Syllabus of lectures in theoretical biology

311
B 62

syllabus of Xectures

IN

ilbeoretical Biology

A-

SYLLABUS OF LECTURES

IN

THEORETICAL BIOLOGY

BY

ROBERT PAYNE BIGELOW, Ph. D.

PREPARED FOR THE USE OF STUDENTS IN THE MASSACHU-
SETTS INSTUrUTE OF TECHNOLOGY.

• BOSTON:
MASSACHUSETTS INSTITUTE OF TECHNOLOGY

I 896

Copyright, 1896,
By Robert P. Biuki.ow.

CONTENTS.

I. Introduction.

1 . Scope of biology.

2. Origin of the science of biology.

II. Characteristics of living matter.

III. Constitution of the individual. Organs and tissues, Cell theory.

IV. What is meant by " Individual."

1. Kinds of individuality.

2. Degrees of individuality.

3. Limits to the divisibility of the individual.

V. Relations between the parts of the individual. Analogy, Homol-
ogy, Symmetry.

VI. Origin of the individual (Morphogenesis).

1 . Abiogenesis 7>s. biogenesis.

2. Evolution Ts. epigenesis.

3. The advance of embryology.

4. Modern theories of fertilization.

5. Phases of ontogeny.

6. Reaction of the individual to its environment.

7. Heredity and variation.

i. General considerations,

ii. Phenomena of individual variation,

iii. Phenomena of heredity,

iv. Theories of heredity and development.

VII. What is meant i:)y " Species."

37345

VIII. Origin of species (I'hylogenesis).

1. Special creation 7's. organic evolution.

i. Special creation.

ii. Unity of Nature as shown by geology.

iii. Organic evolution.

a. Meanings of the word " Evolution.''
d. Evidences of organic evolution.

2. Theories of organic evolution.

i. The rise of the theory of descent,
ii. The theory of direct modification,
iii. The theory of selection,
iv. Neo-Lamarckians ts. Neo-Darwinians.

3. Examination of supposed factors in organic evolution.

i. \'ariation and heredity,
ii. Struggle for existence,
iii. Natural selection.

iv. Panmixia and the reversal of selection.
V. Sexual selection.
vi. Isolation, or segregation,
vii. Inheritance of acquired characters,
viii. Constitutional tendency.

4. General conclusions.

IX. Deductions from the theory of evolution.

I. INTRODUCTION.

1. The scope of Biology.

2. The origin of the Science of Biology.

(See Huxley. Lecture on the Study of Biology, American Ad-
dresses, or Collected Essays, Vol. 3, pp. 262-293.)

Natural history and civil history, Bacon (1561-
1626), and HoBBES (i 588-1679).

Natural philosophy and natural history, Buffon
(i 707-1 778) and LiNN^us (i 707-1 788).

Physical sciences and physiological sciences, Bichat,
(Anatomic Generale, 1801).

Biologic, Lamarck (i8oi).

Biologic, Treviranus (1802).

3. Our object, a philosophical review of Biology as a whole.

II. CHARACTERISTICS OF LIVING MATTER.

(See Hatschek, Zoologie pp. i-ii; Sedgwick and Wilson, General
Biology, pp. 1-6; Foster, Physiology, Introduction last edition; Verworn,
Allegemeine Physiologic, 1895, Trans, by Lee; Howell, American Text-
book of Physiology, Introduction, 1896.)

Chemical composition.

Assimilation, growth and reproduction.

Contractility and irritability.

The organic individual.

Individuals grouped into species.

III. THE CONSTITUTION OF THE INDIVIDUAL.

(See Tyson, The Cell Doctrine, Phila. 1S7S ; HALLiiiURTON, Chemical
Physiology, pp. 183-216; Huxley, Review of the Cell Theory, British and
Foreign Medico-Chirurgical Review. Oct. 1853, Vol. 12, pp. 285-314; Mar-
SHALL, Biological Lectures, pp. 159-191 ; Hertwig, The Cell, 1895; Wilson,
The Cell, 1896.)

Partes .similare.s and partes dissimilares, Aristotle
{384-321, B. c).

Organs and tissues, Galen (130-200); Fallopius
(1523-1562).

Cellular structure of plants, Hooke (1667); Mal-
piGHi (1670); and Grew (1672).

The fibre-theory, Haller (1757).

Wolff's theory (1759).

The globular theory (1779-1842).

Discovery of the nucleus, Robert Brown (1833).

The cell-theory, Schleiden and Schwann (1838).

Sarkode, Dujardin (1835).

Protoplasm, Purkinje (1840); Hugo von Mohl
(1846).

The protoplasm-theory. Max Schultze (1861).

Cell-division, VON MoiiL (1835); Nageli, Kolliker
(1844) ; Remak, Virchow (i860).

Nuclear division. A, Schneider (1873); Butschli
(1875); FoL (1875); Flemming (1882).

Attraction sphere and centrosome. Van Beneden
(1887); BOVARI (1888).

The inadequacy of the cell-theory, Huxley (1853) ;
Whitman (1893).

The search for organisms more elementary than the
cell, Brucke (1861); Altmann (1890), "Bio-
blasts."

IV. WHAT IS MEANT BY "INDIVIDUAL."

(See Haeckel, Ueber die Individualitiit des Thierkorpers, Jenaische Zeit-
schrift, Vol. 12, 1878; Lillie, Smallest Parts of Stentor Capable of Regenera-
tion, Jour. Morph. Vol. 12, 1896, pp. 239-249).

1. Kinds of individuality.

i. Physiological, the bion.

ii. Morphological, the viorphoti.

2. Degrees of individuality in morphons.

i. Plastid.

a. Cytode.
/;. Cell.

ii. Idorgan.

a. Organ.

b. Paramere.

c. Antimere.

d. Metamere.

iii. Person, or Zoon.
iv. Stock, or Cormus.

3. Limits to the divisibility of the individual, Loeb, Mor-

gan, Lillie.

V. RELATIONS BETWEEN THE PARTS OF THE

INDIVIDUAL.

(See Owen, On the Archetype and Homologies of the Vertebrate Skeleton,
London, 1848, pp. 5-8; Gegenijaur, Comparative Anatomy, pp. 58-65;
Bateson, Materials for the Study of Variation, pp. 17-22, 87-90, 475-483.)

Physiological similarity — Analogy.
Morphological similarity — Homology.
Arrangement of homologous parts.
Symmetry and merism.

8

Major and minor symmetries.

Distinction between linear series and bilateral sym-
metry.

Comparison with radial symmetry.

Abnormal secondary symmetry.

Kinds of Homology.

1. General.

a. Bilateral symmetry, homotypy.

b. Serial homology, homodynamy.
r. Radial homology.

2. Special homology.

a. Complete.

b. Incomplete.

VI. THE ORIGIN OF THE INDIVIDUAL.

i^Mo rpJiogciiesis. )

I. Abiogenesis vs. Biogenesis.

(See Huxley, Spontaneous Generation, Lay Sermons, etc., p.
345, also Collected Essays, Vol. 8, pp. 229-271 ; CuEYNE,
Antiseptic Surgery, chapters 8 to 11.)

Spontaneous generation generally accepted, Aris-
totle (384-321 B. c.) ; Helmont (1577-1644);
Harvey (i 578-1657) (Works, p. 427).

Spontaneous generation of the higher animals dis-
proved, Redi (1 664- 1 690).

Spontaneous generation advanced on philosophic
grounds, Buffon (i 707-1 788), and Needham.

Experiments of Spallanz.ani, Sciiultze, Schwann,
SciiROEDER, and Dusch.

Heterogenesis, Pouchet (1859).

Method of pure cultures, Theory of specific organ-
isms, Pasteur {i86i).

Spontaneous generation again, Bastian {1872).

Biogenesis firmly established, Cheyne, Cohn, Rob-
erts, Tyndall, etc.

2. Evolution vs. Epigenesis.

(See article Embryology, Encyclopaedia Britannica, 9th Ed.;
Hertwig, Text-book of Embryology, pp. 23-27.)

