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THE PRINCIPLES OF
APPLIED ZOOLOGY

The Classification of Living Creatures.

THE PRINCIPLES OF

APPLIED ZOOLOGY

ROBERT A. WARDLE, iM.Sc.

PROFESSOR OF ZOOLOGY, UNIVERSITY OF MANITOBA

Formerly
ASSOCIATE PROFESSOR OF ENTOMOLOGY, UNIVERSITY OF MINNESOTA
LECTURER IN ECONOMIC ZOOLOGY, UNIVERSITY OF MANCHESTER

Mitb Jllustratfons

LONGMANS, GREEN, AND CO.
LONDON . NEW YORK . TORONTO

1929

O

&3

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Made in Great Britain.

PREFACE

The difficulties experienced by the unfortunate fisherman of
Bagdad, in persuading a djinn to retire within the limited
confines of a brass bottle, were scarcely more pronounced than
those which face the zoologist who attempts to compress the
vast accumulation of applied zoological knowledge into a
summary, sufficiently restricted to pass into the brass bottle
of the publisher's limits, yet sufficiently informative to be of
value and interest not only to the student of zoology, but to the
student of agriculture, or of medicine, and to the general reader.

The difficulties of the task account possibly for the fact
that previous works dealing with Economic or Applied Zoology
as a whole, can be counted on the fingers of one hand, whereas
as regards component branches — Agricultural Entomology,
Medical Entomology, Sea Fisheries, Livestock Breeding, or even
Fur Farming — books are numerous and, on the whole, good.

Such a general summary is possible within compact limits,
only if discussion and description be limited to general problems
and to general principles. To the general reader, a mass of
detail concerning the classification, morphology, or economic
control of animal life is not essential to his comprehension of
the fundamental problems which concern his food supply,
clothing, health, and so on. As regards the student, whether
of agriculture, medicine, or zoology, desirous of more detailed
information, the comprehensive bibliography which concludes
the book should be a copious source from which to select
according to his needs. jj&

The author must acknowledge gratefully the advice and
active help of the late Mr Philip Buckle of the University of
Durham, and of Dr Geoffrey Lapage of the University of
Manchester, in the arrangement of material ; the help of Miss
Ruth Charles worth, Miss May E. Goodwin, and Miss Sybil
Wildman and Miss Mary Parkes of the University of Man-
chester, and of Mr H. Gray and Mr G. A. Mail of the University
of Minnesota, in the preparation of the illustrations ; and the
generous help afforded by the following in granting permission
for the use of figures from their publications : —

Professor A. Alcock, F.R.S., Colonel W. Byam, Mr R. J.
Daniel, Professor Clifford Dobell, F.R.S., Professor Cossar
Ewart, F.R.S., Dr W. T. Hornaday, Mr H. H. King, Professor
C. A. Kofoid, Professor R. Kudo, Professor R. T. Leiper,
F.R.S.. Professor R. Newstead. Professor G. H. Nuttall,
F.R.S., Professor CM. Wenyon.

Vll

2.G755"

viii PREFACE

Messrs Arnold & Co., for permission to adapt Figs. 27 and
37 of Meek, " Migration of Fishes."

Messrs John Bale, Sons & Danielsson, for permission to
adapt Figs. 4 and 6 from Dobell, " Amoeba? Living in Man,"
and Dobell and O'Connor, " Intestinal Protozoa of Man."

Messrs P. Blakiston's Son & Co., Philadelphia, for permission
to use the first four subjects of Fig. 25, modified from " Stitt's
Practical Bacteriology."

The British Museum, for permission to adapt Fig. 1 of
Austen, " Handbook of Tsetse Flies," and Figs. 3, 4, and 5
of the " Guide to Whales."

Messrs Macmillan & Co. Ltd., for permission to adapt
Fig. 90 of Graham Kerr, " Zoology for Medical Students."

Messrs Macmillan & Co. Ltd., London, and the Macmillan
Company of New York, for permission to adapt Fig. 1 (diagram
of a cell) from Wilson, " The Cell in Development and Heredity'1
(1925).

The Manchester University Press, for permission to use
Figs. 4 and 5 of Wardle and Buckle, *; Principles of Insect
Control," and to use text material from that book.

Messrs Masson et Cie, for permission to use Figs. 577, 580,
585, 589, and 591 of Brumpt, " Precis de Parasitologic"

Messrs John Murray, for permission to use Figs. 214 and 215
and Chart V. of Fowler, " Science of the Sea."

Messrs Oliver & Boyd, for permission to adapt Figs. 8, 9,
and 12 of Wallace, " Farm Livestock of Great Britain."

The Oxford University Press, for permission to copy the
Tsetse Fly in Fig. 8 from By am and Archibald, " Practice of
Medicine in the Tropics."

Messrs Paul Parey, for permission to adapt Figs. 37 and 38
from Keller, " Naturgeschichte der Haustiere."

Mr Henry H. TufTord of the Tuplin-Dalton Silver Fox
Company, Des Moines, Iowa, and the Editor of the American
Fox and Fur Farmer, St Peter, Minnesota, for permission to
reproduce Plate II. from his article on " Ranch Construction,"
in that journal.

The University Press of Liverpool, for permission to adapt
Figs. 15, 21, and 24 of Stephens and Christopher, ''Practical Study
of Malaria." Also for one figure from Newstead, Evans and
Potts, " Guide to the Study of the Tsetse Flies," and the figure
of a Sperm Whale from R. J. Daniel, " Animal Life in the Sea."

University of Manitoba,
September 1928.

CONTENTS

PREFACE .

LIST OF ILLUSTRATIONS

PAGK

vii
xi

PART I
MEDICAL AND VETERINARY ZOOLOGY

CHAPTER

I. Protozoa : The Biology and Classification
II. Protozoa : The Distribution .

III. Protozoa : Enteric Forms

IV. Protozoa : Hsernatophilous Forms
V. Helminthes : The Flukes

VI. Helminthes : The Tapeworms
VII. Helminthes : The Roundworms
VIII. Helminthes : The Pathological Aspect
IX. Arthropoda and Disease : Toxic Inoculation
X. Arthropoda and Disease : Entomiasis .
XI. Arthropoda and Disease : Mechanical Transmission
XII. Arthropoda and Disease : Cyclical Transmission

I

13
21
33

46

58

72

89

97

103

115

126

PART II
AGRICULTURAL AND HORTICULTURAL ZOOLOGY

XIII. Soil Organisms .....

XIV. Insect Pests : The Categories
XV. Insect Pests : The Categories — Continued

XVI. Insect Pests : The Life-Cycle .

XVII. Insect Pests : The Distribution

XVIII. Insect Pests : The Behaviour

XIX. Insect Pests : The Mortality Factors

ix

145
158
177
195
205
213

99s*

CONTEXTS

CHAPTER

XX. Vermin Repression
XXI. Bird Encouragement
XXII. Animal Domestication .

XXIII. Types and Breeds of Farm Animals

XXIV. Livestock Breeding

PAGE

230
239
250
262
276

PART III
ANIMAL INDUSTRIES

XXV. Bee-Keeping

XXVI. Sericiculture and Lac Culture .
XXVII. Fresh- Water and Estuarine Fisheries
XXVIII. Inshore Fisheries .
XXIX. Offshore Fisheries
XXX. Whaling and Sealing
XXXI. Fur- Bearing Animals
XXXII. The Fur Trade .

XXXIII. Fur Farming

XXXIV. Animal Conservation

285
294
300
313
326
336
347
356
365
377

PART IV

BIBLIOGRAPHY

INDEX

387
415

LIST OF ILLUSTRATIONS

FIG.

The Classification of Living Creatures

1. The Protistan and Metazoan Types of Cell

2. Types of Mastigophora

3. Types of Sporozoa

4. Enteric Infusoria

5. Types of Neosporidia

6. Enteric Amoeba?

7. Enteric Mastigophora

8. Life-Cycle of Trypanosoma gambiense

9. Life-Cycle of Plasmodium

10. Types of Spirochetes .

11. Reproductive System of a Distomid Fluke

12. Life-Cycle of Schistosoma haematobium .

13. Reproductive System of a Tapeworm Proglottid

14. Diagnostic Features of the More Important Tapeworm Genera

15. Types of Metacestode

16. Life-Cycle Stages of Ancylosto)na .

17. Helminth Eggs occurring in Human Faeces

18. Posterior Larval Spiracles of some Common Muscid Flies

19. The Principal Genera of Itch Mites

20. Life-Cycle Stages of Culicine and Anopheline Types of Mosquito

21. Diagnostic Features of Culicine and Anopheline Mosquitoes

22. The Characteristics of Gloss Ina

23. Externa] Genitalia of Glossina

24. The Morphological Features of a Hard Tick

25. Types of Soft Tick and Hard Tick

26. Types of Soil Insects .

27. Types of Insect Pest .

28. The Spread of the Cotton Boll Weevil

29. Types of Insect Pest .

30. Types of Insect Pest .

31. Types of Insect Parasite

PAGE

Frontispiece
2

8

10

12

19

25

29

37

40

44

47

55

59

63

69

79

93

105

112

128

131

136

138

141

143

153

160

172

178

181

227

XI

Xll

LIST OF ILLUSTRATIONS

pie.

PAGE

32. The Grey Rat, Black Rat, and Pocket Gopher

. 235

33. The Diet of the Starling in North America .

. 241

34. Berlepsch and Thirlinere Types of Nesting Box

. 246

35. Method of Hanging Bird Boxes .

. 247

36. A Good Type of Bird Food Station .

. 248

37. Types of Asiatic Cattle .....

. 255

38. Types of Sheep .......

. 257

39. Light and Heavy Types of Horse

. 263

40. Types of Wild Cattle, Dairy Cattle, Beef Cattle .

. 269

41. The Bacon Pig ........

. 274

42. The Frame Hive

. 287

43. The Sudan Hive

.289

44. A Salmon Scale ......

. 303

45. Types of Fishing Net

. 305

46. A Fish Trap

. 307

47. Migrations of Herring and Pilchard in Eastern Atlantic

Waters . 321

48. The Atlantic Fishing Banks ....

. 328

49. Types of Whales ......

. 338

50. Types of Seals and Sea Lions ....

. 342

51. Types of Fur- Bearing Animals ....

. 348

52. The Casing of Pelts

. 360

53. A Type of Fox Farm

. 371

54. Types of Fox Farm Formations ....

. 373

55. The Extermination of the Bison in North America

. 380

THE PRINCIPLES OF APPLIED

ZOOLOGY

PART I
MEDICAL AND VETERINARY ZOOLOGY

CHAPTER I

PROTOZOA : The Biology and Classification

The aspect of biology which concerns itself with the micro-
organisms of stagnant water, of infusions, of the animal gut,
and so forth, owes much to the conception of animal and plant
structure referred to generally as the cell theory. Once the
old idea that a cell was an enclosed portion of an animal or
plant tissue, comparable to a compartment of a honeycomb,
had become superseded by the more rational view that regards
it as a mass of protoplasm controlled by a complex cell organ,
the nucleus, it became possible to draw direct comparisons
between the cell units of animal and plant tissues and the
individuals of that extensive assemblage of microscopic creatures
formerly labelled vaguely as ' infusoria ' or ' animalcuhe,"
but now generally referred to as Protista.

It became possible, in fact, to postulate the existence of
unicellular organisms and to compare their biological features
with those of the accepted animals and plants.

A typical Protiston, such, for example, as the common
laboratory type Amoeba, if not possessing necessarily a cell
wall nor a peripheral coagulation of the protoplasm, is essentially
a mass of protoplasm under the control of a nuclear structure
which in many cases is almost indistinguishable from the nucleus
of a tissue cell. Reproduction, too, may be like that of the
tissue cell, a simple division of the individual into two, preceded
by a complicated series of nuclear changes.

There are, however, important differences between the

i l

2 THE PRINCIPLES OF APPLIED ZOOLOGY

Protiston and the tissue cell. In the first place, the protistan
nucleus instead of being of the granular type, the form it usually

.5

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03

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a

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eg
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o

takes in tissue ceils, that is to say instead of consisting of
minute fragments of stainable chromatin distributed over a
non-stainable network of linin, may be of the karyosomatic or
vesicular type (Fig. 1 ) in which the greater part of the chromatin

PROTOZOA: BIOLOGY AND CLASSIFICATION 3

forms a single central mass referred to as the karyosome or
chromatin nucleus, and situated in a vacuole containing
fluid.

In the second place, the chromatin of the Protiston is not
always confined to the nucleus but may occur also as extra-
nuclear granules in the cytoplasm ; that is to say, in the cell
substance outside the nucleus. Such granules, derived from
the nucleus, are termed ' chromidia" In certain phases of
the protistan life-cycle, the whole nuclear structure may be
represented by such scattered granules rather than by a central
aggregation of them. In bacteria, such a chro?nidial condition
is the rule. In other Protista, however, such scattered granules
indicate a departure from the normal. They may represent
products of cell metabolism, derived either from the nucleo-
plasm or from the cytoplasm ; they may be decomposition
products of the nucleus in a dying or dead cell ; or they may
represent a stage in the formation of a number of nuclei from
a single nucleus prior to cell division.

The coexistence of chromidia with a definite nucleus has

been explained by Hertwig on the hypothesis that the relation

N
of nucleus to cytoplasm, in other words — , tends to be a con-

stant ; so that if the nuclear matter increases in bulk faster

N
than the cytoplasm does, the — ratio is maintained by the

\j
nucleus giving up its surplus chromatin in the form of chromidia ;
if, however, the ratio be disturbed by excess of cytoplasm,
the absorption of chromidia by the nucleus will bring about
adjustment.

In the third place, the resemblance between Protiston and
tissue cell is morphological rather than physiological. The
Protiston is physiologically an independent entity, comprising
within itself all the various metabolic activities — locomotion,
assimilation, growth, excretion, reproduction, and so forth —
which are characteristic of the phenomenon called life.

The typical tissue cell, on the other hand, is a specialised
unit, possibly excretory or protective or absorptive or sensory,
but never physiologically complete, never capable of living a
life apart from its co-partners in the metazoan body. Now
these differences which do undoubtedly exist between Protista
and tissue cells have caused some biologists to criticise the
comparison made above between a Protiston and a metazoan
tissue cell. They assert, in fact, that Protista are not com-
parable with Metazoa ; that they are non-cellular and represent

4 THE PRINCIPLES OF APPLIED ZOOLOGY

a type of organisation quite different from that seen in multi-
cellular organisms ; and that they are not by any means simple,
and not necessarily primitive.

It seems clear that this view regarding non-cellularity is
based upon two misconceptions, namely, that a cell is a sub-
division of an animal or plant tissue, and that the terms
homology and analogy are identical.

It can be conceded that if the term cellular implies sub-
division, then the protistan body, since it is not subdivided,
is non-cellular ; but the view that laid stress upon the cell wall
and regarded a cell as a subdivision, has long been replaced by
the conception of a cell as a unit mass of protoplasm controlled
by a nuclear structure, a dynamic centre as essential to it as the
brain is to the body of man. A cell wall is not obligatory,
nor need a cell be a subdivision, unless the ovum or spermatozoon
of an animal are also to be regarded as non-cellular. Again,
the statement that the Protiston is homologous to a tissue cell
implies, according to the accepted biological definition of
homology, merely morphological and embryological resem-
blance. It does not imply functional resemblance, as would
the use of the term analogy, and even the most ardent advocate
of unicellularity would not assert that Protista were analogous
to tissue cells. Unicellularity implies in fact that a Protiston
resembles morphologically and embryologically the cell unit
of a multicellular tissue, but physiologically it must be com-
pared to the v/hole multicellular organism of which the tissue
forms a part.

In structural detail, among Protista, there is a considerable
range of variation. There are forms which, although un-
doubtedly not so simply constructed as was formerly supposed,
do seem to comprise merely a nuclear mass embedded in a non-
differentiated cell protoplasm. There are also forms which
possess definite cytoplasmic structures, conveniently referred
to as ' organelles," which carry out the various functions of
the organism, locomotion or assimilation, or so forth.

Broadly speaking, the way of life is either plant-like or
animal-like.

The protistan individual may behave in every respect like
a minute plant, may have a rigid cell wall of cellulose, may
be immobile, may contain the pigments chlorophyll or xantho-
phyll which enable the plant to synthesise its carbohydrate
requirements from the atmospheric carbon dioxide and the
soil water. That is to say, the Protiston may be holophytic.

On the other hand, however, such pigments may be lacking,

PROTOZOA: BIOLOGY AND CLASSIFICATION 5

and the organism, unable to avail itself of solar energy, will
either have to ingest the insoluble proteins and carbohydrates
and fats of animal and plant tissues and deal with them by
the help of its own internal ferments, or will have to avail itself
of the soluble food-stuffs — amino acids and sugars — produced
by bacterial action or by the action of ferments poured out of
itself upon animal and plant tissues.

That is to say, it will have to be holozoic, a devourer of other
organisms, or it will have to be saprobiotic, a frequenter of
decaying plants or animals, or it will have to be parasitic, an
absorber of the nutritive fluids of other plants or animals.
Quite obviously a holophytic, saprobiotic, or even parasitic
Protiston is not absolutely in need of a mouth nor of organelles
for catching food or for rapid locomotion. The holophytic
organism requires the necessary light -absorbing pigment —
chlorophyll, xanthophyll, haematochrome — whatever it may
be, and requires in addition, if environmental conditions be
favourable, merely a sufficiency of water, mineral salts, and
sunlight. Its cell wall can be of rigid cellulose without any
aperture whatever for food ingestion.

The saphrophytic organism can take in its nutritive require-
ments in soluble form by osmotic transference through the
outer protoplasmic layer, and requires no mouth. Even many
holozoic forms manage perfectly well without definite apertures
for food ingestion. Amoeba, for example, can take in food
particles through any portion of its body surface ; the food
particles, if in contact with the amoeba, may be sucked into the
body without apparently any movement on the part of the
animal, but usuallv the amoeba either flows around the food
particle and engulfs it, or sends out finger-like processes of its
body substance, so-called " pseudopodia," which encircle and
absorb the prey.

Now the amoeba is a crawling organism, and its scope as a
predatory animal is consequently limited.

A successful predator must be speedy ; in an aquatic medium
it must be a fast swimmer ; but organelles for fast locomotion
involve the presence of a firm, limiting cell wall, a morphological
condition which prohibits food ingestion at any point except
through a definite mouth or body- wall pores.

Since, therefore, a sufficiency of suitable food is essential
to the organism, the evolution of organelles of locomotion has
been accompanied in Protista by the evolution of a definite
mouth and of structures for inducing food particles to enter
such a mouth.

6 THE PRINCIPLES OF APPLIED ZOOLOGY

The evolution of speed, in advance of the condition existing
in the amoeboid type of organism, has been accomplished by
the acquisition of one or other of two very different types of
locomotor organelles.

In one large group of Protista the locomotor structures
consist of one or more flagella, whip-like extensions of the
protoplasm which can carry out lashing movements. In
another group of Protista occur slender, hair-like organelles
termed cilia.

Such cilia are usually very numerous, forming as it were
a furry coating to the organism, and are so co-ordinated as to
produce definite waves of motion, each cilium in a longitudinal
row contracting slightly later than the one in front of it.

Reproduction in Protista is an extremely complicated process.
It may be noted that there is always some form of body cleavage
into two or more daughter individuals. That is to say, the
whole or the greater bulk of the parent body is used up in the
process of producing progeny. Such division is always preceded
by division of the nuclear apparatus. The nuclear division
may be followed almost immediately by the division of the
individual into two, a process termed binary fission, or the
nuclear divisions may go on for some time unaccompanied by
cell division, so that a multinucleate condition results ; but
ultimately the body breaks up into as many daughter individuals
as there are nuclei, a process which is termed multiple
fission.

The life-cycle may be one of several types.

Reproduction may be asexual, the organism multiplying
by binary or multiple fission.

It may be sexual, the binary or multiple fission being pre-
ceded by a process of fusion between two individuals ; such
fusion may be temporary or it may be permanent ; the indi-
viduals may be morphologically identical or may be greatly
dissimilar, but there is always an interchange of chromatin
or of cytoplasm or of both between the two individuals ; the
process is termed conjugation.

There may be a sexual or conjugation phase interrupting
a series of asexual phases of reproduction, or there may be
definite alternation of one sexual phase with one asexual phase.

Classification of Protista. — It is usual to subdivide the
Protista into Bacteria., Protozoa, and Protophyta. These
are purely terms of convenience. In fact there are many
objections to such subdivision.

Bacteria, admittedly, are readily separated from the others,

PROTOZOA: BIOLOGY AND CLASSIFICATION 7

but it is extremely difficult, if not actually impossible, to draw
a hard and fast line between the other two groups. It is easy
to assign to the plant kingdom any Protiston which has a
formed nucleus and cell wall of cellulose, which possesses
chlorophyll or an allied pigment, and which lacks organelles of
locomotion and food prehension.

Similarly, it is easy to group with the animals all Protista
that possess a formed nucleus, a mouth and locomotor organelles,
and which are holozoic.

There will still remain, however, a large number of forms
which cannot properly be classed either with Protozoa or with
Protophyta ; forms in which a firm cell wall and chlorophyll
pigment are accompanied by eye spots and locomotor
organelles.

To create for such debatable creatures a separate subdivision,
such as Haeckel suggested when he divided unicellular organisms
into Protozoa, Protophyta, and Protista, would only postpone
the difficulty. There would still remain the difficulty of
deciding whether a creature is a plant, an animal, or a Pro-
tiston ; the use of the term Protista in such a manner would
merely create three alternatives as against the original two.

Using the term Protozoa, therefore, to comprise unicellular
organisms where a definite nucleus is present and where meta-
bolism is usually of the animal type, we may divide the group
into four classes.

The Sarcodina are comparatively large forms where no
definite cell wall is present, and in which locomotion is carried
out by temporary extrusions of the living protoplasm termed
pseudopodia.

Speaking very generally, there are two types of sarcodine
structure : —

(a) The Rhizopod type, represented by such genera as
Amoeba, Arcella, Difflugia of fresh waters and by the Fora-
minifera of the high seas, where the pseudopodia are either
blunt and finger-like in form, or form an irregularly branching
network ; this type is an adaptation to a creeping existence
either upon a muddy pond bottom or upon a surface film.

(b) The Actinopod type, represented by the Heliozoa of
fresh water and the Radiolaria of the high seas, in which, as an
adaptation to a pelagic life, the pseudopodia are stiff, radially
arranged, and unbranched.

The Mastigophora comprise an enormous range and variety
of forms which have explored every biotic resource ; very
many possess chlorophyll and are holophytic ; other forms,

8

THE PRINCIPLES OF APPLIED ZOOLOGY

r^~

Copromonas subtilis
(after Dobell)

— FL0.gclbt.7n

KiTielon uclcus

Rhixoplast

Nucleus

- Flagellum on edge
of undulating membrane

Herpetomonas muscse dome/sticae
(after Swezy)

Trophon ucleus

Kinctonueleus

Trypanosoma evansi

Crithidia
leptocoridis

(after Swezy)

Kin etonucleus

Trophonucleus

Lei sh mania
donovani,

in an endothelial cell

Trophonucleus

Leishmania
donovani

Fig. 2. — Types of Mastigophora.

almost indistinguishable from these, are both holophytic and
holozoic ; yet others, laeking chlorophyll, are saprobiotic
and swarm in sewage, animal excretions, decajdng plant

PROTOZOA: BIOLOGY AND CLASSIFICATION 9

infusions, and the like. Many such forms have passed from
this sphere of action to establish themselves in the animal gut,
or have even adapted themselves to a life in the animal blood
system.

This multifarious assemblage of creatures agrees in that its
members lash their way through a medium, which is always
fluid and sometimes viscid, by the aid of one or more " flagella,"
the basal attachment of which generally necessitates the
presence of a firm, rigid wall cell, and this again precludes the
ingestion of food at any point in the animal's body surface
except through definite openings. Either a short funnel-like
mouth is present or there is no definite mouth at all, and the
nutriment, in this case fluid, is absorbed through pores hi the
cell wall. Where, as in some parasitic forms, the cell wall is
thin, the requisite rigidity of form is supplied by an internal
skeletal rod-like body termed the axostyle.

Co-ordination between locomotor organs, and the connection
of these with the all-controlling nucleus, is attained by a complex
apparatus comparable in some respects to a nervous system
and hence referred to as the neuromotor apparatus.

The flagella, as a rule, arise together at the anterior end of
the animal from a stainable granule termed the blepharoplast,
which again is attached by a stainable thread, the rhizoplast,
to a body on the further side of the nucleus known as the
parabasal body. As to the exact function of this body, some
controversy exists, but the more prevalent view sees in it a
sort of power house for the locomotor organelles. In blood-
frequenting Mastigophora (Fig. 2), this parabasal body is
represented possibly by the so-called kinetonucleus which lies
between nucleus and blepharoplast.

The great contrast that exists between the appearance of a
typical Mastigophoran and a typical Sarcodinan does not
imply that a deep gulf of morphological dissimilarity divides
the two groups. As a matter of fact, many Mastigophora pass
through an amoeboid stage in their life-cycle, and the sarcodine
form Mastigoammba possesses a typical flagellum, yet moves
and feeds in typical amoeboid fashion. There can be little
doubt that the two classes have diverged from a common
ancestral stock.

The Sporozoa is a collection of forms living always inside
other animals and varying from one another very much in
structure, life-cycle, habits, and so forth, but linked together
by the character of spore formation, that is to say, the power
of producing numerous resistant seed-like bodies which can

10 THE PRINCIPLES OF APPLIED ZOOLOGY

resist environmental conditions outside the host until an
appropriate host can be entered again (Fig. 3).

Free parasite
entering red ceif

W;thin red ce/i

Fa r/y stages in
division

Early
stages in
division

Two^daughter parasites

Piroplasma canis, in blood of dog (after Nuttall)

Oocyst of [

Isospora

hominis,

from man

(after Dobell)

Oocyst of

Eimeria wcnyoni, from man

Containing 4 spores each
with <? sporoioites

(after Wenyon)

A typical
Greg-arine

Oocyst of

Eimeria
oxyspora,

from man

Containing 4 spores
each with 2 sporoioites

(after Dobell)

Oocysts of Coccidia
Fig. 3. — Types of Sporozoa.

Spore formation, however, is not a sufficient basis for the
association in one class of such a heterogeneous crowd of
creatures ; it is not different in principle from cyst formation,
and cyst formation occurs in widely divergent Protista ;

PROTOZOA: BIOLOGY AND CLASSIFICATION 11

further, many so-called Sporozoa do not produce spores at all.
It seems certain that the two main subdivisions, the Telosporidia
and the Neosporidia, are quite distinct in origin ; the former
group show affinities with Mastigophora ; the latter group
possess features which suggest descent from Sarcodina.

Typically, there are two phases in the Sporozoan life-cycle: —

(1) A trophic phase, a nutriment absorbing stage, which may
be amoeboid or gregarinoid (worm -like), may be lodged within
a host cell or between host cells, or may be free within some
host cavity. Nutrition is always by osmosis of the host fluids
through the thin cell wall of the parasite. This stage may
multiply and produce other trophic individuals, which are
usually referred to as trophozoites. Such reproduction is non-
sexual and is termed the schizogonous method of reproduction.

(2) A sporont phase, which is a non -feeding stage. This
stage is characterised by the breaking up of the individuals into
gametes or reproductive cells. These fuse in pairs to form a
zygote, as it is termed. The zygote then proceeds to form
around itself a thick cell wall, and may now be termed a spore,
or else its body substance becomes divided into portions, each
of which forms a cell wall and becomes a spore. Within
each spore the protoplasm divides into a number of so-called
sporozoites, which are potentially infective feeding individuals.
The division of a zygote into spores is termed sporogonous
reproduction.

The Telosporidia show a distinct alternation of trophic
and sporont phases in their life-cycle. The Neosporidia show
an overlapping of the two phases, an individual being capable
of undergoing spore formation whilst still in the trophic stage.

The last class of Protozoa, the Infusoria or Ciliata, is a well-
defined and compact group whose members can be considered,
in view of the great complexity of their cell organs, as the highest
of the Protista.

The primitive type of Ciliate is probably the oval gooseberry-
shaped type of creature with terminal mouth and an even coat-
ing of fine hair -like motor organelles termed cilia, whose co-
ordinated movements enable the creature to move with
comparative rapidity. In other forms, however, the mouth
has shifted to the side of the body, midway towards the posterior
pole, and the rows of cilia run obliquely around the body ;
again, in creeping forms, the body has become shaped like an
inverted pie -dish, the cilia being stiff, large, and restricted to
the flattened ventral surface. Other forms, again, are sedentary
and stalked, and the cilia arranged in circles around the free

12

THE PRINCIPLES OF APPLIED ZOOLOGY

end. Nearly all are holozoic and a definite mouth is usually-
present (Fig. 4).

This is an aperture leading into an oesophagus which ends
blindly in the cytoplasm. In the great majority of Ciliata
the mouth aperture is permanently open and the area around
it contains a spiral zone of modified cilia which induce particles
to enter. Further progress down the oesophagus is effected
by the influence of one or more undulating membranes which

Mouth

Mieronueleus

Meg-a nucleus

Food
vacuoles

Contractile
vacuole

Balantidium x 2000

Fig. 4.— Enteric Infusoria.

Nyctotherus x 2000
(After Dobell.)

represent fused rows of cilia ; in certain forms, however, which
inhabit the stomach of ruminant mammals, the mouth can be
closed or opened by a series of rods in the oesophageal wall.

Food debris is evacuated through a pore, the so-called
cytopyge, in the cuticle, but this may only be visible at the
moment of evacuation.

Two nuclei are typically present. There is a large deeply
staining body, the macronucleus, controlling the general
metabolic activities, and a mieronueleus, very much smaller
in size, which is a controlling factor in the sexual phase of
reproduction.

CHAPTER II

PROTOZOA : The Distribution

Protozoa are widely distributed both geographically and
environmentally. The seas and fresh waters of all countries
swarm with an almost infinite variety of unicellular life ; the
surface pools of thawing glaciers and icebergs, the evanescent
puddles produced by the rare and heavy rainstorms upon the
dusty face of the desert, alike are populated with Protozoa ;
there is scarcely any form of soil which will not, when moist,
give evidence of the presence of these creatures ; the very rocks
of the earth's crust are, in some localities, cemented aggregations
of fossilised Protozoa ; there is probably no animal which does
not act as involuntary host to myriads of them.

Nor is it necessarily the case that geographically isolated
areas possess physiologically isolated protozoan faunas. World-
wide occurrence of a particular genus or species is a phenomenon
common in the distribution of this group. The protozoan
species of a Lancashire pond will vary little, if at all, from the
fauna of a pond in Minnesota or elsewhere.

Now such cosmopolitan distribution is attainable by an
animal or plant only if, in the first place, its physiological
mechanism be sufficiently plastic to permit adjustment to a
wide range of environmental fluctuations — different degrees of
osmotic tension, of temperature, of food-stuff distribution, and
so on ; and, in the second place, if it possesses exceptional
opportunities for migration.

Among Protozoa, such conditions are fulfilled particularly
by very many of that vast assemblage of forms whose normal
habitat is fresh water, and it is precisely to this group that the
most cosmopolitan Protozoa belong.

It must be noted, of course, that however adaptable a race
of Protozoa may be to changes of its environment, it will not
readily adapt itself to changes which are outside the normal
experience of the race. Temperatures above 40° C, or sudden
transitions, for example, to distilled water or to chemical
solutions, are usually fatal. It would be a matter of great
surprise if they were not. If, however, such transitions be

]3

14 THE PRINCIPLES OF APPLIED ZOOLOGY

allowed to occur gradually, the race can be educated to with-
stand conditions extremely different from those to which it
normally is subjected. Fresh - water Protozoa have been
successfully acclimatised to saline water, to alcohol, even to
solutions of corrosive sublimate.

Physiological plasticity is a sine qua non to the existence of
forms whose normal habitat is fresh water sufficiently shallow
to be influenced by meteorological changes ; pools and ponds
and puddles, in fact, where temperature, osmotic tension, and
food-stuff distribution are fluctuating factors of existence.
Such forms possess two physiological weapons with which to
meet the menace of fluctuating environment ; defence and
attack are personified by those antithetic phenomena— encyst-
ment and rapidity of reproduction — representing, as it were, the
trough and the crest of the metabolic wave.

Should environmental conditions fluctuate, so to speak,
beyond the limits of endurance, the organism encysts ; that is
to say, its activity ceases, its shape becomes spherical, and,
in accordance with the laws governing surface tension, it loses
much of its tissue fluid so that its tissues shrink, increase in
viscosity and opacity, and there occurs a peripheral coagulation
of protoplasm to form a protective membrane which may be
further strengthened by a carbohydrate secretion.

Such a cyst is extremely minute, and it is extremely resistant,
easily withstanding comparatively low and high temperatures.

It adheres readily to particles of mud or of vegetation, and
is thus easily distributed by birds and amphibia, fishes and
water insects, or by the wind. However dry the external
environment may be, the cyst wall is sufficient to prevent
evaporation of the precious tissue fluid. It can endure, for years,
conditions which would immediately kill the unencysted form,
yet upon the return of favourable conditions of moisture and
temperature, however brief their duration, the cyst will liberate
the active organism which can then proceed to feed, to grow,
and to multiply, until the gradual or sudden onset of unfavour-
able conditions forces it to encyst again.

Encystment, however, as indicated previously, is not
necessarily a passive adaptation to adverse conditions of life.
It may be a normal incident in the life-cycle of the animal.
Particularly is this the case where the life-cycle shows an
alternation between sexual and non-sexual phases of repro-
duction.

The phenomenon is not confined to fresh- water forms of
Protozoa. It is almost universal among internally parasitic

PROTOZOA : THE DISTRIBUTION 15

forms. Such forms, however, are limited in distribution owing
to their dependence upon the distribution of the host. If the
host, however, be a type such as Homo sapiens, which is
cosmopolitan in distribution, there is much probability that
the internal protozoan fauna will be specifically similar, what-
ever the geographical distribution. More knowledge concern-
ing this question is required. Among marine forms, on the
other hand, the phenomenon of encystment is not commonly
met with. With them conditions of life seem to be more
equable ; benthic or bottom-dwelling forms are not subject
to very great fluctuations of temperature ; pelagic or surface-
dwelling forms can adjust themselves to environmental fluctua-
tions by vertical ascents and descents. At any rate, apart from
a few world-wide forms, Noctiluca, for example, cosmopolitanism
has not been demonstrated as a common phenomenon among
marine Protozoa. Possibly further investigations will con-
tradict this.

So far as present knowledge goes, however, we can distinguish
between cold water and warm water forms, between Indian
Ocean and Atlantic forms.

We may conveniently regard Protozoa, from the point of
view of environmental distribution, as falling into four ecological
groups : —

(a) Limnobiotic or fresh- water forms.
(6) Halobiotic or marine forms.

(c) Phytobiotic forms, associated intimately with plants.

(d) Zoobiotic forms, associated intimately with animals.

Saprobiotic forms, associated with decomposing organic
matter, and geobiotic forms or terrestrial forms, may be regarded
as sub-groups of (a).

Limnobiotic Protozoa. — The term " fresh-water Protozoa '
is somewhat of a misnomer.

Fresh water, in the usual sense of the term, as typified by
running water, springs, town water supplies, is singularly free
from Protozoa, owing to its freedom from bacterial life and from
suspended organic matter. On the other hand, stagnant water
foul with organic decay, or sewage or liquid manure, affords
optimum conditions to Protozoa. In such a medium they
abound. Many forms are omnivorous, absorbing any kind of
organic matter which is within their powers of prehension.
Others are gourmets, selecting with epicurean caprice only
Diatoms, Oscillarise, or Bacteria.

From bacteriophagous forms are derivable the great majority

16 THE PRINCIPLES OF APPLIED ZOOLOGY

of so-called terrestrial or moist earth Protozoa, to be discussed
more fully in a later chapter.

From omnivorous forms, very many Protozoa that only
frequent decaying organic matter are possibly derived.

The true saprobiote, however, is an osmotic feeder, to whom
organic compounds in solution are necessary, and this type
has possibly descended from holophytic forms. Such out and
out saprobiotes as Chilomonas and Polytoma have many similar
holophytic relatives. Very many green forms frequent foul
fluids rich in the dissolved products of organic disintegration
and supplement photosynthetic and osmotic methods of
feeding by actual ingestion of Bacteria and small Protozoa
through a sort of mouth. Forms, almost identical morpho-
logically with the green ones, except for the absence of chroma-
tophores, live side by side with them, and it cannot be supposed
that they have lost that osmotic method of feeding so
characteristic of green types.

In a watery infusion of chopped hay, straw, or moss, after
the lapse of a few hours, various types of Protozoa appear in
waves of succession. Thus, the Bacteria are followed by
bacterial eaters, such as the mastigophoran genera Monas,
Oikomonas, and Bodo ; the ciliate genera Colpoda, Colpodium,
Chilodon, Paramecium, and Vorticella ; and such sarcodine
genera as Vahlkampfia and Amoeba. These forms gradually
become overwhelmed and replaced by forms which feed partly
upon Bacteria, partly upon Ciliata, such forms, for example,
as Stylonychia, Euplotes, Gastrostyla ; and, finally, by forms
which feed entirely upon Ciliata, Euchelys and Coleps, for
example. After decomposition has ceased there appear the
Green Algse and Flagellata, accompanied by Rotifera, Nema-
tode worms, Gastrotricha, fresh-water Crustacea, and so forth.

Such a succession of forms is obtainable, it may be pointed
out, even where the infusion aud containing vessels have been
sterilised by methods efficient enough to destroy any pre-
existing cysts of Bacteria or Protozoa. The various components
of the succeeding protozoan fauna must be derived, therefore,
from air-borne cysts.

In very stagnant accumulations of water, where dissolved
oxygen is scarce and dissolved sulphuretted hydrogen is plenti-
ful, there occurs a protozoan fauna which is able to live almost
anaerobically, approximating in biological environment to the
commensal and parasitic forms of an animal's alimentary canal.
These alimentary canal forms may possibly have been recruited
from the forms which live in stagnant infusions.

PROTOZOA: THE DISTRIBUTION 17

Phytobiotic Protozoa. — These forms are few in number,
a fact correlated perhaps with the apparent absence of cellulose-
splitting ferments in the animal body. Certain amoeboid forms
have been noted within holophytic Mastigophora, particularly
in Volvox and Hcematococcus, and a form Yaiwpyrella occurs
within the cells of Green Algae. Such forms are cell robbers.
The Myxomycete, Plas?nodiophora, is a parasite of higher
plants. Certain flagellate forms also have been discovered in
the juices of euphorbiaceous plants.

Zoobiotic Forms. — These forms, on the other hand, are
extremely numerous. It is doubtful, in fact, whether any
metazoan animal is entirelv free from associated Protozoa.
Scarcely any group of Protozoa, except a few rigidly specialised
orders such as Radiolaria and Foraminifera, is without zoobiotic
members.

To generalise zoobiotic Protozoa as parasites would not be
correct. A very large number undoubtedly are parasitic.
Many forms are of proved pathogenicity. Other zoophilous
forms, however, may be possibly of physiological value, rather
than a detriment, to the host organism.

Zoobiotic forms may conveniently be split into two
divisions : —

(a) Ectozoic forms, which frequent the external body surface
or involutions of the body surface such as mouth, gill chamber,
cloaca of the host animal.

(6) Endozoic forms, which live within the host animal.

Ectozoic forms may be entirely harmless to the host animal.

The gills of Crustacea are sometimes infested with sedentary
Ciliata, which merely seek a coign of vantage from which to
secure their minute victims. Many Hydroids and Sponges
are infested with similar forms and with creeping Sarcodina
and Ciliata. The Green Hydra (Hydra viridis), for example,
is commonly infected with hypotrichous Ciliata.

Many ectozoic forms, however, feed on their substratum
and so seriously damage their host.

Costia necatrix, for example, is a flagellate Protozoan which
attaches itself to the skin of fresh-water fishes and damages the
epidermis, so paving the way for bacterial infection and con-
sequent suppuration and ulceration. The Ciliate Ichthyo-
phthirius multiilis has similar habits.

Endozoic Protozoa exploit almost every type of host organ :
skin, peripheral and central nervous system, blood, gut, repro-
ductive organs, muscles, even bony and cartilaginous skeletons.
The majority, however, can be divided into connective tissue

18 THE PRINCIPLES OF APPLIED ZOOLOGY

forms, enteric or alimentary canal forms, and hcematophilous
or blood-frequenting forms.

In each habitat there occur forms which penetrate into the
actual tissue cells, and forms which are content to remain
between the cells.

Connective tissue forms belong chiefly to the Neosporidia
group of Sporozoa, which although in no case include parasites
serious to man, include certain forms of great pathogenic effect
upon fish and insects.

Of the three groups comprising the Neosporidia : —

(1) The Myxosporidia are chiefly parasites of fishes, and
have a comparatively simple life-cycle, without involving any
intermediate host ; they occur in the gall bladder, gills, kidney,
urinary bladder, muscles, connective tissue, spleen, ovary.

A fish becomes infected by swallowing spores. Each spore
is bivalved and has a thick wall or sporocyst, within which occur
two so-called polar capsules containing each a coiled filament
and a mass of protoplasm containing two nuclei. When the
spore is acted upon by the conditions in the fish gut, the filaments
are protruded and anchor the spore to the intestinal wall ; the
mass of protoplasm creeps out as an amceba-like organism,
penetrates the gut wall, and is carried by the blood stream to
the particular habitat characteristic of the species.

(2) The Microsporidia are principally parasites of insects
and include particularly Nosema apis, the organism of Nose-
matosis of bees, Nosema bombycis of the silkworm disease
pebrine, and Thelohania contejeani of crayfish disease. The
spore of these forms possesses only one polar capsule. With
Nosema apis the amcebula, which emerges from the spore,
spends its life-cycle within one of the epithelial cells which line
the intestinal tract of the bee. These cells become filled with
spores, the majority of which pass out with the faeces to infect
other hosts.

In the case of Nosema bombycis, however, the amcebulae
invade other organs of the body, and spores even occur in the
ovary and within the eggs of the moth, so that the disease is
transmitted to the newly hatched caterpillars.

(3) The Sarcosporidia occur as rod-like masses of spores
between the fibres of the striped muscles of mammals,
particularly the muscles of the oesophagus and diaphragm.
These so-called Miesche's tubes are large enough to be visible
to the naked eye. The life-cycle is imperfectly known, but the
spores are said to be motile and, if introduced into the intestinal

PROTOZOA: THE DISTRIBUTION

19

tract of a fresh host, to penetrate the gut wall and make their
way to the muscles (Fig. 5).

Foramen of
polar capsule

Polar
capsule
and
filament

Nucleus

Anterior end
Spore vail

Polar
capsule
and
fila-ment

Myxosporidian
spore (after Kudo)

ierminating"
spore of
Nosema
bombycis
f after \

A Microsporidian spore NiSrempeii,
(after Kudo)

Trophozoite

Chloromyxum
leydig-i
/ after \
\Thelohan;

"5V

Spores

Sarcocystis
(after Alexief f)

-13O*

Sphaeromyxa sabrazesi
(after Schroder)

Spore of Sarcocystis (after Alexieff)

Fig. 5. — Types of Neosporidia.

Enteric and hsematophilous Protozoa will be discussed in
succeeding chapters.

Zoobiotic Protozoa may injure the host in various ways.

20 THE PRINCIPLES OF APPLIED ZOOLOGY

The damage may be mechanical, brought about by pressure
or movement of the Protozoan between the cells of the host
tissue ; or the intruder may clog up a minute duct or blood-
vessel ; or it may affect the host animal by absorbing circulating
fluids which should normally nourish the host itself. Again,
the host may suffer injury owing to actual tissue destruction
by the Protozoan, or may suffer from the toxicity of the
excretions from it.

Many blood parasites have a particularly injurious effect
upon the red blood corpuscles. In such diseases as malaria,
babesiosis, trypanosomiasis, the red blood corpuscles are
destroyed in great numbers, possibly by a hemolytic ferment
excreted from the parasite. Injury to the host from blood-
frequenting Protozoa results from such diminution of red
blood corpuscles rather than from loss of nutrition fluid.

The possibility of Protozoa being able to excrete water-
soluble toxic substances seems to be generally accepted, although
few facts are available. The dying down of cultures of Protozoa,
despite abundant oxygen and food, is probably due to the
presence of such toxins ; the febrile symptoms occasioned in
the host by many blood-frequenting Protozoa probably result
also from excreted toxins.

It may be added that Protozoa themselves are not exempted
from the inconvenience of unbidden guests. Such invaders
may be predatory rather than parasitic, as they directly invade
the protozoan victim, but others are taken in with food and in
their tolerance to the host digestive reactions behave like true
internal parasites. The majority of these parasites are fungi,
belonging to the families Saprolegniacece and Chytridiacece.

Members of the latter familv would seem to be the causative
agents of the so-called ' giant nuclear condition ' of amcebid
and of thecamcebid forms described by many authorities.

Chytridiacece, also, are very prevalent as parasites of the
Euqleiw and Chlamydomonas groups of Mastigophora. Ciliates
seem particularly liable to bacterial infection. Thus, in
Paramcecium, Stylonychia, and some other forms, bacteria
may occur in chains and in clumps in the plasma, and destruc-
tion of the mega-and micro-nuclei may occur. Even Nematode
worms have been observed in the giant Ciliate Pycnoihrix
monocystoides , which occurs in the gut of the coney (Hyrax
capensis).

The genus Stentor is also liable to infection from small
Mastigophora whose presence seems to reduce the host's vitality
considerably and may even bring about disintegration.

CHAPTER III

PROTOZOA : Enteric Forms

An enormous number of protozoan species live as normal
habitants of the alimentary canal of some other animal. There
is probably no animal in possession of a well-marked alimentary
tract which is entirely free from such organisms.

The conditions within an alimentary canal are almost ideal
for forms which can withstand the paucity of oxygen and the
action of digestive juices. There is sufficiency of moisture
and warmth and sufficiency of food, whether in the form of
bacteria, of nutritive juices, or of food debris such as starch
grains or cellulose.

A vast crowd of Protozoa have adapted themselves to this
mode of life, and their derivation from saprobiotic forms would
seem evident from various facts ; from the occurrence, for
example, of both saprobiotic and enteric species of the genus
Bodo, Hexamitus, and other genera ; and from the readiness
with which some intestinal flagellates can be cultivated as
saprobiotes.

Gut-living Protozoa are drawn from all groups, but Ciliata
and Mastigophora predominate naturally, since they are the
most likely types to gain admittance to the alimentary tract,
and since their motor apparatus is well adapted to the great
energy expenditure required for locomotion in the viscous
fluids of an alimentary canal.

It would be far from correct to describe gut Protozoa as
generally parasitic. The great majority are probably harmless
scavengers, subsisting upon food residues which have with-
stood the disintegrating action of the host's digestive ferments.
Attempts have, in fact, been made to show that enteric Protozoa
in host animals whose alimentary canal contains much cellulose,
may be of considerable physiological value, owing to their
ability to decompose this carbohydrate substance. It has
been asserted that such animals as herbivorous mammals
and wood-feeding insects could not carry on without this in-
ternal fauna. There is no doubt, however, that many cases
occur where gut-frequenting Protozoa are actually inimical to

21

22 THE PRINCIPLES OF APPLIED ZOOLOGY

the host, and possibly many more such cases remain to be
elucidated.

Protozoa which have adopted the enteric mode of life show
certain features in common which, occurring as they do in
forms belonging to different taxonomic groups, can be regarded
as adaptations to this mode of life.

Movement in a viscous medium requires, for example, a
locomotor apparatus of considerably greater power than is
required by forms which live in fluids of comparatively low
density.

Flagella, for example, tend to be more numerous, to be
longer, to become fused into undulating membranes, and there is
often, in enteric Flagellata, an extranuclear neuromotor appara-
tus occurring usually as a so-called " parabasal body " attached
laterally to the blepharoplast at the base of the flagellum.

In enteric Ciliata the cilia tend to be powerful and numerous.

Enteric Sarcodina have large, powerful pseudopodia which
propel the animal in one definite direction.

Another feature displayed by probably all enteric Protozoa
is the phenomenon of encystment. Speaking generally, the
life-cycle in these forms consists of two alternating periods : —

(a) A period of comparative freedom and mobility, during
which the organism grows and reproduces ; and

(6) A period of rest, during which metabolism is at a low
ebb, and which is spent outside the host, protected from a
fluctuating environment by a cyst wall. The encysted stage
is usually the infective one, and the organism will emerge from
it only in response to stimuli exerted by the alimentary juices
of the appropriate host.

Infection of the host in the case of enteric Protozoa is
invariably brought about by the swallowing of an encysted
stage ; no intermediate host seems ever to be interposed in
the life-cycle of an enteric Protozoan, although undoubtedly
such animals as flies, in whose gut the cysts do not hatch,
may serve to distribute the enteric protozoan parasites of
higher animals.

Cysts of enteric Protozoa seem to be less resistant to
desiccation than are those of free-living forms. Moisture
would seem to be a necessary adjunct to the success of
their dissemination.

Enteric Protozoa belong chiefly to the two classes Infusoria
and Mastigophora. There are, however, a considerable number
of enteric amoebae and a large number of enteric Sporozoa
belonging to the Gregarinida and Coccidiidea.

PROTOZOA: ENTERIC FORMS 23

Enteric Amoebae. — Enteric amoebae have been recorded
from many different types of animals ; from animals so diverse
even as man, mouse, cockroach, and oyster ; undoubtedly
many more await discovery.

There was formerly very great confusion concerning the
homologies of these amoebae ; material was insufficient, or it was
stale, or it was examined by methods which were far from
efficient.

The widespread occurrence of chronic diarrhoea and
dysenteries of various kinds existing among troops during the
Great War, however, afforded unusual opportunities for the
study of the internal amoebae of man, and these amoebae are
now comparatively well known. It would seem, in the light
of present knowledge, that there occur in man no fewer than
four genera, comprising six distinct species ; these genera are
Entamoeba, Endolimax, Iodamoeba, and Dientamoeba. All these
amoebae are small in size as compared with free living forms,
and they lack contractile vacuoles. They are separable
chiefly upon structural differences of nuclei and cysts.

Of these forms, much the most important from an economic
standpoint is the genus Entamoeba. Strictly speaking, the
generic name of Endamoeba, suggested by Leidy in 1879, should
have priority of application to this genus, but as Leidy's term
was given to the intestinal amoeba of the cockroach, and as it is
doubtful whether this cockroach parasite is cogeneric with the
three principal amoebae of man, it has been suggested by Dobell,
upon whose monograph much of this account is based, that the
term Entamoeba applied originally by Casagrandi and Barbagallo
to the amoebae of man, in ignorance of Leidy's work, should be
preferred.

Three species of Entamoeba are known at present.

Entamoeba histolytica inhabits the large intestine of man and
is probably world wide in its distribution. It can be transmitted
experimentally to Carnivora and possibly to Rodentia, but there
is no evidence that it occurs normally in any animal except man.
It is comparatively large for an enteric form, averaging about
25 microns when observed fresh from the host ; it is very
active, flowing along in a slug -like manner, and fairly rapidly,
by the aid of a single, anteriorly- directed pseudopodium, and
snowing little distinction between ectoplasm and endoplasm ;
but if it has been outside the host for some time, it is sluggish
and throws out clear blade-like pseudopodia composed of
ectoplasm only. The cytoplasm may be clear and free from
foreign bodies, owing to the fact that this species feeds rather

24 THE PRINCIPLES OF APPLIED ZOOLOGY

by absorption than by actual ingestion of food particles, but
very frequently the cytoplasm contains tissue cells and red
blood corpuscles ; the presence of the latter may be taken as
diagnostic of this species. It never seems to feed on bacteria.
The nucleus is characteristic, being spherical, vesicular, and
provided with a layer of darkly staining peripheral granules,
which, in stained preparations, produce a ring -like appearance.
In the centre of the nucleus is a karyosome, surrounded in
stained preparations by a halo-like region produced by an
area of non-stainable substance. In good preparations there
is an absence of chromatin between the karyosome and the
edge of the nucleus (Fig. 6).

Entamoeba histolytica is primarily an inhabitant of the colon,
and produces extensive ulceration of the colon wall ; it is able
to bore its way into the walls of the colon, possibly by the aid
of a cytolytic ferment, and may even get into capillary vessels
and be carried to the liver, brain, or lungs, there to produce
abscesses. Normally it reproduces by simple division into two.
At times, many of the amoebae pass back into the intestinal
lumen, and divide into four or more daughter amoeba?, which
are, of course, very small. These so-called " precystic forms '
generally encyst and are passed out of the host to the exterior.

The ripe cyst has four nuclei and contains also peculiar
shining masses of stainable substance termed chromatoid bodies.
Such cysts can retain their vitality in water or in moist faeces
probably for weeks, but are very susceptible to dryness or to
increase of temperature.

Man is probably infected by contaminated food or water.
The cysts would appear to pass through the human stomach
unaltered, but once past the stomach they hatch and liberate
each a quadrinucleate amoeba, which subsequently divides into
four small uninucleate amoebae.

It is possible that many infected hosts act as " carriers " ;
in such an individual the intestinal tissues regenerate as fast as
they are destroyed, and no dysenteric symptoms develop ;
such individuals can be distinguished from uninfected
individuals only by the presence of the cysts in their faeces.
Carriers are, of course, a permanent menace to the health of the
community.

If, however, in a host individual the rate of tissue regenera-
tion falls behind the rate of tissue destruction by the parasite,
then disharmony will be brought about between host and
parasite, and both will become affected pathologically. The
host will develop typical Amoebic Dysentery, accompanied by

PROTOZOA: ENTERIC FORMS

25

great ulceration of the intestinal epithelium, and sometimes
by secondary complications such as liver abscesses or even
joint rheumatism and skin affections.

Nucleus

Red blood corpuscles
U-5/j)

Glycogen
vacuole

ine pseudopodiu7n

Nucleus

*zooo

Nucleus

X2000

Entamoeba Histolytica and Cyst.
Food vacuoles

Chromatoid body

Nucleus

Glycogen
vacuole

x 2000

xZOOO

Entamoeba Coli and Cyst.

Nucleus

Nucleus

''firomatoid.
body

Entamoeba Muris and Cyst.
Fig. 6. — Enteric Amoebae. (After Dobell and Wenyon.)

Among the amoebae, great mortality and wastage will then
occur, since large numbers are expelled from their habitat
before they have been able to encyst, by the diarrhoeic symptoms
of the host.

26 THE PRINCIPLES OF APPLIED ZOOLOGY

Dysentery, therefore, would seem to be an abnormal result
of the presence of Amoeba histolytica, for, if a normal result,
the parasite would tend towards extermination. At the same
time, it is doubtful whether a host individual can always remain
a passive carrier ; he may remain so for years, and then suddenly
develop an acute attack of dysentery or a liver abscess.
Amoebic dysentery and hepatic abscesses are commoner in the
tropics, but it must be noted that they can occur in temperate
countries. According to Dobell, probably 7-10 per cent, of
the population of the British Isles is infected with Entamoeba
histolytica.

The treatment of amcebic dysentery is too purely a medical
question to be discussed here, but reference may be made to
the specific action of the alkaloid emetine, which has been found
to rid infected individuals from the parasites, although it does
not seem to be particularly toxic to them ; possibly it reacts
through the host.

Entamoeba coli is another widely distributed inhabitant of
the human colon. The average percentage of the population
of England, France, and United States infected with this
amoeba would appear to be about 20, as against 9 for
E. histolytica.

Entamoeba coli is a large organism, similar in size to
Entamoeba histolytica, but less active and without the habit
of suddenly protruding clear pseudopodia. The nucleus is
very conspicuous, even in the living animal, as an eccentrically
placed beaded ring. The cytoplasm is coarser than in E.
histolytica, and may contain all manner of food derived from the
colon, such as bacteria, vegetable debris, cysts of other Protozoa,
and so on, but never, according to Dobell, does it contain red
blood corpuscles. The organism, in fact, is probably a harm-
less commensal. Cyst formation takes place very much as
in the case of E. histolytica, but the ripe cysts differ in contain-
ing eight nuclei (Fig. 6).

Entamoeba gingivalis is a smaller amoeba than the two
already described ; it is a smaller and more active edition of
Entamoeba coli, and occurs not in the gut but on the teeth,
being commonly found in cases of oral suppuration. It has
been suspected of being a contributory factor to the occurrence
of pyorrhea.

Endolimax is a genus containing only one known species,
namely, E. nana. It is probably the commonest amoeba
of the human gut, and is distinguished from the genus
Entamoeba by its smaller size, by the absence of a karyosome

PROTOZOA: ENTERIC FORMS 27

in the nucleus, and by certain peculiarities of cyst formation.
It is believed to be harmless. The cyst has four nuclei.
Endolimax was found to be the commonest amoeba infecting
American soldiers in 1918, the percentage of infection being 28.

Iodoamoeba has one species, namely, I. butschlii ; it was
described by Prowazek in 1912 as E. butschlii. The cysts,
which have a glycogen body within them, were first described
by Wenyon in 1915 in soldiers from Gallipoli, under the term
of ' iodine cysts," owing to the glycogen content of the cyst
being stainable dark red with iodine. This amoeba may possibly
be merely a large race of E. nana.

Dientamoeba comprises the single species D. fargilis. It is
a small gut amoeba, possessing two nuclei ; the cysts are not
known. It is believed to be harmless.

Kofoid has distinguished from E. coli an amoeba which he
claims has been previously confused with it. This amoeba,
which he has termed Councilmania Lafleuri, agrees with E. coli
in size and in the possession of an eight-nucleated cyst, but
it is more active, readily ingests red blood corpuscles, and has
a cyst with a thicker cell wall. As regards the intestinal amoebae
of animals other than man, very little information exists.
A form, Entamoeba meleagridis, living in the ca3ca of turkeys,
has been associated with a hepatic disease of young turkeys
in the United States, called : blackhead ' owing to the dark
colour assumed by the wattles.

Certain subcutaneous tumours of horses, referred to generally
as botryomycosis, have, on very doubtful evidence, been regarded
as caused by an entamoeba, namely, Amoeba letullei.

It must be emphasised that the differential diagnosis of
enteric amoebae, particularly of those living in man, is a matter
of very great difficulty, and a task to be attempted only by a
fully trained and experienced protozoologist. Not only are
the various genera so variable in size and in cytoplasmic struc-
ture as to be readily confused, but their cysts, whose exact
identification is a matter of great importance, may have the
same optic properties as quite different organisms, such as cysts
of the flagellate Chilomastix, yeasts, degenerate leucocytes,
and so on. In carriers and in chronic cases, diagnosis of
amcebiasis depends largely upon identification of the cysts,
since the active amoeboid stages rarely occur in fully formed
stools.

The Enteric Mastigophora. — The great majority of enteric
flagellates belong to that order of Mastigophora known as the
Polymastigina owing to the presence of numerous flagella. All

28 THE PRINCIPLES OF APPLIED ZOOLOGY

the members of this order, in fact, are in some way or other

zoobiotic.

They are comparatively small forms provided with two to
six flagella, of which at least one trails posteriorly and may
be attached to the body so as to form an undulatory membrane

It is in these polymastigine forms that the neuromotor
apparatus, referred to previously, is met with in its most highly
developed form. The plurality of flagella, the complex neuro-
motor apparatus, and the presence frequently in these forms
of something in the nature of an internal skeleton composed of
one or more rods or axostyles, may possibly be points correlated
with life in a medium somewhat more viscous than that of
stagnant water.

Almost all the Polymastigina are holozoic, feeding upon
microscopic organisms and detritus ; many have a definite
mouth leading into a short funnel-like gullet. They have
generally the power of encysting, and such cysts are probably
the chief means of distribution of host infection.

There is great variety of structure, ranging from simple
organisms like Prowazekia in the gut of lizards, provided with
a long anterior flagellum and a long trailing one, to forms such
as the Calonymphidce in the gut of termites, which have many
nuclei, many blepharoplasts, and numerous axial rods bound
into a central bundle ; they have also many parabasal apparati
and numerous flagella, arising in bundles of four from each
blepharoplast.

Of the very many enteric Polymastigina, the following
forms may be noted : —

Trichomonas is a genus recorded from many host animals.
It has been recorded from the mouth, gut, vagina of man, the
gut of the mouse, guinea-pig, amphibian, lizard, pigeon, snails,
leeches, insects, and so on, and from the stomach of ruminants.
Probably the forms thus recorded are specifically distinct, but
if so, their morphological differences are very slight.

Usually they are minute forms and usually oval in shape,
though capable of a certain amount of change of shape. There
are four flagella, which comprise three anteriorly directed, and
one posteriorly directed and fused to the body to form an
undulatory membrane (the Trichomonas form), or free from the
body (the Trichomastix form). The undulatory membrane,
if present, winds slightly round the body, so that the animal
rotates as it swims. There is an internal axial rod which
projects so that the animal shows a posterior spike. There is

PROTOZOA: ENTERIC FORMS

29

a minute mouth, anterior in position and ventral to the
undulatory membrane. The organism feeds on small bacteria.

Chilomastix
mesnili

(after KofoiofS
\ and Swezy /

Trichomonas
falter KofoicH
\and Swezy J

Giardia
intestinalis

(after Dobell)

Cyst of Chilomastix
mesnili
(after Refold and Swezy)

«4800

Cyst of Giardia

(after Simon)

Giardia/ /muris

(after Kofoid and Christiansen)

xSlOO

Fig. 7. — Enteric Mastigophora.

In man, two species of Trichomonas occur : T. vaginalis lives
in the vaginal mucus ; T. hominis lives in the large intestine,

30 THE PRINCIPLES OF APPLIED ZOOLOGY

and is apparently harmless. The latter species may occur also
in the buccal cavity, particularly in decayed teeth, and has
been recorded as numerous in the stomach in a case of stomach
cancer.

Other forms occur in mammals, such as the mouse, guinea-
pig, and ruminants. T. batrachorus occurs in the cloaca of
frogs and toads ; T. augusta in the gut of LTrodela ; T. lacertce
in reptiles. In the caeca of birds there occurs a form with four
free flagella and no undulatory membrane, which is termed
Trichomastix gallinarum.

Chilomastix is another genus of Polymastigina recorded from
the gut of many different animals. It is a form similar in shape
to Trichomonas, but is peculiar in possessing a large, somewhat
spirally directed groove or mouth along the anterior ventral
third of the body ; the lips of this groove are supported by
fibrillar cytoplasmic structures. There are three flagella, placed
anteriorly, and there is no undulatory membrane. The cysts
are minute and lemon shaped (Fig. 7).

C. mesnili is a common gut commensal of man.

Giardia is again a widely distributed genus. It is shaped
somewhat like a flattened pear and is distinctly bilaterally
symmetrical.

The greater part of the broad end of one surface is occupied
by a sucker-like depressed area, by the help of which it is able
to cling to the epithelium of the small intestine of its vertebrate
host. There are two nuclei, small oval structures situated
dorsal to the sucker, and each of the karyosomatic type. Down
the middle of the body runs a pair of closely apposed rods,
axostyles, in fact. Each ends anteriorly and posteriorly in a
blepharoplast. There are four pairs of flagella, one pair situated
at the anterior edge of the sucker, two pairs arising in the middle
of the posterior margin of the sucker, and a fourth pair forming
the posterior pointed tail of the organism (Fig. 7).

Giardia in man is typically an inhabitant of the duodenum
and upper jejunum ; in the hind gut only the oval cysts are
to be found.

General opinion favours the view that it is harmless, although
occasionally in children it may be associated with intestinal
disturbance.

Enteric Ciliata, unlike enteric Mastigophora, are types less
complex in structure than the free living forms, and have a
comparatively simple life history. Of the large number of
species that have been recorded from the animal gut, we need
only mention two forms — Balantidium and Nyctotherus —

PROTOZOA: ENTERIC FORMS 31

which occur together commonly in the alimentary canal of
many animals (Fig. 4).

Balantidium coli, the largest protozoon in the human
intestine, is an irregularly oval organism invested with fine
cilia, which, being arranged in parallel rows, give the creature
a striped appearance. At one end is the mouth, leading by a
short gullet into the endoplasm. The animal is an omnivorous
feeder upon micro-organisms and food detritus in the caecum.
It is probably a natural habitant of the pig, from which animal
man becomes infected. In man, it may provoke violent
dysentery, which may become chronic, accompanied sometimes
by ulceration of the bowel wall similar to that provoked by
Entamoeba histolytica. Nyctotherus is a smaller form. It is
shaped like a bean and has a long mouth extending from the
anterior end to the middle of the body. It appears not to cause
any intestinal disturbance.

Enteric Sporozoa. — Of the seven orders constituting that
somewhat artificial assemblage of entozoic forms collectively
known as Sporozoa, enteric forms belong, with one exception,
to the orders Gregarinida and Coccidia.

Of the two, the former group is confined in distribution
exclusively to Invertebrata, and practically nothing is known
as to the influence exerted by its members upon their hosts.

The Coccidia, however, occur both in Invertebrata and in
Vertebrata, and owing to their excessive prolificacy may cause
serious derangement.

The life-cycle of a typical Coccidian may be illustrated
by reference to Eimeria avium, which infests the domestic
galliform birds.

The host becomes infected primarily by swallowing food or
drink contaminated with spores of Eimeria. The spores dis-
solve under the action of the bird's digestive juices, and liberate
each four minute active banana-shaped organisms — termed
sporozoites — which immediately proceed to bore each into a
living cell of the gut wall. Once within the cell, the parasite
becomes rounded and proceeds to feed and grow at the expense
of the cell contents. When these are consumed, the parasite
breaks up into a number of minute forms similar to the original
sporozoites, and these wriggle away from the parental abode
and proceed to attack other cells. Such an asexual phase of
multiplication — schizogony is the term applied to it — may be
repeated several times. Eventually, however, the final pro-
duct becomes, as it were, too exhausted to carry on the process.
Something akin to sexual differentiation seems to occur.

32 THE PRINCIPLES OF APPLIED ZOOLOGY

Of the final brood of schizonts, some are small and provided
with flagella, others are larger and await in their cell habitat
the visit of a flagellated form. There occurs a phenomenon
similar to the fusion of a spermatozoon with an egg cell.
Instead of a fertilised egg, however, the product of fusion is
termed an oocyst.

In the oocyst there occurs a division of nucleus and cyto-
plasm to form four hard cased spores, which pass out to the
exterior with the faeces of the bird, and in three or four days
elaborate within the spore case two potentially infective
sporozoites. The effect upon the host, whether fowl, duck,
or pheasant or grouse, is distinctly pathological. Coincident
with the schizogony phases, the bird suffers acute and exhaust-
ing attacks of diarrhoea, the so-called " white diarrhoea ' of
poultry. This is accompanied often by a hepatic form of
coccidiosis, the liver becoming studded with yellow or white
nodules filled with pus swarming with bacteria.

If, however, the bird can survive until the sporogony phase
of the parasite occurs, the symptoms disappear and the bird
may recover.

Usually, however, reinfection by contaminated food is going
on all the time, so that the bird eventually succumbs to the
prolonged attacks.

A similar type of coccidiosis may occur in epidemic form in
domesticated rabbits, provoked in this case by Eimeria stiedce.

Cattle may become infected also and are very seriously
affected.

As regards the species of Coccidia which cause human
coccidiosis, present opinion inclines to the view that they are
species peculiar to man, and that man is a true host. The
best known of them is Isospora hominis, which does not seem
to be pathogenic.

CHAPTER IV

PROTOZOA : Hsematophilous Forms

Protozoa which live habitually in the circulatory system of
animals belong exclusively to the two orders Mastigophora and
Sporozoa, constituting in each case a sub-order, the Hsemo-
flagellata and Hsemosporidia respectively. No hsematophilous
Ciliata or Sarcodina are known.

The Hsemoflagellata include particularly the genera Leish-
mania and Trypanosoma.

Leish mania is a minute oval organism, absolutely without
nagellum, which occurs within the cells of the spleen, liver, or
bone marrow of vertebrate animals suffering from very definite
pathological lesions.

Each is somewhat like a cockle shell in shape, the appearance
of the shell hinge being given by a comparatively large stainable
body which is undoubtedly the nucleus ; in addition, there is a
stainable rod-like body which is homologised with the blepharo-
plast of other Mastigophora (Fig. 2).

It must be noted that Leishmania does not live free in the
host body fluids, but is essentially an intracellular parasite
within the endothelial cells of the blood and lymph vessels,
and within the glandular cells of liver, spleen, and lymph
glands. The cell may be distended by a number of the parasites,
and such a cell is said to break loose from the tissue and to be
carried by the blood stream to other parts of the body. There
are three types of Leishmaniasis, corresponding possibly to
three species of parasite.

Kala Azar, a dangerous disease of man in the Orient and the
Mediterranean area, is associated with Leishmania donovani,
which occurs in enormous masses in the endothelial cells of the
spleen, the liver, and the bone marrow.

Infantile splenic anaemia, occurring in children, and possibly
in dogs, in the Mediterranean area, is associated with Leish-
mania infantum.

Oriental sore, Delhi boil, Aleppo button, of Asia, Africa,
and South America, is a cutaneous local lesion associated with
Leishmania tropica.

3 33

34 THE PRINCIPLES OF APPLIED ZOOLOGY

The inclusion of Leishmania in the Mastigophora, despite
the absence of flagellum, is based upon the appearance, in
sodium citrate cultures of Kala Azar material, of a flagellated
organism indistinguishable morphologically from the well-known
flagellate, Herpetomonas, an active cigar-shaped organism with
a single anteriorly situated fiagellum (Fig. 2). It is a form
commonly occurring in the gut of insects. There can be little
doubt, in fact, that this herpetomonad phase of Leishmania is
the primary and the infective one, and that it occurs normally
in the gut of some arthropodan host, although no such trans-
mitter of the disease has yet been determined. On the other
hand, the possibility of infection by faecal contaminated food
or water cannot be negatived.

Trypanosoma (Fig. 2) is a genus comprising a number of
forms whose flagellated condition is most obvious, the sinuous
body being provided with a long fiagellum which, commencing
from a blepharoplast situated between the central nucleus
and the posterior end, runs forward to project beyond the
anterior end. The greater part of this fiagellum, however, is
united to the body by a membrane which, thrown as it is during
movement into well-marked pleats or folds, is well termed the
undulating membrane. This membrane moves in a manner
comparable to that of a sail shivering in the wind, that is to say,
waves of motion run backwards or forwards along it.

The swimming movements of the trypanosome in the blood
of its host are effected, however, rather by the movements of
the free tip of the fiagellum than by the membrane. The
undulations of the membrane certainly cause the body to
rotate, and so favour progress through a viscous medium
such as blood, but such rotation, unless accompanied by flagellar
action, does not move the animal from one position.

Even within the limits of one species there may be great
variation in body shape. It may be that slender pointed forms
are the normal rapidly multiplying forms, and that when
changes in the medium impede the rate of multiplication,
short stumpy forms result. Trypanosomes occur exclusively
as blood parasites of vertebrate animals, swimming freely in
the blood plasma and absorbing the medium by osmosis through
the cell wall. In the peripheral blood, however, of an infected
animal, trypanosomes may be very sparsely distributed or
they may be absent from it altogether, although occurring in
the blood capillaries of internal organs. Thus, in Nigeria,
trypanosomes occur rarely in the peripheral blood of Sleeping
Sickness patients although obtainable by puncturing a lymph

PROTOZOA: H^MATOPHILOUS FORMS 35

gland. Successful demonstration of the presence of trypano-
somes in an animal may necessitate the preparation of artificial
cultures of splenic juice or peripheral blood. In such a culture
there may appear in a few days a swarm of flagellate forms
morphologically identical with the flagellate genus Crithidia,
a cigar-shaped organism possessing a short undulating
membrane, which occurs in the alimentary canal of many
insects. There can be little doubt that these culture forms of
Crithidia represent normal phases in the life-cycle of the
trypanosome, and it seems possible that many of the so-called
Crithidia species, described from various insect species, are in
reality phases in the life-cycle of some trypanosome. On the
other hand, where a form of Crithidia or of Herpetomonas occurs
in the gut of a non-bloodsucking insect, the possibility of these
being distinct organisms must be postulated.

So far as present knowledge goes, a species of trypanosome
is restricted in distribution to a definite host type, generally to
a host genus, but morphological distinctions between these
species are slight, and it has been found convenient to classify
these forms in groups, centring round some definitely established
species. There is, for example, the lewisi group centring round
Trypanosoma lewisi from the sewer rat, and comprising T.
duttoni of the mouse, T. cuniculi of the rabbit, T. rabino-
witschi of the hamster, T. blanchardi of the dormouse, and so on.
These forms are extraordinarily similar in structure but seem
quite unable to live in any other host than the one they normally
infect ; that is to say, they are probably biological species.

Similarly the brucei group centres around T. brucei and
comprises T. gambiense, T. equiperdum, and T. evansi. These
are polymorphic forms, including a range of shape between
short stumpy aflagellate forms and long slender forms with
free flagellum.

There is a small blepharoplast, usually some distance from
the posterior end.

Trypanosoma brucei is the causative organism of Nagana,
the Tsetse fly disease of cattle in Central and South Africa.
The disease is not confined to cattle, but occurs in horses, mules,
and dogs ; possibly in man ; at any rate, the trypanosome of
Rhodesian sleeping sickness, T. rhodesiensis, is said by some
authorities to be identical with it.

Trypanosoma gambiense is the causative organism of human
trypanosomiasis or sleeping sickness, a disease limited to a
belt of Central Africa, including particularly the Gambia and
Congo regions, Uganda, and Tanganyika ; the distribution

36 THE PRINCIPLES OF APPLIED ZOOLOGY

coincides with that of the Tsetse fly Glossina palpalis, now
known to be the chief carrier of infection. The disease com-
prises two stages : —

(a) A long period of intermittent bouts of fever, associated
with enlarged lymph glands ; this phase is chronic and may
of itself lead, after years, to cachexia and death.

(6) A phase characterised by sleepiness and emaciation, and
coinciding with the presence of trypanosomes in the cerebro-
spinal fluid.

T. equiperdum causes, in horses, a pathological condition of
the mucous membrane, particularly of the urinogenital tract,
and appears to be transmitted from one animal to another
during copulation.

T. evansi is the trypanosome of the camel disease surra.

A third group of trypanosomes comprises T. pecorum and
T. simice, small forms, which are probably the most virulent
of cattle trypanosomes.

A fourth group, again, includes T. viva, T. caprce, and T.
uniforme, very active monomorphic forms with simple, slightly
developed undulating membrane. They are associated with
cattle disease in Uganda.

In addition to the African trypanosomes, reference may be
made here to a pathogenic trypanosome of man occurring in
Brazil.

This form, Schizotrypanuin cruzi, is unique in being intra-
cellular.

It occurs occasionally in the peripheral blood, but multiplica-
tion occurs within cells in such places as the wall of the heart,
the striated muscles, the central nervous system, and various
glands. The cell wall swells, becomes cyst-like, and encloses
several hundred rapidly dividing trypanosomes.

The disease produced — Chagas disease — may occur in acute
form associated with high fever, brain inflammation, swelling
of the thyroid glands, spleen, and liver, or in a chronic form
associated with myxoedema, goitre, heart trouble, etc.

The trypanosome is carried by a large black and red bug,
Triatoma, known as the " barbeiro."

In the case of the majority of the African trypanosomes the
insect carrier is a species of Glossina, the Tsetse fly.

The life-cycle in the invertebrate host is not fully known,
but it seems certain that there is no sexual phase there.
Observations on T. gambiense seem to indicate that the organism
multiplies in the insect midgut, very slender forms being
produced ; these move forward to the proventriculus and

PROTOZOA: H^MATOPHILOUS FORMS

37

later to the salivary glands, there to produce crithidial stages ;
these, again, give rise to the free swimming trypanosome stage
resembling that in the vertebrate host, and are probably
conveyed into a vertebrate when the fly feeds (Fig. 8).

Fig. 8. — Life-Cycle of Trypanosoma gambiense. (After various Authors.)

A, Forms in human blood.

B, Forms in midgut of tsetse fly, 48 hours after infection.

C, Long slender forms in proventriculus of the fly, 10-15 days

after infection.

D, Forms newly arrived in the salivary glands of the fly, 12-20

days after infection.

E, Crithidial forms in the salivary glands, 2 or 3 days later.

F, Final forms in the salivary glands ready for re-infection of

man, 20-30 days after initial infection.

38 THE PRINCIPLES OF APPLIED ZOOLOGY

The fly is said not to become infective until after the lapse
of thirty days from feeding.

Prophylactic measures against pathogenic trypanosomes
fall into three groups : —

(1) Destruction of the insect vector. This question will
be discussed in a later chapter.

(2) Destruction of vertebrate reservoirs.

There can be little doubt that trypanosomes, morphologically
indistinguishable from such forms as brucei and gambiense, are
present in the blood of wild ungulates in infected districts,
particularly in the various species of antelope. Whether these
trypanosomes are physiologically identical as well as morpho-
logically identical with the pathogenic forms is another question.
Species of trypanosomes are notoriously difficult to distinguish
on morphological grounds, but must be separated by their
biological properties, such as their pathological effect upon
laboratory animals, cross immunity reactions, and so on. Thus
if trypanosomes be injected into the blood of an animal immune,
owing to previous attack, or even if they come in contact with
serum from such an animal, they agglutinate, that is to say,
they mass together in large numbers with their flagellated ends
projecting from the centres of the mass.

