for the proper metabolism and regulation of body proc-
esses; they were named vitamins because they were thought originally to

contain an amine radicle, which is incorrect.
Viviparous (vi -vip' a rus) (L. vivus, alive; parere, to bear), development of the

embryo within the mother's body and the subsequent birth of a living

young organism.
Vomer (vo' mer) (L. vomer, ploughshare), bony partition in the nose.

Warm-blooded, animals whose blood retains a rather constant temperature re-
gardless of external temperatures, as birds and mammals (contrast with
Cold-blooded).

White blood corpuscle, colorless blood cell; also called leucocyte.

Wolffian duct (after German anatomist, Wolff), the forerunner of the male vas
deferens in vertebrates.

Working hypothesis (hi -poth' e sis) (Gr. hypo, under; tithemi, place or consider-
ation), a basic assumption to guide the study of a problem or subject and
to be proved or disproved by the data accumulated.

Xanthophyll (zan' tho fil) (Gr. xanthos, yellow; phyllon, leaf), yellow-orange pig-
ment of certain higher plants, especially leaves.

X chromosome, a chromosome associated with sex of many organisms.

Xerophyte (ze' ro fite) (Gr. zeros, dry; phyton, plant), plant adapted to dry
conditions.

Xylem (zi' lem) (Gr. xylem, wood), woody, water-conducting portion of a fibro-
vascular bundle.

864 Appendix

Y chromosome, a special chromosome associated with the sex of the organism. In
human beings this chromosome is present only in males.

Yeast (A.S. gist, ferment), unicellular, chlorophyll-less plants capable of fermen-
tation; some are pathogenic.

Yolk (yok) {yolke, yellow), stored food in the egg cytoplasm.

Zone of tissue difFerentiation, the point in young plant roots and stems where
adult tissues are being formed.

Zoogeography (zo o je -og' ra fi) (Gr. zoon, animal; ge, earth; graphein, to write) ^
geographic distribution of animals in space.

Zoology (zo-ol'oji) (Gr. zoon, animal; logos, study), study of animals.

Zoosporangia (zo o spor -an' ji a) (Gr. zoon, animal; sporos, spore; anggeion, ves-
sel), a structure in which motile zoospores develop.

Zoospore (zo'ospor), motile spore.

Zygospore (zy' go spor) (Gr. zygotos, united), spore formed by the union of two
gametes (male and female sex cells).

Zygote (zy' got) (Gr. zygotos, united), fertilized egg cell after fusion with male
gamete.

Zymase (zy'mas) (Gr. zym, leaven; ase, enzyme or ferment), enzyme (in presence
of oxygen) which converts glucose and other carbohydrates into carbon
dioxide and water or (in absence of oxygen) into alcohol and carbon
dioxide or into lactic acid.

Zymogen (zy'mo jen) (Gr. zym, ferment; gen, to form), forerunner of an enzyme
(pre-enzyme) ; a substance which is produced and later becomes an
enzyme when it is activated by another substance (probably another
enzyme).

Zymosis (zy-mo'sis), any form of fermentation, especially morbific (L. morbus,
disease; facto, to make).

Appendix 865
III. NEW AND OLD SYSTEMS OF CLASSIFYING PLANTS CONTRASTED*

NEW

OLD

Kingd(

Dm Plantae

Kingdom Plantae

I. Subkingdom Thallophyta (plants

1. Phylum Thallophyta

not forming embryos)

A. Subphylum Algae (simple
plants with chlorophyll)

Phylum Cyanophyta (blue-

( 1 ) Class Myxophxyceae

green algae)

(Cyanophyceae) (blue-
green algae)

Phylum Chlorophyta (green

(2) Class Chlorophyceae

algae)

(green algae)

Phylum Chrysophyta (yellow-

(3) Class Bacillariophyceae

green, golden-brown algae

(Diatomaceae) (diatoms)

and diatoms)

Phylum Phaeophyta (brown

(4) Class Phaeophyceae

algae)

(brown algae)

Phylum Rhodophyta (red

(5) Class Rhodophyceae

algae)

(red algae)
B. Subphylum Fungi (simple
plants without chlorophyll)

Phylum Schizomycophyta (bac-

(1 ) Class Schizomycetes

teria)

(bacteria)

Phylum Myxomycophyta (slime

(2) Class Myxomycetes

molds)

(slime molds)

Phylum Eumycophyta (true,
higher fungi)

(1) Class Phycomycetes

(3) Class Phycomycetes

(algalike fungi)

(algahke fungi)

(2) Class Ascomycetes (ascus

(4)' Class Ascomycetes (ascus

[sac] fungi)

(3) Class Basidiomycetes

(5) Class Basidiomycetes

(basidium [club] fungi)

II. Su

bkingdom Embryophyta (plants
forming embryos)

Phylum Bryophyta (Atracheata)

2. Phylum Bryophyta (liverworts

(plants without vascular

and mosses)

conducting] tissues)

(1) Class Musci (mosses)

(2) Class Hepaticae (liver-

worts)

worts )

10.

Phylum Tracheophyta

3. Phylum Pteridophyta (club

(Tracheata) (plants with vas-

"mosses," horsetails, ferns)

cular tissues)

A. Subphylum Lycopsida

( 1 ) Class Lycopodineae

(club "mosses")

B. Subphylum Sphenopsida

( 1 ) Class Equisetineae

(2) Class Equisetineae

(horsetails)

{Continued on next page)

*The newer classification is based more or less on the natural relationships of plants. The
complete classification is not given here but only those parts which deal with plants being studied.
When contrasted with the older, traditional method, both methods may be helpful in reading
additional references. More detailed discussions of the newer method are given elsewhere in
the book.

866 Appendix

NEW

OLD

G. Subphylum Pteropsida

(1) Class Filicineae (ferns)

(3) Glass Filicineae (ferns)

4. Phylum Spermatophyta

(flowering plants)

(2) Class Gymnospermae

( 1 ) Glass Gymnospermae

(plants with exposed,

(plants with naked, ex-

naked seeds) (conifers

posed seeds (conifers

and their allies)

(3) Glass Angiospermae

(2) Glass Angiospermae

(plants with seeds en-

closed by carpels)

(flowering plants)

(a) Subclass Dicotyledoneae

(two embryonic seed

leaves) (beans, sun-

flowers, etc.)

(b) Subclass Monocotyle-

doneae (one embry-

doneae (one embryo-

onic seed leaf) (corn,

nic seed leaf) (corn.

grasses, etc.)

INDEX

Abbe, 31

Abdomen, 318, 319, 329, 340, 393,

394*
Aberration, 679, 680
Abiogenesis, 732

Absorption, 82, 226, 227, 353, 430
Acclimation, 813
Accretion, 95, 101
Acetabulum, 423,* 425
Acetylcholine, 503
Achilles tendon, 426*
Achromatic figure, 64
Aciculum, 307*

Acid, 84, 87, 88, 169, 232, 429, 476
Acontia, 291*
Acoustic, 495
Acquired characteristics, 712, 722, 746,

747
ACTH (pituitary hormone), 510
Actinomycosis, 659
Actinopoda, 274
Adaptation, 96, 101, 721-731, 723*-

728*
Adaptive radiation, 729
Adductor muscle, 312,* 313,* 426*
Adipose {see Tissues)
Adrenal gland, 507,* 508, 511
Adrenalin, 511 {see also Endocrine

glands)
Aeciospore, 129, 167, 182, 182*
Aedes {see Mosquito)
Aerobe, 122, 170
Aestivation, 594
African fever, 660

Agaricus (Psalliota) {see Mushroom)
Agassiz, 803

Agglutination, 519, 524
Agranulocyte, 484-486
Agriculture, 775, 776
Air bladder, 331, 332*

cavity, 141,* 147,* 188, 211, 215,

224, 226, 411
sac, 396,* 397, 403,* 405, 490,* 492
sinus, 469*
Albumin, 89, 311, 312*
Alcohol, 252

Aleurone, 210

Algae, 109-119, 150-166, 249, 250
blue-green, 109, 110, 113,* 151-155,

249
brown, 109, 110, 116, 118,* 153,

154, 160-162, 249
desmids, 115,* 116, 153-159
diatoms, 116, 117,* 153, 154, 159,

160, 249
economic importance, 249, 250
green, 109, 110, 114-116, 115,* 153-

159
red, 109, 110, 118, 119,* 153, 154,

162-165, 163*
yellow-green, 109, 110, 116, 117,*

153, 154, 159, 160
Algalike fungi ( Phycomycetes, 109 {see

also Mold)
Allantois, 451,* 453
Allele (Allelomorph), 525, 682, 694*
Alligator, 338*
Allium (onion) {see Mitosis)
Alternation of generations {see Meta-
genesis)
Alveolar, 74, 75,* 464*
Alveoli, 434, 490,* 492
Amboceptor, 520
Ambulacral, 300,* 301,* 302,* 303,

304,* 305*
Ambystoma {see Salamander)
Amino, 88, 429, 476
Ammonia, 651

Amnion, 451,* 452, 453, 455*
Amoeba, 274, 275,* 344-349, 345*-

348*
Amoebic dysentery, 533,* 784
Amoebocyte, 283*
Amphiaster (achromatic figure), 64
Amphibia, 331, 333*-335,* 421-441,

653 {see also Frog)
Amphineura, 309, 309*
Amphioxus, 328,* 329
Amphoteric, 89
Ampulla, 301,* 302,* 304
Amylopsin, 429, 476
Anabena, 113,* 154, 155
Anabolism, 93, 101

*Asterisk following reference indicates page with illustration. Also refer to Glossary in the
Appendix for definitions, principles, theories, and additional references.

867

868 Index

Anaerobe, 122, 170

Analogy, 576, 578

Anaphase (mitosis), 62, 63,* 65, 66,*

67
Anaphylaxis, 520, 773
Anatomy, 24

and physiology of higher animals,

458-529
of plants, 219-248
Anaximander, 732, 800
Ancylostoma, 295, 661
Andalusian fowl, 691*
Anemia, 484, 525
Angiospermae, 110-112, 143-148, 206-

218

Anguillula {see Vinegar eel)
Animal, cellular organization, 46-55
classified, 272-343

economic importance, 530-575 •

kingdom, 272-343
number of species, 273
of past and records, 605-619
pole, 445,* 452
wildlife, 797
Animals and plants contrasted, 104-107
Animate organization, 99-103
Anion, 83
Annelida, 304-309, 307*-309*, 384-392,

540, 541, 788
Annual ring, 214, 221, 222
Annulus, 139,* 196, 198
Anodonta {see Clam)
Anomalies, 582
Anopheles {see Mosquito)
Anoplura (lice) {see Insects)
Ant, 571,* 572 {see also Insects)

lion {see Insects)
Antenna, 318, 319, 321*-324,* 394,*
398, 403* 405, 410,* 411,*
414-418
Antennule, 320,* 321*
Anther, 144,* 146,* 208, 210, 212, 217,

223,* 225, 225*
Antheridiophore, 189
Antheridium, 119, 129, 131,* 132*-
134,* 136, 137,* 138, 138,*
154, 161, 162, 163,* 164, 165,
174,* 175, 186-189, 191-197,
202

Antherozoid, 132,* 136,* 197, 204
Anthocyanin {see Pigments)
Anthozoa, 290, 291,* 292*
Antiaggressin, 520
Antibiotic, 175, 250
Antibody, 519, 772
Antigen, 519
Antimere, 286, 299
Antipodal cell, 206, 207
Antitoxin, 519, 773

Anus, 295, 296,* 298, 299, 301,* 302,
307,* 309,* 311*-315,* 321,*
327, 327,* 328,* 332,* 350,*

381, 396*
Anvil, 466, 498,* 505

Aorta, 311,* 313,* 315,* 332,* 340,*
396, 396,* 403,* 477, 478*-
480,* 482, 741*

Aperture, 310*

Aphid (plant louse), 559, 561* {see
also Insects)

Aphis lion {see Insects)

Apis {see Honeybee)

Apopyle ( see Sponges )

Apothecium, 176

Appendages, 577*

Appendicularian, 327

Applied biology, 115-191

Arachnoid, 503

Arachnoidea, 319, 326,* 544, 545*

Arbacia {see Sea urchin)

Archaeopteryx, 736, 737*

Archegoniophore, 189

Archegonium, 129, 131*- 134,* 136,
136,* 137,* 138, 138,* 140,*
186-189, 191-197, 202-204,
206

Archenteron, 447

Archeozoic era, 614, 617

Archinellida, 306

Aristotle, 732, 801

Aristotle's lantern, 303*

Arm, 301,* 302-304, 307,* 315*

Artery, 430,* 432, 470,* 477-489, 740,*

741*
Arthropoda, 314-325, 393-408, 543-572
Ascaris (roundworm), 295, 298, 379-

382, 380,* 538, 660, 785, 788
Ascaroidea, 295

Ascidian, 327, 328*

Ascocarp, 177

Ascomycetes, 109, 125, 167, 175-177

{see also Yeast; Aspergillus,

Penicillium; etc.)