Aristotle, observations on the chick (History of
Animals, p. J 42).

Harvey (165 i). (See his works pp. 228, 336, 457.)

" Omne vivum ex ovo."

" Epigenesis."
Malpighi (1672) (Appendix to Anatome Plantarum).

" Praedelineation."

Bonnet and Haller (1742-1768), "Evolution."
(See Whitman, Woods HoU Lectures, 1S94, p. 225.)

Discovery of spermatozoa, Hamm and Leeuwenhoek

(1677).

Ovists (Schwammerdam, Malpighi, Haller, Bon-
net, Spallanzani) vs. Animalculists (Leeuwen-
hoek, Hartsoker, Dalenpatius).

Casper Friedrich Wolff (1759), Epigenesis re-
vived.

Christian Pander (18 17), The three germ-layers.

Carl Ernst von Baer (18 19-]-).

The mammalian ovum discovered.
Epigenesis established.
Modern embryology founded.

lO

3. The Advance of Embryology.

The egg a cell, Sch\vaNx\ (1838).

Cell-lineage traced to the egg, Reichert (1840),
KoLLiKER, and Virchow.

Function of spermatozoa, experiments of Kolliker
and Reichert.

The spermatozoon a cell, K lliker, La Vallette,
and Flemmix(;.

Fusion of the nuclei in fertilization, Oscar Hertwig

The same process in plants, Strasijurger (1884);
GuiGNARD (1 89 1). (See Amer. Nat., 1892, p. 424.)

4. Modern Theories of Fkktilizatiox.

Two-fold effect of fertilization.

Parthenogenesis.

Normal and parthenogenetic eggs compared.

Weismann's Theory.

MiNOT (Embryology, p. yy).

Geddes and Thomson (Evolution of Sex, p. 183).

Composition of male and female nuclei.

AuERBACH ( 1 89 1 ). (See Amer. Nat., 1 892, p. 624.)
Watase' (Jour. Morph. Vol. 6, p. 482).

The bearer of heredity ?

Theories of Hertwhv, Weismann.

BovARi's experiments (Amer. Nat., Vol. 27, p. 222).

Seeliger's criticism (Jour. Royal Mic. Soc, 1895,

p. 318). See also Amer. Nat., Vol. 29, p. 286.
Observations of Fol, Guignard, and Conklin.

(Woods Holl Lectures 1893, p. 15).

1 1

Observations of Wheeler, Mead, Wilson and
Mathews, and Bovarl (Jour. Morph., Vol. lo;
and Jour. Royal Mic. Soc, 1895, p. 433 ; Wil-
son, Atlas of the fertilization and karyokinesis of
the ovum, 1895).

5. Phases of Ontogeny.

i. /;/ iinicclhilaj' organisvis (See Hatschek, Zoologie,
pp. 56-60).

Simple fission.

Budding and development.

ii. In multicellular organisms (See Hatschek, Zoolo-
gie, pp. 207-226).

The cycle from egg to ^%g.

Metamorphosis.

Hermaphroditism.

Sexual dimorphism.

Secondary sexual characters.

Polymorphism :

Correlated with division of labor.
Associated with change of season.

Regeneration of lost parts.

Fission followed by regeneration.

Fission preceded by regeneration.

Budding.

Alteration of generations, Chamisso.

a. By fission.

b. By budding.

c. By parthenogenesis.

d. By heterogeny.

12

6. Reaction of the Individual to its Environment.

Use and disuse.
Heliotropism and geotropism.

Chemotropism.
Thigmotropism.
Temperature and color.

Summer and winter coats.

Seasonal dimorphism.

Experiments of Weismann (Studies in the The-
ory of Descent, Vol. i, p. i and p. 126), and
of Edwards (Butterflies of North America,
Vol. I, pp. 7-16).

Summer form changed to winter form by cold.

Winter form not changed by heat.

Poulton's experiments.

The determination of sex.

(See Geddes and Thomson, Evolution of Sex, pp. 32-54.)

Mrs. Treat's experiments on caterpillars.

Young's " " tadpoles.

GiROu's " " sheep.

The Aphides.

The honey-bee.

Maupas's experiments on Hydatina.

(See Watase, Journ. Morph. Vol. 6, p. 483.)
Summary.
Individual acclimatization.
Reactions following change of medium.

Experiment on frog tadpoles.
Amblystoma tigrinum.
Experiments of Schmankewitsch.

Artemia salina.

Artemia milhausenii.

Branchinecta schaefferi.

13

Experiments of Herbst on larvae of sea-urchins.
The potassium larva.
The lithium larva.

Reactions following mutilation.

Healing.

Regeneration of lost parts.

Polarization.

Heteromorphosis (Loeb, Woods Holl Lect.

1893)-
Effects following removal of testes and ovaries.

Comparison with effect of excision of thyroid

gland.

7. Heredity and Variation.

i. General Co7isiderations.

Meaning of heredity.

Prevalence of variation.

Distinction between racial and individual variation.

Distinction between acquired and congenital varia-
tions.

Importance of congenital variations as a measure of
heredity.

Distinction between continuous and discontinuous
variation. Sports.

Distinction between substantive, meristic, and ho-
mceotic variation.

ii. Phenomena of Individual ]^ariatio7i.

(Darwin, Animals and Plants under Domestication ; Darwin,
Descent of man; Galton, Natural Inheritance; Bateson,
Materials for the Study of Variation; Weismann, Studies in
the Theory of Descent; Weismann, Essays upon Heredity;
Ellis, Man and Woman.)

14

a. Slight, or continuous variations.

Variation of stature among brothers.
Variation of children of like parents.
Galton's observations on sweet peas.

/;. Saltatory, or discontinuous variations.
Substantive.
Meristic.
Homoeotic.
Monstrosities.
Tumors,

c. The correlation of variations.

(See Darwin, Animals and Plants under Domestication, Vol. 2,
pp. 311-332; Brooks, Heredity, p. 157.)

Correlation between associated parts.
Correlation between homologous parts.
Darwin's examples.

Monstrosities.

Varieties of pigeons.

Galton on finger prints.

Bateson, bilateral symmetry in variation.

Thompson on correlation in Palaemon.

Anomalous correlations.

Tufts of feathers and perforations of the
skull.

Color and constitutional peculiarities.
Symmetry in monstrosity, Bateson.

15

d. The larval and adult forms of an individual may-
vary independently of each other.

Larva, pupa, and imago of Lepidoptera.

(Weismann, Studies in the Theory of Descent, Vol. 2, pp. 404-
407, and pp. 416-419.)

e. Variation associated with changed conditions of
life.

Acclimatisation.

(vSee Darwin, Animals and Plants under Domestication, Vol. 2,
p. 295; and Wallace, Darwinism, p. 94.)

Dogs and sheep in India.

Geese in Bogota.

Wheat, etc.

Greyhounds in Mexico (Brooks p. 151.)

Domestication.

(Darwin, 1. c, Vol. 2, p. 249-252.)

Variation following cultivation of plants.
Turkeys reared from eggs of wild ones.
Wild ducks.

Effect not direct, but on subsequent genera-
tions.
Bateson's objections.

f. Sexually produced organisms the more variable.
(Brooks, Heredity, p. 143.)

The sweet orange in Italy.

Bud variation (Darwin, Vol. i, pp. 361 and

389).
Contrast with seminal variation.

(T. Males more variable than females.

A

(Darwin, Descent of Man, Vol. i, p. 266; Brooks, p. 160;
Ellis, Man and Woman, p. 35S.)

i6

iii. TJic PJicnomaia of Heredity.

(See Darwin, Animals and Plants under Domestication, Chap-
ters XII, XIII, and XIV; Galton, Natural Inheritance;
Delac.e, Heredite, pp. 186-260.)

The force of heredity.

Pedigrees of domestic animals.
Inheritance of saltatory variations.
Variability itself a variation that is often
strongly inherited.