Authorities are divided in opinion as to whether the wild
game trypanosomes are identical with those of man and
domesticated animals. In any case, a policy of extermination,
apart from ethical reasons, is indefensible until it can be shown
that trypanosomes, in the absence of large game, will not
utilise domestic animals or even small wild mammals and
reptiles.

(3) The use of drugs.

The most effective drugs up to now have been arsenical
organic preparations injected intramuscularly and tartar
emetic injected intravenously. This purely medical question
is referred to here because it would seem that trypanosomes
can become tolerant towards these drugs, and that such toler-
ance is inherited, so that " arsenic fast " and " antimony fast '
strains of trypanosome arise. There is some reason, however,
to think that this acquired immunity is broken by passage
through the invertebrate host.

Hsemosporidia. — As is the case with their close relatives the
Coccidia, haemosporidian organisms are intra-cellular parasites,
in this case within vertebrate red blood corpuscles, and their
life-cycle shows an alternation of asexual multiplicative phases
(schizony) with a sexual phase (sjjorogony).

PROTOZOA : ILEMATOPHILOUS FORMS 39

Unlike the Coccidia, however, transmission of the parasite
from one vertebrate host to another is effected by the agency
of a bloodsucking invertebrate animal, usually an arthropod,
and whereas in Coccidia both schizogony and sporogony occur
in the one host individual, in Hsemosporidia these phases require
alternation of hosts, schizogony, in fact, occurring only within
the vertebrate host, sporogony only within the invertebrate host.

Further, although the term sporogony is convenient to use,
the Ha?mosporidia do not form spores in the strict sense of the
term. The zygote cell which results from the union of male and
female gametes, instead of developing a firm cell wall, remains
naked, and may be even actively mobile, in which case it is
referred to as an ookinete. Within the ookinete, however,
sporozoites are eventually produced, just as they are produced
within the oocyst of the Ooccidian.

The three genera of Hfemosporidia which concern man and
animals more than any others are Plasmodium, Hsemoproteus,
and Babesia.

Plasmodium is the causative organism of the various so-called
malarial fevers and agues of mammals and birds. Speaking
very generally, it is an amoeba-like organism which lives within
the red blood corpuscles, which produces a characteristic black
pigment, and which is carried from one victim to another by
some kind of mosquito. In man three species of Plasmodium
may occur, namely, P. vivax, of Benign Tertian Malaria ; P.
malarice, of Benign Quartan Malaria ; P. falcijmrum, of Malignant
Tertian Malaria.

In a tertian fever the febrile attacks recur every other day ;
in a quartan fever they recur every fourth day.

The genus is not restricted to man ; P. kochi is recorded from
chimpanzees, P. canis from dogs, P. equi from horses. An
allied genus, Proteosoma, causes a form of malaria in birds.

Infection of man follows upon the introduction into his
blood, in the infected saliva of an Anopheline mosquito, of
several thousand minute cigar-shaped sporozoites, which each
actively attack and enter a red blood corpuscle. Each sporo-
zoite then becomes rounded, but retains a certain amount of
amoeboid activity, particularly in the case of P. vivax. It
proceeds to absorb the contents of the cell, and is full grown in
twenty -four to forty-eight hours after entrance, or seventy-two
hours in the case of the quartan fever organism. The signet-
ring appearance of the parasite, due to the appearance of a
pigmented peripheral zone around a non-stainable central
vacuole, and to the peripheral position of the nucleus, gradually

40 THE PRINCIPLES OF APPLIED ZOOLOGY

becomes obliterated by the deposit of black pigment so character-
istic of Plasmodium, and the full-fed organism appears as an
angular pigmented mass filling the cell membrane (Fig. 9, d).

Fig. 9. — Life-Cycle of Plasmodium.

A-F, Schizogony. Production of nierozoites in blood of man.
G-T, Sporogony. Production of sporozoites in mosquito.

PROTOZOA : H^EMATOPHILOUS FORMS 41

The full-fed parasite now breaks up, by successive divisions,
into a rosette-like mass of minute cells similar to the original
sporozoites ; these burst out from the corpuscle and proceed
each to infect another host cell. This process of schizogony,
as it is termed, or liberation of merozoites, reinfects the host
severely, and after a period of two to three weeks, during which
successive schizogonies are occurring, the host shows response
to each new schizogony by developing a temporary but acute
attack of high fever, induced doubtless by the liberation of the
waste products of cell destruction into the blood plasma.

After a succession of such asexual phases of multiplication,
there appear in the blood corpuscles certain forms of modified
merozoite which are preparatory to the sexual phase of the
life-cycle and can be termed gametocytes. Why some merozoites
become gametocytes and others do not, is uncertain. Two
kinds of these gametocytes are produced. They are rounded
bodies, crescentic in P. falciparum, and the two kinds differ
in size and pigment distribution (Fig. 9, H, i).

No further development of them can occur unless they
become swallowed by an Anopheline mosquito, in whose midgut
each gametocyte sheds the encircling host corpuscle and pro-
ceeds to develop further.

The smaller type or microgametocyte undergoes what used
to be termed " exflagellation," that is to say, it gives rise to
four to eight thread-like cells which are the male gametes,
analogous to spermatozoa (Fig. 9, j).

The larger type or macrogametocyte does not undergo division
but prepares, somewhat like a maturing egg cell does, for the
reception of a microgamete. The product of the union of
micro- and macro-gamete is an elongate, active, somewhat
worm -like ookinete (Fig. 9, l), and can bore through the midgut
wall and encyst between muscles and external epithelium of
the gut, as a spherical body, termed an oocyst. There may
be 200-500 such oocysts in one insect individual, and each
grows comparatively enormously and bulges into the body
cavity.

Within each cyst the nucleus and cytoplasm divide to
produce a number of cytoplasmic nucleated areas termed
sporoblasts, within each of which, again, several hundred thread-
like sporozoites are formed (Fig. 9, q).

Rupture of each cyst liberates these thread-like forms and
they squirm their way into the salivary glands of the insect,
from thence to be passed into another human host.

The cycle in the mosquito requires eight to twelve days.

42 THE PRINCIPLES OP APPLIED ZOOLOGY

The mosquito is now infective, and probably remains so for
the rest of its life.

The distribution of the various species of Plasmodium is, of
course, dependent upon the distribution of the particular species
of mosquito which can act as host. External temperature,
however, plays a not inconsiderable part in their geographical
distribution, since exflagellation requires a temperature above
a certain minimum. Thus P. falciparum, of malignant tertian
malaria, is widely distributed over the tropics and sub-tropics ;
but since its sexual phase requires a minimum temperature
of 18° C, it is not likely to become established in temperate
latitudes. P. vivax and P. malarial, however, may occur in
such latitudes, and the quartan form is in fact more a disease
of temperate than of tropic zones.

The establishment of Plasmodium as the causative organism
of malarial fever was made by the French scientist Laveran.
The association of mosquitoes with Plasmodium transmission,
although suggested by Manson, was not made until early in
the present century, when Ross in Bombay showed the associa-
tion of avian malaria with Culicine mosquitoes. Later he
established the cycle of human malaria in the mosquito genus
Anopheles, but was partly forestalled by the Italian workers
Grassi and Bastianelli, who put malaria upon a definite zoological
and cytological basis, and studied the benign tertian and quartan
forms, as well as malignant tertian malaria. Both Ross and
Grassi have contended for priority of discovery. Ross
undoubtedly was the first to suggest the mode of transmission,
but the exact scientific proof and zoological presentation was
made by Grassi.

Heemoproteus occurs exclusively in the red blood corpuscles
of birds as a large bean-shaped or dumb-bell shaped organism,
the so-called Halteridium stage. This represents a gametocyte
stage. No schizogonous phase has been discovered in these
forms.

When blood containing these stages is taken into the insect
host, which is some species of Pupiparid fly, ripening and copula-
tion of the gametes takes place in the insect midgut.

The ookinetes, however, are injected back into a bird and, by
some means not yet clear, obtain admission to leucocytes in the
capillaries of lungs, spleen, kidney, and bone marrow, where they
become sac-like and undergo sporogony. The sporozoites pass
into the peripheral blood and infect red blood corpuscles.

Babesia and Piroplasma are minute parasites occurring
within the red blood corpuscles of mammals, chiefly Ruminants,

PROTOZOA : ILEMATOPHILOUS FORMS 43

Garni vora, and Rodents, and causing certain severe forms of
cattle disease, notably the so-called Red-water fevers and Tick-
fevers of cattle -rearing countries. They are certainly trans-
mitted by ticks, but neither schizogony nor sporogony has
been established in their life-cycle, and they do not produce
pigment. Their relationship to other Haemosporidia is, in fact,
obscure.

They occur in the blood corpuscles in two forms, namely : —

(a) Rounded forms, often ring-like, like young Plasmodium
schizonts, but not pigmented ; the haemoglobin of the injured
corpuscles escapes into the plasma and is excreted in the urine,
tinging it red.

(b) Relatively larger pear-shaped forms, occurring singly
or in two, four, or even eight in number, within one red corpuscle
(Fig. 3).

There appear to be no human parasites included in the
Piroplasmidae, although one form, Bartonella bacilliformis ,
the organism of Oroya fever of man in Peru, is sometimes
admitted into the group.

Other genera and species of Piroplasmidae are Piroplasma
canis, which causes malignant jaundice in dogs ; Piroplasma
bigemi?ia, the organism of Texas cattle fever, the first protozoan
disease known to be transmitted by an arthropod, in this case
the tick Boophilus ; Piroplasma bovis causes red-water fever
in European cattle ; Theileria parva is the organism of East
Coast or Rhodesian red-water fever of cattle in Africa, India,
Macedonia, and Transcaucasia.

Spirochseta. — No discussion of haematophilous protozoa
can be considered complete which does not include some mention
of these pathogenically important forms, even if their exact
relationship to Protozoa is somewhat debatable.

Generally speaking they are minute, corkscrew forms which
are extremely active (Fig. 10). In certain respects they
resemble bacteria, notably in the lack of a differentiated nucleus,
the lack of sexual reproduction phases, and the division by
transverse fission. On the other hand, the possession of some-
thing recalling the undulating membrane of trypanosomes,
the occasional occurrence of longitudinal fission, and their
chemotropic reactions, suggest somewhat that they should be
classed with the Protozoa, particularly since they are often
transmitted by arthropodan hosts. They are not all haema-
tophilous ; some occur in the pus of cutaneous and mucosal
ulcers, some in the contents of the animal gut.

Their average length is about 20 microns, but some forms,

44 THE PRINCIPLES OF APPLIED ZOOLOGY

commensal in Mollusca, and some free living forms, may be
as long as 200 microns. The majority of the pathogenic forms
are scarcely visible under the highest microscopic powers.

Three types of diseases are caused by pathogenic
spirochetes : —

(1) Relapsing fevers, characterised by anaemia, splenic
enlargement, and febrile symptoms. The fever will occur

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for several days, be followed by a period of well-being, and
then re-occur.

The organisms of relapsing fevers belong to the genus
Spironema.

The East and West African relapsing fever is caused by
8, duttoni, transmitted by the tick Ornithodorus moubata.
European relapsing fever is caused by S. recurrentis, and is
probably transmitted by body lice.

Although the tick host is a bloodsucker, the spirochete
is not transmitted via the proboscis of the tick, but is ejected

PROTOZOA: HLEMATOPHILOUS FORMS 45

in the faeces and in the secretion from the coxal glands. It is
thus necessary that the tick puncture become contaminated
by the faeces or gland secretion deposited near it.

In the human host the organism inhabits the blood plasma.
In the tick it penetrates the gut and occurs in the haemoccel as
black granules which even pass into the developing eggs so that
ticks from infected parents may transmit the disease.

In the same category as relapsing fevers may be placed : —

(a) Rat bite fever, caused by Spirochceta morsus inuris
present in the blood of the rat and, by gum haemorrhage, con-
taminating the teeth and so becoming introduced into man.

(b) Yellow fever, demonstrated by Noguchi in 1919 to be
caused by Leptospira icteroides, a spirochaete only 4-9 microns
in length and capable of passing through a bacterial filter. It
is transmitted by the mosquito Aedes argenteus. The spirochetal
nature of yellow fever is now, however, discredited by some
workers.

(2) The second type of spirochaete disease is characterised by
the occurrence of local lesions, followed by general constitutional
symptoms, followed finally by localisation of the causative
organisms in special organs or tissues. The three main diseases
of this type are syphilis, yaws, and jaundice.

Syphilis is caused by the spirochaete Treponema pallidum,
discovered by Schaudinn and Hoffmann in 1905 in various
syphilitic lesions. It averages 8 microns in length, has six to
twelve short, sharp, geometrically regular spirals, and a straight
filament at each end.

T. pallidum is able to produce lesions in almost any organ
of the body, but eventually becomes localised in some special
organ or tissue, such as the skin, bones, central nervous system,
arteries, and so on.

Yaws or frambesia of tropical countries has a causative
organism — Treponema pertenue — almost indistinguishable from
that of syphilis. In fact it is possible that yaws is a variety of
this disease.

(3) The third type of spirochaete disease is characterised by
the presence of local ulcerations of the skin or mucous
membranes. Thus Spirochceta schaudinni produces skin ulcers
in the tropics. Sp. bronchialis attacks the respiratory tract,
producing a certain type of bronchitis. Sp. orientalis, the
cause of " ulcerating granuloma of the pudenda," is localised
in ulcerations of the skin and mucous membranes of the external
genital organs.

CHAPTER V

HELMINTHES : The Flukes

The term Helminthes in general may be said to refer not so
much to all the various types of animal popularly designated
as ' worms," but rather to the two zoological phyla Platyhel-
minthes or flatworms, and the Nemathelminthes or roundworms.

The term flatworm, again, comprises a wide range of
creatures very diversified in appearance and habit ; many are
free living, creeping over stones and plants in marine or fresh-
water pools by means of a coating of cilia which work in the
moist exudation from numerous skin glands ; others are ecto-
parasitic on skin, gills, or in the body orifices of vertebrate
animals, and have lost such motile organs as cilia, but gained,
in compensation, organs of adhesion in the form of suckers and
hooks ; others, adapted to a life spent within the vertebrate
alimentary canal, have lost even alimentary canal and vascular
system.

The flatworms fall readily into three classes, well demarcated
from each other by important morphological features.

The Turbellaria or eddy worms are free-living, ciliated, leaf-
shaped forms found gliding like living films over stones and
weeds in marine and fresh- water pools, and varying in size
from a quarter of an inch long to tropical terrestrial forms
nearly a foot long.

The Trematoda or flukes are parasitic forms which are with-
out cilia, but which are provided with adhesive organs usually
termed ' suckers," a quite unsuitable name, since these are
merely muscular cups without any ability to suck in food-stuffs.

The Cestoda or tapeworms are internal parasites of vertebrate
animals and have diverged very greatly from the ancestral type
if this latter form was similar, morphologically, to the present-
day Turbellaria.

Trematoda. — Flukes retain, to a large extent, the leaf or
tongue-shaped appearance characteristic of free-living forms,
but the absence of cilia, the limitation of muscular mobility,
and the absence of gaudy coloration characteristic of Turbellaria,
quite precludes any possibility of confusing the two groups.

46

HELMINTHES: THE FLUKES

47

They are usually small, the majority being a quarter to three-
quarters of an inch in length, although Nematobothrium, a

Posterior
sucker

Odtype

Germarium

-Anterior sucker
and mouth

Pharynx

(Esopho,gu.\

Uterus

Intestine

Lid

Egg' of Fluke

Fig. 11. — Reproductive Sj^stem of a Distomid Fluke. (Diagrammatic.)

worm-like form on the gills of the tunny, may reach three feet
in length.

The mouth, terminal or ventro -terminal in position, leads

48 THE PRINCIPLES OF APPLIED ZOOLOGY

by way of a muscular, sucking pharynx into a forked alimentary
canal, each branch of which ends blindly ; the absence of anus
is characteristically platyhelminthian. The food consists of
mucus, blood, epithelial cells, or the intestinal juices of the host,
and is thus of a kind easily assimilated ; probably little or no
solid matter remains to be defecated ; the bulk of the nutriment
circulates in soluble form through the spongy tissue between
gut and body wall, and the expulsion of surplus nitrogen in
the form of some substance similar to guanine or xanthine is
carried out almost entirely by the excretory system. The
excretory system is of the type peculiar to flatworms. Scattered
throughout the spongy tissue that fills up the body space not
already occupied by alimentary canal or reproductive organs
are numerous hollow cells. Within each of the cells a flickering
bunch of cilia produces a flame-like effect. Each so-called
" flame cell " communicates by means of a straight, exceedingly
thin capillary tube, with a longitudinal collecting duct. The
collecting ducts, generally two in number, unite at the posterior
end of the animal into a common trunk, which, again, may
discharge into an excretory bladder and so to the exterior.

The animal, as in the case of most flatworms, is hermaphro-
dite, and the arrangement of the reproductive organs is some-
what complex (Fig. 11).

The male organs comprise two testes, variable in shape,
lying either side by side, or one behind the other ; each com-
municates by means of a fine vas efferens with a single median
vas deferens which runs to the genital aperture and ends in a
protrusible hooked organ termed the cirrus or penis.

The arrangement of the female organs will be understood
more clearly if it be realised that the ovary is divided into two
physiologically distinct portions. There is a germarium or
egg-producing portion, represented by a median compact or
sometimes branched structure posterior to the ventral sucker.
There is a vitellarium or yolk-producing portion, represented by
a large number of spherical glands on either side of the animal.
The ducts from these scattered yolk glands converge on each
side into a duct which meets the duct from the germarium
within a chamber, into which a number of shell-secreting
glands open. Into this chamber, the so-called ootype, there
open also certain other ducts to provide for admission of sperma-
tozoa and removal of surplus yolk. Thus in ectoparasitic forms
a paired vagina provides for admission of spermatozoa, and
a median Laurer's canal conducts surplus yolk either to
the exterior or into the gut. In the ootype the egg cell is

HELMINTHES: THE FLUKES 49

fertilised, receives its yolk, and becomes surrounded by a shell
which has a lid. The complete eggs are then transferred to the
tubular uterus, along which they travel to the exterior. In
endoparasitic forms, fertilisation is effected by spermatozoa
which have entered the uterus, there being no other passage
to the exterior.

Classification. — The most logical classification of flukes
is based upon the number and character of the adhesive
organs.

The order Heterocotylea comprises forms which possess a
large posterior sucker, sometimes subdivided into lesser suckers ;
in addition, there may be two small anterior suckers. These
forms are ectoparasitic upon skin, gills, and in the mouth and
bladder of the lower vertebrate animals. The life-cycle is
straightforward, the egg giving rise to a simple ciliated larval
form, which swims about in the water until able to attach itself
to another host individual.

As the parasite utilises only one host individual, the life-cycle
is termed monogenetic.

The order Aspidocotylea comprises a few little known forms
which possess each a very large ventral sucker, sometimes
divided into compartments ; these forms are endoparasitic.

The order Malacocotylea comprises forms with a variable
arrangement of suckers ; thus there may be a tiny anterior
sucker surrounding the mouth and a large posterior terminal
sucker ; this is the amphistomid condition ; or the posterior
sucker may be situated only a little way from the anterior one,
on the ventral surface ; this is the distomid condition ; or
again, only the anterior sucker surrounding the mouth may be
present, the so-called monostomid condition ; or the body may
be divided by a constriction into two regions, of which the
anterior one carries two minute suckers, and the posterior one
bears the reproductive organs ; this is the holostomid condition.
Malacocotylean forms are endoparasitic either in the gut or
associated glands and ducts, or in the lungs, or kidney, or
urinary bladder, or even the blood, of vertebrate animals.

The life -cycle shows a regular alternation between a sexual
form, parasitic in the vertebrate, and a series of asexual forms,
usually termed larvae, occurring either in water or in an inverte-
brate host.

The eggs hatch under moist, external conditions and give
rise to a ciliated larval miracidium stage. This is a fragile,
short-lived form which endeavours to find and enter a secondary
host, usually one that is small, widespread, and easily pene-

50 THE PRINCIPLES OF APPLIED ZOOLOGY

trated, and usually one that is liable to come in contact, as
by becoming swallowed, with the primary host ; in this
secondary host the larva can encyst and await passively the
advent of a primary host individual.

In the majority of cases, the miracidium after entering the
digestive gland of a fresh-water mollusc degenerates into a sort
of hollow bag of cells, termed the sporocyst, rarely exceeding a
few millimetres in length at first, but sometimes increasing
in size at the expense of the snail's tissues. This sporocyst is
able to produce, by budding from its internal wall, a number of
mulberry-like balls of cells which develop into small, tubular
sacs not unlike the parent sporocyst but possessing a simple
pharynx and intestine ; these are termed redise. Similarly,
each redia may bud off a fresh generation of redia? , or it may
produce a type of larval stage termed a cercaria. The cercaria
has a round or oval body similar in internal structure to that
of the adult fluke, but it has a boring spine within the anterior
sucker, has eye spots, and has a propelling organ or tail ; in
some cases the tail is absent, the larva then being designated
as a cercariseum. This cercaria is really the youngest form of
the sexual stage ; if the tail be present, a free-living phase is
passed through. That is to say, the cercaria leaves the
molluscan host and swims around in the surrounding moisture.
Eventually, however, it penetrates some aquatic creature,
discards its tail, and encysts, to await passively the transmission
to the primary host in which alone it can attain maturity.
In some cases the second intermediate host is dispensed with,
and the cercaria encysts in the water or on some water plant, and
is thus taken up in direct fashion by the primary host when it
eats or drinks. The use of the term " encysted cercaria " for
this condition is incorrect. The creature is a miniature fluke
which only requires to grow in size and to differentiate its sexual
organs. A better term for it is that suggested by Stossic of
Agamodistomum.

It is disputed whether the life-cycle of an endoparasitic
trematode is a complicated metamorphosis, that is to say, a
developmental change in the life-cycle of the one individual,
or whether it is a true alternation of one sexual and two asexual
generations, or whether, regarding the cells in the sporocyst
which give rise to redise, and the cells in the redia that give
rise to further redise or to cercarise, as parthenogenetic ova,
the life -cycle is not an alternation of one sexual with two
parthenogenetic generations.

Economic Aspect. — The Trematodes which are of serious

HELMINTHES : THE FLUKES 51

pathogenic importance to man and domesticated animals are
all Malacotylean forms. In particular, two are of outstanding
interest, namely, the liver fluke of the sheep and the blood fluke
of man, known respectively as Fasciola and Schistosoma.

The Liver Fluke. — " Liver rot " of sheep is caused by the
presence in the bile -ducts and branches of the hepatic portal
vein of large numbers of a distomid Trematode — Fasciola
hepatica ; a milder form of liver disease is produced also in some
countries by the smaller fluke — Dicroccelium lanceolatum —
but not in Great Britain.

Though occurring chiefly in sheep, particularly sheep
pastured in damp localities, the liver fluke is not specifically
restricted to sheep, but is found not uncommonly in cattle,
and less commonly in horses, goats, camels, rabbits, deer,
kangaroos, etc. In rare cases it may occur in the bile-ducts
of man, such infection being due probably to the eating of
infected watercress. In the Lebanon district of Syria, Fasciola
hepatica frequently occurs in considerable numbers in the
pharynx of man, giving rise to severe inflammation and swelling
which may endure for several days, until the symptoms are
relieved by vomiting; this so-called " Halzoun " disease is
due to the eating of raw infected goat's liver.

The range of the liver fluke extends over the whole of
Europe, including particularly England and Central France ;
it occurs over Northern Africa ; it is common in North America,
where it coexists in distribution with the scarcely less common
Fasciola magna, a parasite of deer. It is less common in
South America, and has been reported in Australia. The
distribution is local and restricted to damp or marshy localities
where the water snail Limnma is abundant.

Fasciola hepatica is about three-quarters of an inch to an
inch and a half long, is flattened, oval, and dirty- white in colour.
The anterior portion projects somewhat beyond the rest of the
body, like a head on shoulders. The anterior sucker is terminal,
small, circular, and contains the mouth ; the posterior sucker
is larger and lies in the middle line, just behind the junction
of the anterior projection and the shoulders.

Dicrocoslium lanceolatum is smaller, pointed at each end,
and lacks the shouldered appearance. The body is translucent,
so that the internal organs are readily seen. The two intestinal
trunks are not provided with lateral branches as in Fasciola.
In both genera the internal morphology is of the typical
trematode type.

Life History.— Our knowledge of the life-cycle of Fasciola

52 THE PRINCIPLES OF APPLIED ZOOLOGY

hepatica is very complete, owing to the work of Thomas,
Leuckart, Ercolani, and others.

The eggs are laid in enormous numbers in the bile-ducts
of the host, pass down the alimentary canal and are expelled
with the faeces. Given a sufficiently moist environment and
a mean temperature of 70°-75° F., the eggs will hatch, the
ciliated miracidium larva pushing aside the lid of the egg
and escaping into the surrounding moisture. The lease of life
of this ciliated stage is about eight hours ; that is to say, within
that period of time it must penetrate an intermediate host or
perish. The intermediate host in this case is a species of water-
snail, the little water-snail of damp meadows, Limncea ; in
Europe, Limncea truncatula ; in Hawaii, Limncea oahuensis ;
in North America, Limncea viator ; in Australia, Limncea
brazieri.

In the case of Dicroccelium the host would seem to be a
species of Planorbis, P. marginatum or P. complanalus.

Within the respiratory chamber of the mollusc the larva
loses cilia and eyespots and becomes just a hollow, cylindrical
sac or sporocyst, from whose walls mulberry -like masses of cells
arise and become redice ; these are cylindrical sacs, not unlike
the sporocyst stage, but possessing a pharynx and a simple
straight intestine. These redia, if the environmental conditions
be dry, as in summer, give rise to a number of daughter rediae ;
but if the moist environment of a wet autumn or winter be
available, each redia gives rise to a number of cercarice larvae,
tailed motile forms with a forked gut and two suckers ; these
forms leave the snail, swim about for some time in the surround-
ing moisture — thus becoming distributed — and then encyst
upon the stems of the grasses and meadow plants, generally
just at the point where the stem rises above the moisture level ;
that is to say, in an ordinary damp meadow the encysted
cercariae will occur on the lower portions of the grass stems,
so that close-cropping herbivores, such as sheep, are more likely
to become infected than are cattle or horses.

The Effect on the Sheep. — The general effect on the sheep is
to induce progressive pernicious anaemia culminating fatally
in most cases.

Infection is believed to occur most frequently in autumn,
but the migration of the embryo parasites from the host
alimentary canal to the liver does not apparently provoke any
characteristic symptoms. About December or January, how-
ever, there is a period of anaemia, accompanied by abnormal
fattening and by feverish symptoms, and characterised by the

HELMINTHES: THE FLUKES 53

presence of Fasciola eggs in the animal's faeces. Then follows
a period of severe emaciation, accompanied by diarrhoea,
wool-shedding, abortion among pregnant ewes, and a character-
istically dropsical condition of the tissues below the jaw, in
evidence when the head is lowered in grazing. Death eventu-
ally ensues from exhaustion, or in some cases there is spon-
taneous recovery. The parasite remains in the host from nine
to fifteen months.

The post-mortem appearance of the liver is that of an
abnormally swollen and soft structure with the surface rough
instead of smooth ; later there is great vascular congestion of
the organ, the bile -ducts are dilated and inflamed and crowded
with flukes ; the ducts tend to become calcified, and this calcified
condition will persist even in a sheep that has recovered.

Preventive Measures. — There is no royal remedy for the
elimination of the parasites from the host, although claims
have been made for common salt and for extract of male
fern.

An infected pasture can be attacked very successfully,
however, by anti-snail measures comprising treatment of the
land with salt or with iron sulphate, combined with drainage
operations.

Other Flukes of Domesticated Animals. — The liver of herbi-
vorous mammals is liable to infection by some or other species
of Fasciola, Dicrocoelium, or Fasciolopsis ; the liver of carni-
vorous mammals by Opistorchis, Metorchis, or Bilharziella.

Opistorchis felineus of the dog and cat has been recorded
occasionally in man. The host is believed to become infected
by eating certain cyprinid fish.

The gut of domesticated birds, such as the duck, goose,
swan, is infested by a holostomid fluke, Echinostomum
echinatum, whose anterior body region is armed with large
numbers of sharp, backwardly directed spines.

The lungs of pig, dog, and cat are commonly infected in
oriental countries, and even in the United States, by a broadly
oval fluke, Paragonimus wester manni, the provoking agent of
pulmonary distomatosis.

The alimentary tract of herbivorous mammals is liable to
harbour species of Amphistomum and Gastrodiscus.

Schistosoma. — The genus Schistosoma, whilst possessing
the oral and ventral suckers characteristic of distomid flukes,
is remarkable amongst them in that : —

(a) There are distinct sexes ; in the male, the lateral edges
of the body behind the posterior sucker curl inwards to form

54 THE PRINCIPLES OF APPLIED ZOOLOGY

a tube which encloses the thread-like female ; the male has
therefore a cylindrical shape (Fig. 12).

(6) The alimentary canal bifurcates in front of the ventral
sucker, but the two branches unite into a single tube lower down
the body, behind the ovary.

(c) There is no muscular pharyngeal bulb at the commence-
ment of the oesophagus ; since the cercaria in structure is a
miniature adult, this absence of muscular pharynx serves also
to distinguish a schistosomid cercaria from that of other
distomid flukes.

Schistosoma haematobium is the provoking agent of a wide-
spread endemic disease, variously termed bilharziosis, schisto-
somiasis, endemic hematuria, and so forth, in Northern Africa,
especially Egypt ; the disease occurs also in South Africa,
Arabia, India, Persia, Cyprus, etc., and evidence as to its
antiquity has been afforded by the discovery of calcified
Schistosoma eggs in the kidneys of two mummies of the
twentieth dynasty (1250-1000 B.C.).

The adult flukes, which are about half an inch long, occur,
as permanently coupled males and females, in the abdominal
veins of man, especially in the veins comprising the portal
system and the capillary veins of the bladder.

A certain amount of danger to the host may result from the
blockage of capillary vessels by masses of adult worms, but the
serious effects upon the host result from the presence of the
eggs. These are comparatively large and provided with a
stout terminal spine. They occur in masses in the capillary
vessels of the liver, intestine, kidney, and bladder, and cause
lesions not only through mechanical blocking of the blood-
vessels but through laceration of the tissues by the spines of the
eggs. The mucosa of the bladder, in particular, becomes acutely
inflamed, and the presence of blood and eggs in the urine
makes diagnosis of the disease easy and accurate. Coterminous
in distribution with this urinary form of bilharziosis caused by
Schistosoma hcematobium, but occurring also in the West Indies
and Venezuela, there is an intestinal form of bilharziosis,
characterised by intestinal inflammation and by the occurrence,
in the faeces of the host, of schistosoma eggs which have a
lateral spine. This form of the disease is now regarded as being
provoked by a distinct species — Schistosoma mansoni. The
third species of Schistosoma is endemic in man and in domesti-
cated animals in Japan, China, Philippines, and possibly else-
where in the Far East. This is Schistosoma japonicum. The
eggs have a little lateral knob instead of a spine, and occur

HELMINTHES: THE FLUKES

55

in the faeces of the host, but may occur in masses blocking up
the bile-ducts, the capillaries of spleen, pancreas, and even the
brain.

Knowledge regarding the life -cycle of the genus Schistosoma
has been accumulated largely as a result of the observations
and experiments of Miyairi, Leiper, and others in Japan, and

Adult females in
portal bloodvessels

Fig. 12. — Life-Cycle of Schistosoma hcematobium.
(Miracidiuru after Seymour Sewell ; other stages after Leiper. Not to scale.)

of Sonsino, Looss, Lortet, Leiper, and others in Egypt. The
difficulty of establishing the life-cycle details of any one species
is intensified by the considerable number of species of Schis-
tosoma, which occur in mammals and birds. Thus in Egypt,
in addition to S. hcematobium and S. mansoni of man, there
occur S. bovis of cattle and Bilharziella polonica of ducks.

The general life-cycle story of species of Schistosoma is
probably similar for all species (Fig. 12).

56 THE PRINCIPLES OF APPLIED ZOOLOGY

The egg gives rise to a ciliated miracidium, which dies
within twenty -four hours unless it has found a molluscan host.

The miracidium in this latter event enters the digestive gland
and gives rise to a long tubular sporocyst. This gives rise to
similar tubular daughter sporocysts with delicate transparent
walls. These migrate into the tissues of the digestive gland,
which swells greatly.

These sporocysts have neither oral sucker nor alimentary
canal, and must absorb their nutriment through their walls.
They can wriggle along quite readily through the gland tissue.
The sporocysts produce cercarise characterised by a long Y-
shaped tail and an absence of suctorial pharynx. These
cercariae are discharged from the snail in little clouds into the
water. They must enter their vertebrate host within forty-
eight hours or perish, and they enter the host directly through
the skin of the body or through the mucous membranes of the
mouth, to which they can adhere by their suckers and through
which they bore very rapidly.

A Schistosoma species does not limit itself to any species
of mollusc, but usually there is some molluscan species which
is more liable to infection than others. In the case of S.
haematobium, the favourite molluscan hosts are species of
Bullinus ; in the case of S. mansoni, species of Planorbis are
concerned ; in the case of S. japonicum, species of Limncea and
Blanfordia are involved.

Prophylactic measures against Schistosoma infection there-
fore should comprise : —

(1) Avoidance of ablution with water liable to contain
cercariae unless previously treated with antiseptics such as
cresylic compounds, of which as low a dilution as one part in
ten thousand of water is effective in destroying cercarial stages.

(2) Avoidance of drinking water from infected sources,
unless such water has stood for forty-eight hours, or has been
boiled or otherwise sterilised.

(3) Destruction of molluscan hosts either by exposure to
sun temperatures induced by intermittent irrigation, or by
chemical agents such as copper sulphate.

Other Flukes of Man. — A considerable number of flukes
have been described as occurring in man, but chiefly in tropical
countries.

In China, Japan, the Philippines, Formosa, occurs
Paragonimus ringeri, living in cavities in the lungs and
provoking a characteristic blood-spitting ; the expectorations
are a peculiar reddish-brown colour and contain dark-brown

HELMINTHES: THE FLUKES 57

fluke eggs. The molluscan host is said to be Melania libertina,
and the emerging cercaria attacks a second intermediate host, a
fresh -water crab, in whose digestive gland the young fluke
is found within a cyst. When swallowed by a crab -eating
animal the cyst wall becomes dissolved and the active liberated
cercaria bores through the intestinal wall, wanders about the
abdominal cavity, eventually gets into the pleural cavity and
penetrates into the lungs. A closely allied species of lung
fluke, Paragonimus Jcellicotti, occurs in hogs in the United States.

Similar in distribution to P. ringer i is the liver fluke of man,
Clonorchis sinensis. In Japan the percentage of infection
among the population is said to be 60 per cent, and in Korea
80 per cent. It occurs also in dogs and cats. The related cat
fluke, Opisthorchis felineus, of Europe and America also occurs
occasionally in man. All these flukes live in the gall bladder
and bile-ducts and cause serious mechanical obstruction,
resulting in enlargement of the liver and bloody diarrhoea.
Infection results from eating certain fresh-water fishes in whose
muscles the encysted cercarise occur.

The sporocyst stages of Clonorchis sine?isis are believed to
occur in the snail Bythinia striatula var. japonica, at any rate in
Japan.

Fascioloj^sis buskii is the large intestinal fluke of man in
oriental countries. It is probably a normal habitant of the

Pig-

Heterophyes heterophyes occasionally occurs in the intestine

of man in Egypt. The tiny fluke Yokagawa yokagawa is

widely distributed in the Far East as a parasite of the human

intestine. Infection arises from the eating of raw fish.

CHAPTER VI

HELMINTHES : The Tapeworms

Apart from a few forms that consist of a single joint, a tape-
worm always shows three distinct regions : —

(1) A scolex, or organ of attachment ; a bulb -shaped struc-
ture bearing organs of adhesion in the form of four cup-shaped
suckers (in the tsenoid type) or two or four slit-like grooves
(bothriocephaloid type), and generally possessing one or two
circlets of hooks surrounding a swollen apical portion termed
the rostellum.

(2) A neck, or slender unsegmented region merging into

(3) The strobila, or chain of flattened quadrilateral joints
(proglottids), each joint being sexually complete.

Alimentary canal and related structures are completely
lacking.

The excretory system resembles that described for
Trematoda ; the capillaries may, however, form a network,
and the collecting tubes are typically four in number, two on
each side, running the full length of the worm ; in the scolex
the two vessels on each side unite by means of a loop ; in the
first formed proglottis they open into a small bladder and so
to the exterior by a pore in the middle of the posterior edge of
the proglottis.

The nervous system consists of a number of longitudinal nerve
fibres running parallel with the outer edge of the excretory
canals and united by cross fibres (commissures) in the scolex.

The proglottids vary in number, according to species, from
four or five to several thousands, and arise in succession from
the neck region, so that the oldest is the one farthest away
from the scolex. Usually, if the number of joints is large, the
youngest are transversely oblong, the middle ones square, and
the old ones longitudinally oblong.

The proglottids resemble each other and resemble flukes in
the structure of the cuticle, the muscular system, and the
possession of spongy internal tissue ; they differ from each
other, however, in the degree to which the reproductive organs
are developed.

58

HELMINTHES: THE TAPEWORMS

59

It must be borne in mind that each proglottis is not merely
hermaphrodite ; it is protandrously hermaphrodite, that is to

Onchosphere of Tapeworm
Fig. 13. — Reproductive System of a Tapeworm Proglottis.

say, the male organs appear and ripen before the female ones
do ; a proglottis fairly near the scolex will therefore show
greater development of male than of female organs ; a pro-

60 THE PRINCIPLES OF APPLIED ZOOLOGY

glottis in the middle of the chain may have male and female
organs fairly equally developed ; then, as the proglottis becomes
older, the female organs increase in size and development
until in the fully mature proglottis the enormously enlarged
gravid uterus may quite obliterate the remaining male and
female organs.

If, as is conventional, the surface of the tapeworm upon
which the uterine pore opens be termed ventral, then the male
organs may be said to occupy the dorsal portion of each segment,
the female organs the ventral. The male organs consist of
numerous small spherical testes, scattered in the parenchymatous
tissue ; each testis is connected by a small tubule to similar
tubules from the other testes and the whole network converges
to a convoluted collecting duct or vas deferens. This latter may
or may not dilate to form a vesicula seminalis, but always
terminates in a protrusible penis or cirrus, enclosed in a cirrus
pouch.

The male genital aperture opens along with the vaginal
aperture into a common chamber, the border of which is raised
to form a genital papilla ; the position of this latter structure
on the proglottis is of great importance in the identification of
tapeworm species (Fig. 13).

Several methods of fertilisation have been observed. The
proglottis may fertilise itself with or without making use of its
penis ; or the proglottis may be cross fertilised by a proglottis
of the same chain or of a different chain ; or where two sets of
organs occur in the one proglottis, cross fertilisation between the
two sets may occur.

The ovaries are usually two in number, and are compara-
tively large, compound, tubular glands ; there is one common
oviduct, which, a short distance from the ovaries, receives the
vagina, a straight tube parallel in course to the vas deferens ; the
united ducts continue as the fertilisation canal to the tubular
uterus, receiving on the way the common duct from a series of
yolk glands, and numerous ducts from the shell glands (Fig. 13).

Thus the egg cell, after fertilisation, receives a certain amount
of yolk, then receives shell material at the point of entry of the
shell gland ducts, and then moves into the uterus. The uterus,
as the proglottis ages, becomes larger and develops lateral
branches, to accommodate the accumulating mass of eggs.
It may open by a mid- ventral pore, or may be blind, in which
case the escape of eggs has to await the decay and dissolution
of the proglottis.

Actually the egg stage has developed so far by the time it

HELMINTHES: THE TAPEWORMS 61

is free from the proglottis that it contains a larva ready to
hatch, a spherical organism with three pairs of hooks. This
larva or onchosphere, as it is termed, is surrounded before
hatching by a covering or membrane composed of radially
arranged rods. The true egg shell has really gone (Fig. 13).

Life History. — Tapeworms are parasites of the alimentary
canal of vertebrate animals, and in most cases of the intestinal
portion of the canal. The comparatively large size and
restricted habitat of the parasite would thus render the develop-
ment of eggs and embryos in situ a condition of affairs highly
prejudicial to the existence of the species. We find, therefore,
as in flukes, that embryonic and larval development takes place,
in most cases, outside the habitat of the adult, and to compen-
sate for this, the degree of probability of the immature form
returning to the similar conditions of habitat, necessary for
maturation, is intensified not only by the production of large
numbers of eggs, from seven to twenty millions yearly in the
case of Tcenia solium, but also by utilisation of an intermediate
host, a host that is liable to come into intimate contact with
the primary host. In fact, the primary host is in most cases
a carnivorous animal, the intermediate host an animal commonly
preyed upon by the primary host ; and just as the muscular
portion of the intermediate host is more likely to become
swallowed by the carnivore than any other portion of the body,
so the immature stage of the tapeworm, that adapts itself to
life in the intermediate host, occurs usually in the animal's
muscles or in the connective tissue.

The egg is the only stage that can exist outside a host
animal.

The eggs pass out from the intestinal habitat of the adult
in various ways. In the case of Dibothriocephalus , the " broad
tapeworm," the uterus possesses an opening to the exterior
and the eggs are deposited in the intestine of the host and
evacuated with the faeces ; if the environment be sufficiently
moist, the eggs will hatch after a fortnight, and the ciliated,
slow-swimming organism that emerges may, by some means
not yet known, secure ingress to the muscles of a fish. The
ciliated organism, it may be noted, consists of a capsule — the
embryonic capsule — bearing cilia and enclosing a spherical
embryo possessing three pairs of hooks. It differs, therefore,
from the ciliated miracidium of a Trematode.

The embryo plus capsule constitute the so-called onchosjrfiere.

In those tapeworms which do not possess a uterine pore, the
eggs reach the exterior in an indirect fashion. The terminal

62 THE PRINCIPLES OF APPLIED ZOOLOGY

proglottids, as they become ripe, break away from the strobila,
aided possibly by the peristaltic contractions of the host's
intestine, and either force their way independently through the
anal sphincter muscle or pass out in short chains with the
faeces. The eggs are freed by the decay and disintegration of
the proglottis wall, which may occur whilst still in the host's
gut or outside the host, or by the digestive juices of the inter-
mediate host. In any case the onchosphere is not ciliated and
can only enter the intermediate host by the mouth in food or
drink.

Feeding experiments with Tcenia crassicollis of the cat,
whose intermediate host is the mouse, indicate that the embryo
emerges from the shell about the middle of the host's small
intestine, tears its way through the intestinal wall to the
intestinal blood-vessels by means of its hooks, and is then
carried by the portal vein to the liver ; embryos leave the liver
with the circulation and may be distributed throughout the
tissues of the body. Rarely do they remain in the cavity of
the intestine, as does Hymenolepis muriiia of the rat, but settle
in the muscles, mesenteries, etc. Such active migration of
large numbers of embryos through the tissues may give rise
to febrile symptoms — the so-called " acute cestode tuberculosis '
— sufficiently intense to cause death of the host animal, or the
further development of the embryo in its final resting-place
may prove fatal if localised in the liver or brain. Once the
embryo has come to rest, it develops into the so-called bladder
worm or larva or metacestode stage. The term bladder worm
derives its name from the condition shown by metacestodes of
the genus Tcenia, where this stage does consist of a small bladder
about the size of a pea. Protruding into the cavity of the
bladder, and surrounded by fluid, there occurs a scolex in no
way different from the scolex of an adult worm except that,
since it is an invagination from the wall of the bladder, it is
turned inside out. Actually, this is the scolex of a future worm
and only requires the stimulus of gut conditions in the appro-
priate carnivorous host, in order to become everted from the
bladder, so that it can attach itself to the gut wall and proceed
to bud off a chain of proglottids.

In many tapeworm metacestode stages, this bladder-like
appearance is not so apparent as in Tce?iia.

There is, in the first place, the solid metacestode, the plero-
cercus (spherical) or the plerocercoid (elongated), where the
scolex is derived directly from the onchosphere, and is pushed
into the posterior portion of the solid larval body. Secondly,

HELMINTHES: THE TAPEWORMS

63

there are forms which are bladder-like ; the bladder is formed
directly from the onchosphere and is thus a primary structure ;

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the invaginated scolex is formed from the bladder and is thus
a secondary structure. Of these forms, the cysticercoid type

64 THE PRINCIPLES OF APPLIED ZOOLOGY

has the bladder but slightly developed, and may have a tail-
like appendage ; the cysticercus type consists of a bladder and
one scolex ; the coenurus type has a bladder with many scolices ;
and the echinococcus type has a bladder containing daughter
bladders each possessing numerous scolices (Fig. 15).

In practically all cases the metacestode must reach the
alimentary canal of the primary host before it can mature.

We find, therefore, a definite correlation between primary and
intermediate hosts ; tapeworms of cats spend the metacestode
period in mice ; tapeworms of dogs and foxes have metacestode
stages in rabbits and hares ; tapeworms of man have meta-
cestode stages in the pig or ox. In a few cases the intermediate
host seems to be dispensed with. Hymenolepis murina, for
example, a small tapeworm of rats and mice, has its metacestode
encysted in the intestinal wall of the same host. In the case
of such genera as Moniezia, Thysanosoma, Stilesia, and Ano-
plocephala, all parasitic in the alimentary canal of herbivorous
animals, the intermediate host is unknown, and the question
arises as to whether this host may not be some small mollusc
or insect from which the metacestode can actively migrate
in order to encyst upon herbage and so infect the herbivore.
Such active migration has been observed in the case of the
metacestode of the fish tapeworms Ligula and Schistocephalus .

Bionomics. — As we have already noted, the adult tapeworm
is, with few exceptions, a parasite of the vertebrate gut, nourish-
ing itself upon the gut contents which it absorbs through its
whole surface.

On the other hand, the metacestode stage is a non-feeding
stage thus rarely occurring in the gut of its host, but being
found normally in the muscles, mesenteries, occasionally in the
liver, lung, and brain.

From a pathenogenic standpoint, therefore, the metacestode
is much the more injurious of the two in its effects upon the
host ; the tapeworm stage, whilst provoking undoubtedly
gastero-intestinal troubles, nervous symptoms, and more or
less anaemia, is rarely sufficiently injurious to bring about the
death of its host. The metacestode is, however, the cause of
several fatal diseases of man and domesticated animals.

Classification. — If we exclude the few primitive, uniseg-
mental forms, we can divide the genera of tapeworms between
two distinct orders : —

(a) Pseudojihyllidea (bothriocephaloid type) with two slit-
like elongated grooves on the scolex, with a uterine opening,
and with a solid larva from which the scolex of the future

HELMINTHES: THE TAPEWORMS 65

adult is formed directly. Examples — Bothriocephalus, Diplo-
gonoporus.

(b) Cyclophyllidea (tsenioid type) with four round suckers,
no uterine opening, and a vesicular larval stage ; the scolex
of the adult is formed from the bladder and thus indirectly
from the larval one. Examples — Dipylidium, Hymenolepis ,
Tcenia, Davainea, Moniezia.

The Pseudophyllidea includes the family Bothriocephalidw,
certain members of which are of considerable economic interest.

Dibothriocephalus latus, the so-called " broad tapeworm '
of dog, cat, and man, is particularly prevalent in French
Switzerland, in the Baltic regions of Germany and Russia, and
in Turkestan and Japan. It is readily distinguished from other
tapeworms of man by the egg-shaped scolex with its two slit-
like adhesive organs, and by the short, broad proglottids, each
with uterine pore and genital papilla close together in the
middle line.

The metacestode is of the plerocercoid type, and occurs in
the liver, muscles, and other organs of various fresh-water
fishes, particularly pike, perch, trout, and grayling. It has
been shown recently that a second intermediate host is neces-
sary ; that the newly hatched embryo is preyed upon by a
species of the water flea Cyclops, and undergoes a preliminary
development within it, the so-called " procercoid larva " stage ;
if the infected Cyclops is swallowed by a fish, the parasite
migrates into the muscles of the fish and remains there until
eaten by the mammalian host.

Related to Dibothriocephalus is Diphyllobothrium mansoni
of cats and dogs. There is a procercoid stage in Cyclops
leuckartii and a plerocercoid stage in several animals, including
man, but especially in frogs and snakes.

Other plerocercoids have at different times been recorded
from man, and are grouped under the name Sparganum pro-
lifer urn or Sparganum mansoni. The former type occurs in
the form of little oval capsules occurring in thousands in the
subcutaneous tissues and in the internal organs. Each organism
is white, flattened, and irregular in shape. The irregularity
in shape arises from a habit of budding off supernumerary heads
which may become detached, leave the cyst, and form separate
capsules. Nothing is known as to the life-cycle in which these
forms are stages, but there is a possibility that infection in man
arises from the consumption of raw fish.

Of the families which constitute the Cyclophyllidea, the
family Tamiidaz is of considerable economic importance.

66 THE PRINCIPLES OF APPLIED ZOOLOGY

It is divided usually into three sub-families, namely : —

The Anoplocephalince, a family of tapeworms whose meta-
cestode stage has in no single case been observed nor the inter-
mediate host discovered.

The tapeworms occur in herbivorous animals and include
Moniezia of sheep and cattle, Thysanozoon of sheep and pigs,
Stilesia of sheep, Anoplocephala of horses and asses, and
Ctenotcenia of the wild rabbit.

The Tceniince, a family of well-known tapeworms whose
metacestode stage is a cysticercus, a ccenurus, or an echinococcus
stage, occurring, as does the tapeworm, in some species of
mammal.

The family includes Tcenia solium and Taenia saginata of
man, whose cysticercus stages occur in the pig and the ox
respectively ; Tcenia serrata and Taenia marginata of the dog,
with cysticercus stages in the rabbit and in the sheep or ox
respectively ; Taenia crassicollis of the cat, with a cysticercus
stage in the rat or the mouse ; Multiceps of dogs, with a ccenurus
stage in ruminants and rodents ; Echinococcus granulosus of
the dog, with an echinococcus stage in any mammal.

It may be noted that the tapeworms of the genus Tcenia are
restricted each to a particular species of host or to a few closely
allied species. Thus T. solium and T. saginata occur only
in man, and attempts to establish them in other animals have
always failed.

T. marginata, very similar morphologically to T. solium,
is not known from animals other than the dog and wolf ; it
cannot develop in man. On the other hand, T. serrata occurs
in three species of Ca?iis, two species of Felis, and in the gray
fox ( Urocyon). T. crassicollis is known from ten species of
Felis and from Mustela erminea.

The cysticercus stage, however, may be considerably less
restricted in choice of host. Thus Cysticercus cellulosai of T .
solium can develop in no fewer than eleven different animals.
Cysticercus bovis of T. saginata can develop in the muscles of
the ox, pronghorn antelope, giraffe, and llama. Cysticercus
tenuicollis of T. marginata occurs in the liver and abdominal
cavity of probably all ruminants, in seven genera of primates
(except man), and in several species of squirrel.

Petrunkevitch has made the suggestion that those species
with the widest range of intermediate hosts may be the oldest,
and puts forward the further suggestion that the human species
have arisen as mutants from one of the still existing dog tape-
worms, probably T. marginata.

HELMINTHES: THE TAPEWORMS 6?

The Dipylidiince is a family of tapeworms each generally
provided with a long protrusible hooked rostellum, whose
cysticeroid stages occurs usually in some arthropod, the tape-
worm stage occurring in birds or mammals. The family
includes Dipylidium of the dog, cat, man, with intermediate
stage in the dog-flea or louse ; Hymenolepis gracilis of ducks
and geese, with a metacestode in various fresh-water Crustacea ;
Hymenolejpis murina or nana of rodents whose metacestode
occurs also in the gut of the same host as the tapeworm stage ;
Hymenolepis diminuata of rats and mice, with metacestode in
the larva of Asopia farinalis, the meal-moth.

Some of these forms may now be discussed.

Taenia is a genus characterised by the possession, in the
tapeworm stage, of four circular adhesive cups, the so-called
" suckers," on the scolex ; by a non-pro trusible rostellum ; and
by the genital apertures of the proglottids being lateral and
alternately placed on one edge or the other.

Of the two species which infest man, Taenia solium is dis-
tinguished by the double circlet of hooks on the scolex, by the
ripe uterus having seven to ten lateral branches arranged
dendritically, by the ripe proglottids being expelled with the
host's faeces in short chains, and by the mature proglottis being
quadrilateral (Fig. 14).

Taenia saginata has no hooks, has fifteen to thirty lateral
branches of the ripe uterus, arranged dichotomously, has a
pumpkin seed-like mature proglottis, which escapes from the
host gut usually singly (Fig. 14).

Of the two species, the latter is the more common, possibly
because beef infected with the bladder worm stage is more
difficult to detect than is infected pork, owing to the bladder
worm stage of Taenia saginata being much smaller than that
of Taenia solium. The genus Multiceps has three species,
multiceps, serialis, and gaigeri, all occurring in dogs only, all
very similar to one another morphologically, and none differing
greatly from the genus Tainia. The coenurus type of meta-
cestode is, however, characteristic of this genus.

In the species M . multiceps the coenurus may occur in the
brain or spinal cord of ruminant animals, horses, and even man.
In fact, the embryos of this species perish if carried by the
blood stream to any other organ than the central nervous
system.

M . serialis has its coenurus stage in the connective tissues
of rodents, especially species of Lepus, the rabbit.

Coenurus cerebralis, the cause of considerable mortality

68 THE PRINCIPLES OF APPLIED ZOOLOGY

amongst sheep, is a bladder worm about the size of a hen's egg
which occurs frequently in the brain of young sheep, less
frequently in the brain of goat or ox, and rarely in that of the
horse. The victim becomes infected by eating herbage con-
taminated with the eggs of Multiceps multiceps, a tapeworm
of sheep dogs and foxes. The embryos bore their way through
the gut wall, and are probably carried to every organ of the
host by the blood currents, but only those which reach the
brain seem able to develop further. If one or more embryos
reaches the brain, their gradual development brings about a
distinct pathological reaction on the part of the host, constitut-
ing the disease known in Great Britain as " gid " or " staggers."
If the brain contains a considerable number of larvae, say ten
to twenty, the symptoms shown are those of general paralysis ;
there is general weakness and emaciation, partial blindness,
and loss of the sense of balance ; death may come about from
acute brain fever, and the symptoms, in fact, may be confused
with those of sunstroke or of meningitis.

If, however, only one or two ccenuri be present, the victim,
in addition to the symptoms catalogued above, constantly
jerks the head from side to side, and in the later stages walks
round and round in circles, or even pivots on its hoofs, until
paralysis and death intervene.

No certain surgical or medicinal treatment is known.
Removal of a portion of the frontal bone in the hope of localising
and then destroying the : bladder ' is a heroic method fre-
quently practised by shepherds, but with rare success.

Preventive measures are simple, consisting chiefly of pre-
cautions against the contamination of tapeworm by sheep dogs
through eating infected brains. If the brains and spinal cords
of diseased sheep were carefully burned, and measures taken
to free farm dogs from the tapeworm stage, the disease could be
stamped out of every infected district with ease, and a con-
siderable source of loss to the agriculturist thus averted.

Davainea is an interesting genus of Tseniine tapeworm
characterised by the possession of hooks on the suckers as well
as on the rostellum (Fig. 14). It is a parasite usually of birds ;
thus Davainea urogalli infests the grouse.

One species, Davainea madagascarensis, a small form about
ten to twelve inches long, is found commonly in children in
many tropical seaports and on ships, and a suggestion has
been made that some species of cockroach may act as inter-
mediate host.

Echinococcus granulosus (Fig. 14) is the smallest species of

HELMINTHES: THE TAPEWORMS

69

Tcenia, measuring, as it does, only one-tenth to one-fourth of
an inch in length, and having only three to four proglottids ;
it may occur in enormous numbers in the small intestine of
the dog, jackal, wolf, or puma, but has never been found in
man.

The intermediate stage, Echinococcus polymorjrfius, is found

Cysticercoid

Cysticercus

Coenurus Echinococcus

Fig. 15. — Types of Metacestode. (Not to scale.)

chiefly in the liver or lungs of various mammals, especially the
sheep, ox, and pig, and its presence in man may cause very
dangerous pathological conditions. The occurrence of this
so-called "hydatid cyst' in man is common in Germany,
Iceland, Paraguay, Argentina, and Australia ; its favourite
site is the liver (57 per cent, of cases), the lungs (8 per cent.), the
kidneys (6 per cent.), and the spleen (3-8 per cent.). Infection

70 THE PRINCIPLES OF APPLIED ZOOLOGY

results probably from the eating of contaminated vegetables or
salads.

Under the name of Echinococcus multilocularis there has
been designated a sort of liver tumour of man which consists
of numerous small cysts set side by side in honeycomb fashion ;
a few of these cysts contain scolices. It is stated to be
specifically distinct from the hydatid or unilocular echinococcus.
This disease is nearly always fatal to man. The mountainous
region of Southern Europe is the principal centre of distribution.

Dipylidium caninum is a common and widely distributed
parasite of dogs, cats, and by infection from them, of children.
The worm has a rhomboidally-shaped scolex, provided with a
protrusible rostellum armed with three or four rings of hooks
resembling rose thorns. The four adhesive cups are fairly
large, oval, and shallow. The proglottids are easily recognised
by their curved lateral edges, giving them the appearance of
cucumber seeds, and by the presence of two genital openings,
one on each margin ; there are in fact two sets of reproductive
organs in each segment (Fig. 14).

The metacestode is of the cysticercoid type and occurs in
the dog-louse (Trichodectes), the dog-flea (Ctenocephalus canis),
and the human flea (Pulex irritans). The mature proglottids
leave the anus of the mammal and wriggle about somewhat on
the fur ; onchospheres, liberated by disintegration of the
proglottis, are taken up by the louse or flea ; it is stated, how-
ever, that the eggs cannot pass up the suctorial tube of the
adult flea, but are ingested readily by the flea larva. The eggs
are said to hatch in the intestine of the flea larva, and the newly
hatched metacestodes pass through the intestinal wall of the
insect to the body cavity, where they remain through the
further metamorphosis of the insect ; the dog or cat is infected
by swallowing the insect parasite when licking its fur.

Hymenolepis nana is the smallest tapeworm occurring in
man, rarely exceeding one and a half inches in length, although
possessing about two hundred proglottids. The rostellum
has four suckers and twenty-eight to thirty hooks (Fig. 14).

The small size of this tapeworm would seem to negative the
possibility of injury being caused to the host, but actually
such large numbers may coexist in the one host that serious
intestinal irritation may result. In children particularly it
causes considerable disturbance, diarrhoea and even epileptic
symptoms.

It is morphologically indistinguishable from Hymenolepis
murina of the rat and mouse, and by some authorities it is

HELMINTHES: THE TAPEWORMS 71

regarded as synonymous with it. The geographical distribution
of the parasite of man, however, does not appear to coincide
with the distribution of the rodent form ; the latter form is
probably world wide in distribution, whereas heavy human
infection with Hymenolepis is characteristic rather of sub-
tropical and of tropical countries. In the Old World, for
example, it is notoriously prevalent in the circum -Mediterranean
countries and in tropical Asia and Africa. On the other hand,
its presence in man is easily overlooked, unless the faeces are
examined microscopically for eggs. Probably the more justi-
fiable view is to regard the human parasite and the rodent
parasite as biological races of the one species Hymenolepis
fraterna.

The life-cycle is unknown. If it resembles that of H.
murina, the metacestode stages may be expected to occur within
the intestinal villi of the same host individual that harbours
the strobila.

If the human tapeworm is identical with the rodent one,
infection of man should occur through the contamination of
human food by murine faecal matter.

CHAPTER VII

HELMINTHES : The Roundworms

The terms roundworm, threadworm, nematode worm, are
applied to members of the zoological phylum, Nematelmia,
certain free-living and parasitic organisms which, although
sharply marked off from all other groups of worms, agree with
one another very closely in appearance and structure.

As is the case with the internal parasites discussed in the
preceding chapter, there are certain structural features, notably
the smooth resistant cuticle and the absence of locomotor
appendages which may be regarded as associated with the
habit of endoparasitism. The fact that the alimentary canal,
although simple, is developed and functional, and the occur-
rence of many more free -living genera than parasitic ones,
would seem to suggest that the parasitic habit among round-
worms is not of such long standing as is the case with
flatworms.

They agree one with another in possessing those character-
istics, such as the spindle shape of the body and the absence
of definite head which are popularly associated with the term
of " worm." The great majority are minute, even microscopic,
and semi-transparent, but in certain families there occur
forms large as the common earthworm, thickly cylindrical,
with a white opaque body wall.

From the flatworms, they differ in having a cylindrical
body. From the Annelida or segmented worms, they differ
in the absence of segmentation, internally or externally ; in
the possession of a body cavity which is not a coslom, that is to
say is not homologous with the body cavity of annelid or of
vertebrate ; in possessing distinct sexes ; and in not possessing
a ventral chain of nerve ganglia.

The great majority of roundworms live saprobiotically in
decaying organic matter, and these free-living forms are placed
in the one family Anguillulidce. The remaining families
comprise semi-parasitic and parasitic forms.

The majority of endoparasitic forms live in the alimentary
canal of other animals, but a number of forms are known to

72

HELMINTHES: THE ROUNDWORMS 73

inhabit the blood of animals, the connective tissues, the
respiratory organs.

The variations in type of life-cycle can be illustrated best
by description and discussion of certain forms which are of
major economic interest.

Ascarid Worms. — The worms belonging to the family
Ascaridce are gut parasites of vertebrate animals, and may be
described as somewhat long, thick, spindle-shaped forms,
opaque dirty white in colour. The females are oviparous and
the eggs usually possess a thick and sometimes sculptured shell.

The genus Ascaris itself occurs in most vertebrate animals.
Oxyuris is a genus of small, curved, acutely pointed worms,
usually termed " pinworms." Heterakis is a genus particularly
prevalent in the caecum of birds, and somewhat resembling
small specimens of Ascaris.

Belascaris is an Ascarid characterised by wing-like pro-
jections from the anterior end.

Ascaris lumbricoides of man is morphologically indistinguish-
able from, and almost certainly a biological mutant from,
Ascaris suilla of the pig.

Ascaris ovis of the sheep is believed to arise from chance

infection with the eggs of either the man- Ascaris or the pig-

Ascaris, and is said to be always sterile and incapable of

reproduction. Ascaris megalocephala of the horse is, however,

distinct from the human and porcine form.

Our knowledge as to the life-cycle of Ascaris is due in
particular to the work of Ransome with A. suilla in the United
States, the work of Stewart with A. lumbricoides in England,
and the work of Yoshida with the same species in Japan.

The worm is found in groups of five or six in the upper part
of the small intestine of the man or pig, and may easily pass
into the stomach and be vomited therefrom. It is widely
distributed, and the so-called " stomach worm " is very common
in children, especially in tropical countries.

It is a large worm, thick as a lead pencil, the female averaging
about ten inches in length, the male several inches less.

The eggs are ejected with the fseces of the host. They are
oval, have a thick and warty but transparent shell, and when
freshly passed are unsegmented. In damp earth or water
they start to segment, and are fully developed in from ten days
to a month. Under adverse conditions, however, they may
remain dormant for years, being extraordinarily resistant to
extremes of temperature or moisture, even to chemical dis-
infectants or to acids and alkalis.

74 THE PRINCIPLES OF APPLIED ZOOLOGY

Introduced into the host, generally by the medium of salads
or unfiltered water, they hatch in the small intestine. The
liberated larvae penetrate the gut wall and are carried by the
blood circulation to the liver or lungs. They may be found in
the latter organs within a week of infection, and may provoke
there mild bronchitis or even pneumonia. By the tenth day
after initial infection they are 1-1-5 mm. long. They pass
from the blood-vessels into the bronchial tubes of the lungs,
thence through the trachea to the mouth, and are carried down
to the small intestine where, in the appropriate host, they
settle ; in an unsuitable host, such as a rat, they pass out with
the faeces.

That Ascarid worms excrete a toxic substance seems certain.
Most experimenters with Ascaris have noted considerable
laryngeal irritation similar to that caused by formaldehyde
vapour. An infected person may show peculiar mental and
constitutional troubles, such as feverishness, anaemia, epilepsy,
or delirium.

The life-cycle is thus a fairly simple one, only one host being
concerned, and infection being contaminative, that is to say
by the host swallowing the ripe eggs. A similar mode of
infection characterises a large number of other nematode
worms, parasitic in man and domesticated animals.

Enterobius (Oxyuris) vermicularis, the pinworm of man,
lives as a young form in the small intestine ; as a mature adult
in the caecum and appendix. The eggs are, however, not laid
in the parental habitat, but outside it, either in the host's rectum
or even outside the anus in the groove between the buttocks or
in the perineal folds of skin. It is the nocturnal migrations
of ovipositing females which provoke the intolerable perineal
itching characteristic of Oxyurid infection. The eggs measure
50-54 by 20-27 microns, are asymmetrically oval, and are laid
at an advanced stage of development, so that if swallowed
by the host they will hatch immediately. Auto -infection is
possible and is probably very common.

The eggs are thin shelled and cannot withstand adverse
conditions.

Trichocephalus is a genus comprising several morphologically
different species, all found in the intestine of various mammals.
T. trichiurus is the whipworm of man, one of the commonest
human intestinal parasites.

It is a worm about two inches long, the anterior three-fifths
being thread-like and buried between the epithelial folds of the
caecum. The characteristic dark-brown, lemon-shaj)ed eggs,

HELMINTHES: THE ROUNDWORMS 75

with a plugged aperture at each end, occur in the faeces of the
host, develop outside the host in moist soil and, like those of
Ascaris, are extremely resistant to adverse conditions. They
enter the host again in contaminated water or food.

All the forms described above have therefore a life -cycle
that may be described as direct, infection of the host individual
occurring through passive swallowing of the nematode egg
and the egg hatching within the host.

It is possible that the typical life-cycle of a nematode worm
comprises four larval stages between egg and adult stages,
separated by moults. That is to say, there is the newly hatched
or first stage larva, a second stage larva characterised by an
enclosing " sheath," which is the loosened but unshed outer
skin of the first stage, a third stage larva, a fourth stage larva,
and then the adult stage.

In most cases of direct development the first stage is passed
within the egg shell, the newly hatched larva being a second
stage larva.

A second type of direct life-cycle is characterised by the
hatching of the eggs outside the host, the presence of the first
stage larva in moist soil, and its entrance into the host again
as a second stage larva either by passive transference in food or
water, or by active migration through the outer body surface
of the host.

It is a type of life-cycle particularly characteristic of the
family Strongylidse.

The Strongylid worms are pre-eminently the most important
of nematode parasites from a pathogenic standpoint, owing
to the fact that they are in the main tissue eaters, actually
rasping away the wall of their habitat and swallowing the
comminuted tissue and blood.

They are readily distinguished from all other nematode
worms by their mouth parts, which consist, generally speaking,
of a number of thorn-like or hook-like teeth affixed to the
inner wall of a horny cup which surrounds the mouth. They
are therefore popularly termed " hookworms."

The male is characterised further by the possession of a
membranous bell-shaped pouch, the so-called copulatory bursa
which surrounds the cloaca and which is stiffened by ribs some-
what in the manner of an umbrella.

They are divided generally into Lung Hookworms (Meta-
strongylince), Stomach Hookworms (Trichostrongylince), and
Intestinal Hookworms (Strongylince).

Sheep, and to a lesser extent cattle, pigs, and horses, often

76 THE PRINCIPLES OF APPLIED ZOOLOGY

harbour, in their lungs and tracheae, hookworms of the genera
Diclyocaulus, Synthetocaulus, and Metastrongylus. Lambs, in
particular, may succumb in large numbers to the onset of
pulmonary troubles, and concomitant anaemia and exhaustion,
brought about by the presence in the windpipe and bronchioles
of the " white lungworm ' (Dictyocaulus filaria) and the " red
threadworm " (Synthetocaulus rufescens).

The disease thus provoked is in Great Britain termed
' hoose ' or 'husk." The white lungworms are numerous in
the bronchioles, occurring in clusters of what look like four-
inch pieces of white twine surrounded by a frothy mucus and
lying in a swelling of the tube. Their presence causes the
bronchitic symptoms.

The red worms occur in the lung cavities rather than in the
bronchioles, and are much smaller, neither males nor females
exceeding one and a half inches in length. Their presence
provokes the pulmonary symptoms.

The life-cycle, as in the case also of other lung hookworms,
is unknown. Dogs are peculiarly liable to lung trouble of a
serious kind provoked by the presence of Hcemostro7igylus
vasorum, a pinkish threadworm some half to three-quarters of
an inch in length, in the right ventricle of the heart and in the
pulmonary arteries. The eggs of the worm become surrounded
by a capsule of epithelial tissue, and these capsules may simulate
in appearance the nodules of tuberculosis.

Stomach hookworms occur particularly in the abomasum
or so-called " fourth stomach " of ruminants.

Hsemonchus contortus, for example, probably causes more
loss among sheep than any other internal parasite. It is
widespread in distribution, and is regarded with great dis-
quietude not only by sheep farmers in Europe but by those of
Argentina, North America, and North and South Africa.

The worms are small, half to three-quarters of an inch in
length, so that thousands may occur in the abomasum of the
sheep. The name contortus refers to the way in which the
tubular white ovaries twist round the pink alimentary canal,
as seen through the transparent body wall of the living
worm.

The gastric strongylosis thus brought about is not
characterised by specific symptoms. Affected sheep become
weak and emaciated, show symptoms of anaemia and febrility,
tend to shed wool, and just waste away. Whether the effects
are due to mechanica] abstraction of blood by the worms or
to some toxin, is not certain.

HELMINTHES: THE ROUNDWORMS 77

Infection seems due to the eating of grass blades on which
sheathed second stage larvae of the worm are encysted.

The title of stomach hookworm is scarcely applicable to the
Trichostrongylid species, T. gracilis, which lives in the caeca of
the grouse (Lagopus). The worm is minute, less than half an
inch in length, and the caeca of the grouse are unusually large,
so that as many as ten thousand worms may occur in an infected
bird. Their presence produces a chronic inflammation leading
to fibrosis, the epithelial lining of the caeca becoming destroyed.
Since these organs are probably the sole absorptory regions
of the alimentary canal, the bird wastes away and dies. Deaths
from ' grouse disease ' occur most commonly in the spring,
when the birds are exhausted by a wiriter of semi-starvation.

The parasite is widespread, probably 95 per cent, of grouse
on British moors being infected, and every heather tip of a
grouse moor probably swarms with sheathed larvae waiting to
be ingested by a grouse. It would appear therefore impossible
to prevent the infection of birds by this parasite.

The Intestinal Hookworms include several genera of very
great medical and veterinary interest, notably Ancylostoma,
Necator, Strongylus, QUsophagostomum, and Syngamus.

The genera Ancylostoma and Necator have come greatly
into notoriety during recent years owing to the discovery of
their pathogenic influence upon man.

A. duodenale and N. americanus, the two species concerned,
are small worms, the male little more than one-third of an inch
in length, the female a little longer than half an inch. As
with hookworms generally, the males possess an umbrella-
like copulatory bursa, and both sexes possess well-marked
buccal capsules. The differences between the two species may
be summarised as shown on p. 78.

These Strongylid species live in the small intestine of man,
especially in the duodenum ; they have been recorded also
from anthropoid apes and have been successfully introduced
into dogs. In other animals other species of these genera
have been recorded, as well as species of the allied genera
Dochmius and V urinaria.

Ancylostoma and Necator do not seem to be true blood-
suckers. Possibly they bruise the intestinal mucosa and
accidentally take in blood, but their alimentary canal is not
pigmented nor are their excreta black with melanin, as is the
case with true bloodsucking worms.

There is no doubt, however, that they may give rise in the
host to severe progressive anaemia, resulting in degeneration

78 THE PRINCIPLES OF APPLIED ZOOLOGY

of the heart, musculature, liver, and so forth, and accompanied
by emaciation and dyspeptic trouble. Possibly these symptoms
result from the production of hemolytic toxins by certain
glands in the head of the worm. In cases of long standing
there is great retardation of mental and physical development.
Children of twelve or fourteen years old are no farther advanced
than children of half their age. The face has a bloated, stupid
expression ; the eyes have a characteristic hollow stare. A
mania for eating earth or mud sometimes occurs.

Ancylostoma

(I) Ventral margin of capsule with two
pairs of curved teeth, the roots of
which continue backwards and
appear on the external surface of
the capsule as rib-like thickenings.
The dorsal margin has a gap in
the middle, the rounded edge
tips of which form the so-called
" dorsal teeth." Inside the
capsule are also two ventral,
triangular lancets.

(2) Genital aperture of female
posterior half of body.

in

(3) Posterior tip of female with a fine

spine.

(4) In the male, the rib supporting the

dorso-median lobe of the bursa
forks about half-way up from its
base, and each branch divides
into three.

(5) If the worm be slowly killed, the

head lies in the same plane of
curvature as the body.

(6) A similar curvature occurs with the

bursa of the male.

(7) Mean dimensions of eggs are 00 by

40 microns.

Necator

(1) Mouth capsule narrow and without
teeth, merely possessing a thicken-
ing of the ventral edge of the
capsule. There is, however, a
chitinous cutting plate on each
side. A pair of ventral lancets
present.

(2) Genital aperture of female in anterior

half of body.

(3) Female without posterior spine.

(4) In the male, the rib supporting the
dorso-median lobe of the bursa
forks near its base, and each
branch divides into two.

(5) If the worm be slowly killed, the

head is curved in a plane different
to that of the body, so as to give a
hook-like effect.

(6) A similar curvature occurs with the

bursa of the male.

(7) Mean dimensions of eggs are 70 by

40 microns.

There can be little doubt that the endemic presence of hook-
worms among large populations results in tremendous loss of
efficiency and greatly retards the progress of education. The
marked inferiority of tropical labour as compared with temperate
zone labour can be ascribed almost entirely to the destructive
influence of years of hookworm disease and malaria upon
racial stamina.

HELMINTHES: THE ROUNDWORMS

79

The Distribution and Prophylaxis of Hookworm Disease. —

Ancylostoma and Necator occur, one or the other, almost every-
where between latitude 52° N. and 30° S. In Egypt, where
nearly every native is infected, the disease has existed since
earliest times ; it may be ancylostomiasis that is referred to

4*?1 h 5^ Stag-e larva

Skin lung's
intestine
of man

2™ & 3r-a Stag-e
larva

Strong-ylo id.

Fery mobile.

Ab pharyngeal
5ul6s.

Is-* Stag-e
larva

Rhabditi/orm.

Active.

ftapidly growing:

T&o pharyngeal Sulds.

Adults

In small
intestine

Eg-g-S

Laid in host's
intestine.

Hatch in damp,
warm soil.

Fig. 16. — Life-Cycle Stages of Ancyhstoma. (Not to scale.)

in the Ebers papyrus of 1550 B.C. It is equally common in
India, Eastern Asia generally, and occurs in Europe and in
America.

Necator has accompanied the African negro to South and
North America, the West Indies, and the Pacific Islands.
Ancylostoma may have spread from the Mediterranean area to
Asia, Africa, and America.

Both genera are extremely widespread in these areas, and

80 THE PRINCIPLES OF APPLIED ZOOLOGY

their extent of distribution is limited only by conditions of
soil temperature. Outside the latitudes given above, the
hookworm can only establish itself under the conditions afforded
by the interiors of mines and tunnels. It gained admittance,
for example, to the Cornish tin mines in 1902, introduced
probably from the Transvaal, and it was prevalent in the
Simplon tunnel during construction.

As the success of preventive and eradicatory measures, when
applied to an endemic disease, depends so very greatly upon
accurate and simple diagnosis and upon detailed knowledge
of the life-cycle of the causative organism, it is particularly
fortunate that our knowledge of the hookworm is so thorough.

The pathological effects produced by hookworms are not so
clear cut as to enable the presence of these parasites to be
determined from them with certainty. Fortunately, however,
unfailing and certain indication of hookworm infection is
afforded by the characteristics of the eggs.

The thin-shelled eggs commence to segment whilst in the
host intestine, and when observed in the faeces are usually in
the two, four, or eight-cell stage. This segmentation and their
transparency distinguishes them from the eggs of other intestinal
helminthes (Fig. 17).

Further development requires exposure to oxygen, a
moderately high temperature of 65°-80° F., and the presence
of moisture. The newly hatched larva is about 0-2 mm.
long, has a bottle-shaped oesophagus, a simple gut, and no
reproductive organs. If the habitat be moist and well aerated,
and if plenty of decomposing organic matter be present as food,
this larva feeds and grows rapidly until it is 0-5 mm. long by the
end of five days. Then the cuticle separates but remains as a
sheath around the larva, which is now ready to enter the
human host. Feeding stops, and the larva wanders actively
through the moist substratum.

Entrance into the host is gained by boring through the skin
of the legs, probably down a hair follicle, and entering a vein,
whence they pass via heart, lungs, oesophagus, and stomach
to the intestine. Two moults are passed through whilst
wandering in the host, and four to five weeks are required in
the host before maturity is reached (Fig. 16).