Ascospore, 125*-127,* 167, 176, 177

Ascus, 125,* 126

Asexual reproduction {see various or-
ganisms)

Aspergillus, 126,* 127, 129, 175, 176,
250, 251*

Assimilation, 94, 345, 353

Association (animal and plant), 646,
652

Aster {see Mitosis)

Asterias (starfish), 301, 301*

Asteroidea, 301

Astral ray (aster), 63,* 64, 64,* 65

Asymmetry {see Symmetry)

Athlete's foot, 659

Index 869

Atlas, 423, 423*

Atom, 77, 78, 79,* 80, 81,* 82, 83,

83,* 750
Atomic energy (see Atomi)
number, 78, 79*
theory {see Atom)
Atracheata, 109
Atrium, 328,* 477, 478*-481,* 490,*

741* {see also Auricle)
Atrophy, 817
Attachment fiber, 65
Auditory, 394,* 398, 405, 424, 495, 505
AureHa, 290, 290*
Auricle, 311*-313,* 331-340, 332,*

340,* 370,* 371,* 372, 401,*

403, 430, 430,* 470,* 740*

Australian region, 598

Autocatalysis, 92, 94, 680

A-utogamy, 817

Autolysis, 817

Autosome, 675,* 698

Autosynthesis, 92, 93, 101

Autotomy, 299, 304, 443, 576, 578

Autotrophic, 168, 669

Autumnal coloration {see Pigments)

Auxin A and B, 240, 583, 768

Auxospore, 154, 160

Aves {see Birds)

Avoiding reaction, 352,* 355, 359

Axial, filament, 359

gradient, 372, 373, 537

skeleton, 423
Axiate organization, 373, 537
Axis, 372, 373, 537
Axon 47, 54, 54,* 501

brush, 54*
Azotobacter, 651

Babesia, 534, 534,* 786
Back cross, 818
Bacon, Francis, 801

Bacteria, 109, 120-122, 121,* 167-172,
250-256, 650, 659
and nitrogen fixation, 650,* 651, 664
pathogenic, 120, 122, 168, 171, 255,
659, 660

Bacteriolysin, 520
Baer, Karl von, 803
Baeyer, 231

Balance in Nature, 653,* 655
Balanoglossus, 326,* 327
Balantidium, 530, 532*
Baldness, 703
Band, dark and light, 52*
Barb, 406

Bark {see Tissues, plant)
lice {see Insects)

Barnacle, 318, 323,* 544

Barrier, 595, 629

Basal granule {see Paramecium)

metabolism, 93
Basement membrane, 393
Basidiomycete, 109, 128,* 129, 167,

177-183 {see also Mushroom,

etc.)
Basidiospore, 128,* 129, 167, 178,*

179-181, 182*
Basidium, 128,* 129, 167, 178,* 179-

181, 182*
Basket star, 303
Bast fiber, 214
Bat, 340
Bausch, 31
Bean, garden or kidney, 143, 144,* 211-

213
Beche-de-mer (trepang), 540
Bedbug, 558* {see also Insects)
Bee, 319, 398-408

glue, 405
Beetles, 319, 563-565, 563,* 564* {see

also Insects)
Behavior {see specific organisms and

nervous equipments)
Eenthon, 112, 151
Beriberi, 474, 770*
Beroe, 291, 292,* 293
Beverages from plants, 264-266
Bile, 427,* 428, 429
Bihrubin, 493
Bills of birds, 728*
Binomial nomenclature, 819
Biochemical phenomena, 750-774
Bioelectric phenomena, 764 {see also

Electricity)

Biogenesis, 733, 735
Biogenetic, 442, 742
Biogeography, 24, 591, 736, 745
Biologists and their work, 800-806
Biology, 17

applied, 775-791

defined, 17

history of, 800-806

how to study, 19

of higher plants, 219-248

of man, 458-529

subdivisions of, 24, 25
Bioluminescence 762
Bionomics, 620

Biophysical phenomena, 750-774
Biotic, 658

Birds, 339, 339,* 340, 340,* 574, 728*
Bivium, 302*
Black tongue, 772
Blackhead, 788
Bladder, 377

air, 331, 332*

870 Index

Bladder— Cont'd
float, 289*

gall, 427,* 428, 429, 470/ 471*
swim, 331, 332*

urinary, 298, 299,* 427,* 435, 439,*
440, 492, 493,* 494, 514

Bladdervvorm, 379

Bladderwort, 636

Blade, 210, 223, 224

Blastocoele, 445,* 446, 452

Blastocyst (blastodermic vesicle), 451,*

452
Blastomere, 452
Blastomyces, 252
Blastopore, 445,* 446
Blastostyle, 285*
Blastula, 285,* 445,* 446, 451,* 710,*

711
Blight, 129, 177
Blood, 50,* 51, 396
clotting of, 486-487
corpuscles, red, 50,* 51, 484, 485

white, 50,* 51, 484-486
groups, 489, 524-526
"islands," 455
plasma, 51, 396, 405, 486
platelets, 51, 485, 486
vessels, 741*
Blue-green algae {see Algae)
Blue mold {see Mold; Penicillium;

etc.)
Body cavity {see Coelom)
Bog moss, 133, 134*
Bonannus, 29
Bone, 49, 50,* 51,* 462,* 465-467, 495

tissues {see Tissues, animal)
Book lice {see Insects)

lung, 319, 325*
Botany, 24, 249-271
Bouton, 402*

Bowman's capsule, 435, 493,* 494
Bracket fungus, 129, 179

method, 688*
Bract, 216 -

Brain and cranial nerves, 54, 299, 311,*
321,* 332,* 333, 340, 370,*
371, 376, 385,* 391, 396,*
405
Brains of vertebrates, 435-438, 436,*

437,* 495,* 502-506, 743*
Branchia, 302,* 328,* 331
Branchiostoma, 329

Bread mold (Rhizopus) {see Mold,
black bread)
yeast {see Mold, yeast)
Breast bone {see Sternum)
Breathing, 489

Bridges of protoplasm, 357 {see also
Plasmodesma)

Brittle star, 300,* 303
Bronchi (bronchus), 490,* 492
Brown algae {see Algae)
Brown, Robert, 31, 803
Brownian movement, 77, 100
Bryophyta, 109, 130-133, 131*-134,*

185-190, 256
Buccal mass, 312*

pouch, 384, 388*
Buds and budding, 125,* 127, 133,*

145,* 167, 176, 286,* 290,

377
Bugs (true) (Hemiptera) {see Insects)
Bulbus arteriosus, 741*
Burbank, Luther, 804
Burroughs, John, 804
Bursa, 296*
Bursaria, 530, 531*
Busch, 35

Buttercup (Ranunculus), 223,* 224
Butterfly, 319, 410,* 413* {see also

insects)
Butterwort, 668*
Button of mushroom, 128*

Caconema, 539, 661
Caddice fly {see Insects)
Caeca (cecum), 301,* 302,* 332,*
340,* 471*

gastric, 394, 396*

hepatic, 301*

pyloric, 302*

rectal, 403*
Calcarea, 281, 281,* 282*
Calcareous, 280, 281, 299, 303-314
Calcium carbonate, 280, 281, 299, 386
Callus, 580
Calorie, 87, 235, 757
Calyptra, 187

Calyx, 144,* 145,* 208, 212, 224
Cambarus {see Crayfish)
Cambium, 59, 141,* 143, 145,* 207,
214, 221, 222, 223*

Camera lucida, 30, 31
Canal, 350,* 354

auditory, 498,* 505

Bidder's, 440, 440*

circular, 302*

circumoral, 302*

connecting, 282,* 301,* 302*

excurrent, 282,* 284*

incurrent, 282,* 284*

lateral 302*

radial,' 282,* 284,* 288,* 301,* 302*

ring, 288,* 302,* 306*

semicircular, 498,* 505

stone, 302*

Index 871

Canaliculi, 49, 50,* 51*

Cancer, 583

Cane sugar (sucrose), 87, 92

Capillary, 389, 431, 483, 492

Capillitium, 123,* 172

Capsule, 139*, 187-190, 196, 198

Carapace, 322*

Carbohydrate, 85-87, 228-248

Carbon, 79*

assimilation, 229

cycle 650,* 651

dioxide, 150, 228-237, 390, 489-493,
632

fixation, 229

Carbonization, 605, 611
Carcinoma, 583
Cardiac cycle, 478, 479

muscle {see Tissues, animal)

stomach, 426, 427*
Carnivora, 105

Carotene (carotin), 116 {see also Pig-
ments)

Carpel, 140,* 143, 206, 208, 223,* 225,

225*
Carpellate, 140,* 203, 204
Carpogonium, 154, 163,* 164, 165
Carpospore, 119, 154, 163,* 164, 165
Cartilage {see Tissues, animal)
CataboHsm, 93, 101
Cataclysmic, 821
Catalyst, 91, 94, 101, 680
Cation, 83
Cell, 37-45, 40,* 42,* 100, 104, 646

antheridial, 202

bast, 145,* 214

companion, 56, 57,* 60, 147,* 192,
209-214,224

division {see Mitosis)

guard, 56, 57,* 58,* 145,* 210, 211,
215, 224, 226

membrane, 40,* 63,* 65, 66*

plate, 60, 65, 67

pole, 66,* 67, 646

principle, 37-45

prothahal, 194, 202, 204

sap, 39, 40,* 43

sheath, 147,* 151, 157

tube, 202, 204

wall, 39,40,* 59, 66,* 67, 104

wood, 59, 207, 214

Cellulose, 56, 59, 87, 104, 115, 155,

169, 170, 261, 327, 360
Cenozoic era, 614, 616
Centipede, 318, 324,* 543, 544
Central nervous system, 502
Centriole, 40,* 62
Centromere, 678
Centrosome, 41, 62, 63,* 70
Centrosphere, 40,* 41, 62, 63*

Cephalin, 486, 487

Cephalochordata, 328,* 329

Cephalodiscus, 327

Cephalopoda, 311, 315,* 316*

Cephalothorax, 318, 319

Cercaria, 375,* 377, 787*

Cerci, 414

Cerebellum, 54, 340,* 495,* 496,* 502,

503*
Cerebrum, 54, 308,* 312,* 313,* 314,

325,* 371, 371,* 388,* 502,

503

Cestoda {see Tapeworm)

Chaetopoda, 307,* 308

Chalone, 822

Chameleon, 338,* 340

Checkerboard, 686-690

CheHcera, 325*

Cheliped, 320,* 321*

Chemosynthesis, 168

Chemotropism (chemotaxis), 243, 352*

Chevalier, 31

Chiasma, 496*

"Chigger" (harvest mite), 545,* 786

Chilopoda, 318, 324,* 544

Chinch bug, 558* {see also Insects)

Chinese fluke, 785*

Chitin, 314-325, 393, 394, 400

Chiton, 309,* 542

Chlamydomonas, 116

Chlamydospore, 129, 167, 180, 180*

Chlorenchyma {see Tissues, plant)

Chlorogogen, 386, 387,* 390

Chlorophyll, 105, 112, 114, 116, 118,
130, 150-166, 185-190, 191-
198, 200-218, 224-245, 360

Chlorophyllogen, 822
Chlorophyta, 109, 114, 115,* 153, 156*
Chloroplast (chloroplastid), 40,* 43,
56,57,* 113,* 115, 115,* 130,
134,* 147,* 153, 155, 156,
156,* 159, 187, 188, 210-215,
228, 229, 230,* 236, 359, 360,
362

Choanocyte, 283,* 284*

Cholecystokinin, 512

Cholinesterase, 502

Chondriosome, 40,* 41

Chondrus (Irish "moss"), 119, 119,*

249
Chordata, 325-343, 572-574
Chorion, 451,* 453, 455,* 823
Choroid, 497,* 505, 823
Chromatic^ {see Mitosis)
Chromatid, 66,* 67, 679
Chromatin, 40,* 44, 62, 63,* 64, 65,
66,* 70, 151, 152, 154, 344

knot (karyosome), 40*

strands, 66, 66,* 67, 678

872 Index

Chromatophore, 274, 276,* 358,* 359,

532,* 730, 758
Chromomere, 679
Chromonemata, 44, 679
Chromoplast, 43, 161
Chromosomes, 44, 63,* 64, 65, 66,* 67,
673-683, 675*-677,* 696,*
698, 710*

aberration, 679, 680

map, 696,* 698

number in animals and plants, 674
Chrysalis, 413*

Chrysophyta, 109, 116, 117,* 153, 249
Cicada, 319, 561* [see also Insects)
Cilia, 277, 278,* 279,* 304, 349-357,

350,* 368, 369,* 370
Ciliary body, 497*
Ciliata, 277, 278,* 297, 299
Cinclide, 291*
Circulation, 477-489 {see also specific

organisms)
Cirri, 307,* 328*
Clam, 311, 312,* 313*

worm (sandworm) (Nereis), 307,*
308, 541
Classification of animals, 272-343

of insects, 409-420

of plants, 108-148, 865, 866
Claw, 394, 401,* 402
Cleavage, 444, 451,* 452
Clefts, 325-343, 328*
Cleistothecia, 177
CHnorchis, 661, 785*
Clitellum, 384, 389,* 391
Cloaca, 299,* 306,* 340,* 427,* 428,

440*
Clostridium, 121,* 651
Clothes and biology, 776

moth, 567* {see also Insects) '
Club moss, 110, 134, 135,* 191-194,
256

Cnidoblast, 287*

Coat, seed, 208, 210

Coccidia, 534

Cochlea, 495, 498,* 505

Cockroach {see Insects)

Cocoon, 373, 391, 392, 407

Coelenterata, 285,* 286-290, 536

Coelom (body cavity), 299, 302, 302,*
306-309, 314, 325-343, 327,*
384, 387,* 388, 390, 435,
449*
extraembryonic, 451,* 453

Coenurus, 538,* 788
Cohesion, 824
Colchicine, 677
Cold-blooded animal, 331-333
Coleoptera (beetles), 563-565, 563,*
564* {see also Insects)

Coleoptile, 211

Coleorhiza, 211

Collar, 283,* 327, 327*

Collaterals, 54

CoUembola {see Insects, orders of)

Collenchyma {see Tissues, plant)

Collies, heredity, 707*

Colloid, 74, 75, 75,* 78

Colon, 470,* 471,* 475, 477

Colony, 152, 154, 155, 159, 169, 171,

274, 298, 360, 363, 399
Coloration, 421, 423, 758, 760 {see also

Pigments)

Colorblindness, 702*
Colors (dves) from plants, 263
Columella, 124*
Comb, 400,* 401,* 402
Combinations in heredity, 722
Comb-jelly, 292, 292*
Commensalism 634, 658, 664
Commissure, 391
Communal, 646, 652, 658
Companion cell {see Cell)
Comparative anatomy, 736, 742

embryology, 736, 740

physiology, 736, 745
Complement, 520
Complementary gene, 693
Composite flower, 145,* 213
Compound, 84
Conceptacle, 162

Conduction, 227, 494, 500-502, 754
{see also circulation in specific
organisms)

of nerve impulses, 498-502, 498*
Condyle, 333, 340, 424
Cone, 135, 135,* 136, 138, 193-195,
200-205

Conidiospore, 122, 126,* 127, 129, 167,

172, 175, 177, 180
Conifer (Coniferales), 110, 138, 200-

203, 257
Conjugation, 124,* 125, 157, 158,*

159, 173, 277,* 355, 355,*

356*

Conjunctiva, 497*

Connecting strands of protoplasm, 41,

42,* 357

Connective tissues {see Tissues)
Conservation and biology, 18, 792-799

of energy, 751

of fishes, 797

of forests, 793, 793*

of human resources, 797, 798

of minerals, 794

of soils, 794

of water, 795

of wild Hfe, 796

Index 873

Continuity of germ plasm, 523, 747

of organisms, 732-749

physiologic, 363
Continuous variation, 723
Contractility, 47, 498
Control group, 22
Conus arteriosus, 332,* 430, 430*
Convolution, 503
Coordination, 494-513
Copepod, 317,* 543
Copulation, 372, 389,* 391, 392, 406
Coral, 249, 290, 292,* 536
Cord, spinal {see Nervous system)
Corium, 459, 460*