Capriciousness of heredity.

Non-inheritance due to opposing conditions.

Fixedness of character apparently not due to
antiquity of inheritance.

Inheritance at corresponding periods of life.

Particulate inheritance (Galton, p. 7).
Heritages that blend.

Stature : (Galton, p. 83).

Not affected by marriage selection.

Not affected by diversity of parents.

" The mid-parent."

"Mid-stature of population," about 68.4
inches = /'.

Filial regression (pp. 95-97).

Mlial deviation from /-* : to the mid-pa-
rental deviation : : 2:3.

On the other hand, — Mid-parental devi-
ation from /"* : Filial deviation : : i : 3
(See Table 1 1 ).

Galton's law of regression : " The devia-
tion of sons from /' is on the average
equal to 1-3 of the deviation of the pa-
rent from /' and in the same direction."
(When in one parent D = o.)

17

Heritages that are mutually exclusive.

Eye-colors : (Galton, pp. 1 38-1 53 and 212-
218.)

Division into light and dark.
Distribution in the family.

When F has peculiarity D, his sons (S) will
have 1-3 D, each of his parents (G) will have
1-3 D, each of his grandparents (Gg) will
have 1-9 D, etc.

Inheritance as limited to sex.

Prepotency.

Reversion, or Atavism :

In pure breeds.

In crossed varieties and species.

Bud reversion.

In different parts of the same animal.

Latent characters.

Appearance in the children of characters not
found in either parent.

Kinds of characters that may be transmitted.

Telegony.

iv. Theories of Heredity and Development.

(Lloyd Morgan, Animal Life and Intelligence, pp. 130-176;
Thomson, The History and Theory of Heredity, Proc. Royai
Society, Edinburgh, 1889, Vol. 16, pp. 91-116; Darwin, Ani-
mals and Plants under Domestication, 2d. Ed., Vol. 2, pp.
349-399; Brooks, Heredity; Weismann, Essays upon He-
redity; Weismann, The Germ-plasm; Romanes, An E.xamin-
ation of Weismannism ; O. Hertwig, The Cell, 1S95 ; O.
Hertwig, Zeit- und Streitfragen der Biologic, L Prjiformation
oder Epigenese? also trans, under title. The Biological Prob-
lem of To-Day; Driesch, Analytische Theorie der Organ-
ischen Entwicklung, Leipzig, 1894; Delage, Heredite, Paris,
1895, pp. 403-813; Wilson, The Cell in Development and
Inheritance, 1896.)

Requirements of a theory of heredity.

A theory of heredity must be also a theory of
development.

i8

It must include a theory of variation.

It involves a conception of the essential struc-
ture of living matter.

Principles invoked to account for heredity.

The theories in detail : —

Democritus (b. between 494 and 460 b. c).

Seed of animals elaborated by contributions from
all parts of the body.

Aristotle (384-321 r. c). The formative influence
of the soul.

Van Helmont (i 577-1644). Transmission of spir-
itual characters.

Blumenbach (i 752-1 840), Needham, and others.
Nisus foi'mativus, vital force, etc,

Descartes (1662).

First attempt at a mechanical explanation of de-
velopment.

Bonnet (1720-1793). Preformation and " Emboite-
ment."

BuFFON (1749- 1 804).

Organic and inorganic matter essentially dif-
ferent.

Organic molecules.

Spermatozoa not concerned in reproduction.

Conflict of maternal and paternal molecules.

Owen (1849).

Continuity of germ cells. (Afterwards denied.)

19

Spencer (1864).

(Principles of Biology, Vol. i, pp. 179-183 and 209-292.)

Theory of heredity part of philosophical system
of cosmic evolution.

Polarity.

Physiological unites.

Germ cells collections of physiological unites.

Any force affecting a part affects the whole.

Acquired characters inherited.

Darwin (1868). Provisional hypothesis of Pangen-
esis.

Inheritance due to gemmules.

Variation due to latent gemmules, to rearrange-
ment of gemmules, or to the inheritance of
the direct effects of the environment and of
use or disuse.

Galton (1876).

Pangenesis doubtful.

Transmission of acquired characters doubtful,

Continuity of the "Stirp."

His (1875).

Differentiation of areas.

Unequal growth.

Comparison with waves formed in liquids.

Haeckel (1876).

" Perigenesis of the plastidules."
Heredity is memory.

20

Jager (1879).

Continuity of the germ-protoplasm which receives
flavor- and odor-substances from the body-
cells.

Brooks (1876, 1883). Modified theory of Pangenesis.

Continuity of germ-cells.

Gemmules given off by body-cells only under
unfavorable conditions.

Sperm-cells especially modified to collect gem-
mules.

Gemmules cause variation in the corresponding
part of the offspring.

" The occurrence of a variation is due to the di-
rect action of external conditions, but its pre-
cise character is not."

" The structure of the adult is latent in the egg,"
Evolution.

Evidence.

NussBAUM (1880-1887).

Continuity of germ-cells.

Nageli (1884). Theory of the Idioplasm.
Formation of " Micellae."
"Idioplasma" and " Niihrplasma."
Net-work of idioplasm.
Micellar threads, one for each character.
Their union to form idioplasmic cords.
Elementary and complex characters.
Same elements in all jjarts of the idioplasm.
Germ-cells.

21

Sexual reproduction.
The idioplasm in heredity.
Variation.
The nucleus as the bearer of heredity.
O. Hertwig (1875, 1884, 1886).
Strasburger (1884).
kolliker (1886).

BOVARI (1886).

E. B. Wilson (1895).

Roux (1881, 1885+).

Struggle of the elements within the cell.

Struggle of the cells.

Morphogenic effect of functional stimuli.

Heredity due to transmission of chemical com-
position.

The mosaic theory.

Weismann. Earlier theories (1883, 1885, 1886, and
1887).

All inheritance of acquired characters denied.

Theory of gemmules unnecessary and improbable.

Continuity of germ-cells disproved.

Germ-tracts.

Position of the idioplasm in the nucleus.

Distinction between germ idioplasm, or gcrtii-
plasin, and somatic idioplasm.

Improbability of the backward development of
somatic idioplasm into germ-plasm.

Continuity of the germ-plasm.

22

Development a process of epigenesis.

Variation due to the direct effect of external
conditions upon the germ (1883).

Variation in higher organisms due principally
to the mingling of diverse germ-plasms in sex-
ual reproduction (1886).

First polar spindle removes the ovogenic idio-
■ plasm (1887).

Second polar spindle removes half of the ances-
tral germ-plasms.

De Vries (1889). Intracellular pangenesis.

Pangenes (gemmulcs).

Reserve pangenes in nucleus, active pangenes in
cytoplasm.

Protoplasmic net-work and inheritance of ac-
quired characters denied.

Variation due to, — modification, change in pro-
portion, alteration in arragement, or unequal
division, of pangenes in germ-cells.

Continuity of germ-plasm.

Independence of hereditary characters and the
necessity for separate factors.

Control of the cell by the nucleus and the ne-
cessity for material particles.

Weismann. Later theory (189 1, 1893).

Development a process of evolution.

Continuity of the germ-plasm.

The mingling of gerni-i)lasms in sexual repro-
duction, A nipli iiii iv IS.

Each ancestral germ-i^lasni a distinct unite, the
id

23

Each chromosome, or idant, composed of many
ids.

Each id composed of smaller unites, the deter-
viiuauts, one for each independently variable
part of the organism.

Each determinant composed of the ultimate
unites of living matter, biopJiors.

Control of the cell by the nucleus and the ne-
cessity for biophors.

The id in ontogeny.

The division of the id of germ-plasm into

an active id of somatic idioplasm and an

id of reserve germ-plasm.
Growth and multiplication by division of

the determinants and ids.
The qualitative and quantitative divisions of

the active ids.
The migration of the biophors of the active

determinants from the nucleus into the

cell-body.
Fate of the reserve germ-plasm.

The effect of amphimixis.