A campaign against hookworm therefore must comprise : —

(1) Measures for the expulsion of the worms from infected
persons.

(2) Measures to prevent contamination of soil by the faeces
of infected persons.

HELMINTHES: THE ROUNDWORMS 81

(3) Measures to prevent the passage of active larvae into
the human host.

(4) Extensive educational propaganda.

The first measure is effectively carried out by the establish-
ment of travelling clinics where people can be examined and
treated free of charge. It must be remembered that it is the
extremely poor and illiterate sections of a population that are
most subject to the disease. Thymol was until recently the
classic drug for hookworm, but its use is rapidly becoming
supplanted by that of oil of chenopodium.

The second measure requires the establishment of an
efficient system of latrinage and of sewage disposal. In most
tropical countries among the people where hookworm disease
is rife, latrines are, as a rule, unknown, so that the surface
soil around habitations may teem with hookworm larva3.
Contaminated ground can, of course, be treated with dis-
infectants or with salt, but large quantities are required.

The third measure is carried out by the encouragement of
the wearing of boots or shoes by field workers, or where people
habitually do not use foot-gear, or are too poverty stricken to
acquire them, by encouragement of the habit of smearing
feet and legs with some form of tar.

Educational propaganda comprises an extensive campaign
of lectures, free illustrated pamphlets, posters, and school
instruction.

Acting on such lines, the American International Health
Board, financed munificently by John D. Rockefeller, has
carried out an enormous amount of valuable work since 1909
in the eradication of hookworm disease not in the United States
alone, but in South America, Egypt, the West Indies, Eastern
Asia, and elsewhere.

A great many other intestinal hookworms have been reported
from the alimentary canal of horses and cattle and, occasionally,
of man.

Strongylus equinus, for example, is, after Ascaris, the
commonest nematode parasite of the horse, and certainly the
most injurious. Its position in the host is curious. Coupled
males and females occur in the caecum. Larval or immature
stages occur in many of the arteries, in the portal vein, the liver,
pancreas, lungs, testes, and in submucosal swellings of the
caecum, varying from a pinhead to a nut in size.

The worm measures three-quarters to two inches in length,
is straight in shape, greyish-brown in colour, and has a buccal
capsule provided with two cutting plates.

6

82 THE PRINCIPLES OF APPLIED ZOOLOGY

The eggs, expelled with the faecal matter, develop in water
or damp earth, and hatch within eight days. The larvae reach
the small intestine of the host in drinking water. From there
they wander into the circulatory system, but eventually they
encyst in the submucosa of the caecum and complete their
development until provided with buccal capsule and caudal
bursa. Finally they pass into the cavity of the caecum through
an aperture in the cyst, become mature and copulate.

The adult worms in the caecum, despite their number and
blood-sucking propensities, probably provoke no serious trouble
beyond diarrhoea and emaciation. The larvae, however, in the
circulatory system may cause serious aneurisms, especially
on the mesenteric arteries, aneurisms as large as a walnut, and
containing up to a dozen pink larvae. Or the}^ may cause
obstruction of the blood-vessels. Animals infected by the
armed strongylid are prone to attacks of colic.

The genus Syngamus is more particularly a nematode of
birds.

Syngamus trachealis, for example, is a serious parasite of
young Galliform birds. The worms occur in large numbers
attached to the inner lining of the windpipe of infected birds,
especially where the pipe divides into the bronchioles. Each
worm looks like a tiny letter Y ; one of the small arms of the
Y represents the male, the rest of the Y representing the female ;
they are permanently and inseparably coupled. In spite of
the permanent copulation, eggs can pass from the vagina of
the female into the bursa of the male, and are then ejected
forcibly from beneath the dorsal flap of this bursa.

The eggs, as seen in the faeces of infected birds, never show
development beyond the sixteen-cell stage. They are somewhat
different from other strongylid eggs, being oval and having
each extremity thickened to form a little cap.

These eggs take about a week to develop and to produce
infective larvae. A somewhat high temperature, namely
25° C.j is required, but apparently the unhatched egg may also
be infective. The contained embryo moults before hatching,
so that the larva which actually emerges is really a second
stage larva, surrounded by a sheath, and thus not very active.
It reaches the bird almost certainly by being picked up and
swallowed, although possibly the earthworm may serve as a
mechanical intermediate host. From the alimentary canal
of the bird, the larvae in some way, not yet with certainty
determined, reach the lungs, and in so doing lose their sheath.
In the alveoli of the lungs these larvae develop further. Then

HELMINTHES: THE ROUNDWORMS 83

they migrate to the trachea, copulate, and attain sexual
maturity. The whole life-cycle occupies a month. The effect
of these parasites upon a bird is, briefly, to asphyxiate it, an
effect produced not only by their numbers but by the copious
secretion of mucus induced by their presence. Badly infected
chicks run about with beaks widely open, and hence the disease
is termed " gapes " in English-speaking countries. Enormous
losses are caused among young poultry and pheasants by this
disease.

Several remedies have been tried with success. Birds may
be shut up in a box and a fog of camphorated chalk produced
by the aid of a bellows to induce the birds to cough vigorously.
Another remedy which has given excellent results is the injection
of 1 c.c. of 5 per cent, sodium salicylate solution into the
trachea through a hypodermic syringe. Prophylaxis comprises
the isolation of infected birds, removal of non-infected birds to
a fresh site, and treatment of the soil of the old runs with salt
solution or with a 1 in 1,000 solution of sulphuric acid.

A link between the type of life-cycle characteristic of
Strongylid worms and the type seen in the case of Ascarid worms
is afforded by the genus Strongyloides.

S. ster cor alls is a very small worm, about one-tenth of an
inch long, which bores into the intestinal mucosa of man.
Only the female is known, and she is recognisable by the chain
of six or seven eggs lying near the middle of the body and
visible through the transparent body wall. The eggs are laid
deep in the intestinal mucosa and hatch there, so that the
first stage larvae occur in the faeces. They may be mistaken,
sometimes, for newly hatched hookworm larvae in faeces which
have been kept for more than a day before examination, but
the larva of Strongyloides is long and slender and easily dis-
tinguished from the Ancylostoma larva by the fact that its long,
slender oesophagus extends nearly to the middle of the body.
Further development of the larvae requires water of somewhat
high temperature. Under such conditions the larva becomes
an adult, either male or female, very different from the intestinal
form. These copulate, and the females lay thirty or forty
eggs within two days. These eggs produce larvae similar in
form to their free-living parents, but after a moult, similar to
the gut-living grandparent. This larval type penetrates the
body surface of a human host much as the hookworm larva
does, mainly through the hair follicles.

A third main type of life-cycle is characterised by the eggs
hatching in the parental uterus by the liberation of living larvae
within the body of the host, and by the transference of the larval

84 THE PRINCIPLES OF APPLIED ZOOLOGY

stages to another host individual by the intermediate aid of
another type of animal. That is to say, in this case the life-
cycle is an indirect one and comprises a primary or definitive
host and a secondary or intermediate one.

The simplest example of this type of life-cycle is afforded
by the case of the genus

Trichinella. — This nematode lives in the adult condition
in the small intestine of man, the rat, the pig, and occasionally
in other domesticated animals. Rats are more easily infected
than sheep or horses, and the latter are more easily than
cats or dogs. All these animals also serve as intermediate
hosts.

The worms are small and live between the intestinal villi
or even within the crypts of Lieberkiihn. After copulation
the males die, but the females increase as much again in size
and bore through the mucosa into the lymphatic spaces. Here
living larvse are extruded, and these become carried passively
by the lymph stream to the heart, and from thence to various
parts of the body.

Only such larvae, however, as arrive in muscular tissue can
survive. Particularly do they seem to arrive in the muscles
of diaphragm, ribs, neck, throat, and eye, that is to say, in
muscles whose blood supply is rich and where there is a high
oxygen content and a high glycogen content.

Ten days after initial infection these muscles of the host
will contain innumerable lemon-shaped cysts lying among,
and parallel to, the muscle fibres, and each containing a larval
Trichinella, coiled in a loose spiral and living apparently upon
the glycogen of the muscle. The cyst wall appears to be an
inflammation product of the connective tissue, rather than a
secretion from the worm itself.

Incredible numbers of such cysts may occur, as many as
two millions in a pound of infected sausage meat having been
recorded.

The cyst wall is usually calcified, and the cyst may remain
potentially infective for years. If swallowed, however, by an
appropriate host, the encysted worms emerge, and within forty-
eight hours are copulating.

Pigs become infected by eating dead rats. Man becomes
infected by eating undercooked and infected pork. In France
and Great Britain the disease of trichinosis is rare, but in
Germany and North America the custom of eating raw or
smoked ham or sausage has been responsible for many epidemics.
The parasite may have come from the East with the grey rat
at the end of the eighteenth century.

HELMINTHES: THE ROUNDWORMS 85

Invasion of the muscles in man produces muscular tender-
ness or even interference with the respiratory or oesophageal
functions, accompanied by much swelling of face and eyelids.
Lung trouble and death are common sequelse, the mortality in
an epidemic being sometimes as high as 30 per cent.

Prophylactic measures are two, namely : —

(1) The extermination of rats in the vicinities of piggeries
and abattoirs.

(2) The avoidance of pork which has not been subjected to
a temperature throughout of 62°-70° C.

Cold storage for twenty days below 5° C. is effective in
sterilising the meat, according to the Regulations of the United
States Bureau of Animal Industry.

The most complete example of nematode worms with distinct
primary and secondary hosts is afforded by the members of
the family Filariidse. a family of very long, slender worms
whose members occur in the lymphatic vessels, heart, serous
cavities, or the subcutaneous tissues of vertebrate animals,
and whose larval stages occur in the circulatory system and
are carried from host to host by a blood-sucking arthropod.
The best known genera are Filaria, Dracunculus, and Oncho-
cercus. Filaria bancrofti occurs in the form of a hair-like female
two to six inches long, coiled round a slender male about half
the size, in clumps in the lymphatic glands and ducts of man
in tropical and sub-tropical countries.

Obstruction of the lymphatic system by clumps of these
worms provokes certain pathological lesions, in particular an
enormous enlargement of the part of the body where the
obstruction occurs, referred to as " elephantiasis." Such
elephantiasis affects particularly the lower limbs and scrotum.
The disease is characterised by repeated attacks of filarial
fever or lymphangitis, in which chills and high fever accompany
a painful swelling of the part affected. After each attack has
subsided, a hard layer of permanent tissue is left, and so the
hard, unyielding growth is gradually built up. Escape of the
contents of lymph vessels into the kidneys or bladder produces
chyluria, or the presence of a milky, coagulable condition of
the urine.

The embryos or microfilariae occur in the peripheral blood
circulation, and were known long before their connection with
the adult filarise was suspected, under the name of Filaria
sanguinis hominis. They were found to occur always in the
blood of persons suffering from chyluria, elephantiasis, and
lymphatic tumours as minute, wriggling, eel-like creatures
enveloped in a sort of sheath somewhat longer than the body.

86 THE PRINCIPLES OF APPLIED ZOOLOGY

It has long been known that these forms are present in the
peripheral blood during the night and absent during the day,
retiring then, as indicated by post-mortem examinations, to
the capillary vessels of the lungs and heart and to the larger
arteries. No satisfactory explanation of this phenomenon
has yet been put forward, and the difficulty of framing a
physiological explanation which will fit the facts is made
greater by the fact that in Fiji, the Philippine Islands, and the
South Sea Islands the embryos of Filaria bancrofti do not show
this periodicity, and that the very closely related Loa loa has
microfilariae whose appearance in the peripheral blood is diurnal.

It is certain that this appearance of the embryonic filaria3
in the peripheral blood is correlated with the use of the mosquito
as an intermediate host. A large number of mosquito species
are known to serve as intermediate hosts, but only in four or
five has the complete development been observed, namely,
in Culex pipiens, Culex fatiguans, Stegoinyia pseudoscutellans
among Culicines, and Myzomyia rossii and Pyretophorus
costalis among Anophelines.

In the mosquito the embryos pass into the stomach, and
each gradually works its way out of the containing sheath.
The liberated larval stage then makes its way between the
fibres of the thoracic muscles and remains there for a time,
growing rapidly, developing a mouth and alimentary canal,
and becoming thicker and longer. Eventually it leaves the
muscles and passes into the proboscis of the insect, into the
cavity of the labium, in fact, whose thin enveloping cuticle it
punctures so as to arrive between the piercing mouth parts.

When the mosquito bites man, the filarise are deposited on
the skin in the vicinity of the puncture and are said to penetrate
the epidermis and reach the subcutaneous tissue, from there to
migrate to the lymphatic vessels, where they become sexually
mature and copulate.

Loa loa is a form very similar in appearance to Filaria
bancrofti, but characterised by possessing a cuticle studded
with small excrescences. It is native to West Africa, particu-
larly to the Congo region, but has been introduced by the slave
trade into South America, where, however, it is now somewhat
rare.

The adult worm lives in the subcutaneous tissues and is
very active, creeping along at the rate of about an inch in
two minutes just below the skin, especially if the skin be
warmed.

When in deeper tissue the presence of the filariae provokes
painful temporary swellings, the so-called " Calabar swellings."

HELMINTHES: THE ROUNDWORMS 87

The microfilariae occur in the peripheral blood by day and
not by night, so that the possibility of a mosquito serving as
intermediate host seems doubtful. There is some evidence that
Tabanid flies, of the genus Chrysops, may serve as intermediate
hosts.

Filaria immitis, the " cruel worm " of dogs, inhabits the
right ventricle and pulmonary artery of dogs and other carni-
vores. The female is viviparous, and the larvae remain in the
blood until taken up by a mosquito. Since the parasite is
cosmopolitan in distribution, various species of mosquitoes
may transmit it ; in Europe, Anopheles maculipennis and
Anopheles bifurcatus are concerned ; in Australia and North
America the carrier is Culex fatiguans.

Infection is said to be fatal to 50 per cent, of mosquitoes
owing to destruction of the Malpighian tubules by larvae which
have penetrated the wall of the midgut. The disease is fatal
to the vertebrate host owing to destruction of the red blood
corpuscles.

The close related Filaria recondita of dogs is transmitted by
the dog-flea and a tick, Rhipicephalus siculus.

A new species of Filaria described by Theiler in South
Africa, namely Filaria gallinarum, has for intermediate host
not a blood-sucking insect but a termite, Hodotermes pretoriensis .
Worker termites, it is believed, swallow the eggs, and the larvae
undergo development in the ccelomic cavity of the insect, and
complete it in the fowl.

The genus Dranunculus of Filariid worms is peculiar in that,
according to some authors, no genital aperture exists in the
female, and the eggs escape from the body via the mouth.
Other authorities state, however, that an aperture exists just
behind the cephalic shield.

Dracunculus medinensis is an extremely long, slender worm,
sometimes as long as three feet, which lives in subcutaneous
ulcers of man, especially located on the ankles, on the legs, and
backs of water carriers, on the arms of native women. Origin-
ally African and particularly distributed in the Sudan, West
Africa, and Arabia, it has become introduced into tropical
America. It has been known since remote times, and is
undoubtedly the prototype of the " fiery serpents " which
afflicted the Israelites during the wanderings. The common
native method of extracting the adult worm by coiling the
protruding end around a stick and winding the creature out
has probably led to the association of the rod of ^Esculapius
with the twining serpent, familiar as the badge of the British
Royal Army Medical Corps.

88 THE PRINCIPLES OF APPLIED ZOOLOGY

When mature, that is to say about twelve months after the
initial infection, the worm approaches the skin surface, so that
its head lies just below the cuticle. Owing probably to the
discharge of some irritant fluid, a blister large as a florin forms
above the site of the worm. After a day or two this blister
bursts and forms an intensely painful ulcer, from the bottom
of which the head of the worm protrudes. If the ulcer comes
in contact with water, a milky fluid is discharged from a little
bladder near the mouth, representing probably the prolapsed
extremity of the uterus. This fluid swarms with tiny coiled
larvae having characteristically straight tails.

The resemblance of these larvae to those of the Strongylid
Cucullanus, a blood -sucking Nematode parasite of the perch,
whose larvae develop in the water flea Cyclops, led Leuckart
to suspect a similar intermediate host for Dracunculus, and the
work of Fedschenko, Leiper, and others has since fully sub-
stantiated this suggestion.

The larvae enter a species of Cyclops by penetrating the
exoskeleton, or, according to Leiper, by entering the mouth,
and encyst in the body cavity. Experiment shows that slight
acidity of the medium, such as is provided by the hydrochloric
acid of the human stomach, kills the Cyclops but stimulates
emergence of the Nematode larvae, so that man is probably
infected by swallowing Cyclops individuals.

The native method of extracting the worm is that of rolling
the protruded portion around a stick an inch or two per day
until fully withdrawn. The method is dangerous, since if the
worm be broken, larvae will escape into the subcutaneous
tissues and cause severe inflammation and abscess formation.
More satisfactory is the method of securing the worm by a
ligature and injecting into it a solution of 1 in 1,000 corrosive
sublimate or of chloroform. Extraction is then usually easy
after a few hours.

Prophylaxis consists in the avoidance of unfiltered or
unboiled water in regions where the worm is endemic.

Closely related to the Filariae is Onchocerca, a slender worm
several inches long and slender as a hair, which occur in couples
in subcutaneous fibrous tumours, the so-called " onchocerca
nodules " in men and animals. The tumour varies in size from
a nut to a pigeon egg and, in addition to several pairs of adult
worms, contains small spaces swarming with sheathless micro-
filariae. These are believed to migrate into the peripheral
blood and to be taken up by blood-sucking flies.

Onchocerca volvulus affects man in West and Central Africa.

Onchocerca gibsonii affects cattle in Australia.

CHAPTER VIII

HELMINTHES : The Pathological Aspect

It will be apparent from the preceding chapters that there are
few places in the animal body that are not liable to become the
site of infestation by some form of helminth parasite.

Certain organs, however, are more likely than others to
harbour a wide range of such parasites.

The vertebrate alimentary canal is one such organ ; in the
stomach occur particularly many Strongylid and Filariid worms ;
in the blood-vessels and ducts of the liver occur such flukes
as Dislomum, Fasciola, Dicroccelium, Opistorchis, Clonorchis,
Schistosoma, and the liver substance, or the connective tissue
in proximity to it, is a favourite site for metacestode stages of
tapeworms ; in the intestine occur such flukes as Heterophyes,
Echinostomum, Holostomum, Amphistomum, the strobila stage
of tapeworms, Ascarid worms, Strongylid worms, Trichinellid
worms, Echinorhynchid worms, and so forth. The outer skin
and the invaginated epithelium which lines buccal cavity,
rectum, and even the bladder are liable to afford a habitat for
ectoparasitic flukes.

Lungs and trachea may harbour such forms as Paragonimus,
Metastrongylus, Dictyocaulus , Hcemonchus, Syiigamus, and so
on.

Muscles and subcutaneous tissue may be attacked by
metacestode stages of tapeworms, by Filariid worms, by Trichi-
nellid worms.

The circulatory system may contain species of Schistosoma,
Bilharziella, and microfilariid larvae.

The question of the general effect of helminth parasites
upon the well-being of the host is therefore a wide one.

Speaking very generally from the pathological standpoint,
the presence of helminth parasites —

(a) May apparently cause no inconvenience at all to the
host.

(6) May cause general malaise.

(c) May cause definite localised lesions recognisable as
associated with particular parasites.

89

90 THE PRINCIPLES OF APPLIED ZOOLOGY

It is somewhat dangerous to assume that any helminth
parasite is neutral to its host. Our ignorance of the pathology
of animals other than man and domesticated animals is so
profound, and our knowledge of the details of the life history
of even common helminth parasites so full of gaps, that many
parasitic forms regarded to-day as harmless to their host may
be shown by fuller investigation to be of very great pathological
importance. In the past, helminth investigation has been
wedded so closely to tropical medicine that the pathological
importance of parasitic worms to the inhabitants of temperate
latitudes has been to some extent neglected.

Concerning the pathogenic aspect of Schistosoma, Ancylo-
stomum, Filaria, the literature is voluminous ; concerning the
pathogenic aspect of the much more common nematode genera ,
Oxyuris, Ascaris, and Trichocephalus , knowledge is scanty.
Yet the numerous observations recorded of the frequent
association of Oxyuris vermicularis of man with many conditions
clinically recognised as appendicitis, justify a more thorough
investigation of the subject ; the probable identification of the
human and the hog forms of Ascaris and the occurrence in
both hog and man of bronchitic trouble caused by migrating
larvae of Ascaris certainly justify an inquiry as to whether it
may not be the provoking agent of diseases regarded as obscure
and indefinite.

The term helminthiasis is usually applied to a group of
symptoms including particularly severe anaemia, malnutrition,
mental and physical retardation, vomiting, diarrhoea, bron-
chitis, pulmonary disturbance, febrility, when associated with
the presence, in faeces or sputum, of eggs or larval or even adult
stages of helminthes. Where the causative helminth is known,
the group symptoms may be termed ascaridiasis, strongyliasis,
ankylostomiasis, filariasis, and so on. The symptoms arise
indirectly through the presence of the parasite, through its
propensity for absorbing the intestinal juices or the blood of
its host, or through its excretion of toxic products into the
system of the host.

Definite tissue lesions may be produced in several ways ;
intestinal helminths may dissolve away the mucous epithelium,
may actually puncture it, or may break right through into the
submucosa ; in either way they permit secondary bacterial
infection to occur, and so indirectly pave the way for
appendicitis, enteritis, peritonitis, or even typhoid fever.

Again, the mechanical pressure of a large parasite, such as,
for example, a metacestode cyst, upon such an organ as the

HELMINTHES: THE PATHOLOGICAL ASPECT 91

brain, the nerve cord, the liver, or the lung, may cause serious
disturbance in the host. The active migration of larval stages
of helminthes through host tissues may provoke lesions. The
accumulation of large numbers of parasites in capillary blood-
vessels or lymph-vessels, in bile-bucts or pancreatic ducts, or
in trachea or bronchioles, may be of the utmost pathological
importance to the host.

The Diagnosis of Helminth Parasites. — The problems of
helminthology depend for successful solution upon (a) accurate
knowledge of the life-cycle ; (6) accurate methods of diagnosing
the presence of helminthes in the host. The accurate study of
a helminth life-cycle demands a highly trained laboratory
worker, and necessitates : —

(1) A knowledge of the precise morphology of the adult
parasite, its larval stages, its diagnostic differences from related
forms.

(2) Ample sources of material of all stages.

(3) The elaboration of methods of host examination, of
parasite cultivation outside the host, of experimental infection
of uninfected hosts, and so on.

The clinical diagnosis of the prevalence of helminthes within
an animal depends : —

(1) If the animal be alive, largely upon the discovery and
identification of eggs, or more rarely of living worms, in the
faeces, urine, sputum, or blood of the animal.

(2) If the animal be dead, upon the discovery and identifica-
tion of adult worms in the alimentary canal, respiratory tract,
muscles, or connective tissue.

Certain precise and standard methods for the examination
of eggs and worms in faeces or animal secretions are now in
general use, and accuracy of technique is most important.
There are at least four methods that can be used. Each has
its advantages and disadvantages as compared with the others.
They are : (1) the Smear Method ; (2) the Centrifugation
Method ; (3) the Brine Flotation Method ; (4) the Culture
Method.

The Smear Method is simple, quick, applicable to any
suspected body fluid, and affords information as to the presence
of protozoal organisms as well as of helminthes. On the
other hand, it is not to be relied upon in the case of light
infestations. It is carried out by taking a small quantity
of the fluid under examination and smearing it over the
surface of a glass slide so that it can be examined micro-
scopically. The smear should be sufficiently thin to enable

92 THE PRINCIPLES OF APPLIED ZOOLOGY

print to be read through it. Faeces or thick sputum, therefore,
should be first emulsified with a little distilled water.

The Centrifugation Method is applicable to faeces or to urine.
A piece of faeces large as a walnut is emulsified with distilled
water, filtered through a coarse sieve into a tube which is corked
at each end, and then centrifugalised. The sediment is allowed
to settle on one or other of the corks, and can then be removed,
smeared over a slide, and examined.

The Brine Flotation Method depends upon the greater
density of brine over that of some helminth eggs. A piece of
faecal matter should be emulsified with equal parts of glycerine
and saturated salt solution, the floating matter forced below the
surface with a disc of steel wool, and allowed to remain for an
hour. The surface film is then removed with a loop of platinum
wire on to a glass slide and examined without a cover glass.

It must be noted that this method will not indicate the
presence of operculate eggs, such as those of flukes or of bothrio-
cephalid tapeworms, nor, as a rule, does it indicate the presence
of nematode larvae. A precise application of this method, used
in the diagnosis of Ankylostoma infection, is as follows : The
emulsified faecal material is centrifugalised with distilled water.
The supernatant fluid, containing food debris, is poured off. To
the sediment, calcium chloride solution of sp. gr. 1050 is added.
The fluid is again centrifugalised and decanted. Then calcium
chloride solution of sp. gr. 1-250 is added and the fluid centri-
fugalised. The hookworm eggs then float on the surface of the
fluid.

Cultivation Methods are, generally speaking, applicable to
nematode worms only, and they have the disadvantage of
taking up too much time to be useful as routine methods. They
are, however, much more certain in their results, and will
afford evidence of infestations that other methods may overlook.

The faecal sample is mixed with bone black, or with sterilised
sand or humus, and spread out over a quarter inch pile of
circular filter papers in a shallow dish to the depth of one inch.
The surface is kept moist and the culture is incubated for five
or six days at 25°-30° C. Then the culture is flooded with
water which is then decanted, centrifugalised, and examined.

Even after a good smear has been obtained, the identifica-
tion of helminth stages which may occur in it is not an easy
task.

Usually the clear-cut outline of the eggs or of the animals
themselves helps to distinguish them from the various vegetable
cells, soaps, crystals, leucocytes, and other miscellaneous faecal

HELMINTHES: THE PATHOLOGICAL ASPECT 93

debris, but such distinction is not always readily made ;
undigested banana fibres, for example, resemble astonishingly

haematobium S.Mansoni S.Japonicum Ascaris

Trichocephalus ^1 ^ j^- Taenia saginata Taenia solium

Hymenolepis Diphy
dirainuta

lobothrium
latum

-lookworm

eg-g-s

Fig. 17. — Helminth Eggs occurring in Human Faeces. (After various Authors.)

a cluster of small tapeworms ; starch grains or crystals may be
readily mistaken for eggs or for protozoan cysts.

94 THE PRINCIPLES OF APPLIED ZOOLOGY

The possession of an operculum or lid by an helminth egg
relegates it to some species of fluke or of bothriocephalic! tape-
worm ; the presence within it, of a six-hooked embryo, indicates
that it is the egg of a tseniid type of tapeworm. Nematode
eggs are thus fairly easily distinguished from those of flatworms.

Further identification of an egg depends upon : —

(a) Its long and short diameter, expressed in microns.

(b) The nature of the external shell, whether thick and
sculptured, or thin and transparent.

(c) The stage of development of the eggs, whether unseg-
mented, or four-celled, or many celled, or even embryonic.

Fig. 17 indicates the general size and appearance of the
commoner type of helminth eggs. Identification of the larval
or adult worm depends upon various structural characters. .

In adult Trematoda the identification rests upon the number
and position of the suckers and the arrangement and shape
of the reproductive system components.

Adult tapeworms are identified upon characters of the
suckers, the number, arrangement, and shape of the hooks
on the rostellum, the shape of mature proglottids, the arrange-
ment of the genital pores, and the shape of the ripe uterus.

Metacestode stages of tapeworms are identified by the
character and arrangement of the suckers and the rostellar
hooks.

Nematode worms are identified principally from the nature
of the following structural features : —

(1) The shape, whether short and thick, or slender and
thread-like.

(2) The mouth aperture, whether consisting of lips, true
jaws, or of a capsule or cup.

True lips consist usually of three labial projections sur-
rounding the mouth. The largest of the three represents
probably a fusion of two, and occupies the entire dorsal half
of the oral aperture. The two smaller lips are ventral and
separated by a narrow median slit. These lips can grasp and
draw between them small objects. Usually the three-lipped
condition is associated with an oesophagus whose lumen is
triradiate.

Jaws comprise a pair of lateral structures in shape some-
what like a scallop shell. Their outer edges can be opposed
so as to grasp an object, or they can move against each other.
They are separated dorsally and ventrally by very narrow slits.

An oral capsule is shaped like a hemispherical cup, the
opening being circular or oval but never slit-like. The inner

HELMINTHES: THE PATHOLOGICAL ASPECT 95

wall of the capsule may bear cutting or piercing organs. The
outer edge may be serrated, spiny, or papillate. The capsule
is immovable and serves as an attachment organ. The internal
teeth can move and can rasp away the tissue to which the
cup is applied.

(3) The structure of the oesophagus, whether muscular or
triradiate in transverse section, whether capillary and con-
sisting of a delicate tube running through a row of cells, whether
muscular and possessing one or two specialised regions or
" bulbs."

(4) The occurrence of a caudal bursa, a cuticular expansion
surrounding the tail end of the male and used for copulatory
purposes. There are two types : —

(i.) A semicircular membranous cup supported by ribs,
somewhat like an umbrella (Strongylidce).

(ii.) Lateral folds along the posterior part of the body
(Spiruridce).

Prophylaxis and Treatment of Helminth Infections. —
Preventive methods against helminth infection depend, as
regards the details, upon the life history of the helminth whose
prohibition is desired.

Measures against helminth parasites in general, however,
should comprise : —

(1) A pure water supply. Freedom of water from helminth
eggs can be only ensured by a very efficient system of filtering
or by heat sterilisation. Bactericidal treatment by chemicals is
usually of little effect upon helminth eggs.

(2) An efficient system of latrinage and of disposal of human
excreta.

(3) The protection of food-stuffs from flies, rats and mice,
and cockroaches.

(4) Abolition of the practice of using human or hog manure
in vegetable gardens.

(5) Periodical use of antihelminthic drugs.

Against a helminth parasite the ordinary purgatives, which
merely excite peristaltic action of the gut, are of little use, since
most helminth parasites can adhere firmly to the gut wall or
can wrap themselves round the villi of the mucosa and so avoid
being carried down the gut by peristalsis.

There are, however, certain drugs which can affect the
parasite through the host blood supply and cause it to relinquish
its hold on the mucosa.

The usual method, therefore, followed to bring about the
expulsion of helminthes from the animal gut is, in the first place,

96 THE PRINCIPLES OF APPLIED ZOOLOGY

to free the gut from the bulk of contained fseces by the use of
aperients or water enemata ; secondly, to administer the
appropriate dosage of an antihelminthic drug ; thirdly, to follow
tnis up by the administration of a saline purgative such as
magnesium sulphate or calomel.

Against tapeworms, for example, antihelminthic drugs
commonly used are alcoholic extract of male fern (Aspidium
filix mas), pellietierine (an alkaloidal constituent of pome-
granate root), and thymol.

The latter drug was formerly the most commonly employed
specific against hookworm ; its use is not without danger,
since it is soluble in alcohol and in fats, and if absorbed into the
human system owing to the presence of such substances in the
gut, may cause collapse and delirium.

Oil of chenopodium or its alkaloidal antihelminthic con-
stituent ascaridol has been found to be more effective and
somewhat safer than thymol, particularly against hookworms.

In experimental work in the control of hookworm amongst
coolies on tea plantations in India, the drug beta naphthol was
found in 1918-20 to possess hitherto unsuspected vermifugal
properties. It has, however, the objection that it is seriously
toxic to people who have active or latent malarial infections.

Chloroform, again, if dissolved in castor oil, can be given
with as much safety in 3 or 4 grm. doses as can other
antihelminthics ; but unless rapidly eliminated from the system,
may cause degeneration of the liver.

Carbon tetrachloride, a substance similar in constitution
and properties to chloroform, is a comparative recent addition
to the ranks of antihelminthics. It seems to be almost specific
for the hookworm Necator, but is less effective against Ancy-
lostoma. In doses of 2 c.c. for adults it is most efficient in the
removal of hookworms, and is safer than is the use of 1-5 c.c.
doses of chenopodium or 3 grm. doses of thymol or 4 grm.
doses of beta naphthol.

It is cheap, palatable, and easy to administer, particularly
useful qualifications for its use in mass treatment of hookworm
infected populations. It is dangerous, however, to people
whose liver has been already weakened by alcohol or by other
causes.

CHAPTER IX

ARTHROPODA AND DISEASE : Toxic Inoculation

The term disease will be used here in a very wide sense to
express the appearance of lesions or changes in an animal's
tissues, induced by some extraneous influence and inimical
to the well-being of the animal. The term Arthropoda will be
used to indicate the phylum of animals, which includes insects,
spiders, scorpions, ticks and mites, centipedes and millipedes,
Crustacea, and many other similar forms.

The association between such lesions and Arthropoda may
be one of several types.

Tn the first place, the lesions may be produced by direct
inoculation of some toxic substance by an arthropod into an
animal host ; to this type the term toxic inoculation may be
applied.

In the second place, the lesions may be caused by the actual
presence of an arthropod within the host body ; to this condition
the term myiasis is usually applied, an unsuitable term, because
the ability to produce such lesions is not restricted to the larvae of
flies, as the term implies, but is shown by many other arthropods ;
this type of disease relationship would be more aptly termed
entomiasis.

In the third place, the lesions may be caused by some
organism, usually bacterial, of which the attacking arthropod
is a carrier ; this type may be termed mechanical transmission.

In the fourth place, the lesions may be caused by some
organism, usually of a protozoan nature, to which the in-
criminated anthropod serves as an indispensable and alternative
host ; to this type of disease production the term cyclical
transmission may be given.

These various categories are, of course, purely artificial
divisions created for convenience of description, and it is not
always possible to restrict a particular arthropod type to the
one category. Blood-sucking arthropods, such as the mosquito,
may be qualified for inclusion within more than one of the
categories, since they may cause tissue irritation by their bite,
may mechanically infect the host with some bacterial organism,

7 «

98 THE PRINCIPLES OF APPLIED ZOOLOGY

may infect the host with some protozoan organism which has
passed a phase of its life-cycle within them.

The arthropods, which produce lesions by inoculation of
toxic substances, may be divided, for convenience of discussion,
into : —

(a) Venomous biters, including certain spiders and camel
spiders, certain ticks and mites, certain blood-sucking insects.

(6) Venomous stingers, including scorpions, bees, and
wasps.

(c) Irritant caterpillars.

The common belief that spiders in general are venomous
is unfounded, at any rate as regards their possibility of injuring
large animals ; and the romantic legends of the remarkable
dancing mania or tarantism of mediaeval Italy, supposed to be
provoked by the bite of the tarantula and curable by a dance
termed the tarantella, are based upon the occurrence, among
a population exhausted by malnutrition and disease, of epidemic
hysteria.

Lycosa tarantula, a large spider of Southern Europe, and
Trochosa singoriensis of Russia, are certainly spiders whose
bite is one to be respected but not dreaded by man.

Similarly, as regards the formidable Avicularidae or bird
spiders of Central and South America, although they are suffici-
ently venomous to kill small birds, especially nestling birds,
there is no evidence that they can endanger the life of any large
bird or mammal.

There are, however, a number of authenticated records,
from different parts of the world, concerning the danger to man
of certain small insignificant spiders belonging to the genus
Latrodectus, of the family Theriidse, a genus distributed across
the world. The bite is said to be painful as the sting of a bee,
and to be followed by general rather than local symptoms.
The clinical evidence, and evidence derived from the results of
injecting extracts from the spider into cats, show conclusively
that species of Latrodectus possess a venom which is a heart
poison and a nerve poison to higher animals. It is possible
that the European spider Chiracanthium nutrix has a venom
with properties similar to those of Latrodectus.

The Camel spiders or Solpugida of the desert regions of the
Old and New Worlds are usually dreaded by the natives of their
areas of distribution, despite the fact that there are neither
poison glands nor pores in their fangs for the exit of any
venomous secretion. On the other hand, the fangs are very

ARTHROPODA: TOXIC INOCULATION 99

powerful, and secondary infection may lead to severe local
effects as a sequel to a bite.

Certain ticks (Ixodidse) seem able to cause temporary or
even complete paralysis of heart or respiratory organs. In
particular, Dermacentor andersoni (venustus) of the United States
has been shown to be capable of causing in man and animals
a form of paralysis involving the limbs, larynx, and thorax.

Intense irritation of the skin, or dermatitis, may be caused by
the members of several families of mites.

The symptoms are similar, irrespective of the species of mite
concerned, and consist usually of an intolerable itching of the
skin, followed later by an outbreak of wheals or tiny blisters
surrounded by a bright red or violet halo.

Frequenters of pasture or harvest fields in late summer or
early autumn may be thus attacked by larval stages of the
predacious mite Trombidium. The adult mite is innocuous,
but the minute scarlet larval stage, normally an external
parasite of insects, will readily attack the mammalian skin and
can cause the most intense irritation for several days. It feeds
on the surface of the skin, but can retreat rapidly into a hair
follicle or sweat gland, and is thus somewhat difficult to remove,
although amenable somewhat to the effect of hot saline baths
or applications of sulphur ointment.

Similar dermatitis may be produced by the Tarsonemid
mite Pediculoides ventricosus, an external parasite of certain
grain -infesting insects, upon men handling such infested grain ;
and various species of Tyroglyphid mites, feeding normally
on dried food products, may cause severe dermatitis upon
persons handling such substances. Thus Tyroglyphus siro
is the cause of ' grocer's itch," Tyroglyphus longior castellani
is the cause of " copra itch " in Ceylon, conditions which may
be mistaken for scabies.

The irritant effects which follow the bite of such insects as
mosquitoes, gnats, bed bugs, fleas, and so on, vary somewhat
according to the person attacked, there being considerable
variation in personal susceptibility. The effect, too, seems to
vary according to the species of mosquito.

A former view regarded the irritant principle as resident
in the salivary glands in the form of a hemolytic substance
intended primarily to prevent coagulation of blood whilst the
mosquito was feeding, but later experiments suggest that the
poisonous action of the mosquito bite is due to an enzyme
produced by commensal fungi in the three oesophageal
diverticula.

100 THE PRINCIPLES OF APPLIED ZOOLOGY

In the case of biting Hemiptera, however, general opinion
regards the salivary secretion of the two pairs of salivary
glands as being the cause of the irritation produced by the bite,
although in the case of the giant bug Belostoma the very
prominent so-called " cephalic glands ' on the ventral side of
the head have been suspected.

Of the bugs which are capable of producing bites intensely
painful to man, Belostoma, certain Jleduviidse such as Reduvius
and Conorhinus, and certain Cimicidce are the most important.

Reduvius personatus, the masked bed bug hunter of North
America, derives its popular name from its habit of having
body and legs completely covered with dust and lint, and
from its supposed habit of preying upon the common bed bug.
The bite has been described as being almost as painful as
that of a snake, and to be followed by swelling and irritation
lasting a week.

Conorhinus sanguisuga, the " big bed bug " of the Southern
United States, is known to inflict a very painful bite, but no
satisfactory study of the secretion has been made.

Biting Diptera, other than mosquitoes, comprise the
Simuliidae or Black Flies, small black, hump-backed flies haunting
notoriously the vicinity of running streams, where their larvse
occur attached to stones, logs, or vegetation. In some regions
they are a terrible scourge, and enormous losses have been caused
to farmers and stockmen in certain areas of North America
and Europe by the attacks of these flies on cattle and poultry.
Only dense clouds of smoke produced by the burning of leather,
cloth, etc., will keep them at bay.

The minute midge flies known scientifically as Ceratopoginse
and called variously sand-flies or punkies, are widespread over
the world, and are all persistent bloodsuckers.

The Tab a nidge or gadflies are well-known blood-sucking
pests of cattle and horses and sometimes of man, and are able
to inflict painful bites whose effects last for some hours. Other
biting insects that can pierce the skin of man and animals will
be discussed in the following chapters.

Venomous stingers comprise the scorpions, among Arachnida,
and the bees and wasps among Insecta.

In the case of the scorpion, the stinging organ consists of a
sharp spine on the last segment of the abdomen, containing a
pair of highly developed poison glands. Normally, the sting
is used against insects, which are held between the pedipalps
of the scorpion and stung by the spine being brought forward,
in a curve, over the back.

ARTHROPODA: TOXIC INOCULATION 101

The effect of the sting upon larger animals is very painful
but not necessarily fatal, except to very young or small animals.
The effect on mammals is to produce great swelling and intense
tenderness at the site of the puncture, and there may be con-
vulsions and death from asphyxia. Desert animals are said
to be extremely tolerant to the effects.

The usual treatment against scorpion sting in man is immedi-
ate slitting of the wound with a knife, and the application of
potassium permanganate crystals to the wound.

Stinging insects belong exclusively to the order Hymenoptera,
and the sting is in reality a modified ovipositor connected with
certain venom-producing glands.

In the case of bees the secretion is not, as was formerly
supposed, merely formic acid, but is the product of two distinct
glands ; and although little is known concerning its chemical
structure, it appears to be neither of a proteid nor of an alkaloid
nature. It is a limpid fluid with an acid reaction, readily
soluble in water, coagulable in alcohol. A 2 per cent, aqueous
solution shows no irritant action upon the skin, but a distinctly
irritant action upon mucous membranes. On the other hand,
if injected in the skin or applied to a break in the skin, there
is produced a local necrosis accompanied by hyperemia and
swelling.

The danger arising from the stinging powers of bees or
wasps to man depends chiefly upon the quantity of poison
injected rather than upon the quality. A person in a weak
state of health may be seriously affected by the attack of large
numbers of the insects simultaneously, and a frequent sequel
to a neglected wasp or bee sting is septicaemia, which may prove
fatal.

In the case of a single sting from a wasp or bee, the effect
is dangerous when the site is on the tongue or in the mouth,
where local swelling may produce suffocation.

Poisonous caterpillars of many species of butterflies or
moths have been described from various parts of the world.

Thus, caterpillars of the Brown-tail Moth (Euproctis
chrysorrhea), a foliage-eating caterpillar of great economic
importance in Europe and north-eastern United States, are
liable to provoke serious dermatitis when handled, owing to
certain short barbed hairs which readily break off and penetrate
the human skin.

The trouble is caused by a poison within the hair which has
a hemolytic action. As is the case with other dermatitis-
provoking caterpillars, the hairs occur in bunches of three to

102 THE PRINCIPLES OF APPLIED ZOOLOGY

twelve on minute papillae which cover the surface of the sub-
dorsal and lateral tubercles. According to Kephart, the
hypodermis of each tubercle has two types of cell, namely :

(a) slender, fusiform cells, each of which is a hair-forming cell ;

(b) larger, more prominent cells, one to each papilla, possessing
a granular protoplasm with large nucleus. Each of these cells
connects by one pore canal with the tuft of poison hairs on the
papilla.

The condition known as ophthalmia nodosa of man is a
nodular conjunctivitis, somewhat resembling tuberculosis of
the conjunctiva. The conjunctiva shows a number of yellowish -
grey flattened nodules, apparently each formed around the
barbed hair of some kind of Woolly Bear or Tussock caterpillar.
Numerous cases of this condition have been recorded.

The irritation from nettling caterpillars can be very severe,
but relief can usually be gained by weak lotions of ammonia,
bicarbonate of soda, or other alkaline substances.

In conclusion, reference may be made to certain insects
whose blood plasma contains some substance which has poisonous
properties. Thus caterpillars of the European cabbage butterfly,
Pieris brassicw, are said to cause severe colic, salivation,
stomatitis, or even paralysis of the hind limbs, when accidentally
swallowed by domesticated animals or birds.

The Melosidce or blister beetles are well known for the
possession of a peculiar volatile, crystalline substance, can-
tharidin, in their reproductive organs, and certain species when
dried and ground to powder are used medicinally under the
term of Spanish Fly as a local irritant, or even internally as a
stimulant and diuretic. The flesh of birds which have fed on
meloid beetles is stated to be poisonous to man, and cases
have been recorded of human beings poisoned by eating the
flesh of cattle which, in their turn, have been affected by
accidentally eating meloid beetles when grazing.

In South Africa, a Chrysomelid beetle, Diamphidia simplex,
occurs, whose larva has in its blood a toxalbumin which has a
haemolytic action upon mammalian blood, and is said to produce
death from paralysis. Certain Bushman tribes use the body
fluid of these larvae as an arrow poison.

CHAPTER X

ARTHROPODA AND DISEASE : Entomiasis

It is preferable to dissociate the term entomiasis from the
production of lesions by the accidental or casual attack of
arthropods. As already noted, many blood-sucking arthropods,
many with acrid secretions, many with irritant hairs, can
produce temporary lesions of the animal skin. Eggs or larval
stages of arthropods which breed in fruits, vegetables, meat-
stuffs, may be swallowed accidentally by animals. Such forms
as breed usually in faeces or in carrion may be attracted to
septic wounds or to the body orifices of animals which suffer
from catarrhal or dysenteric discharges ; thus in Europe,
larvae of the house-flies Fannia scalaris and Fannia canicularis,
which usually live in human excrement, are quite frequently
expelled from the stomach, rectum, or urethra of man, the
victim having been infected by female flies when using an earth
privy. Very many cases are known, also, of the blow-flies
Calliphora, Lucilia, Sarcophaga, depositing eggs or larvae in
the body orifices or open wounds of animals. On the battle-
fields of the Great War such cases were of common occurrence.

The term entomiasis should, in fact, be restricted to lesions
caused by Arthropoda which are known to attack invariably,
or, at any rate, very frequently, the tissues of living animals,
and in particular of healthy, un wounded animals, and which
may be incapable of breeding in dead tissues.

Such habitual entomiasis production is associated partic-
ularly with the families Muscidae, Sarcophagidae, and (Estridse
of two-winged flies (Diptera), with the family Sarcopsyllidse
of fleas, and with several families of Acarina or mites, notably
the Gamasidse, Trombidiidse, Sarcoptidse, and Demodecidae.

Muscid Entomiasis. — The problem of distinguishing between
true habitual entomiasis and casual entomiasis is particularly
difficult in the case of the Muscidce, that large family of flies
whose members are of the house-fly or blue-bottle type.

In almost every sheep-raising country in the world, cases
are known of sheep being attacked by maggots of some type of
blue-bottle or blow-fly. That many such flies will attack normal

103

104 THE PRINCIPLES OF APPLIED ZOOLOGY

healthy sheep is beyond question, and that many others will
lay their eggs only upon wounded or strong -smelling sheep
seems also certain. Further, it has been observed that certain
species of blow-fly which, within living memory, were restricted,
as regards the oviposition habit, to carrion, have passed through
a phase of casual entomiasis production and entered upon a
phase of habitual entomiasis production.

Among Muscid larvae which are associated with entomiasis,
there occur two varieties of habit : the larva either feeds upon
the subcutaneous tissues of the victim, or it sucks the blood.
Strictly speaking, the latter habit is not a form of entomiasis, but
for convenience the larvae which possess it will be discussed here.

The Muscid larva is a soft-skinned, white, cylindrical
limbless maggot, tapering anteriorly to a pair of mouth hooks
and, apart from these, devoid of anything in the way of head.
Of the twelve segments which compose the body, the first is
provided with a pair of fan-shaped spiracles or breathing
organs. The last segment has a pair of posterior spiracles in
the form of circular or oval plates perforated with slits. The
shape of these slits is of considerable importance in the identifica-
tion of species of Muscid larvae.

Each plate may be described as a ring of chitin, within which
are three sieve-like openings and a small raised area known as
the " button."

Three types of such plate exist (Fig. 18) : —

(1) Chitinous ring intact : button well within the ring,
D-shaped, broad ; slits are sinuous. This type may be typified
by Musca, Pseudopyrellia.

(2) Chitinous ring intact : button enclosed by the ring itself ;
slits straight. This type is exemplified by Calliphora.

(3) Chitinous ring very thin on lower, inner margin, so that
there appears to be a break in it. In this gap the button is
situated. Slits straight. This type occurs in Chrysomyia and
Cochliomyia.

The maggot is quite incapable of swallowing or chewing
solid particles of food, but has first to liquify the food medium
by the secretion of its salivary glands, and then to suck the
fluid product into its alimentary canal. The transition to a
blood-sucking habit is therefore not so strange as would at
first sight appear.

In the case of sheep attacked by blow-flies, the eggs are laid
in clusters upon the wool near the root of the tail, and the
resulting maggots eat away skin and superficial muscles in that
region. The adult flies are not readily deterred from oviposition

ARTHROPODA AND DISEASE: ENTOMIASIS 105

by chemical substances applied to the wool, particularly as
such substances cannot feasibly be applied at short intervals.

Muscid larva

Calliphora

Cochliomyia

Pseudopyrellia

Fig. 18. — Posterior Larval Spiracles of some Common Muscid Flies.

The eggs usually hatch within twelve to twenty -four hours,
or, in some cases, living larvae are deposited and the various
larval stages are passed through very quickly.

106 THE PRINCIPLES OF APPLIED ZOOLOGY

Sheep dipping, therefore, is impracticable against blow-flies,
since in practice sheep would require to be dipped every few
days.

In Australia, much is being hoped at present from the
establishment of certain European parasites of blow-flies, in
particular the Chalcid wasps Nasonia brevicornis and Chalcis
calliphorce, which are being liberated in numbers in sheep-
raising districts. In Great Britain and North-West Europe,
Lucilia sericata is the sheep maggot fly. In North America,
sheep are attacked by Cochliomyia macellaria, by Phormia
regina and by Lucilia sp. In Australia, where the problem
is acute, several species are concerned. Chrysomyia albiceps
is the commonest, but it is not certain whether the larvae of
this fly are feeding on the sheep's tissues or are preying upon
associated blow-fly larvae. Other sheep maggot flies are
Chrysomyia varipes, Calliphora (Anastellorhina) augur, and
Pollenia stygia.

Probably all these sheep blow-flies are what Patton terms
semi-specific myiasis producers, that is to say they attack
animals secondarily, breeding mainly in the bodies of dead
animals. The same may be said, too, of the notorious Screw -
worm fly — Cochliomyia macellaria — of North America and
Central America, a brassy-green fly which deposits egg clusters,
large as a pea, in the body orifices or wounds of horses, cattle,
and even human beings.

In man the favourite site of attack is the nasal cavity,
particularly the nasal septum and cartilage of the nasal fossae,
and great disfigurement or even death may be caused if the
larvae cannot be quickly dislodged by injections of chloroform
or carbon tetrachloride.

A true entomiasis producer, and one which will not breed in
dead tissues, is Chrysomyia bezziana of India, Burma, Ceylon,
and Africa. Its larvae commonly occur in the nasal, oral,
aural, vaginal apertures and the wounds of man and animals,
in India, and of cattle in Africa.

A similar habit in Russia is shown by Wohlfartia magnifica,
which again is believed to breed only on living animals.
It is, however, strictly speaking, not a Muscid fly but a
member of the related family Sarcopimgidce.

In Africa, cutaneous lesions are caused by the larvae of
Cordylobia anthrophaga (Bengallia depressa) and Cordylobia
rodhaini.

The first-named species is widely distributed in the grass
areas between the Sudan and Senegal and as far south as Natal.

ARTHROPODA AND DISEASE: ENTOMIASIS 107

Its larval stage is normally a parasite of dogs, and the female
fly oviposits in dust, sand, earth, etc., in places where the host
usually lies. The newly hatched larva bores its way through
the epidermis and eventually forms a sort of boil beneath the
skin of the buttocks and lower limbs.

Cordylobia rodhaini is restricted to the damp forests of the
Congo, and is normally, in the larval stage, a parasite of duiker
antelopes (Cephalophus) and of the large rodent Cricetomys
gambianus.

Throughout Central Africa there occurs a yellowish-brown
Muscid fly known scientifically as Auchmeromyia luteola,
haunting shady places near human dwellings, particularly in
the vicinity of latrines. The larvae occur beneath the mats in
native huts, and emerge at night to suck blood.

The larva of Cheeromyia, a similarly distributed fly, sucks the
blood of wart hogs (Phacochcerus) and ant-eaters (Orycteropus).
The adult fly is said to live permanently in the darkest, deepest
portion of the wart hog or ant-eater burrow.

The genus Passeromyia in the larval stage sucks the blood
of Passerine bird nestlings. A similar habit in Europe and
North America is shown by Phormia (Protocalliphora) azurea
and Phormia chrysorrhea, the larva? occurring attached to
the tarsi, mandibles, and under- wing surface of nestling birds.

CEstrid Entomiasis. — The (Estridse comprise large thick-set
flies, somewhat furry and bee-like in appearance, with large
heads and rudimentary mouth parts, whose larvae are exclusively
parasitic within the bodies of mammals. The eggs are laid
usually upon the hairs of the victim, and the larvae, which are
somewhat barrel shaped and possess rings of dark hook-like
spines, either bore directly through the skin or are carried into
the host's pharynx by the tongue. The full-fed larva always
leaves the host and pupates in the ground. The exact nature
of the food of the larva is not understood. It does not
appear, however, to consist of blood but of the exudations pro-
duced by the irritant action of the mouth hooks on mucous
tissues. The adult stage is a short one, the entire larval
stage a very long one. The family is divided into a number
of sub -families.

(1) Sub-family Gastrophilinse. This group comprises forms
whose larvae live in the stomach of the horse and its allies,
and are sometimes termed bots.

Among domesticated Equidae the commonest species are
Gastrophilus intestinalis, Gastrophilus veterinus, and Gastro-
philus hsemorrhoidalis.

108 THE PRINCIPLES OF APPLIED ZOOLOGY

The first-named species deposits its eggs upon the long
hairs on the side of the forelimb. The eggs require a certain
amount of warmth and friction in order to hatch, and these
conditions are supplied by the teeth and tongue of an irritated
horse. The friction causes the first stage larva to emerge,
and this is carried into the mouth on the horse's tongue, reaches
the alimentary canal, and spends its life attached to the mucosa
of stomach or duodenum.

The second species lays eggs upon the hairs of the lower
jaw ; the third species lays eggs on the hairs of the lips. In
these cases the friction is supplied by the animal rubbing
chin or nose against fence or manger, and the larva secures
admittance to the alimentary canal in food or water.

The eggs of these species present marked difference, but all
agree in the possession of a terminal lid and of two longitudinal
flanges that grip the hair. Ten months are spent by the larvae
in the alimentary canal ; in the spring following infection, the
larvae pass out with the faeces, pupate in the soil, and eventually
emerge as adults for a few days' existence in May or June.

A similar life history probably occurs in the case of the
species of Cobboldia, parasitic in the stomach of elephants ; and
of Gyrostigma in the stomach of the rhinoceros.

(2) Sub-family CEstrinse. This group comprises forms
parasitic in the frontal sinuses of various herbivorous mammals.
Eggs are laid within the animal's nostrils ; the larvae are sucked
in when the animal breathes. The larval stage is spent within
the frontal sinuses or nasal passages. (Estrus ovis attacks the
sheep. Other species of (Estrus attack other ruminants.
Rhincestrus attacks horses, pigs, and the hippopotamus.
Cephalopsis attacks the camel and dromedary.

(3) Sub-family Hypodermatinae. This sub-family contains
all those (Estridae whose larvae cause cutaneous entomiasis in
ruminants. The mature larvae occur lying just beneath the
skin of the back and produce boil-like swellings, with a central
aperture through which the larva takes in air, and through which
it eventually emerges to pupate in the ground. These boils
are termed " warbles."

In the case of Hypoderma bovis and Hypoderma lineata of
European and North American cattle, the eggs are laid on the
hairs of the legs of the cattle, and the newly hatched larvae
penetrate the skin near the point where the egg was laid, and
slowly migrate to the gullet region, there to rest awhile. They
select this region probably because of the greater supply of
free oxygen there and the little resistance to growth offered

ARTHROPODA AND DISEASE: ENTOMIASIS 109

by the areolar tissue. The later stage larvae migrate to the
subcutaneous tissues of the back, by way of the neural canal,
and produce the " warbles."

Similar warbles are produced upon the backs of reindeer by
(Edemagena, whose eggs have a terminal flap recalling the lid
of the Gastrophilus egg, and suggesting the possibility of
infection bv the mouth.

Remedial measures against warbles are hopeless from the
point of view of saving injury to the individual hide.
Systematic and collective larva destruction over a wide area
would go far to stamp out the fly from cattle-raising countries.
The method of larva destruction consists of squeezing out the
warbles during winter, or of injecting each one with 1 c.c. of
iodine. The ripe larvae do not emerge normally until March or
April, but where cattle are stabled throughout the winter,
emergence may be earlier.

(4) Sub-family Cuterebrinse. This sub-family comprises
a number of forms whose larvae are subcutaneous parasites
chiefly of small rodents in North and South America, and of
squirrels and chipmunks in North America. Cuterebra tenebrosa
occurs beneath the skin of rodents in the same region.

Dermatobia ho minis is found in the skin of cattle, and,
rarely, of man, in tropical America. The female lays her eggs
in packets upon leaves. These packets become attached to
the ventral abdominal surface of blood-sucking or sweat-
sucking insects which walk over the leaves, in particular of the
mosquito Janthinosoma lutzi and species of Authority ia, and
these insects carry the eggs to the mammalian host. This
so-called " macaque worm ' is a peculiar pear-shaped larva
which penetrates the mammalian skin and forms a local tumour.
The other Cuterebrinae are believed to deposit their eggs on the
hairs of the host, and these are licked off and enter the
alimentary tract, where the emerging larvae commence their
migration to the subcutaneous tissues.

Sarcopsyllid Entomiasis. — One family of fleas, the Sarco-
psyllidce, is remarkable in that its members cause direct
cutaneous lesions in man and other animals.

Dermatophilus penetrans is a flea indigenous to South
America, but which has become established in West Africa
probably by transportation in slave ships. The fleas occur
particularly in sandy places where there is undergrowth, and there
they lie in wait to attack the naked feet of passers-by. The
female burrows into the skin, especially beneath the toe nails,
and owing to the development of eggs she swells up to the

110 THE PRINCIPLES OF APPLIED ZOOLOGY

size of a pea. The end of the abdomen protrudes, however,
through the host's skin, and through it the eggs are expelled.
Secondary infection, following on the attack of large numbers
of the ' chiggers," as they are termed, may produce tetanus,
gas gangrene, and even eventual loss of the toes.

Wherever Dermatophilus occurs, it is spread very largely by
pigs. Pigs seem, of all animals, the most closely related to
man as regards the possibility of parasite nutrition. In previous
chapters it has been noted that very many intestinal protozoa
and helminthes are harboured by pigs and transferred to man.
Blood-sucking Muscid larva? attack equally man and wart
hogs. In Rhodesia, the vector of relapsing fever of man,
the tick, Omithodoros moubata, has been found in the burrows of
wart hogs far removed from human habitations. It may be
noted, too, that the pig louse, Hcematopinus suis, can live a
long time on man, and that the human louse, Pediculus, can
live at least a week on pigs.

Another Sarcopsyllid species, Echidnophaga gallinacea, the
" stick-tight flea," commonly attacks poultry in nearly all
tropical and sub-tropical countries. It collects in dense masses
on the heads of poultry, in the ears of mammals, and else-
where.

Acarid Entomiasis. — The mites which produce entomiasis
of animals belong chiefly to the family Sarcoptidae, the Itch
and Scab Mites.

They may be described as minute, square-shaped mites
without any division between cephalothorax and abdomen,
with a short conical rostrum formed by a pair of pincer-like
mouth parts and a pair of pedipalps, and with four pairs of
stumpy legs arranged in two sets, two pairs occurring near the
rostrum, two pairs occurring near the posterior end of the
body. The tarsi of some of the legs end in a sucker.

Of the five sub-families which constitute the Sarcoptidse,
the Canestrince are parasites of other insects, the Analgince live
within the feathers of birds, the Listiophorince are cutaneous
parasites of bats and other small mammals, the Cytolichince
are subcutaneous burrowers of birds, and the Sarcoptince are
subcutaneous burrowing parasites of mammals and birds.

The lesions produced by the Sarcoptine mites are usually
termed scabies, itches, manges.

The principal genera concerned are Sarcoptes, Notoedrus,
Psoroptes, Chorioptes, and Otodectes, and it is permissible to
speak of sarcoptic mange, psoroptic mange, chorioptic mange,
and so on.

ARTHROPODA AND DISEASE: ENTOMIASIS 111

Anus terminal .

Sarcoptes.

Anus dorsal

Notoedrus.

• • • • •

Cnemidocoptes

On 1st, 2nd, 3rd pair of

legs of male ; on 1st, 2nd,

and 4th pairs in female .

Psoroptes.

On all feet of male ; on 1st,

2nd, 4th in female .

Chorioptes.

On all feet of male ; on 1st

and 2nd in female .

Otodectes.

The following key to the genera of Sarcoptince follows that
suggested by Neveu-Lemaire : —

Male without copulatory suckers ;\

foot suckers on the first two

pairs of legs in both sexes, and V

in addition on the fourth pair,

in the male J

Male with or without copulatory

suckers ; foot suckers on all

legs of the male, on none in the

female ....

Male with copulatory suckers ; ,
foot suckers present

Sarcoptes is predominantly a burrowing mite. The male
and the immature female stages live beneath the loose scales
of the stratum corneum or outer layer of the skin, or under
the scabs of exudated serum which result from the irritation
caused by the bites. The pregnant female burrows down as
far as the stratum Malpighii, each female making a separate
burrow which may run in tortuous fashion for as long a distance
as half an inch. The eggs are laid in the burrow and the
extremely minute mite occurs at the bottom of the burrow.
As the surface of the skin constantly wears away and is renewed
from below, the six-legged larvae appear on the surface of the skin.
When the eggs have hatched, the feeding habits of the parasites
produce intense itching of the skin of the host. In man the chief
seat of attack is the skin of the finger clefts or the wrists.

The various forms of Sarcoptes which occur on domesticated
and wild animals are probably mainly biological races of
Sarcoptes scabei, and though normally restricted to one host
species, can establish themselves to some extent upon other
hosts. Sarcoptes scabei crustosa?. is the cause of the so-called
Norwegian itch of man, characterised by the presence of white
or yellowish crusts on hands, arms, or feet, or even scalp or
face. It is more contagious and more difficult to eradicate
than is ordinary scabies.

Sarcoptes scabei bovis and Sarcoptes scabei equi cause sarcoptic
mange in cattle and horses respectively, and usually infest the
inner surface of the thighs, the under surface of the neck, and
the root of the tail. Notoedrus cati of the cat was formerly
regarded as a species of Sarcoptes, but is separated by the
position of the anus, which is dorsal instead of terminal as in

112 THE PRINCIPLES OF APPLIED ZOOLOGY

Sarcoptes. Notcedrus cuniculi occurs on the rabbit. Both
are communicable to man but less stubborn to treat than is
Sarcoptes scabei.

Female

female

Sarcoptes
scabei

Psoropte
long-irost

Choriopt
setife

Jfale

Fig. 19. — The Principal Genera of Itch Mites.

ARTHROPODA AND DISEASE: ENTOMIASIS 113

The genus Psoroptes lives in groups on the surface of the
skin, protected, however, by the scabs of exuded serum and
pus produced by the irritant bites of the mites.

Psoroptes communis ovis is the cause of a very common scab
disease of sheep, the so-called sheep scab, one of the most con-
tagious and injurious diseases that affect sheep, and one dating
back from the beginning of civilisation. Enormous financial
loss is caused in sheep -raising areas owing to the decrease
produced in quantity of wool and to the injury and death of
animals. Fortunately, the disease is readily amenable to
treatment. All stages of the mite are passed on the host,
on the skin at the base of the wool fibres, where the eggs are
laid, the young mites brought to maturity, and copulation
between the sexes carried out.

The life-cycle is short, probably much shorter than was
formerly thought to be the case, and varies between eight and
fourteen days. The duration of the life-cycle is of some con-
siderable practical importance, since, although dipping or
immersion of infected animals in chemical solutions will kill
young and adult mites, it will not destroy the eggs ; a second
dipping, therefore, should follow within an interval sufficiently
short to ensure destruction of the immature mites which,
in the meantime, have emerged from the undestroyed eggs.
Thus, such a second dipping should be not later than ten days
from the first one.

Psoroptic mange is also the commonest scab disease of cattle,
and although less dangerous than sarcoptic mange, causes
greater financial loss to the cattle industry owing to its wider
prevalence.

Psoroptic mange is also common among horses.

The genus Chorioptes is also the cause of mange diseases
in horses, cattle, and sheep. Chorioptic or symbiotic mange,
as it is sometimes called, is particularly common among
horses. Usually chorioptic mange diseases affect particularly
the limbs or the base of the tail.

The species of Otodectes frequent the ears of carnivorous
mammals. 0. cynotis canis affects the domesticated dog ;
O. cynotis cati, the domesticated cat. It is prevalent particu-
larly among packs of hounds and on fox farms, and the irritating
effect of the parasites within the external ear may produce
fits of frenzy or even attacks similar to epilepsy. The mite is
similar in structure to Chorioptes but the legs are more slender.

Cnemidocoptes is a mite which attacks particularly the feet
of birds, producing the disease usually called " scaly leg ' in

8

114 THE PRINCIPLES OF APPLIED ZOOLOGY

poultry and turkeys. The parasite lives beneath the loose
scales which appear between the toes, or under hard crusts,
beneath which the tissues are inflamed and septic. Secondary
infection may even lead to loss of one or more toes.

In addition to the Sarcoptidce, other families of Acaridse
may cause cutaneous lesions in animals. The family Demo-
decidse in particular is responsible for the severe follicular
manges of domesticated animals. The mite Demodex lives
in the hair follicles and even in the sebaceous glands, and so
becomes very firmly established and difficult to remove. Loss
of hair occurs over the regions of the animal attacked, and the
surface becomes covered with septic pustules or nodules, the
contents of which swarm with the mites. The progress of the
disease is slow, but it is practically incurable. The body of
the mite is elongate and tapering and the posterior portion is
worm-like. The limbs are very stumpy. The follicular mite
of man is one cause of the skin condition termed " blackheads,"
but follicular mange in man is nothing like so serious as it is,
for example, in the dog. How the mite is transmitted from
animal to animal is somewhat uncertain, but the disease is not
highly contagious.

Reference may be made here to the family Gamasidse, a
family of mites somewhat resembling small ticks and in the
main predatory upon other mites or insects.

Dermanyssus, however, is a blood-sucking parasite of birds,
hiding by day in crevices and attacking the host by night.
Rhinonyssus occurs in the nasal cavity of birds, and
Pneumonyssus has been found in the lungs of monkeys.

Treatment of the various sarcoptid skin diseases consists
in principle of the application of toxic chemicals to the skin of
the animal attacked. The most effective way of applying such
treatment is by ' dipping," that is to say, by immersing the
animal in a solution of the remedial substance. Cattle or
horses or sheep are usually swum through tanks containing a
solution of sodium arsenite, or a solution obtained by the
interaction of alkalis and sulphur or nicotine, or solutions
"containing phenols, cresols, pyridine, coal tar creosote, or the
like. Small animals can be immersed in warm 3 per cent,
solution of potassium sulphide, 2 per cent, solution of creolin,
or similar insecticides.

The chemistry of dipping fluids and the technique of apply-
ing them is, however, too wide a subject in itself to be dealt
with adequately here, and reference should be made to the
special literature that has grown up concerning this subject.

CHAPTER XI

ARTHROPODA AND DISEASE : Mechanical

Transmission

The potentiality of acting habitually as a carrier of the
pathogenic organisms of disease in man or other animals requires
of the arthropod concerned : —

(a) That it be of common occurrence in the vicinity of such
animals.

(b) That it be a frequenter of faecal matter, sputum, or other
source of pathogenic organisms.

(c) That its structure or habits are such as to convey such
organisms from the source of infection to man or the animal
concerned ; that is to say, the arthropod must be hairy, or
possess the habit of regurgitating food or be a bloodsucker.

These conditions are fulfilled by a somewhat small number
of non-blood-sucking arthropods, including particularly the
house-frequenting flies, cockroaches, and house ants ; and by
a somewhat wider range of blood-sucking forms, notably the
blood-sucking Muscid flies, the gadflies, the fleas, lice, and bugs.

House-Flies. — Of the house-frequenting flies, the most
important is undoubtedly Musca domestica, which constitutes
90-98 per cent, of the fly population of houses all over the world.
To a lesser extent occur Fannia canicularis, the so-called
lesser house-fly, and Fannia scalaris, the latrine-fly.

The genus Fannia may be readily distinguished from Musca
by the fourth vein of the wing, which runs straight to the
margin of the wing instead of bending anteriorly as it does in
Musca. Fannia, too, has a peculiar darting motion when in
flight, which readily serves to distinguish it from Musca.

Several species of blow-fly, Calliphora in particular, come into
houses. In tropical countries, species of the brassy -green
blow-fly Pycnosoma, a breeder in human excrement, are also
numerous in the vicinity of human habitations.

Musca domestica lays clusters of 120-140 eggs generally,
but not invariably, in decaying vegetable matter. The favourite
site is undoubtedly fresh stable manure, to which the female
flies are attracted by ammonium hydrate or carbonate in con-
ns

116 THE PRINCIPLES OF APPLIED ZOOLOGY

junction with butyric and valerianic acids, according to Richard-
son ; and, according to Crumb and Lyon, stimulated to oviposit
by the carbon dioxide thus given off.

The species of Fannia are more catholic in choice of ovi-
position media, laying eggs readily and breeding readily in
rotting paper or rags, so that Fannia will breed in quantities
in rubbish where the amount of actual vegetable matter is

low.

The eggs are laid within the top six inches of the upper
surface, and the larvae, which hatch within twelve to twenty-four
hours, according to temperature, work upwards, feeding in the
fresh material that is added each day to the surface of the
manure pile.

The larva is a typical maggot, a headless, legless, conical
creature, provided at the conical end with a pair of chitinous
mouth hooks, at the broad posterior end with a pair of oval
plates, in each of which occur three S-shaped spiracular slits.

When full fed, which happens within a period varying from
five days in the tropics to several weeks in the cold spring or
autumn of northern latitudes, the larva migrates downwards
towards the dryer portion of the manure pile, usually avoiding
the superheated interior of the heap. Periodical forking of
a manure heap will, in fact, destroy large numbers of larvae
by precipitating them into the hot interior of a fermenting
manure heap.

The larva emerges from the heap usually near the ground-
level and at the edge of the heap, rests awhile in order to empty
the alimentary canal, and then pupates ; that is to say, it
contracts to a cylindrical shape away from the outer skin,
which remains around the pupating larva as a dark-coloured,
barrel-shaped pupa case.

The migration of larvae from the manure heap in order to
pupate may be taken advantage of, as in the ingenious maggot
trap invented by Hutchison at the Maryland Agricultural
College of U.S.A., by using as a foundation for the heap a
platform of laths, one inch wide and one inch apart, standing
above a shallow concrete trough containing weak disinfectant
solution. The heap must be kept continually soaked by
drenching with water, to induce the full-fed larvae to leave it
and fall into the trough ; otherwise they will merely pupate
in the drier parts of the heap.

Within the pupa case the larval organs are remodelled into
those of the future fly, and after some days the latter emerges.

The actual total period occupied, from oviposition to maturity

ARTHROPODA: MECHANICAL TRANSMISSION 117

of the succeeding fly, depends upon conditions of temperature,
of food, of moisture, and so on. The egg may take eight hours
to several days to hatch. The larval stages may occupy
five to eight days, or if in non-fermenting food-stuffs, may occupy
several weeks. The pupal stage may last from three to twenty -
six days. Under favourable conditions of temperature and
food medium, however, the period elapsing between generations
is about three weeks.

One of the most disputed questions concerning the house-fly
relates to the manner in which the winter is spent, and a great
deal of somewhat contradictory evidence has been brought
forward.

It would seem that the adult fly can spend the winter in a
dormant condition in cool, sheltered places such as attics or
cellars, but that in heated buildings it is liable to attack by the
fungus Empusa, and out of doors is killed by frost. In localities
where the winter is mild, or beneath large heaps of manure,
larvae or pupae or even immature flies may survive through
the winter. In places where there is warmth, food, and breeding
facilities, the house-fly can continue breeding throughout the
winter, and probably an over- wintering succession of broods
is more common than is realised, particularly in restaurants,
bakeries, stables, zoological gardens, and similar places.

When the habits of the adult insect are taken into con-
sideration, its journeys to and fro between the garbage tin,
the latrine, the spittoon, and so on, and the food larder or food
table, and its habit of vomiting forth a previously swallowed
mass of sputum or excrement upon the more tempting food of
man, it is not surprising that, once the bacterial origin of
infectious diseases had become established, the attention of
sanitarians and bacteriologists should be directed with suspicion
towards an insect so obviously adapted by its habits and by
its hairy body to act as a conveyor of disease. During the past
twenty-five years, justification for such suspicion has been
amply provided by an enormous accumulation of evidence.
An intimate correlation between the prevalence of house-flies
and the prevalence of typhoid fever and summer diarrhoea
has been fully proved ; much evidence has been obtained
concerning a similar correlation between house-flies and the
occurrence of cholera, tuberculosis, and ophthalmia ; and there
is a strong suspicion that amoebic dysentery, yaws, anthrax,
diphtheria may also be carried by house-flies.

The house-fly is a true intermediate host of three species
of Habronema, a Spiropteran nematode worm which infests

118 THE PRINCIPLES OF APPLIED ZOOLOGY

the stomach of the horse and donkey. The embryos of the worm
pass out in the faeces of the host, are swallowed by fly larvae
and remain in the insect right through the metamorphosis,
occurring eventually in the head of the adult fly ; from thence
they pass into the proboscis, are deposited on a horse, and
become licked into its alimentary canal.

It has been shown that house-flies are greatly attracted by
the eggs of parasitic worms which may occur in faeces or
sputum, and try hard to swallow them ; small eggs so ingested
pass through the fly uninjured and may be disseminated.

Prophylactic measures against house-flies comprise chiefly
the removal of stable manure or similar breeding media from
the vicinity of dwelling-houses, or the treatment of it with
larvicidal chemicals. It is, of course, a difficult matter to hit
upon a method of sterilising manure which will kill fly larvae
but not kill bacteria, and so lower the manurial value. A
wide range of chemical substances has been at various times
recommended. Probably the most efficient are green tar oil,
mixed with forty parts of soil and used as a surface dressing
over the manure heap, tetrachlor ethane applied to the manure
at the rate of two ounces per ten cubic feet of manure, or
borax applied at the rate of about half a pound per ten cubic
feet of manure ; borax is applied with a flour sifter or similar
fine sieve around the outer edges of the pile, and two or three
gallons of water is then sprinkled over the treated manure.
Not more than fifteen tons per acre of such treated manure,
however, should be applied to the field ; in fact, if intended
for market garden purposes, where large quantities per acre
are used, manure is preferable that has been treated with
hellebore, rather than borax, at the rate of half a pound to ten
gallons of water per eight bushels of manure.

There is, however, one serious objection to the use of larvi-
cidal chemicals, apart from the effect on manurial value, and
that is their effect in delaying fermentation and so allowing
stable manure to be suitable for fly oviposition longer than it
otherwise would be. A more natural method of reducing the
number of larvae in a manure heap is to utilise the heat produced
by the natural fermentation of the medium. Before placing
a layer of fresh manure on the surface of a heap, the upper
layers should be raked away so that the fresh stuff will come
into contact with the deeper fermenting manure, and the
fresh manure should be covered with a layer of hot manure.
Frequent forking over of a manure heap will bring about a
considerable diminution in the number of larvae contained in

ARTHROPODA: MECHANICAL TRANSMISSION 119

it, since large numbers are killed instantly by falling into the
hot, deep portions of the manure during the raking.

It should be noted that chemical treatment of manure
heaps applies particularly to manure heaps in the vicinity
of dwelling-houses. The farm manure heap, far from houses,
is little frequented by house-flies, and manure several days old
will attract no flies at all. Treatment of farm heaps, however,
should be carried out, since they are a prolific breeding source
of the stable fly (Stomoxys calcitrans).

Stomoxys is a small biting fly, similar in size to the house-
fly, but easily distinguished from it by the rigid projecting
proboscis. It is cosmopolitan and coextensive with the house-
fly almost everywhere where horses are kept. It appears,
however, to be considerably more abundant in temperate than
in tropical countries. It breeds for preference in horse dung
or stable manure, but will breed quite freely in rotting cereal
straw and in manure too old to attract Musca ; unlike the latter
fly, however, the stable fly rarely breeds in dust-bins or in
rubbish tips.

Stomoxys is a vicious biter, particularly when the atmosphere
is moist. It is of interest from a medical point of view as being
a possible carrier of the organism of a trypanosomiasis of horses,
cattle, and camels in South-Eastern Asia, known as Surra ; as
being a carrier of the nematode worm Filaria labiatopapillosa
which occurs in the peritoneal cavity, and occasionally in the
eye, of cattle and deer in India ; and in being a suggested carrier
of acute epidemic poliomyelitis or infantile paralysis of America
and of Europe. The possibility of Stomoxys being a conveyor
of the latter disease is somewhat doubtful in the light of recent
evidence which indicates that the disease is contagious and not
transmitted indirectly by insects.

The related Muscid genera Hcematobia and Lyperosia,
although in habits similar to Stomoxys, rarely attack man and
are more particularly pests of cattle.