Cork, 141,* 261 {see also Tissues, plant)
Corn, borer, 568*

hybrid, 704*

Indian (maize), 146,* 209-211

Cornea, 397, 497,* 505

Corolla, 145,* 224

Corpus luteum, 509, 512, 516

Corpuscles {see Tissues, blood)

Correlation, 239 {see also specific or-
ganisms)

Corrodentia {see Insects)

Cortex, 141,* 145,* 214, 216, 220,
223,* 354,* 503

Cortin, 511

Cotyledon, 110, 140,* 144,* 148, 194,

202, 204, 207-213
Coxa, 394, 400, 401*
Crab, 318, 319, 323,* 544, 547

horseshoe (king), 319, 325*
Crane fly {see Insects)
Craniata, 329

Cranium, 329-343, 423, 462*
Crayfish, 318, 320,*-322,* 543

appendages, 577*
Cretin, 508,* 511
Cricket {see Insects)
Crinoidea, 304, 307*
Cristispira (in moUusca), 535
Crocodile, 340
Cro-Magnon man, 589
Crop, 308,* 312,* 385,* 386, 394, 396*
404

Cross, heredity, 686, 695, 696,* 698
sex-influenced, 703
sex-linked, 699-702, 700*-702*
Crossing over of genes, 695, 697
Crustacea, 317,* 318-324, 543
Crystalloid, 75

Ctenophora, 291-293, 292,* 537
Cuff, 30

Culex (mosquito), 411,* 569*
Cup fungus, 127,* 129
Cuticle, 141,* 145,* 147,* 295, 296,*

298, 358,* 373, 379, 381,

387,* 393, 459

Cutin, 39, 56, 214, 215,226

Cuttlefish (sepia), 311, 542

Cuvier, George, 802

Cyanophyta, 109, 113, 113,* 151-155,

249
Cycadales (sago palm), 142,* 203, 204
Cycas, 142,* 203, 204
Cycle, carbon, 650,* 651

estrous, 516

nitrogen, 649, 650*

oxygen, 650,* 652
Cyclops, 317,* 318
Cyclosis, 346, 353, 359, 360, 366
Cyclostomata {see Lamprey)
Cyst, 296,* 297, 358,* 360, 377, 377,*

379, 787
Cysticercus, 379
Cytogene {see Plasma gene)
Cytogenetic, 673
Cytology, 24

Cytolymph (see Cell sap)
Cytopharynx, 278,* 351, 358
Cytoplasm, 39, 40,* 47, 54, 62, 63,*

66,* 70, 156,* 344-367
Cytoplasmic gene, 357

granule, 40*

strand, 40,* 118, 153, 157, 162, 164
Cytosome, 39, 350, 358, 359

Daddy longlegs, 319, 326,* 547

Damsel fly {see Insects)

Daphnia, 324,* 543

Dark and light bands (striated mus-
cle), 467, 468
field, 32, 33

Dart sac, 311,* 312*

Darwin, Charles, 803

Data, 23

Deafness, heredity, 717*

Defense of body, 518, 519

Demospongia, 281

Dendrite, 47, 54, 54,* 501

Denitrification, 649, 650*

"De novo," 826

Dentalium, 314, 316*

Dentine, 464*

Dermis, 421, 422,* 459, 460*

Descent with change (evolution), 24,
94, 732-749

Desmid, 115,* 116, 154, 159

Determinate variation, 724

Development, 101, 732-749 {see also
Embryology)

Devilfish (octopus), 316,* 542

Diabetes, heredity, 716*

Dialysis, 827

Diaphragm, 340, 470*

Diarrhea. 784

874 Index

Diastase, 476

Diastole, 478

Diatom, 116, 117,* 154, 159, 160, 249

Diatomaceous earth, 160, 250

Dicotyledoneae, 110, 143-148, 207, 211,

213
Diecious, 164, 186, 189, 200, 202, 203,

295, 382
Differentiation, 46, 94, 95, 241, 242,

683
Diffraction, 759

Diffusion, 39, 80, 100, 730, 754
Digestion, 344, 352, 369, 388, 472-477

{see also specific organisms)
Digit, 333, 425

Dihybrid cross, 686-690, 686,* 689*
Dimorphism, 381
Dinosaur, 608*
Dioscorides, 801
Diphvllobothrium, 537
Diploid, 162, 206, 207, 357, 679, 680,

709
Diploplastic, 280, 286
Diplopoda, 318, 324,* 544
Disaccharide, 87
Discontinuous variation (mutation),

724
Diseases caused by animals, 660, 661,

784-789
by fungi, 252-254, 253,* 659, 660
by plants, 659, 789
by viruses, 789-790
human, 516-522, 659, 784-786
Disk, 189, 216, 286,* 291,* 297, 302,

303, 699
Dispersal, 76, 78, 593, 655, 656
Distomum {see Liver fluke)
Distribution, 591-604, 593*
Divergence, 729, 827
Diverticulum, 308,* 328,* 369, 371*
Division of labor, 828
Dizygotic, 828

Dobson fly, 562* {see also Insects)
Domestication, 638
Dominance, 682-692
Dominant and recessive traits, 682-692
Dorsal horn, 55*
Dourine in horses, 786
Dragonfly {see Insects)
Drone, 399, 399*
Drosophila {see Fruitfly)
Drugs, 269
Duct of Cuvier, 741*

of Wirsung, 477
Ductless glands (endocrine), 495,*

506-513, 507*
Dugesia {see Planaria)
Dujardin, 31, 37
Duodenum, 340,* 426, 427,* 429, 470,*

473, 509, 512

Dura mater, 503
Dyes, 263
Dynamic, 100
Dysentery, 784

Ear, 146,* 439, 495, 498,* 505
Early man and records, 585-590, 587*
Earthworm, 309, 384-392, 385,* 540
Earwig, 562* {see also Insects)
Eberthella typhosa, 121,* 255
Ecdysis, 393, 398
Echinococcus, 537, 788
Echinodermata, 299-304, 300,* 540

regeneration of, 98, 98*
Echinoidea, 303, 303,* 305*
Ecology, 24, 620-645, 723
Economic botany, 249-271

beverages, 264-266

coloring (dyes), 263

cork, 261

fibers, 260

flavoring substances, 266

foods, 264

fuels, 258, 259

gums and resins, 262, 268

medicines and poisons, 267-270

oils, 259, 267

savory substances, 267
zoology, 530-575

insects {see Insects)
Ectoderm, 280, 286, 286,* 287, 288,*
291,* 292, 293, 295, 299, 306,
309, 314, 325, 368, 373, 445,*
449,* 454

Ectoparasite, 653

Ectoplasm (ectosarc), 39, 40,* 345,*

349
Efferent nerve, 494, 497

vessel 322*
Egg (ovum), 134,* 136, 136,* 140,*

143, 154, 161, 162, 163,*

164, 174,* 175, 188, 189,

194-197, 201-203, 361,* 363,

396,* 398, 406, 410
sac, 225,* 317,* 389,* 391*
Ejaculatory duct, 380,* 382, 398, 406,

513
Elasmobranchii, 329, 331
Elater, 136, 137,* 189, 195
Electricity, 77, 353,* 647, 746-766
Electrocardiogram, 479
Electrolyte, 84, 751
Electron, 79,* 81, 81,* 83*

microscope, 32, 34,* 35
Elements, 78, 79,* 80, 85
Elephantiasis, 297, 297,* 298, 539, 661,

785
Elodea, 40*

Index 875

Elytra, 829 {see also Beetles)

Embolus, 487

Embryo, 129, 130, 134, 137,* 138, 143,
147,* 185-198, 200-205, 206-
218, 296,* 382, 442-457

Embryology, 24 {see also specific organ-
isms)

of animals, 442-457

of frog, 444-450, 445*-457*

of man, 450-456

of vertebrates, 442-457

of whitefish, 64*
Embryonic disk (embryonic shield),
451,* 453

seed leaf, 207
Embryophyta, 109-112, 129-149, 185-

198, 200-205, 206-218
Empedocles, 801
Emulsoid, 78
Enamel, 464*
End organ, 495

Endamoeba, 274, 532, 533,* 784
Endocardium, 478

Endocrine glands, 495,* 506-513, 507,*
767-772

hormones, 506-513, 507,* 767-772
Endocyst, 277*
Endoderm {see Entoderm)
Endodermis, 141,* 145,* 216, 220
Endometrium, 452, 514
Endoparasite (entoparasite), 658
Endoplasm, 39, 40,* 344, 345,* 349,
354*

Endopodite, 320*
Endoskeleton, 423
Endosome, 358

Endosperm, 143, 147,* 202, 204, 206-
208, 210

Endospore, 121,* 122, 167, 172

Endostyle, 328*

Energy, 79, 86, 87, 101, 105, 215, 229,

751, 756, 759
Enterobius, 539, 661
Enterokinase, 476
Enteron, 286, 287,* 445*
Enteropneusta, 327
Entoderm, 280, 286, 286,* 288,* 291,*

292, 293, 295, 299, 306, 309,

314, 325, 368, 373, 445,*

449,* 454

Entomology {see Insects)

Environment, 621, 625-645

Enzymes, 91, 94, 101, 122, 171, 232,

236, 344, 353, 360, 428-430,

443, 668, 766
digestive, 344, 353, 360, 388, 476
Eohippus {see Horse)
Ephyra, 290*
Epicotyl, 147,* 202, 204, 213

Epidermis, 141,* 145,* 147,* 368,
380,* 384, 459, 460* {see also
Tissues, epidermal)
Epididymis, 513, 514, 514*
Epigenesis, 830
Epiglottis, 469,* 492
Epimysium, 52,* 53
Epinephrine {see Endocrine glands)
Epipharynx, 410
Epiphysis, 509, 512
Epiphyte, 113, 114, 151, 152, 658, 669,

670*
Epithehum, 283,* 284* {see also Tis-

' sues, epithelial)
Equatorial plate, 63,* 65, 66,* 70
Equihbrium, 439, 496, 505
Equisetineae (horsetail), 110, 135, 194-

195
Equisetum, 110, 137, 137,* 194, 195
Eras, 613-618
Ergosterol {see Vitamins)
Ergot, 252

Erythrocyte {see Blood)
Esophagus, 296,* 299, 306,* 315,*
321,* 327,* 328,* 332,* 374,*
376, 381, 385,* 386, 394,
396,* 427,* 469,* 471,* 473
Estrin {see Endocrine glands)
Ethiopian region, 598
Eugenics, 526, 527, 715-718
Euglena, 274, 276,* 357-360, 358*
Eumycophyta, 109, 124-129, 124*- 128,*

173-184
Eustachian, 427,* 439, 469,* 498,* 505
Evagination, 830
Evergreen, 200-204
Evolution (progressive development),

24, 94, 729, 732-749
Excretion, 106 {see also specific organ-
isms)
Excretory pore, 369, 370, 376, 380,*

381
Excurrent canal {see Sponges)
Exopodite, 320*
Exoskeleton, 314, 393, 400 {see also

specific organisms)
Experimental cross, 673

method, 22
Extraembryonic coelom, 831
Eye, 307,* 310,* 311,* 312,* 321,*
325,* 332,* 371, 421, 456,*
497, 497,* 505
brush, 401*
compound, 393, 394,* 403,* 406,

410,* 411,* 412*
muscle, 438
simple (ocellus), 393, 394,* 396,

397, 403*
spot (stigma), 156, 293, 301,* 308,
359, 370-372, 370*

876 Index

Facet, 397

Factor {see Gene)

"Factor B," 232

Facultative, 831

Fallopian, 452, 514, 515*

P'amily chart (family tree), 715 {see

also Heredity)
-Fasciola hepatica, 373-377, 537, 660,

661, 786, 787* {see also Liver

fluke)

Fat body, 332,* 439, 441

Fatigue, 499

Fats, 85, 87, 153, 160, 161

Fauna, 639

Feather, 340

star, 304, 307*
Female gamete {see Sex cell)
Femur, 394, 394,* 400, 401,* 423,*

425, 462,* 466
Fenestra cochlea (rotunda), 505

vestibuli (ovalis) 505
Fermentation, 671, 831
Fern, 110-112, 137, 138, 138,* 139,*

191, 195-198, 196,* 256, 257
Fertilization, 143, 201-204, 207, 355-

357, 382, 710*
Fetus {see Embryology of man)
Fever {see Malaria; Texas; Typhoid;

etc.)

Fibers, 65, 498,* 505
from plants, 260

Fibrillae, 40,* 47, 53

Fibrillar (filar) theory, 74, 75*

Fibrin, 486, 487

Fibrinogen, 486, 487

Fibrous tissue {see Tissues)

Filament, 208, 210, 223,* 225*

Filaria, 295, 539

Filarioidea, 295

Filicineae (ferns), 110, 137, 138,* 139*

Fin, 315,* 328, 331, 331,* 332*

Fish, 330,* 331, 573
moth, 550, 551*

Fission, 114, 122, 152, 154, 167, 171,
373 {see also Reproduction)
binary, 348,* 349, 354, 355, 356,*
358*

Flagella, 114, 115, 118, 121,* 122,
123,* 124, 153, 155, 156,
156,* 157, 159, 161, 162, 171,
173, 186, 189, 274, 276,*
283,* 286,* 311,* 312,* 357-
360, 358,* 361,* 362*

"Flagellated body," 365*

Flame cell, 299, 369,* 370

Flatworm, 368-374, 660, 786 {see also
Planaria; Flukes; Tapeworm;
etc.)

Flavone (flavonol) {see Pigments)
Flavoring materials from plants, 266
Fleas, 570,* 571 {see also Insects)
Flies, 568* {see also Insects)
Flora, 639
Floret, 145,* 213

Flower, 143-148, 145,* 146,* 206-218,
223,* 224, 225, 225*

Fluctuations, 723

Flukes, 294 {see also Liver flukes;
Trematoda; etc.)