The homologous determinants in the ids may
be homodynamous or heterodynamous.

Hence a possible struggle of the ids in
ontogeny.

Significance of the polar bodies.

The maturation of the Qgg and the forma-
tion of the spermatozoon preceded by the
doubling of the idants and ids.

The first subsequent division (first polar
spindle) reduces this number by half.

The second division (second polar spindle in
the Q^g^ reduces the remainder by half.

Advantage of two reducing divisions in in-
creasing variability.

Origin of variations.

24

Reversion due, in hybrids, to the effect of the
reducing divisions and favorable combinations ;
in pure races, to ids becoming dominant after
a latent period.

Sexual dimorphism due to doubling of the de-
terminants for the sexual characters.

Regeneration of lost parts due to special deter-
minants in the germ-plasm.

Reproduction by fission the same process carried
farther.

Budding due to a doubling of the ids of germ-
plasm.

Alternations of generations due to the presence
of two kinds of germ-plasm in each reproduc-
tive cell.

Weismannism criticised.

Points probably well founded : —

Inheritance of acquired characters unproved.
Idioplasm contained in chromatin of the

nucleus.
Continuity of idioplasm between successive

generations.
The characters of the offspring of germinal
and not of somatic origin.

Main questions now under discussion : —

Is there a real difference between germ-plasm

and somatic idioplasm ?
Is development a process of evolution or of

epigencsis .''
May qualitative cell-division occur ?
How far is ontogeny due to the structure of

the idioplasm and how far to environment ?
Is VVeismann's interpretation of the reducing
divisions correct ?

25

Is Amphimixis sufficient to account for the
main facts of variation ?

The mosaic theory of development as evidence
for qualitative divisions.

Experiments of Roux on Frogs' eggs.

Formation of half embryos.

Post generation.

Roux's explanation.
Chambry's experiments on eggs of Ascidia as-

pera.
E. B. Wilson on the cell lineage of Nereis.

Evidence against qualitative divisions.

1. In normal development.

a. Lack of correspondence between first

cleavage plane and any plane of adult

body.
Morgan on frogs and teleosts.
Miss Clapp on toad fish.

b. Variations in cleavage.

H. V. Wilson on sea-bass.

Jordan on Amphibia.

E. B. Wilson on Amphioxus.

Three types with all grades between.

Result normal embryos.

2. Experimental evidence.

a. Effects of pressure.

Hertwig, pressure on frogs' eggs, —
Abnormal cleavage but normal embryos.

Morgan, removal of yolk from c^^ of
Fnndiilns, —
Abnormal cleavage but normal embryos.

b. Isolation of blastomeres.

Driesch, eggs of Echinus in 2-cell stage.
Result : half blastulas, becoming com-
plete dwarf blastulas, gastrulas and
plutei.

LoEB, on eggs of sea-urchins.

26

Morgan, one blastomerc killed in 2-cell
stage of Fiimiiilus. Result perfect em-
bryos 2-3 normal size.

Wilson on eggs of Ampliioxus.

2-cell stage, perfect blastulas gastrulas

and nearly perfect larvae 1-2 size.
4-cell stage, less perfect larvae 1-4 size.
8-cell stage, imperfect blastulas.

Wilson's arguments against qualitative
divisions and the theory of determi-
nants, and in favor of epigenesis.

c. Effects of abnormal stimuli on develop-
ment.
Herbst, Formative stimuli in ontogeny.

Evidence against distinction between germ-
plasm and somatic idioplasm afforded by the
phenomena of regeneration and budding.
G. Wolff, regeneration of the lens in Trito?i.

Evidence against Weismann's view of the re-
ducing divisions.

Strasburger, different number of chromo-
somes in sexual and asexual generation of
plants.
Corresponding phenomena in animals.

Brooks's criticism of amphimixis as a cause of
variation.

The extermination of families.

O. Hertwig (1892, 1894).

The idioblasts.

Their fusion during fertilization.

The structure of the adult only indirectly the
result of the structure of the idioplasm of the

Every cell-division quantitative only.

Development a process of epigenesis.

Each stage in ontogeny determines only the next
stage.

27

The differentiation of the cell, a function of its
position.

Comparison of organic development with devel-
opment of the state.

VII. WHAT IS MEANT BY "SPECIES."

(Jevons, The Principles of Science, pp. 698-734 ; Article Zoology in En-
cyclopaedia Britannica, 9th Ed. ; Carus, Geschichte der Zoologie, p. 434 et
seq.\ Wallace, Darwinism, pp. 1-2.)

The discontinuity of living forms.

Genus and Species in Logic.

The terms used in this sense by the early naturahsts.

Organic species defined by John Ray (1686).

LlNN^US (1753).

Best definition by de Condolle.

SWAINSON.

Variety, species, and genus contrasted.
Species the unite group.
The next problem.

VIII. THE ORIGIN OF SPECIES.
( Phylogenesis)

I. Special Creation vs. Organic Evolution.
i. Special Great io7i.

(John Ray, The Wisdom of God manifested in the Works of
the Creation ; John Ray, Three PhysicoTheological Dis-
courses; H.ECKEL, The History of Creation, Vol. i,pp- 37-71 ;
Bridgewater Treatises, Vol. i, pp. 17-55, ^"<^ Vol. 3, pp. 1-32
et set].; L. Agassiz, Essay on Classification, Contributions to
the Natural History of the United States, Vol. i, pp. 3-232;
The Duke of Argyle, The Reign of Law, pp. 20S-273.)

Antiquity of the theory. Book of Genesis, i and ii.

28

John Ray (1691). Design in Nature.

LiNN/EUS. Each species descended from a single
pair.

CuviER. The immutability of species and the doctrine
of catastrophes.

Agassiz {1857). Each species created with full num-
bers and in position where discovered. His ideal-
istic view of species. ^

The Duke of Argyle (1866). Creation by law is
nothing but the reign of an intelligent and pur-
poseful Creative Force. Criticisms of Darwin (See
below).

ii. TJie Unity of Nature as shown by Geology.

(Lyell, Principles of Geology, 1830, ist. Amer. Ed. 1S37 ; Cu-
viER, Discours sur les Revolutions de la Surface du Globe,
1825, see also trans., entitled Theory of the Earth.)

The shortness of the earth's history as calculated
from the Jewish scriptures.

Date of creation 4004 b. c, according to Archbishop
Usher.

Early geologists, — catastrophes, changes in the laws
of Nature.

HuTTON (1788). No changes in natural laws, catas-
trophes a part of the permanent order of Nature,

Sir Charles Lyell (1830). The doctrine of catas-
trophes without scientific basis.

All geological changes may be explained by
forces now at work.

The establishment of an orderly course in the devel-
oi)ment of the earth's surface makes possible a
theory of evolution of organic forms.

iii. The Meanings of the luord " Evolution.

29

In philosophy : —

" A change from an indefinite, incoherent homo-
geneity, to a definite, coherent heterogeneity,
through continuous differentiation and integra-
tion." Spencer (First Principles).

In biology : —

As applied to the origin of the individual, —

" The becoming perceptible of preexisting
latent diversities," Roux. (See above, VI, 2.)

As applied to the origin of species, —

Descent with modification from preexisting
species.

The theory of organic evolution stated.

iv. The Evidence of Organic Evolution.

(Romanes, Darwin and after Darwin, Vol. i,pp. 23-248; Spen-
cer, Principles of Biology, Vol. I, pp. 346-401 ; Wallace,
On the Law which has Regulated the Introduction of New
Species, Annals and Magazine of Natural History, Sept. 1855,
(Ser. 2), Vol. 16, p. 184; Fritz Muller, Fiir Darwin, 1864,
see also Trans., Facts and Arguments for Darwin, 1869 ;
Wiedersheim, Structure of Man, 1895.)

1. The evidence from Classification.

Failure of the linear arrangement.

True relations shown only by tree-like arrange-
ment, e. g. Scyphomedusae.

This arrangement best explained by evolution.