Gadflies. — The term gadfly, breeze-fly, clegg, horse-fly,
seroot, and so on, refers usually to some member of the family
Tabanidoe, a family of large, stoutly built flies possessing
mouth parts adapted for stabbing and cutting. The flies
frequent marshy areas, the eggs being laid in masses on the
leaves or stems of marsh plants, and the larvae live a carni-
vorous life in damp mud or rotting vegetation, or in the water
of the swamp. The males are said to be suckers of plant
juices, but the females are persistent and extremely painful
biters of man and animals.

120 THE PRINCIPLES OF APPLIED ZOOLOGY

The possibility of Tabanid flies acting as mechanical carriers
of disease germs has been indicated in several cases.

They have been shown to be capable of transmitting
Trypa?ioso?na evansi of Surra, of transmitting anthrax, and,
with less certainty, of transmitting Leishmaniasis in South
America. West African species of Chrysops have been in-
criminated as carriers of the microfilarial larvae of the nematode
worm Loa loa.

Fleas. — The term flea refers to a type of insect probably
possessing close affinities with the Diptera, but sharply marked
off as the order Siphonaptera by a number of characteristics
of structure and habit, in particular by being always wingless,
by being laterally flattened, by being always ectoparasites of
feathered or hairy warm-blooded animals, and by possessing
mouth parts adapted to pierce the cutaneous surface of the host
and to suck blood.

From the point of view of successfully identifying any
particular species of flea, the particularly important points of
structure are the antenna?, the eyes, the combs, and the
pygidium.

The antenna? consists each of two small basal segments and
a larger oval segment termed the club, more or less distinctly
divided into nine rings.

The degree of segmentation of the club is an important point
in distinguishing different genera. Each antenna lies in a
groove on the side of the head. The eyes may be present or
absent. If present they are quite conspicuous, black, but
non-faceted structures.

The combs are rows of tooth-like bristles which may occur,
one on each margin of the cheek or lower edge of the head —
the so-called genal comb — one on the posterior dorsal margin
of the first thoracic segment — the so-called notal comb. The
pygidium is a sieve-like sensory plate which is situated on the
dorsal surface of the ninth abdominal segment, and may be
flanked by one or more bristles on each side.

The mouth parts of the flea consist of : —

(a) A pair of conspicuous triangular, blade-like maxillae.

(b) A pair of stout, segmented maxillary palps projecting
in front of the head, like antenna?.

(c) A pair of smaller segmented labial palps, which form a
tube for the piercing lancets.

These comprise (d) a pair of longitudinally grooved, serrated,
needle -like mandibles, whose apposition form an efferent
tube down which saliva passes ; (e) an unpaired bristle, the

ARTHROPOD A: MECHANICAL TRANSMISSION 121

epipharynx, which, by fitting against the mandibles, forms an
efferent tube up which blood from the host is sucked.

The eggs of a flea are not glued to the hairs or feathers of
the host, but are laid loosely among them so that they fall to
the ground. After a variable period of two to twelve days
they liberate footless maggots which crawl actively about,
feeding on organic debris.

They occur particularly in the sleeping-place or nest of the
host ; and animals, such as Ungulates, which do not resort to
a particular sleeping-place each night, are usually free from
fleas; whereas birds, burrowing rodents, or carnivorous mammals
are usually infested with them.

Eventually the larvae spins a minute, pearly- white cocoon
within which, after the usual period of quiescence, it pupates.
After about a fortnight, the cocoon liberates the fully formed
flea. The whole life-cycle may be completed within five weeks.

The majority of flea species are specific, restricting
themselves to one particular species of host. Others, however,
are wandering fleas, which, although preferring some particular
host species, are not averse to other animals if opportunity
occurs. It is particularly the species of wandering fleas which
is the important one from a pathogenic standpoint.

In previous chapters the intermediate part played by the
cat or dog-flea in the life-cycle of the tapeworm Dipylidium
and the part played by the rat-flea in the life-cycle of Trypano-
soma lewisi have been alluded to.

The most important example, however, of a pathogenic role
played by a flea species is afforded by the proved transmission
of Bacillus pestis of bubonic plague by the rat-flea Xenopsylla
cheopis of tropical Asia ; by the rat-flea Ceratophyllus fasciatus
of Europe ; by the squirrel-fleas Hoplopsyllus anomalus and
Ceratophyllus acutus of California ; and by the marmot-flea
Ceratophyllus silantiewi, in this case conveying pneumonic
plague of Manchuria.

The part of the flea Xenopsylla cheopis in conveying the
bacilli of what is really a disease of the tropical or black rat,
Mus rattus, from rat to man, was definitely established by the
Second Plague Commission of the Indian Government in 1905.
Bacot and Martin showed, in 1913, that plague bacilli multiply
in the proventriculus of this particular flea species, and the
alimentary canal becomes thereby blocked. The flea, receiving
no nourishment, becomes ravenous, and as it is still able to
suck blood, will attack not only other rats, but will migrate
from perishing rats to man. Apparently infection of man is

122 THE PRINCIPLES OF APPLIED ZOOLOGY

due to the regurgitation, by the flea, of blood that has been
sucked into the oesophagus, into the wound again, bearing with
it, of course, masses of plague bacilli.

The common rat-flea of Eastern India, of Madras and
Colombo, is a very closely related species, Xenopsylla astia,
which appears not to suffer from blocking of the alimentary
canal by plague bacilli. It is therefore not liable to convey
the bacilli from rat to rat, or from rat to man, and the compara-
tive rarity of plague epidemics in these cities, as compared with
Bombay, must be ascribed to the predominance of X. astia in
Madras and Colombo, and of X. cheopis in Bombay.

The freedom of Europe and North America from plague
epidemics can be ascribed to the fact that, except in seaports,
the Black Rat, although frequently imported by shipping,
cannot establish itself in competition with the sewer rat M us
?iorvegicus. In mediaeval Europe, however, before the Grey
Rat had spread from Northern Asia, and when houses were
wooden and sanitation non-existent, the Black Rat flourished
and plague epidemics were frequent.

Xenopsylla very closely resembles the cosmopolitan Pulex
irritans of man. Both lack the genal and notal combs.
Xenopsylla, however, shows a vertical chitinous ridge on the
mesosternum, the ventral plate to which the basal joint of each
middle leg is attached.

The human flea is said to hide by day in cracks and crevices
in floors, and in rugs and bedding and so forth, coming out at
night to attack human hosts. In some areas the commoner
flea attacking man, however, is the dog or cat-flea Cte?wcephalus
canis or C. felis. The difference between these two fleas is
very slight, but both are easily distinguished from Pulex
irritans by the possession of both genal and notal combs.

Ceratophyllus of rodents and birds includes species which
will readily attack man, notably C. fasciatus of the Grey Rat
and G. galling of poultry. Ceratophyllus differs from Pulex
and from Ctenocephalus in possessing only the notal combs.

In California, bubonic plague has spread from rats to the
ground squirrel Otospermophilus beecheyi, probably by the
intermedium of the flea Ceratophyllus acutus. The danger of
plague being conveyed from squirrel to man is, of course, slight,
but there is the danger that squirrels may provide a more or
less permanent reservoir of disease from which rats may become
infected, and through rats, man himself.

In North Manchuria a fur-bearing rodent known as the
tarbagan ( Arctomys bobac) is the primary source of epidemics

ARTHROPODA: MECHANICAL TRANSMISSION 123

of a pneumonic variety of plague which can be conveyed to
man and which can spread from man to man directly by sputum
contamination .

Bugs. — The term bug applies, strictly speaking, to any
member of the large insect order of Hemiptera, but in a medico -
entomological sense refers more particularly to the species of
Cimex, the " bed bug."

Cimex affords a complete contrast in structure and habits
to the flea. In the first place it is dorso-ventrally flattened, and
is a runner rather than a jumper. In the second place, it does
not remain on its host a longer time than is necessary for it
to fill its crop with blood, hiding at other times in crevices in
panelling, plastered walls or ceilings, wooden furniture, loose
wall-paper, and so forth. It is therefore less restricted in its
choice of host, a dead mouse or a living cockroach being nearly
as acceptable as a human being. It has the most astonishing
powers of fasting, cases of adult bugs existing nearly a year
without food having been recorded.

In the third place, the life-cycle is without a metamorphosis,
the newly hatched insect being a miniature replica of the parent,
and attaining sexual maturity and adult size after a series of
moufts, between which the insect grows and develops further.

The mouth parts are enclosed within a sharp beak-like
proboscis, which is bent backwards somewhat beneath the
head. This proboscis or labium is deeply grooved along its
length, and in the groove there lies a pair of needle-like
mandibles, and a pair of needle-like maxillce ; when the
mandibles are opposed, a double-barrelled tube is created. Up
one barrel, blood passes from the host ; down the other there
passes a hsemolytic salivary secretion into the wound.

Of the true bed bugs or family Cimicidae, Cimex lectularius
is the usual form in temperate latitudes ; Cimex rotundatus the
form in tropical latitudes. The differences between them are
slight.

Cimex columbarius infests fowl houses and pigeon houses.
Cimex hirundinis infests swallows' nests. Cimex pipistrelli
infests the sleeping places of bats.

Of the family Reduviidee or Assassin bugs, the genus Conor -
hinus is the most notorious. C. infestans is the " great black
bug of the Pampas " of Argentina. C. sanguisuga is the
cone -nosed bed bug of the Southern United States, the West
Indies, and Central America. C. megistus is the " barbeiro '
of Brazil, the intermediate host of the Schizolrypanum cruzi of
Chagas Disease.

124 THE PRINCIPLES OF APPLIED ZOOLOGY

Lice< — The term lice may be applied to two distinct orders
of insects, in many respects very distinct morphologically and
bionomically, namely, the Mallophaga or biting lice of birds
and certain mammals, and the Anoplura or sucking lice of
birds and mammals.

From the pathogenic standpoint, only the latter order need
be considered.

They are small, flattened, wingless insects, parasitic on the
skin of mammals, and usually possessing modifications of the
claws to enable them to cling fast to a hair. The eggs are
comparatively large and conspicuous, are glued to a host hair,
and the newly hatched louse is a miniature replica of the parent,
and reaches maturity by a series of growth phases separated
by skin moults.

The mouth parts consist of two retractile tubes, one within
the other. The outer tube, considered to be homologous to
the labium of other insects, has a serrated edge and serves
to anchor the feeding insect to the host skin. The inner tube,
representing possibly fused mandibles and maxilla?, is the real
penetrating and sucking organ. The host distribution of
Anoplura seems to be determined rather by genetic relationships
than by geographical factors ; that is to say, a species of louse
will be found restricted to a particular species of mammal
all over the world.

The genus Pediculus, for example, attacks only man and
the great apes, and occurs on man all over the world. The
genus Pedicinus is characteristic of the monkeys, and never
attacks man or apes.

The limitation of Pediculus to man and apes affords further
evidence, to some authorities, of the closer relationship between
man and the great apes than between man and the monkeys.

The genus Pediculus of man came into prominence during
the Great War, owing to an accumulation of evidence that
incriminated it as the mechanical carrier of exanthematous
typhus, relapsing fever, and trench fever.

There are two species, or more probably two biological races
of the one species, namely, Pediculus humanus capitis, the
head louse, and Pediculus humanus vestimentii, the body louse.
They coexist with man everywhere, but are undoubtedly less
prevalent in hot than in cold climates. The louse-borne
diseases are all typical of cold or mountainous rather than of hot,
low -lying countries, and are more prevalent in winter rather
than in summer. Lice are, of course, more prevalent in such
areas, and are more prevalent in winter than in summer, owing

ARTHROPODA: MECHANICAL TRANSMISSION 125

to the wearing by the human host of additional clothing, to
a lesser tendency towards thorough body washing in winter,
and to greater crowding of sleeping quarters.

The organism of typhus and trench fever is not with
certainty known, but a minute organism termed Rickettsia
proiuazekia, resembling diplococci or bipolar bacilli, has been
observed in the intestinal epithelial cells of lice taken from
tj^phus patients, and is believed by some authorities to be a
life-cycle phase of a protozoan causative organism of typhus.
Similar bodies have been observed in the blood of trench fever
patients and in the tick Dermacentor that conveys Rocky
Mountain spotted fever. Other authorities, however, deny
that Rickettsia bodies are micro-organisms at all.

Very little information is available concerning the connection
between other louse species and animal disease. Impetigo of
hogs is essentially a skin disease produced by inoculation of a
bacillus (Bacillus enter idis qairtner) into the skin by the louse
Hamiatopinus suis.

General prophylactic measures against fleas, bugs, and lice
will vary somewhat according to the insect concerned.

In the case of fleas, the sleeping places of domesticated
animals and flea-infested rooms can be controlled by spraying
with 5 per cent, formalin or with 1 in 1,000 solution of corrosive
sublimate.

Bed bugs are a stubborn pest to deal with. In a badly
infested room or house containing much old woodwork, the
only drastic remedy is that of stripping off all paper and fumigat-
ing with hydrocyanic acid gas, or, failing this, with sulphur
dioxide. If the source of infection can be localised in some
particular area of woodwork or of wall, much can be done by
injecting crevices with gasoline or with crude creosote.

Destruction of lice require actual contact of the host animal
with some toxic substance or pediculicide, either by immersion
in a solution of the substance or by application of the substance
in the form of a smear or ointment. In the ordinary civilised
community, ordinary methods of cleanliness of body and clothing
are sufficient to prohibit lice. Under the conditions of field
warfare, however, and of savage communities, cleanliness of
body and person is not always possible, and recourse has to be
made to pediculicidal substances or to louse deterrents.

CHAPTER XII

ARTHROPODA AND DISEASE : Cyclical Transmission

The term cyclical transmission implies that the arthropod
vector of the pathogenic organism concerned does not act
merely as a mechanical carrier, but that it acts as an essential
intermediate host for some phase in the life-cycle of the organ-
ism. It follows, therefore, that the type of pathogenic organism
thus conveyed is itself animal in nature, and is usually either
a protozoan or a nematode worm.

The chief arthropods, in which the potentiality occurs of
acting as intermediate hosts of organisms pathogenic to man
and domesticated animals, are certain blood-sucking flies,
notably the mosquitoes, the tsetse flies, and the Pupiparid
flies, and certain arachnids belonging to the order Acaridea
or ticks.

It would not, however, be correct to assert that all these
forms are proved carriers of pathogenic organisms. Even
among mosquitoes the number of species actually known to
carry disease is in the minority, and even in a locality where
mosquito-borne disease is endemic, only a small percentage of
individuals of the incriminated species may prove to be infected.
At the same time, all such insects may be looked upon as
potential carriers of blood diseases, and to a civilised community
their presence is a menace.

Mosquitoes. — The term mosquito is applied generally to
certain small flies, popularly and somewhat erroneously referred
to in temperate English-speaking countries as midges or gnats,
which are sharply distinguished from other two -winged flies by
certain peculiarities of structure.

These structural peculiarities concern particularly the wings
and the mouth parts. The wings are long and narrow and are
completely enclosed by the first or costal vein which runs all
round the wing margin. The second, fourth, and fifth longi-
tudinal veins all fork, but the third vein is short and comes
off from the middle of the second almost at a right angle.

All the wing veins are provided with scales, which may be
of several different types.

126

ARTHROPOD A : CYCLICAL TRANSMISSION 127

The anterior wing border has scales almost bristle -like.
The posterior border has a fringe of scales of two forms, namely,
short, broad border scales and long, narrow fringe scales of two
lengths. The scales on the wing veins usually comprise short,
broad medium scales which lie flat against the vein, and long,
narrower lateral scales that stand out on either side of the vein.

Scales occur also on the legs and on the rest of the body.

The head of the mosquito bears a pair of prominent eyes, a
pair of antennae which in the male resemble test-tube brushes
but which in the female have scantier whorls of hairs, and a
pair of palps or organs of touch ; these latter organs may be
short, or they may be as long or longer than the proboscis.

The proboscis is a conspicuous projection from the head. It
consists essentially of a soft, fleshy rod, ending in a pair of small
lobes termed labellse. The rod is deeply grooved dorsally, and
in this groove there lie (a) a pair of needle-like maxillae ; (b) a
pair of lancet-like structures, the modified mandibles ; and (c) a
median tube consisting of (i.) a long grooved incomplete tube,
in section like the outer cover of a cycle tyre, that is to say,
incomplete ventrally, and (ii.) a blade-like structure that fits
against this ventral slit and converts it into a tube ; this blade-
like structure is termed the hypopharynx ; the ventrally grooved
structure against which it fits is termed the labrum epipharynx.
The tube formed by apposition of hypopharynx to labrum
epipharynx serves for the upward suction of blood or plant
juices. A channel tunnelled in the hypopharynx serves for the
downward passage of saliva.

In the male mosquito the food consists of plant juices only,
and the maxillary and mandibular lancets are absent. Only
the female mosquito is capable of biting animals. It must
be clearly understood that when the proboscis is thrust against
the surface of an animal's skin, the labium bends back and acts
as a guide for the lancets and for the labrum epipharynx and
hypopharynx. That is to say, the proboscis, strictly speaking,
is not thrust into the animal's skin, as is the case with the
proboscis of a biting Muscid fly or of a bug. The bite of a
mosquito is thus not so painful as is the bite of, say, Stomoxys,
or a Tabanid fly or a bed bug.

Once the lancets are inserted in the host animal, the power-
ful pharyngeal muscles which take up almost the whole of the
head cavity enable the insect to suck blood from the victim
up the epipharyngeal tube into the pharynx. When these
muscles relax, the walls of the pharynx collapse and the blood
is forced into the oesophageal region, which is provided with a

128 THE PRINCIPLES OF APPLIED ZOOLOGY

large ventral outgrowth and two smaller ones, usually termed
reservoirs, but whose function is disputed. The more modern
view is that they contain carbon dioxide and a commensal

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fungus, and that their contraction forces the gas and fungus into
the wound made by the insect and so brings about the irritation
which follows a mosquito bite. From the oesophagus the food
passes to the real absorptive portion of the alimentary canal,

ARTHROPODA : CYCLICAL TRANSMISSION 129

the midgut, whose swollen posterior end is usually but errone-
ously termed the stomach, and from thence the unabsorbed
residue passes by the hind gut to the exterior. On either side
of the pharynx there occur three salivary glands. Their ducts
converge into a single median one that ends in a salivary
pump by which the flow of saliva down the duct of the hypo-
pharynx is regulated. In a Plasmodium -infected mosquito
these glands are the site of the sporozoites (Fig. 9).

The Distribution and Life- Cycle. — Mosquitoes are cosmo-
politan in range. In tropical regions, of course, there is greater
variety of species and they are prevalent all through the year,
but in Arctic latitudes during the short summer the abundance
of mosquitoes is probably more intense. The former view
that the blood-feeding habit is essential for the propagation
of the species is not correct. Swarms of mosquitoes occur in
localities where their chance of a meal of animal blood is slight.
Areas in Greenland, practically destitute of terrestrial mammals,
swarm nevertheless with mosquitoes. Probably both male
and female mosquitoes habitually suck plant juices. They
are strongly attracted to warm surfaces, and such thermotropic
reaction towards the bodies of warm-blooded animals may
have brought about the transition in habit from plant sucking
to blood sucking.

The life-cycle is very constant throughout the group.
The eggs are nearly always laid upon the surface of water,
either in raft-like masses (Culicine mosquitoes) or singly and
provided with a pair of floats (Anopheline and Stegomyine
mosquitoes) (Fig. 20).

Species which lay eggs in rafts usually avoid running streams
or agitated pools, and select temporary puddles and the shallow
margin of protected pools. Salt marsh mosquitoes oviposit
when the meadows are almost dry, and the eggs will remain
unhatched for months or even years until covered with water
again. Of the forms which lay eggs singly, those whose eggs
hatch quickly, such as species of Anopheles, frequent open,
permanent swamps or clear pools containing weeds and algae,
whilst others which lay eggs that sink down to the bottom of
the water and remain unhatched for nearly a year prefer
evanescent woodland pools.

The resulting larvae are always aquatic and, as regards
respiratory habit, may be divided into five groups : —

(1) Larvae which hang head downwards from the surface
film by means of a posterior respiratory tube (Culicine
mosquitoes).

130 THE PRINCIPLES OF APPLIED ZOOLOGY

(2) Larvae which are suspended from the surface film by
branched hairs and lie parallel to it, their breathing tubes
opening on the dorsal surface (Anopheline mosquitoes).

These two types were formerly believed to depend entirely
upon atmospheric oxygen, but recent experiments seem to
indicate that oxygen dissolved in the water may be absorbed
through the branchial leaflets and the body surface.

(3) Larva? which live a pelagic life and breathe dissolved
oxygen through the body surface. This is the case with the
larva? of the non-blood-sucking genera Corethra and Mochlonyx.

(4) Larva? which breathe oxygen contained in submerged
water plants. Thus in the Panama Canal zone, Tceniorhynchus
titillans attaches its eggs to the under surface of a leaf of the
water lettuce (Pistia). The young larva descends into a mass
of rootlets, pierces one with its pointed respiratory siphon,
and so takes in air from the plant, remaining thus attached.

The larva of Aedes is believed to penetrate plants in similar
fashion with its antenna?.

(5) Larva? which possess air tubes but which frequent the
bottom of stagnant pools and are provided with large gills.

The water need not be pure. Some species breed in clear
pools or springs. Others prefer stagnant water or even sewage.
Others are brackish water forms, in salt marshes, or even in
rock pools, containing as much as 60 grm. of salt per litre.

In general, the larva feeds on alga? or on minute organic
matter swept into its mouth by currents produced by tufts
of mouth bristles ; others are predacious upon other mosquito
larva?.

The pupal stage of the mosquito is also aquatic and motile,
and provided with a pair of respiratory siphons, but of course
does not feed.

Mosquitoes may be roughly divided according to habitat
into salt marsh forms, swamp forms, woodland and jungle
forms, and domestic forms. Their scientific classification is
somewhat chaotic, a consequence of the new species and new
facts which are discovered almost daily.

For practical purposes, however, we may recognise two
distinct groups of species, namely : —

(a) The Anopheline mosquitoes, and (6) the Culieine
mosquitoes.

Anopheline mosquitoes are characterised by the following
points (Fig. 21) : —

(1) The female possesses palps as long as the proboscis.

ARTHROPODA: CYCLICAL TRANSMISSION 131

(2) The wings are generally, but not invariably, spotted with
patches of dark scales.

(3) The adult rests upon a surface with its body at an angle
to it, thus appearing to stand on its head.

Anopheles
maculipennis

Culex pipiens

Anopheles

Culex

Fig. 21. — Diagnostic Features of Culicine and Anopheline Mosquitoes.

(After Brumpt.)

132 THE PRINCIPLES OF APPLIED ZOOLOGY

(4) The larva is a surface feeder and floats parallel to the
water surface, moored to the surface film by lateral tufts of
brached hairs on the abdomen ; there is no posterior respiratory
tube, but the tracheal trunks converge to a hollow at the base
of a papilla on the dorsal surface of segment 8 ; the body has
long, feather-like hairs (Fig. 20).

The chief genera of Anopheline mosquitoes are Anopheles,
Myzomyia, Pyretophorus, Arribalzagia, Myzorhynchus, Nyssor-
hynchus.

These are the forms chiefly concerned in the transmission
of malarial fever. It may be noted that in Great Britain three
species of Anopheles occur, two of which are potential malarial
carriers, namely, A. maculipennis and A. bifurcatus, the latter
of which is a form whose wings are not spotted.

Culicine mosquitoes are characterised by the following
points (Figs. 20 and 21) : —

(1) The female possesses palpi shorter than the proboscis.

(2) The wings are usually unspotted.

(3) The adult rests upon a surface with its body parallel
to it.

(4) The larva possesses a posterior breathing tube, and hangs
head downwards in the water with the tip of this tube applied
to the surface film ; the position is due partly to the heavy head
and jaws.

The chief genera of Culicine mosquitoes are Culex, Stego-
myia, Mansonia, Aedes.

Culex pipiens and Culex fatiguans, two cosmopolitan species,
have been shown to convey the larva? of Filar ia hancrofti and
to act as intermediate hosts to the organism of bird malaria
(Plasmodium prcecox). Culex fatiguans is suspected also to
carry the organism of Dengue Fever.

Stegomyia and Aedes are small black mosquitoes with snow-
white markings on head and thorax, and white crossbands on
the abdomen. They are popularly termed " tiger mosquitoes."
They usually bite at daybreak.

Aedes argenteus is the intermediate host of the organism of
Yellow Fever (Leptospira icteroides).

It is essentially a house-frequenting mosquito of tropical
coast-lines and river banks, and is the commonest mosquito
occurring on ships. Yellow fever has therefore probably been
carried by ships from the chief endemic foci — the coast-line of
South and Central America — across to West Africa, northwards
to the southern United States, and to other parts of the world.
The spirochete of yellow fever was of course only described by

ARTHROPODA: CYCLICAL TRANSMISSION 133

the Japanese worker Noguchi at Guayaquil in 1918, but its
connection with Aedes was suggested by the brilliant experi-
mental work of the American Yellow Fever Commission of
1900, and has since been fully confirmed by the results of anti-
Aedes work in vellow fever areas.

This mosquito is essentially a domestic species, and is rarely
found breeding at more than a hundred yards from human
habitations. The black eggs are laid singly at night upon the
surface of almost any accumulation of filthy water, however
small ; they are very resistant and are apparently not affected
by evaporation of the water. The larvae, distinguishable by
their transparency and by the short black respiratory siphon,
can live in large numbers in extremely small quantities of water,
and so are very susceptible to anti-mosquito measures. Such
measures, together with careful isolation of yellow fever patients
from mosquitoes have almost stamped the disease from many
tropical cities.

Anti-mosquito Measures. — Measures against mosquitoes in
the vicinity of habitations comprise : —

(1) Drainage, where water can be disposed of.

(2) Use of larvicides, where water cannot be drained and is
not required for domestic or commercial use.

(3) Oiling, where water is thus required or where conditions
militate against the use of larvicides.

Drainage problems occur in connection with lakes, swamps,
ponds, and their solution varies according to the source of the
water. Rainwater ponds and swamps are usually dealt with
by the provision of " V-shaped " ditches, preferably lined with
concrete, to carry off water left behind after the main flood
waters have passed. If, however, the pond or swamp be a
basin in a channel of a sluggish stream, the problem is more
difficult, since the water supply is continuous and fluctuating ;
the usual treatment is to deepen the stream below the basin
so as to increase the outflow.

The destruction of mosquito larvae in large ponds and lakes
is possible to some extent by the encouragement of fish, but their
use is very limited. The stock of fish constantly requires
replenishment, as the small fish are themselves devoured by
larger fishes.

Larvicides are as a rule too expensive for large scale use
unless chemical by-products are available. Sodium cyanide
at the rate of 1-100,000 parts of water is frequently recom-
mended. Cresol is also an effective larvicide. In the Panama
Canal zone a black liquid resin soap, prepared by boiling

134 THE PRINCIPLES OF APPLIED ZOOLOGY

together resin, soda, and crude carbolic acid in the proportions
of 5 : 1 : 40 by weight, is used with great success, one part of
it in 5,000 of water being sufficient to kill an Anopheline larva
in ten minutes. This larvicide, however, does not emulsify
in brackish water, is affected in efficacy by the presence of
decaying vegetation, and is fatal to fish. Paris green (copper
aceto-arsenite) is also becoming much used as a larvicide.

Oiling in principle consists in the application of a thin film
of mineral oil to the surface of the water. The exact toxic
action of mineral oil upon mosquito larvae is disputed. It has
been asserted (1) that the larva? are suffocated ; (2) that altera-
tion in the surface tension of the water renders the larvae
unable to hang on ; (3) that the larvae are poisoned by oil
dissolved in the water ; (4) that the larval spiracles become
choked.

The most recent and probable view is that it is the vapour
which actually kills, and that the lower the boiling point of
the oil used, the more toxic it will be.

No definite type of oil can be recommended above all others.

Ordinary kerosene is effective, spreads rapidly, and forms a
thin film ; but it evaporates quickly and the film is difficult
to see. It is preferable when mixed with crude oil in proportions
varying from 3-1 to 1-3. The most satisfactory mixture is
nearly black in colour and slightly thicker than kerosene. On
stagnant water such a mixture can be applied as a spray ;
where there is a current, various devices are used — drip cans,
bags of oil-soaked waste, for example. Small accumulations
of water, such as hoof-prints, can be quickly and effectively
treated with oil-soaked sawdust. In the Panama zone crude
oil of asphaltum is extensively used, half a million gallons per
annum, according to one authority ; it is cheap, but its poor
spreading qualities would make it unsuitable to cooler climates.

Vegetable oils give more permanent films than do mineral
oils, but do not spread so easily. A mixture of two parts of
castor oil to 100 of kerosene, however, spreads even better than
kerosene, is more permanent, and the film is not readily broken
up by wind or by vegetation.

Such oiling should be repeated every ten or eighteen days.

Many cases occur where drainage and oiling methods cannot
readily be carried out, notably the cases of rapidly flowing hill
streams and the case of rice fields.

The first case can usually be dealt with by the erection of
dams to allow sufficient accumulation of water to flush the
stream bed from time to time.

ARTHROPODA: CYCLICAL TRANSMISSION 135

Rice fields are very difficult to deal with, since they are too
shallow usually for fish, and of course cannot be treated with
chemicals or with oil. Alternate drainage and flooding every
fortnight has been tried in British Guiana, but this adds con-
siderably to the cost of cultivation. Rice cultivation is in fact
inseparable from the occurrence of mosquitoes in large numbers,
but it must be remembered that rice-growing areas may be
remarkably free from malaria. Many notorious mosquito
carriers of malaria will not breed in rice fields.

Reference may be made to two families of flies whose
members are closely related to the mosquitoes, namely, the
Chironomidae or true midges, and the Psychodidse or owl midges.

The first family has one sub -family, the Ceratopoyonince.
whose females are bloodsuckers. They are minute flies,
generally blackish in colour. A mosquito net is no obstacle to
them, and they can bite through a stocking. The chief genera
are Ceratopogon, Culicoides, and Johanssienella. They breed
in water or in moist vegetable matter in woodlands, under
decaying bark, etc.

They have not yet been shown to transmit any disease.

The Owl Midges are minute hairy flies, somewhat resembling
tiny moths, which breed in decaying organic matter, in sewage,
etc. There is one blood-sucking genus, Phlebotomies, the sand-
fly, one species of which, Phlebotomus pappatasii, has been
shown to carry the Pappataci fever of Mediterranean countries.
This fly is found commonly in the vicinity of old ruins, walls,
or rock heaps, owing probably to the prevalence in such places
of lizards, upon which the flies are believed to feed normally,
and owing to the conditions in such places, moisture, coolness,
and darkness being optimum conditions for the larva?. The
latter are eyeless and haunt dark crevices among rubbish.
They feed chiefly on the excreta of wood-lice, lizards, and bats.

The Tsetse Flies. — The term tsetse refers to the genus Glossina
of muscid flies, a blood-sucking genus restricted in distribu-
tion to Africa, and sharply distinguished from other Muscidae
by the fact that the mature fertilised female gives birth to a
single larva, large nearly as the abdomen of the mother, at
intervals of several days ; the hatching of the egg and the
nourishment of the three larval stages takes place in the uterus.
The extruded larva has the mouth parts and alimentary canal
reduced to vestiges, and so cannot feed ; it buries itself immedi-
ately after birth in earth or sand, and within a few hours has
changed into a pupa.

The shape of this pupa and certain peculiarities of antenna?

136 THE PRINCIPLES OF APPLIED ZOOLOGY

and wings shown by the adult may be understood by reference
to Fig. 22.

Glossina

palpalis

Tsetse fly"

Arista

Majcillary
palps

Epipharynx

Hypopkarynx

Head of
Glossina

Pupa of Glossina palpalis

Before feeding-

After feeding*

Fig. 22. — The Characteristics of Glossina. (After Alcock, Brumpt and Austen.)

The genus is at present restricted to areas of Africa lying
between 18° N. and 31° S. ; probably it was more widely dis-
tributed in former times. Several fossil tsetse flies have been
found in the Miocene strata of North America, a pala?ontological

ARTHROPOD A: CYCLICAL TRANSMISSION 137

discovery which throws a light upon the disappearance of
ungulate fauna, horses in particular, from America since the
Tertiary period.

The prevalence and distribution of tsetse flies is influenced
greatly by conditions concerning the prevalence of game
animals, the presence of vegetation, and weather conditions.
They are therefore not found continuously across Central
Africa, but are confined to certain districts known as ' fly-
belts." Outside such belts there would seem to be factors
inimical to the tsetse ; probably the absence of moisture is one
snch factor. The fly-belts, in the case of the majority of tsetse
species, are usually regions affording deep shade and proximity
to water, together with dry, loose sand or soil convenient for the
pupation of the larva ; such conditions, in fact, as are provided
by the wooded shores of lakes and rivers. The most widely
distributed species, however, Glossina morsitans, seems less
dependent upon the presence of water but requires, in particular,
moderate but not excessive cover and a hot, moderately dry
climate such as is provided by savannah or parkland where
game is abundant. It occurs usually all the year round in
certain places where the vegetation is non-deciduous, so-called
dry season foci or primary centres, such places, for example, as a
dried up stream bed where there is subsoil water. It must be
emphasised that these dry season foci are the areas to which
the term fly-belt should be applied in the case of G. morsitan,
for during the rainy season the fly may range over a wide extent
of bush countrv.

The classification of the species of Glossina is based largely
upon the characters of the male and female external genital
organs. Three distinct groups of species may thus be dis-
tinguished (Fig. 23).

In the I usca group the males have the large claspers more or
less claw-like and not united by a membrane. The external
genital armature of the female consists of five plates, one dorsal
pair, one lateral pair, and a single median sternal one (Fig. 23).

This group contains large forms somewhat varied in habitat.

G. fusca itself is a large form with dark wings which inhabits
the forest areas of West and Central Africa, and is not so
dependent upon proximity to water as are other species. It
rests during the day and feeds during one or two hours after
sunset.

G. brevipalpis is the common large tsetse of Southern Central
and Eastern Africa. This species again is active in the early
evening and the early morning.

138 THE PRINCIPLES OF APPLIED ZOOLOGY

In the palpalis group the males have the large claspers
connected by a thin membrane, which, however, is deeply

Dorsal
plate

Lateral plate

Fusca Group

porjaZ, * '"<

Membrane

Median
dorsal plate

Palpalis Group.

Fused dorsal plates

Morsitans Group.
Fig. 23. — External Genitalia of Glossina. (After Newstead, Potts and Evans.)

divided in the middle. The external armature of the female
consists of six plates, a small median dorsal plate being present

ARTHROPOD A: CYCLICAL TRANSMISSION 139

in addition to those described above. This group contains
particularly the species Glossiria palpalis and Glossi?ia tachi-
noides.

G. palpalis occurs along the edges of rivers and lakes where
the vegetation is dense, but occasionally, as along the shores
of Lake Tanganyika, where there is little shade. It is probably
a true intermediate host of Trypanosoma gambiense, the organ-
ism of human sleeping sickness, and is probably the only
carrier. It is also a carrier of the cattle trypanosomes and of
the crocodile trypanosome, since it feeds freely upon these
animals.

G. tachinoides is one of the smallest of tsetse flies, and is
similar in habits to palpalis. It prefers, however, the upper
reaches of rivers, and is prevalent particularly in the districts
along the southern border of the Sahara Desert. It is, too, the
only tsetse fly which occurs outside Africa, since it occurs in
Southern Arabia. It seems to rely chiefly upon the blood of
reptiles, particularly the monitor lizard and the crocodile, but
is a carrier of the cattle trypanosomes T. cazalboui and T.
dimorphon in West Africa.

In the morsitans group the males have the large claspers
completely united by a membrane, and they are also fused
in the middle line (Fig. 23). The armature of the females
consists of a pair of fused dorsal plates and a median sternal
plate. The group includes G. morsitans, G. longipalpis, G.
pallidipes, and others. All are flies which haunt open country
with a moderate amount of shade but not necessarily in
proximity to water.

Of the three chief species, longipalpis is essentially West
African, pallidipes essentially East African, and morsitans a
species distributed in fly-belts from Senegal on the west coast
to Zululand on the east coast. G. morsitans is probably the
carrier of more trypanosome diseases than any other tsetse.
It has been shown to be the carrier, and probably the only
carrier, of T. rhodesiense, the organism of the virulent Rhodesian
form of sleeping sickness ; it is the carrier of T. brucei, the
organism of the cattle disease Nagana ; it is also the carrier
of several other trypanosome diseases of cattle and horses.

Anti-glossina Measures. — The chief measures advocated
against tsetse flies are as follows : —

(1) The clearance of scrub and undergrowth from the banks
of rivers and for three hundred yards around villages, or, in
the case of the wide ranging morsitans, the destruction in the
dry season of located primary foci.

140 THE PRINCIPLES OF APPLIED ZOOLOGY

(2) Elimination of game animals from the fly-belts has been
advocated by many authorities, but in the absence of fuller
knowledge the value to be derived from such measures is a
matter of dispute. It is not proved that trypanosomes of game
animals become pathogenic when introduced into domesticated
animals ; it is not certain whether other animals, reptiles, and
rodents, for example, may not also serve as trypanosome
reservoirs ; it is not clearly known whether the tsetse flies are
dependent for food supply upon game animals, or whether they
have other sources of supply, or can live on plant juices.

(3) The collection and destruction of pupae has also been
recommended. The difficulty of applying such measures
and the trapping of adults on a large scale are almost
insuperable.

Pupiparid Flies. — Pupiparid flies, like tsetse flies, give birth
to full-grown larvae, one at a time, which pupate almost immedi-
ately after birth.

The flies themselves are blood-sucking ectoparasites chiefly
of mammals and birds, but one form, Br aula cceca, exists on
bees.

They are characterised by a tough, leathery outer skin, a
head which is jammed back against the thorax, or even turned
back upon it, by the broad thorax, the reduced antennae, the
stout legs ending in remarkably strong grasping claws. The
proboscis is somewhat like that of Glossina, but is retractile.
Wings may be present, may be vestigeal, may be present for a
short time only, or may be altogether absent.

Of the various families which make up the group, the
Hippoboscidae are parasitic on birds and mammals. Hippo-
bosca attacks cattle, horses, and sheep. Melophagus ovinus is
the ' sheep ked." Both genera are hosts of the crithidial
stages of mammalian trypanosomes.

The Streblidae are parasitic on bats.

The Nycteribiidae also infest bats.

The Braulidae include the pupiparid parasite of bees.

The Ticks. — The term " tick " is applicable to a member of
the acaridean family Ixodidae, the remaining families of Acaridea
constituting the so-called mites. They are, of course, not
insects but Arachnida, that is to say, belong with the spiders,
scorpions, etc., and so are characterised by the division of the
body into two regions, cephalothorax and abdomen, and by
the possession of not more nor less than four pairs of walking
limbs.

As in the case of all Acaridea, the body is unsegmented, and

ARTHROPODA: CYCLICAL TRANSMISSION 141

owing to the fusion between cephalothorax and abdomen, is
globular. At the anterior end is a depression, the camerostoma,
into which the mouth parts are inserted. These are collectively
termed the rostrum, or, more correctly, the capitulum (Fig. 24).
A typical adult tick ranges in size from that of a pea to a
hazel nut. The capitulum consists chiefly of a quadrangular

ffupostome

Palp

ff alters organ

Tarsus

-Metatarsus

■ - Basis capituli

- Tibia

- Trochanter

- Femur
•Coxa

Genital opening-

Genital groove

Median plate

■ Stigmal "

• Epimeral •>
Anus

■ Adanal plate
Anal groove

V S \J %/ / \ \/\....\J. -■/- --Festoons

Fig. 24. — The Morphological Features of a Hard Tick. (Ventral view.)

or polygonal plate whose ventral surface is somewhat convex ;
this plate is the basis capituli ; its dorsal surface bears in the
female a pair of median areas perforated in sieve-like fashion
and regarded as sensory.

The basis capituli bears (a) a pair of finger-like pedipalps,
consisting of three large joints with a small fourth joint on the
dorsal surface of the third ; the pedipalps are sensory structures.
(6) A pair of chelicerse, each of which consists of a straight shaft

142 THE PRINCIPLES OF APPLIED ZOOLOGY

which bears a movable terminal digit, an irregularly-shaped
piece of chitin articulating with the end of the shaft and having
two movable joints each armed with teeth ; the chelicerse are
covered dorsally by a sheath formed by an extension of the
cuticle of the basis capituli. (c) A median hypostome, a poker-
like structure consisting of two closely opposed halves armed
with backwardly directed teeth ; this hypostome, which is not
visible in dorsal view, is the real piercing organ.

The mouth lies between the chelicerse and the hypostome.

The body bears on its ventral surface four pairs of legs
which have large coxse or basal joints ; a pair of stigmatic
plates each perforated by a respiratory aperture and lying
behind the last pair of coxae ; a genital opening in the middle
line, not far behind the capitulum ; an anal opening, a little
way from the posterior edge ; and in some ticks prominent
grooves round the genital aperture and anus, the genital and
anal grooves.

The ticks may be grouped into two sub-families.

The Argasinse or Soft Ticks are flattened, or rounded ticks
with a somewhat soft, flabby body, and with the capitulum
invisible from above. They do not remain on the host for
longer than it takes them to gorge themselves with blood, but
usually spend the daylight in crevices somewhere in the vicinity
of the host animal, and come out at night in order to find a
host individual upon whom to feed. There are two genera,
namely, Argas and Ornithodorus.

Argas has a flattened oval body with a thin striated edge.

Its eight species are particularly parasites of birds, and
infest the nests and houses of fowls, ducks, geese, turkeys,
pigeons all over the world.

A. persicus carries the spirochete of fowl cholera, Spirochceta
gallinarum, and seems to be a true intermediate host of it.

The other genus, Ornithodorus, is distinguished from Argas
by its rotund, wrinkled body. 0. moubata is common in African
villages, and in addition to its power of inflicting a very painful
bite, is the intermediate host of Spirochmta duttoni, the organism
of African relapsing fever.

The Ixodinse or Hard Ticks are characterised by the
hardening of the dorsal surface of the body to form what is
termed a shield.

In the male tick the shield covers almost the whole dorsal
body surface, but in a female or an immature tick the shield
only covers a portion of the dorsal body surface.

The usual life history is somewhat as follows. The eggs are

ARTHROPODA: CYCLICAL TRANSMISSION 143

laid on grass or herbage and may take two to six months to
hatch. The larva has only three pairs of legs. It has to search

Arg-as persicus

Ornithodorus moubata

Rhipicephalus sang-uineus

Amblyomma hirtum

Ventral
view

Ixodes hexag'onus
Fig. 25. — Types'of Soft Tick and Hard Tick. (After various Authors.)

for a host animal upon which to feed. After a few days on the
host it is gorged and it falls to the ground. Here it moults, and
the moulted form now possesses four pairs of legs, but as it
lacks still the genital opening, it is termed a nymph. This

144 THE PRINCIPLES OF APPLIED ZOOLOGY

again has to find a host upon which it can gorge itself, and
again, after gorging, it must come to the ground in order to
moult and to mature. The adults copulate on the ground, and
the fertilised female must again seek out a host, must again
gorge herself with blood, and must again come to the ground
in order to lay her eggs.

Usually the number of eggs laid by a Hard Tick is large,
from 5,000 to 20,000 ; this counterbalances somewhat the very
slender chance that any individual larva possesses of completing
its life -cycle. It must be noted that the larval tick or ' seed
tick," as it is popularly termed, may have to hang about on
the tip of a blade of grass for weeks or months before a host
animal comes along. In the majority of ticks it is not
usual for the larva to go in search of a host, as is done by
those of Soft Ticks. Further, even if a host be secured for the
larval period of the life history, this host must be left, and the
chances of the nymph securing a host are as slight as those of
the larva. Even if successful, this host again must be left and
eventually another host animal secured.

On the whole, therefore, the odds against any tick success-
fully completing its life-cycle are very heavy ones.

All tick stages, however, are extraordinarily resistant to
lack of food. Larvse have been known to live six months
without food ; adults can be kept alive in corked tubes for
five years. Further, when a host is attacked, the tick usually
secures itself in some position such as the interior of the external
ear, where its feeding is not likely to be interrupted.

In some species, the risk involved by leaving a host animal
in order to moult is to some extent minimised by the tick
remaining on the host from larval to adult stage, as is done by
Margaropus annulatus ; in others, the first moult is spent on the
host, but the rest of the moults are spent on the ground.

The importance of ticks in the transmission of disease con-
cerns the veterinarian more than the medical practitioner.

Two classes of diseases are associated particularly with ticks,
namely, spirochetoses and babesioses. These diseases have
been discussed in Chapter IV.

Rocky Mountain spotted fever of man, prevalent in the
Rocky Mountain states of North America, and caused probably
by an invisible virus, is almost certainly conveyed by ticks,
probably by Dermacentor andersoni and Hcemaphysalis leporis-
palustris.

PART II

AGRICULTURAL AND HORTICULTURAL

ZOOLOGY

CHAPTER XIII

SOIL ORGANISMS

The term soil organism, referring as it does to any living creature
whose whole life-cycle is spent within the surface layers of the
soil, can be applied to a very wide range of animal organisms.

It is applicable to a very large number of protozoa, for
example ; to a number of genera belonging to the nematode
family Anguillulidae ; to those families of segmented worms
to which the popular term " earthworm " is applied ; to those
families of molluscs termed ' snails and slugs " ; to a large
number of insects and arachnids ; even to certain soil-burrowing
vertebrate animals.

In addition, there is a wide range of protozoa, flatworms,
nematode worms, and insects which, if not soil dwellers
exclusively, spend some portion of their life-cycle within the
surface layers of the soil.

In this chapter, discussion of soil organisms will be confined
to two groups of animals, the soil protozoa and the earthworms,
whose activities bear upon the question of soil fertility ; and to
certain groups which are directly inimical to the plant grower,
notably the eelworms, slugs, termites, ants, and certain types
of insect larvae.

Soil Protozoa. — The presence of protozoa in the soil, together
with fungi, algae, bacteria, and worms, was demonstrated by
Ehrenberg so far back as 1837, but the possible economic signif-
icance of Soil Protozoa only came to light between 1909 and 1913,
when Russell and Hutchinson propounded what may be termed
a Protozoan Theory of Soil Fertility, an explanation, in terms
of protozoan metabolism, of the well-known fact that, when
soil is partially sterilised by heat or by chemicals, it can produce
a greater yield of crops than it did before,
io 145

146 THE PRINCIPLES OF APPLIED ZOOLOGY

The soil used by Russell and his collaborator was taken from
an arable field and contained moderate but not large amounts
of calcium carbonate, nitrogen, and organic matter. It was
partially sterilised by heating to 98° C. or by adding 4 per cent,
of its volume of toluene ; when toluene was used it was allowed
to act for three days, after which time the soil was spread out
in a thin layer so that the bulk of the chemical would evaporate.

Speaking generally, such treatment of soil enables it to pro-
duce a greater yield of non -leguminous crops than untreated
soil is capable of doing.

There is an increase in the amount of soil ammoma, a fact
which suggests that partial sterilisation removes some inhibiting
agent which in normal soil restricts bacterial reproduction and
ammonia formation. Russell and Hutchinson, after excluding
the possibility of the restricting agent being chemical rather
than biological, definitely concluded that the factor inhibitive
to ammonia production in normal soil is the presence of protozoa
predatory upon soil bacteria.

This view requires, of course, the assumption that, under
natural conditions, there is an equilibrium between the sapro-
biotic soil organisms, such as ammonia-producing bacteria, and
the protozoa which prey on them, so that the rate of ammonia
production in untreated soil neither increases nor decreases
very greatly. If, however, the soil be subjected to thermal or
to chemical influences sufficiently intense to kill the free-living
bacteria and the protozoa, both free -living and encysted,
but not so intense as to kill bacterial spores, then the flora
which ensues from the surviving spores will multiply with
great rapidity owing to the absence of restrictive agents, and
consequently there will be an increase of ammonia production
and subsequent increase in crop yield. If, however, the soil
be completely sterilised so that bacterial spores as well as
protozoa are destroyed, there will not be, of course, any marked
increase in fertility. The work of Russell and Hutchinson
gave a very great impetus to the study of soil fertility, and
during the last ten years an enormous amount of experimental
work has been carried out upon the question of soil sterilisation.

It may be asserted that many facts have come to light
which appear to support the Protozoan Theory, but that there
are very many facts which appear to controvert it. In fact,
this theory is not accepted by the majority of investigators in
the subject.

Alternative explanations look to a chemical or to a physio-
logical cause of the increased productivity of partially sterilised

SOIL ORGANISMS 147

soils. The following are the main alternative suggestions that
have been put forward : —

(a) Heating destroys toxins present in untreated soils ; such
toxins have been produced by the plants or by bacteria.

(b) Heating leads to the formation of a nitrogenous com-
pound whose presence brings about an increase of soluble
nitrogenous matter in soil ; soils treated with carbon bisulphide,
chloroform, ether, benzene, and so on, undergo a chemical change
which increases the amount of soluble nitrogen.

(c) Partial sterilisation has a selective action upon the
ammonia-producing bacteria ; such as survive belong to
groups which are more active decomposers of organic matter
than are other groups, and so the amount of ammonia increases.
This last view has received much support.

Whilst probably, as Russell and Hutchinson assert, bacteria
after partial sterilisation are less potent as individuals, and
the increased ammonia production is due solely to the numerical
increase, yet it is well known that various groups of bacteria
differ from one another in their power to produce ammonia ;
thus Bacillus mycoides is a better ammonifier than Bacillus
subtilis. It remains to be established how each of the various
groups of soil bacteria is affected by partial sterilisation.

It must be noted, too, that partial sterilisation does not
necessarily destroy all fungus spores, and that many species
of fungi, Cephalosthecium roseum, for example, can produce
considerable quantities of ammonia.

The predominant protozoa in soil, as regards variety of
species, are Mastigophora ; possibly many of these are not
distinct species at all but are stages in the life-cycles of amoebae ;
the commonest protozoa, numerically, are certain ciliates,
particularly Colpoda cucullus and Colpoda steinii.

The more important protozoan species after these two are : —

Mastigophora. — Monas guttula, Monas vivipara, Salpin-
goeca concullaria, Bodo ovatus, Bodo augustus, Bodo caudatus,
Phyllomitus undulans, Bodo euromonas, Euglena viridis, Poly-
toma uvella, Chlamydomonas , Monadina.

Ciliata. — Nassula elegans, Glaucoma scintillans, Colpidium,
Colpoda, Balantiophorus minutus.

Cutler gives the following list as common in Rothamsted
soil : — Ncegleria gruberi, Heteromita sp., Cercomonas sp.,
Oicomonas termo. Less numerous are Amoeba gleboe, Amoeba
verrucosa, Hartmanella hyalina, Arachnula impatiens, Difflugia
sp., Copromonas subtilis, Spiromonas augusta, Tetramitus
rostatus, Tetramitus spiralis, Helkesimastix fcecicola, Phyllomitus

148 THE PRINCIPLES OF APPLIED ZOOLOGY

amylophagus, Optidomonas sp., Bodo edax, Colpoda steinii.
Colpoda cucullus, Colpidium colpoda, Pleurotricha, Gastrostyla
sp., Balantiophorus sp., Euchelys sp. All these protozoa are
typical members of stagnant pools, and are not peculiar to the
somewhat more precarious environment of moist earth.

There is both a daily and a seasonal fluctuation in the
numbers of soil protozoa. The numbers of individuals of
one species may vary from a few hundreds per gram of soil to
40,000 or more within twenty-four hours.

The soil population reaches a maximum at the end of
November in Great Britain, and falls to a minimum at the end
of February. The reason for these fluctuations is not clear.
It has not yet been found possible to connect them with meteoro-
logical or general soil conditions.

Earthworms. — According to Charles Darwin's classical work
upon the influence of earthworms in converting vegetable
mould into plant food, some ten tons of soil per acre are passed
annually through the bodies of earthworms on an English farm.

The quantity of soil per acre thus made use of by earth-
worms will vary, however, according to the number of worms
present in an acre of land, and this number will vary according
to the quality of the soil.

On manured farm land in Great Britain the number of worms
may exceed one million per acre, whereas in adjacent unmanured
land the number may be below half a million. In an acre of soil
from 200 to 1 ,000 lbs. weight of worms may occur, belonging chiefly
to the genera Lumbricus, Allolobophora, Eisenia, and Helodrilus.

The food of earthworms comprises not only plant residues
but soil organisms, algae, fungus mycelia, yeasts, and so on.
Earth is passed through the alimentary canal, the contained
organic matter is decomposed, and the finely comminuted
soil, containing nitrogenous waste matter, becomes deposited as
castings at the surface of the burrows. There is thus a continual
ascent of sub-surface soil to the surface in consequence of
earthworm activity, and there can be little doubt that soils
containing earthworms will contain a higher ammonium content
than will soils in which earthworms do not occur.

The chief value of earthworms, however, arises from their
action in loosening and mulching the soil, and in facilitating
aeration and drainage by their burrowing habits.

In moist soils, especially if rich in organic matter, the earth-
worms present include large numbers of small white forms
belonging to the family Enchytrseidse, and comprising chiefly
species of Fredericia and Enchytraeus and Anachseta.

SOIL ORGANISMS 149

Soil Nematodes. — The majority of soil nematodes belong to
the family Anguittulidce or eel worms, a family of minute worms
characteristic in the fauna of decaying organic matter. Their
abundance in the soil depends upon conditions of moisture and the
occurrence of plant life or of decaying organic matter or of other
micro-organisms. Their mode of nutrition varies considerably.

(1) They may be omnivorous, feeding upon living bacteria,
fungi or algae, or upon the bodies of such forms, or upon the
organic matter in process of decomposition by such forms.
This group includes the genera Rhabditis, Diplogaster,
Cephalobus, Dorylaimus, Plectus, Monohystera, all common
and cosmopolitan in distribution.

(2) They may be partly free-living, partly parasitic on
animals and plants. The genera Tylenchus, Heterodera, and
Aphelenchus are notorious pests, for example, of cultivated plants.

(3) They may be predaceous upon other eel worm species.
This is the case with the very common eelworm Mononchus,
which readily attacks other forms, either swallowing them
outright or sucking out their contents. As many as eighty-
three Heterodera radicicola have been observed to be killed in
one day by a single Mononchus individual.

Tylenchus is a genus occurring in peaty and in moist soils
and around the roots of plants. Certain species are of consider-
able economic interest. Tylenchus dipsaci attacks a great
variety of plants, including clover, oats, rye, onions, tomatoes,
tulip bulbs. It confines its attack to the lower portion of the
stem of the attacked plant, never attacking the roots, and
hence is usually termed the " stem eelworm." In the swollen
portion of the stem occur large numbers of minute worms not
exceeding 1 mm. in length, each provided with a chitinous
mouth spine and two oesophageal swellings. The female
produces oval eggs within the invaded plant tissue. The larval
stages pass into the soil when the swollen stem portion decays
and can remain there in an encysted coiled condition throughout
the winter. They attack the plant seedlings in early spring
usually, autumn sown plants rarely suffering. Remedial
measures should comprise deep ploughing in autumn so as to
bury the top eighteen inches of soil, the avoidance of crops which
are liable to attack, and the avoidance of stable manure which,
in an infected district, is a fruitful cause of infection. Tylenchus
scandens attacks wheat. The young larvae make their way
from the soil to the nearest rootlings of seedling wheat plants,
and bore between leaf, sheath, and haulm. They gradually
climb higher up the growing plant to the future ear, bore each

150 THE PRINCIPLES OF APPLIED ZOOLOGY

into an ovule, and produce a purple gall formation within which
occur thousands of larval stages. In an infested plant sixteen
to twenty such purple " ear cockles " occur in the lowest flower
of the ear, ten to twelve in the next, four to five in the top
blossoms. Within the gall the larva? are said to survive desicca-
tion for as long a period as twenty years, but when the gall is
moistened, as by falling upon damp earth, the larvae can
emerge, make their way to a young wheat plant, and attack it.

Heterodera schachtii attacks the sugar beet, potato, etc.,
and sometimes proves very injurious. Unlike most eelworms,
there is marked sexual dimorphism in this form, the female
being lemon shaped and fixed to a rootlet of the attacked plant.
The swollen condition of the female is due to the fact that the
eggs develop within her, and the larvae are liberated by the
death and disintegration of the female parent. The larvae
bore each into a rootlet of the beet and produce swellings upon
it. The male larvae coil up spirally, undergo a resting stage
followed by a shedding of the cuticle and a migration into the
soil, in order to seek the female individuals on the root swellings,
who have meanwhile become exposed by the rupture of the
swellings which enclose them.

Caconema radicicola, the "root knot nematode," produces
knot-like swellings along the roots of tomatoes, cucumbers,
marrows, cotton, beans, celery, egg plant, potatoes, lettuce, peas,
and many other plants. The eelworms swarm within these galls
and escape when the plant root decays, to pass into the soil and
attack other plants. Soil may remain infested with resting eel-
worm stages for a long time and may require partial sterilisation.

Aphelenchus comprises a number of forms which occur
around the roots of plants in moist humus or in water. Five
species are recognised as being distinctly injurious, namely,
A. fr agar ice, which is endoparasitic in the stem tissue of straw-
berry plants, producing a hypertrophic condition termed
" cauliflower disease," or ectoparasitic in the strawberry buds ;
A. cocophilus, endoparasitic in stem, leaf, and roots of the
coconut palm in West Indies, and causing " red ring " disease,
so called from the characteristic internal ring of red tissue
developed in the stem of the plant attacked ; A. ritzema bos,
endoparasitic in the leaves of chrysanthemums ; A. ribes,
ectoparasitic in the buds of the black currant ; and A . olesistus,
endoparasitic in the stems of ferns, begonias, and cypripediums,
causing destruction and discoloration of tissue ; A . olesistus var.
longicollis attacks the stems of cultivated violets, causing
hypertrophy and gall formation.

SOIL ORGANISMS 151

The only effective remedy for eelworm disease is soil sterilisa-
tion, but sterilisation measures are usually impracticable
except in glass houses. Some machine is required that can be
wheeled over a field like a plough and which will automatically
lift up the surface layers and submit them to a temperature
sufficient to sterilise the soil, but such machinery is still in
the experimental stage.

Soil Insects. — The insects which frequent the surface or
subterranean layers of the soil may be grouped, according
to food habit, into : —

(1) Insects which find food and shelter within the soil
layers. This group includes phytophagous insects, such as in
particular those larval forms referred to as white grubs, as
leather jackets, as wire worms ; zoophagous insects, such as
the carnivorous Carabid and Staphylinid beetles, and certain
carnivorous larvae of the two-winged flies ; and saprophagous
insects, such as are the Collembola, and the majority of soil-
dwelling larval forms of flies and beetles.

(2) Insects which find shelter within the soil layers but
feed on the surface vegetation. This group includes particularly
the termites and the ants, but is linked up to the first group
particularly by certain forms of termites which are always
subterranean feeders and by the cutworms or Noctuid cater-
pillars, some of which are surface feeders, sheltering in the soil
when not feeding, others of which are sub -surface feeders.

(3) Insects which spend a phase of their life-cycle within the
soil, either as internal parasites of soil insects or as resting,
non-feeding pupal stages, or again as hibernating or activating,
non-feeding stages.

The number of insects in the soil is very large, and is
distinctly larger in samples of uncultivated soil than in samples
of cultivated soil. Morris at Rothamsted has recorded 3,586,088
insects in an acre of permanent pasture, a number comprising
Collembola, 566,680 ; Rhynchota, 15,140 ; Thysanoptera,
43,258; Lepidoptera, 15,140; Coleoptera, 744,038 ; Diptera,
2,193,180 ; Hymenoptera, 8,652. The family most represented
was the Bibionidse, whose species made up 32-4 per cent, of the
total number of soil insects ; Mycetophilidse made up 16-7
per cent. ; and Staphylinidae made up 12-2 per cent.

The fauna of cultivated land is not, as a rule, peculiar to
such land, but is made up of migrants from adjacent woodland
or grassland.

From the standpoint of the crop grower, the more important
types of soil insect are certain larval types referred to as white

152 THE PRINCIPLES OF APPLIED ZOOLOGY

grubs, leather jackets, wireworms, cutworms, and certain
social soil insects known as white ants or termites.

White Grubs. — The term white grub applies to the larvae of
chafers or May beetles, a sub -family of beetles included in the
Scarabaeidae or Sacred Beetles. The adult chafer is a clumsy,
dull-coloured insect which feeds upon the flowers and foliage
of plants ; the grub is a white fleshy curved creature with a
somewhat swollen posterior segment and very short legs ; it
is a voracious feeder upon the roots of plants (Fig. 26).

The eggs are laid usually in early summer, or, in tropical
countries, at the commencement of the rainy season. Usually
grassland in the vicinity of timber is preferred. The eggs are
enclosed within a ball of cemented earth particles and placed
below the soil surface. The emerging larvae feed upon the roots
of adjacent plants until the onset of cold or of dry conditions
forces them to migrate downwards, sometimes to a depth of
six feet. The winter or dry season is thus spent as a non-feeding,
deeply buried larval stage. In the spring the larva ascends
to near the surface and feeds voraciously through the summer,
descending again when soil conditions become unfavourable.
The second spring sees the larva again near the soil surface,
but usually in the second summer the larva pupates within an
earthen cell about two feet below the soil surface. The pupa
transforms into the beetle stage before winter, but the insect
remains within the soil until the following spring, thus com-
pleting a three-year cycle. In many cases the cycle is four
or five years in length. In favourable latitudes, however, it is
only two years or even one year in duration.

In Europe great damage is caused, particularly in forested
areas, by enormous numbers of the cockchafer (Melolontha
vulgaris and Melolontha hippocastani), which feed as adults
upon the foliage of oak, elm, etc., and as larvae upon the roots
of grasses and seedling trees. Similar but lesser damage is
caused also by species of Anomala and Phyllopertha. In North
America, species of Phyllophagus (Lachnosterna) constitute a
limiting factor to continuous wheat production in certain
sections, the infestation increasing with each generation so
that rotation with an unfavoured crop, such as rye or oats,
becomes necessary. Little direct action is possible against
white grubs. They are well below the plough line during the
usual ploughing season. If, however, severely infested grass-
lands be ploughed during the summer, large numbers of eggs,
larvae, and pupae become exposed and are eagerly sought for
by birds, especially poultry, rooks, crows, and crow -blackbirds.

SOIL ORGANISMS

153

Certain mammals, also, notably hogs and skunks, will seek and
devour white grubs with avidity, and it may be noted, as some

Popillia japonica

(after Clausen {(King-)

White grub

Leather
jacket
(after Alexander)

Wireworm Ag'HoteS obscUfUS (after Ford)

Cutworm Noctua clandestina
(after Sling-erland)

Queen

Worker ^°*y Soldier

White ants
Termes flavipes (after Marlatt)

Fig. 26. — Types of Soil Insects. (Not to scale.)

evidence of the antiquity of the taste shown by the hog for
white grubs, that in Europe the invertebrate host of a parasitic

154 THE PRINCIPLES OF APPLIED ZOOLOGY

worm, Echinorhynchus gigas, found in the hog, is the white
grub of the cockchafer.

Leather Jackets. — The leather jacket is the larval stage of a
crane-fly, which again is a type of two-winged fly belonging
to the superfamily Tipuloidea.

Only a minority of crane-fly larvae are injurious to cultivated
crops, and these are usually species of Tipula or Pachyrhina.
In temperate latitudes considerable endemic annual damage
is produced by the attack of leather jackets upon the roots of
vegetation in grassland, root-crop or cereal-growing areas,
although, owing to the work of insectivorous birds and mammals,
epidemic outbreaks of leather jacket damage are rare.

In circumscribed areas, such as golf courses, crane-fly damage
can be reduced considerably by the use of arsenically poisoned
bran baits.

Wireworms. — The wireworms are larval stages of the " click
beetles " (Elateridse), and are, in the main, grassland pests,
although such crops as potatoes, root crops, cereals, suffer
greatly. In many respects their habits are like those of the
white grub, in that they live underground and attack the
planted seeds, roots, and underground stems of cultivated
plants, and in that they remain in the ground as larval stages
for four or five years. In appearance, however, the wire worm
is a cylindrical yellowish-brown hard larva from one-half to
one and a half inches long (Fig. 26). The injurious wireworms
belong in particular to the genera Agriotes, Athous, Limonius,
Melanotus, and Ludius (Corymbites). Wireworms are, in
particular, pests of newly cultivated grassland rather than of
land that has been cultivated over a period of years. One
common control method is that of using mustard as the first
crop upon newly broken grassland, and ploughing this crop
under before sowing the first cereal crop.

Cutworms.- -The term cutworm applies generally to cater-
pillars of the Noctuidse family of moths, but should be restricted
to caterpillars of the sub-family Agrotince. The moths are
usually coloured dull grey or brown and are night-flying in
habit. The caterpillars are mainly smooth, protectively
coloured in brownish or dull green patterns, and generally
nocturnal in feeding habit, hiding by day in the surface soil
layers (Fig. 26).

The cutworms fall into three groups according to habit,

namely : —

(1) Climbing cutworms, which actually climb up the plant
and eat the foliage rather than the stem.

SOIL ORGANISMS 155

(2) Surface cutworms, which feed at or just above the surface
of the ground and cut off the stems of plants.

(3) Sub-surface cutworms, which feed entirely below the
soil surface and cut the plant from one to two inches below
ground. This is a comparatively uncommon habit, but is
shown in particular by the Pale Western Cutworm (Porosagrotis
orthogonia), a notorious pest of the north-western states of
North America.

The cosmopolitan cutworm species, such as the species of
Agrotis and Euxoa, are surface feeders as a rule.

Surface caterpillars are controlled by the use of poison
baits or by the use of stomach poisons applied to the food plant.

Termites. — Termites or white ants are members of the insect
order Isoptera. The term " white ant " is not a very suitable
one. Their affinities with the ants are remote. Like ants and
bees and wasps, however, termites are social and live in large
communities which are polymorphic, that is to say are made up
of several structurally different types or castes.

In a typical termite community five such castes occur,
three of which are potentially reproductive, the remaining two
being composed of sexually sterile individuals (Fig. 26).

These castes are as follows : —

(a) Macropterous forms, provided with well-developed cuticle
and with two pairs of well-developed wings. At certain times
of the year, varying with geographical locality, dense swarms
of winged males and females will issue from a termite colony.
The great majority of the individuals of the swarm fall a prey
to numbers of birds, lizards, even small mammals, which are
attracted by the phenomenon. The survivors eventually come
to the ground, cast off their wings, copulate, and found a new
colony, in which the initial pair becomes the king and queen.
The queen gradually increases in size, owing to the development
of her ovaries, and may become comparatively enormous.
The pair live secluded in a special royal cell.

(b) Brachypterous forms, with short, scale-like wings, weak
eyes, and thin, yellowish transparent cuticle. The part played
by these forms in the community is not fully known, but that
they are capable of providing substitutes for the reigning royalty,
if required, seems very probable.

(c) Apterous forms, without wings, with vestigeal e}^es and
with a weak transparent cuticle. The conditions under which
these forms occur and utilise their reproductive powers are not
understood. They are rarely found among the higher termites.
The two remaining castes are sexually sterile.

(d) Workers form the great majority of the individuals in

156 THE PRINCIPLES OF APPLIED ZOOLOGY

the community and carry out most of the work of the colony,
whether tending eggs and young, feeding and tending royalty,
excavating galleries, bringing in food, and so on. They are
wingless, blind, and have a thin cuticle, but the jaws are power-
ful and well adapted to the crushing of woody tissue.

(e) Soldiers, like the workers, are blind, wingless, and sterile,
but characterised by possessing a powerfully developed head ;
in the nasute type of soldier the head projects forwards as a
conical snout-like structure, and the jaws are small and
vestigeal ; in the mandibulate type the head does not so project,
and the jaws are powerful and large. In some cases both types
may be again separated into major and minor forms, or even
into large, intermediate, and small forms, according to size.

The soldiers are concerned with defence of the colony ; their
capacity for dealing with intruders is aided by the power in some
forms with weak jaws of supplementing the use of their jaws
by the ejection of a repellent fluid, through a pore at the tip of
the snout-like projection.

The habits of termites vary considerably in detail, but the
food in all cases is primarily wood and other vegetable tissue,
the cellulose in their diet being dealt with, according to some
authorities, by certain commensal, gut -dwelling flagellate
protozoa which are peculiar to termites and which, by breaking
down cellulose, are possibly of considerable benefit to their host.
In young nymphs and in royalty they are said not to occur,
and it is significant that these termite forms have to be fed by
the workers with a special diet.

Three types of termite community may, speaking generally,
be distinguished, namely : —

(1) Colonies occurring as a series of galleries in woody plants,
either in decaying fallen logs, in actively growing trees and
bushes, or in worked timber such as furniture, wooden buildings,
telegraph posts, and the like.

(2) Colonies occurring in labyrinthine nests below the ground
surface ; from such colonies the workers issue forth to attack
the roots of growing plants, or to tunnel in any woodwork that
is in contact with the ground ; when working above ground they
usually construct covered passage-ways of earth or faecal matter
so that they can travel without annoyance from sunlight,
sun heat, desiccation, or predatory enemies.

(3) Colonies which occur as a network of galleries within a
mound of soil cemented together by salivary secretion ; these
mounds are a prominent landscape feature in Africa and
Australia, and may be from six to twenty feet in height and as
hard as concrete.

SOIL ORGANISMS 157

The prevalence of termites in tropical and sub-tropical soils,
their subterranean and social habits, and their preference for
woody tissue causes them to be amongst the most stubborn
enemies of the tropical agriculturist. Crops and habitations
are alike endangered by termite colonies.

Speaking very generally, measures against termites may be
divided into offensive and defensive categories.

Offensive measures comprise : —

(1) The fumigation of nests or mounds with carbon bi-
sulphide, or with a mixture of arsenic bisulphide and arsenic
trisulphide and pentasulphide fumes, injected into the mound
by the use of an ant exterminator. This machine consists
in principle of an arrangement by which air can be blown over
a mixture of arsenic trioxide and sulphur placed upon a bed of
red-hot charcoal, and the resulting vapour forced into the
termite nest through a tube.

(2) The addition of a slight percentage of kerosene to
irrigation water.

Defensive measures comprise : —

(3) The use of concrete and metal as foundation materials
for buildings, and of termite resistant timbers such as teak
(Tectonia grandis), greenheart (Nectandria rodiaci), and
mahogany, or of timbers proofed with termitifugal chemicals,
in building construction. Books, leather, small wooden articles
must be proofed with corrosive sublimate, zinc chloride, or similar
substances of known repugnant effect upon these insects.

Ants. — Speaking generally, ants do not constitute a menace
to the agriculturist. Certain ant species, however, which culti-
vate plant lice and scale insects for the saccharine secretion
produced by these insects, may help considerably in spreading
such plant-attacking insects throughout an agricultural district.
A case in point is afforded by the Citrus Mealy Bug (Pseudococcus
citri), a citrus pest of world-wide distribution. In Southern
California the mealy bug is protected by the Argentine Ant
{Iridomyrmex humilis), and it has been shown that in orchards
where the ant has been kept in check by poison baits, the mealy
bug has been distinctly checked by natural enemies.

Leaf-cutting ants may cause considerable damage to culti-
vated plants in tropical and sub-tropical countries. House-
frequenting forms such as Monomorium, the small black house
ant, and Iridomyrmex, the Argentine ant, can also be of con-
siderable annoyance to man. Measures against ants comprise
the fumigation or the destruction of nests, and the destruction
of foraging ants by the use of syrups poisoned with sodium
arsenite.

CHAPTER XIV

INSECT PESTS : The Categories

The insect pests of the world's crops may be classified according
to their wideness of distribution and severity of damage inflicted,
or according to the type of agricultural product they attack,
or according to the type of damage they inflict. Thus we may
speak of First Class and Second Class Pests ; or we may speak
of General Pests, Fruit Tree Pests, Truck Crop Pests, and so on ;
or again we may speak of Cutworms, Moth Borers, and so on.

In the career of an insect pest certain phases occur. In the
first place, it may have the status merely of a local insect and
not that of an economically important species, and may enter,
probably unobserved, a new territory. Immediately, the
insect may find itself in a new environment, and consequently,
even if its numbers do not suffer a severe check, its progress is
necessarily slow. Later, its numbers begin to increase unduly,
owing possibly to a lack or infrequence of natural enemies,
and in about ten years time, or even less, it becomes noticeable
in epidemic form. Should its habits be such as to annoy the
community, it will be classed as a " Second Class Pest," that is
to say, a pest severe in its infestation but confined to a limited
area. At this stage vigorous control measures will probably
check the insect, but should the infested article be a commercial
commodity with a wide distribution, the chances are that the
insect will have spread extensively and become well established
before detection, or before there is anything approaching a full
realisation of its economic significance. It will be, in fact, a
' First Class Pest," and its extermination cannot be hoped for ;
control measures in this case can aim only at limiting its spread
and mitigating its ravages as far as possible.

It will be seen, therefore, that there are two main stages in
the progress of an insect pest : firstly, when it is newly estab-
lished or an indigenous pest within a limited area ; secondly,
when it has become firmly established and is widely distributed.

Speaking very generally, the major pests of the world's
crops can be placed into two groups.

The first group comprises insects which are polyphagous,

158

INSECT PESTS: THE CATEGORIES 159

that is to say, which have a wide range of food plants and which
are widely distributed over a wide continuous area where they
cause steady endemic annual damage to crops. They are,
however, liable to become massed in particular local areas and
to become in consequence the cause of severe epidemic
outbreaks, owing to their own powers of migration, to the
agricultural practice of growing large contiguous blocks of some
particular type of plant, or owing to dissemination by human
agency. This group comprises the following types of insect
pest, namely, locusts, red spiders, plant bugs, leaf hoppers,
plant lice, thrips, flea beetles, weevils, noctuid caterpillars,
loopers, tussock caterpillars. It also includes a considerable
number of species of scale insect. The second group comprises
insects which are oliphagous or monophagous, that is to say,
restricted in choice of food plant, and which may be more or
less restricted in distribution owing to some peculiarity of habit,
such as, for example, that of attachment permanently to the
host plant, or the habit of plant mining, gall-making, leaf rolling,
and so on. Owing, however, to these same peculiarities of
habit, this group of pests is peculiarly liable to become intro-
duced into a fresh area of distribution by the agency of man.
In such a fresh area the absence of its natural enemies will enable
the insect species to increase to a degree unknown in its native
habitat, and to become the cause of intensively severe outbreaks ;
on the whole, the worst cases of epidemic attack are those caused
by insects of this second group imported into a fresh area.

The group includes particularly the scale insects, mining
insects, blister mites, gall-making insects, and in it also may be
placed the insects which infest stored products. The various
types of insect pest can now be briefly discussed.

Locusts. — The term locust or hopper is one usually applied
to the migratory phase of certain members of the Orthopteran
family Acridiidse ; the term grasshopper refers more particularly
to non-migratory phases, or to members of the family Locustidse.

Both families consist of comparatively large insects which
have the femora of the hind legs thickened and enlarged in
adaptation to a leaping habit (Fig. 27). The Acridiidse possess
antennas shorter in length than the body, and so are referred to
sometimes as " short-horned grasshoppers " in contradistinction
to the ' long-horned grasshoppers " or Locustidse, whose
antennas are longer than the body. The latter, again, differ
from the Crickets (GryllidaB) in that the horny first pair of
wings slope downwards at the sides and are not flat above,
except for a short space near the base.

160 THE PRINCIPLES OF APPLIED ZOOLOGY

All these forms are able to make some kind of noise as a love
signal to the opposite sex, either by rattling the horny wings

Leaf hopper

Eutettix
tenella

Canker worm
(afterTheobald)

Tussock caterpillar
(after Schiebeek)

Oat aphis
(after Davis)

Locust
(after Lefroy)

Chinch bug-
(after Flint)

Fig. 27. — Types of Insect Pest. (Not to scale.)

or by rasping the hind legs against the horny wings or by
rubbing one wing cover over the other. Acridiids have an

INSECT PESTS: THE CATEGORIES 161

auditory organ on each side of the first abdominal segment ;
Locustids and Gryllids possess a similar organ on the foreleg.

The eggs are usually deposited in holes in the ground made
by the valves of the ovipositor of the female. The eggs remain
in the soil for a considerable period. A series of nymph al
phases ensues, each nymphal phase resembling the adult form
except in development of wings, which are absent or small, and
in its immaturity. Hibernation or aestivation is passed, in
most cases, in the egg stage.

Whether migratory or non-migratory these insects are
extremely catholic in their choice of food plants, and are a
potential source of damage to cultivated crops almost every-
where. Grasshoppers, crickets, and non-migratory locusts are
endemic in every cultivated area, and are productive of steady
annual crop loss, probably greatly exceeding in aggregate financial
value the more spectacular ravages of the migratory phases.

Certain migratory forms characterise the majority of the
great crop-raising areas of the world's surface. Thus Southern
Europe and Asiatic Russia are periodically ravaged by migratory
hordes of Locusta migratoria ; Northern Africa by Schistocerca
gregaria ; South Africa by Locusta pardalina ; Western India
by Acridium succinctus ; North-West India by Schistocerca
gregaria ; Canada and Northern United States by Melanoplus
spretus ; South America by Schistocerca paranensis, and so on.