Flytrap, 636

FolHcle, 461, 509, 515

Food, 472-477, 633

and biology, 264, 776

manufactured by plants, 227-239

Foot, 132,* 134,* 137,* 189, 190, 193,
194, 197, 298, 299,* 309,
309,* 310, 310,* 311, 311,*
312,* 316*

Foraminifera, 531* {see also Protozoa)

Forebrain, 445*

Formaldehyde, 232

Fortuitous variation, 724

Fossils, 605-619, 606*-609,* 725,* 726,*

736
Four-o'clock flower, 691*
Fragmentation, 115, 131, 154, 155, 157,

161, 162, 185, 188, 189

Frog, 333, 333,* 421-441, 422*-440,*

573
circulation, 430-434
coordination and sensory equipment,

435-441
excretion, 435

ingestion and digestion, 425-430
integument and skeleton, 421-425
motion and locomotion, 425
reproduction and life cycle, 440-441
respiration, 434-435

Frond, 137, 138,* 139,* 195, 198
Fruit, 212

fly, 675,* 676,* 691,* 700,* 701*
Fucoxanthin {see Pigment)
Fucus (rockweed), 1 18, 1 18,* 154, 161,
162

Fuels from plants, 776
Fungi, 109-112, 119-129, 167-184
economic importance, 250-256
kinds, algalike, 109, 124,* 125, 167
ascus (sac), 109, 125, 125,* 167,

175
bacteria {see Bacteria)
basidium, 109, 128,* 129, 167,

178-183, 178*
bracket, 129, 179
cup, 127,* 129, 176
fission, 120-122, 121,* 167-172

Index 877

Fungi, kinds — Cont'd

slime, 122-124, 123,* 167
yeast, 176 {see also Yeast)
pathogenic, 252-254, 253,* 659, 660

Funiculus, 212, 225*

Furniture and biology, 776

Gapes (gapeworm), 539, 540, 661 "

Galen, 801

Galls, 546,* 547

Galton, Francis, 803

Galvanotropism, 353*

Gametangia, 112, 130, 150, 158, 185,

191
Gamete, 124,* 130, 156, 157, 159, 160,

164, 174, 174,* 178,* 277,*

361 * 363
Gametocyte, 277,* 365,* 366
Gametophyte, 117, 130, 131*- 133,*

136, 137, 137,* 143, 160, 161,

164, 185-190, 191-198, 200-

205, 225

Ganglion, 54, 55,* 308,* 312,* 313,*
325,* 328,* 386,* 391, 403*
Gastric caeca, 394, 396*
gland {see Glands)
filament, 290*
Gastrin, 512
Gastrocoel, 284*
Gastropoda, 310
Gastrovascular cavity, 286, 287,* 288,*

289, 291,* 293, 369, 370
Gastrula, 445,* 446, 451,* 710,* 71 1
Gel (gelation), 76, 833
Gemma, 131,* 185, 187, 189
Gemmule, 284*

Generations, alternation of {see meta-
genesis)
Generative cell, 202, 225*
Genes (determiner, factor), 92-94, 357,
443, 622, 678-683, 693, 694

Genetics (heredity), 24, 102, 673-720,

736
Genie action, 680-683. 692-695
Genital opening, 296,* 310,* 311,*
312,* 371,* 373, 376, 378,*
380,* 382,* 396, 398

Genome, 679
Genotype, 684-690

Geographic distribution, 591-604, 736,
745

regions of world, 592,* 597-602
Geologic time table, 614-618
Geotropism, 243
Germ cell, 706-712

primordial, 708-712, 708,* 710*

layers, 445,* 451,* 454

Germ — Cont'd

plasm, 708-712, 708,* 747

tube, 181
Gesner, 801
Gestation, 453
Giardia (diarrhea), 532
Gid, 537, 538,* 661, 788
Gill, 178,* 179, 309,* 311, 313,*
315,* 322,* 328,* 331, 434,
447, 448*

arch, 331, 332,* 445, 445*

cover (operculum), 447

filament, 310

plate, 307,* 313,* 331

slits, 325-343, 326,* 328,* 329, 449,*
738*

Girdle, pectoral, 423, 424, 465, 466

pelvic, 423, 425, 465, 466
Gizzard, 385,* 386, 394
Glands {see also Endocrine)

adrenal, 439,* 440*

accessory, 311,* 398, 406

albumin, 311*

calciferous, 385,* 386

cement, 298, 396*

Cowper's, 513, 514, 514*

gastric, 299,* 473, 476

green, 320,* 321*

intestinal, 476

mammary, 340

mucous, 311,* 312,* 421, 422* '

oil, 340,* 461

pedal, 298, 299*

poison, 325,* 404,* 406, 421, 422*

prostate, 513, 514, 514* ^

salivary, 312,* 394, 396,* 403,*

471,* 473, 476, 498
shell, 374,* 378*
silk 325 *

swe'at, 460,* 460, 463, 464
yolk, 371,* 373, 378*

Glass, 536
Glenoid fossa, 425
Gleocapsa, 113,* 152, 154
Glochidium of mussels, 541, 661, 788
Glomerulus, 493,* 494
Glottis, 427,* 435
Glucide, 85-87
Glucose, 86, 87, 92
Glycerine (glycerol), 87, 429, 476
Glycogen, 86, 87, 114, 152, 153, 428-
430

Gnat {see Insects)

Goiter, 511

Golgi apparatus (body), 40*, 41, 47

Gonad (testis or ovary), 288,* 291,*

295,* 302,* 306,* 313,* 316,*

322*

878 Index

Gonidia, 122, 167, 172
Gonionemus, 288,* 289
Graafian follicle, 450, 515
Grana, 229, 230*

Grantia (scypha, sponge), 279, 281,
281*-284*

Granular theory, 74, 75*
Granules, 47, 349, 353*-355*
Granulocyte, 484-486
Grasshopper, 319, 393-398, 412* (see
also Insects)

Graves' disease {see Endocrine glands)
Gravity, 627
Gray, Asa, 803
Gray matter, 55,* 503, 505
Green algae {see Algae)
Gregarious, 658, 665
Grew, Nehemiah, 29, 802
Ground pine, 192, 257
Growth, 70, 94, 95, 101, 105
Guanin, 758

Guard cell, 56, 57,* 58,* 145*
Guinea pig heredity, 686, 686,* 687,
688

Gullet, 290, 291,* 350,* 358, 358*
Gums from plants, 262, 268
Gymnospermae, 110-112, 138, 200-
205
economic importance, 257

Gynandromorph, 834

Habitat, 318, 319, 594
Hair, 211, 340, 391, 459-461, 460*
Halters, 409

Hammer bone, 466, 498,* 505
Haploid, 162, 357, 679, 680, 709
Harvestman, 326,* 547
Harvey, William, 801
Haustoria, 177

Haversian canal, 49, 50,* 51*
Head, 308,* 310, 311, 318, 319, 329
393, 394*

Health and biology, 778

Heart, 314, 315,* 321,* 322,* 325,*

326,* 385,* 388, 390, 395,

396,* 403,* 405, 430, 430,*

477-481, 478*-481,* 491*

chambers of v^ertebrates, 331-340,

740,* 741*
urchin, 303

Heat, 87, 231, 760, 761

Helianthus {see Sunflower)

Helix, 311,* 312,* 542 {see also Snail)

Hellbender {see Salamander)

Hellgrammite, 562,* 563

Hematin, 237, 263

Hemichordata, 326,* 327, 327*
Hemocoel, 314, 393, 396, 400, 405
Hemoglobin, 390, 434, 484
Hemolysis, 659

Hemophilia, 702 {see also Heredity)
Hemopyrrole, 237
Henle's loop, 493*
Heparin, 487
Hepatic, 301*

Hepaticae, 109, 130, 131, 131,* 132,*
186 {see also Liverwort)

Herbaceous, 207
Herbivorous, 105, 835
Heredity (genetics), 24, 102, 621-625,
673-720, 722, 746

blood groups, 489, 524-526

chromosomes {see Chromosomes)

definition, 673

genes {see Gene)

human, 522-526, 712-719

Mendehan, 683-685

methods of study, 673

Hermaphroditism, 292, 309, 312,* 372,
376, 391, 699

Heteroauxin, 240, 768
Heterocyst, 118,* 154, 155
Heterodera, 539, 661
Heterogamous, 115, 118, 125, 154, 155,
161, 162, 167

Heteronomous, 835
Heterosis, 705

Heterospory, 142, 143, 192, 200, 203,
206

Heterotrophic, 119, 167, 168
Heterozygous, 682, 685
Hexactinellida, 281
Hexagonal area, 349, 353,* 354*
Hibernation, 594
Highways, 595, 629
Hiilier, 35
Hilum, 144,* 212
Hindbrain, 743*
Hippocrates, 801
Hirudinea (leeches), 308,* 309
Hirudo (leech), 306, 308,* 309, 541,
788

Histology, 24

Histomonas, 534

History of biology, 800-806

Holdfast, 116, 151, 160, 161, 304, 307*

Holoblastic, 444

Holophytic nutrition, 359

Holothurioidea, 303, 306*

Holozoic nutrition, 836

Homo sapiens, 589 {see also Man)

Homologous chromosomes, 682

Homology, 576, 577,* 578*

Index 879

Homonomous, 836
Homospory, 136, 192-196
Homozygous, 682, 685
Honeybee, 398-408, 399*-404,* 571
Hooke, Robert, 28, 37, 802
Hooks, 377, 377,* 379, 400, 538*
Hookworm, 295, 296,* 298, 539, 785
Hoppers {see Insects)
Hormogonia, 113,* 154, 836
Hormones, animal, 506, 510-513, 767-
772
plant, 239-242, 767-772

Horse, origin and development, 725,*
726*

Horsetail (scouring rush), 100-112, 137,

137,* 191, 194, 195, 256
Host, 664
How science solves problems, 804, 805

to study, 19
Human muscles, 467-472, 467,* 468*

resources, 797
Huxley, 803
Hybrid vigor, 705
Hybridization, 684

of corn, 704,* 705, 706
Hydatid (tapeworm larvae), 537, 788
Hydra, 286, 286,* 287, 289
Hydranth, 285*
Hydrogen, 79,* 81,* 83,* 169
Hydrogen-ion concentration, 631, 751,
836

Hydroid, 289, 290
Hydrolysis, 92
Hydrophyte, 206, 653
Hydroponics, 775, 776
Hydrorhiza, 285*
Hydrostatic, 836
Hydrotropism, 243
Hydroxyl, 751, 836
Hydrozoa, 285,* 289, 289*
Hymenium, 127,* 128,* 176
Hymenoptera, 398-408 {see also In-
sects)

Hyoid bone, 423, 424, 466, 469*
Hypersensitiveness, 520, 772, 773
Hypertonic, 753
Hypertrophy, 837

Hypha, 124, 124,* 126, 126,* 127,*
167, 173-176, 179

Hypocotyl, 144,* 147,* 202, 204, 210,
213

Hypodermis, 837
Hypopharynx, 410, 411*
Hypophysin {see Endocrine glands)
Hypophysis, 495,* 496,* 507
Hypostome, 286*
Hypotheses, 22
Hypotonic, 754

Ichneumon, 572* {see also Insects;

Hymenoptera)
Ileum, 427,* 470,* 471, 475*
Ihum bone, 423, 425
Im.munity, 518-522
Impressions (imprints), 605, 611
Improvement by heredity, 704,* 705,

706
Impulse in nerve, 498-502, 489*
Inanimate things, 99-103
Inbreeding, 703, 705, 706
Incomplete dominance, 690-692 {see

also Heredity)
Incrustation, 610
Incus bone, 466, 498,* 505
Indeterminate variations, 724
Indian pipe, 671

Indirect cell division (mitosis), 62-72
Individuality, 97
Indusium, 198
Industrial plants, 257-271
Infusoria, 276, 278*-280,* 349, 354,
531,* 532,* 534 {see also
Protozoa)
Ingestion, 344 {see also specific organ-
isms)
Ink, 315,* 542, 547
Inner cell mass, 451,* 452
Innominate vein, 488,* 490,* 741*
Inorganic salts, 89
Insanity, heredity of, 717*
Insectivorous plants, 658, 668, 668*
Insects, 319, 393-408 {see also Grass-
hopper; Honeybee; etc.)
classification and identification, 409-

420
economic importance, 550-572
metamorphosis, 410, 414-418
mouth parts, 409, 410,* 411,* 414-

418
orders of:

Anoplura (lice), 415, 553

Aptera (Collembola; Thysanura),

414, 450
Coleoptera (beetles), 417, 563
Collembola, 414, 550
Corrodentia, 416, 557
Dermaptera, 417, 561
Diptera, 418, 568
Ephemerida (Ephemeroptera),

414, 550
Hemiptera, 416, 557
Homoptera, 416, 558
Hymenoptera, 418, 571
Isoptera, 415, 555
Lepidoptera, 418, 565
Mallophaga, 415, 551
Mecoptera, 417, 565

880 hid ex

Insects, orders of — Cont'd-

Neuroptera, 417, 563

Odonata, 414, 550

Orthoptera, 415, 554

Plccoptera, 415, 551

Siphonaptera, 418, 571

Thysanoptera, 416, 557

Thysanura, 414, 550

Trichoptera, 417, 565
Instar, 413*
Instinct, 665
Insulin, 511 {see also Endocrine

glands)
Integument, 140,* 202, 203, 225,* 344,
349, 368, 384, 459-465 (see
also specific organisms)
Intersex, 699
Interzonal fiber, 65

Intestine, 296,* 299,* 306,* 311*-313,*
321,* 322,* 327,* 328,* 332,*
369-380, 384, 396,* 473, 507*
Intussusception, 95, 101, 838
Invaginate, 838
Ions, 77, 83, 89, 751
Iris, 497,* 498,* 505
Iron, 169

Irritability, 96, 101
Ischium bone, 423,* 425
Isogamous, 115, 116, 118, 125, 154-

157, 160, 161, 167
Isotonic, 754
Isotope, 82

Jacket layer, 129, 130, 132,* 164, 165,

185
Janssen, 27

Jaw, 298, 331, 423, 424
Jejunum, 411,* 475
Jellyfish, 289, 290, 290*
Joints, 465, 466
Juices, digestive, 430 (see also specific

organisms; Digestion)
Jussieu, Bernard, 802

Kappa particle, 357

Karyokinesis (see Mitosis)

Karyolymph, 44

Karyosome, 40,* 44

Katabolism (see Catabolism)

Katydid {see Insects)