Gradations of species into one another.

Calcareous sponges.

2. The evidence from Geographical Distribution.

The continuous distribution of a species.

Distribution of the species in a genus often dis-
continuous.

30

Similarity between the distribution of species and
varieties. Cya7iura stclleri.

" Present distribution cannot be accounted for by
difference in physical conditions.

Importance of barriers (Darwin, pp. 322-329).

Affinity of productions of the same continent.

" Centres of Creation."

Some facts accounted for by the past history of
the earth (See Wallace, pp. 338-355).

Facts to be explained.
Conditions of distribution.
Permanence of oceans.
Oceanic and continental areas.
Madagascar and New Zealand.
The thousand fathom line.
The distribution of Marsupials.
The distribution of Tapirs.
Powers of dispersal.

3. The evidence from Palaeontology.

(Romanes, 1892, pp. 156-203.)

Incompleteness of the record.

Difficulty of preservation.

Full history of specific changes not to be ex-
pected.

Palaeontology furnishes no proof against evolu-
tion.

Le Conte's diagram of the succession of animals.

Missing links.

The development of horns.

The tails of fishes.

The tails of birds.

Arclueoptcrix.

31

Mammalian limbs.

Baptanodon.

Chelydra.

Evolution of ungulate limb,

Zygapophyses,

Teeth.

The brain.

Evolution of Planorbis at Steinheim,

Strombiis in Florida.

4. The evidence from Embryology.

(Romanes, pp, 147-154.)

Recapitulation of geological stages in ontogeny.

Antlers of the stag.

Tails of fishes,

This also a recapitulation of the classification
of existing forms.

Law that higher forms pass through ontogenetic
stages corresponding to lower forms well shown
by Scyphomedusae.

The earlier stages in ontogeny are common to
the largest groups while the latter stages are
restricted to smaller and smaller groups.

Egg not found in Protozoa, but is the protozoan
stage in all higher groups.

Gastrula present in higher coelenterates and is
coelenterate stage in all higher forms.

Early stages of echinoderm larva of one type for
whole group. This developes into a different
type of larva for each sub-group.

The nauplius (Korschelt and Heider.)

Special larval forms of groups of Crustacea.

The life history of Decapods.

Appearance in embryo of oro^ans only functional
in lower forms, e. g., gill-slits in vertebrates.

5. The evidence from Vestigial Organs.
(Romanes, pp. 65-97 ; Wiedersheim.)

Teeth and ear of foetal whale.

Limbs of python.

Wings of Apteryx.

Wings of insects of Madeira and Kerguelen.

Blind animals in caves.

Agassiz's views.

Universal occurrence of vestigial organs.

Man.

Nictitating membrane.

Muscles of external ear.

Feet and hands of infants.

Tail.

Vermiform appendix of the coecum.

Ear.

Hair.

Teeth.

6. The evidence from Homologies.

(Romanes, pp. 50-65.)

Homology without analogy.
Whales and seals.

Homology with analogy.
The wings of vertebrates.

Analogy without homology.

Contrast between eye of octopus and of fish.

Structure of Dinornis opposed to the idea of
special creation of types.

The cocoanut crab of Keeling Island.

33

7- Summary of the evidence.

All points towards evolution, no evidence against
it.

Evidence largely circumstantial.

The succession of horse-like forms, the Planorbis
shells of Steinheim, and similar cases afford
direct evidence.

2. Theories of Organic Evolution.

(OsBORN, From the Greeks to Darwin ; Haeckel, The History
of Creation, Vol. i, pp. 70-174; Huxley, Article Evolution,
Encyclopaedia Britannica, 9th Ed., Vol. 8, pp. 741-754 ; Pack-
ard, Introduction, Riverside Natural History, Vol. i, pp.
1-lxii; Darwin, Autobiography, Life and Letters, Vol. i, pp.
26-107 ; Wallace, Natural Selection and Tropical Nature,
pp. 3-33 and 450-475; Marshall, Lectures on the Darwinian
Theory, pp. 1-24, and 200-228.)

i. The Rise of the Theory of Descent.

The Greeks.

Aristotle, etc.

The " Naturphilosophen."

Goethe (1790). Metamorphosis of Plants.

Theory of the skull.

Treviranus. Adaptation.

Erasmus Darwin (1795). Effects of new condi-
tions.

Oken. Theory of the skull. " Urschleim."

ii. The TJieory of Direct Modification.

Lamarck (1809). Habit and the effect of use and
disuse.

Geoffrey St. Hilaire. Effects of changes in exter-
nal conditions.

The debate of 1830.

34
iii. The Theory of Selection.

Charles Darwin.

The voyage in the Beagle (183 1.)

L yell's Geology.

The fauna of the Pampas.

The South American affinities of the productions
of the Galapagos and their relations to one
another.

Malthus on population (1803).

Alfred Russell Wallace.

The journey to the Malay Archipelago.

The paper of 1855 — "Every species has come
into existence coincident both in space and
time with a preexisting, closely allied species."

The discovery of the principle of the survival of
the fittest, February (1858).

Darwin and Wallace (1858).

Origin of Species (1859).

The cue furnished by Malthus and Franklin
(1751)-

The theory of natural selection stated.
The tendency to multiply.
Heredity and variation.
The struggle for existence.
The survival of the fittest.
The .struggle against enemies.
The struggle against physical conditions.

35

iv. Neo-Lamarckians, vs. Neo-Daiivmiatts.
The inheritance of acquired characters.
The all-sufficiency of natural selection.

3. The Factors of Organic Evolution.
i. Variation and Heredity.

(Darwin, Origin of Species, Chap. V. ; Brooks, Heredity, pp.
140-165; Wallace, Darwinism, pp. 41-125 ; Lloyd Morgan,
Animal Life and Intelligence, pp. 61-75; Bateson, Materials
for the study of Variation ; Cope, Primary Factors of Organic
Evolution, pp. 21-73.)

Variation and the inheritance of variations, the basis
of any theory of evolution.

a. Kinds of Variation.

(i) As to distribution.

Variation in the individual.

Acquired.
Congenital.

Variation in the species, Racial Variation.

Race. Variety. Sub-species.
No sharp line to be drawn between charac-
ters of the family, variety, and species.

(2) As to quality.

Substantive.

Chemical composition. Color. Size. Pro-
■^ portions.

Meristic.

Pattern. Symmetry. Homoeosis.

Other qualities.

Age at which various characters are acquired.

Acclimatization.

Habits.

Change of function.

36

Instincts.

Intelligence.

Variability.

(3) As to quantity.

Moderate variations.
Sports.

Prevalence and Extent of Variation.

That variation in wild species is not infrequent
nor always slight in amount pointed out by
Wallace,

Foraminifera.

Sea-Anemones.

Nerita.

Cassiopea, and other Medusae.

Gulick's studies on the land shell of Oahu.

Helix in France.

Mollusca of Colorado.

Insects.

Milne-Edvvards's measurements Of lizards.

Allen's measurements of birds.

Variation in size i ^% to 20^.

Each part varies independent of the others.

Same result from Allen's measurements of
squirrels.

Also Llovii Morgan's measurements of bats'
wings (Animal Life, pp. 63-75).

Variation in internal organs.

Beddard on earthworms.

Skulls of orang-utans.

Skulls of wolves and bears.
Batkson on the frequency of sports.

37

Distribution of individual variations within the
species.

(i) The normal curves of variations.

Galton's observations on the English people.

{See Galton, Natural Inheritance, pp. 35-70.)

The curve of distribution.

The curve of frequency.

Relations of these curves.

The curve of frequency of error.

Mechanical illustration of the cause of the
curve of frequency.

Weldon's observations on Crangon and Car-
ciniis.
(Proc. Roy. Soc, Vol. 47, p. 445, and Vol. 54, p. 318).

(2) The correlation of variations.

(See Darwin, Animals and Plants under Domestication,
Vol. 2, pp. 311-332 ; and Brooks, Heredity, p. 157.)