In the control of a locust invasion, methods vary according to
the area attacked ; but on the whole the control measures com-
prise (1) the provision of barriers to the progress of the hopping
stages, formed by trenches or by low metal fences ; (2) the use
of poison baits, mixtures of bran, or sawdust or horse manure or
similar substances with Paris green — an arsenical compound —
and made attractive by the addition of molasses, fruit juice, or
amyl acetate ; (3) the use of " hopper-dozers," a kind of trap
drawn over the fields by a horse ; (4) the artificial distribution
of a bacterial disease of locusts.

Red Spiders. — The term " red spider ' is applied usually
to certain members of the arachnid family Trombididse. That
is to say, they are not insects at all in the strict sense, nor are
they, for that matter, spiders.

They are extremely minute, rusty -red or green or even
transparent creatures, provided with four pairs of legs.

The genus Tetranychus spins fine webs of silk upon the
under surface of leaves ; beneath these webs all stages of the
pest are to be found sucking out the juices of the leaf.

Bryobia is a genus whose members do not spin webs ; it

1 1

162 THE PRINCIPLES OF APPLIED ZOOLOGY

differs further from Tetranychus in that its members have the
first pair of legs longer than the others.

Red spiders are extremely injurious foliage-sucking pests
of a wide range of cultivated plants. On field crops they
are extremely difficult to control. In greenhouses they can
be checked by fumigation measures. In orchards, high-pressure
spraying with water or with contact poisons or dusting with
sulphur dusts will usually keep them within bounds.

Plant Bugs. — The term " bug," though applied often in the
American sense to mean any sort of insect, is restricted by the
entomologist to members of the Hemiptera, an order of insects
which is characterised by the possession by its members of a
suctorial beak in which the lower lip or labium forms a sheath
for the needle -like mandibles and maxilla ; these are the
actual piercing organs and these alone penetrate the tissues
of the host plant. Usually two pairs of wings are present ; in
the sub -order Homoptera, both pairs are thin and transparent ;
in the sub-order Heteroptera, the anterior pair have the basal
half thickened and horny.

The life-cycle consists of a series of stages termed nymphs,
each differing from the preceding stages, and from the adult,
only by the extent to which wings and reproductive organs are
developed.

Plant bug is a term applied to members of the sub-order
Heteroptera, and particularly to members of the families
Pentatomidse, Corseidse, Lygseidae, Pyrrhocoridse, Capsidae.
The Pentatomidse are usually referred to as Shield Bugs owing
to the possession of a large scutellum, a term applied here to the
dorsal portion of the thorax, anterior to the insertion of the
first pair of wings. They are insects between a quarter of an
inch and an inch in length, often brightly coloured, often
protected by the foul smell from certain stink glands. Nezara
is a notorious genus of injurious Pentatomid bugs. N. viridula
is a green form common on potatoes all over the world.

Murgantia histrionica — the Harlequin Bug — is to the
cabbage grower of the Southern United States what the boll
weevil is to the cotton planter.

The Corseidae or Squash Bugs are immediately recognisable
by the small scutellum and straight beak, and by the insertion
of the antennae above an imaginary line from eyes to base of
beak. Leptocorisa varicornis is a serious pest of the developing
seeds of rice and millet in India. In the United States an
allied species, Leptocoris trivittatus, is the Box Elder Bug. The
Squash Bug, Anasa tristis, of the same area, is an evil-smelling

INSECT PESTS: THE CATEGORIES 163

brown insect three-quarters of an inch in length, which infests
pumpkins and squashes.

The Lygseidse are similar in appearance to the Corseidae, but
on the whole are smaller forms. Oxycarcenus lotus and Oxy-
carcenus hyalipennis are the Dusky Cotton Bugs of India and
Egypt respectively, whose eggs are laid in the lint near the
cotton seeds, and whose nymphs live within the boll, sucking
the seeds, until adult.

Few insects have caused more pecuniary losses to the
agriculturalist than has the Lygseid bug Blissus leucopterus,
popularly termed the Chinch Bug, of the United States.

It is a native pest, supposed to have come from Central
America previous to the settlement of the United States by the
white man. It appeared first, in economic numbers, about the
time of the Revolutionary War in North Carolina, the first
place to grow wheat intensively. As the settlers moved west-
wards they disturbed the natural balance of the insect and
introduced a plant upon which it could thrive. To-day it
occupies practically the whole winter wheat belt. It requires,
in order to become well established, suitable grasses on which
to winter and a winter temperature not lower than 25° F. ;
sufficient rainfall (twenty to forty inches) through the year ; suit-
able food plants, preferably wheat and corn, in the early summer.

These conditions are provided in the Central United States,
notably in Kansas, Missouri, Illinois, Ohio, Indiana, and
Nebraska.

In the north, winter temperatures keep it in check ; in the
east, excessive rainfall and the consequent spread of a fungus,
Sporotrichum globuliferum, among hibernating forms, keep it
in check ; in the south and south-east, heavy rains and excessive
summer temperatures and small acreage of wheat, limit its
numbers ; in the west, lack of suitable hibernation quarters
and lack of summer rainfall militate against it.

It is a narrow black and white insect about one-fifth of an
inch long (Fig. 27).

During the winter the bugs hibernate in clumps of grasses,
particularly in prairie bunch grass, or in rubbish. The females
emerge in spring and lay their eggs on the roots or stem bases
of wheat or grasses. The resulting generation when mature
migrates on foot to other plants, such as corn, upon which eggs
are laid. There are thus two broods a year. Control measures
comprise, therefore : —

(a) The destruction of grasses or rubbish in the vicinity of
fields.

164 THE PRINCIPLES OF APPLIED ZOOLOGY

(6) The trapping of crawling bugs ; the time of migration is
induced by the ripening of the wheat and its consequent loss
of succulence. If the food supply holds out until the bugs
are mature, they migrate both on foot and on the wing. Bugs
migrating on the wing can neither be trapped nor destroyed.
If the wheat ripens, however, or is cut before the wings have
developed, the crawling bugs can be caught in large numbers
in trap trenches or in a broad furrow six to eight feet wide of
fine dust, or in a " tar line," a strip of smooth surface, about
one foot wide, covered with tar or asphalt road oil. At intervals
along the tar line, passages are left which conduct the bugs
towards holes about a foot deep in which they are trapped.

The Pyrrhocoridse or Stainer Bugs are scarlet or brown
coloured bugs, recognisable further by the absence of ocelli
and by the position of the antennae on the sides of the head.
The vivid coloration is possibly a warning coloration, since the
bugs feed openly on their food plants. The genus Dysdercus is
the so-called ' cotton stainer," whose species occur in scarlet
or brown masses on cotton plants in various cotton-growing
areas. Thus D. cingulatus occurs in India, D. suturellus in the
West Indies and United States, D. superstitiosus and D.
nigrofasciatus occur in Africa.

The Capsidse or Leaf Bugs are characterised by the posses-
sion of an area termed the cuneus at the base of each anterior
wing. They are small, delicate, dull-coloured insects. Helo-
peltis is a genus destructive to tea, cacao, and cinchona in India
and Africa. H. theivora is the notorious " mosquito blight "
of the tea plant in Northern India. Lygus pratensis, the
Tarnished Plant Bug, injures fruit and flower buds. Lygus
communis, the False Tarnished Plant Bug, is a serious pest of
hops in Great Britain. Plesiocoris rugicollis is a serious pest of
apple trees in Europe.

Leaf -Hoppers. — The term leaf -hopper embraces the members
of the sub -order Homoptera of Hemiptera. In these forms the
wings are of one consistency throughout, and lie over the
abdomen at an angle to one another much like the roof of a
house (Fig. 27).

The Cicadidae or Cicadas are large bugs distinguishable from
other Homoptera by the possession of three ocelli. In size
they range between one and three inches. On the whole they
are forest pests, the adults sucking the bark of trees. The
Cicadas are remarkable for the loud whistling sounds producible
by the males and for the extreme length of the life-cycle.

Cicada septendecem, the Periodical Cicada or Seventeen

INSECT PESTS: THE CATEGORIES 165

Year Locust of North America, remains in the nymphal phases
for seventeen years in the ground, feeding upon the juices of
roots and of soil humus. They moult four to six times, at
intervals of two to four years.

The Fulgoridse is the largest family of Homoptera and
comprises both large, brightly coloured, day-flying, moth-like
forms and small, dull coloured, grass-dwelling forms. They
are feeders upon plant juices. Perkinsiella saccharidida, the
Sugar Cane Leaf-Hopper, is a serious pest of sugar canes in
Hawaii, although the damage to canes has been greatly reduced
since the establishment of certain egg parasiting Hymenoptera
from Australia, the original home of the leaf-hopper.

The Jassidse or Leaf -Hoppers are small linear insects easily
recognised by the spiny tibia?. Their coloration usually
harmonises with the surroundings. They occur commonly
on grasses, low vegetation, on soil, more rarely on trees.

Some attack the cotton plant and cause leaf curling.
Empoasca facialis is the Cotton Jassid of East and South
Africa. Empoasca flavescens is the Greenfly of the tea plant,
well known not only in India and Ceylon, but recorded also from
Brazil, East Africa, Europe, North America. By sucking the
apical shoots it checks the growth of the plants and lessens the
yield, although said to improve the flavour. Eutettix lenella
(Fig. 27) attacks beets in North America and acts as the carrier
of " Curly Top," a virus disease of beets.

The Membracidse or Tree-Hoppers are characterised by the
presence of two ocelli below the eyes, by the insertion of the
antennae in front of and between the eyes, and by the backward
prolongation of the prothorax into a conspicuous process.

They are small brown insects sometimes resembling stiff
thorns. A few are recorded as pests in the United States,
notably Ceresa bubalus, the Buffalo Tree Hopper, of orchards
and shade trees ; but on the whole the group is not of serious
economic interest.

The Cercopidse or Frog-Hoppers are distinguishable from
Membracidse by the simple prothorax and from the Jassidae
by the absence of tibial spines. To this family belong the
" cuckoo spit " insects whose nymphs live within a mass of
bubbles of liquid produced by themselves on the plant.

Tomaspis sacrharina is a serious pest of sugar cane in
Trinidad.

The measures for the control of plant bugs and plant-hoppers
comprise : —

(1) The use of contact washes — kerosene emulsion, nicotine

166 THE PRINCIPLES OF APPLIED ZOOLOGY

sulphate, and so on — to which they are amenable ; on field crops,
however, such measures are often difficult or uneconomical.

(2) The destruction of weeds and organic rubbish in the
vicinity of crops.

(3) Trap cropping.

(4) The encouragement of natural enemies.

Plant Lice. — The term is applied to the members of the
families Psyllidae, Aleyrodidse, and Aphididae of Homoptera ;
these, together with the Coccidae or Scale Insects, are sometimes
classed together as Phytophthires, a group characterised by : —

(1) A tendency towards a close parasitic interrelationship
with the host plant.

(2) A tendency towards winglessness.

(3) The growing differentiation of an inactive nymphal
condition, leading to the almost wholly inactive male " pupa '
of Coccidge.

Aphididse. — The aphids are small rounded insects with
two-jointed tarsi, and the abdomen usually provided with a
pair of tubes through which a sweet liquid, honey dew, is
emitted ; this secretion is a favourite food of ants. Wingless
forms are common, and wingless generations may alternate
with winged forms in the life -cycle of the one species.

Under favourable conditions, aphids are usually partheno-
genetic, producing eggs or living young without the inter-
vention of a male ; usually upon the onset of wintry or dry
conditions, a generation of winged males and females is pro-
duced, and this generation may leave the summer host plants,
usually a number of unrelated herbaceous plants, and fly to a
definite winter host plant type, usually a single species or a few
closely related species of woody stemmed plant. On the
winter host plant fertilised eggs are laid ; these " winter eggs '
can withstand winter or dry season conditions, and at the onset
of more favourable conditions can hatch into a generation of
winged parthenogenetic females, the " stem mothers," which
migrate to the summer host plants and commence the series
of parthenogenetic wingless summer generations. The powers
of increase of an aphid species are very great, owing to their
rapid maturity and high egg production powers, but their
natural enemies are proportionately numerous.

Aphids are universally feeders upon the sap of plants and
many are serious cosmopolitan pests.

Aphis gossypii, the so-called Melon Aphis or Cotton Aphis,
attacks a wide range of plants over the world. In the United
States the winter eggs occur on purslane and strawberry.

INSECT PESTS: THE CATEGORIES 167

Brevicoryne brassicce, the Cabbage Aphis, is a cosmopolitan
pest of cruciferous crops. The summer may be passed on
cabbages and the winter on cabbage stumps.

Phorodon humuli, the Hop Aphis, is a serious pest in Europe
and North America, spending the summer on hops and the
winter on plum trees.

Aphis avence, the European Grain Aphis, attacks cereals in
spring and summer, but winters on apple trees. It is established
in Europe and North America (Fig. 27).

Rhopalosiphwn persicce, another aphis common to Europe
and North America, infests garden crops such as spinach,
potatoes, tomatoes, cabbages, lettuce, and so on in summer,
but winters on peach trees or in greenhouses. On potatoes it
is claimed that they convey the causative organism of a mosaic
disease.

Some of the worst aphid pests are root-feeding forms, the
transition from foliage feeding to root feeding having in many
species been brought about possibly through the agency of
ants. In many root-feeding species the migratory habit has
become suppressed and the aphis spends the whole year upon
the roots of a particular host type.

The Woolly Aphis, Eriosoma lanigera, attacks the roots
and twigs of apple and pear trees in every apple-growing area
of the world. It occurs on the twigs and branches as little
white wool-like patches, each composed of a number of aphids
which bear long threads of wax. Swellings and enlargements of
the branches are caused. Root-feeding forms lack the waxy
threads.

In North America there is a cross migration from apple to
the elm ( Uhnus americana) in autumn, and a return migration
to apple in early summer, although some aphids remain on
apple all the year round. Outside America this cross migration
seems not to occur except in districts where the American elm
has been introduced.

Originally a native of North America, the Woolly Aphis
although seriously destructive in the warmer regions of that
area, is checked there considerably by the Chalcid parasite
Aphelinus mali, and attempts are being made to establish this
parasite in other apple-growing regions of the world.

Some varieties of apple, notably Northern Spy and Majetin,
are considerably resistant to woolly aphis attack, and in some
apple-growing areas it is customary to graft susceptible varieties
of apple on to root stocks of such resistant varieties.

The Vine Aphis, Phylloxera vastatrix, is another aphis

168 THE PRINCIPLES OF APPLIED ZOOLOGY

indigenous to North America, but established in Europe and
other areas. This aphis has a life -cycle confined to the grape
vine, but including root feeders and leaf feeders. The leaf
feeders (gall-makers) are comparatively harmless ; the root-
feeding aphids produce (a) small galls (nodosities) near the tips
of the young rootlets, (b) large swellings (tuberosities) upon
older rootlets and roots. The first class of root gall occurs
on all vines, resistant or susceptible, if Phylloxera be present,
and is not particularly injurious. The difference between
susceptibility and resistance to Phylloxera is, in fact, a question
of the numbers, size, and penetration of the tuberosities. The
original home of this species of Phylloxera is generally regarded
as being North America, although a certain amount of evidence
has been brought forward to indicate the possibility of the region
around the Black Sea of Europe as being the place of origin.

Certainly North America is the home of the majority of the
Phylloxeran species, and nearly all species producing leaf galls
occur there exclusively. The interesting suggestion has been
made that the original habitat of Phylloxera vastatrix was the
uniformly moist rain forests of tropical and sub -tropical America
where, infesting the genus of vine Euvitis, the insect was able to
live not only in leaf galls but on all parts of the plant above
and below ground. The present-day type of root form may
have become fixed in adaptation to life in drier regions.

The vine louse was discovered on an American vine by
Fitch m 1864, and later on it was found on wild vines in the
Mississippi basin. It was not known in Europe before the
'sixties, and was almost certainly introduced upon vines
imported from America. The wild vines of America show all
gradations of resistance to Phylloxera vastatrix, from almost
complete immunity to complete susceptibility. Probably
the insect has gradually adapted itself to certain varieties.
The more resistant species belong to the genus Euvitis, and are,
in order of resistance, expressing the maximum or absolute
immunity as 20, as follows : E. rupestris, 18-19 ; E. riparia
and E. cordifolia, 18 ; E. berlandieri, 17 ; E. cinerea, 16 ;
E. aestivalis, E. linsecomii, and E. candicans, 14-15.

On the other hand, the species of vine to which the three
thousand or so European varieties belong, viz., Vitis vinifera
and Vitis silvestris, have proved highly susceptible to the
introduced Phylloxera, so much so that viticulture in Southern
France and Italy was severely checked by its appearance.

The hope that it would be possible to obtain hybrids between
resistant American vines and Vitis vinifera, equal in size,

INSECT PESTS: THE CATEGORIES 169

quality, and yield to the latter parent, has proved futile, since
resistance to Phylloxera and quality of fruit seem to a great
extent to be antagonistic qualities ; the hybrids yielding the
best wine are usually insufficiently resistant, and vice versa.
The only practicable method, in fact, of dealing with Phylloxera
in an infested district lies in the use of graft hybrids, the graft-
ing of vinifera varieties upon Euvitis root- stocks. In the main,
root-stocks of the species rupestris and riparia are used, or
hybrids between riparia and berlandieri, or of crosses between
such hybrids and certain varieties of vinifera.

Anuraphis maidiradicis, the Corn Root Aphis, attacks the
roots of maize and other plants in spring and summer, and of
grasses in winter. It is a North American species. It is culti-
vated and carried from winter hosts to summer hosts by a small
ant, Lasius niger, known as the cornfield ant, and the aphis
depends solely upon the ant for its existence. It is, in fact, a
domesticated animal.

The control of aphids comprises generally the use of contact
poisons, usually emulsions of soap and water containing kero-
sene, nicotine, and so on.

Psyllidse. — The jumping lice or PsyUidse are minute insects
similar in size and appearance to aphids, but lacking the siphons.
The older nymphs are flat, inactive, scale-like forms, often living
within plant galls ; the young nymphs and the winged adults,
however, are capable of active, leaping movements.

Psylla pyricola of Europe and North America infests pear
trees.

Psylla mali is the Apple Sucker of Europe.

Aleyrodidae. — The Whiteflies are minute, moth-like insects
with white, floury wings. They are distinguished sometimes
with difficulty from Scale Insects, but the adult males and
females, however, have two pairs of wings, whereas the Scale
Insects are winged only in the adult male stage, and this has
only one pair of wings.

Asterochiton vaporariorum is the Greenhouse Whitefly of
Europe and North America. Dialeurodes citri is a citrus pest
of North America.

Thrips is a term applied to the members of the order
Thysanoptera, a family of minute insects with two pairs of
fringed wings which includes several notorious pests of plants.

Thrips tabaci, the Onion Thrips, is cosmopolitan and attacks
a wide range of food plants besides the onion. Heliothrips
hmmorrhoidalis is the principal greenhouse thrips of Europe
and North America. Heliothrips indicus attacks indigo in

170 THE PRINCIPLES OF APPLIED ZOOLOGY

India and cotton in the Anglo-Egyptian Sudan, being there the
major pest of cotton. Heliothrips rubrocinctus is the Cacao
Thrips of most cacao-growing regions. Frankliniella tritici
is a serious cereal pest of wheat-growing regions.

Flea Beetles. — The term flea beetle refers to a member of
the beetle family Chrysomelidce, a large and varied collection
of small, smooth, often hemispherical beetles which feed on
plant foliage. The larval stages may be foliage feeders also,
or may be foliage miners or may be root feeders.

The Chrysomelince or foliage-eating forms include partic-
ularly Leptinotarsa decemlineata, the Colorado Potato Beetle.
This black and yellow striped beetle is a pest of potatoes
in the United States, having spread from the buffalo bur, a
wild species of Solanum in Nebraska, where it was observed in
1859, from potato field to potato field, right across the States
to the Atlantic seaboard. It is also established in France.

Among root-feeding forms may be mentioned Diabrotica
vittata of North America, the black and yellow adults of which
feed openly on the foliage and flowers of cucurbitaceous plants,
the larval stages being root burro wers.

Similar root-feeding habits are shown b}^ the larvae of
Phyllotreta, a small leaping beetle which attacks cruciferous
crops, particularly mustard and turnip, in Europe and North
America.

Nisotra is a flea beetle which seriously attacks cotton plants
in Northern Africa.

Weevils. — The Curculio7iidce, popularly known as weevils or
billbugs, form the largest natural family in the animal kingdom.

They are characterised among beetles by the projecting
snout and the clubbed, elbowed antennae.

The larvae are small, limbless white grubs, usually somewhat
curved, and they show considerable variety of habitat ; all
agree, however, in being herbivorous, and the great majority
are subterranean or internal feeders.

Among the varieties of larval habitat may be mentioned : —

(a) General plant eaters, such as the species of Apion.

(b) Foliage eaters, such as Hyper a, Clonus, whose larvae
adhere to the foliage by means of a gummy secretion, and
Attelabus, Apoderus, and Ehynchites, whose larvae live in a
portion of the leaf rolled into a tube by the parent.

(c) Root feeders, such as Otiorhynchus , Sphenophorus ,
Sitones, Tanymecus, Myllocerus. Otiorhynchus is a notorious
genus of wingless weevils whose adult stages feed on foliage
and whose larval stages feed on the roots of fruit trees and other

INSECT PESTS: THE CATEGORIES 171

plants. Sphenophorus comprises the Corn Billbugs of the
U.S.A. Sitones does great damage to young peas and beans.

(d) Stem dwellers, such as Ceutorhynchus, Cryptorhynchus,
Ryncophorus, Hylastes, Hylobius, Pissodes, Lixus, Apion,
Cylas, Phylaitis. Ceutorhynchus, the Turnip Gall Weevil,
with species in Europe and North America, attacks cruciferous
crops, the larvae living within large galls on the roots. Hylobius
abietis, the Pine Weevil, is one of the worst forest pests in
Europe to coniferous trees. The adults gnaw the tender bark
in such a manner as to present the appearance of rabbit damage ;
the eggs are laid, however, on trees which have been felled two
or three years before, and the larva? make winding galleries
below the bark of the roots. Pissodes is another dangerous
genus with similar habits.

Oryctes rhinoceros, the Rhinoceros Beetle, is an enormous
weevil which feeds on the soft tissues and unopened leaves of
the coconut palm in India and the East Indies ; the larva?
live around plant roots and in decaying vegetable matter.
Coconut, toddy, and date palms are attacked also in India,
the Straits Settlements, and Ceylon by the Red Palm Weevil,
Rhyncophorus ferrugineus , whose larva? tunnel in the soft tissues
of the palm.

(e) Bud borers, such as Anthonomus, Conotrachelus, Dorytoma.
Anthonomus grandis, the Mexican Cotton Boll Weevil, may be
said to be, as concerns the financial aspect of its ravages, the
world's major cotton pest, although restricted to the cotton-
growing belt of North America.

It appeared in 1892 at Brownsville in Texas, and has since
spread over the entire cotton belt, although not doing serious
damage every year over the whole of the belt (Fig. 28).

It is a small, dark coloured weevil which feeds and lays eggs
in the young square, that is to say, the bud prior to blooming,
and in the young fruit or boll. The larva hatches in a few
days and begins feeding within the square (Fig. 29). After
about eight or ten days, pupation takes place within the same
square, which by this time has usually fallen to the ground,
and within a few days the weevil emerges. The entire life-
cycle requires about twenty-two to twenty-five days, and the
number of generations per year varies from one to three.

The weevil is a strong flier, even against prevailing winds,
and migration flights from a field seem to occur after the degree
of infestation of the plant has become as high as 60 per cent, of
bolls infested. The flights are dependent on the occurrence
of moderate winds, and the extent of the flights depends again

172 THE PRINCIPLES OF APPLIED ZOOLOGY

upon whether the new area contains small scattered cotton
fields or whether it is almost exclusively devoted to cotton.

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In the latter event the spread of the insect will be slower and

more limited than if the fields are scattered.

Common practices in the control of the boll weevil are : —
(1) Dusting with calcium arsenate, a very efficient control,

INSECT PESTS: THE CATEGORIES 173

especially if the dusting be carried out by aeroplanes, but
having the drawback that the area that can be covered is small.

(2) Early planting.

(3) Use of quickly maturing varieties.

(4) Spacing of plants closer together in the drill and farther
apart as regards distance between rows.

(5) Liberal fertilisation.

(6) Frequent and rapid cultivation.

(7) Collection and destruction of infested squares. Some-
times as high as 30-40 per cent, control has been obtained
in this way, but many parasites may be destroyed also unless
the squares are put in screened cages which allow the smaller
sized parasites to escape but retain the emerging weevils.

(8) Chopping and ploughing under of stalks in the fall.

(9) Cleaning up hibernation quarters.

There are fifteen parasites which are known to attack the
weevil in more or less economic numbers. Of these, Bracon
mellitor is the most important, since it occurs over the entire belt.

Some work has been done also in breeding a variety of
cotton whose bolls will be too hard for the weevil to puncture,
but results so far have not been conclusive.

Anthonomus pomorum of Europe and Anthonomus quad-
rigibbus of North America are close relatives of the Boll Weevil,
similar in appearance, similar in habits.

The female weevil drills a hole into an expanding blossom
bud of the apple and inserts eggs. The resulting larvae remain
feeding within the buds which, consequently, do not open but
fall to the ground. Pupation takes place within the dead bud,
and the beetle eats its way out when mature. The adults feed
on apple foliage.

Control methods comprise the destruction of winter shelter
by keeping tree trunks free from loose and rough bark ; the
shaking of infested trees to bring down injured blossoms which
can then be burned ; the jarring of adult beetles from the trees
on to cloths and their subsequent destruction.

Anthonomus signatus attacks strawberries in similar fashion
in the United States.

(/) Seed eaters, such as Balaninus, Sitophilus, Alcides,
Cryptorhynchus, Craponius. Sitophilus granarius and Sito-
philus oryzse are small, reddish-brown beetles, cosmopolitan in
distribution, which attack stored cereals. The eggs are laid
in a tiny cavity gnawed out of the grain. The larval stage is
passed within the grain, and pupation occurs within it, but
the adults live on the outside.

174 THE PRINCIPLES OF APPLIED ZOOLOGY

They will breed all the year round in stored grain in warm
buildings. They are susceptible, however, to a high carbon
dioxide content, to a low degree of dryness, and to low tempera-
tures. Oryzce become dormant at approximately 7-2° C.
(45° F.) and granarius at 1-6° C. (35° F.), and in this condition
they will perish in seventeen and thirty-eight days respectively.

Craponius incequalis, the Grape Curculio, is one of the worst
pests of the grape in North America, east of the Rocky
Mountains.

Noctuid Caterpillars belong to the family Noctuidce of moths,
a family of night-flying, somewhat robust and densely hairy
moths. According to their economic activities, these cater-
pillars may be grouped into : —

(a) Cutworms or surface caterpillars, which have been
already discussed.

(b) Army worms, which are caterpillars of the sub-family
Hadenince, and are forms which occasionally become excessively
abundant and migrate in hordes from one area to another.
The best known army worm is the cosmopolitan Cirphis
unipuncta, originally a native of North America, but occurring
now in South-east Asia, Europe, Australia, New Zealand, and
South America ; it tends to appear in enormous numbers,
stripping the fields of cereals of their leaves and ears, and then
will migrate in masses to fresh fields. The winter is passed by
the caterpillars in hiding among bunches of grasses ; they
pupate in early summer, and the emerging moths produce the

' July brood ' of caterpillars ; these again give rise to moths
which emerge in August and produce the " September brood "
of some caterpillars. In some latitudes three or even four
broods a year may occur.

(c) Bollworms, a name applied to caterpillars which bore
into the seed receptacles of the fruits of Malvaceous plants,
the cotton plant in particular, and feed on the developing seeds.

The more important Noctuid bollworms are : —
The Spiny or Egyptian Bollworm, Farias insulana, of
India, Egypt, and East Africa ; the Sudan Bollworm, Dipa-
ropsis castanea, of Africa ; the South American Bollworm,
Sacadodes pyralis ; and the Cotton Bollworm, Chloridea obsoleta,
which attacks cotton only in North America, and is primarily a
pest of corn, cotton being only attacked by the third brood
at a time when the maize heads are too hard to penetrate.

(d) Leaf eaters, a term which covers a large number of
Noctuid pests. In a few leaf -eating genera, notably Cosmophila,
Eublemma, the first two pairs of sucker feet are lacking and the

INSECT PESTS: THE CATEGORIES 175

caterpillar is termed a " semi-looper." Prodenia littoralis is a
cosmopolitan pest of many crops, particularly of tobacco,
flax, and cotton. Caradrina, Plusia, Hadena, Mamestra are
all important genera to the economic entomologist. Mamestra
brassicce is the Cabbage Moth of Great Britain.

For a discussion of the majority of injurious species, reference
may be made to Sorauer.

Loopers or Cankerworms are caterpillars of the family
Geometridse, a very large family of slender moths with relatively
large wings. The caterpillars are long and slender, and possess
abdominal legs or sucker feet only on segments six and ten ;
in walking, therefore, owing to this gap between the two pairs
of sucker feet, the caterpillar's body is alternately arched
dorsally to form a loop, and then straightened out again (Fig. 27).

The great majority of Geometrid caterpillars are extremely
similar in colour to twigs or leaf ribs, and so resemble very
closely their normal surroundings. Although not, as a family,
very important economically, they include some important pests.

In North America the cankerworms, Alsophila pometaria
and Paleacrita verbata, and the Apple Span Worm, Ennomos
sunsignaria, strip the foliage from apple trees. In Great
Britain species of Cheimatobia, Hybernia, and Anisopteryx do
similar damage ; these moths have wingless females, and one
common preventive method used against them is that of placing
bands of sticky grease around the tree trunks in autumn in
order to trap the wingless females as they crawl up the trunk
in order to reach the twigs on which they prefer to oviposit.

Tussock Caterpillars belong to the families Lasiocampidse
and Lymantriidse of moths. They are hairy caterpillars with
thick compact tufts of poisonous spines or hairs along the
dorsal surface (Fig. 27).

The Lasiocampidse include in particular the genus Malaco-
soma, the Lackey Moth. Malacosoma neustria is a defoliating
shade tree and fruit tree pest in Europe, Western Asia, Siberia,
China, and Japan. T^he eggs are laid in a band around a twig,
and the young caterpillars feed under a common web and are
hence sometimes termed " tent caterpillars."

The allied species, Malacosoma americana, is the Apple Tree
Tent Caterpillar of North America.

Control measures comprise the collection and burning of
egg rings during autumn, winter, and spring ; the destruction
of wild cherries and seedling apple trees ; the spraying of
infested trees with arsenate of lead just as the buds are opening.

The true tussock caterpillars include the Gipsy Moth

176 THE PRINCIPLES OF APPLIED ZOOLOGY

Porthetria dispar, and the Brown Tail Moth, Nygmia
phreorrhea, feeders upon a wide variety of forest, orchard, and
shade trees. The eggs are laid in spongy masses of 400-500
in crevices during late summer, remain unhatched during the
autumn and winter, and hatch in the following spring.

Although indigenous to Western and Central Europe, these
two moths were introduced accidentally into Massachusetts, the
Gipsy Moth by a Harvard professor of Physics in 1869, and
the Brown Tail on plants from Holland about 1893. Both
pests have become firmly established in New England generally,
and have spread with alarming rapidity in spite of the enormous
expenditure of money and effort that has been put forward by
the States concerned.

Control measures comprise : —

(a) The creation of a barrier zone on the fringe of the in-
fested areas in western New England and eastern New York,
within which infestation is reduced as far as possible by high
pressure spraying of trees with arsenate of lead and by destruc-
tion of the egg clusters with creosote ; all plants coming west-
ward through this zone are rigorously inspected.

(6) The importation of parasitic insects from Europe.
Intensive collecting by United States agents in Europe has,
during the last twenty years, resulted in large shipments of
parasites to the Melrose Highlands Laboratory in Massachusetts,
from which centre the parasites are distributed for liberation
in the infested areas.

CHAPTER XV

INSECT PESTS : The Categories— Continued

In the previous chapter, discussion has been confined to such
types of insect pest as are not, in general, closely restricted in
choice of food plant nor in powers of migration. Some con-
sideration may now be given to types which show a tendency
towards close limitation in range of food plants and, owing to
plant attachment or plant mining or other similar habits,
show a tendency to be restricted in area of distribution, unless
carried from one area to another by human agency.

Scale Insects. — The Hemipterous family Coccidse or scale
insects affords some of the most striking examples of the
readiness with which an insect type, feeding in its indigenous
habitat possibly upon wild plants, may be transferred
accidentally by man into a new area and rapidly adapt itself
to cultivated food plants.

In agricultural areas the scale insects of economic importance
are almost always orchard pests, and occur upon the outer
surface of the fruit-tree twigs or foliage or fruit as tiny shell-
like structures, comparable in shape often to oyster or mussel
shells. Beneath each scale is the wingless, degenerate female,
her suctorial proboscis imbedded in the plant tissues, completely
incapable of moving from the particular site she selected when
in the active larval state. The eggs are laid beneath the
scale or beneath the parent body. The newly hatched young
emerge from beneath the parent scales in early summer, swarm
over the trees, and in a few hours settle down, insert their beaks,
and begin to manufacture the circular grayish scale.

Some species are parthenogenetic, males being unknown.
In other species males are more abundant than females. The
male is winged, active, and incapable of feeding.

The so-called " scale," or covering, varies in its nature ;
it may be a true scale formed of felted threads and cast skins,
or it may be the thickened dorsal cuticle ; it may be a covering
of wax plates or of resinous material ; or, again, it may be
merely a powdering of waxy dust.

Of the wide range of injurious scale insects, the species

12 177

178 THE PRINCIPLES OF APPLIED ZOOLOGY

probably of greatest importance to the world's fruit-growing
industries is the San Jose Scale, Aspidiotus ptmiciosus, so

Cotton s-qruare
showing- larvd
of Bolt Weevil
in position

(after Hunter
and Coad)

Cotton

Boll
Weevil

Mediterranean
Fruit fly

Larva inside a coffee berry
(after Back ft Pemberton)

xEg-g- cavity
and eggs

Larva of Mediterranean Fruit fly

Fig. 29. — Types of Insect Pest. (Not to scale.)

called because it appeared as an economic pest first in the
orchards of San Jose in California, probably as an immigrant
from China on the flowering peach. Since then it has spread

INSECT PESTS: THE CATEGORIES 179

into all the fruit-growing districts of North America. It occurs
in the form of a dense incrustation of perfectly circular yellowish
scales, one-sixteenth of an. inch in diameter each, with a dark
central spot, covering usually the surface of the twigs but
occurring also on the foliage and fruit (Fig. 30). It is a wide-
spread feeder. Peach and pear are particularly susceptible and
are quickly killed, but the Chinese pear and the Kieffer and
Leconte varieties of pear, hybrids between Pyrus sinensis
and Pyrus communis, show considerable resistance.

The control measures adopted in American orchards against
the scale comprise :- —

(1) The destruction of the adult insects by spraying with
contact poisons, particularly with lime-sulphur (solutions of
alkaline sulphides and polysulphides), emulsions of mineral
lubricating oils, and so on.

(2) The encouragement of enemes and parasites. Much was
hoped from the ladybird beetle, Chilocoris similis, which was
imported from China to California in large numbers, but un-
fortunately it is an easy prey for certain native parasites, and
where spraying is carried on, cannot procure enough food to
maintain its existence in numbers.

Aspidiotus belongs to the sub -family Diaspinse or Armoured
Scales ; in these the scale consists of three distinct products,
namely, the moulted skins of the first and second nymphal
stages of the female, or the first of the male ; a mass of silken
threads poured out through openings in the dorsal surface ;
and an excretion from the Malpighian tubules emitted through
the anus.

Belonging also to this sub -family are many other notorious
pests, notably : —

The Oyster Shell Scale, Lepidosaphes ulmi, a pest of the elm,
apple, pear, plum, willow, dogwood, etc., in North America,
Brazil, Japan, Australia, Europe.

The Purple Scale, Lepidosaphes pinnceformis , on orange,
lemon, fig, grape-fruit, oak, croton, Banlcsia, Taxus, etc., in
Europe, America, Asia, Africa, and Australia.

The European Fruit Tree Scale, Aspidiotus ostrceformis, on
shade and fruit trees in Europe and America.

The Red Scale, Aonidiella aurantii, and Florida Red Scale,
Chrysomphalus, cosmopolitan pests of a wide variety of fruits.

The Peach Scale, Aulacaspis pentagona, a world-wide pest
of orchards.

To the sub-family Monophlebinse, characterised by a woolly
or powdery covering of wax which surrounds the insect or under-

180 THE PRINCIPLES OF APPLIED ZOOLOGY

lies it, belongs Icerya purchasi, the Fluted or Cottony Cushion
Scale. The popular name refers to a large cushion of wax,
with a fluted surface, which intervenes between the body of
the female and the surface of the plant. This waxen cushion
is the ovisac and encloses a mass of eggs.

The Fluted Scale was accidentally introduced from Australia
into California, and threatened at one time to destroy the citrus-
growing industry of that state. However, an agent of the
United States Department of Agriculture, Professor Koebele,
discovered in Australia a ladybird beetle, Vedalia cardinalis,
which in that area keeps the Fluted Scale down to proportions
harmless to the horticulturist.

These beetles were imported into California in large numbers
and established there. Within five years the number of
Fluted Scales was so greatly reduced that the menace to the
citrus industry was removed. Similar beneficial results followed
upon the introduction of this beetle into other areas where the
Fluted Scale was a pest, notably into New England, South
Africa, Portugal, Italy, Southern France, Egypt, Formosa,
Hawaii, Syria.

Vedalia cardinalis seems to afford a perfect remedy against
the Fluted Scale. There are, however, many reasons in its
favour which do not hold in the case of other beneficial insects.
In the first place, the host insect is fixed to the plant and
cannot escape the mobile beetle. Secondly, Vedalia is a rapid
breeder, producing two generations to the Coccid one, and
both larval and adult stages are egg feeders. Thirdly, it is
able to adapt itself to new environmental conditions. Finally,
it seems to have no enemies, a remarkable feature since, as a
rule, these beetles are liable to attack by many species of
parasites.

Somewhat variable results, in fact, have followed attempts
to introduce other species of ladybird beetles. Thus Koebele
introduced also from Australia the ladybird beetle, Crypto-
lazmus montrouzieri, into California to fight various species of
scale insects, and great success was claimed ; but other areas
have been unable to obtain results of appreciable value. Many
ladybird beetles, belonging to the genera Rhizobius, Lipernes,
Serangium, Frithionyx, Scymnus, Chilocoris, and most promising
of all, Oreus chalibcenus , have been introduced into California
to fight San Jose Scale but without marked success.

The sub -family Eriococcinae, or Mealy Bugs, comprise scale
insects whose bodies, both dorsal and ventral aspects, are
enclosed in a fine granular wax which makes them look as if

INSECT PESTS: THE CATEGORIES

181

they had been rolled in coarse flour ; the family includes some
of the most injurious cosmopolitan scale insects, notably the
Citrus Mealy Bug, Pseudococcus citri.

Hessian Fly. Adult
(after Marl at t)

Hessian Fly
maggots
SeneatA
the soil

(after Walton)

Aduttfemales
on fruit

Adult

fe7nales

enlarged

San Jose

Scale
(after Quaintance)

La.7~va
eniarg-ed

Fig. 30. — Types of Insect Pest. (Not to scale.)

The sub-family Lecaniinse, or Tortoise Scales, comprises
scale insects varying in appearance from hemispherical forms,
like half peas, with no proper scaly covering, to forms enclosed
in a large mass of wax.

Saissetia olece, the Black Scale, is one of the worst citrus pests

182 THE PRINCIPLES OF APPLIED ZOOLOGY

in the world ; it attacks a wide variety of fruit trees, however,
in addition to citrus. It is a hemispherical scale, dark brown
in colour, with an H-like dorsal mark. In California, attempts
are being made to control this insect by the establishment of a
South African Chalcid parasite, Scutellista cyanea, and an
Australian parasite, Aphycus lounsburyi. Saissetia olece may
be destroyed to the extent of 70-80 per cent, b}^ these egg-
devouring parasites, yet even this large percentage mortality
does not suffice to check excessive multiplication of the scale
insect when conditions afforded by the host plant are favourable.

Mining Insects. — The habit of mining in the foliage, stem,
root, or fruit of plants is one not confined to any particular
insect order.

Among Lepidoptera, where of course the habit occurs only
among the caterpillars, the following families are character-
istically miners : the Clear Wings (Sesiidse), Goat Moths
(Cossidse), Seed Moths (Gelechiadae), Clothes Moths (Tineidse),
Fruit Moths (Tortricidse), Moth Borers (Pyralidae).

Among Coleoptera the habit occurs in the Powder Post
Beetles (Lyctidse), Furniture Beetles (Anobiidse), Flat-headed
Borers (Buprestidae), Round-headed Borers (Cerambycidse),
Shot-hole Borers (Scolytidse), Pulse Weevils (Bruchidse), Bud
Weevils (Curculionidse), Drug Store Beetles (Ptinidse). Among
mining beetles, usually both larval and adult forms have the
habit.

Among the Diptera, the chief mining families are the Gall
Midges (Cecidomyiidse), Root Maggot Flies (Anthomyiidse),
Fruit Flies (Trypetidse), and Grass Stem Flies (Oscinidae).

Among the Hymenoptera, where as in Lepidoptera and
Diptera the habit is confined to the larval stages, the following
families are characteristically mining in habit : Stem Saw-Flies
(Cephidae), Wood Wasps (Siricidae), Gall Wasps (Cynipidae),
Stem Chalcids (Chalcidoidae), and Seed Chalcids (Chalcidoidae).

The Clear Wing Moths, Sesiidse, constitute a family of small
moths, most of which differ from the usual type of moth in
possessing transparent wings. They bear a superficial resem-
blance to Hymenoptera, especially as they are rapid fliers and
appear during hot sunshine.

A Sesiid moth usually lays her eggs on the side of the main
stem of a living plant ; the caterpillar bores laterally to the
centre of the stem, then tunnels downwards for several inches
in the sap wood ; in some cases the subterranean portion of
the stem is attacked. When full fed, the caterpillar tunnels
laterally until just below the bark and remains there all winter ;

INSECT PESTS : THE CATEGORIES 183

in spring it completes the tunnel to the surface, pupates in the
tunnel or beneath a loose piece of bark, and the moth emerges
in early summer.

Sesia, Trochilius, Melittia, Membecia, JEgeria, Memythrus,
Sanninoides are Sesiid genera whose caterpillars attack fruit
trees in Europe and North America. Sesia tipuliformis is the
Currant Borer of these areas. Mgeria exitiosa is the Peach
Tree Borer of North America.

The Goat Moths, Cossidse, are medium to large-sized moths,
usually greyish-brown in colour, with long narrow wings and
long abdomen. The larvae mine usually in hardwood trees,
eating large tunnels through the wood, and in many cases give
off an unpleasant goat-like smell. Pupation occurs in the
tunnel, and the moth emerges by a hole made by the caterpillar
prior to pupation.

The Leopard Moth, Zeuzera pyrina, is a white moth with
steely-blue round spots on the wings, whose larvae bore in the
trunks of hardwood forest trees. It is a common pest in the
forests of Europe and Northern Africa and has become estab-
lished in North America.

An allied species, Zeuzera coffew, is a pest of coffee, tea,
cinchona bushes, sandalwood trees, etc., in India, Ceylon, Java,
and East Africa.

The Seed Moths, Gelechiadse, are small moths somewhat like
clothes moths in appearance, with the hind wings characteristic-
ally pointed at the apex. The term " seed moth ' is a con-
venient one in that some of the more important species have
the larval habit of tunnelling in seeds, but actually the larval
habits vary considerably between species.

The Pink Boll worm, Pectinophora gossypiella, is the major
pest of cotton in India and Egypt, and is established also in
China and Japan, in the Philippines, Hawaii, America, West
Indies, and the Sudan.

In India it is controlled somewhat by the Braconid parasite
Rhogas, but in Egypt great annual damage is done to the
cotton crop, despite rigorous seed sterilisation measures enforced
in every ginnery. The eggs are laid on all parts of the plant,
singly, or, when at the base of the squares (flower buds), in
masses. The larvae enter the squares and feed on the future
floral organs. Later they enter developing bolls (fruits), eat the
seeds and lint and pupate within the emptied seed. It is
this pupation habit which renders the insect one that is easily
carried from country to country in consignments of seed.

No adequate control measures exist beyond an efficient

184 THE PRINCIPLES OF APPLIED ZOOLOGY

system of sterilisation of all seed by steam heat, sun heat, or
chemicals in the ginneries.

The Angoumois Grain Moth, Sitotroga cerealella, is similar
in habit to the Pink Bollworm, but lives as a caterpillar within
the grains of cereals. It is a European pest which has become
firmly established in other areas of the world.

The Potato Tuber Moth, Phthorimcea operculella, is a cos-
mopolitan Gelechiid whose caterpillar mines in the foliage and
in the tubers of the potato plant. It attacks tubers in the
field or in storage, and may be extremely destructive to stored
seed potatoes.

The Clothes Moths, Tineidae, are minute, dull coloured
moths, whose wings are narrow, fringed with scales, and fold
flat over the body when at rest. The caterpillars are usually
leaf miners or case bearers. The Case-making Clothes Moth,
Tinea pellio?iella, attacks particularly furs, woollen clothing,
carpets, and feathers ; the caterpillar lives within a cylindrical
case of silk and fragments of the material upon which it is
feeding.

The Tapestry Moth, Trichophaga tapetzella, attacks usually
coarser materials than does pellionella ; the caterpillar may
tunnel through the pile of a carpet, lining its galleries with silk,
or it may feed on the surface of its medium but within a silken
gallery.

The Webbing Clothes Moth, Tineola biselliella, makes
neither case nor gallery ; the caterpillar feeds on woollen stuffs,
furs, even on cobwebs.

Other Tineid caterpillars may be found feeding on dried
refuse, dead wood, dried fruit, fungi, bird nest debris, etc.

The Fruit Moths or Tortricidse are a large family of small
dull coloured moths with densely scaled wings ; the forewings
are long and have often a characteristic hump on the anterior
margins ; when at rest the wings wrap round the body.
Usually the moths are nocturnal fliers. The caterpillars are
usually greyish-white in colour, with very few hairs. The
majority roll the leaf they feed upon into an enclosing tube, or
they weave several leaves together to cover themselves, but
some larval forms burrow in fruit, in flower heads, or in plant
stems.

Of such tunnelling forms, the most important from an
economic standpoint is the Codling Moth, Cyclia pomonella, a
moth indigenous to Europe, but now one of the most destructive
pests in every apple-growing area of the world.

The moth is small, about three-quarters of an inch across

INSECT PESTS : THE CATEGORIES 185

the wings, greyish-brown in colour, and a night flier, being on
the wing usually within a fortnight from the fall of the petals
of the apple blossom. It attacks all varieties of apple, and
within three weeks from the fall of the petals the adult female
will lay sixty to seventy-five eggs on the leaves, twigs, or
commencing fruit. The caterpillar is whitish, with black body
tubercles and a black head. For a short time it feeds on the
leaf on which it has hatched, but eventually it finds its way to
a young fruit and enters it, in the majority of cases, at the calyx
end. It gradually eats its way to the core, and in three or four
weeks is full fed and ready to emerge from the apple. From
the apple it drops to the ground and then commences to ascend
the nearest apple tree trunk in order to find a suitable loose
piece of bark beneath which to spin its cocoon.

In the case of the second brood, the larva enters the apple
from the side. In Great Britain, New England, Canada, only
one brood occurs during the summer, but farther south there
may be as many as three. The winter is spent usually within
the cocoon as a full-fed larva, pupation occurring in the spring
and coinciding usually with the blossoming time of the apple
trees. Some, however, are known to winter as pupae.

Control measures against the Codling Moth comprise spray-
ing the trees with arsenicals just after the fall of the blossoms,
and banding of the trees with bands of coarse canvas to provide
a trap shelter for hibernating caterpillars ; the bands are
removed in winter and destroyed.

The Lesser Apple Worm, Laspeyresia prunivora, of North
America, is sometimes confused with the Codling Moth, but the
larval galleries are nearer to the surface of the fruit than those
of the latter form.

Laspeyresia molesia is the notorious Oriental Peach Moth of
North America.

Laspeyresia nigricana, the Pea Moth, injures pea-pods in
Europe and North America. Laspeyresia pseudonectis is the
Sann Hemp Borer of India. Polychrosis botrana of Europe
and P. viteana of North America are vine moths. The first brood
of caterpillars feeds on the blossoms and young fruit, webbing
the clusters together ; the second brood tunnels within the fruit.

Clysia ambiguella bores into the flower buds of the grape
vine in Europe.

Eucelis funebrana is the Plum Moth of Europe.

The caterpillars of the Apple Bud Moth, Tmetocera ocellana,
of Europe and North America, do serious damage to the unfold-
ing flower and leaf buds of apple and other fruit trees.

186 THE PRINCIPLES OF APPLIED ZOOLOGY

The leaf-rolling Tortricid caterpillars are of less economic
importance than the fruit miners.

Species of Cacoacia attack fruit and shade trees in North
America. Species of Ancylis have so-called ' leaf-tying '
caterpillars which fold or roll together leaves of strawberry,
apple, and other plants. Capita coffearia rolls the foliage of the
tea plant in Ceylon.

The Moth Borers or Pyralidae form a family of small moths
with long narrow fore wings, whose slender caterpillars live
concealed either as borers in stems or fruits, or below ground
among decaying leaves or bark, or within the shelter of rolled
leaves. A large number feed upon cultivated plants, and
several upon grain, flour, etc.

The majority of the smaller moths in grass or which come
to light are Pyralids, but they are readily confused with small
Noctuids or with large Tineids.

The caterpillars agree with Tineid caterpillars in having a
complete circle of hooks on the sucker feet, whereas in the
caterpillars of other moths the hooks are in two opposed series
on the sucker feet.

The caterpillars of Ephestia kuehniella, the Mediterranean
Flour Moth, feed on flour, bran, biscuits, cereal foods.
Each caterpillar feeds within a silken tube and spins silk
wherever it goes, especially when travelling about before
pupation. The food medium thus becomes matted together,
and in flour mills the machinery may be fouled by such silken
webbing.

Similar habits are possessed by Plodia interpunctella, the
Indian Meal Moth, another cosmopolitan pest, and by Pyralis
farinalis, the Meal Snout Moth.

The most effective control measure against these flour
moths is the fumigation of the infested mill or warehouse with
chloropicrin or hydrocyanic acid, or sterilisation by steam heat.

Of the leaf -rolling Pyralids, one of the more important is
Sylepta derogata, the Cotton Leaf -roller of India, Africa, and Java.

The most important Pyralid pests, however, are those whose
caterpillars tunnel in plant stems.

The Sugar Cane Moth Borers Diatroea and Chilo, cause great
damage in this way in sugar cane growing regions.

Diatroea saccharalis is the most important enemy of sugar
canes in Mexico, the West Indies, and the United States. The
eggs are laid in clusters upon the leaves, and the emerging
caterpillars gnaw their way into the stalks of the cane, kill
the central shoot of the young plant, and produce the so-called

INSECT PESTS : THE CATEGORIES 187

" dead heart " condition. In the Southern United States the
caterpillar is often termed the Larger Cornstalk Borer, but the
latter pest is now considered to be a distinct species, Diatrcea
zea colella.

Chilo simplex is the Sugar Cane Borer of India, attacking,
in addition to sugar cane, such plants as corn, sorghum, rice,
and millet.

Polyocha saccharella is the Cane Root Borer of India.

Another boring Pyralid of great importance is the European
Corn Borer, Pyrausta nubilalis, whose introduction and estab-
lishment within the United States is causing great alarm
there.

This pest has a wide climatic range, being found over
practically all of Central and Southern Europe, and has been
recorded from Western Asia, Siberia, Northern India, the
Philippine Islands, and Japan. The larvse, whilst preferring
maize, can thrive on a host of other plants — millet, hops, hemp,
broomcorn, sunflowers, mugwort, pigweed, rhubarb, field root
crops, small grain. The eggs are laid on the food plant ;
the emerging larvae feed on the tender foliage and eventually
enter by a mid-vein and tunnel into the stem ; with maize they
enter the developing ear.

The adult is a strong flier, and distribution is effected
through the flight of adults and influenced by prevailing
winds. In the United States, where the corn borer was intro-
duced probably in 1910 from Italy on broomcorn, the area
of distribution has increased from 100 square miles, in
Massachusetts, in 1917 to 93,786 square miles in 1927. At
present the infestation occurs in regions such as Ontario, New
England, Ohio, Michigan, and North-Western Pennsylvania,
where corn growing is of little importance as compared with its
status in the great corn belt ; but the spread of the insect
into the great corn-growing States seems inevitable.

A very large number of parasites have been introduced from
Europe and liberated in the infested areas, and some appear
to have established themselves, although their ultimate effect
upon the degree of infestation cannot as yet be estimated.

The Powder Post Beetles, or Lyctidse, are small, cylindrical,
reddish-brown beetles, both larval and adult stages of which
lie in dry wood, either in cylindrical tunnels or just below the
bark. The interior of an infested piece of timber may be
reduced to powder before the presence of the beetles is dis-
covered.

Lyctus brunneus and Lyctus linearis are widely distributed

188 THE PRINCIPLES OF APPLIED ZOOLOGY

over the world ; the female beetle lays her eggs in the pores
of the cut surface of hardwood timbers, and the larvae tunnel
in the sapwood in a direction parallel to the fibres ; only dry
timber such as old stumps and posts, furniture, tool handles,
railway sleepers, and so forth are attacked. These species
are among the most harmful of timber pests.

The Bostrychidse are somewhat small beetles, similar in
appearance to the Anobiidce and Scolytidce, but distinguishable
from the former beetles by the more cylindrical shape and
the imperfect separation of the first tarsal joint from the
second, and distinguishable from the latter beetles by the
rounded and prominent eyes, and by the loosely jointed club
of the antenna as contrasted with the oblong eyes and compact
antennal club of the Scolytidce.

The larvae and adults of these beetles bore tunnels in cut
timber and dried wood. In tropical countries, bamboo boring
species cause considerable damage. Some species attack
growing fruit trees.

The Furniture Beetles, or Anobiidse, constitute a family
of some 1,400 species of small brown or black beetles whose
larval stages are small white, fleshy grubs similar to White
Grubs, but much smaller. Both adults and larvae are feeders
on dried organic material, such as timber, furniture, books,
tobacco, drugs, dried fruits, cereals.

Anobium punctatum, Xestobium rufovillosum, and Ptilinus
pectinicornis all occur commonly in old furniture and in old
timbering of buildings, and may cause, over a long interval of
time, very serious damage. In several cases in Europe the
timbering of ancient buildings has had to be replaced owing
to the ravages of these beetles. Westminster Hall, in London,
whose rafters dated back to the time of William Rufus, affords
a case in point.

The term ' death watch beetles ' applies strictly to the
second species mentioned, and refers to a peculiar tapping
noise, a mating call, made by both sexes after the emergence
from their pupal cells within the timber. The round exit
holes made by the emerging beetles are characteristic features
of the surface of furniture or timber that has been attacked.

Lasioderma serricorne and Sitodrepa paniceum are cosmo-
politan Anobiids which injure stored products, the former species
frequenting more particularly cigarettes, cigars, drugs, the
latter species being found to attack biscuits, flour, drugs.

Niptus hololeucas, a small spherical silky-brown beetle, and
Ptinus fur, a similar form, attack household provisions, drugs,

INSECT PESTS : THE CATEGORIES 189

books, furs. Gibbium scotias, a blood-red mite -like creature,
feeds upon the paste of wall-paper and book-bindings.

The Flat-headed Borers, or Buprestidse, are somewhat large,
brilliantly coloured beetles, primarily inhabitants of the tropical
rain forest. The larval stages are plant tunnellers, and are
distinguishable from all other beetle larvae by the small, flat
head, the greatly swollen prothorax, and the slender hind body,
which gives them a characteristically club-shaped appearance.

The larvse occur in broad galleries beneath the bark of trees
or in the stems of herbaceous plants, all, in a few cases, between
the surfaces of a leaf.

Chrysoboihris femorata is the Flat-headed Apple-tree Borer
of North America. Sphenoptera neglecta is the Cotton Stem
Borer of Africa, Sphenoptera gossypii that of India.

The Round-headed Borers, or Cerambycidse, are forest-
frequenting beetles provided with very long antenna?, and for
this reason often referred to as Longicornes or Longhorn
Beetles. In shape they are usually rectangular, with parallel
sides, and they have a distinct spur on each tibia.

The adults are foliage feeders, but the yellowish, tapering
larvae are tunnellers in the trunks or branches of trees, or
burro wers just below the bark. A few genera, such as Saperda,
tunnel the stem of herbaceous plants, but most species attack
only dead or dying trees.

Saperda candida,the Round-headed Apple-tree Borer , is second
only to the Codling Moth as an apple pest of North America.

The Shot-hole Borers, or Scolytidse, are small cylindrical
beetles similar to weevils in appearance, but distinguishable
by the absence of snout and by their habits.

Nearly all are borers in woody tissues, only a few species
being known to attack herbaceous plants. The tunnels occur
between the bark and wood of a tree, and are constructed on a
complex pattern which is usually distinctive of the species of
beetle that has made it.

There are monogamous and polygamous species. With
the first named, the initial tunnel is made by the female before
mating ; after mating she makes a number of lateral tunnels
at right angles to the first one, laying an egg at the end of each ;
the male remains in the original tunnel. The tunnels are
generally in one plane, between bark and wood.

In the case of polygamous species, the first tunnel is made
by the male ; the females gather within it and make each a
tunnel from it ; from this secondary tunnel, again, each female
makes a number of tunnels in which to lay her eggs.

190 THE PRINCIPLES OF APPLIED ZOOLOGY

In both cases the hatched larva bores farther along the egg
tunnel, and eventually burrows outwards to the surface in
order that the emerging beetles may escape.

In some forms, the so-called " ambrosia beetles," the galleries
contain the fungus Ambrosia, which the insects cultivate and
use as food.

Xyleborus dispar, the " Shot-hole Borer," attacks fruit
and forest trees in Europe. Scolytus (Eccoptog aster) rugulosus
is the Fruit Bark Beetle of Europe and North America.
Xyleborus fomicatus is the Shot-hole Borer of tea in Ceylon
and Assam.

The Spruce Bark Beetle, Ips typographies, is one of the most
dangerous bark beetles in Europe ; both adults and larvae
bore into the bark and sap wood of conifers, particularly of
spruce.

Other dangerous bark beetle genera are Scolytus, Hylastes,
Hylesinus, Hylurgus, Cryphalus, Tomicus, Xyleborus, and
Dendroctonus . The last-named genus is the forest bark beetle
of North America and comprises some ten economically
important species.

The control of bark beetles is difficult, but cutting and bark-
ing of infested trees and burning of the bark during winter or
early spring are measures usually adopted.

The Pulse Weevils, or Bruchidse, are small, thick-set, hairy
beetles whose larval stages occur within the seeds or seed pods
of leguminous plants. Usually they eat out the starchy portion
of the seed but avoid the germ.

Bruchus pisorum is a cosmopolitan pest of growing peas,
dried peas not being attacked. Acanthoscelides obtectus, on the
other hand, readily attacks dried beans.

The Gall Midges, or Cecidomyiidse, are minute, delicate flies
possessing long antennas with whorls of hairs at the joints, long
slender legs, and rather broad, heavy wings whose veins are
few and weakly developed. The larval stage is a small-headed
pink maggot, tapering slightly at each end, possessing fourteen
body segments instead of the usual thirteen, and having a little
horny hook on the ventral surface of the segment immediately
behind the head, termed the " anchor process " ; it is used
for locomotor purposes and for smashing up the substance of
the plant gall within which the larva may live.

The majority of the gall midges spend the larval stages within
galls produced by the proliferation of injured plant tissue,
but many forms live within the stems of plants.

The Hessian Fly, Mayetiola destructor, is probably the major

INSECT PESTS : THE CATEGORIES 191

cereal pest of the North American wheat and barley growing
areas. It is an importation from Europe and is believed to have
been introduced in straw when Hessian troops landed in Long
Island during the Revolutionary War. The larval stages occur
within the plant stem or between stem and leaf sheath (Fig. 30),
and there also they pass the winter as a hard puparium similar
to a flax seed. They are thus readily transported in infested straw.

The only practicable method of avoiding the ravages of
Hessian Fly is that of delaying the sowing of the crop until
the flies are no longer on the wing. This " fly-free date," as it
is called, varies in date according to latitude, longitude, and
altitude, but in most of the North American areas where winter
wheat is grown the date falls between 10th September and
1st November.

Delayed sowing is, of course, only a precaution against the
autumn brood of Hessian Fly. The crop is still liable to
infestation in the spring from the main brood, which may
come from neighbouring infested fields or from self-sown
wheat present at the time of the autumn sowing.

One of the most destructive enemies of the pear tree in
Europe and North America is Contarinia pyrivora, the Pear
Midge, whose larvae tunnel into the young fruit and cause
shedding. Another Cecidomyiid introduced from Europe into
North America is the Wheat Midge, Diplosis tritici, whose larvae
attack the maturing head of the wheat plant.

The Root Maggot Flies, or Anthomyiidse, are flies somewhat
of the house-fly type, but differing from the true house-fly,
Musca domestica, in that the fourth longitudinal vein of the wing
is straight and does not turn forwards to meet the third vein
and make an enclosure or cell as it does in true Muscids.

The larvae are maggot-like, but usually possess four rows of
thread-like processes on the segments.

The adult flies are flower haunters, except for a few pre-
dacious species, but the larvae vary in habit, some tunnelling
in dung, others in decaying vegetable matter, others in the roots
of living plants.

The root burrowers include particularly Phorbia cepetorum,
the Onion Fly, whose maggots burrow into the onion bulb in
Europe and North America ; Chortophila brassicce, the Cabbage
Root Fly, which attacks the rootlets of cabbage and cauliflower
in the same area ; Pegomyia betce, the Beet Leaf Miner, makes
galleries between the surfaces of beet foliage in Europe ;
Hylemyia coarctata is the Wheat Bulb Fly of Europe and
Northern Asia.

192 THE PRINCIPLES OF APPLIED ZOOLOGY

The Fruit Flies, or Trypetidae, are flies of moderate or rather
small size, marked usually with bands of yellow or brown,
and with wings usually mottled or with dark bands. They
constitute a family of the so-called Acalyptrate Muscidce, that
is to say, flies with the general appearance of the house-fly
but lacking the squamce, the scale-like structure posterior to
the base of each wing.

In the usual fruit fly life-cycle, the eggs are inserted just
under the skin of a fruit by the long horny ovipositor of the
female ; the larval stages tunnel in the fruit ; after about a
fortnight they are full fed, whereupon they leave the fruit,
fall to the ground, burrow therein, and pupate. The majority
of the fruit fly pests of cultivated fruits belong to the genera
Ceratitis and Dacus.

Ceratitis is a genus with dark banded wings, and with the
thorax and wing bases spotted with black.

Ceratitis capitata, the Mediterranean Fruit Fly, is indigenous
probably to West Africa, but is now established in Europe,
Asia, Africa, Australia, and Hawaii, but not, fortunately, in
the North American fruit-growing areas. It is one of the most
serious dangers that the fruit industry is liable to meet, and
has already destroyed the commercial production of fruit in
several areas. Its establishment in the United States would
be a calamity to the fruit-growing industry there.

It is a yellow fly about the size of a house-fly, with red eyes,
and with the wings crossed by two irregular brownish-yellow
crossbands and possessing a brownish-yellow base.

The glistening white eggs are placed beneath the skin of a
ripe fruit (Fig. 29), and the larvae feed in the pulp for two or
three weeks. Then they leave the fruit and pupate in the
ground, remaining there for twelve to twenty-one days. Un-
ripe citrus fruits are usually protected to some extent by the
essential oils of the rind which are toxic to the eggs, although
no fruit juice is sufficiently acid to inhibit the development of
the larva ; ripe citrus fruits are readily attacked.

The eggs and larvae are fatally affected by cold storage
temperatures, failing to survive refrigeration at 40°-45° F. for
three weeks, or 32°-35° F. for two weeks.

Control measures comprise the clearing up and destruction
of fallen fruits ; the protection of trees with netting ; the use of
arsenically poisoned syrup as a poison bait spray ; the cold
storage of fruit. In Hawaii the establishment of certain Hymen-
opterous parasites, notably Opius humilis from South America
and Diachasma tryoni from Australia, is being attempted.

INSECT PESTS : THE CATEGORIES 193

Of the species of Dacus, the best known is Dacus cucurbitce,
the Melon Fruit Fly of India, Ceylon, Hawaii, which feeds on
cucurbitaceous fruits ; and Dacus ferrugineus, the Mango Fruit
Fly of India, Ceylon, Java, and the Philippine Islands.

Dacus olece, the Olive Fruit Fly of the Mediterranean
countries and India, does enormous damage to olives.

The genus Bhagoletis includes R. pomonella, the Railroad
Worm of apples in North America ; R. cerasi of Europe, R.
cingulata, and R. fausta of North America, all infest cherries.

Anastrepha is a South American genus with several de-
structive species.

Bactrocera (Choetodacus) tryoni is the Queensland Fruit Fly
of Oriental and Australasian countries.

Acidia heraclei, the Celery Fly of Europe and Asia Minor,
occurs in the larval stage as a leaf miner of celery, parsnip, and
parsley.

The Grass Stem Maggot Flies, or Oscinidse, are yellow or
yellow and black Acalyptrate Muscids, minute in size, and
occurring commonly among grasses. The larvae live generally
within the stems of grasses, but some are leaf miners and others
inhabit galls on grasses.

Oscinis them mines the leaves of the tea plant in India.

Oscinella frit, the Frit Fly, is a stem tunneller of cereals in
Europe and the United States.

Chlorops tceniopus, the Gout Fly, is a stem miner of wheat,
rye, and barley in Europe.

The Stem Saw-flies, or Cephidse, are small, slender, narrow-
bodied insects whose larvae, which somewhat resemble limbless
caterpillars, live within the stems of plants. In Great Britain
the best known is Cephus pygmazus, which tunnels in the stem
of the wheat plant. In North America, Cephus occidentalis, the
Western Grain Saw-fly, has similar habits.

The Gall Wasps, or Cynipidse, are again widely distributed.
The larvae live and feed within a " gall," a mass of proliferating
plant tissue induced by the presence of the living larva.
Eighty-six per cent, of the known species of Cynipidae have
been reared from galls on species of the oak ; another 7 per cent,
are confined to species of Rosa, and the remainder occur particu-
larly on Compositae. The family is one of intense interest to
the biologist, and the reader should refer to the work of Adler
for a full account of Cynipid biology.

A certain number of mining forms occur within the group
Chalcidoidea, a very extensive superfamily of minute Hymen-
optera, the majority of which are parasitic in the egg, larva, or

13

194 THE PRINCIPLES OF APPLIED ZOOLOGY

pupa of other insects. There are many phytophagous forms,
placed usually in the family Eurytomidce. Some species produce
galls at or near the joints of cereal and grass stems, and are
therefore known popularly as " joint worms." Thus Harmolita
tritici attacks wheat in Europe and North America. Harmolita
grandis, the Wheat Straw- worm of North America, has two
alternating generations, one termed minutum, which attacks
wheat in the spring and deforms the stem, the other termed
grandis, which destroys the embryonic heads of the wheat.

Other species live within seeds. Thus Bruchophagus funebris
lives within the seeds of clover and alfalfa ; Euoxysoma vitis
within grape seeds ; Megastigmus spermolrophus within the
seeds of the Douglas fir.

The Blister Mites are not insects, strictly speaking, but
members of the Arachnoid family Eriophyidaz. They are
minute, elongated creatures with only two pairs of short,
stumpy legs.

Eriophyes ribis, the Currant Gall Mite, produces a swollen
condition of black currant buds, all stages of the mite being
found within an infested bud ; it is a serious pest of currants in
Europe.

Eriophyes pyri lives beneath yellow blisters, like galls, on
the foliage of pear and apple in Europe and North America ;
the winter is passed beneath the bud scales.

Eriophyes gossypii infests cotton in the West Indies, causing
blisters on the leaves.

CHAPTER XVI

INSECT PESTS : The Life- Cycle

It may be laid down as an axiom of Applied Entomology that
effective control of an insect pest cannot be hoped for until
an accurate and comprehensive conception has been established
concerning the four groups of data which deal respectively
with the life-cycle, the distribution, the behaviour, and the
mortality factors of the pest under review.

The term life-cycle refers, strictly speaking, to the whole
period of time elapsing between the fertilisation of an egg,
and the ultimate death of the insect which develops from that
egg. Since, however, the longevity of an insect is difficult to
estimate, even approximately, and the period of time between
fertilisation and deposition of an egg is again difficult to esti-
mate, the life-cycle as referred to by the entomologist comprises
more usually the number of days elapsing between the point
of time when an egg is laid and the attainment of sexual maturity
of the resulting insect ; or it may even refer only to the period of
time between the emergence of the insect stage from the egg and
the emergence of the immature insect stage from the so-called
pupal condition. Using the term in its fullest sense, however, the
life-cycle may be said to comprise three periods, namely : —

(1) The duration of the egg stage between fertilisation and
hatching, that is to say the embryonic period.

(2) The duration of the period between emergence from the
egg and attainment of sexual maturity, that is to say the
prematuration period.

(3) The duration of the period between attainment of sexual
maturity and death, that is to say the maturation period.

In a large number of insects, grouped generally as hemi-
metabolous insects, the prematuration period comprises a
number of phases, all actively feeding — that is to say, trophic
phases — demarcated one from the other only by the skin
moults necessitated by continuous growth, and by increasing
development of wings and sexual glands up to the condition
characteristic of the imago or adult insect.

That is to say, the phases are merely growth phases of one

195

196 THE PRINCIPLES OF APPLIED ZOOLOGY

stage, the nymphal stage, and the nymphal stage is an immature,
stumpy-winged replica of the adult.

In the majority of the other insects the so-called holo-
metabolous insects, the prematuration period consists of several
stages which may differ from one another very considerably,
morphologically and biologically. The egg stage is succeeded
by an active, trophic stage — the larva — very different in
appearance from the imago, but representing a nymph in which
the wing buds are developing internally instead of externally.
There may be a succession of growth phases of this stage, the
so-called larval instars. Then succeeds an actively mobile
but non-trophic prepupa which passes eventually into the
relatively quiescent pupa. The pupa again differs consider-
ably from larva or imago. Within the pupal integument the
tissues break down and are reorganised, and finally there
emerges from it the immature but fully winged imago.

Thus, if the larva represents a series of trophic nymphal
phases, the pupa can be looked upon as representing a telescoped
series of quiescent, non -trophic nymphal phases. The meaning
of this quiescence will be discussed later.

Now the actual duration of an insect life-cycle is not a
period of time constant in length for each individual of the
species. The average length of life-cycle of a species under
certain conditions can be estimated, but the life-cycle may be
affected by physical factors, notably by temperature and
moisture, so that the life-cycle of the individual may be longer
or shorter than the average, according to the acceleration or
retardation produced by physical factors upon the rate of
metabolism. If one or more of the life -cycle stages be
lengthened or curtailed, the total length of the life-cycle is not
necessarily altered likewise. It is so affected in very many
insects certainly. Thus, for example, the life-cycle of the house-
fly is shorter in Southern Europe than in Northern Europe,
owing probably to differences of mean summer temperature.
It has been shown that in the case of the bean weevil, Acantho-
scelides obtectus, a lowering of the temperature by so small an
amount as 10° F. can double the duration of the life-cycle.

In many forms, however, the normal rhythm of existence
is apparently so fixed by heredity that a shortening or lengthen-
ing of any stage is compensated by an inverse alteration of the
succeeding stages. Thus, for example, Baumberger has shown
that in the life-cycle of the Oak Eggar Moth, Lasiocampus
quercus, when the length of the caterpillar stage was reduced
gradually from the normal 245 days to 112 days by refrigeration

INSECT PESTS: THE LIFE-CYCLE 197

methods and by judicious selection of precocious larvae, the
pupal stage always lengthened accordingly, so that the average
length of the whole life-cycle remained unaffected by tempera-
ture changes.

A considerable accumulation of data is available concerning
the effect of temperature upon the insect life-cycle. There
would seem to be for each species of insect a range of
temperatures between whose maximum and minimum extremes
the insect is active ; beyond either extreme, metabolism is
retarded and dormancy or death may happen to the insect,
according to the degree of temperature and according to the
length of exposure to this temperature.

This range of temperatures may be termed the range of
Effective Temperatures, and the point upon it at which metabolic
activity is greatest may be termed the optimum temperature.

Similarly there is for each species a range of Effective
Humidities, bounded by maximum and minimum limits of
metabolic activity and having upon it an optimum point.
Probably also, there are ranges of effective atmospheric
pressures, light intensities, wave lengths, atmospheric oxygen
content, and so on

Thus for any given insect there are definite boundaries of
temperature, humidity, and so on, which limit metabolism,
activity, and development. There is, for example, a tempera-
ture below which life is impossible even for a moment— the
infra - minimum temperature. Similarly there is an ultra-
maximum temperature at which, and beyond, death is in-
stantaneous. Similarly, absolute dryness, that is to say
infra-minimum humidity, is prohibitive of life, and so is ultra-
maximum humidity or saturation, although insects can
withstand extremes of humidity better than extremes of
temperature.

The minimum effective temperature for insects generally
is considered to be round about 5°-6° C, and the infra-
minimum temperature may be as low as 10° below zero centi-
grade. Insects, however, are very resistant to low temperatures.
At the infra-minimum temperature, death is probably caused
through crystallisation of the body fluids, and when this occurs
a certain amount of heat is given off and the internal temperature
of the insect rebounds upwards for several degrees. The
temperature at which crystallisation occurs is termed the
undercooling point. The highest point of the rebound is termed
the freezing point. It has been asserted by earlier workers,
notably Bachmetjew, that if the insect is then restored to

198 THE PRINCIPLES OF APPLIED ZOOLOGY

normal temperature it will revive after an interval dependent
upon the length of time it has been undercooled, but that if
the insect be undercooled a second time it will die. Such a
fact would explain the tendency for frosts in late spring or
following a spell of mild weather, to cause great mortality
among insects, when similar mortality has not been caused
by more severe frosts earlier on. Recent work, however, by
American and European entomologists suggests that a great
many species of insects cannot survive even a single under-
cooling. It has been shown that certain insect species which
are able normally to endure long periods of dormancy at low
temperatures are killed when their tissue fluids freeze, and that
other species can endure such freezing. The freezing point of
the tissues of an insect, further, may be lower after a spell of
subjection to low temperatures, a hardening process so to speak,
than if following a period of subjection to high temperatures
such as those of late spring or summer. That is to say, the
gradual approach of cold weather ' hardens ' insects
accustomed to hibernate during winter and enables them to
withstand very low temperatures, but in the case of insects not
accustomed to hibernate, dormancy and eventual death may
occur after exposure to comparatively high temperatures.
Thus, according to the American entomologist, Robinson, the
grain weevil Sito'philus oryzce becomes dormant at 7' 25° C. ;
its fellow-species Sitophilus granarius becomes dormant at
1*6° C. ; oryzce dies after seventeen days of such dormancy ;
granarius dies after thirty-eight days of such dormancy. These
weevils do not hibernate normally, and exposure to low tempera-
tures, instead of hardening them, makes them more susceptible
to dormancy and death. The moisture content of their medium,
however, influences the degree of susceptibility to low tempera-
tures. They are more susceptible if the grain is damp and
if it is absolutely dry.

In an insect's tissues, water exists partly in a free condition
and partly in a bound condition, that is to say adsorbed by the
colloids and occurring as thin shell around each colloid particle.

The phenomenon of hardiness in certain insects is apparently
bound up with this condition of affairs ; the greater the pro-
portion of bound water to free water, the greater the ability
of the insect to withstand low temperatures, since such bound
water will not freeze at temperatures higher than 5° below
zero Fahrenheit (-20° C.) and can undergo considerable
compression ; in certain insects, apparently, subjection to
gradually decreasing temperatures stimulates the conversion

INSECT PESTS: THE LIFE-CYCLE 199

of free water to bound water, and the insect becomes hardy ;
in other insects the converse occurs and subjection to decreasing
temperature renders the insect more susceptible.

Although low temperatures may not be immediately fatal
to insect life, they always impede development, so that low
temperature storage is an excellent method of protecting stored
goods against the ravages of insect pests. Injury by clothes
moths to furs, woollens, carpets, can be minimised by
storage at 40° F. Damage to peas and beans by weevils can
be retarded by storage at temperatures as high as 64° F. ;
tobacco similarly may be freed from the tobacco beetle Lasio-
denna better by exposure for three weeks to a temperature of
3° or 4° C. below zero than by exposure to heat, as heat treat-
ment darkens the tobacco and makes it brittle ; rice, infested
with Sitophilus oryzce, is sterilised preferably by exposure to
low temperatures than to high ones, since heat cracks the enamel
of the seed and spoils the rice for milling.

Low temperatures, again, are useful in sterilising fruits ;
the susceptibility of eggs or larvae of the Mediterranean Fruit
Fly to low temperatures is very important from the point of
view of ship transit of fruits from infected areas to countries
where the entrance of such fruit is restricted.