Keel of flower, 144,* 212

Kelp (Laminaria), 116, 118, 118,*

160, 161
Keratin, 459, 460*
Kidney, 311,* 312,* 316,* 340,* 435,

439, 440, 492, 493, 493*

Killer (in paramecia), 357

Kinesthetic, 496

Kinetic energy, 79, 105

Kinetochore, 679

Knoll, 35

Koch, Robert, 804

Koelreuter, 802

Labium, 313,* 395,* 409, 410,* 411*
Labrum, 395,* 404, 409
Lac, 559*

Lacewing {see Insects)
Lacteal, 481,* 488*
Lacuna, 49, 50,* 51*
Lamarck, 802
Lamella, 39, 49, 50*
Lamellibranchiata, 311
Lamina, 223

Laminaria (kelp), 118, 118,* 154, 161
Lamprey, 328,* 331, 573
Lancet {see Amphioxus)
Langerhans, islands of, 508, 511
Larva, 399,* 407, 413,* 419, 447
Larynx, 434, 469,* 490,* 491
Lateral line, 331,* 331
Leaves, 133-148, 191-198, 200-204, 206-
218, 223, 223,* 224

absorption bv, 226, 227

parts, 206-218

transpiration by, 226, 227

Leech, 306, 308,* 309, 541, 788
Leeuwenhoek, 27, 274, 802
Leguminous plants, 144,* 211, 212
Lens, 398, 456,* 497,* 505
liCthal gene or factor, 694
Leucocidin, 659

Leucocyte, 390, 396, 434, 484-486 {see
also Tissue, blood)

Leucopenia, 486
Leucoplast (leucoplastid), 43
Leucosin, 116, 153, 159
Leucosolenia (sponge), 282*-284*
Lice, 786

bark, 556,* 557

biting bird, 551, 553*

book, 556,* 557

dog, hog, rat, 553, 554*

human, 553, 554*

Lichen, 113, 114, 116, 151, 152, 155,

662, 663*
Life cycle {see reproduction of specific
organisms)
from life, 733
Ligament, 47, 49
Light, 233, 234, 626, 633, 762
Lignin, 39, 59, 209, 261
Ligule, 193

Index 881

Limulus (horseshoe crab), 325,* 547

Linin, 40,* 44

Linkage in heredity, 695, 697

Linnaeus, 802

Lipid (fats), 87, 476

Liver, 311*-315*, 321,* 328,* 427,*

429, 470,* 471,* 479, 493,

512, 513
fluke, 293, 294, 373-377, 374,* 375,*

538, 785, 785,* 787*
rot (see Liver fluke)

Liverwort (Marchantia), thalloid, 109-
112, 130, 131, 131,* 132,*
188-190
Porella (leafy), 131, 132,* 189
Living and nonliving contrasted, 99-103
animals and plants contrasted, 104,
107

Lizard, 336,* 340
Lobster, 318, 543

Locomotion, 106 (see also specific or-
ganisms)
Locus of genes, 696,* 698
Locust (see Insects and Grasshopper)
Loligo (squid), 315*
Luciferase, 762
Luciferin, 762

Lumbricus, 384-392 (see also Earth-
worm)
Lung, 311,* 331, 333, 340, 434, 470,*
489-493, 490*
book, 319, 325*
Lycogala (slime mold), 123,* 124, 173
Lycopodineae, 110, 134, 136,* 191-193
Lycopodium, 135, 135,* 192, 193
Lycopsida, 110, 134, 135,* 191, 192
Lymnea (snail), 310,* 376, 538, 786
Lymph, 51, 390, 425, 487-489, 488*
Lymphatics, 481,* 488*
Lymphocyte (see Tissues, blood)

Macrogamete (megagamete), 840
Macromere, 444

Macronucleus, 279,* 349, 350,* 356*
Madreporite, 302, 302,* 303, 304, 306*
Magnesium, 79*
Maize (see Corn, Indian)
Malaria, 275, 276, 363-367, 364,* 532,
784

Malleus bone, 466, 498,* 505
Malpighi, Marcello, 29, 801
Malpighian layer, 421, 422,* 435, 459,

494
tubule, 325,* 394, 396,* 397, 403,*

405
Maltose (malt sugar), 92, 429, 476
Mammalia (mammals), 340, 341,* 574

Mammoth, 606*
Man, 340

biology of, 458-529

blood groups, 489

chromosomes (see Chromosomes)

circulation, 477-489

coordination and sensory equipment,
494-506

diseases, 516-522

ductless glands, 506-513 (see also
Endocrine glands)

early, and records, 585-590, 587*

embryology, 450-456

excretion, 492-494

ingestion and digestion, 472-477

inheritance, 522-526

integument and skeleton, 459-465

motion and locomotion, 467-472 .

race improvement, 526-527

reproduction and life cycle, 513-516

respiration, 489-492

Mandible, 320,* 321,* 331, 393-404,
395,* 409, 411,* 424, 462,*
^66, 469*

Mantle, 309, 310, 310,* 311, 312,*
313,* 328*

Marchantia, 188-190 (see also Liver-
wort)

Marl, 152

Marrow of bone (see Tissues, bone).

Marton, 35

Mastax, 298, 299*

Mastigophora, 274, 276,* 358, 358,*

361,* 531*-534* (see also

Protozoa)

Matrix, 49, 50,* 51, 67, 360
Matter, 73, 78

Maturation of germ cells, 706-712
Maxilla, 331,* 395,* 409, 411,* 423,*
424

Maxilliped, 320,* 321*
May fly (see Insects)
Mechanistic view, 841
Medicine and biology, 778
Medicines from plants, 267
Medium, 76, 78

Medulla, 54, 340,* 496,* 502, 504
Medullary fold, 447

plate, 447

ray, 141,* 221

sheath, 54, 54*

Medullated nerve, 54

Medusa (medusoid), 285,* 289, 290*

Megagamete, 842

Megagametophyte, 136,* 137,* 140.*

142, 143, 194, 200-203, 206,

225*
Megaphyll, 137

882 Index

Megasporangia, 136,* 140,* 193, 200-

203, 225
Megaspore, 136,* 140,* 142, 143, 193,

194, 200-203, 206, 225
Megasporophyll, 138, 140,* 142, 193,

200-203, 206, 225*
Meiosis (reduction division), 187, 357,

697, 709

Meissner's corpuscle, 495
Melanin, 422,* 758 {see also Pigments)
Melanoplus {see Grasshopper)
Membrane, cell, 39, 40,* 393

nictitating, 438

permeability of, 39

plasma, 39, 40*, 156*

sieve, 282*

undulating, 279*
Mendel, Gregor, 683-685, 803
Mendel's laws, 683-685
Meninges, 503
Menstruation, 516
Merle collies, 707*
Merozoite, 365,* 366
Mesenchyme, 46, 280, 284,* 295, 309,
381, 449,* 454

Mesentery, 289, 290, 291,* 306, 488*
Mesoderm, 292, 293, 295, 299, 306,

309, 314, 325, 368, 373, 445,*

449,* 451, 453

Mesoglea (mesogloea), 280, 286, 286,*
287,* 288*

Mesonephros, 842
Mesophile, 122, 170
Mesophyte, 653
Mesothelium, 842
Mesozoic era, 614, 616
Metabolism, 92, 101, 625
Metacarpal, 423, 425, 462,* 466
Metagenesis, 117, 130-149, 154, 160,
164, 185-198, 285,* 286

Metamere and metamerism, 314-340,
738*

Metamorphosis {see also Reproduction)
of frog, 448*
of insects, 410, 414-418
complete, 413,* 418
gradual, 411, 412*
incomplete, 411, 412*
none (ametamorphosis), 410, 411*

Metaphase (mitosis), 62, 63,* 65, 66,

67
Metaplasmic granule, 40,* 43
Metaplast, 44
Metastasis, 583
Metatarsus (metatarsal), 400, 401,*

423,* 425,* 462,* 466
Metridium {see Sea anemone)
Microgamete, 843

Microgametophyte, 142, 143, 194, 201-

204, 206, 225*
Micromere, 444

Micronucleus, 279,* 349, 350,* 356*
Microphyll, 135
Micropyle, 140,* 142, 144,* 201-203,

213, 225,* 406

Microscope, 27-36, 28,* 30,* 32*-34*
Microsome, 349, 354*
Microsporangium, 136,* 140,* 193,

201-203
Microspore, 136,* 140,* 142, 143, 193,

194, 200-204, 206, 225
Microsporophyll, 140,* 142, 193, 201-

203, 225*
Midbrain, 54, 445,* 456,* 502, 503
Migration, 655, 656
Mildew, 127, 129, 177
Millipede, 318, 324,* 543, 544
Mimicry, 730

Mimosa {see Sensitive plant)
Mineral salts, 89
Mineralization, 611
Miracidium, 375,* 376, 787* {see also

Liver fluke)

Mites, 319, 326,* 543, 544, 545,* 554*

Mitochondria, 40,* 41

Mitosis, 62-72, 63,* 64,* 66,* 68,*

69,* 349, 673, 680
Mixture, 85
Mohl, von, 37

Mold, black bread (Rhizopus), 124,*
125, 173
blue (Aspergillus), 125-129, 126,*

175
blue (PeniciUium), 125-129, 126,*

167, 175
bracket fungus, 128,* 129
cup fungus, 127,* 176
mushroom, 128,* 129,* 177-179,
178* {see also Basidiomycete)
slime, 122-124, 123,* 172
water (Saprolegnia), 125, 173, 174*
yeast, 125,* 176

Molecule, 77-79, 79,* 81,* 83,* 750

Molgula, 328*

Mollusca, 309-314, 309*-316,* 541, 542

Molting, 944

Monecious, 175, 186, 200, 202, 309,
372, 376, 391

Monilia {see Yeast)

Monkey, 340

Monocotyledoneae, 110, 143-148, 207,
209, 222

Monocotyledons and dicotyledons con-
trasted, 143, 207

Monocystis, 275, 277,* 534

Monohybrid cross, 686, 688

Monosaccharide, 87

Index 883

Monozygotic, 844

Morphogenesis, 241, 242, 442-456, 576,
580

Morula, 444, 451,* 452, 710,* 711
Mosquito, 364,* 366, 569* {see also
Insects)

mouth parts, 411,* 569*
Moss, club, 110, 112, 134, 135, 135,*
191-194, 256

Irish, 119,* 249

peat (bog), 133, 134,* 187

Polytrichum, 133, 133,* 186

Sphagnum, 133, 134,* 187

Mother cell, 202, 203
Mother-of-pearl, 541
Moths, 319, 549, 567,* 568* {see also
Insects)

Motor root, 844

Mouh, 393

Mouth, 278,* 286,* 288,* 290,* 293-
297, 296,* 299,* 300,* 304,
305,* 309, 310,* 312*-316,*
321,* 326,* 327, 332,* 350,*
358,* 368-374
parts, 394-404, 409, 410,* 411,* 414-
418

Mucus, 293, 368, 387*
Mud puppy, 335*
Muller, Johannes, 803
Mulatto, 692

Multiceps, 537, 538,* 661, 788
Musci (moss), 109, 132, 133,* 134,*
186

Muscle, 312,* 425, 426,* 467-472,
467,* 468,* 497,* 498-499,
505 {see also Tissues, muscu-
lar)
spindle, 505

Mushroom (Psalliota [Agaricus]), 128,*

129, 177-179, l78*
Mussel (Anodonta, Lampsillis), 311
Mutation, 93, 624, 695, 722, 724 {see

also Heredity)
Mycelium, 124,* 125, 126, 127,* 173,

178*

Mycorrhiza, 664
Myelin, 54
Myocardium, 478
Myofibril, 53
Myogenic theory, 844
Myoneme, 279,* 359
Myotome, 328*
Myriapoda, 318
Myxamoeba, 124, 167, 172
Myxedema, 511

Myxomycophyta (slime mold), 109,
122-124, 123,* 167, 172-173
Myxophyta, 114, 151

N
Nacre, 541
Naiad, 411, 412*
Nails, 459, 461
Nares, 332,* 427,* 434, 439
Nasal {see Nostril)
Natural selection, 844
Nautilus, 311
Nearctic region, 597
Necator (hookworm), 295, 296,* 539
Nectar and nectary, 208, 223,* 404
547, 785

Necturus, 335*

Needham, 732

Negro, inheritance, 692

Nemalion, 119, 154, 163,* 164

Nemathelminthes, 295-298, 374-382,

538, 539
Nematocyst, 286, 286,* 287*-291*
Nematoda, 295, 298
Neoplasm, 583, 845
Neoteny, 845
Neotropical region, 598
Nephridia, 318, 375,* 385,* 386, 387,*

390

Nephridiopore, 390
Nephrostome, 390, 435
Nereis (sandworm), 307,* 308
Nerve cells, 54, 55*

cord, 54, 55,* 308,* 314, 321,* 322,*
325-343, 327,* 329, 370,*
371,* 378,* 387,* 391, 397
cranial, 54, 438, 496,* 502-504
ending, 437
fiber, 459, 498*
impulse, 498-502, 498*
motor, 844

olfactory {see Olfactory)
optic, 497,* 498,* 505
peripheral, 54, 435
radial, 302*

ring, 296,* 308,* 376, 381
sensory, 502, 503
^ spinal, 54, 55,* 502
Nervous equipment {see also specific
organisms)
system {see also specific organisms)
autonomic, 502, 506
central, 54, 435, 502
enteric, 502, 506
parasympathetic, 502, 506
peripheral, 54, 435
sympathetic, 54, 397, 435, 437,
502, 506
Neural arch, 424

groove, 445,* 446, 449,* 455
plate, 449*
spine, 424
tube, 447, 449*

884 Index

Neurilemma, 54, 54*

Neurofibril, 47, 459, 498,* 505

Neuroglia, 845

Neurohumor, 501

Neuromotor apparatus, 352*

Neuron (nerve cell), 47, 54, 54,* 501

Neutron, 79,* 80, 81,* 83*

Newt, 333,* 334*

Nictitating membrane, 438

Nissl granule, 47, 54*

Nitrogen, 79,* 650, 651

fixation, 169, 650, 651, 664
Noctiluca, 763

Node of Ranvier, 54, 54,* 845
Nodus, 412*

Nondisjunction, 680 {see also Heredity)
Nonelectrolyte, 751, 845
Nonmedullated {see Nerve)
Nosema, 534
Nostoc, 113,* 154
Nostril, 328,* 331, 331,* 332,* 421,