Correlation between associated parts.
Correlation between homologous parts.

Galton's function (See Galton, Proc. Roy.
Soc, Vol. 45, p. 135 ; Weldon, /. c, Vol.

55» P- 234)-

M^ mean, Q = "probable error."

Qa. = the Q of organ A.

Qb = the Q of organ B.

V =z any deviation of organ A from its M.
Xm = mean associated deviation of organ

B from its M.
X = any deviation of organ B from its M.
Ym = mean associated deviation of organ
A from its M.

X». ^ Qb Y,n ^Qa

^=: -— = r, a constant,

Y -^Qa X -^Q,

38

Where the variations in two organs are per-
fectly correlated ^ = -j- i .

Where two organs vary entirely independ-
ently r^ o.

Value of r the same for any given pair of
organs through )ut the species, Weldon.

Value of ;' higher between homologous parts
and between adjacent parts, than between
parts not so related, Weldon, Thompson.

(3) Parallel variation.
Peacocks.
Nectarines.

d. Laws of Racial Variation.

Specific characters more variable than generic.

" A part developed in any species in an extraor-
dinary degree or manner, in comparison with
the same part in allied species, tends to be
highly variable."

Secondary sexual characters.

Usually confined to males.

Often developed in an extraordinary manner

or degree.
Highly variable.

Law of " equable variation."

" The species of the larger genera in each coun-
try vary more frequently than species of the
smaller genera."

'• Wide ranging much diffused and common spe-
cies vary most."

Crossing leads to variability.

39

e. The Inheritance of Variations.

The force of heredity.

Capriciousness of heredity.

(See above VI. 6, iii.)

Racial variations arise from the inheritance of
individual variations.

ii. The Struggle for Existence.

(Benjamin Franklin, Observations concerning the Increase of
Mankind, Collected Works, Vol. 2, p. 231 ; Malthus, Essay
on the Principle of Population, 1803 ; Darwin, Origin of
Species, Chap. Ill; Wallace, Darwinism, pp. 14-40; Hud-
son, The Naturalist in La Plata, pp. 59-68 ; Brehm, From
North Pole to Equator; Romanes, Darwin and after Darwin,
Vol. I, pp. 259-270.)

The apparent peace in nature.

Species on the average contain a constant number of
individuals.

This in spite of the tendency to increase in geometri-
cal ratio.

Examples — The elephant.

Man.

The carrion fly.

The common birds.
Effect of introduction into a free field.
Our common weeds.
The English sparrow in our country.
The horses and cattle of the plains.
Rabbits in New Zealand.
Hogs in Central America.
The tendency of plants to increase.
The great number of seeds produced.

40

European thistles on the La Plata.
Cotton weed in the tropics.
White clover in New Zealand.
Other plants in New Zealand.
Lantana in Ceylon.

The lack of increase ordinarily, in spite of the number
of young produced, shows that there must be a
large death rate.

The checks on population and the struggle for exis-
tence.

a. The scarcity of food.

The struggle for food between individuals of the
same species.

Between different species.

Examples — The trees in a forest.

Darwin's experiment with the turf.

The beech and birch in Denmark.

The water cress and the willows.

b. Enemies.

Dependence of herbivorous animals upon plants
and of carnivorous animals upon herbivorous
ones.

The struggle to escape being eaten.

Seeds.

Absence of trees on the Pampas.

The struggle on the river banks.

Darwin's example of the game animals.

P^ishcs.

Parasites.

41

c. Unfavorable climate.

The winter of 1854-55 in England.

Recapitulation.

The Complexity of the Struggle.

Hypothetical example.

Cats and the crop of clover seed.

Salmon and the inland birds.

Trees on the heath in Staffordshire.
Birth rate proportional to the risk of destruction.

Contrast fishes and petrel.

The passenger pigeon.

iii. NaUiral Selection.

(Darwin, Origin of Species, Chap. IV ; Wallace, Darwinism,
pp. 102-151, 187-267, and 301-337; Lloyd Morgan, Aninial
Life and Intelligence, pp. 77-121 ; Romanes, Darwin and after
Darwin, pp. 251-378 ; Marshall, Lectures on the Darwinian
Theory, pp. 27-52 and 116-172.)

a. Evidences for the theory.

(i) The observed fact that the struggle for ex-
istence leads to the extermination of forms
less fitted for the struggle and thus makes
room for forms more fitted.

(2) Not a single structure or instinct in the ani-

mal or vegetable kingdom is developed
for the exclusive benefit of another spe-
cies.

Apparent objections : —

Secretion of aphides useful to ants.

Vegetable galls of use to insects.

(3) The efficacy of artificial selection.

(See Romanes, figs. 91-107 ; Marshall, figs. 1-3 ; Bailey,
Plant-Breeding.)

42

Apparent objections : —

The selecting agent differs in natural and
artificial selection.

Varieties produced by artificial selection
differ from true species in not being
mutually infertile.

b. Applications of the theory : —

(i) Adaptations of flowers for fertilization by
insects.

(2) Structures and movements of climbing

plants.

(3) Protective coloring in animals.

(4) Warning colors.

(5) Mimicry.

All of these facts can only be explained by
the theory of natural selection.

c. Criticisms of the theory.

(i) Owen: Figurative language explains nothing.

(2) Duke of Argyll : Natural selection can

produce nothing,

(3) If some, why not all species improved by nat-

ural selection }

(4) Why have not superior forms exterminated

inferior ones inhabiting the same locality }

All the above objections arise from a
misunderstanding of the theory.

(5) Similar organs or structures are met with in

widely different groups.

This is true as to analogy, but never as
to homology.

(6) Beginnings of organs are useless and can-

not be selected.

43

Some organs useful, however slightly de-
veloped.

Change of function.

Correlation of variations.

(7) Difficulty of explaining electric organ in

skate.

An isolated case that probably will be ex-
plained with increased knowledge.

(8) Uselessness of many specific characters.

(9) Cross infertility between species cannot be

due to natural selection.

(10) Free intercrossing renders divergent evolu-
tion impossible.

The last three not valid objections unless
natural selection is regarded as the sole
factor of organic evolution.

iv. Panmixia and the Reversal of Selection.

(Lloyd Morgan, Animal Life and Intelligence, pp. 189-197;
Darwin, Origin of Species, Vol. i, pp. 182-183, and Vol. 2,
pp. 255-263, Amer. Ed. pp. 149-151 and 404-410; Weis-
MANN, Retrogressive Development in Nature, Essays upon
Heredity, Vol. 2, pp. 3-30; Romanes and Lankester, Let-
ters in Nature, Vol. 41, pp. 437-486, 511, 558, and 584, and
Vol. 42, pp. 5, 52, and 79; Romanes, Darwin and after Dar-
win, Vol. 2, pp. 291-306; Weismann, Germinal Selection,
1896.)

Dwindling and disappearance of organs during phy-
logeny.

Inadequacy of the inheritance of the effects of dis-
use as an explanation.

Loss of parts in flowers.

Loss of protective structures in animals.

Loss of wings in neuter insects.

L I B R A R Yi3o|

— ,.-^

#/ _ V %/

44

Panmixia, or the cessation of selection, Romanes,
Weismann.

The reduction from survival mean to birth
mean.

Economy of growth and reversed selection, Darwin.

Loss of carapace in parasitic barnacles.

Loss of wings in insular insects.
Difficulty as to the final disappearance of organs.

Reversed selection, Panmixia, Weismann.

Failure of heredity, Romanes.

Germinal selection, Weismann.

v. Sexual Selection.

(Darwin, The Descent of Man, Vol. i, pp. 245-409, and Vol.
2, pp. 1-387 ; Wallace, Natural Selection and Tropical Na-
ture, pp. 338-394; Wallace, Darwinism, pp. 268-300; Ro-
manes, Darwin and after Darwin, Vol. i, pp. 284-335 ! Lloyd
Morgan, Animal Life and Intelligence, pp. 197-209; Brehm,
North Pole to Equator.)

a. The law of battle.

b. The aesthetic sense of birds.

c. Courtship.