The ultra-maximum temperature, the temperature which
will kill an insect instantly, is about 60° C. for most species. A
moderately high temperature, however, if applied for several
hours, is usually as effective as a much higher temperature applied
for a shorter time. The following pests of stored products are
destroyed instantly at the following temperatures : —

Acarids, 150° F. for one hour ; pea and bean weevils
( Acanthoscelides), 146° F. for fifteen minutes ; weevils, in
general, 122° F. ; larder beetles (Dermestes), 140° F. for an
hour ; furniture beetles ( Anobium), 130° F. ; insects infesting
flour mills, 118°-125° F. for several hours.

Heat as a sterilisation agent for stored products is, at
present, as regards large scale work, used chiefly in : —

(1) the treatment of cotton seed in Egypt against the
hibernating larvae of the Pink Bollworm, Pectinophoragossypiella ;

(2) the treatment of flour mills in U.S.A. and Canada
against the various pests of flour and grain, notably against
the Mediterranean Flour Moth, Ephestia Jcuehniella.

In Egypt, since 1912, when the presence of the Pink Boll-
worm began to be a serious factor in cotton cultivation, much
experimental work has been carried out with methods of seed
sterilisation devised to kill the larvae hibernating within the

200 THE PRINCIPLES OF APPLIED ZOOLOGY

seed. In the Sudan, infected seed can be sterilised quite
effectively by exposure to sun heat ; but in Egypt, sun tempera-
tures are not sufficiently high, and sterilisation is carried out
by some type or other of hot air machine, which each ginnery
is compelled by law to install.

The difficulty in high temperature treatment is to decide
upon the range of temperatures non -injurious to the seed but
fatal to the contained larvae ; it would seem that to kill the
larvae instantaneously, a minimum temperature of 140° F. is
necessary, but five minutes' exposure to a minimum of 124° F.
is just as effective. As regards the seed, wet seed can be raised to
140° F. and dry seed to 150° F. without impairing germination.

The use of high temperatures for sterilising cereal mills
was first suggested and successfully attempted by Dean, of the
Kansas Experimental Station, during 1910-13. The use of
hydrocyanic acid gas, whilst efficacious against most insects,
has never been known to give complete satisfaction against the
Flour Beetle (Tribolium spp.), the " cadelle ' (Tenebrioides),
and the Saw-toothed Grain Beetle (Silvanus surinamensis).
On the other hand, all stages of cereal insect pests are killed
by one or two hours' exposure to a temperature of 122°- 131° F.

Such temperatures can be obtained in a mill by steam pipe
radiation, one square foot of radiating surface being usually
sufficient to heat 50-100 cubic feet of space at a steam pressure
of 25-50 lbs. It is necessary to heat the mill to a temperature
higher than actually required, in order to allow for inequalities
in the distribution of the heat. Only one treatment per year
is required, no preliminary cleaning is necessary, and the
method is non-injurious to operator and property.

Maximum and minimum limits to insect activity and
development occur in both the ranges of temperature and
humidity. The effect on the insect is a combination of tempera-
ture and humidity influences, and since maximum, minimum,
and optimum points of temperature for an insect stage will
vary according to the humidity value, these points upon a
graphical figure, expressing the correlated influence of tempera-
ture and humidity upon insect metabolism, will appear as
curves, and the range of temperature between successive
curves may be referred to as zones of metabolic activity. Thus,
starting from the curve of infra-minimum temperatures, as
the temperature increases, a longer and longer period of exposure
will be required to kill the insect, until a curve of temperature
points will be reached at which life continues indefinitely.
The range of temperatures between the two curves may be

INSECT PESTS: THE LIFE-CYCLE 201

termed, using the nomenclature of Dwight Pierce, the Zone of
Low Fatal Temperatures. Again, between the upper extreme
of this zone and the curve of minimum temperatures there will
occur a Zone of Inactivity. At the lower margin of this zone
complete dormancy will characterise the insect, but as the
temperature increases the increasing rate of metabolism will
bring about a gradual approach to sensibility, followed by
movement, followed by the necessity for feeding.

Above the curve of minimum temperatures, activity is at
first sluggish but increases with temperature until the so-called
" optimum " is reached, beyond which the rising temperatures
are accompanied by less and less activity, and are finally
accompanied by stupor. At the curve of stupor a second
Zone of Inactivity commences. As the temperature increases,
the sleep becomes more and more sound until a curve occurs
at which death comes after long exposure. At this curve
begins the Zone of High Fatal Temperatures, at which death
occurs after shorter and shorter periods of exposure until it is
instantaneous at the ultra-maximum temperature.

Humidity may affect the insect by bringing about variations
in the amount of free water, at any rate in insects which do
not take in water and whose free water depends upon the
liberation of bound water. The American observer, Headlee,
has attached importance to the water optimum, that is to say
to the amount of body fluid which permits the maximum of
metabolic reaction, the necessary chemical and physical changes,
to take place. For example, if the amount of body fluid be
above the optimum, a dry atmosphere will remove the surplus
and so speed up the rate of metabolism, whereas a saturated
atmosphere by impeding evaporation from the body surface
would slow down the rate of metabolism and thus prolong
an egg or pupal stage. Similarly, if the body fluid were just
about the optimum, dry air would reduce it below that point
and decrease the rate of metabolism, whereas moist air by
impeding evaporation would permit the water content of the
life-cycle stage to rise toward the optimum and so increase
the rate of metabolism.

Such a view explains the discrepancies in the responses of
different insect species or different stages of the one species
to the same degree of atmospheric humidity. For example,
laboratory experiments made by Headlee indicated that the
rate of metabolism in pupae of the Bean Weevil (Acanthoscelides
obtectus) and the Angoumois Grain Moth (Sitotroga cerealella)
varies inversely with the atmospheric humidity ; in the adults

202 THE PRINCIPLES OF APPLIED ZOOLOGY

of the former it varies directly, in the adults of the latter it varies
inversely with the humidity ; in the larvae of both types the rate
varies directly and in the egg stage inversely with the humidity.

A view that has gained considerable support from entomolo-
gists during recent years is the conception, borrowed really
from the work of European botanists, that the passage from
one life -cycle stage into the next stage will only occur when the
mean daily temperatures have reached a certain sum total,
the particular total being necessary to the particular stage.
This sum total may be termed the Total Effective Temperature
for that particular stage.

It must be noted that in the case of insects, when summing
up the daily temperatures, only the excess of temperature above
the minimum effective temperature should be taken into con-
sideration. Further, if the value of the total effective tempera-
ture is to hold good for both winter and summer, a temperature
curve must be obtained for the species based upon the observa-
tion of a considerable number of individuals kept at different
constant temperatures, or, better still, at temperatures having
a daily variation with constant maximum and minimum, and
with fairly constant humidity conditions. With such a curve
plotted it is possible to give each degree of temperature a
definite value in relation to the accumulation of temperature
necessary for any stage of growth or activity at the optimum
temperature. Thus, suppose the optimum temperature for an
egg stage happens to be 30° C, at which temperature, let us
assume, the egg stage has a duration of twenty-five hours,
then each hour at 30° C. has a value of 4 per cent, of the whole.
If thirty hours are required at 25° C, then each hour at 25° C.
has a value of 3' 3 per cent, of the whole, and so on, each hour
having some percentage value less than that of the optimum
and dependent upon the hourly mean temperature. A table
for the value of each degree between the optimum, minimum,
and maximum effective temperatures can be constructed, and,
using these values, the true total effective temperature has
been reached when an accumulation of 100 has been obtained.

It has been assumed by some authorities that the product of
the duration of a stage multiplied by the number of degrees centi-
grade at which development of the stage occurred, is a constant.

That is to say, that DT = K, where D is the duration in hours,
T is mean hourly temperature in degrees centigrade, and K
is a constant expressed in degree-hours, or developmental units,
if we follow the nomenclature recently suggested by Shelf ord.

The equation will approximate more towards accuracy,
however, if it be expressed D(T -t) =K, where t is the minimum

INSECT PESTS: THE LIFE-CYCLE 203

effective temperature below which metabolism is dormant.
Even thus the equation probably holds good only for a very
limited range of temperatures lying on either side of the optimum
effective temperature.

Further, values of D must be used that have been obtained
under conditions approximating as nearly as possible to normal
outdoor conditions of humidity and air currents and sunshine.
The interest of the equation lies in the possibility of predicting
from it whether an insect pest, whose duration of life-cycle is
known under the conditions prevailing in one area, could
establish itself under the conditions existing in an area that is
as yet free from it.

The formula could also be employed in estimating the
probable date when a generation of an insect, whose date of
oviposition is known, will appear on the wing, or in estimating
the probable date of oviposition, and thus the date of arrival
into an area, of a generation whose initial date of appearance
on the wing has been noted.

No pretence of absolute accuracy, however, can be claimed
for it, since the rate of development of any life-cycle stage is
influenced by other factors in addition to temperature. The
theory may be used with a fair degree of safety if the insect
concerned is in its native locality and if the temperatures at
which its stages are developing do not lie outside a range of
5° C. on either side of the optimum effective temperature.
Outside this range, such factors as abnormal humidity, precipita-
tion, air currents, temperature variation, variations in vitality
of individuals or of successive generations, and so forth, will
affect the conclusions.

The relationship between temperature and the phenomena
of hibernation and aestivation remains to be discussed.

The ability of some insects, especially Lepidopterous larva
and pupae, to withstand low temperatures is well known, and
it has been suggested that this ability may be associated to
some extent with the habit of periodical hibernation indulged
in by insects of temperate zones. If the insect before hiberna-
tion or aestivation loses 30 per cent, of its gross weight by loss of
water, as Tower asserts is the case with the Colorado Potato
Beetle (Leptinotarsa decemlineata) , its tissues can possibly with-
stand more severe extremes of temperature than if the proto-
plasm were not thus condensed. It may be noted that hiberna-
tion is apparently lacking from the life -cycle of tropical insects
or the life-cycle of insects which are able to propagate wherever
favourable conditions exist.

Temperature, however, is not the only factor conducive to

204 THE PRINCIPLES OF APPLIED ZOOLOGY

hibernation. Many species commence to hibernate before any
marked fall in temperature occurs. Tropical insects and non-
hibernating insects cannot be induced to hibernate by applica-
tion of low temperatures ; they become torpid, it is true, but
they regain their activity when the temperature is raised.
Tower was able to keep the Colorado Potato Beetle in
hibernation for eighteen months at a high temperature, if the
atmosphere were sufficiently dry. A similar effect of drought
has been shown to occur in autumn broods of the Hessian Ely
(Mayetiela destructor). Such facts, namely, that extreme
drought and extreme cold conduce towards hibernation cer-
tainly support the possibility of this phenomenon being prefaced
by a reduction of body fluid in the insect.

Rouband, the French biologist, discussing the questions of
hibernation, and retardation of the life-cycle, among Muscid
flies, postulates two causes for such retardation : —

(1) Low temperature (athermobiosis) or low humidity
(anhydrobiosis), which, in one physiological group, the homo-
dynamic flies, exemplified by Musca domestica and Stomoxys
calcitrans, influence all the generations of the year ; that is to
say, homodynamic flies can produce a rapid succession of
generations throughout the year if conditions of temperature
and humidity be suitable ; should these conditions be unsuitable,
the flies remain dormant until conditions improve.

(2) Uraemic intoxication (asthenobiosis), occasioned by a
progressive inability, increasing from generation to generation,
for the Malpighian tubules to eliminate the uric excretory
products, so that these accumulate in the adipose tissue. At
the end of a number of generations which can be retarded or
accelerated by temperature or humidity, this degree of intoxica-
tion eventually reaches a point at which further development
of the animal is inhibited. Only prolonged exposure of the
organism to low temperature or to low humidity will, by reduc-
ing metabolism to a minimum, permit this accumulation of
waste products to be transferred to the Malpighian tubules
and so eliminated, in which case development recommences.
Ursemic intoxication characterises, according to Rouband, a
physiological group of flies which he terms heterodynamic.

That is to say, in probably very many insects whose meta-
bolic activity is intense, hibernation or aestivation results from
metabolic exhaustion brought on by an exaggerated accumula-
tion of urates in the tissues. The prolonged exposure to cold, of
hibernating insects, or to drought, of sestivating insects, reduces
metabolic activity to a low ebb and enables the tissues to
recuperate.

CHAPTER XVII

INSECT PESTS : The Distribution

The numerical abundance and potential economic status of an
insect species in any particular area are dependent upon three
factors, namely, the influence of climate upon the number
and duration of generations, the availability of suitable food
media and oviposition media, and the rate of mortality from
climate, diseases, parasites, and predators. The likelihood of any
extension of its area of distribution depends upon the intensity
of these factors, upon its powers of transportation, and upon
the existence of indirect agents of transportation. Its ability
to establish itself in a new area depends again upon questions
of climate, food, and enemies.

The inherent power of an organism to reproduce and survive,
that is, to increase in numbers, is defined by the American
entomologist, Chapman, as the biotic potential. In speaking
of biotic potential, however, distinction must be made between
reproductive potential and survival potential. Reproductive
potential may be defined as the potential number of progeny
in one season, starting with one pair of insects, and assuming
that there was no prematuration mortality whatever ; thus,
in the case of the house-fly, Musca domestica, assuming an
equal number of males and females, the sex ratio is 0-5 ; the
number of eggs per female is 120 ; the number of generations
per year under optimum conditions of physical environment
is, let us say, seven ; then the reproductive potential or number
of flies produced during the season is pzn, where p is the number
of flies at the beginning of the season, and z is the product of
the sex ratio and the number of eggs per female, and n is the
number of generations. That is to say, starting with one male
and female fly, pzn = {2 x 60)7 = 5,598,860,000,000 flies at the end
of the season.

Survival potential may be defined as the actual number of
descendants that survive at the end of a season ; that is to say,
it represents the reproductive potential minus the resistance
of the environment. Thus, in an environment in which all the
ecological factors were at the optimum, the survival potential
would approximate in value to the reproductive potential ;

205

206 THE PRINCIPLES OF APPLIED ZOOLOGY

in an environment in which all conditions were near the limit
of toleration, the survival potential would be very much lower
in value than the reproductive potential.

The fact that climatic conditions exercise some kind of
control over the prevalence of insects has always been realised,
but the manner of the occurrence of insect infestation and its
relation to climatic conditions have never been clearly under-
stood and have not until recently been investigated. Confusion
has arisen because, although many records of climatic
phenomena associated with seasonal variation in the appearance
of insects have been made, they have not been based upon
sufficiently accurate and authenticated observations.

One great difficulty in the interpretation of such facts as have
been recorded arises from the physical inability of the few isolated
investigators who have studied the subject to cover more than a
small portion of the field of climatic phenomena, and the tendency,
therefore, for such investigators to ascribe to a single factor the
credit for predominant influence upon insect life. Thus the
establishment of a single climatic factor as a standard that will
express the exact measure of meteorological influence over the
animal has been attempted by many writers, and among others the
following factors have been put forward: Mean Daily Tempera-
ture above 6° C. ; Total Temperatures ; Minimum Temperature ;
Atmospheric Moisture ; Relative Humidity ; Saturation Deficit.

So far back as 1894, Merriam postulated that in North
America : —

(1) Animals and plants are restricted in northward dis-
tribution by the total quantity of heat, that is to say, the sum-
total of mean daily temperatures above 43° F. during the season
of growth and reproduction.

(2) Animals and plants are restricted in southward distri-
bution by the mean temperature of a brief period during the
hottest part of the year.

The attraction to an investigator of this idea of a standard
will be understood when it is realised that if the occurrence
of the insect pest could be attributed, say, to a certain total
temperature during the growing season, the whole art of insect
control could be reduced to a mathematical calculation, for
it would not be difficult to ascertain under given conditions
the time of the year that general infestation would commence,
and preventive measures could be taken accordingly.

Howard, for example, has endeavoured to show how the
range of the Yellow Fever Mosquito ( Aedes azgypti) is deter-
mined by temperature, and how the exact limitations of the

INSECT PESTS: THE DISTRIBUTION 207

regions in which this mosquito, if accidentally introduced, might
be expected to become established, can be determined by
calculating the accumulated daily mean temperatures.

Improved experimental methods, however, have indicated
that in the case of many insects, probably in the great majority,
the animal is influenced to a great extent by several factors
acting together, so that even if it be granted that one particular
factor may be more influential than the others, it is still not
possible to accept any of the standards suggested, since they
do not express completely the influence of a sum -total of factors.
In searching for a convenient standard to indicate this complex
of factors, Shelford and others have advocated the adoption
of what is termed the Evaporative Power of Air, that is to say
the total effect of air temperature, relative humidity, average
wind velocity, air pressure, upon a free water surface in the
shade or sun, as expressed in the amount of water evaporated.
Such a standard would be convenient, since it is capable of
precise measurement by an instrument termed an atmometer,
which measures the number of cubic centimetres of water
evaporated from a surface per hour.

The mode of operation of this complex of factors upon the
metabolism would seem, according to Shelford, to be somewhat
as follows : —

The body temperature of an animal, whether a " warm-
blooded " or a " cold-blooded " animal, is nearly always higher
during activity than the temperature of the surrounding
medium. A moist, cold atmosphere (very low evaporation)
will, owing to rapid conduction of heat, decrease the body
temperature and decrease metabolism in a cold-blooded animal
and increase metabolism in the case of a warm-blooded animal
within the limits of its capacity for heat regulation. Such a
heat loss is less pronounced in a dry, cold atmosphere owing
to less rapid conduction of heat. In a dry, warm atmosphere
(high evaporation) the rapid rate of evaporation keeps down
the peripheral temperature of the animal, prevents excessive
metabolism and too rapid rise of temperature, which would
be fatal to a cold-blooded animal ; in a warm-blooded animal
the high evaporation permits regulation of the body temperature
and so saves the animal from heat-stroke and death. In a moist,
warm atmosphere, heat-stroke and death occur readily, owing
to lack of evaporation and lack of peripheral cooling, in the
case of warm-blooded animals, even if the surrounding tempera-
ture is only normal or subnormal.

Wind movement increases evaporation and encourages

208 THE PRINCIPLES OF APPLIED ZOOLOGY

radiation of body heat. The animal's body is thus cooled, and,
within limits, metabolism is increased in warm-blooded animals
and decreased in cold-blooded ones.

In studying the limitation of insects by climatic conditions,
Hopkins has suggested, for the United States at any rate,
the use of what he terms the Bioclimatic Law. That is to
say, according to Hopkins, if the date of a periodical event,
such as, for example, the date of emergence of the first Hessian
Fly brood of the year, be established for one particular locality,
then a corresponding date for the same phenomenon in another
district can be determined by calculating a variation which is
at the rate of four days for each degree of latitude, five degrees
of longitude, and 400 ft. of altitude. There may be slight errors
in this computation, due to topographical differences, soil con-
ditions, and weather variations, but the amount of such error
is in direct proportion to the intensity of the controlling in-
fluences, which can be measured, therefore, in terms of days,
or the equivalent in degrees of latitude or feet of altitude
with the computed date as a constant. In a similar way the
geographical limits of an insect might be computed.

The Southern Pine Beetle (Dendroctonus frontalis) of the
United States, for example, has two complete generations a
year in the northern and highest limits of its range, but in more
southerly areas may have five or more generations, the broods
overlapping from late spring to early autumn. Remedial
measures, consisting, generally speaking, of removal and
destruction of infested bark, should be undertaken during the
period when all stages of the beetle are to be found in the tree
that is to say during the period between the end of autumn
and the commencement of spring. This period varies accord-
ing to latitude and altitude, commencing in September in the
north and higher altitudes, and in December in the south
towards sea-level, ending about the middle of May in the north,
about the end of February in the south. The period of control
possibility can, in fact, be calculated quite accurately from
climatological data, and Hopkins would seem to have founded
his generalisation upon data derived chiefly from observation
of this type of insect. Whether the Bioclimatic Law is of
general application to other types of insects and to other
countries remains to be settled.

In the United States this principle is used to determine
the dates of sowing wheat in areas infested by the Hessian Fly
(Mayetiola destructor). The general method of avoiding Hessian
Fly damage in the winter wheat regions is late sowing in the

INSECT PESTS: THE DISTRIBUTION 209

autumn. The autumn brood of flies appears and disappears
within about a week, so that if the date of emergence, being
controlled primarily by climatic conditions, and secondarily
by weather, soil, and topographical influences, can be calculated,
a " fly-free " date for the sowing of wheat can be recommended
for any particular district.

It may be added that the Bioclimatic Law holds very closely
for the eastern climatic provinces of North America, but breaks
down at the Rocky Mountains and does not account for con-
ditions on the Pacific Coast. The climatological basis of the
generalisation is, of course, the distinction between a continental
climate where temperatures rise rapidly in spring and fall
rapidly in the autumn because of the low specific heat of soil,
and a marine or seacoast climate where the higher atmospheric
humidity retards the rise of spring temperatures and the fall
of autumn temperatures.

The ability of an insect to increase its area of distribution
depends upon food and oviposition facilities and upon its powers
of locomotion. Even an insect of feeble locomotor powers
and of restricted food habits may increase its area of distribution
fairly rapidly if its food resources occur in large, contiguous
blocks, such as happens under conditions of large scale agri-
culture and horticulture.

In the great majority of insects, probably, the rate of area
increase depends upon the degree of contiguity of food plants.
Insects which are restricted in food habit to one particular genus
or species or even family of food plants will be at a disadvantage,
therefore, in this respect as compared with insects which have
a wide range of food plants, unless favoured by the agricultural
or horticultural practice of growing large blocks of the one kind
of plant in close proximity. Similarly, an insect with sedentary
or semi-sedentary habits such as a borer or a leaf miner or
a gallicole, will not increase its area so rapidly as will a foliage
feeder, unless favoured by the possession of a migratory phase
in its life-cycle, or by possession of an active, non-trophic
imaginal stage.

That such migratory phases do occur and that such phases
may be aided by air currents is a well-observed fact, especially in
the case of semi-sedentary insects such as Aphididce and Coccidce.

Lepidoptera are known to be carried upwards by con-
vectional air currents over heated areas and to drift in swarms
on prevailing winds.

The Monarch Butterfly (Anosia plexippus), for example,
has extended its range widely over the islands of the Pacific

14

210 THE PRINCIPLES OF APPLIED ZOOLOGY

Ocean during the last fifty years, largely through the agency
of winds.

The island of Krakatau, between Java and Sumatra,
twelve miles from any other land, was completely sterilised
of all life by a volcanic outburst in 1883 that covered the whole
island with pumice and ash to a depth of 100-200 ft. Yet in
1921 an insect fauna of over 400 species was collected.

The most important example, however, of an extension of
area by migration is afforded by migratory locusts. In the
case of these insects, the general opinion has been that there is
in each case a regular breeding ground in regions remote from
the cultivated areas which are periodically ravaged by locust
swarms. In this remote breeding ground they exist in numbers
insufficient to constitute a danger to vegetation, and only during
periods of abnormal rate of breeding do they mass in swarms and
migrate in search of more favourable feeding grounds.

Recent work by Russian entomologists has somewhat
modified this view. The migratory locust of South Europe,
Locusta migratoria, is now to be regarded as a swarm phase of
a form, Locusta danica, formerly regarded as a separate species,
which is a non -migratory form. Apparently both forms can
be bred from the same egg mass, laid by a single female, and
can be changed one into another by altering the conditions
of breeding. Similar evidence, brought forward by Faure,
has shown that Locustana pardalina in South Africa also
possesses two phases, and that the solitary or non-migratory
phase which mingles with the swarms of migratory locusts is
also the locust which occurs on the veldt singly and in small
loose swarms during the off season of the non-migratory phase.
Similar evidence has been brought forward by Johnston for the
migratory locust of the Sudan, Schistocerca gregaria, which he
shows to be a swarm phase of the non-migratory form, Schisto-
cerca peregrina.

The correctness, therefore, of the Phase Theory of locust
migration put forward by the Russian, Uvarov, can hardly be
doubted. According to this view, migratory locusts are swarm
phases of solitary or non-swarming forms already existing in
the area subject to ravage. The reasons for this periodical
appearance of the swarm phase, beyond that it depends upon
some acceleration of the breeding rate, are as yet far from clear.

An interesting suggestion, put forward by Nikolski, from
observation of Locusta migrator ia in Turkestan, is that swarming
takes place between separate permanent breeding grounds, or
between a present-day breeding ground and an area which

INSECT PESTS: THE DISTRIBUTION 211

was formerly a breeding ground but is now unsuitable owing to
cultivation. In the latter event, since no adequate return
migration occurs, owing to restriction of breeding, the numerical
abundance in the true breeding area will be severely checked
and the periods between the production of swarm phases will
become gradually longer.

Another instance of mass migration is afforded by the case
of the so-called Army Worms or Processionary Caterpillars.

The true Army Worm is a North American caterpillar of a
Noctuid moth (Cirphis unipuncta). In ordinary years the
caterpillars feed on wild, succulent grasses, and occur in low-
lying situations where such food plants occur. In some years,
however, caterpillars appear in enormous abundance, owing
probably to some interference with the ordinary mortality
factors, and they migrate in enormous numbers to the cultivated
crops, especially to cereal crops.

Thaumatopcea processioned, the European Processionary
Moth, is a moth belonging to the family Eupterotidse, and its
caterpillars march in columns, each being headed by a leader,
the column becoming gradually broader behind.

Restriction of Spread. — The measures which can be taken
by the entomologist to restrict the spread of insects are too
varied and cover too wide a range to be described in detail
here. It may be said, however, that restrictive measures
fall roughly into the following groups : —

(1) Destruction of diseased and infected material.

(2) Collection of the insects themselves.

(3) Isolation of infested areas.

(4) Selection of pest-free seeds, plants, or stock.

(5) Rotation of crops.

(6) Disinfection of infested areas, crops, and stock.

The accidental introduction of a dangerous insect or a potential
pest into a new area through the agency of man is a contingency
much more important from the standpoint of the entomologist
than the powers of migration which the pest may itself possess.

In its indigenous habitat, an insect may be aided by agri-
cultural conditions to a degree sufficient to enable it to rank
as a minor pest, capable of steady endemic damage, but it will
rarely be able to increase its numerical abundance to such an
extent as to provoke an epidemic outbreak, owing to the presence
of a steady degree of mortality from various factors. In a
fresh area, however, many of such mortality factors may be
absent, and the insect will be capable of increase and epidemic
damage to an extent not previously possible.

212 THE PRINCIPLES OF APPLIED ZOOLOGY

One of the most important ways, therefore, of limiting the
spread of insect pests is by the enactment of legal measures.
It must be clearly understood that the popular impression that
the object of legislation against insect pests is necessarily to
exterminate them is erroneous. To annihilate an insect pest is
rarely possible.

Where the insect is in the " Second Class Pest ' stage it
may be possible to exterminate it ; where it is a " First Class
Pest " it is only possible to control it.

The meaning and function of legislative control of insect
pests is thus : —

(a) To prevent the introduction and establishment of new
pests from other countries.

(b) To prevent the further increase or spread of pests already
established in the country itself.

Such legislation may be considered, therefore, as external and
internal legislation. External legislation will include statutory
orders against pests liable to be imported. Internal legislation
will cover domestic enactments against established or newly
introduced pests within the country.

Generally speaking, all countries which grow crops liable to
heavy infestation by particular insect pests have either specific
or general restriction orders against the importation of such
pests. The importation of plants and plant products is usually
only permissible when accompanied by a foreign inspection certi-
ficate, or after subjection to sterilisation at the port of entry.

An ideal system of legislative protection against the possible
importation of insect pests should provide for : —

(1) Inspection of the crops of the importing country when
growing. The official entomologists of the importing country
should have full information on this point.

(2) Certification as to freedom from pest of all plant ship-
ments, carried out by competent entomologists at the port of
departure.

(3) Fumigation certificates issued at the port of departure.

(4) Inspection of shipments at the port of arrival.

(5) Fumigation on arrival.

(6) Quarantine of certain plants.

(7) Prohibition of entry.

In actual practice the most effective system is that of
inspection on arrival, carried out by a fully competent staff in
a well-organised plant inspection station ; the inspection
should be supplemented by certificates of inspection or fumiga-
tion issued at the port of departure and by quarantine measures.

CHAPTER XVIII

INSECT PESTS : The Behaviour

One of the most promising fields of entomological inquiry, from
the economic standpoint, is that phase of insect physiology
which deals with the reaction of the insect to the various
stimuli of its environment, the likes and dislikes of the animal
when subjected to sensations affecting its senses of sight,
smell, touch, hearing, and so on. The general way in which
an insect responds to such stimulus may be termed a tropism,
a term borrowed from the botanist, or, better still, a sense-
reaction. Of such tropisms, the more important are thermo-
tropism (response to temperature), phototropism (to light),
geotropism (to gravity), stereotropism or thigmatotropism (to
contact), rheotropism (to currents of air or water), and chemo-
tropism (to chemical substances).

Such tropisms may be positive or negative ; the insect may
be attracted or repelled. Many nocturnal Lepidoptera, for
example, are positively photropic to a source of intense light
such as an electric arc, but are negatively phototropic to day-
light. Many insects are positive to the less refractive colours
of the spectrum, to yellow and green. Soil insects are generally
negatively photropic.

Response to light determines the choice of location of many
insects, forces some to live in full light, others in darkness ;
some have to seek food by day, others by night.

Positive stereotropism is shown in the gregarious habits of
many insects, and in the tendency of soil insects to insert
themselves into crevices, into soil, or under stones, to have
their bodies in contact with something solid.

Positive rheotropism is seen in the behaviour of many
insects which float upon or glide upon a water surface, or in the
air, with their bodies head on to the prevailing current. The
Rocky Mountain Locust (Melanoplus spretus), for example,
flies with the wind in a light breeze ; it is negatively rheotropic ;
if the velocity of the wind increases, the insects act positively ;
they fly against the wind.

Application of these various tropisms to the question of

213

214 THE PRINCIPLES OF APPLIED ZOOLOGY

insect control has been made from time immemorial, though
of course in quite empirical fashion. The majority of insect
control methods depend in fact for success upon the utilisation
of this principle of tropic response, and the failure in the field
of methods which are of proved merit in the laboratory is often
due to some tropism factor overlooked in the small scale
experiments.

Upon the response of insects to temperature are based the
various methods of high temperature and low temperature
sterilisation. Response to temperature and humidity influences
very largely the distribution and migration of insect species.
Moisture, whether in soil or in stored products, may be of the
utmost importance in a scheme of control. Thus, for example,
air-tight storage of grain and flour against grain pests, depend-
ing as it does upon the liberation of carbon dioxide produced
both by grain and insect, is most effective when the moisture
content of the stored product is greater than 17 per cent. On
the other hand, air-tight storage, though fatal to Acarid pests of
grain or flour, is not fatal to their eggs unless the moisture content
is below 11 per cent., so that freedom from Acarid infestation
is best secured by keeping the moisture content of grain and
flour below 11 per cent. In a climatically temperate country
such as Great Britain, the usual percentage is between 12-5 and
14, so that flour intended for long storage ought to undergo
some drying process.

Phototropism is the basis for many ingenious light traps,
ranging from the simple lantern set in a tray of kerosene to the
elaborate electric installations used in the French vineyards
of Champagne for catching and destroying vine moths (Clysia
and Sparganothis).

Stereotropism, again, is the basis of most traps — the belt
round fruit trees, the use of flat stones and boards, for example.

Chemotropism is one of the most important tropisms of all,
since upon it depends the attraction of an insect to its food
medium, to its mate, and to its oviposition medium.

Insect Food Habits. — From what we know of the feeding
habits of primitive orders of insects, for example the Orthroptera
and Isoptera, it would seem that the ancestral type of insect
was an indiscriminate feeder, attacking impartially any type
of plant ; that is to say, it was polyphagous.

The liability of the plant, however, to be attacked by any
species of insect would become discounted by the evolution
of resistance factors, such as would tend to discourage a certain
number of insect species. The plant would become resistant

INSECT PESTS: THE BEHAVIOUR 215

to insect attack. Such resistance in plants is well known.
It may be of a general nature, a resistance to insects in general,
as in the case of ivy or yew ; or it may be partial, that is to say,
the plant although attacked by a considerable number of insect
species has established a state of equilibrium, the degree of
insect attack being rarely sufficiently intense to cause serious
injury. Such partial resistance is shown by most wild plants
to indigenous insects. Or again, the plant or animal may be
resistant to one particular kind of insect.

Thus the Northern Spy and Majetin varieties of apple are
almost immune to the well-known apple pest, Woolly Aphis
(Eriosotna lanigera). The American species of grape vine
(Euvitis) are highly resistant to the attacks of Phylloxera,
the vine aphis. The Chinese pear is resistant to San Jose Scale.
Wild plants and animals are invariably less susceptible to the
attacks of local insects than are domesticated or introduced
varieties.

The variations which enable a plant to resist insect attack
fall into two categories : —

(1) Physico-chemical : thickness of cuticle, of seed coat,
presence of hairs, of alkaloids, essential oils, acids, gums, etc.

(2) Physiological : vigour, precocity, quick recovery from
wounds, seasonal adaptation, absence of response to specific
stimuli, etc. Such factors are often weakened by cultivation
of a plant, so that the cultivated plant is usually more sus-
ceptible to insect attack than is its wild ancestor. Such a plant
as the cultivated apple is notoriously susceptible to insect
attack, whereas the crab apple is rarely severely injured.

It is, of course, very unlikely that any plant can develop
resistance factors sufficiently powerful to keep all insects at
bay. Even the most poisonous and noxious plants serve
generally as hosts to at least one or two species of insect. The
plant will have achieved a sufficient measure of success if the
number of its insect guests becomes limited.

Now the effect on a polyphagous type of insect of a
gradual evolution of resistance factors among its customary
food plants will be a restriction of its range of food plants,
for the insect will either have to confine itself to plants whose
resistance factors are not sufficiently repellent, or it will have to
adapt itself so completely to the resistance factors of one plant
or type of plant that it becomes incapable of normal develop-
ment upon plants where such factors are lacking.

It is, of course, well known that many insects with a wide
range of food plants show marked avoidance of certain plants ;

216 THE PRINCIPLES OF APPLIED ZOOLOGY

the field entomologist would say that they showed a preference
for certain plants, a statement that very often conceals the real
physiological significance of the habit. The San Jose Scale
(Aspidiotus perniciosus), for example, a notoriously wide-
spread feeder, attacks all fruit trees except chestnut, fig, cherry,
and vine ; it readily attacks poplar, hawthorn, beech, Eibes,
Salix, lime elm, acacia, but avoids cedar, hazel, magnolia,
plane, oak, and holly.

The Gipsy Moth (Porthetria dispar), again, is generally
considered to be an indiscriminate feeder on tree foliage,
but investigations would seem to indicate that even this
notorious pest is restricted in habits and that its food plants
may be divided into : —

(a) A group of plants particularly favoured, including
apple, mountain ash, poplar, willow, and hazel.

(b) A group suitable only to older caterpillars, including
chestnut, most pines and spruces.

(c) A group on which only a few caterpillars can develop,
including varieties of elm, hickory, hornbeam, maple, pear, and
cherry.

(d) A group avoided by the moth, including arbor vitse,
arrow wood, species of ash, cedar, red currant, cypress, grape
vine, poison ivy, holly, sycamore, tulip tree, viburnum, walnut,
honeysuckle, blackberry, raspberry, sarsaparilla, mulberry,
juniper, and some varieties of pine.

The second way in which a primitively polyphagous insect
may become dietetically restricted, namely, by becoming so
adapted to certain resistance factors as to be unable to thrive
in their absence, is exemplified by the numerous cases of species,
genera, or even whole families of insects which feed only upon
the members of certain food plant families, or upon plants
which possess similar factors.

Thus the larvae of the common butterflies, Pieris brassicce
and Pieris rapce, feed for choice upon plants containing a
particular glucoside, one of the mustard oils, but can be induced
to feed upon leaves of other plants which have been smeared
with a paste containing this substance.

The extreme type of specific food habit, restriction to one
particular genus or species of food plant, may be exemplified
by the Cotton Boll Weevil ( Anthonomus grandis), which is
restricted to the cotton plant ; and by Coccus fagi, a Coccid
which is never found upon any other plant but beech, and is
even extremely rare on the copper variety of this plant.

The gulf between the indiscriminate type of feeder such as

INSECT PESTS: THE BEHAVIOUR 217

the locust and such a specialised feeder as the Beech Coccus,
is bridged by several stages that afford evidence as to the way
one type may have evolved from the other.

Thus, for example, there is the case of the specialised feeder
retaining to some extent the primitive polyphagous habit,
a case illustrated by the aphid family. Most aphid species
show migration from summer to winter host plants. The
winter host plant is generally single or consists of a few closely
related species, usually woody stemmed plants. The summer
host plants may be numerous and are not necessarily related
botanically, but agree in being herbaceous. The exact physio-
logical reasons for this migration habit are not as yet clear.
Possibly the onset of autumn conditions brings about the
development in the herbaceous plant of physiological changes
inimical or repellent to the aphis ; development of a high degree
of tannin, for example. In a semi-tropical climate, aphids
may remain breeding and feeding on herbaceous plants all
the year round, whereas in a temperate climate the same species
of aphis shows migration in autumn from herbaceous to woody
plants.

Aphis prunifolice, for example, in the Southern United States
remains on grasses and cereals all the year round, whilst in the
Northern States it spends the winter on apples.

It may be suggested that the winter host plant represents
the type of plant to which the aphis is becoming restricted,
and that the spring migration to herbaceous plants is a survival
of the old polyphagous instinct. Now, suppose that when the
aphid species migrates from summer host to winter host, some
individuals to whom apparently the resistance factors of the
summer plant, developing towards autumn, are not sufficiently
repellent, remain behind ; and likewise when the return migration
occurs in the spring, individuals remain upon the winter plant.
Such a habit has become established, for example, in the
aphid genus Chermes, where we find : —

(a) Colonies which spend their whole existence on larch.

(b) Colonies which spend their whole existence on spruce.

(c) Forms which migrate from larch colony to spruce colony.

(d) Forms which migrate from spruce colony to larch
colony.

That is to say, the cross migration habit has become partially
suppressed in Chermes.

A complete or nearly complete suppression of the cross
migration habit, arising after definite alternation of hosts has
become established, would bring about the occurrence of distinct

218 THE PRINCIPLES OF APPLIED ZOOLOGY

biological races of one species ; one race confined to one type
of food plant, the other confined to another type of food plant.
Instances of such biological races are numerous. They may
be morphologically identical, but usually slight differences in
appearance between the two races arise. Thus in Canada the
biological race of the Apple Maggot ( Rhagoletis pomonella) that
infests huckleberries is below the normal size ; the normal apple -
bred race will not lay eggs upon the huckleberry, nor will the
huckleberry race oviposit upon apple.

The test of a biological race is, of course, the possibility of
changing race A into race B by subjecting A to the environ-
mental conditions of B ; such a test established the fact that
the migratory locust Locusta migratoria is a biological race of
Locusta danica, despite the colour differences. Again, biological
races, unless varying greatly in size, should be fertile inter se.
Thus the two forms of louse, Pediculus, which attack man,
although formerly looked upon as extraordinarily closely related
species, P. humanus and P. capitis, were shown by Bacot to
be fertile inter se and thus shown to be biological races, a con-
clusion supported by the success of Sikora in obtaining the
morphological peculiarities of P. humanus in individuals of
P. capitis reared on the body.

Possibly many parallel instances occur, particularly in the
more recently evolved insect families, such as the Tachinidse
and among the Acalyptrate Muscidae ; and many forms now
claimed as distinct species may, in the light of fuller knowledge,
prove to be biological races.

The border line between the biological race and the true
specific feeder is thus often — very often — vaguely demarcated,
and probably all such specific feeders, though now distinct
morphologically and biologically, have passed through a
biological race stage.

Of course, such biological races need not always have arisen
from forms like Chermes that show cross migration between
different hosts. Biological races could quite well arise from
a form that, having become restricted to a few plant orders,
became divided into biological groups, each adapted to a single
order, as in the case of the Australian species groups of Dacus.
Within each group, again, biological differentiation of forms
adapted to particular plant species could arise.

Chemical Control of Insects. — The subject of chemical
control is based upon the question of insect responses to stimuli,
and therefore requires to be mentioned. The subject, however,
is so vast that little more than the guiding principles can be

INSECT PESTS: THE BEHAVIOUR 219

discussed here. It may be said that insecticides fall into the
following groups : —

(1) Stomach Poisons. — These may be defined as toxic sub-
stances which can be applied to the surface of the food medium
and thus introduced into the insect via the alimentary canal.
They are therefore applicable only to mandibulate insects
and are useless against suctorial insects. The range of sub-
stances which can be used is wide, but the majority of stomach
poisons belong to one of the following groups : —

Arsenical Compounds, particularly the ortho-arsenates of
lead, calcium, iron, copper, and sodium, and the arsenites of
copper, calcium, and sodium, all of which, except the sodium
compounds, are comparatively insoluble and stable in water
and so are not likely to injure the plant ; the sodium salts
being soluble, cannot be used upon foliage, but are valuable
as a basis of preparation for the others.

Copper Compounds, particularly the basic sulphates, the
double sulphates of copper and calcium, and the double hydrates
of copper and calcium, in the form of Bordeaux mixture, obtained
by precipitation of a solution of copper sulphate with an equal
weight of lime.

Alkaloids, such as nicotine, quassiin, hellebore, and derris.

Stomach poisons are applied either as a suspension in water,
or as a dust, diluted with talc, limestone, china clay, or similar
substances. Stomach poisons, therefore, should be in a very
fine state of division and should be used in conjunction with a
slight percentage of soap, size, resin, saponin, sodium silicate,
or similar substances, to induce the wash to adhere to the plant.

(2) Contact Poisons. — These may be defined as toxic
substances which affect the insect by blocking up the spiracles,
by penetrating the chitinous lining of the tracheal tubes, or
by actually penetrating the external body chitin. The most
successful contact poisons are substances of low volatility
such as certain paraffin compounds, but poly sulphides, partic-
ularly those of calcium (lime-sulphur), act as successful contact
poisons owing to their strong affinity for oxygen restricting the
supply for the insect and so killing it. Paraffin compounds
are usually applied in the form of an emulsion in soap solution,
or in colloidal aqueous solutions of iron hydroxide, basic sul-
phates of iron and copper, soluble silica, zinc sulphide or gelatine.

(3) Fumigants. — These are gaseous insecticides with which
the atmosphere of an enclosed space such as a greenhouse,
a tent enclosing a tree, or the hold of a ship, can be diluted or
saturated.

220 THE PRINCIPLES OF APPLIED ZOOLOGY

There is no known chemical vapour which possesses the ideal
combination of high toxicity to insects and low toxicity to plants
or vertebrate animals, and in practice only two are known to
come anywhere near the ideal ; these two are hydrocyanic acid
gas and sulphur dioxide, and these two gases are the two fumi-
gants most generally employed. The former gas is used
particularly for tent fumigation of fruit trees against scale
insects, for greenhouses against a variety of pests, for ships,
dwelling-houses, mills, warehouses, etc., where no plants are
present. The latter gas is used chiefly as a fumigant for
dwelling-houses and ships. It cannot be used where plants
are concerned.

Nicotine has a certain limited use as a greenhouse fumigant
in Great Britain ; formaldehyde and carbon bisulphide are used
occasionally for dwelling-houses, but are in greater demand
as sterilisation agents ; carbon dioxide and carbon monoxide
are employed in certain ship fumigation processes ; such
substances as chloropicrin, cresol, nitrobenzene, dichlorobenzene,
and the chlorine derivatives of methane, ethane, and ethylene,
though full of promise, cannot be said to have got beyond the
experimental stage.

(4) Insectifuges. — The range of substances which repel
insects is wide, but their practical use is limited. A good
repellent will not merely mask the attraction of a plant or
animal for an insect, as do many of the deterrents recommended
against mosquitoes, sheep maggot flies, onion flies, and so on,
but should cause the insect intense sensory annoyance, should
be pungent, or should be viscous enough to clog its spiracles
or its mouth parts.

In practice this result is generally obtained by using pungent
oils, but since such oils are always more or less volatile, the
majority of repellents in common use are not completely
successful. Repellents intended for application to animals
differ somewhat from those intended to protect plants, but
both kinds agree in having to be cheap, non-injurious to plant
or animal, moderately volatile, and oily or pungent.

The most satisfactory repellents for use on animals are
castor oil, crude petroleum, and fish oil, generally in the form of
a soap emulsion. Certain essential oils — aniseed, laurel,
citronella, camphor — are markedly repellent to insects but are
evanescent. The consequent necessity for frequent reapplica-
tion somewhat debars their employment upon cattle, but is
not such a drawback to their use as culicifuges (anti-mosquito),
and they are usually so utilised.

INSECT PESTS: THE BEHAVIOUR 221

Repellents for the protection of plants consist frequently
of crude oils or coal tar products mixed with sand or chalk
and applied to the base of the plant.

(5) Dipping Fluids. — Insecticides applied to animals for the
purpose of mitigating or preventing the attacks of blood-
sucking and disease-producing ectoparasites may be in the
form of hand dressings, or powders, or liquid dips.

Hand dressings are ointments of fat or Stockholm Tar
containing arsenious sulphide, free sulphur, cresols, pyridine,
nicotine, mercury, and paraffin compounds. They are usually
difficult to apply, necessitate shaving the hair from the affected
area, and are somewhat uncertain in their action. They have
been superseded almost entirely by liquid dipping preparations.

Powders are used for domesticated birds chiefly, and consist
of a small percentage of cresol, sulphur or sodium fluoride
diluted with plaster of Paris or slaked lime.

Dipping fluids are of three types : —

(a) Arsenical dips, that is to say 0-1 or 0-2 per cent, solutions
of sodium arsenite ; they are used chiefly against ticks on cattle.

(6) Carbolic dips, usually mixtures of phenols and cresols,
or of pyridine and its bases, or containing coal tar creosote.

(c) Sulphur dips, that is to say dipping fluids whose chief
ingredient is a combination of sulphur and alkali, or sulphur
and nicotine.

The last two classes of dipping fluids are extensively used
against scab diseases of sheep.

It must be added in conclusion, that the old view which
selected insecticides from substances known to be toxic to
higher animals, and which regarded cost, killing power, and ease
of manipulation as the chief qualities required in an insecticide,
is gradually giving way to the more scientific conception of
an insecticide as a substance not necessarily toxic to higher
animals, and one in which such factors as spreading power,
wetting and penetrating power, and toxic action as distinguished
from mere toxic effect, are important adjuncts to the commercial
qualities mentioned above.

CHAPTER XIX

INSECT PESTS : The Mortality Factors

The various factors of mortality which normally prevent an
insect species from increasing to an extent which might give it
the status of a pest are, apart from climatic factors, those of
disease, of animal parasites, and of animal predators.

The bacterial flora of insects is scarcely surpassed in rich-
ness and variety by that of vertebrate animals. The most
commonly occurring pathological consequence of bacterial
action upon insects, however, is septicaemia, and, in fact, the
bacteria of insects never seem to show such a specificity for
the host tissues as is shown by such parasites of man as Meningo-
coccus and Gonococcus. Insects seem also to be immune to
bacteria which are pathogenic to man and higher animals.
Thus larvae of the Bee Moth ( GalJeria melonella) have been shown
to be completely immune to a group of organisms, including the
various agents of tuberculosis, tetanus, diphtheria ; to be less
immune to the organisms of plague, fowl cholera, Asiatic
cholera, typhus, anthrax ; and to be highly susceptible to
Bacillus coli communis, Bacillus pyocyaneus , B. prodigious,
B. subtilis, B. proteus. That is to say, while susceptible
to saprophytic bacteria, these insect larvae are immune to
bacteria which are highly pathogenic to the higher vertebrates.
Whether this immunity is due to active phagocytosis of patho-
genic bacteria, or whether it results from a physico-chemical
modification of the organism brought about by the blood,
and varying in intensity according to the insect individual and
the character of the micro-organism, is not definitely settled.

The possibility of bacterial disease as a factor in insect
control was first noted by D'Herelle in 1911, when he drew
attention to a severe epidemic among the hordes of the Mexican
Locust (Schistocerca pollens) in Yucatan which was associated
with the presence, in the gut of attacked insects, of a cocco-
bacillus, later named Coccobacillus acridiorum.

By passing the bacteria through the bodies of many grass-
hoppers in rapid succession, each insect being inoculated with
a diluted extract from the gut of the preceding host, it is possible

222

INSECT PESTS: THE MORTALITY FACTORS 223

to obtain a strain of bacillus which will kill within three hours
after injection. Such a strain has been shown to be capable
of inducing an artificial epidemic in another area among locusts,
when cultivated and then distributed by spraying, but it must
be admitted that large scale experiments in the propagation
of this locust disease have given somewhat contradictory
results.

Several conditions seem essential if such artificial propaga-
tion is to be successful. The locust concerned should be
migratory and cannibalistic ; infestation should be dense ;
normal food should not be excessively abundant ; weather
conditions should be warm and dry.

Speaking generally, experiments on species of Schistocerca
have been very effective. Against locusts of less cannibalistic
habits, such as Pachytylus migratoroides , the Philippine locust,
Schistocerca paranensis, the Argentine Locust, and Stenobothrus ,
Melanoplus, and Xiphidium, of Canada, the disease seems to
be less successful. Some authorities, in fact, assert that Cocco-
bacillus acridiorum, or the group to which it belongs, is a normal
inhabitant of the locust gut, and therefore, whilst probably
pathogenic when injected into the body cavity, as in
laboratory experiments, cannot be expected to be so when
merely ingested.

A considerable number of fungi are known to bring about
pathological conditions among insects. They may affect the
insect host in various ways : —

(1) They may live on the outer body surface without either
seriously injuring the underlying tissues, or injecting toxic
substances into the system of the host.

(2) They may pierce the chitin and destroy the underlying
tissues.

(3) They may send branching mycelia into the body,
choking up the tracheae, and causing suffocation. In the
case of Botrytis and Cordyceps, the tissues become replaced by
a secretion and a characteristic mummification, the so-called

' Muscardine condition " of the insect, is brought about.

In the lower fungi the Zygomycetes, saprophytic generally
upon decaying organic matter, include two groups, the Mucorales
and the Entomophthorales, which are of particular entomological
importance, the latter group, in fact, being almost exclusively
parasitic on insects. Empusa muscce, for example, belongs to
this latter group, and has long been known as a parasite of
various Muscid and Syrphid flies, appearing under damp
autumnal conditions as a halo -like mould enveloping the fly

224 THE PRINCIPLES OF APPLIED ZOOLOGY

and ramifying throughout its tissues. Infection is probably
via the alimentary canal. An interesting suggestion, albeit
a disputed one, is that Empusa muscce is a biological race of the
saprophytic fungus, Mucor racemosis.

Among the higher fungi the class Ascomycetes includes the
group Laboulbeniales, almost exclusively parasitic upon Cole-
optera, and also many entomoparasitic representatives among
the groups Hypocreales, Sphceriales, and Erysiphales.

Of the various Ascomycete fungi responsible for insect
diseases, the best known genus is probably Cordyceps, better
known in its conidial stage, the so-called Isaria. It is a
fungus which occurs commonly among Lepidopterous larvae
and pupae.

Although fungi do exercise a considerable degree of natural
control over insect abundance, it cannot be said that the
numerous attempts to propagate fungus epidemics artificially
have obtained results which were in proportion to the amount
of ingenuity expended in obtaining them.

Many such attempts have been made, notably, the use
of Sporotrichum globuliferum in Illinois against Chinch bug
during 1888-96 ; the Green Muscardine Fungus, Metarrhizum
anisoplice, against the Sugar Cane Frog-hopper in Trinidad ;
Aschersonia spp. against Citrus White-fly in Florida ; Spicaria
farinosa against Vine Moth pupae in France ; Botrytis bassiana
against Flea-beetles in France ; and so on.

It must be pointed out that such fungi destroy insects in
large numbers only when such numbers are excessive ; it is
doubtful in the extreme whether a fungus can initiate an
epidemic ; it only appears in epidemic form when the insect
outbreak itself is epidemic. Such insect outbreaks are
frequently periodic. Thus in Florida the citrus white-fly
appears in epidemic form every three years, and thus there is
apparently an epidemic of fungus disease every three years.
It seems impossible to create such an epidemic at any time when
it does not appear naturally. Further, during an epidemic of
fungus disease it is very doubtful whether the outbreak can
be intensified by the spraying of spores, or by other distribution
of the fungus disease. Neither does it seem possible to create
an epidemic in countries where the fungus does not occur by
the introduction of it, since there is generally some combination
of factors which inhibits its establishment. On the whole,
therefore, the use of entomogenous fungi as a method of check-
ing insect pests is not warranted by such results as have so far
been obtained.

INSECT PESTS: THE MORTALITY FACTORS 225

The protozoa which may bring about disease in insects
have not been studied to the same extent as have the fungi
and bacteria, but the few that we know most about are
members of the Sporozoa, the predominantly parasitic division
of the phylum.

The earliest known protozoan disease of insects to be in-
vestigated was undoubtedly Pebrine, an epidemic disease of
the Mulberry Silkworm (Bombyx mori) caused by the Neo-
sporidian, Nosema bombycis. The recognition of the small,
ovoid, shining, and motile bodies, in the tissues of infested
caterpillars, as protozoa, is due to the work of Balbiani (1866),
and the life-cycle was worked out by Stempel (1909), although
Pasteur, in 1864, had discovered the method of infection. The
latter observer showed that caterpillars may become infected
in two ways : —

(1) They may ingest leaves contaminated with spore-
containing faeces from infected caterpillars.

(2) The egg may contain dormant spores, so that the
caterpillar is hatched in an infected condition.

The life history of Nosema apis, associated with a disease of
bees, is similar.

It is not beyond possibility that a protozoan causative
organism may yet be established for the so-called polyhedral
diseases or nuclear diseases of caterpillars ; these comprise a
group of infectious diseases referred to under such names as
" grasserie " or " jaundice ' or ' wilt disease," which agree
with one another in the occurrence of polyhedral bodies in the
cell nuclei of the insect victims. In a caterpillar suffering from
this type of disease the tissues degenerate, and a smear will
show in addition to fat globules, urates, cellular debris, hairs
and pigment granules, myriads of bodies varying in size between
one and six microns in diameter, and in shape approximating
to a polyhedron with rounded angles. They seem to be tough
and elastic in nature, rather than brittle as inorganic crystals
would be.

Opinions as to the significance of these bodies vary. It
seems certain that they are not the actual causative organisms,
but are reaction products, possibly of a nucleoprotein nature.
It has been asserted that in the case of grasserie of the Nun
Moth (Liparis mo?iacha), the causative organism resembles the
micro-organisms known as Chlamydozoa, and that the poly-
hedral bodies are a final stage in the life-cycle of the organism,
and an infective stage, since, when a caterpillar dies and decom-
poses, the polyhedral bodies remain upon the leaves. On the

i5

226 THE PRINCIPLES OF APPLIED ZOOLOGY

other hand, Gipsy Moth caterpillars fed upon leaves that have
been soaked for some time in water are said to develop the
symptoms of Wilt Disease.

Parasites and Predators. — It is not easy to draw a definite
line of division between the terms parasite and predator. Both
are organisms which live at the expense of another. The
parasite, however, strictly speaking, obtains its nutriment from
its host in an indirect manner ; the predator supports itself
in a cruder, more direct fashion ; it is the difference between the
thief and the robber.

The parasite may be a sucker of blood or of ccelomic fluid,
or may absorb the fluid products of its host's digestive powers,
but a true parasite does not attack the vital host tissue. It
may live throughout its existence within its host, or may simply
attain full size and quit the host without in either case causing
fatal lesions. Death of the host, when it does occur, is due
rather to exhaustion, to deficiency of those nutritive fluids
abstracted from it by the parasite, or to general metabolic
disturbance resulting from excessive activity of multiplication
of the parasite, rather than a result of definite tissue injury.
The more completely adapted the parasite is to its host, the
longer will be its connection with it, and the less its liability
to injure it. Tolerance of a parasite by a host, therefore, would
seem to imply an interrelationship of long standing ; an
organism that kills its host is, comparatively speaking, a new-
comer to the ranks of parasitism ; it is just as much a predator
as is the organism which lives by violently assaulting and
devouring weaker forms of life.

To the entomologist, however, any carnivorous insect stage
which limits itself to one, or at most two, host individuals ranks
as a parasite ; an organism that requires a succession of host
individuals ranks as a predator ; in the vast majority of cases,
therefore, the so-called parasite of the entomologist is merely
a parasite in its earliest stages only, and is afterwards a predator,
since it proceeds to devour its host.

Speaking generally, the great majority of parasites of
insects, using the term in its entomological sense, are themselves
insects, and the great majority of predators are also insects or
belong to the Vertebrata. Within the class Insecta, several
families of Petiolate Hymenoptera are almost exclusively
parasitic upon other insects, and are grouped together, in fact,
as Hymenoptera Parasitica. Of these families, the Procto-
trypidse and Chalcididse (Fig. 31) are large families of minute
insects of various parasitic habits, but containing the majority

INSECT PESTS : THE MORTALITY FACTORS 227

of egg parasites. The Ichneumonidae and Braconidse (Fig. 31)
are larger insects, attacking particularly the larger types of
insect larvae. The Chrysididse or Ruby Wasps frequent the

Braconid. Adult

/stSt:ag-e

Larvae of Ichneumon
Fig. 31. — Types of Insect Parasite. (After various Authors.) (Not to scale.)

228 THE PRINCIPLES OF APPLIED ZOOLOGY

nests of Solitary Wasps, and there are parasitic bees which
live at the expense of Solitary Bees and Social Bees.

Amongst Diptera the family Tachinidse (Fig. 31) is ex-
clusively parasitic, and chiefly so at the expense of insects.
Numerous other families, such as Bombyliidse, Nemestrinidse,
Pipunculida?, Cyrtidse, Conopidae, Anthomyiidse, Sarcophagidse,
Muscidse, Braulidse, are also more or less parasitic in habit.

Among Coleoptera, the Mordellidse, Cantharidae, and Stylo-
pidse are parasitic upon other insects, particularly upon solitary
bees and wasps.

The chief predators upon insects are either insects themselves
— particularly the Coleopterous families Carabidaa, Staphy-
linidse and Coccinellidaa, and the Wasps — or they are Verte-
brata. Fresh-water fishes are largely insectivorous ; Amphibia
and Lacertomorphous reptiles largely so. The great majority
of birds largely depend upon insects, and amongst mammals
the orders of Insectivora (mole, hedgehog, shrew), Edentata
(ant-eaters and armadilloes), one division of bats, and the great
majority of lemurs and monkeys, depend upon a diet of insects.
In Barbadoes, for example, the only species of fresh-water fish
in the island is a small Cyprinodont known popularly as the
" Millions ' fish, technically as Girardinus pceciloides. This
fish feeds very largely upon mosquito larvae, and is undoubtedly
of very great value as a destroyer of mosquitoes. Attempts
have been made, therefore, to introduce this fish into West
Africa via London, but without marked success.

The Artificial Introduction of Parasites and Predators. —
When the native home of an imported insect, which has the
status of a pest, is known, and when the insect is definitely
known to be controlled in its native home by certain parasites
or predators, the importation and acclimatisation of such
controlling agents in the new area would seem to be a feasible
policy to adopt. During recent years many such experiments
have been made. Some of the experiments have met with
almost spectacular success ; in others the success has been
either slow in maturing or almost negligible. Among the really
successful instances of parasite or predator introduction may
be mentioned the introduction of the Coccinellid beetle, Vedalia
cardinalis, already discussed previously.

The success of the Australian Vedalia is almost unique,
although approached in efficiency and speed by the establish-
ment of certain egg-attacking Hymenoptera in Hawaii against
the Sugar Cane Leaf -hopper (Perkinsiella saccharicida) ; by
certain parasites of the Sugar Cane Borer in the same locality ;

INSECT PESTS : THE MORTALITY FACTORS 229

and by the introduction of the Chalcid parasite, Prospaltella
berlesei, from America and Japan into Italy to control the
Diaspine Scale, Diaspis pentagona, whose attacks on mulberry
threatened the silkworm industry. Similar success may possibly
result from the introduction of the Braconid, Aphelinus mali,
into Australia and New Zealand to control the Woolly Aphis
{Eriosoma lanigera).

On the other hand, the large scale experiments in the intro-
duction and acclimatisation of parasites of the Gipsy and Brown-
tail moths from Europe into Massachusetts, although un-
doubtedly of very great value in controlling these pests, have
not met with so rapid and spectacular results as was the case
with the examples quoted above.

Of course, the selection of a suitable subject for such an
experiment is not so simple a matter as was formerly sup-
posed, and the successful introduction and acclimatisation of
a parasitic or predaceous insect into a new area depends upon
a thorough consideration of each of a complex of factors which
can only be briefly mentioned here : —

(1) The parasite should really control the pest in the native
habitat. The attempt made by Riley many years ago, for
example, to check the introduced Cabbage White Butterfly
(Pieris rapce) in America, by the introduction of the European
Braconid parasite, Apanteles glomeratus , was doomed to failure
from the outset, since the parasite is unable to control the
butterflv even in its native habitat.

(2) The parasite or predator should be capable of out-
numbering its host, owing to greater fecundity, or greater
number of generations, or such habits as parthenogenesis or
polyembryony, and so on.

(3) The parasite should be specific in its action.

(4) It should be adaptable to fresh climatic conditions and
should possess the migratory habit, or at any rate should have
greater powers of dispersion than its host.

(5) It should be comparatively free from enemies or from
the competition of other parasites.

Its value will be entirely negatived if it is liable itself to
severe parasitism.

The most suitable parasite or predator for experimental
acclimatisation is, in fact, an exclusively specific parasite
with few enemies ; next in order of efficacy comes a poly-
phagous parasite ; then a specific predator ; and finally, a
polyphagous predator.

CHAPTER XX

VERMIN REPRESSION

The term vermin is one capable of various definitions according
to whether the point of view adopted be that of the medical
officer of health, the game warden, or the farmer.

The term, however, is one applied usually to certain
mammals and birds whose activities are inimical to the interests
of the farmer and stockbreeder, and it may be said to include
particularly the following categories, namely : —

(a) Certain exclusively graminivorous birds, notably the
Fringillidce or finch family, the pigeons, and the parrots.

(6) Certain herbivorous mammals of the rodent order,
notably the various species of rats and mice ; the field voles or
meadow mice (Microtus, Micromys, Apodemus, etc.) ; the pocket
gophers (Geomys), rabbits (Lepus), hamsters and cotton rats
(Cricetus, Sigmodon), ground squirrels or spermophiles (Citellus),
prairie dogs (Cynomys), and the lemmings (Myodes).

(c) Certain mammals and birds which are predatory upon
domesticated or semi -domesticated animals, notably the wolf,
coyote, dingo, fox, house cat, weasel, stoat, polecat, and to a
lesser extent the larger cats ; among birds, certain hawks
and owls such as Cooper's Hawk, the Sharp-shinned Hawk, and
the Eagle Owl, all of North America, and the Sparrow Hawk
and Little Owl of Europe ; the Kea Parrot of New Zealand.

It must be noted in fairness that animals and birds of this
latter category are often seriously destructive only when
transferred to a new environment, or when in excessive numbers,
or through scarcity of their normal food.

The great horned owl and the coyote are cases in point.
Where rabbits or field rodents are numerous, the owl and the
coyote are very rarely tempted to attack domesticated stock ;
coyotes are known to feed very largely at times on large insects
such as grasshoppers and crickets. Even the much maligned fox
relies very largely upon field mice, rabbits, ground squirrels,
and insects ; in Algeria it has been found difficult to establish
the large predatory beetle Calosoma, imported from Europe,
owing to foxes.

Injurious Rodents. — The most injurious rodents belong to

230

VERMIN REPRESSION 231

the genus Mus, and comprise some 300 species, seven-eighths
of which are classed as rats, the remainder as mice ; the differ-
ence is chiefly one of size, those with feet longer than 30 mm.
being distinguished as rats. Of these species, three in particular,
owing to cosmopolitan distribution, adaptability to various
conditions, and omnivorous habits, are world pests. These
three species are : —

Mus rattus, the Black Rat or Ship Rat, with several sub-
species, in particular Mus rattus alexandrinus (the roof or tree
rat of the Mediterranean area) and Mus rattus concolor of
Java and Burma. It is pre-eminently the common house rat
of tropical Asia, and the most important agent in the dissemina-
tion of bubonic plague. Although occurring in Europe in
mediaeval times, and probably concerned in the plague out-
breaks of Europe in those times, it has now been driven to the
seaports, largely through competition with the Grey Rat.
Outbreaks of plague, therefore, although always liable to be
epidemic in Asiatic cities such as Bombay and Hong-Kong,
only occur in Europe or America or Australia, rarely, in minor
form, in such ports as Sydney, Adelaide, San Francisco, Liver-
pool, and so on, particularly in the Asiatic quarter. It is the
predominant rat of Asia, owing possibly to the infrequency of
stone houses, sewers, and cellars, and owing to its superior
climbing powers is more commonly found in ships than is the
Grey Rat. The typical colour is not the bluish-black of
European varieties, but a soft reddish-brown with belly white
or pale yellow. It is a slender rat, with large ears, long tail,
and prominent eyes (Fig. 32).

Mus norvegicus (decumanus), the Brown, Grey, or Norwegian
Rat, is a larger species than the preceding one. It has a reddish-
brown or grey back and a silvery-grey belly, and has the tail
shorter than the rest of the body. A black variety occurs,
often termed the Irish rat, which is said to be on the increase.

The original home of Mus norvegicus was probably China,
and Mus humiliatus of that country may represent the ancestral
form, although a wild form, Mus norvegicus primarius, has
been reported from the region west of Lake Baikal. It was
probably introduced into Great Britain in ships from the
Baltic about 1728, into America about 1775, and in both
countries it rapidly ousted the Black Rat. It is essentially a
burrower, a frequenter of drains and sewers, and can establish
itself in stone or brick-built erections unfavourable to Mus
rattus. Unlike the latter, however, it requires to be near fresh
water, being a great drinker and a ready swimmer and diver.

232 THE PRINCIPLES OF APPLIED ZOOLOGY

Mus musculus, the House Mouse, in all probability came
from Asia also, but its establishment in Europe must date from
a long way back, certainly not later than the Neolithic period.
It is a miniature replica, in appearance and habits, of the Black
Bat. Several local races exist, particularly in isolated island
communities such as St Kilda and the Faroe Islands.

All these forms of M us are very prolific and attain sexual
maturity early, at four months at the latest. They breed
throughout nine months of the year, and as gestation only
lasts three weeks, some five or six litters may be produced
annually, a litter averaging eight to ten in number. It must
be remembered, however, that as wild rats will rarely breed
in captivity, such figures are based upon observation of the
domesticated white rat, and are probably far too low for the
wild forms. Litters of twenty-one and twenty-two young
brown rats have been recorded.

The rat is omnivorous, and will eat almost everything that
is edible, will gnaw wood, ivory, leather, lead piping ; will
destroy textile stuffs, paper, books ; and will attack chickens,
rabbits, young lambs and pigs, even horses' hoofs. They
have, however, several preferences, and cultivated cereals are
particularly favoured. They will attack newly sown seed,
young shoots, or the mature grain. Where maize is grown they
will even climb the stalk and strip the cobs clean. Malt is
proverbially a favourite food.

Of little less importance than the rats and mice of habita-
tions are the true field rats and prairie mice, belonging also to
the Murid sub -family Murinse ; the voles or meadow mice and
lemmings belonging to the sub -family Microtinse, and dis-
tinguished from the Murince by their heavier build and stumpy
tails ; the family Geomyidse or pocket gophers, ground tunnel-
ling forms peculiar to North America and causing great damage
there to forage crops ; the family Sciuridae, including tree
squirrels, ground squirrels or spermophiles, and prairie dogs ; the
Leporidse, including the rabbit, now such a plague in Australia.

Field rats include the Bandicoot Rats (Nesokia) and the
Mole Rats of tropical countries ; in temperate latitudes, how-
ever, field-dwelling Murince are not numerous, their place
being taken to a large extent by voles and lemmings, gophers
and ground squirrels.

In Great Britain there are three species of field mouse,
namely, the prehensile tailed Harvest Mouse (Micromys
minutus) whose spherical nest, large as an orange, is suspended
on a cereal stalk some distance from the ground, the long-

VERMIN REPRESSION 233

tailed Field Mouse (Apodemus sylvaticus), and De Winton's
Field Mouse (Apodemus flavicollis wintoni).

The voles, meadow mice, and lemmings belong to a sub-
family of Muridse known as the Microtince, a group of small
animals distinguishable from true mice by the heavier build,
blunt muzzle, short ears and tails. They are, in general,
feeders upon coarse herbage and grasses.

In Great Britain five species of vole occur : the Bank Vole
(Evotomys glareolus), the Short-tailed Field Vole (Microtus
hirtus), and the Highland Field Vole (Microtus agrestis neglectus)
are all forms about the size of a mouse, and, with the exception
of the last-named species, are distributed throughout the
country ; the Water Voles ( Arvicola amphibius and Arvicola
amphibius reta) are larger, rat-like forms, adapted to aquatic
life, although as the feet are not webbed, such adaptation would
seem to be recent.

In North America the economically important forms belong
to the genus Microtus, and are usually termed Meadow Mice, the
commonest species, Microtus pennsylvanicus , occurring in at least
twenty-five States from Maine to the Dakotas. In North America
occurs the aquatic Musk-rat belonging to the genus Fiber.

The habits of Microtince differ greatly ; there are forest
forms and prairie forms, burrowing forms and surface forms,
dry ground forms and aquatic forms. The nests are compact,
spherical bundles of dried grasses, placed in depressions in the
ground, in shallow burrows or on grass stems above the ground.
From the nest, trails of great length lead to neighbouring
feeding grounds. The trails of some species are below ground,
and short tunnels are common with most species. Surface
nests are usually for shelter only ; the young of most kinds
are born in underground nests. The animals are enormously
prolific, four to six litters of eight to twelve young within a
year being usual.

The Lemming (Myodes) is distributed throughout Northern
Europe, with the exception of Great Britain, usually living
upon the slopes of mountains above the pine belt. It is a thick-
set, clumsy rodent about the size of a small rat, yellowish-
brown in colour, with blunt muzzle, short tail, and short ears.
It is remarkable for its periodic migrations, during which vast
hordes, numbering millions of individuals, move westwards,
surmounting all obstacles, until in Scandinavian countries they
reach the sea, into which they are even said to continue their
movement and so to perish.

The Hamsters (Cricetince) are somewhat primitive forms

234 THE PRINCIPLES OF APPLIED ZOOLOGY

which include the Old World genus Cricetus and the Cotton
Rats (Sigmodon) of North and Central America.

The common hamster {Cricetus frumentarius) is abundant
in some districts of Germany, and is a glossy-coated animal
about a foot long, possessing cheek pouches. It constructs two
kinds of burrow, a summer one for a nursery and a winter
one for food storage and hibernation.

Hamsters are very destructive to crops, and hoard up large
quantities of grain. As much as 120 lbs. weight of seeds (wheat,
rye, beans, etc.) have been taken from a single burrow.

The family Geo?nyidce comprise the so-called Pocket Gophers, a
family of rodents restricted to North and Central America, and in
North America distributed chiefly west of the Mississippi basin.

In some districts in this area, pocket gophers are probably
of greater economic importance than all the other species of
rodents combined. The damage done by pocket gophers in the
United States was estimated so far back as 1908 to exceed
12,000,000 dollars (£2,500,000) per year, and the statement
was probably grossly underestimated. It is no exaggeration
to state that on many farms of Western North America, 10-30
per cent, of the crop is lost annually through the activities of
pocket gophers, aided to a lesser extent by prairie dogs, ground
squirrels, and rabbits. The animal is a thick-set, short-legged
rodent, a little smaller than the house rat, provided with fur-
lined cheek pouches which open outside the mouth (Fig. 32).

It is entirely fossorial, living in underground tunnels, about
two feet below the ground surface, which form a complicated
labyrinth. At intervals of a few feet, shafts run up to the
surface and are marked by a mound of earth, the so-called
gopher hill, about a foot high and several feet in width.

The food consists of roots of plants which are attacked
from below, and without the animal emerging from its burrow.
The gopher is particularly destructive to alfalfa, grazing land,
hay meadows, and root crops. Alfalfa may be entirely ruined
by the cutting of the main branches of the root system.

In irrigated districts much damage may be done to the banks
of irrigation ditches by leakage of water from them through
gopher burrows. Bell quotes the example of an irrigation
canal in Idaho, whose bank broke down through the weakening
caused by gopher burrows ; the break cost 5,000 dollars (£1,000)
to mend, and before repairs could be completed the enforced
drought caused a loss of 25 per cent, of the hay crop over
30,000 acres of country.

The family Sciuridce includes not only the Tree Squirrels, but

VERMIN REPRESSION

235

certain North American terrestrial burrowing forms variously
known as Prairie Dogs, Spermophiles, Woodchucks, and classified
as a separate sub -family Marmotince. They are gregarious

■ v / ~

> " -

Mus decumanus Mus rattus

(after Hossack)

Pocket Gopher
(after Herrick)

Fig. 32. — The Grey Rat, Black Rat, and Pocket Gopher.

burro wers, inhabiting a " town " or warren of burrows con-
nected by a labyrinth of tunnels ; they are diurnal feeders
and are said to hibernate through the winter and so do not
need to store up food for the winter.

236 THE PRINCIPLES OF APPLIED ZOOLOGY

The economic aspect of the rodent question may be
discussed under three headings : —

(1) Habitual, steady damage to food-stuffs and property.
Many statements have been made concerning the total annual
damage to property and materials in various countries caused
by rodents, but accurate information is difficult to come by
and the figures are sheer guesswork. In addition to the amount
of food actually eaten, there is the almost incalculable loss from
wastage and spoliation, and the damage caused is so gradual
and unobtrusive, such a chronic tax on food-stuffs, that statistics
can rarely be made concerning it.

(2) Damage caused by rodent plagues.

The habit of assembling in large numbers and migrating
has been observed frequently among rodents. Such migrations
are often only seasonal, brought about by the presence in some
area of a large accumulation of favourite food. In Great
Britain, for example, there is a large influx of rats into the
East Coast fishing ports during the herring season, and a
corresponding return to inland farms when the season closes.
In South Australia and Victoria the large accumulation during
1916 and 1917 of wheat sold to the British Government on the
wharves awaiting shipment attracted billions of mice, and
damage to the extent of £1,000,000 was done. In one
wheatyard 10,000 were killed in one afternoon. Great numbers
died from a disease resembling syphilis.

Such mouse plagues or rat plagues are, however, more
frequently due to an abnormal increase in numbers, following
a succession of mild winters and abundant summer harvests.
Inadequacy of food forces myriads of rodents to spread over
less populated areas. Such migration is particularly character-
istic of voles and lemmings. Such a plague of meadow mice
in 1907-08 devastated four-fifths of the cultivated areas of
Nevada, Utah, and north-east California. One-third of the
alfalfa crop was ruined, three-quarters of the potatoes, and
an enormous number of young shade trees killed.

Such plagues resemble one another in being preceded by
one or two favourable years during which mice are abundant,
and in rarely lasting beyond one year. The importance of the
natural checks afforded by owls, hawks, weasels, stoats, crows,
rooks, gulls, etc., is enormous. The field mouse and meadow
mouse are sufficiently prolific to produce a plague every four
or five years in the absence of such enemies, and the general
tendency of gamekeepers and agriculturists to destroy such
natural enemies is to be deplored. The great field vole plague

VERMIN REPRESSION 237

that ravaged the South of Scotland in 1892 was undoubtedly
the result of years of systematic persecution of owls and hawks.

(3) Conveyance of disease.

The connection between rats and bubonic plague has already
been discussed in this and previous chapters, and the relation
that exists between rats and trichinellid worms has also been
referred to. In addition, rats are suspected of carrying the
virus of horse influenza, and Japanese observers claim that
Spirochceta icterhcemorrhagice, the causative organism of an
infectious jaundice in man known as Weil's Disease, is trans-
mitted from rat to man by urine contamination of food.

Methods of Destruction. — The destruction of injurious
mammals and birds can be carried out by poisoning, or by
trapping or hunting.

Poisoning is the cheapest and most convenient method of
dealing with burrowing mammals or with the larger carnivora,
although a method which requires great care in poultry-raising
districts.

Strychnine-coated wheat or barley is undoubtedly the most
satisfactory way of dealing with sparrows, with ground squirrels,
meadow mice, rats, rabbits, and so forth, especially if used in
winter, but strychnine is less successful against the cunning of
large carnivora. The substance used is usually strychnine
sulphate, which is soluble in boiling water. The intense
bitterness of this salt may be neutralised by mixture with an
equal weight of sugar or orange juice, or better still, of
saccharine. The bait used will vary with the habits of the
pest whose destruction is aimed at, but the following may be
used : cereal or leguminous seeds, bran, alfalfa, cubes of potato,
sweet potato, carrot, beet, parsnip. The bait should be soaked
overnight in a syrup made up, for example, of one ounce of
strychnine, one ounce of sugar, one pint of boiling water, and
a few drops of aniseed oil.

With burrowing animals the bait is placed in the mouth
of the burrows. With other rodents it is best placed under a
board resting on thin cross-pieces, so as to exclude birds.