424, 434
Notochord, 325-343, 326,* 327,* 328,*
329, 332,* 447, 449*

Nucellus, 201-203, 225
Nuclear framework, 40,* 43-44

membrane, 40,* 43, 62, 63,* 65-67

sap, 44
Nucleolus, 40,* 44, 62, 66*
Nucleolymph, 43-44
Nucleoplasm, 40,* 44
Nucleus, 40,* 43-44, 62, 65, 66,* 70,
143, 153-156, 156,* 157-162

of the atom, 79,* 80, 81,* 83*

Nuda, 293

Nurse cell, 709

Nutrition, autotrophic, 120, 168

chemosynthesis, 120

heterotrophic, 119, 120, 167, 168

holophytic, 359

holozoic, 836

parasitic, 120

photosynthetic {see Photosynthesis)

saprophytic, 120, 123, 125
Nymph, 398, 411, 412,* 419

Obelia, 285,* 289

Obligate, 846

Ocellus, 393, 394,* 398, 406

Octopus, 311, 316,* 542

Oestrone {see Endocrine glands)

Ogliole, 536

Oil, 153, 159

from plants, 259, 267
Olfactory equipment, 311,* 398, 405,

424, 439, 447, 505 {see also

specific organisms)

OHgochaeta, 308
Ommatidia, 397
Omnivorous, 846

Onion root, 68,* 69,* 71 {see also
Mitosis)

Ontogeny, 442, 742
Onychophora, 318, 324*
Oocyst, 365,* 367
Oocyte, 709, 710*

Oogamy, 115, 118, 119, 130, 154, 155,
161, 187

Oogenesis, 709, 710*
Oogonia, 161, 162, 174,* 175, 709,
710*

Ookinete, 365,* 366
Opahna, 534, 534*
Operculum, 303
Opsonin, 520
Optic chiasma, 496*

lobe {see Brain)

nerve, 497, 497*
Oral groove, 350, 350*
Orbit, 79*, 81, 81,* 83,* 427, 438*
Organ, 55, 60, 647
Organelle, 274 {see also Protozoa)
Organicism, 847

Organisms, continuity of, and descent
with change (evolution), 732-
749

Organization, 97, 100
Oriental region, 598
Orientation, 847
Origin of Hfe, 732-735
Orthogenesis theory, 847
Orthogenetic variation, 724
Orthoptera, 393-398
Oscillatoria, 113,* 152, 154
Osculum, 281,* 284*
Osmosis, 38, 752, 753, 753*
Osmotic pressure, 226, 752, 753, 753*
Ossicle 302*

Ostium', 282,* 284,* 291,* 321,* 324,*
425,* 395, 514

Otolith, 496

Outbreeding, 703

Ovary, 143, 144,* 145,* 146,* 207-217,
223,* 225, 225,* 286,* 292,
296,* 299,* 321,* 328,* 332,*
371-383, 389,* 439,* 440, 450,
507,* 509, 512, 514, 515*

Oviduct, 299,* 311,* 312,* 320,* 321,*
332,* 371-378, 389,* 391,
396,* 398, 406, 427,* 439,*
514

Oviparous, 847
Ovipositor, 394,* 398
Ovotestis, 311,* 312*
Ovoviparous, 847

Index 885

Ovule, 140,* 142, 143, 200-204, 206,

208, 216, 225, 225*
Ovum (egg), 133,* 143, 201-203, 286,*

389,* 450,* 514, 515, 708,*

709, 710*
Oxygen, 79,* 81,* 83,* 228, 489-493,

632
Oxyhemoglobin, 434, 484
Oxytocin {see Endocrine glands)
Oxyuris, 661
Oyster, 311

Paedogenesis (pedogenesis), 848

Palaearctic region, 597

Palate, 469*

Paleobotany, 605

Paleontology, 24, 605, 736

Paleozoic era, 614, 617

Paleozoology, 605

Palisade tissue, 145,* 195 {see also

Tissues, plant)
Palm, 142,* 143, 203, 204, 261
Palp, 307,* 313,* 395,* 404,* 410, 410*
Pancreas, 340,* 427,* 428, 429, 471,*

476, 477, 507,* 508, 511
Pangenesis, 848
Papilla, 302,* 381, 421, 448, 459, 460,*

494
Parallelism, 593,* 729, 738*
Paramecin, 357
Paramecium, 278,* 279, 349-357, 350*-

356*
Paramylum, 359
Paraphyses, 127,* 162, 176, 186
Parapodium, 306, 307,* 308
Parasite, 129, 133, 151, 152, 168, 177,

179, 183, 197, 201, 293, 297,

635, 658 {see also Bacteria;

Fungi; etc.)

Parathormone, 507*

Parathyroid, 507,* 508, 511 {see also

Ductless glands)
Parenchyma, 130, 141,* 145,* 220,
293, 373 {see also Tissues,
plant)
Parthenogenesis, 162, 168, 298, 301,

361,* 363
Parthenogonidia, 363
Passenger pigeon, 610*
Pasteur, Louis, 733, 803
Pathogenic, bacteria, 120, 122, 168,
171, 255, 659, 660
molds (fungi), 659, 660
protozoa, 274, 660
viruses, 789, 790
yeasts, 660
Pathology, 24, 848
Peat moss, 133, 134,* 189, 258

Pebrine (silkworm disease), 535, 786
Pecten, 401,* 403
Pedicellaria, 302,* 304
Pedigree, 673, 715, 716,* 717*
Pedipalp, 325*
Pedogenesis, 848
Peduncle, 216
Pelecypoda, 311, 312*
Pellagra, 474, 771,* 772
Pellicle, 276,* 278,* 349, 350,* 353,*
354,* 358*

Peltate, 203
Pelvic, 462,* 466
Pen, 290, 315*
Penial seta, 380,* 382
Penicillin, 250, 251*
Penicillium, 126,* 127, 129, 175, 250,
251,* 671

Penis, 311,* 312,* 315,* 371,* 372,

374*
Pentamerous, 301, 303
Pepsin, 429, 476
Peptone, 476
Perch, 330*-332,* 331
Perennial, 200, 214
Perianth, 208, 224
Pericardium, 309, 311,* 313,* 324,*

325,* 395, 478

Pericarp, 210

Pericycle, 145,* 214, 220 {see also

Tissues, plant)
Peridinium, 530
Periosteum, 849
Peripatus, 318, 324*
Peristome, 187, 307*
Perithecia, 177
Peritoneum, 47, 302,* 387*
Permeabihty, 743, 752, 753*
Petal, 144,* 208, 212, 217, 223,* 224,

225,* 305*

Petiole, 195, 215, 223

Petrifaction, 605, 611

Peziza (cup fungus), 127,* 129, 176

Phaeophyta (brown algae), 109, 116,
118,* 153, 160-162, 249

Phagocyte, 485, 518, 773 {see also Tis-
sues, blood)

Phalanges, 423,* 425, 462,* 466
Pharynx, 276,* 279,* 296,* 308,* 311,*
325-343, 328,* 368-380, 385,*
• 396,* 469,* 471,* 491

Phaseolus, 144,* 211-213 {see also
Bean)

Phases, 76
Phenotype, 684-690

Phloem, 133, 141,* 147* {see also Tis-
sues, plant)
Phosphorescent, 530

886 Index

Photosynthesis, 105, 112, 130, 150-166,
168, 169, 186, 210, 211, 359,
360, 363

Phototropism, 243, 347,* 348, 359

Phycocyanin, 114, 118, 151-154

Phycoerythrin, 118

Phycomycete (algalike fungi), 109,
124,* 125, 167, 173-175, 174*

Phylogeny, 442, 742

Physiology, 24 {see also specific organ-
isms)

Phytogeography, 591

Phytomastigina, 274

Phytopathology, 850

Pia mater, 503

Pieris (calabage butterfly), 413*

Pigeon {see Birds; Aves)

Pigment, 153, 156,* 243-247, 421, 732

anthocyanin, 206, 208, 245, 246

carotene (carotin), 115, 153, 155,

159, 208, 228, 229, 244, 245

chlorophyll {see Chlorophyll)

chromatophores, 758, 759

erythrophore, 758, 759

flavone (flavonon), 245, 246

fucoxanthin, 116, 153, 160, 161, 244

guanophore, 758, 759

melanin (melanophore), 422,* 758,

759

phycocyanin, 114, 118, 151, 152, 162,
94.4.

phycoerythrin, 118, 153, 162, 164,
94-4-

plant, ri5-118, 227-247
xanthophyll, 115, 153, 228, 229,
244, 245, 758, 759

Pileus, 179

Pine tree (Pinus), 138-143, 140,* 141,*

201-203
Pineal gland, 495,* 507,* 509, 512
Pinna, 138,* 195, 203
Pinnule, 138,* 304, 307*
Pinworm, 539

Pisces, 330,*-332,* 331 {see also Fish)
Pistil, 143, 146,* 208-216, 223,* 225,

225*
Pitcher plant, 636, 668*
Pith of plants, 145,* 147* {see also

Tissues, plant)
Pitocin {see Endocrine glands)
Pitressin {see Endocrine glands)
Pituitary, 507,* 507, 510
Pituitrin {see Endocrine glands)
Placenta, 340, 453, 455,* 509, 512
Planaria (Dugesia), 293, 368-373,

369*-371,* 537
Plankton, 112, 151
Plant, anatomy and physiology, 219-

248

Plant — Cont'd

breeding {see also Heredity)

cellular organization, 55-61

coloration, 758-760

classification, 865, 866

ecology {see Ecology)

economic importance, 249-271

fossils, 605-619

geography, 591

hormones, 239-242, 768

lice (aphids) {see Insects)

number of species, 110

quarantine, 637

tropism, 242, 243

wild life, 796
Planula, 285,* 290*
Plasma, 390, 396, 405, 486 {see also
Tissues, blood)

gene, 357
Plasmodesma (Plasmodesmata), 41,42*
Plasmodium, 123, 123,* 124, 167, 172,

275, 276, 363-367, 532, 784
Plasmolysis, 105, 754
Plasmosome, 40,* 44 {see also Nucleo-
lus)
Plast (plastid), 43, 114-116, 118, 130,

153, 159, 160, 162, 164
Plate, calcareous, 309, 310

genital, 304*

horny, 333
Platelet, 485, 486 {see also Tissues,
blood)

Platyhelminthes, 293-295, 537, 538

Pleura, 492

Pleurococcus {see Protococcus)

Pliny the Elder, 801

Plumule, 144,* 210, 211, 213

Pod, 144*

Poisons, 404,* 406

from plants, 267-270
Polar body (polocyte), 452, 516, 709,
710*

nucleus, 206, 225*

transportation, 240
Polarity, 241, 242, 499
Pole, 445,* 452
Polian vesicle, 306*
Pollen, 405, 407, 634

basket, 401,* 403

brush, 401,* 402

comb, 401,* 404

grain, 140,* 142, 143, 146,* 201-
204, 206-213, 225, 225*

spur, 401,* 402

tube, 140,* 143, 201-204, 206-212,
225*

Polocyte {see Polar body)
Polychaeta, 308
Polygordius, 308

Index 887

Polymorphism, 851
Polynesian region, 598
Polyneuritis, 474, 770,* 772
Polyp, 289,* 290
Polyploidy, 673, 676-680
Polypodium (fern), 138, 139,* 198
Polysaccharide, 87

Polysiphonia, 119, 119,* 154, 164 (see
also Algae, red)

Polytrichum, 133, 133,* 186 {see also
Moss)

Pond scum, 157

Pons, 54, 495,* 496,* 502, 504

Porella, 131, 132,* 189 (see also Liver-
wort, Porella)

Porifera (sponges), 279-286, 535, 536

Pork worm, 539 g

Porocyte, 283*

Portuguese man-of-war, 289, 289*

Postcaval vein, 315,* 480, 741*

Potential energy, 105

Pounce, 542

Praying mantis, 554, 667*

Prebus, 35

Precipitin, 520

Predacious (predatism), 635, 636, 658,
666, 667*

Preformation, 842
Prenatal, 852

Primary germ layers, 445,* 451-454
Primordial germ cells, 708-712, 708,*
710*

Principle, barriers, 595

cell, 37-45

definite habitats, 594

discontinuous distribution, 596

dispersion, 593

hibernation, 594

highways, 595

longitudinal distribution, 591-604

migration, 591-604

vertical distribution, 597
Proboscis, 326,* 327,* 369, 375,* 410*
Proctodeum, 447 (see also Embryology)
Progesterone {see Endocrine glands)
Progestin, 452
Proglottid, 293, 377, 377*
Prophase (mitosis), 62, 63,* 66*
Prophylaxis, 520
Propolis, 405

Prosecretin {see Endocrine glands)
Prosopyle, 282,* 284*
Prostate, 513, 514, 514*
Prostomium, 307,* 384, 385,* 388*
Protective resemblance, 730, 760
Protein, 85, 88, 92, 476
Proterozoic era, 614, 617
Prothallus, 137,* 138, 138*, 188, 192,
193, 197

Prothrombin, 486, 487

Protococcus (pleurococcus) (green

Alga), 115,* 116, 154, 157
Proton, 79,* 80, 81, 81,* 83*
Protonema, 134,* 187, 188
Protoplasm, 37-45, 73-103

chemical properties, 84-92, 750
physical properties, 93-103, 750
Protoplasmic strands, 41, 42,* 362,*

363
Protoplast, 44, 123,* 160
Protopodite, 320*
Protozoa, 274-279, 275*-280,* 344-367,

530-535, 660
Protractor muscle, 312*
Proventriculus, 394
Psalliota (Agaricus) {see Mushroom)
Pseudopodia, 123, 172, 173, 188, 274,

275,* 286,* 344, 345, 345,*

346*
Pseudospora, 535
Psychology, 853
Psychrophile, 122, 170
Pteridium (Pteris), 138, 138,* 195-198

{see also Fern)
Pteropsida, 110, 137, 138, 138,* 191,

195, 200-205, 206-213
PtyaHn, 476

Puccinia, 181-183, 182*
Pulmonary, 311,* 312,* 480,* 741*
Pulvillus, 394, 401,* 402
Punnet square, 686-690
Pupa, 399,* 407, 413,* 419
Pupil, 438, 497, 505
Pure line in heredity, 853
Putrefaction, 671