Among birds.
Among spiders.

d. Ornamental secondary sexual characters developed
by sexual selection.

e. Evidence.

(1) These characters are confined to the sex that

is active in courtship, almost always the
male.

(2) They are as a rule developed only at matur-

ity and often only during the breeding
season.

45

(3) Are always and only displayed in perfection

during courtship.

(4) Often appear to have the desired effect.

/. Wallace's objections (See Tropical Nature).

(i) Theory can only apply to the more intelli-
gent animals.

(2) Brilliancy of males due to lack of need of

protection, absence of selection.

(3) Brilliancy of males correlated with greater

vigor, therefore preserved by natural se-
lection.

(4) No evidence of females being affected by

display.

(5) Display merely due to general excitement.

(6) Sexual selection nullified by natural selec-

tion.

(7) Every bird finds a mate sooner or later.

(8) Impossibility of uniformity of taste in all

females of a species.

g. Romanes's reply.

(i) Pattern of colors cannot be due to vigor,
e. g. Peacock, Angus phaesant.

(2) Remarkable elaboration of structures, e. g,

the Bell-bird.

(3) Objection 7 begs the question.

(4) Decorative (as distinguished from brilliant)

coloring, melodious song (as distinguished
from cries), arborescent antlers (as dis-
guished from merely offensive weapons),
and the Hke, cannot be explained by nat-
ural selection.

46

vi. Isolatio7i or Segregatioji.

(Lloyd Morgan, Animal Life and Intelligence, pp. 99-112;
Romanes, Physiological Selection, Journ. Linn. Soc, Zool.,
Vol. 19, pp. 337-411, 1886; GULICK, Divergent Evolution
through Cumulative Segregation, Journ. Linn. Soc, Zool.,
Vol. 20, pp. 189-274.)

The difficulties of Natural Selection viewed as the
sole cause of evolution.

(i) The difference between natural species and
domesticated varieties in respect of fer-
tility when crossed.

(2) General inutility of specific characters.

(3) Swamping effects of intercrossing.

Importance of Segregation, or the prevention of in-
tercrossing, in the origin of domesticated varieties.

Modes of Segregation in nature.

Geographical.

Variations of habits.

Preferential mating.

Particulate inheritance.

Physiological isolation.
Evidences for physiological isolation.

Immense number of variations.

Sexual organs most variable.

Variation often toward sterility.

47
vii. Inheritance of Acquired Chaj'acters.

(Lamarck, Philosophic Zoologique; See also Translation in
American Naturalist, Vol. 22, pp. 960-972 and 1054-1066;
Darwin, The Origin of Species; Darwin, Animals and
Plants under Domestication; Eimer, Organic Evolution;
Cope, Origin of the Fittest ; Osborn, Palaeontological Evi-
dence for the Transmission of Acquired Characters, Amer.
Nat., Vol. 23, pp. 561-566; Ball, Are the Effects of Use and
Disuse Inherited.' Osborn, Are Acquired Variations Inher-
ited.' Amer. Nat., Vol. 25, pp. 191-216; Spencer, The Prin-
ciples of Biology, Vol. i, pp. 402-475; Spencer, Factors of
Organic Evolution; Weismann, Essays upon Heredity, Vol.
I, pp. 387-448; Poulton, Theories of Evolution, Proc. Bos-
ton Society of Natural History, Vol. 26, pp. 371-393 ; Spen-
cer, The Inadequacy of Natural Selection, Contemporary
Review, Vol. 63, pp. 153-166 and 439-456; Romanes, Mr.
Herbert Spencer on " Natural Selection," I.e., pp. 499-517;
Spencer, Professor Weismann's Theories, /. c, pp. 743-760;
Romanes and Hartog, The Spencer-Weismann Controversy,
I.e. Vol. 64, pp. 50-59; Weismann, The All-Sufficiency of
Natural Selection, /. e., pp. 309-338 and 596-610 ; Spencer,
A Rejoinder to Professor Weismann, /. u, pp. 893-912 ; Ro-
manes, Weismannism ; Romanes, Darwin and after Darwin,
Vol. 2 ; Hyatt, Phylogeny of an Acquired Characteristic,
Proc. Amer. Phil. Soc, Vol. 32, pp. 349-647, 1894 ; Cope, Pri-
mary Factors of Organic Evolution; Bailey, Plant-Breed-
ing-)

a. Evidence in favor of the inheritance of acquired
characters.

(i) Indirect evidence.

"Appearances."

Apparent uselessness of nascent adapta-
tions (palaeontology).

Reflex actions.

Instinct.

(2) Direct evidence.

Inherited effects of use and disuse.

Climate.

Food.

(3) Experimental evidence.
Brown-Sequakd's experiments.

48

Repetition of these by Romanes.
Experiments on plants, Hoffmann, Car-

RIERE, BUCKMAN.

b. Evidence against the inheritance of acquired char-
acters.

(i) Indirect evidence.

Theoretical difficulties in the way of inher-
itance of acquired characters.

(2) Direct evidence.

Migration of germ-cells.

Early differentiation of germ-cells.

(3) Experimental evidence.

Negative results obtained by Romanes.

Graft-hybridization.

Transplantation of ovaries.

Transfusion of blood.

Transplantation of ova, Heape and Buck-
ley.

Amputations, Weismann.

c. Summary.

Small amount of evidence in affirmative.

Inheritance of acquired characters involves a theory
of pangenesis.

viii. Cofistttntional Tendency.

(MiVART, Genesis of Species ; Hyatt, Genesis of the Arietidae,
Smithsonian Contriljutions, 673, 1889; Hyatt, Bioplastology
and the Related branches of liiologic Research, I'roc. l^oston
Society Natural History, Vol. 26, pp. 59-124 ; Weismann, Ger-
minal Selection.)

Innate tendency, Mivart.
Perfecting principle, Nacem.

49

Youth, maturity, and senescence of species, Hyatt.

Germinal selection, Weismann.
General Conclusions.

The prime factors in organic evolution are Variation
and the Struggle for Existence with the resulting
Natural Selection.

Other important factors are Sexual Selection, Segre-
gation, Panmixia, and the Reversal of Selection.

Supposed effects of the inheritance of acquired char-
acters and of constitutional tendencies improbable.

The doctrine of evolution well founded in fact and es-
tablished in theory.

IX. DEDUCTIONS FROM THE THEORY OF

EVOLUTION.

Ontogeny and phylogeny.

Significance of Sex.

Origin of death.

Color.

Relations of animals and plants.

Social evolution.

Philosopical results.

" There are more things in heaven and earthy Horatio,
Than are dreamt of in your philosophy.^''

/

SYLLABUS OF LECTURES IN THEORET-
ICAL BIOLOGY.

SUPPLEMENT, J 897.

The following section may he substituted for the corresponding one in the
text, pages 17 to 27.

iv. Theories of Heredity and Development.

(For list of references see page 17.)

1. Importance of the subject.

2. Requirements of a theory of heredity.

It must include a theory of variation.

It must inckide a theory of development in the
deepest sense.

It must explain all the phases of development.

It involves some conception of the essential struc-
ture of living matter.

3. The fundamental conceptions in theories of heredity.

4. Animism.

Van Helmont (i 577-1644).

5. Physiological units.

BuFFON (1 720-1 793), organic molecules.

Spencer (1864), physiological units.

Haeckel (1876), plastidules.

Weismann (189 1, 1893), biophors, determinants.

Nageli {1884), micellae, micellar threads.

Darwin (1868), gemmules.

De Vries (1889), pangenes.

BuTCHLi (1892), Andrews (1897), protoplasmic
foam.

Heredity as a form of motion, or as memory.

Spexcer (1864), polarity of the physiological units.
Congenital variations diK' to changes in polarity.
Inheritance of acquired characters thus ex-
plained.

Nageli {1884), morphogenic stimuli transmitted
through micellar threads.