Other poisons used are arsenic, potassium cyanide, barium
carbonate, squills, phosphorus. All have their advantages
and their drawbacks. Barium carbonate is much used against
rats, owing to its absence of odour and taste, and its low toxicity
towards larger animals. It is mixed with four parts of flour
into a dough, flavoured with aniseed, and disposed in lumps
about the size of a hazel nut. It is, however, like the more
dangerous phosphorus, slow in action.

238 THE PRINCIPLES OF APPLIED ZOOLOGY

Fumigation with poison gas has proved successful against
ground squirrels, gophers, and prairie dogs. The favourite
substance employed is the volatile liquid, carbon bisulphide.
It should preferably be pumped into burrows by means of a
" destructor," a sort of pump, but may be simply placed in
the mouths of burrows on a sponge or handful of rags, and the
external entrance blocked. Coarsely powdered calcium cyanide
is also much used. Fumigation is useless where burrows are
long and deep, or labyrinthine. It is useless against rats.

Fumigation of ships is, however, a much practised and
successful method against rats. Usually the Clayton process
is used, a method of wafting sulphur dioxide into the space
to be disinfected. This gas kills ship insects — cockroaches,
fleas, bugs, mosquitoes — very readily, but as it does not
penetrate into the deeper recesses of the hold, owing to the
mechanical difficulties offered by tightly packed cargo, and
owing to the absorption of much of the gas by such cargoes
as cotton and jute, a considerable number of rats are liable to
escape. A mixture of carbon dioxide and carbon monoxide,
although without toxic action on insects, is lethal to rats, and
at many American ports this mixture is introduced into ships
by a method invented by Dr Harker, of the University of
Sydney. The Harker apparatus can deliver 180,000 cub. ft. of
waste furnace gases per hour, chiefly carbon dioxide, carbon
monoxide, and about 10 per cent, of oxygen. It has been
adopted in many shipping ports primarily as a fire extinguisher.
In other ports opinion favours the use of hydrocyanic acid gas
as a ship fumigant.

Trapping is a very safe method, can be used at any time,
and is very effective in the hands of a skilled man. Traps are
especially adapted to buildings, to pastures where livestock are
running, to gardens, orchards, and to banks of ditches and
streams. Against wolves, foxes, dingoes, coyotes, it is one of
the few successful methods. The notorious " Custer Wolf " of
South Dakota, U.S.A., which destroyed thousands of pounds
worth of cattle, was taken eventually in a trap after all other
methods failed. It is interesting to note in this connection
that in the Western United States no fewer than 109,346 coyotes,
15,374 lynxes, and 2,936 wolves were killed by shooting or
trapping during five years, 1st July 1915 to 30th June 1920,
apart from the very large numbers poisoned. This work was
carried out by the Bureau of Biological Survey of the U.S.
Department of Agriculture.

CHAPTER XXI

BIRD ENCOURAGEMENT

Blrds may be divided, according to food habit, into three
groups : —

(1) Birds that are insectivorous or carnivorous, a group
including particularly aquatic and marine birds, falcons and
hawks, owls, plovers, cuckoos, swifts, woodpeckers, and such
families of Passerine birds as the fly-catchers, swallows, Turdidce
(thrush, blackbird, robin), and the Paridce (tits), although the
last two families are to some extent graminivorous.

(2) Birds that are graminivorous, relying almost exclusively
upon a diet of seeds and fruits ; this group includes particularly
the pigeons, parrots, and finches (sparrow, chaffinch, etc.).

(3) Birds that are omnivorous, accepting seeds or insects
with equal readiness ; a group of birds which includes the
Galliformes or Game birds (pheasant, quail, bobwhite, grouse,
partridge, fowl), the larks, the starlings, and the Corvidce (rook,
crow, magpie, jay).

At first glance, birds in the first group would appear to be
potentially beneficial to the agriculturist. Birds in the second
group, if sufficiently numerous or gregarious in habit, would
appear to be potentially injurious ; birds in the third group
might be either injurious or beneficial, according to the nature
of the crops grown in the locality or the season of the year.

A superficial knowledge of the food habits of any bird or
class of bird is, however, not sufficient to warrant any definite
statement concerning the bird's economic status. An insect-
eating bird, for example, cannot discriminate between the
injurious and the beneficial insect, so that of the six and a half
million insects destroyed by a tit in one year, a large number
has to be reckoned against the bird. Of the animal food taken
by the European rook, probably quite one-third must be
reckoned against the bird. As a matter of fact, the importance
of birds as factors in the control of insects has probably been
exaggerated in recent years. It is indisputable that very many
insects are eaten by birds, but there is very little evidence of
any epidemic of insect attack having been checked by birds.

239

240 THE PRINCIPLES OF APPLIED ZOOLOGY

On the other hand, there is abundant evidence as to the value
of predatory insects in such epidemics. It cannot be said that
countries such as France or Italy, where small birds are ruth-
lessly hunted, suffer more severely from insect attack on crops
than do countries such as Great Britain or the United States,
where public opinion is opposed to the unnecessary destruction
of birds. It must be added that carnivorous insects are often
more conspicuous in size or habit than herbivorous forms,
and thus may suffer more severely from the attack of birds
than do the latter forms.

Again, the activities of a carnivorous bird may be in some
respects detrimental to the interests of the agriculturist. The
European sparrow-hawk preys upon the small Passerine birds,
particularly the hedge-loving insectivorous forms ; a similar
habit is shown by the North American sharp -shinned hawk ;
Cooper's hawk, of the same region, attacks poultry ; and the
similarly distributed goshawk and great horned owl kill large
numbers of game birds.

Birds whose habits are graminivorous may not be wholly
injurious to the farmer. The English chaffinch has been
proved to take large quantities of such troublesome weed seeds
as chickweed, hawk weed, dock, and knotgrass, the percentage
of weed seeds in the crop being sometimes as high as 95 per
cent. In the United States the score or more of native species
of sparrow are most efficient weed consumers, and even such
notorious grain eaters as the English sparrow, bobolink, dove,
and blackbird ( Agelaus, Ouiscalus) will at times consume
quantities of weed seeds.

The economic position of such weed-consuming birds, how-
ever, depends upon whether weed seeds can pass through the
alimentary canal of the bird intact and capable of germination,
for in such an event the diminution of weeds in a particular
area will be counterbalanced by a wide distribution of such
weeds elsewhere. Unfortunately, the evidence bearing upon
this question is somewhat contradictory. It would appear
that, generally speaking, birds which possess muscular gizzards
and are accustomed to feeding upon hard seeds crush the seed
coats so effectively as to prohibit any possibility of germination ;
such is the case with the turkey, fowl, pigeon, duck, crossbill,
siskin, tits, serin-finch. On the other hand, in the case of birds
whose diet is chiefly insects, such birds, for example, as the
thrush, robin, blackbird, seeds are readily excreted and a high
percentage of such seeds are able to germinate.

Another factor that must be taken into consideration in

BIRD ENCOURAGEMENT

241

estimating the economic status of a species of birds, is the
nature of the food taken by the nestlings, for not only is the

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16

242 THE PRINCIPLES OF APPLIED ZOOLOGY

their young upon an animal diet, irrespective of the diet of the
adult. As nestlings increase in weight from one-fifth to one-
third daily, and at certain stages of growth require daily more
than their weight of food, it is essential that the food should
have a high nutritive value and should be easy of digestion.
Spiders, caterpillars, and grasshoppers are therefore a favourite
nestling food with many species of Passerine birds. Birds
such as finches that are largely vegetarian, mingle fruit or
grain in constantly increasing quantities with the insects fed
to their young, though insects predominate in the diet until
maturity is nearly reached. These birds, however, generally
make use of hard insects — carabid beetles, weevils, and so
on ; but sparrow nestlings will consume a comparatively large
number of caterpillars.

Sweeping statements concerning the utility or the useless-
ness of this or that species of bird are based too often upon the
most superficial field observations, and are to be distrusted.
Such statements are in fact valueless and even mischievous,
unless based upon stomach examinations of large numbers of
individuals from widely distributed localities throughout all
months of the year for several years. The economic position
of a species of bird may depend to a large extent upon its
abundance, upon the availability of food other than its favourite
food, upon the nature and times of crops in the locality. Evi-
dence from isolated observations, from stomach examination
of only a few individuals, shot perhaps in restricted localities or
at some definite time of the year, is worse than useless. Partic-
ularly is this the case with birds such as rooks or starlings, whose
diet is a mixed one.

Further, the exact locality of each specimen should be known,
the character of the land, the crops grown there, whether the
district is wooded, whether broken up by hedges, ditches, or
walls, what the bird was doing when shot, whether it was in a
flock, what the weather was like, and so on. Such evidence
must be supplemented by well authenticated field observations
and by stomach examination of nestlings.

Investigations on such lines have been carried out in North
America and in Europe by several observers, but considerations
of space will not permit of any detailed account of the mass of
facts thus available regarding the dietary of many common birds.

It may be affirmed, as regards Europe, that most authorities
are agreed that the house sparrow, tree sparrow, and wood
pigeon are inimical to cereal production. That the rook,
bullfinch, lark, blackbird, and missel thrush are injurious if

BIRD ENCOURAGEMENT 243

in excessive numbers ; the starling, chaffinch, and sea-gull
beneficial on the whole ; cuckoos, swifts, lapwings, wood-
peckers, and the majority of Passerine birds, particularly
Paridce (tits), Turdidce (thrushes), Muscicapidce (fly-catchers),
and Hirundinidce (swallows), are of the utmost value.

In North America opinion favours the protection of the
following birds : the blue jay, one of the very few birds fond of
hairy caterpillars such as tent caterpillars (Malacosoma sp.) ;
the crow, which controls June beetles (Lachnosterna), white
grubs, and young field mice ; the sparrow-hawk (Falco
sparverius), which feeds chiefly on grasshoppers and crickets ;
robins, thrushes, and cat-birds, the last of which will feed its
young on cabbage worms ; the cuckoo, which also eats hairy
caterpillars ; woodpeckers, which destroy ants, borers, and
insect eggs in winter ; the flicker, which eats ants in large
numbers ; orioles, which are particularly fond of aphides ;
and quails, which are in special need of protection owing to
their destruction for food, and which devour the Colorado
Potato Beetle (Leptinotarsa decemlineata) , the Striped Squash
Beetle (Diabrotica vittata), the Boll Weevil (Anthonomus
grandis), the Chinch Bug (Blissus leiwopterus) , grasshoppers,
cutworms, and many other injurious insects. As regards the
horned lark, although the belief of farmers that the bird eats
newly sown wheat appears to be supported by stomach examina-
tions, the percentage of wheat eaten is small and is compensated
for by the large percentage of insect food, so that on the whole
the bird may be regarded as beneficial.

Opinion is unanimous in both Europe and North America
as to the economic status of the English sparrow (Passer
domesticus) and its numerous sub-species and races. Careful
examination of the crop contents of sparrows in both Europe
and the United States has established the fact that up to 75
per cent, of the food may be cereal in nature. The nestlings,
it is true, are fed chiefly on caterpillars, but the nestling season
is short. The sparrow's ability to rear young under urban
conditions, where it is protected to a large extent from predatory
birds and mammals, its prolificacy, its boldness and hardiness,
and its gregarious habits, are all factors which produce the
enormous flocks of sparrows which issue from the urban centres
to attack adjoining cereal-growing districts. Even in a town
it is not wholly desirable, since its pugnacious habits discourage
many more desirable types of Passerine birds which tolerate
urban conditions. In the eastern United States the sparrow,
since its introduction from Europe, has increased to such an

244 THE PRINCIPLES OF APPLIED ZOOLOGY

extent that its numbers constitute a veritable scourge to
agricultural districts.

Bird Protection. — Legislative measures for the protection
of bird life may be classed as State or Provincial, Federal or
National, and International Legislation.

Speaking generally, a wild bird protection scheme of legisla-
tion should be based upon the following principles : —

(1) It should be in keeping with present-day notions of
bird protection.

(2) It should give some general protection to all birds by
prohibiting certain methods of destruction and capture involv-
ing obvious cruelty.

(3) It should not otherwise protect a bird species which
careful investigation has shown to be harmful. In this respect,
since the economic status of a species may vary according to
locality, the measure should permit of modification according
to local conditions.

(4) Remaining species of birds should be divided into three
categories, according to their economic status, their aesthetic
value, their degree of abundance, the categories being as follows : —

(a) Species which should receive absolute protection at
all times for adult, nestling, egg, and nest.

(b) Species which should receive absolute protection for
adult, nestling, egg, and nest only during a specified portion
of the year, to be denoted the closed season.

(c) Species which should receive absolute protection for
adults, but not for nestlings, eggs, or nest during the closed
season.

(5) The onus of responsibility for evading the protective
measures should rest with the person in possession of illegally
taken birds, eggs, or nests. In this respect taxidermists should
be compelled to keep a register concerning the nature and origin
of specimens received by them.

In most civilised countries to-day there exists some form
of bird protection legislation incorporating some or all of the
above principles. It is true that, even in contiguous States, the
results accruing from bird protection measures may differ
considerably, according to the interpretation placed upon the
question as to what decides the economic or aesthetic value of
a bird species to the community, and according to the stringency
with which penalties for evasion are applied. Any legislative
protection of wild life is of doubtful value unless accompanied
by a system of educational propaganda to enlighten the
community as to the necessity for such measures.

BIRD ENCOURAGEMENT 245

In North America, State or Provincial Laws concerning bird
protection vary in detail between one State and another, but
they are usually based on the assumption that all game and
wild birds are the property of the State and may only be
killed as the State Government permits. Landowners have no
privileged position in this respect.

This is in striking contrast to the system in European
countries, where Wild Bird Protection Acts are hampered in
their application by undue consideration for the rights of
landowners.

International Legislation concerns, or should concern, itself
with three outstanding problems in bird protection, namely :
(a) the case of birds which migrate from one country to another ;
(6) the question of plumage hunting and marketing ; and (c)
the question of pollution of extra-territorial waters by refuse
oil from ships.

In North America the problem of the migratory bird has
been dealt with by the Migratory Bird Convention Act of 1916
between Canada and the United States. This international
measure is one of the most important and far-reaching bird
protection enactments ever made. It affects more than
one thousand species and sub-species of birds from the Gulf
of Mexico to the North Pole. The important articles in the
Convention are those which provide for a close season of
migratory game birds from 10th March to 1st September with
certain limitations, and an absolute protection throughout the
whole year for migratory insectivorous birds. The open season
for wild fowl is limited to three and a half months between
1st September and 10th March.

Some years ago, efforts to secure international protection of
birds in Europe broke down owing to the diversity of interests
and opinions, and the apathy of the governments concerned.
Such difficulties are less marked in North America, and there
exists there an increasing sentiment in favour of wild life
preservation. It may be added that within the confines of the
United States themselves, migratory birds are protected by the
so-called M'Lean Federal Migratory Bird Law.

Attempts to secure international agreement concerning the
prohibition of the trade in the plumage of rare birds have not
as yet been successful.

In the United States, owing largely to the efforts of the New
York Zoological Society and the National Association of
Audubon Societies, the importation or sale of the plumage of
wild birds, either raw or manufactured, except for educational

246

THE PRINCIPLES OF APPLIED ZOOLOGY

or scientific purposes, has been absolutely forbidden since 1913.
Since 1915 the Dutch Colonial Government has prohibited
the destruction and exportation from Dutch colonies of all birds
except the lesser bird of paradise (Paradisea minor), the twelve
wired bird of paradise (Seleucides nigricans), and the rifle bird
(Ptilornis magnificus). The importance of this measure may be
judged by the fact that the Dutch East Indies were the chief
centres from which birds of paradise, crown pigeons, and other
tropical birds were exported to Europe ; the Papuan hunters
of Dutch New Guinea employed by the Chinese traders of
Ternate used to secure an average number of 200,000 skins per
year. Of the eighty -one or eighty-two species of paradise birds,

"Berlepsch" "Thirlmere"

Fig. 34. — Types of Nesting Box.

about twenty are now nearly extinct on the smaller islands
owing to these depredations.

In Great Britain, despite considerable opposition not only
from the feather trade but from certain naturalists, the
Importation of Plumage Act was passed in 1921 and, with
certain scheduled exceptions, the plumage and skins of wild
birds are not allowed to enter the country. Germany and
Austria may follow these examples. France and Belgium
are too greatly under the influence of the plumasserie or
feather trade to be in a position to enact similar measures.

The Himalayan species of pheasant, however, is still
accessible to the feather trade. The laws of British India
forbid the exportation of skins or plumage taken in British
India, but Nepal, an independent State, can still export
thousands of pheasant skins to Europe, and the Nepalese have

BIRD ENCOURAGEMENT

247

almost exterminated the Minal and the Tragopan and possibly
others of those gorgeous pheasant species.

One common objection raised by opponents of these legisla-
tive measures against plumage importation is that it will tend
to discourage the domestication of birds of plumage value.
The usual retort has been that by the time experiments could
be made and bird farms established on a scale sufficient to
supply the feather markets, all the wild birds would be ex-
terminated.

Actually in India the successful raising of egrets for plumes
has been carried on for some years in the province of Sind,

Prevail in

Wrong

Bo jc hanging too
low down

Exposed to
weather
Tilted upwards

Right

/oft. aSove
ground

Sheltered from
weather

Tilted down vards

Fig. 35. — Method of Hanging Bird Boxes.

the birds being kept in mat-enclosed pens about eight feet
square and fed on small fish. The birds become tame and can
be readily handled, and the plumes plucked without injury
to the bird. That the farming of such birds is a practicable
scheme has been demonstrated by the National Association of
Audubon Societies in the United States, which established a
colony on a small island in the Stono River near Charleston,
and in 1917 the colony was tenanted by more than 400 birds.
On the other hand, the egret, like other herons, subsists almost
exclusively on fish, and the establishment of such rookeries
would be bound to have an injurious effect on neighbouring
fresh -water fishing grounds.

The European markets still are able to obtain large

248 THE PRINCIPLES OF APPLIED ZOOLOGY

quantities of such birds as humming birds, egrets, rheas,
and so on from South America.

Bird Encouragement. — A rational system of bird protection
should not confine itself to the enactment of legislative pro-
tection measures that are too often allowed to become a dead

Fig. 36.— A Good Type of Bird Food Station. (After Beal.)

letter, but should include active measures that will tend toward
an increase quantitatively and qualitatively in bird life. This
can only be done by the creation of bird sanctuaries, definite
reservations for bird life, ranging in size from huge tracts of
country down to artificial coppices in the public parks of urban
districts. Within the bounds of such reservations the Bird
Protection Laws must be rigidly enforced ; outside the bounds

BIRD ENCOURAGEMENT 249

the laws could be relaxed sufficiently to avoid hampering the
agriculturist. The number of such bird sanctuaries is on the
increase in most countries.

In such sanctuaries the conditions should approximate as
closely as possible to those of the woodland, the swamp, or the
precipitous sea island. Clean forestry is incompatible with
bird profusion. Decayed and fallen trees, plentitude of brush-
wood, standing pools and meres should not merely be tolerated
but should be supplemented by the provision of nesting facilities,
whether in the form of artificial boxes, or niches in masonry, or
dense impenetrable thickets of thorny shrubs.

Many nesting boxes of different types have been invented.
Such birds as the wryneck, woodpecker, or stock-dove prefer
the Berlepsch type of box, invented by Baron von Berlepsch
of Eisenbach in Thuringia, with its bottle -shaped cavity and
pointed oval base. Other birds, tits, robins, starlings, fly-
catchers, and the like, will nest in any sort of flat-bottomed
bird box roughly constructed from slabs of refuse bark (Figs.
34, 35). Other birds prefer the half-open type of box. Many
birds, of course, will not use a box at all but nest in thickets
or on the ground, so that special protection from predatory
mammals is desirable where the sanctuary is small.

It may be added, in conclusion, that the indiscriminate
protection of all birds in a natural sanctuary may, and often
does, lead to a superabundance of hardy, virile species at the
expense of less adaptable birds. Thus, in a gullery, the protection
of the egg-eating, nestling-eating herring gull militates against
the encouragement of kittiwakes, guillemots, razor-bills, and
puffins ; the presence of peregrine falcons or jackdaws dis-
courages the chough ; on the Orkney and Shetland Islands,
protection of the great skua has been inimical to whimbrels ;
on the Feme Islands, herring gulls have discouraged the develop-
ment of the tern colonies. It may be added further, that
natural factors such as food shortage, floods, and so on, and
such necessary artificial causes as lighthouses, are responsible
for more wholesale loss among birds than is caused by direct
human agency.

CHAPTER XXII

ANIMAL DOMESTICATION

The original wild types from which domesticated animals
have descended are, in many cases, to be recognised only with
the utmost difficulty and doubt, so long is it since they became
tamed to the service of humanity. In many cases domestica-
tion must have commenced in early Neolithic times, so that
there is every possibility that the original wild type has died
out. Certainly, with the exception possibly of the ostrich and
the African elephant, there is no example in modern times of
the domestication of a large wild animal.

Further, the distinction that we make between animals of
draught or burden, animals of food or milk, animals of value in
hunting, and so on, probably did not exist among the early
domesticators of animals.

Neolithic man would require a general utility animal, an
animal that could serve equally well for burden or for help
in the chase or, if need arose, for food. Thus the dog and the
horse were probably among the first animals to be tamed.
Cattle, sheep, goats, swine came later. Domestication of birds
later still.

In Europe, domesticated animals were not possessed by
Paleolithic man, with the doubtful exception of the horse and
the dog, but were introduced by invasions of Neolithic peoples,
some of whom came into Europe from the Central Asiatic
plateaux, others from the direction of Asia Minor, others again
possibly from the region of Northern Africa.

Thus, animals whose domestication dates from Neolithic
times, such as the horse, ox, sheep, dog, are represented to-day
by a vast number of breeds derived by the hybridisation of
domesticated types, themselves produced in different centres
of domestication from different wild species. That is to say,
they have originated from a number of ancestral species, most
of which may to-day be extinct.

On the other hand, in the case of animals whose domestica-
tion has occurred probably since Neolithic times, and which
have not become widely distributed, the breeds are few and not
greatly different from each other, and the wild ancestor may be

250

ANIMAL DOMESTICATION 251

looked for in one or two species, often still living. Such is the
case, for example, with the elephant, yak, llama, reindeer, and
many domesticated birds.

To-day most of man's work is carried out by ten animals,
five of which — the horse, ass, mule, ox, and dog — are of world-
wide distribution, the remaining five — elephant, yak, llama,
reindeer, and camel — being of local distribution. His meat
supply is furnished chiefly by various species and breeds of Bos,
the ox, of Ovis, the sheep, and of Sus, the hog, supplemented
in various localities by the goat, reindeer, rabbit, and domes-
ticated birds. Valuable products are supplied by the sheep,
milch cow, rabbit, ostrich, and so forth. Useful services are
supplied to him by the dog, cat, cheetah, and so on.

Horses. — The term " horse," in a zoological sense, comprises
the species of Equus, a genus of hoofed animals characterised
by the possession of only one functional toe, the middle one,
on each limb, the lateral toe being represented by bony vestiges.
The genus includes, therefore, in addition to the true horses,
the asses and zebras.

The true horse, Equus caballus, is distinguishable from the
other forms by a number of minor characters, notably the
possession of callosities on the inner side of the hind limbs,
in addition to those on the fore limbs. These so-called " chest-
nuts " are probably vestigeal glands. The mane and tail are
much hairier than those of ass or zebra, the head proportion-
ately smaller, and the coloration, except in very rare cases,
does not show striping. Apparently no truly wild individuals
of E. caballus exist, and the species comprises some fifty or
sixty domesticated breeds or races.

The asses and zebras differ from the domesticated horse
in the characters mentioned. They resemble one another in
having a more or less striped coloration, more pronounced in
the zebra than in the ass.

Living species of asses comprise : —

The onager (E. onaga) of the deserts of Persia and North-
western India, and the very similar hemippus (E. hemippus) of
Northern Arabia and North-western Persia, yellowish animals
with a dark mid-dorsal stripe ; they are extremely swift
animals and are said to be impossible to domesticate.

The kiang or Dzeggetai (Equus hemionus) of the high
plateaux of Thibet and the region east and south of Lake Baikal ;
this is a dark, shaggy-coated animal with a dark erect mane
and a dark mid-dorsal stripe ; the Abyssinian ass (E. asinus) of
Abyssinia and the Nubian desert, with a mid-dorsal stripe and

252 THE PRINCIPLES OF APPLIED ZOOLOGY

a horizontal shoulder stripe ; the Somali ass (E. tamiopus) of
Eastern Somaliland, a greyish animal with no shoulder stripe,
a very faint dorsal stripe, and with cross stripes on the legs.

Of the zebras, which are all African in distribution, there
are six or seven acknowledged species, the best known of which
are : the Grevy zebra (E. Grevyi) of Southern Abyssinia and
Somaliland ; this is the largest of the zebras, and is character-
ised by the narrow, brilliant dark-brown stripes on a silver-
grey ground, the very long head and the hairy ears ; the stripes
do not meet along the under surface of the belly : Grant's
zebra (E. Granti) of British East Africa, on the other hand, has
broad, brilliant stripes completely surrounding the body and
uniting with a mid-ventral dark line, and has a conspicuous
set of horizontal stripes extending down the legs to the hoofs ;
this zebra, together with the extinct Burchell's zebra (E.
Burchelli), and the extinct quagga (E. quagga), both of South
Africa, formed a group of allied species extending in range
from the north of British East Africa down to the Cape of Good
Hope, and showing a transition between the universal striping
of the Grant's zebra and the limited striping, on shoulders
only, of the quagga: the Mountain zebra (E. zebra), now very
rare, and carefully preserved by the South African Government,
has also very broad stripes and is characterised further by a
broad gridiron of transverse stripes over the hips, by a short
head, very long ears, and very short, heavily built limbs.

The modern breeds of domesticated horse (Equus caballus)
seem to represent the intermingling by generations of hybridisa-
tion of three distinct types of wild ancestral horse, namely : —

(a) A forest type, represented probably by the extinct E.
robustus, whose bones and pictured representations occur so
freely in the excavations of Solutre in France. It was a horse
adapted to life in woods and thorny thickets, and to narrow
paths amidst wet and marshy ground. It was a thick-set
animal, coloured probably dark yellow, with darker stripes on
face, body, and legs, with short neck, straight nose, long pre-
hensile upper lip, thick projecting lower lip, long and flowing
mane and forelock, dark wavy coarse hair, no lock of hair at
the root of the tail, very rounded hindquarters, wide hoofs,
hairy fetlocks. This type may be represented considerably
to-day in the Norse horse (Equus caballus typicus), and to a
lesser extent in the Highland pony, the Ardenne and Flemish
black breeds, the Clydesdale, Shire, and Suffolk heavy breeds,
and the Connemara pony.

(b) A steppe type, represented by the sole living type of

ANIMAL DOMESTICATION 253

wild horse, Equus przewalskii, of the Gobi and Altai deserts of
Central Asia. It is a horse readily distinguishable from all
modern breeds by the entire absence of forelock, by the short
upright mane similar to that of asses and zebras, and by the
mule-like tail with short stiff hairs on the upper portion. It
has a sheep-like nose, bent downwards and enabling it to feed
conveniently on the short grasses of the steppes. Traces of
this type may possibly exist in the Connemara pony, Clydesdale,
Welsh, and Shetland ponies.

(c) A plateau type, descended perhaps from E. siv)alensis of
the Indian Pliocene. It was probably a slender type, fifteen
hands high, and not unlike an inferior modern Arab horse.
It had possibly a long flowing mane and forelock, a bunch of
hairs at the root of the high-set tail, a small straight head, and
slender, fine bones. It has left representatives in the modern
Arabs and Barbs, and through them in the modern Thorough-
bred ; in the Mexican ponies ; and in the so-called Celtic pony
of Iceland ; the latter breed represents, according to Cossar
Ewart, a species which branched off at an early period from the
Arabian or North African stem and spread northwards, becoming
dwarfed in adaptation to a severe climate, but retaining many
characteristics in common with the present Arab breeds, such,
for example, as a similar shape of head, absence of hind chestnuts,
and absence or reduction of the fetlock callosities (ergots).

The Ass (Equus asinus) may have been domesticated as
early as the horse, but if so its distribution must have been
more localised, for there is no record of its use in Western Europe
before the Neolithic period.

The general opinion is that modern breeds of ass are all
derivable from the Nubian wild ass of North-eastern Africa,
and are quite distinct from the Asiatic onager and kiang. These
latter forms seem nearer to the Przewalskii horse than to the
African wild ass.

Cattle. — The term " cattle " may be applied to the members
of the Bovine section of the Bovidse, a family of hollow-horned
ruminant animals which includes oxen, sheep, goats, and
antelopes.

The true oxen form but a single genus, Bos.

The earliest known remains of domesticated cattle are those
from the early Neolithic remains of Anau in Turkestan, and
date from about 10,000 B.C. They seem to represent a
domesticated variety of Bos primigenius, the giant black
wild ox which inhabited the forests of Northern Europe
and Asia in Pleistocene times.

254 THE PRINCIPLES OF APPLIED ZOOLOGY

Similar domesticated varieties of this type had reached
China, Chaldea, and Babylon by 4000-3000 B.C. The type may
be represented to-day by the Ankoli cattle of Uganda, them-
selves descended possibly from the Ancient Egyptian cattle ;
by the Roman ox, the Polish cattle, the Castilian and, to a
lesser extent, the Andalusian breeds of Spanish fighting bull, the
Hereford cattle of Great Britain, and the semi- wild Chillingham
and Chart ley Park cattle of Great Britain. The earliest
European domesticated breed was the so-called Celtic Short-
horn (Bos longifrons), sometimes described as a dwarfed variety
of the Bos primigenius, but more likely a hybrid between the
latter and some eastern strain of hump-backed type. It is
represented to-day particularly by the Kerry breed of Ireland,
the Scottish Mountain breeds, and to a lesser extent by Dutch
and North German cattle. An eastern strain is present also
in the gallego cattle of North Spain.

The origin of the various breeds of Asia and Africa is un-
known. Such breeds differ from those descended from Bos
primigenius, in the lyrate shape of the horns, which grow
upwards and backwards, rather than forwards, and may be
very large. Other characters of the humped cattle, apart from
the hump, are the large dewlap and the white rings round eyes
and fetlocks (Fig. 37). Such characteristics appear in the
North Spanish and other light-coloured South European cattle.

The true Asiatic and African zebu or humped cattle are
generally considered as belonging to the distinct species Bos
indicus, represented by the cattle of India and the Galla, Nuer,
Moshi, and Hausa breeds of Africa.

A domesticated or semi-domesticated breed of the wild
Asiatic buffalo (Bos bubalis) occurs in India, China, Java,
Malay States, Egypt, Hungary, Italy, and Spain, under the
name of the ' water buffalo," and is used for milk, which is
richer than that of the ordinary European cattle, for agricultural
and for draught purposes (Fig. 37).

A domesticated breed of the wild Gaur (Bos gaurus) occurs
among the hill tribes of North-eastern India under the name
of the Gayal. Throughout Malaya the domesticated cattle
are domesticated Bantings (Bos sondaicus). Large numbers
are exported to Singapore for food (Fig. 37).

The Yak (Bos grunniens) is a long-haired peculiar type
confined to the Thibetan Plateau, and occurring there in
domesticated form.

No attempts seem to have been made to domesticate the
African wild buffalo, despite the enormous value of an indigen-

ANIMAL DOMESTICATION

255

ous domesticated animal in the tsetse fly belts of Central
Africa, and the Water Buffalo does not seem to thrive south of
Upper Egypt.

Sheep and Goats. — The difficulty in deciding from what

Water
Buffalo

Banting"

Fig. 37.— Types of Asiatic Cattle. (After Keller.)

256 THE PRINCIPLES OF APPLIED ZOOLOGY

wild types the present-day races of domesticated sheep have
originated, arises not so much from the fact that no wild sheep
are known to possess wool, since many domesticated breeds have
a coat of hair or a mixture of hair and wool, but from the fact
that all wild sheep are short tailed, whereas most domesticated
breeds are long tailed. If the long-tailed condition be a
character acquired during domestication, as are the woolly
coat and the lack of horns in some breeds, then, at any rate
for Europe and Asia, the origin of domesticated breeds from
types akin to certain living types can be postulated.

There would seem to have been two centres of domestication.
In the Mediterranean region of prehistoric Europe the type
domesticated was probably some species now extinct but akin
to the present-day " mouflon ' (Ovis musimon) of Corsica,
or to the Armenian mouflon (O. orientalis typica). On the other
hand, in Persia or in Central Asia, the type domesticated was
akin to the present-day " urial " (Ovis vignei) or to the Steppe
Sheep (Ovis arlcal). The Asiatic types of domesticated sheep
were probably brought into Europe by the Neolithic races.
Possibly the " Peat sheep " of the Swiss lake dwellings, a small
sheep with goat-like horns, was of this Asiatic type (Fig. 38).

Domesticated goats differ from sheep in the absence of a
face gland below each eye, in the absence of pits for these
glands on the facial part of the skull, in the absence of inter-
digital glands from the hind feet or even from all feet, and by
the presence of a beard in the male. The horns, too, are usually
sabre-like or twisted corkscrew fashion, whereas those of sheep
are twisted spirally in a more or less horizontal plane. There
are, however, hornless breeds of goats lacking a beard, and there
are species of wild sheep without face glands, so that it is not
always possible to draw a strict line of demarcation between the
two groups.

Most domesticated goats (Capra hircus) are considered to
be derived from the " Bezoar," Capra hircus cegagrus, of the
Mediterranean Islands, Asia Minor, and Persia. The Cashmere
breed, however, may be derived from the " markhor ' (C.
falconi) of the Himalayas, and the Angora breed may represent
a mixture of these two types.

Dogs and Cats. — Both the dog and the cat offer an example
of a domesticated animal originating from a number of wild
ancestral species, domesticated independently in various centres.

In the case of the dog, there can be little doubt that the
various breeds which exist to-day have arisen through the
indiscriminate hybridisation of different types of domesticated

ANIMAL DOMESTICATION

257

dogs, originating in widely separated centres from ancestral
species of present-day jackals, coyotes, and wolves. There
is no near kinship between dogs and foxes.

^,)fe#

Border Leicester

Ram
(after Wallace)

Fig. 38.— Types of Sheep.

17

258 THE PRINCIPLES OF APPLIED ZOOLOGY

The dog of European Neolithic dwellings was of the jackal
type, and hybridisation between such a type, brought possibly
by Neolithic races from the east, and local varieties of wolf,
would account for most modern breeds. The original ancestor
of the Neolithic importation may have been an ancestral form
of the Indian wolf (Canis pallipes).

In glacial deposits near Lake Bologoia in Russia, remains
of a wolf -like dog (Canis po?itiatini) have been discovered.
This may have played a great part in the ancestry of European
dogs. Thus the Bronze Age dog (Canis matris optimal), a
collie or sheep-dog type, may represent a cross between a
European race of wolf and C. pontiatini.

The cat, similarly, represents a composite product resulting
from the hybridisation of distinct types of domesticated species
of Felis. The chief source of the European breeds of cat was
probably the Egyptian cat, a domesticated form of Felis
ocreata, whose sandy or tortoise-shell colouring characterises
many European cats. This cat interbred in Europe with the
wild cat (Felis catus) and produced the blotched or tabby
varieties of cat. European cats have been also affected by
Persian and Indian importations, representing domesticated
races possibly of the Bokharan Steppe Cat (F. caudata).

Other Domesticated Animals.— In the case of the remaining
types of domesticated animals, there is little difficulty in
deciding as to their wild progenitor.

There is little doubt that all the European and North
American varieties of domesticated hog have originated from
the Wild Hog (Sus scrofa) of Europe, Asia, and North Africa,
although young hogs of domesticated breeds do not show the
stripes characteristic of many young wild swine.

The llama and alpaca of South America are varieties of the
wild camel Auchenia vicugna. The Indian elephant is a tamed
Elephas indicus. The domesticated races of rabbit, rat, guinea-
pig are all easily derivable from living wild species. Domestic
breeds of poultry descend from the Red Jungle Fowl (Oallus
bankiva) of Northern India, Siam, Cochin China, Malaya.

Ducks and geese originate from the Mallard ( Anas borcas)
and the Gray Lag ( Anser ferus) respectively. Pigeons, in spite
of the great variety of races, all originate from the Blue Rook
(Columbia livia).

The camels, however, cannot be derived from any known
wild ancestor, since the so-called wild camels of Central Asia
are feral, that is to say, descended from domesticated forms.

The Possibilities of Domestication. — With the exception of

ANIMAL DOMESTICATION 259

the pigeon and the ostrich, man has not succeeded in modern
times in domesticating any wild species of mammal or bird,
despite the fact that there are several types which offer great
possibilities in this respect. Notable examples of such types
are the musk ox and bison of North America, the zebra, eland,
and elephant of Africa.

The musk ox (Ovibos moschatus), an animal intermediate
in most respects between cattle and sheep, and about the size
of a small ox, is peculiar to the Arctic regions, although its former
wide range has become limited to Northern Canada, some of the
islands of the Arctic, and Greenland, owing to the depredations
of Eskimos, Indians, and white traders. In fact, the animal
is rapidly becoming exterminated, although the Canadian
Government is endeavouring to protect it. The animal's body
is covered by long hairs, arising through a thick coat of under
fur, and the value of its skin to the trader is the main reason
for its decrease in numbers.

The value of this animal as a potential domestic animal
has been urged by several authorities, notably by the explorer
Stefansson, who has pointed out that the animal is readily
tamed, inoffensive, a meat producer, milk producer, and wool
producer, and the only large animal except the reindeer which
in domesticated form can withstand the climatic conditions of
the northern fur-producing regions. In Alaska and Northern
Canada, for example, such an animal would be of tremendous
value if it could be readily domesticated and reared.

The domesticated reindeer of Europe has, it may be added,
been introduced into Alaska with very great success by the
United States Government, and they are now extremely
abundant, the consequence being that nomadic tribes of fishers
and hunters are rapidly becoming converted into raisers of
reindeer and self-supporting herders and teamsters. The
method adopted was the establishment of reindeer stations,
under skilful Lapp or Finn instructors, centring around the
various mission stations. The reindeer is now the basis of an
established livestock industry employing large numbers of the
native population, and reindeer meat and tanned skins are
shipped to the cities of Canada and the United States.

The introduction of reindeer from Norway to Newfoundland
was similarly carried out by Dr Grenfell, and the imported herd
increased ; but lack of Government support, either financially
or in checking poaching, ruined the experiment, and the
remaining animals were transferred to the north shore of the
Gulf of St Lawrence in 1918, where, under the protection of

260 THE PRINCIPLES OF APPLIED ZOOLOGY

the Canadian Government, they are increasing rapidly in
numbers.

The surplus stock of bison which has resulted from the
successful measures adopted by the Canadian Government to
protect this animal, has brought forward the question of the
possibility of domesticating this animal. It is an animal producing
meat and skins of great value, an animal pre-eminently adapted
to the treeless, blizzard-swept prairie regions, and an animal
that can be readily crossed with the domestic cow to produce
a hybrid, the cattalo, which is resistant to Texas Cattle Fever.
Experimental work by the Division of Animal Husbandry of
the Canadian Department of Agriculture has shown that
certain initial difficulties, particularly sterility and abortions,
in the raising of cattalos can be overcome, and a very thriving
herd of cattalos is now located in Alberta. Experiments are
also being made in the crossing of bison with the yak.

Attempts to domesticate the eland in Africa have not been
successful, as under ranch conditions in Africa it seems very
susceptible to cattle diseases such as rinderpest, and in captivity
in European countries does not breed freely.

In Africa practically nothing has as yet been attempted
towards the establishment of a domestic race of draft or of
food animals suitable to the conditions of the tsetse fly-belts,
despite the enormous value of such an animal in the develop-
ment of these areas of Africa.

The zebra is capable of hybridisation with the ass or the
horse, but the zebrule so produced is somewhat intractable
in harness and has not the strength and endurance of an ordinary
mule.

As regards the elephant, attempts have been made since
1905 by the Belgians to domesticate young elephants at Agri
in the Uele River District of Belgian Congo, with a certain
degree of success, about a hundred animals now being employed
there in carrying bricks, dragging timber, and so on.

There are several difficulties in the way of large scale
domestication of the African elephant. It must be remembered
that in India domesticated elephants are not obtained by
ordinary stock-breeding methods, but are obtained by the taming
of wild adult elephants captured in a huge stockade trap called
a keddah, and the capture of a herd of wild elephants is a long
process employing a great number of trained beaters and
trained domesticated elephants.

The African negro would be useless as a keddah man or as
a mahout, and the large scale capture of elephants in Africa

ANIMAL DOMESTICATION 261

would necessitate the importation of a keddah staff of men and
trained elephants from India, an enormously expensive process ;
as a matter of fact, the African elephant can travel so fast and
so far that it is doubtful whether a wild herd could be captured
by keddah methods.

Again, in India the value of domesticated elephants is due
largely to their employment in such work as the loading of
teak logs. The use of elephants merely as beasts of burden
would be uneconomical.

In India the daily ration of an elephant comprises 860 lbs.
of sugar cane and 60 lbs. of flour chappaties ; that is to say,
an elephant eats more than 900 lbs. of food per day, and it will
carry a load of 12 cwt. at a pace no faster than a man's walk,
whereas the same load could be carried as fast and as far by
twenty-four porters, who in one day would require only 48 lbs.
of food altogether.

It must be noted, too, that elephants require a great deal
of water, and many of the African safari routes are deficient
in this for a good part of the year.

Nowhere in Africa is the timber industry sufficiently
developed to justify the capture and feeding of elephants for
that purpose alone, and for any other form of work the animal
is uneconomical.

Certain species of deer probably offer the most favourable
prospects of domestication in the future. Complete domestica-
tion is not necessary ; animals kept in large preserves with
surroundings as nearly natural as possible would be as profitable
as a domestic herd to a breeder, and would probably be a great
deal healthier. Past experience has shown that certain species
can be acclimated very readily in new areas. Such has been the
case, for example, with the Axis deer, the Japanese and Pekin
Sika deer, the red and fallow deer of Europe, the North
American wapiti, and Virginia deer.

The wapiti or elk appears to adapt itself readily to almost
any environment, and will breed as freely within the narrow
limits of a menagerie paddock as in its native environment.

CHAPTER XXIII

TYPES AND BREEDS OF FARM ANIMALS

Even the briefest description of the multifarious breeds of
domesticated animals and birds that occur in the world would
extend far beyond the limits of this chapter, and for that matter
beyond the limits of the whole book itself. This chapter,
therefore, will concern itself merely with the salient features
of the breeds of horses, cattle, sheep, pigs, and poultry that
occur in the agricultural districts of Western Europe and
North America. It must be pointed out, however, that in
limiting description to the farm animals of these areas, no
injustice is done to the question of stock-breeding as a whole,
since the livestock breeds of Europe, and particularly of Great
Britain, are easily the most important of the world's breeds
of domesticated animals, if one may judge by their distribu-
tion over the world's surface and by the financial value of the
livestock breeding industry in Western Europe and North
America.

It may be noted that the pre-eminent position held formerly
by British livestock breeders as exporters of pure bred stock
has been encroached upon considerably of late years by stock-
breeding industries established in North and South America,
in South Africa, and in Australia, where improved types of
West European livestock have been created. One may instance
the Corriedale breed of sheep in New Zealand, the Australian
Merino sheep, the Australian improved Orpington or so-called
Australalorp breed of fowl, the Australasian dairy shorthorn
and Friesian strains of cattle, the American Wyandotte and
Rhode Island breeds of fowl, Poland-China and Duroc -Jersey
and Chester-White breeds of hog, American Percheron horse,
and American Merino sheep.

Horses. — The breeds of domesticated horses can be divided
into two groups, namely, heavy horses and light horses ; the
second of these groups may be further subdivided into the
Driving Class and the Riding Class, the heavy types being all
classed as Draft horses (Fig. 39).

Of the draft breeds, the chief are the Shire, Clydesdale, and

262

TYPES AND BREEDS OF FARM ANIMALS 263

Suffolk of Great Britain ; the Percheron of France ; and the
Belgian draft horse.

Fig. 39. — Light and Heavy Types of Horse.

As regards the light horses, there are a number of different
breeds. The most important are the Thoroughbred, Arab,
Hackney, Cleveland Bay, Yorkshire coach horse, and the

264 THE PRINCIPLES OF APPLIED ZOOLOGY

Mountain and Moorland ponies of Great Britain ; the Standard-
bred or American trotter ; the Orloff or Russian trotter ; and the
Oldenburg or German coach horse.

The Shire horse, which takes its name from the south-
eastern counties of England, is the modern representative of
the old English Black Horse or Great Horse, a native breed
whose size and strength was increased by importation of large
built horses from Flanders and Germany during the reigns
of Norman and Plantagenet kings in order to produce a horse
capable of carrying a man in heavy armour. The invention
of gunpowder relegated the Shire horse to agricultural purposes.

This breed is the largest and heaviest breed of horse, and
finds its chief use to-day in draft work in the seaports and
manufacturing towns of England. The export trade in Shires
has fallen off, owing to a slackening of demand from North
America, where the breed is considered to be rather too heavy
and slow moving, and its hairy legs rather a handicap on muddy
land.

The Clydesdale is a native of Scotland and is used
commercially for lighter draft work, especially in the northern
ports of Great Britain. There is no doubt that the Clydesdale
has been influenced by Shire blood. There is very little
difference between a well-bred Clydesdale and a Shire, beyond
the possession by the former of cleaner, flatter bones and less
feather on the legs. The Clydesdale, however, is slower in
coming to maturity but has a longer working life. In both
breeds the prevailing coat colours are bays and browns. On
the whole, however, it is safer to regard both types as belong-
ing to the one breed, and it would probably be to the advantage
of both if they were amalgamated and registered in one stud
book. The tendency towards loss of size in the Clydesdale
and towards coarseness in the Shire could be counteracted by
the use of Clydesdale stallions on Shire mares.

The Clydesdale is a popular breed in Canada, where it rivals
the Percheron in the public esteem.

The Suffolk horse is indigenous to the eastern counties of
England, and until recently its distribution was quite local.
It has a thick-set body and short legs, and from its appearance
it has received the name of Suffolk Punch. There is no feather
on the legs, as with Shires and Clydesdales, so that the leg does
not become caked with mud from agricultural lands. While
there is no question that the Suffolk is a hard worker, there
was not long ago a prejudice against it in the districts of England,
outside East Anglia, on account of its supposed stupidity.

TYPES AND BREEDS OF FARM ANIMALS 265

The Percheron, which gets its name from the La Perche
district of Normandy, France, is very similar in build to the
Suffolk, but the body and legs are more in proportion. The coat
colour is grey or black, and the legs are without feather. The
origin of the breed is not certain, but apparently native horses
were improved by Arab and Barb blood, and later by importa-
tion of horses from Belgium and Denmark,

The Percheron is now the most numerous and popular of
the draft breeds in the United States. Its advantages he in
its clean limbs and its slightly greater speed than the Shire and
Clydesdale. In Great Britain the breed is not widely known.

The Belgian draft horse bears some resemblance to the
Percheron, but the chest is fuller and the body deeper and
broader. The legs are clean, but there is a tendency towards
small, narrow feet. The prevailing colour is chestnut, although
bays, browns, and roans appear. It is a very ancient breed,
famous throughout the Middle Ages, and imported into England
to improve the Old English horse. It is specially suited for
heavy draft work on the Belgian quays, although its action is
rather slow.

The Thoroughbred or English racehorse is of mixed origin.
There were running horses in England before the Stuart kings,
but the foundation of the breed is due to Charles II., who
imported Eastern mares, the so-called Royal mares. The
three present lines of Thoroughbred descent originated from
three famous sires— the Byerley Turk, imported in 1689 ; the
Darley Arabian in 1706 ; and the Godolphin horse of 1724.
The influence of Barb, Arabian, and Turk combined, with the
drastic selection of racecourse competition, has produced the
modern Thoroughbred with its long limbs and greyhound
appearance. Coat colour is generally bay or brown, less
commonly chestnut or grey and, rarely, black. The value
of the Thoroughbred is not confined to racecourse work but is
applicable to the improvement of almost all breeds of light
horses.

The Arab horse, to which the English Thoroughbred owes
so much, is, as its name implies, an Eastern breed, but its origin
is not clear. Whilst it is probable that horses existed in Arabia
at a very early period, it is not certain that the Arabs possessed
this type until after the commencement of the Christian era.
The Arab type has always been kept pure, and no animal
is considered as pure bred unless it can be traced back to the
five mares of Al Khamseh.

The characteristics of the breed are similar to those of the

266 THE PRINCIPLES OF APPLIED ZOOLOGY

Thoroughbred. The rather broad forehead with prominent
eyes is very distinctive. The hardiness of the Arab horse
is traditional, for in endurance trials it has no rival. As in the
Thoroughbred, the predominant coat colour is bay, but greys,
browns, and chestnuts are common. The breed has been
introduced into Spain, England, America, and Eastern countries,
but apart from its influence on the Thoroughbred, the Arab has
been little favoured in Great Britain until recently.

It is a matter of convenience, at this juncture, to refer to
the Hunter, which, although not a distinct breed of horse,
deserves some description on account of its use and value.

Since the greater number of Hunters are not pure bred, there
is some variation in type. Constitution is of great importance,
owing to the arduous nature of its work, and in consequence
an Arab cross is particularly valued. While the very best
Hunters must necessarily be thoroughbred or nearly so,
a cross-bred animal suits the requirements of the majority of
followers of hounds. A useful Hunter can be obtained from
a Thoroughbred sire and a light cart mare, but probably the
best cross is between a good Hunter and a Thoroughbred.
In Great Britain there is a Hunter's Improvement and National
Light Horse Breeding Society which has the object of improv-
ing and promoting the breeding of Hunters, whether for riding
or driving or for military requirements.

The Hackney is native to the eastern countries of England,
and is usually believed to have originated at the end of the
nineteenth century from crosses between the early Norfolk
Trotter and the Shules or Shields horse, which gave an infusion
of Arab blood. While the Hackney was first associated with
the eastern countries, it spread into Yorkshire and became a
distinct strain, the Yorkshire Hackney.

The Hackney, which is well known to the sight-seeing public
at agricultural shows on account of its very showy action in
trotting, stands at a height of 15-2 to 15-3J hands, and its
general appearance indicates considerable strength. It is a
popular export breed, and finds numerous buyers in North
America and the Argentine.

The Cleveland Bay is indigenous to Yorkshire and is a large
size carriage horse. The breed was highly esteemed in the
middle of the nineteenth century, but was faced with extinction
by the advent of railways and the disappearance of the stage
coach. Fortunately, however, it is suitable for farm work, and
so the breed has been saved. The animal stands 16-1 to 16-2
hands high, has good sloping shoulders, short legs, oval back,

TYPES AND BREEDS OF FARM ANIMALS 267

powerful loins, and long quarters. The colour is bay. A
white blaize or white foot is an indication of foreign blood.

A later breed, arising in the same area, is the Yorkshire
coach horse. It is probably a branch of the Cleveland Bay
breed, and is similar to it but is taller, and has a higher and more
free action. While of course there is a reduced demand for
coach horses owing to motor transport, the ruling prices
indicate that a good class coach horse of exceptional appear-
ance, as is the case with the Yorkshire breed, will always find
a market.

There are a number of distinct breeds of ponies in the
mountain and moorland districts of the British Islands. While
differences in size and appearance occur, a common origin of
the British forms is probable. The various breeds — Welsh,
New Forest, Dartmoor, Exmoor, Fell, Dales, Shetland, High-
land, and Connemara — are distinguished by their hardiness,
their adaptability to severe climate and poor food, and their
great strength. While the conditions of their existence make
them surefooted and active on rough ground, these conditions
are disadvantageous in that indiscriminate breeding under
them produces such defects as ewe-neck, low withers, narrow
quarters, and sickle hocks. In this connection some reference
must be made to the work of the National Pony Society in
Great Britain, whose aim is to encourage the production of
high class riding ponies. For entry in the Stud Book, ponies
must not exceed 14-2 hands high. At such a height, such a
pony as a polo pony must be a powerfully built animal, since
it has to carry weights which are considered ample for a Hunter.

The Standard Bred or American Trotter is the national horse
of the United States. There is some doubt as to the origin
of the breed. The grandsire of " Hambletonian," the most
famous of American trotting horses, was an animal believed
to be of Norfolk blood. " Hambletonian " was foaled in 1849,
and, between 1867 and the present day, every trotter, except
one, that has lowered the record, has had Hambletonian blood.

For registration it is laid down that the animal must be
the progeny of a registered standard trotting horse and a
registered standard trotting mare. If a stallion, he must have,
himself, a trotting record of 2-30 minutes for the mile, or better,
or be the sire of three trotters with records of 2-30, or better.
If a mare, she must have a trotting record of 2-30, or be the
dam of one trotter with a record of 2-30.

The American trotter is distinguished by great shoulder
development, arising through the increased size of the pectoral

268 THE PRINCIPLES OF APPLIED ZOOLOGY

muscles. There is a tendency for the forefeet to come very
close together in consequence, and there is a greater liability
to interfere, that is to say, to strike the limb with the opposite
foot when moving.

The breeding of trotting horses is an important industry
in the United States, and whilst in the Atlantic States flat
racing receives more attention than trotting, in the west and
south the reverse is the case.

The other trotting breed is the Orloff or Russian Trotter.
This breed was founded by Count Alexis Orlov-Tchetmensky
at Khrenovoya, south of Moscow, and is of mixed origin. An
Arab, imported from Greece in 1775, was the first great sire,
and his offspring, by a Danish cart mare, mated to a well-built
Dutch mare, produced the sire from which all the Orloff trotters
are descended. In consequence of their ancestry, the breed
is not fixed in type, the draft horse characteristics tending to
appear as regards head and legs, and the Oriental blood as
regards body. Of the three trotting breeds, the American is
much faster than the English Hackney or the Russian trotter.

The Oldenburger or German coach horse is a light draft
horse, 16-1 6 J hands in height. The body is rather large,
with a long and arched neck, high withers and rump, and
comparatively long legs. The colour is bay, brown, or black.

Cattle. — The history of the introduction of cattle to England
has been told by Wilson. He has shown how, starting with the
Celtic Shorthorn, introduced by Belgic tribes, the Romans,
Anglo-Saxons, and Norsemen in the later invasions, each
brought with them new kinds of stock.

The Romans introduced a heavy breed, mainly white, with
black markings on muzzle, ears, eyes, and lower limbs, and
with long up-turned horns. From this strain the wild white
cattle are believed by some authorities to be descended. The
Anglo-Saxon cattle are believed to have been small, red in
colour, and to be represented to-day in the Lincoln, Suffolk,
Sussex, Devon, and Hereford breeds. The Norse invasion
is believed to have been responsible for the introduction of the
small, short-legged, hornless or polled cattle, of dun colour,
possibly represented to-day by the Aberdeen-Angus and
Galloway breeds.

The modern breeds of domesticated cattle are usually
grouped, according to their aptitude for producing milk or
beef, into Dairy Cattle and Beef Cattle. Certain breeds which
are noted for both milk and for flesh-forming characteristics,
are classed as an intermediate group of Dual Purpose Cattle.

TYPES AND BREEDS OF FARM ANIMALS 269

It must be understood that an aptitude for milk production
and one for flesh production are to some extent antagonistic
qualities. An animal cannot possess the best points of the

Chartley
Wild Cattle.

Dairy
Shorthorn.

^i

Beef
Shorthorn.

;(£."«-

Fig. 40.— Types of Cattle. (After Wallace.)

dairy and beef breeds at one and the same time, so that this
intermediate grouping, while convenient from the economic
point of view, is really somewhat artificial.

A hundred years ago probably all breeds were dual purpose,

270 THE PRINCIPLES OF APPLIED ZOOLOGY

and the modern exaggerated importance attached to milk
and flesh production is a consequence of the prominence
at the large agricultural shows of certain breeds in which
there has been a concentration either upon the production of
meat or of milk. Such single purpose cattle are not bred
under normal conditions on the farm, but require special
attention which cannot be given by the ordinary farmer.
Nearly all the prominent beef breeds are claimed to have good
milking strains, and probably 80 per cent, of European cattle
and 98 per cent, of American cattle are dual purpose.

Wallace, whose arrangement we follow here, divides breeds
. of cattle, therefore, into the two following groups : —

(a) Beef Cattle, those breeds kept mainly for beef production,
and including the Shorthorn, Hereford, Aberdeen -Angus,
Galloway, Devon, Sussex, West Highland, Longhorn, Welsh
Black, Red Poll, Park, Devon breeds of Great Britain ; and

(b) Milch Cattle, including the Ayrshire, Kerry and Dexter,
British Friesian, Jersey, Guernsey breeds.

It is desirable at this point to indicate the general characters
of the Beef, Dual Purpose, and Dairy cattle.

The Beef breeds should have a compact, deep body, set low,
with heavy quarters. The Dairy breeds have a refined appear-
ance, as compared with beef cattle ; owing to the greater depth
and width of the hindquarters, the general outline of the body
is wedge shaped ; the dairy animal has a lean look, the body
being long and not so well filled (Fig. 40). In the bull of the
dairy type, a pedigree showing heavy milk production in
the dam and grandams is of the greatest importance, since the
quality of milk production is apparently transmitted by the
female through the male line.

Dual purpose cattle, as stated above, rarely possess dairy
and beef characters in the one animal ; but the name is given to
breeds where the cows are good milkers, and when dry, fatten
quickly and provide a good carcass. The bullocks can be
readily fattened and are in demand by the butcher.

The Shorthorn breed, which in numbers equals the remain-
ing breeds put together in the British Isles, originated in the
north-east district of England. The history of Shorthorn
breeding will be discussed in the following chapter. The
success of the breed is largely due to its dual purpose character,
to its suitability for various climates, and to its value in grading
up native cattle in foreign countries. Some strains of Short-
horn are beef animals, but the majority of Shorthorn strains
can be regarded as dual purpose. At the same time the breed

TYPES AND BREEDS OF FARM ANIMALS 271

can compete with the purely dairy breeds, and there are there-
fore Dairy Shorthorn strains which, while being excellent milkers,
will, when dry, fatten rapidly.

The Dairy Shorthorn Association in Great Britain has paid
much attention to milk records, registering in this respect not
only pedigree animals, but also non-pedigree animals which
have authentic milk yields. It is hoped that, by mating non-
pedigree cows with pedigree Dairy Shorthorn bulls, the offspring,
after several generations, will qualify for registration in Coates'
Herd Book, and thus increase the number of pedigree animals.

The coat colours of Shorthorn cattle are red, white, and roan.
Roan arises from the red by white cross, and is the commonest
colour in Great Britain. White is not a popular colour, since
it is avoided by importers in tropical countries owing to the
tendency of white cattle to suffer skin blistering, but white
animals are used in obtaining the so-called " blue-grey " cross-
bred animal, a cross between Shorthorn bull and Galloway cow.

The Hereford breed is, as the name implies, native to the
county of Herefordshire and neighbouring districts of England.
It is one of the oldest of modern breeds, and had no little reputa-
tion even before its improvement in the latter half of the
eighteenth century. It is noted for its strong constitution,
resistance to disease, and early maturity. The coat colour is
very distinctive, the body being deep red with head, chest, and
under surface pure white. Owing to its hardiness, immunity to
disease, especially to tuberculosis, and its suitability for grading
up range cattle, the Hereford is always in demand in North and
South America. It is distinctly a beef breed, the practice of
permitting the cows to suckle their calves having prevented
the improvement in milk production of the breed, since there
has been no selection of heavy milkers to use for breeding.

A hornless strain of Hereford has been created in the United
States during the present century, and a separate Herd Book
has been established.

The Aberdeen-Angus breed is indigenous to the north-
eastern districts of Scotland. Its origin is not clear, but
apparently such black, hornless cattle have existed in these
districts for centuries. Its improvement started at the begin-
ning of the nineteenth century, and the work of M'Combie of
Tillyfour, Aberdeenshire, is classical in this connection. At
the Smithfield Fat Stock Show, the Aberdeen-Angus has more
successes to its credit than any other breed. In twenty-one
years, eleven championships and five championships have been
secured by the breed, and for fourteen years in the carcass

272 THE PRINCIPLES OF APPLIED ZOOLOGY

classes an Aberdeen -Angus has won the championship. This
unrivalled position of the breed as a beef animal keeps it in
demand by the butcher and by stock buyers in Canada and
the United States. It is an animal of early maturity and of
excellent quality meat. It also fills out very well, the pro-
portion of dead to live weight being very high, and there is
consequently very little waste in the carcass. Black coat
colour and the polled or hornless condition are characteristic
of the breed, and while the animal appears to be smaller than
other beef breeds, on account of its short legs, it actually is one
of the heaviest breeds.

The Galloway breed arose in the south-western part of
Scotland, and is probably one of the oldest of our modern
breeds. So ancient, indeed, is its ancestry that no trace can be
found of the breeds which went to its formation. The Galloway
is in many respects the grandest and most impressive looking
of British breeds. It is black and polled, but differs from the
Aberdeen -Angus in that the bones are heavier, the hair longer,
and the poll not so pointed. It is a noted beef breed, the milk
yield being deficient. The cross-bred animal, known as the
" blue-grey," obtained by mating a white Shorthorn bull with
a Galloway cow, is celebrated as an excellent butcher's animal.

Sheep. — There are several ways of classifying sheep, but
probably that of (a) Long wools, (6) Shortwools, and (c)
Mountain breeds is as convenient as any other.

Long wool breeds are distinguished by their large size, long
wool, heavy fleece, absence of horns, and the white colour of face
and shanks. They include the following breeds : British
Leicester, Border Leicester, Lincoln, Cotswold, Romney Marsh,
South Devon, Devon Longwool, Wensleydale, and Roscommon.

Of the Shortwools, true Shortwools are represented in the
Merino, which is characterised by a firm, closely packed fine
white wool, rather giving the appearance of a cauliflower.
The breed is white in body colour, and the skin in some strains
is much wrinkled in the neck region (Fig. 38).

The Down breeds, which have all been influenced more or
less by English Southdown blood, are hornless, dark faced, and
dark legged. The wool is short and fine and of medium weight.
The Shortwool breeds include the following so-called ' Down
Breeds," namely, the Southdown, Shropshire, Suffolk, Oxford
Down, Hampshire Down, Dorset Down, and in addition, include
the Dorset Horn and Ty eland breeds of Great Britain, the
Merino breed of America, and the Rambouillet breed of
France.

TYPES AND BREEDS OF FARM ANIMALS 273

The Mountain breeds are characterised by their hardiness
and rather small size. They are very active and can thrive on
poor food. The wool is coarse in most of the constituent breeds.
In their natural surroundings, which are hillv or mountainous
regions, they are slow in reaching maturity, but if brought
down to the lowlands they thrive more quickly.

They include the Scotch Blackface, Cheviot, Lonk, Derby-
shire, Gritstone, Rough Fell, Swaiedaie, Limestone, Penistone,
Herdwick, Welsh Mountain, Exmoor Horn, and Dartmoor.

In such areas of the world as Australia, New Zealand, and
Argentina, the earliest object of sheep farming was the pro-
duction of fine wool, and for this purpose the Merino was far
and away the most suitable breed. The perfection of refrigera-
tion and cold storage methods, however, so enlarged the market
for mutton that the carcass became of greater importance than
the fleece. The big fat sheep, half-bred or three-quarter-bred
Lincolns, or similar breeds, have gradually tended to
supplant the small and lean, fine wool breeds. There has
been as a result a disturbance of the wool market in that a
scarcity of fine wool and a superabundance of coarse wool
has come about. In Australia, where the droughts make it
impossible always to fatten sheep for the market, this change
from fine wool breeds to carcass breeds has been less pro-
nounced. In Europe, except for Great Britain, the develop-
ment of sheep farming in these newer countries has caused a
general decline in the sheep-rearing industry.

An interesting development of the possibility of producing
a breed which whilst being a good mutton producer will also
produce fine fleece, is the Corriedale breed, produced by the
New Zealand breeder Games Little, by crossing a Lincoln ram
with a Merino ewe, and carefully selecting and inbreeding the
succeeding progeny. There are now more than a score of
registered flocks of this breed.

Pigs. — The prolificacy of the pig, its rapidity of growth,
and the catholicity of its tastes as regards food, make it the
most important and the most easily reared of meat^producing
animals ; but the requirements of the pig for food of a high
protein content, since it is not a grazing animal, limits the
distribution of the hog-rearing industries to areas where such
food is easily and cheaply obtainable ; areas, for example,
where potatoes or cereals are produced, such as Ireland, Belgium,
Holland, Germany, Denmark, the corn belt of North America ;
or to areas where natural food is available, such as the forests
of Servia or South-western Germany or Spain and Portugal.

18

274 THE PRINCIPLES OF APPLIED ZOOLOGY

The type of animal required varies according to locality.
On the whole, in North-western Europe the " bacon ' type of
pig is bred, that is to say, a long-bodied animal with lean back
and thick belly, in whose flesh the muscle and fat occur
alternately in streaks (Fig. 41).

In North America the so-called "lard hog" is bred, an animal
useless for bacon production but admirable for meat or for lard.
The lard hog is a natural consequence of a plentiful cereal
supply in the form of corn. The bacon pig of the barley-
growing regions of Canada and Europe is a natural consequence
of the cost of cereals, since the swine breeders feed their
animals as much as possible on grasses and clover, which
produce more lean meat than does a corn diet.

Fig. 41.— The Bacon Pig.

Of the enormous varieties of domestic pig, the really
important commercial breeds are those derived or cross
bred from the west European and, in particular, from the
British breeds. These are divided into (a) White breeds,
comprising the Large, Small, and Middle White or Yorkshires,
the Curly-coated Lincoln, the Cumberland, Old Glamorgan,
and the Large White Ulster ; and (6) into Dark breeds, com-
prising the Large Black, Berkshire, Tamworth ; (c) the Belted
breeds, such as the Essex, Wessex, and Saddleback ; and (d)
the Spotted breeds, comprising the Gloucester varieties.

Poultry. — The various breeds of poultry are usually classified,
according to their economic use, into : —

(a) Laying or non-sitting breeds.

(b) General purpose breeds.

(c) Table breeds.

(d) Ornamental breeds.

The laying breeds include the medium-sized and small

TYPES AND BREEDS OF FARM ANIMALS 275

birds with a strong inclination towards egg production ; they
are naturally active and seldom sit on their eggs, thus requiring
exercise if they are to do well. As a rule they are quickly
maturing birds, but their flesh is inferior for table purposes.

They comprise the following breeds : namely, the Ancona,
Andalusian, Compine, Hamburg, Hendon, Leghorn, Minorca,
and Redcap.

General purpose breeds, as the name implies, occupy an
intermediate position between laying breeds and table birds,
and include most of the various neglected, semi-wild breeds
of backward countries. In Europe and America they include
the La Br esse, Faverolles, Longshin, Orpington, Plymouth Rock,
Rhode Island Red, Wyandotte, Sussex, and Australorp breeds.

The table breeds are valuable chiefly for their flesh. They
are poor layers, slow in movement, with a tendency to put on
flesh. They include the Dorking, Coucon de Malines, Game,
and Indian Game breeds.

Ornamental breeds comprise particularly strains of the
Bantam, Brahma, Cochin, and Silky breeds.

A good practical guide as to the category in which to place
a particular fowl can be obtained by regarding the bird from
the side and drawing an imaginary line from the front of the
neck to the thigh. If the greater part of the body is found to
He behind this line, it is an indication of good laying qualities ;
should the greater part fall in front of this line, the fowl will be
found to be a table bird. If the body is apparently evenly
balanced on each side of the line, the bird will be a general
purpose or utility fowl, since both the laying and the flesh-
forming qualities are equally developed.

CHAPTER XXIV

LIVESTOCK BREEDING

Speaking generally, the livestock breeder can choose between
three lines of policy in order to obtain animals which show
the particular qualities he desires ; he may either go in for
inbreeding, outbreeding, or genotype selection.

Inbreeding methods are based upon the occurrence of animals
which possess to an unusual degree the power of stamping their
characters upon the offspring, this impressive ability being
termed " prepotency."

The principle adopted is that of selecting a foundation stock
of rigidly selected animals, and, from this stock, to breed the
resulting herd, no outside blood being admitted. Inbreeding
may be carried to such length that an animal is mated to his
own dam or sister.

Inbreeding was the method used by Bakewell, the founder
of the Longhorn breed of cattle, a breed which, during the
eighteenth century and the first ten years of the nineteenth was
the most widely distributed and valuable British breed of cattle.
He used inbreeding methods also to produce his famous Leicester
breed of sheep. Bakewell started his Longhorn breeding
at Dishley, in Leicestershire, about 1750, by obtaining the two
best Longhorn heifers he could obtain. From these two,
and a famous bull, ' Twopenny," derived from one of these,
he built up his famous Dishley herd. His breed became
anxiously sought after, and eventually the Longhorn, from a
large, lean, big-boned, slowly maturing animal local to North-
western and Midland England, became the chief beef animal
all over the country, until, owing to the weakened constitution
and lessened milk capacity that inbreeding had brought about,
it was ousted from popularity by the modern Shorthorn breed.

The methods of the first eighteenth century improvers of
the old English Shorthorn cattle — the Collings of Darlington —
were modelled upon those of Bakewell, and consisted in principle
of the rigorous selection of a foundation stock and close in-and-in
breeding of these selected animals. The breed of Shorthorn
cattle they produced became known as the Durham or Tees-

276

LIVESTOCK BREEDING 277

water breed, and is still known under the name of Durham on the
Continent and in America. The Shorthorn, before improve-
ment, was a bulky animal, but although larger than the
improved breed, weighed really less, since its body was less
round and deep. As in the case of the Longhorn, improvement
was made at the expense of constitution and milk production.
Two notable successors of the brothers Colling were the Booths
and Bates, both Yorkshire families of stock-breeders who, from
animals procured from Collings, founded noted strains of the
breed; similar methods were followed by Cruickshank in
Scotland in producing the Cruickshank strain.

Although there is a popular belief that inbreeding results
in decreased fertility and loss of stamina, the scientific evidence
does not bear this out. The method in itself does not result
in weakened constitution, but just as the good qualities of
particular animals may be intensified in offspring whose parents
are blood relations, so defective characters occurring in these
parents may be intensified also. In a private herd subject to
rigorous selection there is nothing harmful in the system of
inbreeding. In the absence of such selection, however, a larger
and larger proportion of animals will show sterility and lack
of stamina.

A later development of inbreeding is line-breeding, that is to
say the breeding from animals within the same line of descent
but not immediately related.

Line-breeding has undoubtedly given good results in the
improvement of most breeds. The desirable result of in-
breeding, namely, the fixity of type, can be attained just as
surely, although more slowly, by this less drastic method, and if
line-breeding is accompanied by systematic and drastic weeding
out of defectives, the proportion of such misfits that appear will
in time be considerably fewer than will occur under a system
of intensive inbreeding.

Out of the system of inbreeding has arisen the belief in
pedigree breeding, that is to say, of selecting breeding animals
partly on their own merits, partly upon the merits of their
ancestors. From this has arisen the practice of keeping stud
books and herd books in the different breeds of horses, cattle,
sheep, and pigs. Thus, in Great Britain, no Shorthorn bull
can be registered in Coates' Shorthorn Herd Book unless it has
five crosses of Shorthorn blood, no cow unless it has four
crosses. In the North American Shorthorn Herd Book, no
animal can be registered unless its pedigree is recorded in
Coates' Herd Book. No animal can be registered in the

278 THE PRINCIPLES OF APPLIED ZOOLOGY

Argentine Shorthorn Herd Book unless its pedigree can be
traced in unbroken succession of named dams and registered sires
to a named dam born in or before 1850, or to a named sire born
in or before 1845. In Great Britain, unless a Thoroughbred
horse can trace back in the female line to one of the original
mares in the first volume of the Stud Book, it is impossible to
get it entered in the Stud Book of to-day.

Obviously the defects of such a system are that breeders are
led to neglect individual merit in a non-pedigree animal. An
inferior animal with an irreproachable pedigree will not make
a good breeder, since its inferiority is due to the loss of certain
characters upon which the excellence of the breed is based,
and it will only produce animals similarly lacking the desirable
characters. Where the presence or absence of the desired
characters can be indicated by some rigid test, as is afforded
for the Thoroughbred horse or the American trotter by the
practice of public racing, the danger of inferior animals propa-
gating their like is of course minimised.

The converse method to that of inbreeding is that termed
outbreeding, in which system care is taken to avoid mating
animals which are related to one another. While this method
is free from the disadvantages attendant upon inbreeding
methods, its defect is that it leads to lack of uniformity in the
herd.

The system of outbreeding is closely related to the earliest
method of breeding, mass selection, or phenotype selection, the
principle of which is to breed from the best individuals of each
generation. Mass selection thus stakes everything upon
individual merit. Now the outward appearance of an animal
is not necessarily an indication of inward qualities.

Such characteristics as vigorous constitution, exceptional
milk or egg-production ability and so forth, are not always
correlated with external characters. Further, such qualities
are not necessarily handed down directly to the children.
Exceptionally tall human beings, for example, do not neces-
sarily produce tall children, but more usually produce children
whose height is nearer the average height for the race.

Outbreeding and mass selection methods, however, are
capable of successful results if the individuals used as foundation
stock have already shown their capacity to produce offspring
possessing the desired quality. Thus, for example, in an
endeavour to produce a herd of cows with high milking capacity,
the ordinary method of outbreeding would be to employ a
bull whose mother had been a noted milk producer. Such a

LIVESTOCK BREEDING 279

method might or might not result in the production of cattle
of high milk-producing capacity, but would be in any case
less successful than the employment of a bull which had been
known already to have produced, say, half a dozen daughters
of high milk production. The use of parents whose ability
to produce good stock has been tested, may be termed genotype
selection. It is of course a method only applicable to the
selection of male animals, since the testing of a female animal
on the basis of the quality of half a dozen of her daughters would
take too long. With quickly maturing animals, or with animals
which may produce six to twelve young at a time, such as
hogs or poultry, however, it is possible to test the breeding
capacity of either sex of the animals selected as foundation
stock.

The application of Mendelian methods to genotype selection
may, however, in the future make this method of breeding
the only scientific one. At present, however, there is very little
Mendelian data available concerning the inheritance of animal
qualities.

The discoveries of Mendel, the Austrian monk, were of course
made with plants, and since his time a great deal of similar
work has been done with regard to the inheritable characters
of plants, whereas comparatively little is known about the way
the characteristics of animals are inherited. Coat colour of
animals, however, seems to behave according to the Mendelian
laws. Thus, if black Aberdeen-Angus cattle be crossed with
red Aberdeen-Angus cattle, the offspring are all black. If these
black offspring be crossed with one another or with similarly
produced cattle, the resulting generation would be 75 per cent,
black and 25 per cent. red. The red would breed always red
cattle. Of the blacks, 25 per cent, would always produce blacks ;
the remaining 50 per cent, would produce again blacks and reds.

According to the Mendelian view, the black of the original
parent is a characteristic produced by the presence in the tissue
cells of a double dose of a certain factor ; let us call it B. The
complete absence of this factor is the cause of the red coloration
of the other parent. The germ cells — spermatozoa or ova —
of the black parent will each contain a single dose of B. The
germ cells of the red parent will not contain B.

Now each individual of the first generation is the product
of the union of a germ cell from the black parent with one from
the red parent. Thus all the first generation will contain germ
cells with only a single dose of B., whose presence, however, is
sufficient to ensure that this generation is black in colour.

280 THE PRINCIPLES OF APPLIED ZOOLOGY

The germ cells of this first generation, however, will be of two
sorts, some containing a single dose of B., others not containing
B. at all. When this first generation is hybridised, therefore,
some individuals will contain a double dose of B. in their tissue
cells and will be capable of producing black cattle ; they are
pure dominants, to use Mendel's term. Others will not contain
any B. at all in their tissue cells, and will produce always red
cattle ; they are pure recessives. The remainder will have
tissue cells with a single dose of B. and, although themselves
black, their offspring will again be a mixture of 75 per cent,
black to 25 per cent. red.

The two characters black and red colour, in this case, form a
pair of contrasted characters or allelomorphs. The hybrid
generation, which when interbred produces the mixture of red
and black, again is said to be composed of impure dominants.
The term heterozygote, however, is preferable. Certainly in this
case the hybrid resembles superficially the dominant parent,
but in other cases the hybrid does not resemble either parent,
or may be exactly intermediate between both parents. If the
term heterozygote be used, the pure dominant or pure recessive
should be referred to as homozygote.

The condition in cattle of hornlessness, generally termed the
" polled condition," again forms with the horned condition a
pair of contrasting characters.

Thus, if an Aberdeen-Angus animal, which is black and
polled, be crossed with an Hereford, which is of red body colour
with a characteristic white face, and is horned, the hybrids
will be found to be white faced with black body colour, and
without horns. That is to say, the white face of the Hereford
and the black coat and polled condition of the Aberdeen-
Angus are dominant characters, whilst the plain coloured face
of the Aberdeen -Angus and the red body colour and long
horns of the Hereford are recessive characters.