Pycniospore, 129, 167, 181, 182, 182*
Pyloric, 302,* 321,* 332,* 426, 427,*

473
Pyrenoid, 115, 115,* 117, 118, 153,

155, 156, 156,* 157, 162,

276,* 358,* 359

Quarantine, 637
Queen, 399, 399,* 406

Race improvement, 526-527
Radial symmetry {see Symmetry)
Radicle, 210-213
Radioactive, 82
Radiolaria {see Protozoa)
Rafinesque, 802
Rana {see Frog)
Ranunculus {see Buttercup)
Ranvier, node of {see Nerve)
Raphe, 213

888 Index

Rays, 141,* 301, 301,* 303, 307,*

328,* 331
medullary, 222
sting, 329*
Reaction, 348, 352,* 355,* 359 •
Recapitulation, 442, 854
Receptacle, 161, 208, 216, 224, 225*
Recessive, 682, 684
Records of ancient life, 605-619
Rectal gland {see Glands)
Recti muscles, 497,* 498,* 505
Rectum, 308,* 313,* 315,* 327,* 380,*

381, 394, 396,* 403,* 404,

471,* 477
Red blood corpuscle {see Tissues,

blood)
Redi, Francesco, 733, 801
Redia, 375,* 377, 787*
Reduction division, 607, 709, 854
Reef, 536
Reflex, 503, 505
Refraction, 730, 759
Regeneration, 98, 98,* 293, 299, 304,

372, 373, 576, 579

Renal, 483, 493, 494

Rennin, 476

Reproduction, 96, 102 {see also specific

organisms)
Reptilia (reptiles), 333, 336*-338,*

573
Reservoir, 276,* 358,* 358, 359
Resin, 262, 263

Respiration, 100, 239, 306,* 310,* 318,
319, 489-492 {see also specific
organisms)

Respiratory tree, 74, 75,* 306*

Resting stage {see Mitosis)

Reticular theory, 74, 75*

Retina, 438, 456,* 497, 497,* 505

Retractor muscle, 312,* 313,* 384

Reversion in heredity, 855

Rh factor, 525

Rhabdite, 293, 368

Rhabdom, 398

Rhabdopleura, 327, 327*

Rheita, 29

Rheotropism, 855

Rhizobium, 650

Rhizoid, 125, 126,* 130, 131,* 132,*
133, 134,* 136, 137,* 138,*
173, 186-189, 193-198

Rhizome, 135, 137,* 138,* 139,* 192-

198, 197*
Rhizoplast, 359

Rhizopoda, 274 {see also Protozoa)
Rhizopus (black bread mold), 124,*

125, 173, 671

Rhodophyta (red algae), 109, 118,
119,* 153, 162-165, 163,* 249
Rhomaelia {see Grasshopper)
Ribs, 462,* 466
Richards, 34
Rickets, 475
Riddell, 31

Ringworm {see Athlete's foot)
Rockweed (Fucus), 118, 118,* 161
Rods and cones, 497
Root, 133-148, 137,* 140,* 144,* 147,*
191-198, 200-205, 206-218,
219-222

absorption by, 226

cap, 215, 219

hairs, 'l45,* 210, 216, 219, 226
pressure, 227

regions of growth, 219-222
tissues {see Tissues, plant)
ventral, 55*

Rotifer, 297, 298, 299,* 539, 540
Roundworm, 379-382, 661, 788 {see

also A s c a r i s ; Hookworm ;

Trichinella, etc.)

Royal jelly, 407
Rubber, 262
Ruska, 35
Rusts, 129, 181, 182*

Sac, embryo, 206
Saccharomycetes {see Yeast)
Sacculus, 496
Sachs, Julius, 803
Salamander, 333, 334*
Salivary gland, 311,* 312,* 498
Sand dollar, 303, 305*
Sandworm (Nereis), 307,* 308, 541
Saprolegnia (water mold), 125, 173,
174*

Saprophyte, 113, 120, 123, 151, 168,

172, 173, 176, 177, 635, 658,

671
Sarcodina, 274, 275,* 343,* 531,* 533*

{see also Protozoa)
Sarcolemma, 52,* 53
Savory substances from plants, 267
Sawfish, 329*
Sawfly {see Insects)
Scale, 331

insects, 558, 560*
Scallop, 311

Scaphopoda, 311, 316*
Schistosoma, 660, 661
Schizogony, 367
Schizomycophyta (bacteria), 109, 120-

122, 121,* 167-172, 250-256

Index 889

Schizont, 365,* 366
Schleiden, 31, 37, 803
Schultze, 38
Schwann, 31, 37, 803
Scientific method, 17, 20-24, 804, 805
Sclera, 497,* 505

Sclerenchyma, 141,* 197* {see also
Tissues, plant)

Scleroblast, 283*

Scolex, 293, 377, 377,* 379, 538*
Scorpion fly, 319, 326*
Scouring rush, 110, 137, 137,* 256
(see also Horsetail)

Scrotum, 514*
Scurvy, 475

Scypha (Grantia), 279-281, 281,* 284*
{see also Sponge)

Scyphistoma, 290*
Scyphozoa, 289, 290*
Sea anemone, 290, 291*

cucumber, 304, 306*

fan, 290

lily, 304

pen, 290

squirt, 328*

urchin, 303, 303,* 304*

walnut, 293

weed {see Algae)

Sebaceous gland {see Glands; Skin)
Secondary sexual traits {see Heredity)
Secretin {see Endocrine glands)
Sedentary, 856

Seed, 138, 140,* 142, 143, 144,* 146,*
200-218, 225*
coat, 210, 213
leaf, 194
Segmentation, 304, 307,* 309, 314, 325
Segregation law, 685
Selaginella, 135, 136,* 193
Semen, 514

Seminal receptacle, 311,* 312,* 371,*
372, 373, 385,* 389,* 391,
398
vesicle, 296,* 371,* 372, 380,* 382,
385,* 389,* 391, 406, 513,
514*

Sensitive plant, 106
Sensitivity of protoplasm, 357
Sensory equipment, 494-506 {see also
specific organisms)

Sepal, 144,* 208, 212, 223*-225*
Septa, 173, 179, 308, 384, 385,* 386,
387*

Serpent star, 303
Sertoli cell, 709
Serum, 478
Sesamoid bone, 466
Sessile, 106, 116

Seta, 132,* 134,* 189, 304-308, 307,*

380,* 384, 387*
Sewage, 781-783
Sex cell, 162 {see also Reproduction)

chromosome, 675,* 694,* 697,* 698

determination, 697,* 698

-influenced traits, 703

-Hnked traits, 699-703, 700*-703*

ratio, 698
Sexual dimorphism, 857
Sharks, 329,* 331, 573
Shelf fungus, 128,* 129, 179, 671
Shell, 79,* 81, 81,* 83,* 309, 310, 311,
313,* 316,* 377, 377,* 406

Shellac, 559*

Shipworm, 311, 314,* 542
Shrimp, 318, 322, 324,* 543
Sieve membrane, 282*

tube, 145,* 147,* 192, 220, 224
Sigmoid, 471,* 477
Silicon, 159, 160, 194, 280, 281
Silk, 146,* 567*
Silkworm, 565, 567,* 786
Silverfish, 550, 551,* {see also Insects)
Sinus, 314, 322,* 395, 479,* 480

venosus, 332,* 431, 431,* 741*
Siphon, 164, 312,* 313,* 315,* 328*
Siphonoglyphe, 291*
Skate, 331

Skeleton, 329-343, 423-425, 423,* 465-
467, 462* {see also specific
organisms)

Skin, 421,- 422,* 437, 459-465, 460,*

493, 504, 518
Skipper {see Insects)
Skull, 587*

Sleeping sickness, 660, 784
Slime mold (Myxomycophyta), 109,

122-124, 123,* 172, 173, 252
Slug (snail), 310, 542
Smut, 129, 179, 180*
Snail, 310, 310,* 311,* 312,* 542

variations in, 723*
Snake, 337,* 340
Snow flea, 411,* 550
Society, human, 585-590
Soils, 794
Sol, 76
Solation, 857

Somatic modifications, 722
Somatoplasm, 708-712, 708*
Somite, 304, 307,* 385*
Sorus, 137, 139,* 182,* 192, 196, 196,*

198

Sound production and reception, 393,

435, 761, 762
Sowbug, 317,* 318, 544
Spallanzani, 733
"Spanish moss," 669, 670*

890 Ijidex

Spectrum, 757, 757*

Spemann, 581

Spencer, 31

Sperm, 119, 133,* 136, 136,* 137,*
138,* 138, 143, 154, 161-164,
163,* 186, 189, 194, 195, 201-
204, 286,* 320, 361,* 363,
365,* 372, 374,* 391, 398,
406, 450,* 514, 708*
mother cell, 277*
nucleus, 206

Spermatheca, 325,* 391, 398, 406
Spermatid, 709, 710*
Spermatium, 163*
Spermatocyte, 709, 710*
Spermatogenesis, 708-710
Spermatogonia, 514, 675,* 709, 710*
Spermatozoa {see Sperm)
Spermogonium, 181

Sphagnum (moss), 133, 134,* 187, 256
Sphenopsida, 110, 135, 191, 194
Spicule, 281,* 282*
Spider, 319, 325,* 326,* 543, 544,
544,* 547

Spinal cord, 54, 55,* 328,* 332,* 340,*
436,* 437, 449,* 462,* 466,
496,* 502, 505
nerves, 54, 55,* 436,* 437, 502
Spindle, 63,* 64, 65, 66,* 67
cell, 434
muscle, 505
Spine, 300,* 303, 303,* 304
Spinneret, 325*

Spiracle, 394,* 396,* 397, 403,* 448
Spirogyra (green alga), 115,* 116, 154,
157, 158*

Spittle insect {see Insects]

Splanchnic layer, 858

Spleen, 332,* 427,* 507*

Split protein, 772

Sponges, 279-286, 281*-284,* 535, 536

{see also Scypha; Leucoso-

lenia; etc.)

Spongilla (sponge), 284,* 286
Spongin, 280, 281
Spongocoel, 284*
Spontaneous generation, 732
Sporangiophore, 112, 119, 124,* 125,
136, 173

Sporangium, 112, 119, 123,* 124,* 125,
130, 131,* 133,* 135, 135,*
136, 136,* 137, 150, 154, 165,
172, 173, 187-190, 192-195

Spore, 112, 119-129, 172, 186-190, 192
mother cell, 132,* 187, 197
swarm, 156, 174

Sporocyst, 275, 277,* 375,* 376, 787*

Sporogony, 367

Sporophore, 126,* 128,* 179, 192-195
Sporophyll, 135, 135,* 136,* 138, 192,

196, 200-204
Sporophyte, 117, 128,* 130, 131,*
132,* 133-135, 136,* 137,
138, 138,* 140,* 143, 161,
164, 191-198, 200-204, 206,
207

Sporozoa, 275, 363-367, 534* {see also

Protozoa)
Sporozoite, 277,* 365,* 366, 367
Sporulation {see Spore)
Springtail, 411,* 550, 551* {see also

Insects)
Squalus {see Sharks)
Squid, 311, 315,* 542
Staggers, 537, 661, 788 {see also Multi-

ceps)

Stalk, 190, 198, 223

Stamen, 144,* 208-216, 223,* 224,
225*

Staminate, 140,* 202-204

Standard (of a flower), 212

Stapes bone, 466, 498,* 505

Starch, 115, 118, 153, 155, 162, 204

Starfish, 300*-302,* 301, 540, 666

Statocyst, 288*

Statocyte, 284*

Steapsin, 429, 476

Stele, 145,* 214, 216, 220

Stem, 133-148, 191-198, 200-205, 206-

218, 222, 223, 223*
dicotyledonous, 143
monocotyledonous, 143
Stemonitis (slime mold), 123,* 173
Stentor {see Protozoa)
Sterigma (sterigmata) , 128,* 178,* 179
Sternum, 424, 462,* 466
Stigma, 143, 145,* 207-217, 223,* 225,

225,* 276,* 358,* 359, 361,*

363, 763

Stimulus, 100, 106, 348, 494

Sting, 404,* 406

Stipe, 161

Stirrup bone, 466, 498,* 505

Stolon, 173

Stoma (stomata), 56, 57,* 58,* 133,
141,* 145,* 147,* 189, 191,
192, 210, 211, 215, 224, 226

Stomach, 299, 301,* 306,* 308,* 311*-
315,* 327,* 328,* 332,* 396,*
470,* 471,* 473, 507,* 509,
512

Stomodeum, 290, 447
Stone cell (sclerenchyma) {see Tissues,
plant)

fly {see Insects)

lily, 304

Index 891

Strands of cytoplasm, 153, 157, 162,

164, 362,* 363
Stratum compactum, 422, 422*

corneum, 421, 422,* 459, 460*

granulosum, 459, 460*

lucidum, 459, 460*

mucosum, 459, 460,* 461

spongiosum, 421, 422*
Striation, 381, 384
Strobila and strobilization, 290,* 377
Strobilus, 135, 135,* 136, 136,* 137,*
192-195

Strongyloidea, 295, 788

Struggle for existence, 747

Style, 143, 144*-146,* 207-217, 223,*

225, 225*
Subclavian, 741*
Suberin, 39, 59
Substrate, 91, 131

Successions of organisms, 646, 652, 654
Succus entericus, 476
Suckers, 293, 308,* 309, 311, 315,*

375,* 376-379, 538*
Sucrose (cane sugar), 87, 92, 472-477
Suctoria, 279
Sugar, 87, 92, 472-477
Sulcus (sulci), 503
Sulfur, 79*
Sundew, 636, 668*

Sunflower (Helianthus), 145,* 213-217
Supplementary genes, 693
Suprarenal (adrenal), 508, 511
Surface tension, 755
Survey of animal kingdom, 272-343

of plant kingdom, 108-149
Suspensor, 193, 194, 202, 204
Suture, 466
Swammerdam, 29, 802
Swarm spore, 123, 123,* 156, 167, 172,

174

Swimmeret, 320,* 321*
Syconoid (sycon) {see Sponges)
Symbiosis, 151, 155, 169, 535, 634, 658,
662

Symmetry, asymmetry, 309, 310

bilateral, 292, 293, 298-304, 309-314,
325-343, 368, 372

biradial, 292

radial, 279, 286, 292, 299
Sympathin, 502
Synapse, 54, 501, 502
Synapsis, 696,* 697, 709
Syncytium, 53
Synergid cell, 206, 859
Syngamus, 539, 540, 661, 788
Syngamy, 859
Synura, 530, 532*
Systems, 60, 647, 648

of classification of plants, 865, 866

Tactile, 303, 398, 405, 460, 460,* 495

Tadpole, 447, 448*

Taenia {see Tapeworm)