Haeckel (1876), branched wave motion, perigen-
esis of the plastidules. Heredity is memory.

Okr (1893). Heredity is habit.

Cope.

Objections to these theories.

a. Their fanciful character.

b. All founded on the supposed inheritance of
acquired characters.

c. Absence of mechanism.

Pangenesis.

Democratus (400 B. C). Seed of animals formed
by contributions from all parts of tlie body.

BuFFON (1720-1793).

Darwin (1868). Pangenesis of gemmules.
Latent gemmules.
Acquired characters inherited.

Galton (1872). Great number of gemmules.
Their imaginary character.
Experiments on rabbits.
Acquired characters seldom inherited.

Brooks (1876, 1883). Modified pangenesis.

New gemmules formed only under unfavorable
conditions.

Hybrid gemmules induce variation.

Latent gemmules in egg, new gemmules in sper-
matozoon.

Acquired characters not inherited.

De Vries (1889). Pangenes produced by nucleus.
Summary.

8. Idioplasm and trophoplasm,

Nageli (1884). Idioplasm the truly living sub-
stance, trophoplasm its nutritive matrix.

Weismann (1885). Idioplasm restricted to the
nucleus, and distinguished from cytoplasm.

Andrews (1897). Continuous and discontinuous
substance.

9. Somatic idioplasm and germplasm.

Weismann (1883, 1885, 1893). Germplasm dis-
tinguished from somatic idioplasm.

MiNOT (1896). Panplasm.

10. The nucleus as the seat of the germplasm.

O. Hertwig (1875). Fusion of nuclei during fer-
tilization of the egg.

Van Beneden (1883). Equal number of chromo-
somes in male and female pronuclei.

Strasburger (1884). Same process in plants.

GuiGNARD (1891). Fertilization in the lily.
Later observations on fertilization.

BovERi (1887), Hertwig (1890). Maturation.

Pfluger (1883). Isotropism of the egg.

Hertwig (1884). Position of the spindle deter-
mines the plane of cleavage.

Brandt (1877), Nussbaum (1884). Enucleated
fragments.

Verworn, Lillie. Dependence of nucleus upon
cytoplasm.

Haberlandt (1877), KoRSCHELDT (1889), position
of the nucleus in relation to growth and nutri-
tion of the cell.

Hodge. Ganglion cells.

BovERi (1889). Fertilization of enucleated frag-
ments.

1 1. Continuity of the germplasm.

Continuity of germ cells.

Contrast between pangenesis and continuity of
germplasm.

Owen (1849). Continuity of germ cells.

Galton (1872, 1876). Stirp.

Brooks (1876, 1883). Continuity of germ cells
and their contained latent gemmules.

Jager (1869). Continuity of germ-protoplasm
which receives flavor and odor substances from
the body cells.

Nussbaum (1888). Continuity of germ cells.

Weismann (1883). Continuity of germi:)lasm, con-
trasted with continuity of germ cells.
The germ tract. Diptera, medusae, ascaris.
No doubt that there is some form of continuity.

12. Preformation.

The theory of continuity leaves unanswered the

questions of differentiation and variability.
The new aspect of the theory of preformation.

Darwin (1868). Every i')art of the embryo rep-
resented in the egg, by one or more gemmules.

Brooks (1883). Similar theory.

His (1875). Theory of gemmules rejected.
Principle of the differentiation of areas.
Principle of iinccpial growth.

5

Roux (1888). Experiments with frogs' eggs.
Distinction between quantitative and qualitative

nuclear division.
The mosaic theory of development.

De Vries (1889). Intracellular pangenesis.

Differentiation explained by migration of pan-
genes.

Weismann (1893). Inheritance of acquired char-
acters denied.
Dynamical and pangenesis theories rejected.
Variations due to changes in the germplasm.
Amphimixis, the mingling of germplasms.
Id, the unit of germplasm.
The id composed of determinants.
Biophor, the unit of protoplasm.
Migration of biophors.

The process of ontogeny.

Division of the id.
Division of determinants.
Qualitative and quantitative divisions.
Reserve germplasm.

Effect of amphimixis.

Struggle of the ids causing variation.
Homologous determinants.

Homodynamous.

Heterodynamous.
Variation as the result of new combinations

of old characters.

Reversion,

Sexual dimorphism.

Regeneration.

Budding.

Alternation of generation.

Preformation of every detail.

13- Epigenesis.

O. Hertwig (1892, 1894). Doctrine of continuity

accepted.
Control of the cell by the nucleus.
Units of idioplasm, idioplasts representing cell

characters only.
Theory of determinants rejected.
Comparison of organism to a state.

Evidence concerning the mosaic theory.
For the theory : —

Experiments of Roux on frogs' eggs. Forma-
tion of half embryos.

Crampton on Ilyanassa.

E. B. Wilson on normal cleavage of Nereis.

Presence of independently variable parts.

Against the theory : —

a. In normal development.

Lack of correspondence between first cleav-
age plane and any plane of adult bod)-.
Miss Clapp on toad fish.
Morgan on frogs and tclcosts.

•

Variations in cleavage.

H. V. Wilson on sea bass.
Jordan on Amphibia.
E. B. Wilson on Amphioxus.
Three types with all grades between.
All result in normal embryos.

b. Experimental evidence.
Effects of pressure.

Driescii, on cchinoderm eggs,
Hertwig on frogs' eggs.
E. B. Wilson on Nereis.
Morgan on Fundulus.

Isolation of blastomeres.
ZojA, on medusae.
Wilson, on Amphioxus.
Morgan, on Fundulus.
Driesch, on Echinus.
Driesch and Morgan, on Beroe.
LoEB, on sea-urchins.

c. Summary of the evidence.

Result unfavorable to the theory of qualita-
tive divisions.
External conditions a factor in differentiation.

Hertvvig's theory of development.

Effects due to the constitution of the egg,

yoke, shape, etc.
New relations established by cleavage.
" The differentiation of the cell is a function

of its position." (Driesch).
No preformation of the embryo in the ^g^.
Each stage in development determines the

next stage.
Development purely a process of epigenesis.

Driesch (1894). All nuclei equivalent.

Reactions of the idioplasm and the cytoplasm
upon one another.

Pre-existing differences of the cytoplasm con-
dition the activity of the idioplasm in the
different regions of the egg.

Wilson (1896).

Relations of blastomeres not purely mechan-
ical.

Differentiation of cytoplasm in one stage has
a determining influence upon the next.

Nucleus undergoes a change during develop-
ment, but not because of qualitative divi-
sions.

14. General summary.

Two factors in development — the nature of the
idioplasm, and the stimuli affecting it.

Similarity of parent and offspring due to common
origin of germinal idioplasm, and to similar con-
ditions of development.

Changes in conditions affecting germplasm may
induce inlieritable variations.

Balance of evidence favors epegenesis.

Much still to be learned.

ERRATA.

Page 5 add, — Andrews, The Living Substance. Supple-
ment to Journal of Morphology, Vol. 12, No. 2,
1897.
Pages 6, 10, II. For Bovari, ;r«^ Boveri.
Page 12. For Young nv?c/ Yung.
Page 12 add, — Semper, Animal Life.
PouLTON, Colour in Animals.
Sachs, Lectures on the Physiology of Plants. 1S87.

Lecture 39.
Davenport, Experimental Morphology. 1897.
T. H. Morgan, Development of the Frog's Egg.

1897-
Page 15. For Acclimatisation /yv?^/ Acclimatization.
Page 28 add, — Geikie, The Founders of Geology. 1897.
Page 29 add, — Bi:di)ari), Te.xt-book of Zoogeography.

1895.
^^'^'i<^ 35 add, — Bailev, Survival of the Unlike.
Page 46 add, — Romanes, Darwin and after Darwin.

Vol. 3, 1897.
Page 47 add, — Lloyd Morgan, Habit and Instinct ; Os-

IJORN, Organic Selection. American Naturalist,

November, 1897.

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