Tails, 738*

Tapeworm, 293, 294, 377-379, 377,*

378,* 537, 538,* 660, 785,

786

Tar pool, 608*

Tarantula, 547 {see also Spider)

Tarsal (tarsus), 394, 394,* 400, 401,*

425, 462,* 466
Tassel 146 * 210

Taste,' 398, '406, 440, 472-477, 495, 505
Taxonomy, 24, 736, 737, 865, 866 {see

also Classification)
Teeth, human, 461-464, 463,* 464,*

473
palatine (maxillary), 427*
vomerine, 424, 425, 427*
Telegony, 859

Teliospore, 129, 167, 181, 182*
Telophase (mitosis), 62, 63,* 65, 66,*

Telson, 320,* 321*

Tendon, 49, 53, 426*

Tentacle, 278,* 286-293, 286,* 288,*
289,* 291,* 304, 306,* 307,*
310,* 311, 311,* 312,* 327*

Tentaculata, 293

Tentaculocyst, 290*

Teredo, 314,* 542

Termite, 556* {see also Insects)

Terraphyte, 653

Terrestrial, 653

Test, 303,* 304*

Testes (testis), 286,* 292, 296,* 328,*
371,* 372, 374,* 378,* 380,*
382, 389,* 391, 398, 440,
440,* 507,* 509, 512, 513,
514*

Testosterone {see Endocrine glands)
Tethelin {see Endocrine glands)
Tetraspore, 119, 154, 165
Texas fever of cattle, 534,* 786
Thales, 800

Thallophyta, 109-112, 150-166,167-184
Thallus, 131,* 188, 189
Theelin {see Endocrine glands)
Theophrastus, 801

Theories, acquired characteristics, 746,
747

Allen's, 734

atomic {see Atom)

axial gradient, 372, 373

biogenetic, 442, 742

cell {see Cell)

cosmozoa, 734

892 Index

Theories — Cont'd

Creation, 735

Darwin's, 726, 746

demonic, 517

de Vries', 747

Eimer's, 747

gene {see Genes)

germ, 518
plasm, 706

humoral, 518

hybridization, 748

Lamarck's, 746

membrane (nerve), 498,* 498-502

Moore's, 734

mutation, 747 {see also Mutation)

natural selection, 729, 746

organicism, 847

organismal, 847

orthogenesis, 847

Osborn's, 735

parallelism, 738*

Pfliiger's, 734

pythogenic, 518

recapitulation, 442

species specificity, 88

"struggle for existence," 729, 747

surface tension, 345

"survival of fittest," 747

transcendental (Creation), 735

Troland's, 735

viscosity, 345

Weismann's, 706, 747
Thermophile, 122, 170
Thermotropism, 243, 348
Thigmotropism, 243, 346,* 348*
Thorax (thoracic), 318, 319, 329, 340,

490*
Thrips, 557* {see also Insects)
Thrombin, 486, 487
Thromboplastin, 486, 487
Thrombus, 487, 659
Thumps, 539
Thymus, 507,* 509, 512
Thyroid, 507, 507,* 511
Thyroxin, 511 {see also Endocrine

glands)
Thysanura {see Insects, orders of)
Tibia, 394, 394,* 400, 401,* 423,* 425,
462,* 466

Ticks, 543

Tiedemann's body, 302*
Time chart, 614-618
Tissues, 46-61, 647

adipose, 49, 50*

animal, 46-55, 48,* 50,* 51,* 52,*
54*

areolar, 49, 50*

bast, 214

blood and lymph, 50, 51*

Tissues — Cont'd

bone (osseous), 49, 50,* 51*
cambium, 59, 141,* 143, 145,* 207,
214, 221, 222

cartilage, 49, 50*

chlorenchyma, 56, 229

collenchyma, 55, 56

companion cells, 56, 57,* 60, 192,

209, 214, 216, 224
conducting, 57,* 59, 207-216
connective, 46, 49, 50*
cork (plant), 55, 56, 57,* 59
cortex (cortical), 214, 220, 222
endodermis, 197,* 216, 220, 223*
epidermal (epidermis), 55, 56, 57,*

58,* 195, 197,* 209-216, 220-

222, 223,* 224,* 368, 421,
422,* 459, 460*

epithelial, 46, 48, 48,* 283,* 284,*

459-461
fibrous, 49, 50*
germinal, 48, 48*
goblet, 48
mechanical (plant), 57,* 59, 220,

223

medullary (rays), 59, 60, 221
meristematic (growth), 55, 56, 57,*

207, 214, 215
mesophyll, 224-229
muscular, 47, 52,* 53*
nervous, 47, 54, 54,* 55*
neuroepithelium, 47
pahsade, 215, 224
parenchyma, 55, 56, 57,* 59, 60,

185, 197,* 209, 214, 216, 220-

223, 223*
pericycle, 197,* 214, 216, 220
phloem, 56, 57,* 60, 191-198, 197,*

209-216, 220-222, 223*
pith, 213, 214

plant, 55, 56, 57,* 58,* 59, 60
plasma, 51
rays, 214

reproductive, 48, 48*
reticular, 49, 50*
sclereid, 55, 57,* 59
sclerenchyma, 55, 57,* 59, 197,* 209
sieve plate, 57,* 60, 209, 214
spongy, 206-218, 224
stele, 214, 216
tracheal tube (vessel), 56, 57,* 59,

207-216
tracheid, 56, 57,* 59, 207-216, 220,

224
tube, 56, 57,* 60, 192, 209-216, 220,

224
vascular bundle, 191-198, 197,* 200-

205, 222, 223*
white fibrous, 49, 50*

Index 893

Tissues — Cont'd

xylem, 56, 57,* 59, 191-198, 197,*

207-216, 220, 223*
yellow elastic fibrous, 49, 50*
Toad, 333, 333,* 336,* 340, 573
Tolles, 31
Tongue, 469,* 473
Tooth shell, 314, 316*
Toxin, 659, 772
Tracers, 82
Trachea, 318, 319, 325,* 396,* 397,

397,* 403,* 407, 434, 469,*

470,* 490,* 492
Tracheophyta, lio' 133-148, 191-198,

200-205, 206-213
Trails, 605, 611
Transformation, 860
Translocation, 680, 860
Transmutation, 860
Transpiration, 226, 227
Transportation, 240, 638
Traumatin, 240, 768
Travertine, 114, 152
Tree of life, 104

respiratory, 306*
Trematoda, 293, 294, 373, 537
Trepang, 540

Trial-and-error theory, 861
Trichinella, 295, 296,* 297, 298, 539,

661, 785
Trichinelloidea, 297
Trichinosis, 295-299, 539, 661, 785
Trichocyst, 278,* 349, 350,* 353,* 354*
Trichogyne, 163,* 164, 165
Trihybrid cross in heredity, 686-690
Trilobite, 609*
Triploblastic, 292, 293, 295, 299, 306,

309, 314, 325-343, 368, 373
Triploid, 207, 679
Trochanter, 394, 400, 401*
Trochelminthes (Rotifers), 297-299,

299*

Trochophore, 308

Trophectoderm (trophoderm), 451,*

452, 453
Trophozoite, 277,* 365,* 366
Tropisms, 242, 243, 861
Truncus arteriosus, 430, 430,* 741*
Trypanosome, 275, 532, 533,* 534,

534*

Trypsin, 429, 476
Tsetse fly, 534*
Tube cell, 202

foot, 299, 300*-304,* 304

nucleus, 207, 225*
Tubercle, 304*
Tumor, 180,* 583
Tundra, 599,* 600
Tunic, 327, 328*

Tunicata, 327

Turbatrix {see Vinegar eel)
Turbellaria, 293, 369*
Turgor, 754, 861

Turtle, 337,* 340 {see also Reptilia)
Twinning in heredity, 717*
Two-, four-, eight-cell stages of em-
bryos, 444, 451*

Tympanic, 398, 421, 438
Tyndall's cone, 77
Typhlosole, 386, 386,* 387*
Typhoid, 255

Ulothrix, 115,* 116, 154, 157

Ultraviolet, 32, 33

Umbilical, 451, 453, 455*

Umbo, 312*

Uniformitarianism, 961

Unit character, 685

Unity in living organisms, 646-657

Uranium, 82

Urea, 493

Uredospore, 129, 167, 181, 182, 182*

Ureter, 311,* 332,* 340,* 427,* 439,*

440,* 492, 493,* 494, 514,*

515*

Urethra, 493,* 513, 514*
Uriniferous tubule {see Kidney)
Urochordata, 327, 328*
Uroglena, 530, 531*
Uropod, 320,* 321*
Urostyle, 423,* 424
Used spindle (mitosis), 65
Ustilago, 180*

Uterus, 296,* 374,* 377,* 378,* 380,*
382, 440, 452, 455,* 514

Utricle, 496
Utricularia, 668*

Vacuole, 40,* 43, 160, 162

contractile, 156, 156,* 276,* 278,*
279,* 345,* 346, 350,* 354,
355, 358,* 359, 360, 362*
food, 279,* 344, 345,* 350,* 351,
352, 369

Vagina, 311,* 312,* 374,* 378,* 380,*
382, 398,406, 514, 515*

Valve, 159, 311, 395, 405, 477, 480*
Variations, 93, 721-731, 723*-728,*
736, 746

Vas deferens (vasa deferentia), 311,*
312,* 371,* 372, 378,* 380,*
382, 389,* 391, 398, 406, 513,
514, 514*

894 Index

Vasa efferentia, 371,* 440, 513
Vascular bundle, 133-148, 145,* 147,*
191-198 {see also Tissues)

Vegetal pole, 445,* 452
Vegetation areas of North America,
599-602, 599*

Veins, 311,* 312,* 400
of frog, 430, 431,* 433
of leaves, 145,* 147,* 210-215, 224
of man, 470,* 477-489, 740,* 741*

Velum, 288,* 289, 310,* 328,* 400,
401*

Vena cava, 431, 478*-481,* 480-489,
488,* 493,* 741*

Venter, 186, 187, 197, 202

Ventral horn, 55*

Ventricle, 311,* 312,* 331-340, 332,*
340,* 430, 430,* 431, 456,*
470,* 477, 478*-480,* 495,*
503, 504, 740*

Venus's flower basket (sponge), 281
Venus's-flytrap (plant), 106, 636, 668*
Vermiform appendix, 863
Vertebral column, 329-343, 423, 423,*
424, 449*

Vertebrata (vertebrates), 329-343,
340,* 421-441

Vertebrate brains, 743*

embrvos, 738*

heart^ chambers, 331-340, 740,* 741*
VesaHus, 801
Vesicle, 306,* 452
Vestibule, 505

Vestigial structure, 516, 744
Vigor, hybrid, 705
Villus (vilH), 451,* 453, 475
Vinegar eel (Turbatrix), 295, 296,*
298, 539

Viosterol (see Vitamins)
Virus, 789-790
Visceral, 311*
Vision, 398 (see also Eye)
Vitalism, 863

Vitamins, 90, 169, 176, 474, 475, 486,
487, 769-772, 769*-771*

Vitelline, 455

Vitreous body, 497,* 505

Viviparous, 863

Vocal fold (vocal cord), 469,* 492

sac, 427*
Volutin, 160

Volvox, 274, 360-363, 361,* 362,* 535
Vomerine, 424
von Mohl, 37

Vorticella, 278,* 279 {see also Pro-
tozoa)
de Vries, 676, 684

Walking stick, 554, 730 {see also In-
sects)

Wallace, 803

Warm blooded, 340-343

Wasps, 319 {see also Insects)

Waste elimination, 100, 106, 390, 435,

492-494, 633 {see also specific

organisms)

Water, 90, 226, 228, 235, 492-494, 629-
633

"bloom," 114, 152, 249

farming, 776

flea, 318, 324*

mold-, 173, 174* (see also Sapro-
legnia)

molecule of, 83*

silk, 157

storage, 187, 188

supply, 781-783

vascular system, 302*
Wax, 404

Wealth and biology, 779
Web of life, 655

toe, heredity, 716*
Weevil {see Insects)
Weigert, 804
Weismann, 706, 803
Welfare and biology, 778

and heredity, 693
Wheat rust (Puccinia), 129, 181-183,
182*

Wheel organ, 298

Whelk, 310

White "ant" (termite) {see Insects)

corpuscle (leucocyte) {see Tissues,
blood)

matter, 55,* 503, 505

Whitefish embryo, 64*
Whorl, 194
Why study biology, 17
Willstatter, 233 {see also Photosynthe-
sis)

Wilson, 29
Windpipe, 434

Wings, 140,* 144,* 202, 203, 212, 318,
340, 393, 400, 414-418

Wollaston, 30

Wood, 145,* 201-203, 207, 214, 220,
258, 261

Wooden tongue of cattle, 789
Worker honeybee, 399, 399* {see also
Honeybee)

Working hypothesis, 22
Wormian bone, 466

Wuchereria (filaria), 297, 297,* 298,
785

Index 895

X chromosome, 187, 697,* 698 (see

also Heredity)
Xanthophyll, 863 {see also Pigments)
Xerophthalmia, 474, 769,* 772
Xerophyte, 653, 963
Xylem, 133, 141,* 145,* 147* (see also

Tissues)

Y chromosome, 187, 697,* 698 (see also

Heredity)
Yeast, 125,* 127, 129, 176, 252-254

pathogenic, 252-254, 253,* 660
Yolk granule, 375,* 445*

gland, 371,* 373, 374,* 378

plug, 445,* 456

sac, 451,* 452, 455, 455*

Zamia, 142,* 203, 204
Zea mays, 146,* 209-211 (see also
Corn)

Zein of corn, 89
Zernike, 34
Zona pellucida, 452
Zoogeography, 591
Zooglea, 170
Zooid, 289*
Zoology, 864

Zoomastigina, 275 (see also Protozoa)
Zoosporangium, 125, 154, 157, 161,
174, 174*

Zoospore, 115, 116, 118, 125, 154-157,
159, 161, 167, 174, 174*

Zygapophysis, 424
Zygodactyly, 716*

Zygospore, 124,* 125, 158,* 173, 175,
361,* 363

Zygote, 119, 124, 124,* 125, 130, 136,*
138, 143, 150, 157, 158,* 159,
161-164, 173, 175, 185-189,
193-195, 202, 204, 207, 277,*
285,* 361,* 363, 366, 444,
708,* 710,* 711

Zymase, 671, 864
Zymogen, 864
Zymosis, 864

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