If animals of this first generation type are interbred, the
resulting offspring fall into eight groups according to their
characteristics. These groups, together with the numerical
proportions of the groups to one another, are as follows :-—

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

White

White

White

Plain

White

Plain

Plain

Plain

faced

faced

faced

faced

faced

faced

faced

faced

Black Black Red Black Red Black Red Red

Polled Horned Polled Polled Horned Horned Polled Horned
27 9 9 9 3 3 3 1

LIVESTOCK BREEDING 281

The cattle in group (4) are like the Aberdeen-Angus ; those
in group (5) resemble the Hereford. Group (1) contains all
the dominant characters ; groups (2), (3), and (4) contain two
dominants and one recessive ; groups (5), (6), and (7) contain
one dominant and two recessives ; and group (8) contains all
the recessive characters.

The limitation of our knowledge concerning the inheritance
of Mendelian characters of animals is due chiefly to the expense
and time required for such experiments. In the breeding of
plants, many thousands of varieties may be bred quickly at
little expense. On the other hand, the breeding of farm live-
stock is a comparatively long process, owing to the time it
takes for each generation to reach maturity. More serious
than this is the great expense entailed in breeding even a few
animals where the offspring, though possibly invaluable from
the point of view of the geneticist, do not possess the commercial
qualities which determine saleable value.

The following data, however, are available : —
Chestnut coat colour in horses is homozygote. It is recessive
to bay and brown colours.

Grey colour in horses is dominant to dun, bay, black, and
chestnut.

Trotting in horses is dominant to pacing. In trotting, the
near foreleg of course moves with the off hind leg, whereas in
pacing the two legs of the same side are moved together.

In cattle, black coat colour is dominant to red. In Short-
horns, red is apparently homozygous and so is white. The
hybrid generation of a red and white cross is a blend of red and
white and is termed red roan. The hybrid of a black and white
cross is a blue roan or blue-grey, such as is the Black Galloway
and white Shorthorn cross.

In Sheep, black wool colour is homozygous and recessive
to white.

The horned condition in sheep curiously enough is dominant
to hornlessness in males but recessive in females. Thus, if a
horned breed be crossed with a hornless breed, the hybrid
generation is composed of horned rams and hornless ewes.
When this generation is interbred, males occur in the ratio of
three horned to one hornless, and females occur in the ratio of
one horned to three hornless.

In hogs, white coat colour is dominant to coloured coat,
but spotted individuals may occur in the cross.

When breeds are crossed together, generally for some com-
mercial purpose such as beef, milk, or wool production, the

282 THE PRINCIPLES OF APPLIED ZOOLOGY

method is called cross-breeding. The idea in cross-breeding
is to combine as far as possible the best points of both breeds.
The well-known " blue-greys," the cross between the Black
Galloway cow and the White Shorthorn bull, provide a classic
example. This cross may also be made between the Aberdeen-
Angus breed and White Shorthorns. In fact, such was the
popularity of the blue-greys, that in the early nineteenth
century the Aberdeen -Angus as a breed nearly faced extinction.
The blue -grey is noted for its early maturity and superior
quality of beef, and is always in demand by butchers.

Cross-breeding is a system of breeding which does not meet
with approval on all sides. There is a tendency to neglect
the breeding of the pure bred stocks, as happened in the
case of the Aberdeen -Angus, and there is a temptation to
breed from the exceptionally fine animals which are sometimes
produced by the cross. Both of these practices are unsound,
since cross-breeding has its basis in the excellence of the pure
bred stocks : and breeding from cross-breds is bad, in that it
speedily leads to loss of the superiority and uniformity of the
original cross-breds.

The crossing of different but related species of domestic
animal is termed hybridisation.

The most important example of hybridisation is the mule,
or cross between a male donkey and a female horse. Both
sexes of the hybrid are sterile, at any rate in the very great
majority of cases. It is also possible to obtain a cross between
zebra and horse or ass, the product being termed a zebrule.
Such hybrids are undoubtedly stronger and more vigorous
than either parent, and are very often more resistant to
disease.

Thus, the Texas cattle fever of the United States, peculiarly
fatal to imported Herefords and Shorthorn cattle, rarely attacks
zebu cattle owing apparently to some quality of the zebu's
skin that repels the Acarid host of the fever organism. A
Zebu-Hereford cross apparently inherits this power of disease
resistance whilst inheriting the build and beef qualities of the
Hereford parent, and further, is fertile for both sexes, a some-
what unusual character in hybrids between species of the ox.
Usually in crosses between such species the female is fertile
and the male hybrid sterile.

In the case of the cattalo or ox-bison cross, mentioned in a
previous chapter, the hybrids are intermediate in character
between the parents, but superior to either in strength and size.
The male hybrid is sterile, but the females are fertile and can

LIVESTOCK BREEDING 283

be crossed with bison or ox, the progeny again being inter-
mediate between its parents in characters.

Bound up with this practice of cross-breeding and hybridisa-
tion is the question of telegony, the rooted belief of very many
practical animal breeders in the influence of a particular male
animal to stamp his characteristics not only upon his own
offspring by a particular female, but upon the offspring of that
female and other succeeding males. The prevalence of this
belief among stock-breeders is evident in the rules of entry
into many flock books. Breeding ewes cannot, for example,
be registered in certain breeds if they have been crossed with
rams of other breeds.

The classic example of telegony, of course, is that of Lord
Morton's mare, a chestnut Arab which was mated to a male
quagga and produced a hybrid of evident cross-bred character.
The mare was subsequently mated to a black Arabian stallion
and bore a filly, and, a year after this, a colt. The filly and the
colt were very decidedly, as regards body structure, of the
Arab breed, but in the colour and hair of the mane they
resembled the quagga ; both had dark stripes across the withers
and neighbouring parts of the neck, and dark bars across the
back of the legs. The bars on the legs both in the hybrid
and the foals were more strongly marked than on the legs of
the quagga, and the stripes on the withers of the hybrid were
fewer and less apparent than in the foals.

This case, however, has not been able to withstand the fire
of later scientific criticism.

Striping in the horse, especially in Oriental breeds, is not
uncommon. The original yellow dun horse of the forest type
had, it is believed, a band down the back and bars like a zebra
across the legs, with faint striping on neck and withers. The
striping of Lord Morton's foals may therefore have been a
reversion to some ancestral type.

Cossar Ewart of the University of Edinburgh carried out
some classic experiments which in their results oppose this
belief in telegony. He crossed the Burchell zebra stallion
" Matopa "to a chestnut polo pony. The offspring were twin
hybrids. The next year the pony was mated with a light
chestnut thoroughbred stallion, and one foal resulted. Again,
she was mated with ' Matopa " and had a third hybrid foal.
Later, mated with a dark chestnut thoroughbred, she produced
another foal. The three hybrids were strongly striped, whereas
the two foals in no way resembled the hybrids, but were chestnut
in colour without the slightest trace of striping. Similar

284 THE PRINCIPLES OF APPLIED ZOOLOGY

experiments by other investigators also support the view that
there is no scientific basis for a belief in telegony.

It may be added there is similarly no scientific support for
the breeders' belief in maternal impression, and that the Scots-
man M'Combie, the founder of the modern Aberdeen-Angus, had
no necessity to build his famous high black fence around his
fields to prevent his black Aberdeen-Angus cows dropping
anything but black calves.

PART III
ANIMAL INDUSTRIES

CHAPTER XXV

BEE-KEEPING

The value of the three principal insect products useful to man,
namely, honey, silk, and lac, to a civilised community is still
of very great importance despite the competition of sugar,
of artificial silk, and of cellulose varnishes.

Quite apart from the commercial value of bee products,
apiculture is a branch of agriculture almost essential to a fruit-
growing area, since bees are the chief insect agents in the cross-
fertilisation of many varieties of fruit trees, and experience
has proved that there is a definite correlation between the yield
of fruits of certain kinds, particularly apples and plums, and
the abundance of bees in the area.

In every country where bee-keeping is practised, the insect
utilised is some race or other of Apis mellifica. This species
has been made use of from time immemorial, and deserves
perhaps as well as many other animals the term ' domes-
ticated." The only other species of Apis are three Indian
representatives. Of these, Apis dorsata, the Rock Bee, is a
large bee, whose worker is as big in size as the queen of Apis
mellifica. Each colony builds a huge comb on the face of a
cliff or on a branch of a big tree, the comb being as large as
five feet across. The bees are very ferocious and will not
tolerate domestication in a hive. Their combs are extensively
robbed by the wild hill tribes, not only for the honey, but for
the large quantity of wax.

Apis florea, the Little Bee, builds a single comb as big as a
man's hand in bushes or under the eaves of buildings. It is
not prone to sting, but will not tolerate domestication, which
in any case would hardly be worth the small quantity of honey
to be obtained.

Apis indica, the Indian Bee, is probably a sub-species of

285

286 THE PRINCIPLES OF APPLIED ZOOLOGY

Apis mellifica, and occurs both wild and semi-domesticated
throughout India. The colony builds several parallel combs
generally in semi-enclosed places such as hollow trees or rock
crevices. The yield of honey is nothing like so great as that
produced by European races of Apis mellifica.

In the tropics of the Old and New Worlds, wild bees of the
genera Melipona and Trigona, minute bees characterised by
vestigial stings, make large nests in hollow trees, or in holes in
rocks and walls. The nest often possesses a projecting entrance
like a funnel, which can be closed at night by cerumen, a mixture
of wax and earth or resin. The honey of these so-called
" mosquito bees " is sought for and much used by natives of
their area of distribution.

Apis mellifica itself comprises a number of races, each of
local origin. Thus there is the North European Black Bee,
with its grey Carniolan variety, from Austrian Tyrol ; the
golden banded Italian race, the Caucasian race, the Tunisian,
Syrian, Cyprian, and so on.

The most favoured races in Great Britain and North America
are Black and Italian and Black-Italian hybrids.

The Housing of Bees. — A healthy colony of Apis mellifica
will comprise 30,000 - 40,000 worker bees, a single queen, and
a varying number of male or drone bees. In a state of
nature, such a colony will suspend its vertical combs of cells
from a tree branch or a rock, relying upon the overhang of
tree or rock for protection from the elements. Under the
conditions of Northern Europe or America, such a wild colony
would be unable to tolerate winter conditions unless it had
been so fortunate as to occupy a hollow tree or a rock crevice.

The old system of bee-keeping, and one, unfortunately,
still too prevalent, is to house the bees in a box or a skep,
that is to say, a straw structure like an inverted basket. In
such a box hive or skep the vertically suspended combs become
cemented to the sides of the house, and the colony has
to be killed before any honey can be obtained ; periodical
examination of the insects, or artificial feeding, is impossible.

The great advance in the technique of modern bee-keeping
dates from the introduction of the Frame Hive, devised by
Langstroth in 1857. The Frame Hive (Fig. 42) consists in
principle of a square box made up of a number of horizontal
stories.

The box rests upon a platform about nine inches from the
ground, and the platform projects in front of one side of the
box base so as to form an alighting board ; at the junction of

BEE-KEEPING

287

alighting board and box a horizontal slit provides an entrance
into the hive.

Roof

Super

Queen
Queen-excluder
sheet

Brood
chamber

Floor
board

A frame in
position

Fig. 42.— The Frame Hive. (After Ghosh.)

The lowermost story is termed the brood chamber ; the
remaining stories are termed supers, and will vary in number
according to the size of the colony. Commencing with the
alighting board, a brood chamber, and a roof, the hive can be

288 THE PRINCIPLES OF APPLIED ZOOLOGY

increased by the interpolation of supers to keep pace with the
growth of the colony throughout the summer. The best type
of frame hive is made with a double wall, there being an outer
shell, which is just a square box, within which there is the
tower of supers, separated from the outer shell by a space of
one or two inches.

In each super a number of rectangular frames are fitted.
Each frame consists of a sheet of wax, on each side of which
ready-made cell bases have been stamped, enclosed in a
rectangular frame of thin strip wood one and three-eighth
inches in width. The frames are arranged parallel to one
another and vertically, not touching each other nor touching the
sides of the super, nor the top nor base of the adjoining supers.
The frames are just sufficiently clear of one another to allow
the bees to crawl over the waxen faces. A super will contain
ten such frames.

In such a hive the frames are easily examined or removed.
The roof of the hive can be removed, the bees driven down
from the uppermost super by a few puffs of smoke from a
bellows containing smouldering tinder, and any individual
frame can be removed and examined, or can be replaced by a
fresh frame. A super of frames can be removed bodily and the
honey in the combs readily extracted, without the necessity
of killing a single bee. Furthermore, in a frame hive, winter
feeding of the colony is possible, cakes of candy being placed
periodically on the top of the uppermost super.

A simple but ingenious form of hive for use in tropical
countries where ground hives are a disadvantage, is the
Khartoum Hive, designed by Mr H. H. King for the cultivation
of Apis mellifica subsp. unicolor in the Southern Sudan. It
is an improved type of native hollow palm -log hive, but is
woven of basketwork, dom palm leaves being utilised, and,
as shown in Fig. 43, consists of two sections, one to act as a
brood chamber, the other to act as a honey chamber. The
honey chamber and its contained combs can thus be removed
without the necessity for destroying the colony and the brood
combs. Further, the hive can be suspended in a tree and so
protected from honey-loving ground animals.

Problems of Apiculture. — The most important general
problems of the modern apiculturist concern : —

(1) The control of swarming.

(2) The prevention of disease and parasites.

(3) The care of bees in winter.

Swarming is the natural corollary of the increase in abund-

BEE-KEEPING

289

ance of individuals in an already overcrowded hive, and a
swarm usually consists of a number of workers led by the
old queen who has become superseded in the old hive by a new
queen reared by the colony.

Such a swarm may settle on the bough of a bush or tree

Entrance
hole

Pole

Brood chamber

Honey chamber

Cap

Entrance hole

Brood
chamber

Honey chamber

Wide opening1

Flange

Queen excluder
Fig. 43.— The Sudan Hive. (After King.)

near at hand, and can be readily shaken into a skep and trans-
ferred to an empty hive ; but very often the swarm travels some
distance across country and may be irrecoverable. The
tendency of a swarm to travel can be overcome to some extent
by clipping the forewing of one side of the queen with a pair
of fine scissors, early in the spring, so that if swarming does

19

290 THE PRINCIPLES OF APPLIED ZOOLOGY

occur, the queen cannot fly and the swarm will not leave the
vicinity of the hive.

The chief causes of swarming are an overcrowded condition
of the hive and an inability of the queen to find empty cells
in which to lay eggs.

In a hive of bees there are, so to speak, two categories of
working bees : there is a stay at home category, or nurses —
usually worker bees of less than a month old — queen attendants,
guards, drones, and ventilators — that is to say, old workers
whose duty it is to create a circulation of air through the hive
by continuous wing movement ; there is a category of outside
workers, or foragers, who bring in the supplies of nectar and
pollen from the flowers. All these bees require their share of
honey before any can be taken by the bee-keeper. The amount
of honey used by a colony simply to maintain its existence
during a year is large, probably at least 400 lbs. Therefore
what the bee-keeper can appropriate is the surplus beyond this
400 lbs., a surplus which will depend very largely upon the
weather conditions during the period of summer when blossoms
are secreting nectar freely, a period usually termed the honey
flow, and will depend upon the number of field workers available
after the duties inside the hive have been allowed for.

In an average season the amount of surplus honey per
hive should average 50 lbs. Now the bee-keeper cannot
influence weather conditions during the honey flow, but he can
influence, to some extent, the margin of field workers over
home workers by restricting the amount of brood that is being
reared, since brood rearing absorbs a very great deal of labour
within the hive.

A queen honey-bee is capable of laying 3,000 eggs per day
throughout the honey gathering season, and the resulting larvae,
unlike those of other bees, are fed individually by nurse bees
at frequent intervals throughout the period of larval life, a
period of eight days. Such feeding involves an average of
1,300 visits per larva per day. Thus, brood rearing involves
heavy cost in labour and in food, which is, of course, honey
and pollen.

The usual policy in apiculture, therefore, is to encourage
brood rearing in early spring, to replace the losses due to
winter mortality ; to discourage brood rearing during early
summer, the period of the honey flow ; to encourage brood
rearing in late summer so as to establish a strong colony before
the winter arrives.

Brood rearing may be discouraged by shutting off the

BEE-KEEPING 291

lowermost one or two supers from the upper supers by a queen
excluder, a perforated zinc plate whose openings permit worker
bees to pass through to the storage cells above, but prevent the
passage of the larger queen. Other methods are the removal
of brood comb and imprisonment of the queen in a wire cage.
Thus during the summer the queen's opportunity to lay eggs
is restricted, the hive becomes overcrowded from the progeny
of the spring broods, the hive temperature, in sympathy with
the outer temperature, is high, and conditions conduce to
swarm production. Unless the overcrowding is minimised
by provision of extra supers, and unless a keen watch is kept
upon the brood combs for the conspicuous projecting cells of
future queens, and these cells removed, swarming is inevitable
and a consequent loss of potential surplus honey will result.

Bee Diseases. — The diseases to which bees are subject may
be divided into two groups, namely, diseases affecting the adult
bees and diseases aifecting the brood.

Of all these diseases, the two affecting the brood which are
known respectively as European Foul Brood and American
Foul Brood, are by far the most serious and a menace to
apiculture everywhere.

Both diseases are bacterial in origin, American Foul Brood
being probably caused by Bacillus larva3, and European Foul
Brood being probably caused by Bacillus alvei or Bacillus
pluton, and both diseases are highly infectious, infection occur-
ring via the alimentary canal through contamination of food
with spores of the causative organisms. Infected larvae
usually become dark in colour, become semi-liquefied, and
eventually dry up to what is termed a " scale."

Sac Brood is an infectious brood disease of bees caused by
a filterable virus.

There are at present two methods for the treatment of a hive
in which a brood disease occurs. These two methods are : —

(1) The removal of the adult bees to a new hive, and the
disinfection of the frames of the infected hive by immersion
for forty-eight hours in a mixture of 20 parts of formalin with
80 parts of water, or, preferably, of 90 per cent, of alcohol.
The frames after disinfection are thoroughly dried and aired,
and can then be placed in the new hives.

(2) The Alexander method, in which the queen is removed
and the bees are left in the infected hive in a queenless condition
for twenty-seven days, during which period the workers clean
up the cells and polish them in readiness for the eggs of the
new queen. A young Italian queen is then introduced. Weak

292 THE PRINCIPLES OF APPLIED ZOOLOGY

colonies must be strengthened or united with another colony
before treatment.

The following table, as given by A. H. M'Cray and G. F.
White of the United States Department of Agriculture,
summarises the difference between these three important brood
diseases : —

Table I. — Differential Features in the Diagnosis of the Brood
Diseases of Bees by Laboratory Methods.

General appear-
ance of brood

Proportion of
affected brood

Position within
cell

Age of the larvae
Coloration

Odour

Consistency

Kind of brood
affected

Scales

Microscopic find-
ings

Cultures .

European Foul Brood.

Brood irregular. Large
amount of affected brood
unsealed

Varying number of young

larvae affected, usually

many
Usually curled at bottom.

Larva? soft, with melting

appearance

Usually die before capping

Larvae yellow, grey, and
brown

Slight, inoffensive

Soft, rather friable .

Often considerable amount
of drone brood as well as
worker brood

Usually small and lie at bot-
tom of cell. Yellow, grey,
or brown in colour. Some-
times a few larger, brown,
rubber-like scales. All
scales separate readily
from cell wall

Bacillus pluton always.
Bacillus alvei usually.
Streptococcus apis some-
times. Bacillus orpheus,
Bacterium eurydice. Bacil-
lus vulgatus, and Bacillus
mesenteric us, occasionally

Any of the above organisms
except Bacillus pluton

American Foul Brood.

Very irregular ; affected
brood sealed, sunken
and perforated caps
present

Usually a large amount
of brood affected

Extension along lower
cell wall. Larvae soon
become a shapeless
mass

Usually die after capping

Usually dark chocolate

Usually strong character-
istic odour. More or
less offensive

Viscid, can be " roped "
out a distance of three
or four inches

Any considerable amount
of drone brood less
likely to be seen

Extension along lower
cell wall dark brown
in colour. Surfaces
somewhat smooth.
Separate from cell
with difficulty

Usually only Bacillus
larvce. Occasionally
Bacillus vulgatus and
Bacillus mesentericus

Frequently negative.

Never Bacillus lance
on common media

Sac Brood.

Brood less irregular,
perforated caps pres-
ent, dark sunken
caps not so pro-
nounced as in Ameri-
can foul brood.

Small amount of brood
affected.

Extension along lower
cell wall. Head

turned upward.
Normal form main-
tained.

Almost invariably die
after capping.

Soon become dark
brown to almost
black.

None.

Contents watery and
granular. Larvae can
be removed from cell
without rupturing
body wall.

Greatest ravages among
worker brood.

Extension along lower
cell wall. Dark in
colour, often black.
Somewhat rough-
ened appearance.
Separate readily from
cell wall.

Negative as a rule.

Nearly always wholly
negative.

The most serious disease to which adult bees are subject
is that peculiar form of wing paralysis accompanied by
abdominal distension, by putty-like excreta, and by death, to
which in Great Britain the name of Isle of Wight Disease
used to be applied.

This term apparently has been applied to a combination

BEE-KEEPING 293

of symptoms characterising two separate diseases, namely,
Microsporidiosis, a Protozoan disease caused by the presence of
a Microsporidian Protozoan — Nosema apis — in the chyle
stomach of infected bees, and the main cause of the " dry
diarrhoea " ; and Acaridiosis, caused by the presence of a
mite — Acarapis woodii — in enormous numbers in the tracheae
of the thorax. The bee thus becomes semi -suffocated and
incapable of flying, and its abdomen becomes distended owing
to inability to defecate, as it normally does, whilst flying.
Acaridiosis is apparently peculiar to Great Britain.

Parasites and Predators. — The principal animal enemy of
hive bees is the Large Wax Moth (Galleria mellonella), a Pyralid
moth, and its companion species, the Lesser Wax Moth ( Achroia
grisella). These moths creep into the hive at dusk and lay
eggs on the combs, usually becoming stung to death before
they emerge again. The caterpillars, which grow to the size
of an inch, tunnel through the combs, and although essentially
scavenging in habit, cause great destruction. The tunnelling
habit, aided by a silken protective web, protects the caterpillars
from the bees.

CHAPTER XXVI

SERICICULTURE AND LAC CULTURE

Natural silk, although produced by a variety of insects and
spiders, is obtained on a commercial scale only from the cocoons
of moths belonging to the families Bombycidce and Saturniidce.

The Bombycidce includes the domesticated silk moth,
Bombyx mori, and a number of other species characteristic
of the Oriental region ; Bombyx mori is unknown in the wild
state. The Saturniidce, of which the only British species is the
Emperor Moth Saiumia pavonia, includes a number of semi-
domesticated and wild silk-producing genera, notably Attacus,
Anther cea-t Philosamia, and Anaphe.

The silk is formed in the body of the caterpillar as a fluid
in the salivary glands, which open by two small apertures on
the lower lip. The silk is poured out as a thick, gummy,
transparent fluid, which rapidly hardens and dries, assuming
then a yellow or brown tint. When used in cocoon building,
the silk occurs as an outer layer, whose thread is not neces-
sarily continuous, to fix the cocoon to some object, and as an
inner layer, formed of practically one continuous thread wound
regularly round and round and ending at some point inside the
cocoon where the caterpillar finishes. From such a cocoon,
the greater part of the silk can be reeled off in a continuous
thread. The cocoon must first be heated, however, to kill
the enclosed insect, which would otherwise injure the silken
wall when biting its way out. In other Saturniidce, however,
the cocoon consists of distinct layers, composed of somewhat
irregularly disposed threads, and the emerging moth merely
pushes its way through the end of the cocoon. Such cocoons,
if required to produce commercial silk, must be teased up and
the tangled fibres spun by machinery.

There are thus two categories of silk, namely, reeled silk
and spun silk.

The principal kinds of reeled silk are Mulberry silk, Shantung
silk, Japanese silk, Tasar silk, Muga silk.

The principal kinds of spun silk are Eri silk and Anaphe silk.

Mulberry Silk is the product of Bombyx mori, originally a

294

SERICICULTURE AND LAC CULTURE

295

native probably of Northern China, but now established as a
domesticated insect throughout China, in Japan, India,
Kashmir, Burma, Siam, Corea, Afghanistan, Persia, Central
Asia, Armenia, Syria, Turkey, Egypt, Algeria, Greece, Italy,
France, Spain, America, Australia ; in every region of the
world, in fact, where it has been possible to acclimatise the
White Mulberry (Morus alba), the only food plant on which
the insect will thrive.

The original race of Bombyx mori was probably bivoltine,
that is to say, possessing two broods in the year, but domestica-
tion has produced a number of races or variations which differ
considerably in the number of broods per year.

In countries where the summer is short and hot and the
winter long, univoltine races have evolved ; in countries where
hot, damp conditions prevail, multivoltine races occur. The
cocoons of univoltine races are much superior to those of multi-
voltine races. European and Japanese races are chiefly
univoltine. Chinese and Indian races are chiefly multivoltine.

The general methods of rearing the caterpillars and of
obtaining the silk are much the same in all the producing areas.
The caterpillars are reared in round or oval trays of wicker-
work on a bed of chopped mulberry leaves, to which fresh food
is added at frequent intervals varying from nine times a day
for the youngest caterpillars to five times a day for the oldest.
The caterpillars moult at intervals of three or four days, and at
that time take no food for twenty or thirty hours. They must
be then left undisturbed.

The trays of caterpillars are kejot on shelves under cover
of a roofed building.

In a cool climate, such as that of Southern Europe, there are
five caterpillar stages separated by moults. The approximate
number of days of each stage, the amount of food, and the
area required by the caterpillars which hatch from one ounce
of eggs (30,000-35,000) are, according to Lefroy, as follows : —

Area in Square Feet.

Stage.

Days.

Food in Lbs.

Univoltine.

Polyvoltine.

1

5

4

1

1

2

4

12

5

9

3

6

40

10

30

4

7

112

20

100

5

10

700

40

200

296 THE PRINCIPLES OF APPLIED ZOOLOGY

When the worms are full fed they become restless and are
transferred to a special tray in which they spin their cocoons,
the process taking three days. Those cocoons which are
required to produce moths for egg laying are picked out. The
remainder are sterilised by baking or by exposure to sun heat.

The moths from unheated cocoons emerge, copulate, and
lay eggs, which are received usually on paper, to which they
stick. The parent female, after death, is pounded up with a
little water and examined microscopically for the shining
pebrine bodies (vide Chapter XIX.), and if infected, that batch
of eggs is rejected.

The eggs do not hatch, in the case of univoltine races,
until after the lapse of ten months. They are kept, therefore,
for six months in a refrigerator, then removed and gradually
introduced to a temperature of 60°-70° F., at which they remain
for thirty days before hatching.

One ounce of eggs will produce about 36 lbs. of dried cocoons,
or about 30,000 cocoons, and the length of the thread from a
cocoon averages 1,300 yds.

After the cocoons have been heated in an oven, or by sun
heat, or by steam, they are soaked in warm water until the
silk glue is softened. Several loose ends from several cocoons
are then twisted together, and the combined thread is reeled
off by a machine. The product is raw silk. The waste resulting
from damaged cocoons, the irregularly spun and tangled
outer layers, and the unreelable portion of the inner layer,
constitutes floss silk after it has been teased and spun.

Shantung Silk is the product of the Saturniid Anthercea
pernyi, the Chinese oak silkworm, a wild and semi-domesticated
moth of China. As the name implies, the chief food is oak leaves,
and the silk is of a pale buff colour. The caterpillar itself is also
yellow. The cocoon is large, nearly two inches long, and firm.

Japanese Silk, or Green Silk, is the product of Anthercea
yami-mai, a green caterpillar which also feeds on oak leaves.
It is reared on a large scale in Japan and was introduced into
Europe in 1861.

Tasar Silk and Muga Silk are the products respectively of the
Indian silk moths Anther cea paphia and Anthercea assami, poly-
phagous forest-frequenting Saturniids of Northern India. Tasar
silk varies in colour from yellow to greenish-brown, according to
the particular race of Anthercea paphia which has produced it.

Muga silk is white or yellow, and is consumed locally in
Bengal and Assam, where it is produced.

These moths cannot apparently be domesticated, the

SERICICULTURE AND LAC CULTURE 297

caterpillars not thriving in captivity. Cocoons, therefore, are
collected in the forests, the search involving considerable labour,
although attempts are being made here and there to establish
the insects in plantations of favourite food plants, as is done
in China and Japan with the oak silkworms.

In Assam, however, the Muga silkworm, although fed on the
trees, is carefully supervised and removed to the rearers' houses
when ready to spin. The cocoons are killed by exposure to
the sun, are boiled in an alkaline solution, and are then reeled
by primitive hand methods. In European factories, however,
cocoons of Anthersea species are usually teased or carded, and
the products then spun by machinery.

Eri Silk, the chief variety of spun silk — a term which,
unfortunately, also embraces the spun product of mulberry
silk refuse — is also the product of an Indian Saturniid, Philo-
samia ricini. This insect is reared in Assam almost as readily
as the mulberry silkworms can be reared, and very much in
the same way. Although polyphagous in habit, it is reared
in captivity on leaves of the castor-oil plant (Ricinus communis).
The worms are, of course, much bigger than those of Bombyx
mori and take up more room. When full fed, they are put into
baskets with dried mango leaves. All the moths are allowed to
emerge naturally from the cocoons, and the cocoons are then
treated by crude, local methods. They are first turned inside
out, in order to remove the cast pupal skin, either by hand or
by the little Coryton machine introduced by the Agricultural
Department of India. They are then soaked in 12 per cent,
sodium carbonate solution, teased up by hand, and hand spun.

In West Africa, a Saturniid moth Anaphe is being experi-
mented with as a possible source of spun silk. The species
which are being experimented with are Anaphe infracta,
Anaphe ambrizzia, and Epanaphe moloneyi. The larvae are
gregarious and pupate in large communal nests of silk attached
to branches of trees. The larvae are extraordinarily susceptible
to extraneous interference, so that domestication on the fines
of that practised with Philosamia ricini is apparently imprac-
ticable. There seems, however, a distinct possibility that in
French West Africa, in Nigeria, and in Belgian Congo the
collection of these silken nests as a source of spun silk will
develop into a commercial proposition.

Lac Culture. — Shellac, the basis of most commercial varnishes
and enamels, and a raw material in the manufacture of gramo-
phone records, sealing wax, and a host of miscellaneous house-
hold articles, is the product of a Scale Insect, Tachardia lacca,

298 THE PRINCIPLES OF APPLIED ZOOLOGY

which is deliberately cultivated on various food plants in India,
particularly in the Central Provinces. An inferior quality
of shellac, containing a much greater percentage of wax, is
obtained in Madagascar from another Coccid species, Gascardia
madagascarensis , closely allied to the Indian lac insect.

The lac itself is a resinous substance exuded by the female
insect and forming a protective covering around her, preventing
her from moving from the particular spot on the plant upon
which she settled as a larva.

A large proportion of the trees selected by Tachardia as
food plants contain a gummy or resinous sap, and the colour
and quality of the lac are influenced by the particular tree upon
which the insect happens to settle. Thus the best lac is obtained
from insects cultivated on the Kusumb (Schleichera trijuga) ;
but since this tree does not grow well below an altitude of
2,000 ft., the insects are frequently cultivated on more widely
distributed trees such as Ber (Zizyphus jujuba), Palas (Butea
frondosa), Peepal (Ficus religiosa), Siris (Albizzia lebbeh), and
in Assam on the herbaceous plant Cajanus indicus.

On a tree infected with Tachardia, the twigs will appear to
be covered with resinous globules adhering to the bark and so
close together that it is difficult to see any unattacked areas
of bark. Twigs from such a tree are referred to as brood lac.

The eggs are laid by the female beneath the resinous outer
covering, and the newly hatched larva?, which are scarlet in
colour, emerge through a hole at the posterior edge of the scale
and migrate to succulent unattacked parts of the plant. Having
selected a suitable spot, each larva settles down, and if it happens
to be a female, does not move again from that point. If a
male, however, the insect will migrate again after a period of
time dependent upon the particular brood. This swarming
of newly emerged larvae occurs twice a year, there being a hot
weather brood and a cold weather brood.

Male insects appear about one month after the fixation of
the larvae, in the case of the hot weather brood, and are either
winged or wingless. The males of the cold weather brood
emerge about three and a half to five months after fixation
and are wingless. The exudation of the lac commences soon
after fixation of the larvae, proceeds very slowly at first,
but much more rapidly after fertilisation.

After the emergence of the young brood the parent females
die rapidly, and all that is left is an almost black shrivelled skin
lying in the central cavity of the lac encrustation.

It is important to note that the female ceases to feed three

SERICICULTURE AND LAC CULTURE 299

weeks before the emergence of the larvae, so that a twig carrying
brood lac can be cut from the plant as long as a fortnight before
the emergence of young larvae, and sent to distant places by mail,
without any harm being done to the females or developing eggs.

It is of course a matter of great importance to the cultivator
that he should know the approximate dates of emergence of
brood for his own particular locality.

The general principle of carrying on lac culture is the
inoculation of suitable trees, generally prepared beforehand by
pruning, by tying to them a number of twigs bearing brood lac.
Branches of brood lac are cut from an infected tree about a
fortnight before brood emergence is expected, are cut into
short pieces of eight to eleven inches, and are then spread on
bamboo racks in an airy place. About a fortnight after, when
a few tiny deep red insects are seen crawling over the sticks, the
sticks are taken to the trees already pruned and tied to their
branches with some cheap fibre ; about five to twenty sticks
are tied in each tree, according to the size and condition of the
tree, and they are tied in such a way that their ends touch the
branches. After the larvae have ceased to emerge, a period
of ten days to as long as four and a half weeks, the brood sticks
are removed, brought home, and the resin scraped off with
knives or twisted off with the hand. The scraped material is
termed commercially stick-lac. This stick-lac should be washed
as soon as possible from the red dye which it contains. After
repeated washing and straining, the lac is like a coarse pale
orange powder, and constitutes the seed-lac of commerce.
This, when mixed with 2-3 per cent, of yellow orpiment to
impart colour, and with 4-5 per cent, of pine resin to lower the
melting point, is melted down and recooled into sheets of
commercial shellac.

The lac dye, which was formerly more valuable than the
lac itself, and was extensively used before the introduction
of aniline dyes for the colouring of wool and leather and silk,
is now of little commercial value and is used by Hindu women
for colouring the soles of their feet, or is used as a manure,
being rich in nitrogen.

The lac insect suffers considerably from the attacks of
predaceous caterpillars of a small Noctuid moth, Eublemma
amabilix, which eat both lac and the scale insect inside. A
predaceous Tineid caterpillar, Hypatina pulverea, is even more
abundant than Eublemma, and almost equally destructive.

Like other Scale Insects, Tachardia is also heavily para-
sitised by Chalcid and Braconid Hymenoptera.

CHAPTER XXVII

FRESH-WATER AND ESTUARINE FISHERIES

The term " fishing industry " is not necessarily to be restricted
to methods of capturing food fishes, but is a term which covers
various commercial methods of capturing or cultivating a large
variety of aquatic invertebrate and vertebrate animals, destined
either for human consumption or for other uses. The term can
thus be applied to the procuring of precious corals, sponges, pearls,
shellfish, cuttle fish, beche-de-mer, fishes, seals, and whales.

The fishing industries can be divided into three cate-
gories : —

(1) Fresh- water and estuarine fisheries.

(2) Inshore or coastal fisheries.

(3) Offshore or bank fisheries.

The fresh- water and estuarine fishing industries, again, may
be divided into three categories, namely : —

(1) Those concerned in the capture of the migratory phases
of certain fishes.

(2) Those concerned in the breeding and rearing of food
fishes in artificial fish-ponds or in lakes.

(3) Those concerned with the rearing of young fishes in
hatcheries, for the restocking of streams and lakes with fishes
intended either as food, or to provide sport for anglers.

A considerable number of fishes, probably the great majority,
migrate when desirous of spawning to water of density less
than that of the normal habitat. Such fishes are termed
anadromous.

The degree of migration undertaken varies with different
fishes. The salmon, for example, a deep sea fish, migrates
from the seas right up to the shallow headwaters of European
and western American rivers in order to copulate and to pro-
duce eggs, and the young salmon must therefore undergo a
return migration to the sea. The sturgeon migrates from the
seas to the lower reaches of rivers. The shad, a sort of herring,
migrates merely from seas to estuaries. The herring migrates
from offshore to inshore waters ; the pike, an exclusively fresh-
water fish, migrates up stream to spawn.

300

FRESH-WATER AND ESTUARINE FISHERIES 301

On the other hand, a number of fishes are known to be
katadromous, that is to say, to migrate to water of greater
density than that of their normal habitat in order to spawn.
Thus the fresh- water eel migrates, when four or five years
old, from the upper reaches of rivers and streams, down-
stream and to the great depths of an area of the Atlantic
Ocean lying south-west of the Bermudas. The conger eel
migrates from inshore waters to offshore waters. The plaice
migrates from inshore waters to offshore waters, and so on.

There are many examples of fishing industries of consider-
able importance in which this habit of migration is taken
advantage of, and fish are caught on a large scale in the river
estuaries either as migrating adults or as returning young
forms. The chief methods involved may be illustrated by
reference to the capture of the following fishes, namely, the
Pacific Salmon, the Sturgeon, and the Fresh- water Eel.

The Salmon Fisheries. — The family Salmonidce, an ancient
family of fishes, comprises a number of fishes of the salmon and
trout type, not all of which are classed as migratory. The
Atlantic Salmon (Salmo salar), the Pacific Steel-head Salmon
(Salmo gairdneri), and the Pacific Sock-eye and Dog salmons
(Oncorhynchus) are extremely anadromous, passing from the
deep waters of the Atlantic or Pacific oceans to the head
waters of west European rivers or of the rivers of the Pacific
Coast of North America. Salmo salar is seldom known to enter
rivers south of the Loire, but prefers the rushing turbulent
rivers of Scandinavia, Western Ireland, and Britain ; the
Pacific Salmon species, however, have a wider area of dis-
tribution, being known from the Santa Ynez Mountains in
California to as far north as Alaska.

On the other hand, the stream and loch species of Salmonidse,
such as the Brown Trout (Salmo fario), the American Brook
Trout (Salvelinus fontinalis), the Alpine Char (Salvelinus
alpinus), the Black Spotted Trout (Salmo clarkei), the Canadian
Great Lake Trout (Coregonus), the Bavarian Great Lake Trout
(Salmo lacustris), the Loch Leven Trout (Salmo levenensis), the
Grayling (Thymallus) , and so on, are generally classed as non-
migratory, but do show some degree of migration in order to
spawn in shallow water. The migratory habit is therefore
probably an ancient habit in this family. It may be noted
that the Rainbow trout (Salmo irideus) of Pacific North America
is migratory in some rivers, non-migratory in others. The
Canadian Land-locked Salmon (Salmo salar var. sebago) offers
an example of a stock of the Atlantic salmon which became

302 THE PRINCIPLES OF APPLIED ZOOLOGY

cut off from the sea by geological disturbances, and has in con-
sequence had to dispense with the extreme migratory habit.

The life-cycle of Salmo salar or of Oncorhynchus is as
follows : —

The season of spawning is autumn and winter, usually
November and December in Europe, but commencing as early
as July in the case of Oncorhynchus. The salmon commence
to run up the rivers in spring or may run up in autumn. It
would seem that salmon of all stages tend to migrate from
the sea towards coastal waters every season, and some
individuals may even reach the lower reaches of rivers, but
only spawning salmon push forward as far as the shallow upper
reaches. The sea trout (Salmo trutta) and the Pacific salmon
apparently do not wander far from the inshore waters near to
the estuary of their parent stream, and the Parent Stream
Theory, the view that salmon always return to the rivers they
were born in, may thus apply to these forms, but almost certainly
does not hold good for Salmo solar.

As the spawning period approaches, the fish lose their silvery
colour, the flesh becomes pale from loss of oil — " white meated "
as the salmon canner terms it — the males become hook jawed
and distorted. These changes are most marked in autumn,
so that spring running fish are far more valuable commercially
to the salmon fisher, who relies upon catching the running fish
in trap nets in the lower reaches, than are autumn running fish,
which, in fact, may be worthless as food.

Spawning takes place in extremely shallow water, to reach
which the fish may have had to make their way up the rapids
of torrential rivers. The eggs are laid in a hole scooped in the
gravel. After spawning, the fish float helplessly down-stream,
tail first, and probably few reach the sea again. This is
particularly the case with Oncorhynchus, owing to the vast
distance between head waters and mouth of the North American
rivers.

The embryo, or alevin, when hatched, measures about half
an inch in length. After one summer in fresh water the young
fish is termed a parr. It is trout-like, with a colour pattern
of dark vertical bars on an orange ground. After one or two
winters in the stream the parr changes into the migratory
phase or smolt, the orange ground colour changing to a silver
hue. The smolt travels down to the sea, probably in spring.
After one winter at sea the fish is termed a grilse ; after more
than one winter the fish may be termed a salmon.

The life-cycle of the salmon is reflected to some extent

FRESH-WATER AND ESTUARINE FISHERIES 303

in the arrangement of the concentric rings of growth shown
by the scales. As shown in Fig. 44, the growth ridges formed
during the parr life are fine and close together. The growth
ridges formed during sea life are coarser, and those formed
during winter are closer together than the summer ones.
Further, if the fish has successfully returned from a spawning

Fig. 44. — Diagram of Scale of a Salmon five years old to show Summer Rings,
wide apart, and Winter Rings, close together, and Spawning Mark a*.
e — exposed part of Scale, on which all but First Year Rings are
indistinct.

migration, the former ragged edge of the scale, a consequence
of the loss of condition produced by fasting and spawning
exhaustion during the run, is marked on the scale by a scar.

Salmon are caught in the European estuaries for com-
mercial sale in considerable numbers, but not to the extent
that prevails in the estuaries and lower reaches of the rivers
of British Columbia and Alaska, whose salmon canning establish-

304 THE PRINCIPLES OF APPLIED ZOOLOGY

ments have supplied the world with the preserved flesh of the
Pacific Salmon.

The local names of the five species of Oncorhynchus upon
which the North American salmon canning industry is based
are, according to Tressler, as follows : —

Scientific
Name.

Puget
Sound.

Columbia
River.

Alaska.

Other
Names.

0. nerka

0. tachawytscha .
0. kisutch .

0. gorfaischa
0. keta

Sock-eye

Spring
Coho, Silver

Pink
Chum

Blue-back

Chinook
Silver

Pink
Chum

Alaska red,

Sock-eye

King, Chinook

Medium red,

Coho

Pink

Chum

Quinnault

Quinnat
Silversides,

Masu
Humpback
Keta, Dog

Of these five species, the Sock-eye and Quinnat Salmon form
the greater bulk of the canned output. The remaining species
are autumn running salmon and their flesh is consequently
much inferior, although much of it is smoked or dried and used
as food for man and dog by the Indian population of Columbia
and Alaska.

In recent years, however, quantities of the Pink Salmon
have been put on the market in canned form. In the rivers of
Hokkaido, the northern island of Japan, the Dog Salmon and
the Silversides, both autumn running species, are caught and
salted in considerable quantity for human food.

The usual method of salmon catching is to catch the running
adults in gill nets, that is to say, perpendicular nets with a
mesh sufficiently large for the fish to push the head through but
not the body, so that the salmon attempting to withdraw is
caught fast by the gill covers. Such nets are either arranged as
stationary nets, held in position by stakes or by buoys and
sinkers across the estuary in zigzag fashion, or they are arranged
as drift nets, hanging from buoys but drifting with the tides.
In some localities nets of smaller mesh are used, either as
seine nets whose ends can be drawn together so as to enclose
the salmon in a circular enclosure or bag which can be drawn
to the shore, or as trap nets, so staked as to form an elaborate
labyrinth -like trap.

In other localities fish wheels are used, operated by the
current. These, as they revolve, pick up the salmon and
throw them into a box by the side of the wheels.

Gill nets and seine nets are usually termed " floating gear " ;
trap nets and fish wheels are termed " fixed gear."

FRESH-WATER AND ESTUARINE FISHERIES 305

The great objection to fixed gear is, of course, that large
numbers of other fishes in addition to salmon, and numbers

Part of a Train of Drift Nets (diagrammatic)

(after Fowler)

SeineNet (after Fowler)

Brail Cork line

Lead line

Italian type of Sardine Round-haul Net

or Lampara

(after Thompson)

Fig. 45. — Types of Fishing Net.

of small salmon, are caught, and since no trouble is taken to
return them to the water, the destruction of fish life is great.

The canneries, which are worked chiefly by Chinese labour,
are situated close to the fishing sites, on the shore, so that at

20

306 THE PRINCIPLES OF APPLIED ZOOLOGY

most only a few hours elapse from the time the fish is swimming
freely until it has been caught and delivered to the cannery,
beheaded and gutted, washed and skinned, packed into pound
cans, steam cooked, and hermetically sealed.

It is obvious that however carefully controlled the methods
of salmon catching may be, there is bound to be an enormous
restriction of the number of fish that reach the spawning
grounds and great danger of the salmon rivers becoming
exhausted. Since, however, the discovery of methods of
efficiently rearing salmon fry, the danger is being met to
a considerable extent in Canada, United States, Japan, and
to a less extent in Europe, by the establishment of salmon
hatcheries along the head waters of the principal salmon
rivers. Female salmon are trapped, their eggs obtained by
gently squeezing the animal over a dish, the milt obtained
similarly by squeezing the male, the fertilised eggs hatched,
and the larvse reared through to parr in perforated boxes
submerged in troughs of swiftly flowing water.

Sturgeon Fisheries. — The sturgeon (Acipenser) is, like the
salmon, a marine fish, which is rarely caught at sea but can
be caught in numbers in the estuaries of rivers to whose lower
reaches the fish migrates in order to spawn. A. sturio, the
North Atlantic sturgeon, ascends the rivers of North America
and Europe, and can be caught in drift nets, although not in
such numbers as is the case with salmon.

Acipenser guldenstadti and Acipenser ruthio (the sterlet)
occur in the Black and Caspian seas and are extensively caught
in the Volga, the roe of the females being salted and sold as
caviare, the swim bladders being exported as isinglass.

Acipenser transmontanus and Acipenser medirostiis ascend
the Fraser, Columbia, and Sacramento rivers of North America,
but they are so outbid in importance by the salmon that their
capture is not carried out on a commercial scale.

Eel Fisheries. — The economic importance of the fresh- water
eel as a food fish is considerably less than it was a century ago
when numerous Dutch eel boats brought cargoes of live eels
up the Thames to Billingsgate market, and eel catching is now
but a local industry in Europe. The adult animal is, of course,
an inhabitant of streams and ponds, and may be captured
therein by trapping or by spearing.

After a period of seven or eight years in the fresh waters, the
eel undergoes a katadromous spawning migration to the deep
waters of the Atlantic. Prior to and during this migration, the
eel takes on the coloration of a deep sea fish, becoming darker

FRESH-WATER AND ESTUARINE FISHERIES 307

dorsally and silvery ventrally, and developing larger eyes.
These silver eels descend the rivers in autumn. They are
rarely caught at sea, however, despite the vast numbers that

Depth of pound 38'
Funnel 10'from bottom

— o

Fig. 46. — A Fish Trap. (From Park Museum Bulletin,
Providence, Rhode Island.)

must cross the North Sea fishing grounds every year. The
eggs are laid apparently in very deep water, and the trans-
parent ribbon-shaped larvae, formerly regarded as representing
a distinct fish genus Leptocephalus, are carried by currents
towards the European rivers, or the North American rivers

308 THE PRINCIPLES OF APPLIED ZOOLOGY

in the case of American eels. Before entering the river
mouth the larva metamorphoses into a glass eel, becoming
rounded and eel-like. The eel is now an active swimmer
rather than a drifter. It apparently hesitates at the river
mouth until more deeply pigmented and then ascends the river
in enormous masses of eel fry. This ascent of vast compact
columns of young eels is a well-known annual feature of
many European and American rivers, and the eels are
captured in enormous numbers but used chiefly for local
consumption.

Fish Rearing. — Fish rearing or pisciculture may concern itself
primarily with fish hatching, the rearing of young fishes intended
for the restocking of depleted rivers or lakes, in which case the
young fishes are not reared beyond the early stages following
the larval one ; or may concern itself with fish culture, the rear-
ing of certain fresh-water food fishes from egg to mature fish.
The provision of fish hatcheries for the restocking of salmon
streams has already been referred to. Apart from this type
of hatchery, the bulk of fish hatcheries in Europe and America,
excluding of course the marine fish hatcheries, are intended for
the commercial production of trout larvae or of very young trout.
The rearing of trout to a size sufficiently large to be of com-
mercial food value would be a troublesome operation, although
actually carried out in some countries, owing to the cannibalistic
habits of most trout and to the requirement by captive trout
of very cold and well aerated water. In Great Britain the
principal species of trout which are reared for restocking of
lochs and trout streams are Salmo levenensis (Loch Leven trout),
Salmofario (Brown trout), Salvelinus fontinalis (American brook
trout), and Salmo irideus (the Rainbow trout). Other species,
however, are supplied by some hatcheries. The stages supplied
are what is termed eyed ova, that is to say fertilised eggs in an
advanced stage of development ; fry, that is to say three month
old larvae ; yearlings, which vary between three to five inches
in length ; and two year olds, which range from five to nine inches
in length.

It must be remembered, with regard to the restocking of
trout streams and lochs, that many Salmonidae are inveterate
cannibals. Salmo fario, for example, can be a veritable fresh-
water shark in ponds or lakes where food is scarce. The Loch
Leven trout (Salmo levenensis) in lochs where food is scarce,
becomes one of the worst of cannibals, and is apt to become
a deep-water frequenter and so useless to the angler.

In Canada and the United States, fish hatcheries have been

FRESH-WATER AND ESTUARINE FISHERIES 309

established also for the hatching and liberation of shad fry
(Alosa) and White-fish fry (Coregonus).

Actual fish rearing, from egg to adult fish, is carried out on
a considerable scale in certain European countries, particularly
Denmark, France, and Germany, the fish concerned being
species of carp. In North America and in Great Britain the
commercial rearing of carp is not carried out, since the com-
petition of sea fish keeps the price of fresh-water fish down
to a level at which carp culture would not pay.

The Cyprinidae or carp family includes the Carp (Cyprinus
carpio), introduced into Europe from the rivers of Russia,
China, and Japan; the Crucian carp (Carassius carassius),
widely distributed over Europe and Northern Asia, and exten-
sively reared as goldfish and silver fish in China and Japan ;
the barbel (Barbus barbus) of Central European rivers ; the
gudgeon (Gobio gobio), of Europe; the bitterling (Rhodeus
sericeus), of Central Europe and Asia ; and numerous other species
under the names of roach, chub, dace, minnow, bream, tench,
and so on. With a few exceptions they are small and feeble
fishes, forming most of the food of predatory river fishes, and
owe their great abundance to the prolific power of reproduction.

The true carp itself, Cyprinus carpio, a native originally of
Northern China, where it has been domesticated for centuries,
is a dull and sluggish fish which thrives in stagnant ponds or
reservoirs and is as omnivorous as the domestic pig. It is, in
fact, one of the easiest of fishes to rear in captivity.

The usual practice in Europe is to use shallow artificial
ponds or natural drainage ponds, normally covered by water,
in the bottoms of valleys too wet for ordinary farm crops, and
kept wet by drainage from the fields. The ponds are occasion-
ally manured with liquid manure to encourage the multiplica-
tion of small Crustacea and other creatures. The ponds should
be calm, exposed to sun heat, and not deeper than eight or nine
feet. They are stocked in early summer with fry, purchased from
hatcheries, or hatched in small breeding ponds. After three
years in the pond the carp are about 2J-3 lbs. in weight, and
are sold at this age, as larger and older ones are coarser. Females
for spawning purposes are kept up to ten years, but are then
useless for food. A little cereal food or household scraps is
given occasionally, but the carp feed mainly on the natural
resources of the pond. As a matter of fact, intensive feeding
methods will produce very rapid growth in carp, particularly
in sub-tropical and tropical climates. Thus in California,
Mexico, and other sub-tropical areas, carp have reached 15 lbs.

310 THE PRINCIPLES OF APPLIED ZOOLOGY

in three years. In China a weight of 30 lbs. in five years is
obtained by supplying abundant food.

In Japan, where almost incredible quantities of carp and
eels are reared in ponds, a common practice is to place young
carp when one or two inches long in the flooded rice fields, in
June ; by October, when the rice is cut, these have grown to
eight to ten inches long and are quite marketable.

The Goldfish (Carassius carassius) is also a common
Chinese fish which has become introduced into Europe and
America. The wild fish is really an olive-green colour, and
a reversion to this colour is commonly shown by races not
subjected to rigid selection.

In the hands of Japanese breeders the goldfish has become
modified into a number of races, many of the most bizarre and
monstrous description.

The eel and the mullet, although often reared in ponds with
carp, are not hatched therein, but are caught with the net in
spring in any brackish water near at hand and placed in the
pond. In the case of eels, special precautions are necessary
to prevent them escaping, but their response in growth to
intensive feeding well repays the trouble of rearing, provided
that there is a market for them.

Fish Diseases. — Fresh- water fishes in the artificial environ-
ment of fish pond or aquarium or hatchery are subject to a
number of ailments, the majority of which, being parasitic in
origin, are liable to become far more intensely epidemic under
these conditions than is the case under natural conditions.

Whirling sickness or " gill trouble " is caused by an
intestinal Protozoon, Octomitus salmonis. The fish loses its sense
of balance and turns over repeatedly in the water with a cork-
screw motion. Affected fishes become eventually so weak that
they lie on their backs with gills distended. The intestines are
filled with a watery fluid swarming with the organisms, and the
walls become yellowish translucent. Transmission of the
disease occurs through an encysted stage of the parasite, which
passes from the fish into the water and becomes ingested by
another fish.

Costiasis is a disease of the external epithelium caused by
the Protozoon, Costia necatrix. The skin of an infected fish
is marked by slimy patches where the epithelium has sloughed
away. In the final phase the gills are attacked and the fish
dies of suffocation.

Remedial measures comprise the transference of infected fish
to a bath of 2 J per cent, solution of sodium chloride (21 lbs.

FRESH-WATER AND ESTUARINE FISHERIES 311

table salt to 100 gals, of water), in which they are immersed
for ten to fifteen minutes ; four treatments at intervals of three
days should be applied. Salt may be used also to disinfect
contaminated hatchery troughs.

Ichthyophthiriasis, another skin disease, is caused by the
burrowing Ciliate Protozoon, Ichthyophthirius multi fills. In
nature, fish are seldom killed by this disease as, owing to the
bulk of medium and the wide range of movement possible to
the fish, individual infestation does not become sufficiently
intense. In ponds and hatcheries, however, the disease may
cause heavy mortality. The skin becomes covered by small
whitish-grey pimples, which occur particularly on head, flanks,
fins, mouth, and gills ; these are the young parasites. As
each parasite grows, the spots become of course larger and tend
to run together into patches. There may be hundreds of
such spots over the surface of the fish. In later stages the fish
is covered with a heavy slime and its skin shows red blotches
or " scalded areas." It stops eating and, as the gills become
covered, eventually suffocates.

Two methods of treatment are possible. The first method
aims at killing the parasites whilst they are on the fish, and
consists of immersing the fish for one minute in a bath of 5 per
cent, solution of aluminium sulphate ; the second method aims
at killing the parasites after they leave the fish, which they do
when fully adult, and consists in placing infected fish in troughs
of swiftly flowing water, whereby the parasites as they leave
the fish are swept away ; it may be added that in an aquarium
the presence of tadpoles or of goldfish, which will eat these
free swimming adults, does much to restrict the severity of an
epidemic of this disease.

Gyrodactyliasis or fin disease is another epithelial ailment
caused in this case by an ectoparasitic Trematode, Gyrodactylus.
This animal sucks away the superficial tissues of the fish and
produces slimy open sores. The fins may become so abraded
that the rays protrude as spines, or the fins may be reduced to
mere stubs.

This disease is frequently epidemic in hatcheries among
fishes of all species and ages. No cure is known. Salt solutions
are not effective. Immersion of the infected fish in 6 per cent,
aqueous solution of cider vinegar for eight to ten seconds is
sometimes recommended.

A family of saprophytic fungi, the Saprolegniaceae, is
notorious in including several genera which attack living fishes.
Saprophytic normally on dead and decaying insects and the

312 THE PRINCIPLES OF APPLIED ZOOLOGY

like, they can attack fish which are in an enfeebled con-
dition or which have skin abrasions, wounds, torn scales,
and so offer a foothold for the parasite. The fungus covers the
body first as a film, then as a series of white or coloured blotches
on head and body, mouth and gills, on the fins and under the
scales. From the living fish the fungus can spread to a dead
one or a dead insect, and from these again to living fishes.
Species of Saprolegnia and Achyla, in particular, attack salmon
during their fresh- water migrations.

Infected fishes may be treated successfully by saline baths
or by painting the fish with 50 per cent, solution of hydrogen
peroxide in water when the disease is commencing. Once the
fungus has secured a hold on the fish, no remedial measures are
of anv use.

CHAPTER XXVIII

INSHORE FISHERIES

It is not easy to draw a clear line of demarcation between
the terms inshore and offshore fisheries, but in this chapter
the term inshore will be taken as referring to fisheries carried
out within ten miles of the coast.

Such fisheries fall naturally into two categories, namely : —

(1) The obtaining or cultivation of sedentary or semi-
sedentary animals which live permanently within the inshore
limits ; this category comprises the shell fisheries, that is to say
the procuring of edible molluscs such as the oyster (Ostrea),
the soft clam (Mya), the mussel (Mytilus), cockle (Cardium),
hard clam ( Venus), scallop (Pecten), periwinkle (Litter ina),
etc. ; of useful molluscs such as the pearl oyster (Margaritifera),
the abalone (Haliotis) ; of edible Crustacea such as crabs,
lobsters, prawns, shrimps.

This category also includes certain minor fisheries of inverte-
brate animals such as sponge fisheries, coral fisheries, trepang
fisheries, and the collection of cuttle-fish and even of barnacles.

(2) The catching of fishes or other animals which come from
offshore waters to inshore waters in order to spawn or reproduce.
This category includes the various herring fisheries, the fur-seal
fisheries, and such minor industries as the obtaining of sea-
birds' eggs and edible bird nests.

The general principles involved can be illustrated by a
description of the oyster fisheries, pearl fisheries, and herring
fisheries.

Oyster Fisheries. — The term " oyster " refers to an edible
mollusc of the Lamellibranch or bivalve genus Ostrea, of which
a number of species exist.

The North European oyster, for example, is Ostrea edulis ; the
South European oyster is Ostrea angulata ; the Eastern American
oyster is Ostrea virginiana ; the Western American one is Ostrea
lurida.

The oyster is completely sedentary, being attached usually
to a stone by one valve of the shell, and it occurs in colonies
or beds generally off the mouths of rivers where the water

313

314 THE PRINCIPLES OF APPLIED ZOOLOGY

abounds in the minute sea organisms upon which the oyster
feeds. The oyster, however, requires pure water and a firm
substratum. The female oyster, or the hermaphrodite oyster,
according to species, produces an enormous number of eggs.
The newly hatched larvae, technically termed fry, swim about
for a period probably of several weeks and each develops a
bivalve shell ; then the larvae sink to the bottom, fasten them-
selves to a stone or to old oyster shells, and each begins to build
a new shell ; they are now described as spat. Spat are oysters
in the first year of life. In the second year they are termed
brood oysters. Between two and three years old the oyster
is termed half-ware, and usually spawns for the first time.
Marketable size is reached when four to five years old, and the
oyster reaches perfection, from the epicurean standpoint, when
six or seven years old.

Marketable oysters are termed ware.

A very high degree of mortality occurs among the fry ;
many are devoured by predatory animals ; many are swept
out to sea by tidal currents ; many cannot find a suitable sub-
stratum upon which to settle. The increase in numbers of a
bed of oysters under natural conditions, therefore, is very small,
in comparison with the numbers of potential individuals
produced, and a natural bed of oysters will be very quickly
exhausted by commercial dredging methods unless reinforced
by some system of artificial cultivation and planting of spat.

The great oyster -breeding grounds of the world, therefore,
are almost all artificial, in the sense that they are controlled
by human agency.

The methods pursued in oyster cultivation may be illustrated
in principle by a description of those made use of in the French
oyster beds of Arcachon, probably the earliest and certainly
the most famous centre of oyster rearing.

An oyster-rearing site should be situated, preferably, on a
firm substratum of fine gravel or hard mud, should not be
subject to violent tidal movements which would sweep large
numbers of fry out to sea, and should be provided with suitable
objects for spat to settle upon.

The physical feature which makes Arcachon such an ideal
centre for the production of oyster spat is the existence of a
vast inland sea, the " bassin d' Arcachon," of about 30,000
acres in area, connected with the Atlantic by a narrow entrance
through which the tide runs in and out. In the middle of the
basin there is a small island, He des Oiseaux, and on the shores
of this are situated the oyster farms or ' pares." Some of

INSHORE FISHERIES 315

these belong to the Government and are reserved for the pro-
duction of spat. Others are leased to individuals and com-
panies. The oyster spawns at Arcachon between May and
early July, so that at some time during this period the cultivators
place in position numbers of earthenware tiles covered with
lime cement for the fry to settle upon.

These tiles are stacked in layers in wooden frames to a height
of three feet. By October the tiles are covered, each with
hundreds of well-established spat. They are then removed
and the tiny oysters are flaked off with a knife and placed in
" ambulances," which are flat trays having a floor and lid of
half -inch wire netting. These trays are placed between short
posts in the sea on the oyster pare so that the tide can run
freely through them. They are constantly examined, and
enemies and impurities removed. In these trays the young
oysters grow rapidly and have soon to be thinned out.

A considerable area of the oyster pare is divided into little
fields demarcated by hedges made of bunches of the local heath
(Erica scoparia). These enclosures at low tide are covered
by about six inches of water, swarming with micro-organisms,
especially diatoms, and the young oysters after transference
from the " ambulances " to these enclosures grow very rapidly.
The choicest French oysters, however, are those reared at
Marennes, farther along the coast. Young oysters from
Arcachon are sent there and fattened in shallow artificial
ponds, termed ' claires," in the salt marshes. These claires
swarm with diatoms, particularly a species termed Navicula
fusiformis var. ostrearia, and oysters fed in these claires become
particularly fat and acquire a greenish-blue colour ; such
oysters are particularly esteemed by the epicure.

Methods of oyster cultivation in other parts of the world
are similar to those of the French areas. In Holland the
chief area is a land-locked lake, formed by the damming of
the east arm of the Scheldt. In England, off the coast of
Essex, the method is to lay out numbers of oyster and cockle
shells on the foreshores just before the spawning season and to
strip the spat during the summer of the following year. All
oysters are dredged up in autumn, kept in pits near high- water
mark during winter, and sown out again in the following
March or April. This course is adopted because of the ice-cold
water which comes down the rivers in winter and kills large
numbers of ovsters.

In Canada and the United States the oyster is the most
valuable fish product ; it furnishes one -third of the total value

316 THE PRINCIPLES OF APPLIED ZOOLOGY

of all fisheries of the latter country. In fact, the shallow,
gravelly bays and estuaries along the eastern coast of North
America, especially between Cape Cod and Cape Hatteras,
seem to offer the best conditions in the world for oyster pro-
duction. Good beds, however, occur as far north as Prince
Edward's Island and as far south as the Gulf States. On the
tidal flats of the western coast, particularly of California and
Washington and British Columbia, carloads of spat are planted
annually with Ostrea virginiana from the eastern coast. The
larvae of this oyster, however, are killed by the low tempera-
tures prevailing during the spawning season on the Pacific Coast,
so that the beds have to be constantly replanted. The oyster
fisheries have developed in importance largely through the
establishment of a considerable canning industry.

There is also a large oyster culture industry in Japan,
particularly at Hiroshima, the beds being parcelled out in
enclosures. The methods employed are similar to those of
Europe, but branches are used instead of tiles for collecting
the spat.

Shortage of Ostrea edulis in European oyster beds brought
about some years ago an introduction of American oysters into
many of the British oyster fisheries. Unfortunately, with the
American oysters came the American Slipper Limpet ( Crepidula
fornicata), which, although not a predator on the oyster, attaches
itself in large numbers to the oyster valves, and competes
very seriously for space and food. In some localities it is
possible to dredge 20 tons per day of Crepidula on the oyster
beds. It is a prolific breeder and, when once established,
impossible to eradicate.

Other Shellfish Industries. — Apart from the oyster, the
collection of edible molluscs such as the cockle, mussel, scallop,
clam, and so on, has no more than a local value, and these
industries are the most miserable and poorly remunerated of
fishing industries. Crab, lobster, and shrimp fisheries, however,
are of considerable importance in certain areas, but owing to
the difficulty of transporting such perishable food-stuffs, the
products are as a rule consumed locally.

In Eastern Canada and Newfoundland, however, owing to
the establishment of canneries, the lobster fishery has become
very valuable, and is probably the most productive lobster
fishery in the world. In spite of the establishment of artificial
hatcheries and of severe legislation, however, the lobster
fisheries of Canada and North-eastern United States are
declining owing to the difficulty of enforcing legislation

INSHORE FISHERIES 317

concerning close seasons, size limits, and protection of the
egg-bearing females.

Methods of capturing Crustacea are much the same in all
countries. Crabs and lobsters are trapped in basket traps or
box traps ; prawns and shrimps are taken in hand nets or are
trawled for by half -decked fishing boats of about 10 tons
register. Prawns and shrimps are also brought in from off-
shore waters by the steam trawlers.

Pearl Fisheries. — Natural pearls are produced by a variety
of Molluscan species. They may be produced, for example, by
the fresh-water Mollusca, Unio and Anodon, of Europe and North
America, by the edible oyster, by the edible mussel (Mytilus),
by the abalone (Haliotis), and so on ; but the finest pearls, the
so-called Oriental Pearls, are the product of the Pearl Oyster
(Margaritifera or Meleagrina), which occurs in shallow water
lagoons in the Pacific and Indian Oceans.

Pearl formation by the mollusc may be described as a
disease, inasmuch as it represents a secretion of the pearly
substance, that forms the inner layer of the shell, around some
foreign body which is causing the oyster considerable irritation.

There is some difference of opinion as to what this foreign
body may be. The prevailing opinion seems to be that, in
a certain number of cases, it is a grain of sand, in other cases
a particle of calcareous substance within the muscles, and
in the great majority of cases a parasite, a larval stage of a
fluke or tapeworm.

That the presence of a particle of inorganic matter can
stimulate the pearl oyster to produce pearls seems evident from
the remarkable success of the Culture Pearl industry, established
by Professor Mitsukuri in Japan and peculiar to that country.
Margaritifera is cultivated in millions by methods similar to
those used in the production of Ostrea.

Many natural pearls are of course obtained, but many more
are obtained by introducing a particle of inorganic matter —
the exact method is a secret — between the valves of the oyster.
The culture pearls thus produced, however, are very often
attached to the inner shell layer, and do not lie freely in the
space between the valves as do true pearls. A really good
culture pearl, however, is almost impossible to distinguish
from a natural one, except by X-ray methods, and is just as
effective ornamentally.

The term culture pearl must, of course, be distinguished from
the term artificial pearl. Artificial pearls are now produced
in enormous quantities by coating solid opal glass beads with

318 THE PRINCIPLES OF APPLIED ZOOLOGY

" pearl essence," which is a suspension of crystals of guanidine
in gelatine, obtained by treating fish scales with aqueous
ammonia, acetone, amyl acetate or similar solvents.

Pearl Fishing Grounds. — With regard to the geographical
situation of pearl fisheries, a distinction must be made between
those fisheries whose primary object is the securing of pearls
and those fisheries whose chief object is the pearl oyster shell
or mother-of-pearl. The chief fisheries for the pearls themselves
are the Persian Gulf, the Gulf of Manaar, the Red Sea, and to
a less extent those of Venezuela and Panama.

The Persian Gulf fisheries employ about 35,000 persons,
and cover an area of about 600 by 100 miles with Bahrein
Island as headquarters. The beds consist of level areas of
rock, coral debris or sand, two to eighteen fathoms deep. The
oyster concerned is Margaritifera margaritifera. The fishing
is carried out by Arab divers, who fasten heavy stones to their
feet to bear them down. The pearls are sold chiefly to the
Mahomedan and Hindu merchants of Bombay.

The Manaar fisheries have been almost extinguished by a
succession of barren }^ears. They were carried out in the
Gulf of Manaar, an arm of the Indian Ocean, 65-150 miles
wide, separating Ceylon from Southern India, and in the
neighbourhood of Tuticorin on the Madras coast of India.
These fisheries, which are very ancient, depend upon the fact
that certain patches of rock termed " paars," which lie within
half a mile to eighteen miles from the shore, and in water
not more than fifteen fathoms in depth, are covered in certain
years with copious deposits of the pearl oyster, Margaritifera
vulgaris. The occurrence of these deposits is most erratic,
and two or three years of productive fishery may be followed
by a number of years when scarcely any oysters are to be found.
Thus, prior to 1903, there had been a break of twelve years.
In 1903, 1904, and 1905, oysters were present in phenomenal
abundance, and then ensued another barren period of years, so
disastrous as to bring about in 1912 the failure of the Ceylon
Company of Pearl Fishers Ltd., which had been formed in 1906
to lease the oyster paars from the Ceylon Government and to
exploit them. A biological Commission, appointed by the
Royal Society of England at the instigation of the Ceylon
Government, had made an extensive faunistic survey of the
area between 1903-06, and had attributed the intermittent
character of the fisheries primarily to the destruction of oyster
beds by shifting sands and by predatory fishes of the Skate-
ray family, and secondarily to overcrowding.

INSHORE FISHERIES 319

Recommendations of the Commission to the effect that
transplanting and cultching, that is to say, the strewing of
sandy areas of the sea bottom with broken rock for spat to
settle upon, should be undertaken, were faithfully carried
out by the Company but without appreciable success in provok-
ing the appearance of oysters.

Very great stress has been laid by some authorities upon
the importance of protecting the paars from predatory rays
either by destruction of such fishes or by guarding the beds with
wire netting, but until it is established with certainty that
the provoking cause of pearl secretion in the Ceylon oyster is
or is not a stage of a Tetrarhynchid tapeworm living in these
rays, destruction of these fishes can hardly be recommended.
On the other hand, it is apparently not beyond possibility
that years of oyster abundance on the Ceylon beds arise, not
from abundant spatfall of preceding years, but from the con-
veyance of floating oyster larvae on surface currents from the
south-eastern coast of India during very strong and prolonged
south-west monsoons.

The Red Sea fisheries are of minor importance. The oyster
fished for is Margaritifera margaritifera erythrcensis, closely
related to the Persian Gulf species. Pearls are rare but the
shell affords a good quality of mother-of-pearl.

The shell of the pearl oyster is in considerable demand for
the manufacture of mother-of-pearl ornaments, jewellery,
buttons, and so on. The chief species of oyster whose shell is so
made use of are : Margaritifera maxima, the large white shell of
Australian, Papuan, and Malayan waters, commercially known
as " silver lip," ' gold edge," ' manila shell," or " Queensland
Mother-of -Pearl." It is fished for in the Persian Gulf :

Margaritifera cumingii, a, dark coloured shell from
Polynesian waters, known commercially as ' Auckland Shell,"
" Taluti Shell," " Black Shell," and used for the production
of smoked pearl buttons :

Margaritifera vulgaris, commercially known as " lingahs,"
valuable only for cheap qualities of shirt buttons.

The chief fisheries for pearl shells are those along the coast
of West Australia from Cape York to North-west Cape, in
Torres Straits and off Queensland.

Other molluscs besides Margaritifera are valuable in this
way. Thus certain species of Haliotis, popularly termed
abalones, notably H. splendens, H. iris, and H. mida, are
fished for along the coast of Japan and California. They are
obtained, as are pearl oysters, by divers. Apart from the shell

320 THE PRINCIPLES OF APPLIED ZOOLOGY

value, occasional pearls occur, and there is a considerable flesh
value, large quantities of dried abalones being shipped from
Japan and California to China.

The Herring and Mackerel Fisheries. — The majority of the
Herring family ( Clupeidce) and the Mackerel family (Scombridce)
of fishes are marine fishes of considerable food value. From
the economic standpoint, the more important members of
these families are the Atlantic herring (Clupea harengus),
the sprat (Clupea sprattus), the pilchard or sardine (Sardina
pilchardus), the anchovy (Engraulis encrasicholus) , and the
shad ( Alosa), of the Clupeidae ; the mackerel (Scomber scom-
brus), the bonito (Sarda sarda), and the tunny (Thunnus
thynnus), of the Scombridse.

These fishes possess the anadromous habit to a more or less
extent. The shad migrates into the estuaries of rivers ; the
others migrate from offshore waters into inshore waters to
spawn, and the presence of adult fishes and of young fishes in
the coastal waters at certain times of the year has determined
the extent to which these fishes form the basis of fishing
industries.

The herring appears at certain times of the year in enormous
numbers, termed " shoals," covering an area of one to fifteen
square miles, within the coastal waters along the eastern and
southern shores of Great Britain, the Irish Sea, the Scandinavian
coast, the shores of the Baltic, and Eastern Canada. These
shoals appear at night, swimming against the tidal currents,
and near the surface. The usual method of catching them,
therefore, is by drift nets, perpendicular walls of gill netting
fastened together to form " trains," often two to three miles
long, but only eight yards deep. These trains are buoyed and
weighted, and are sunk at right angles to the direction of the
tide to a depth at which the shoals are likely to be swimming.
The nets are allowed to drift with the tide. The fishing takes
place, of course, at night (Fig. 45).

The boats are usually privately owned, but gather together
in large fleets composed chiefly of British, Norwegian, French,
and Dutch boats. The steam drifter, which is replacing the
sailing boat, carries a crew of ten, who share profits. The
fleet works in proximity to some landing centre, for herrings
must be landed quickly. This centre moves south as the
season advances, for reasons which will be discussed presently.
The principal centres are Stornoway, Peterhead, Fraserburgh,
Yarmouth, Lowestoft, and to a less extent Boulogne.

At these centres the bulk of the catch is either salted in

INSHORE FISHERIES

321

Spawning//

ground

Fig. 47.— Probable Migrations of a Shoal of Pilchards carried in the " 0 "

Stage up Channel ( ) and the General Migrations of the

Spent Fishes ( ->). Spawning Grounds and Drift of

Fry of Herrings (O ^). Roman numerals indicate months

of year. (All after Meek.)

21

322 THE PRINCIPLES OF APPLIED ZOOLOGY

barrels of 800-1,200 fish, an extensive export trade being
carried out with Baltic countries, or is sold to the curers for
preparation as smoked bloaters, kippers, and red herring. A
comparatively small proportion of the catch appears on the
market in fresh form.

The important feature of the herring fishery, from the
scientific standpoint, is that the shoals of fish appear in inshore
waters progressively later in the year in the south than in the
north. Thus they appear in Norwegian waters in March ;
off the Shetlands, Orkneys, and the Northumberland coast
during the so-called " Scottish Season " of June, July, and
August ; off the Yorkshire coast during the so-called " Yar-
mouth Season " of September ; and do not appear in the Channel
until December (Fig. 47).

The explanation of this progressive appearance of herring
shoals formerly put forward was that the herrings came down
from the Arctic Circle as a great army and divided into western
and eastern divisions, the latter of which travelled southwards
between Great Britain and the Continent, but returned north-
wards along the western coast of Britain and Ireland.

This interesting theory, however, has become discredited
by the enormous amount of information accumulated by the
Fishery Research Boards of those countries concerned in the
fisheries, especially Norway, Denmark, Scotland, and England.

The explanation seems to be somewhat as follows : —

(1) There are a number of spawning grounds situated as
shown in Fig. 47, that is to say, off the Scandinavian coast,
along the eastern edge of the North Sea, the Dogger Bank,
Skager Rack, English Channel, and so on.

(2) Each of these grounds is visited annually by a particular
local race or school of herrings whose individuals show common
features of size and age, and tend to keep together during the
years of immaturity and even after maturity.

(3) These local races form two groups, a coastal group of races
which are winter or spring spawners and come farther inshore
than the others, and an oceanic group of races which are summer
and autumn spawners and do not come so far inshore.

The coastal group includes the herrings of the Channel, Irish
Sea, western Scottish lochs and estuaries, Orkney and Shetland
Islands, Norwegian fiords Zuider Zee, Western Baltic.

The oceanic group comprises the schools of the Western
North Sea, and the schools which spawn at the Shetlands in
September, at the Dogger Bank and Skager Rack in October.

The young herrings produced from the spawning of these

INSHORE FISHERIES 323

schools are carried down the coasts with the tidal currents.
Enormous masses of young fish, almost certainly the product
of coastal races, are brought by favourable currents between
April and September into the Norwegian fiords, the bays of the
Northumberland coast, the mouth of the Thames, Morecambe
Bay, and so on, and are captured in seine nets to be put on the
market as whitebait ; the Norwegian whitebait form the basis
of an extensive canning industry located at Stavanger which
competes with the sardine industry. Whitebait consist chiefly
of herrings about six months old, and of sprats.

There is a so-called sardine fishing industry carried on also
in the coastal waters of Eastern Canada and New England,
but the fish used are young coastal herrings which come so far
inshore that they can be captured in " brush weirs," that is to
say, labyrinthine traps made of wickerwork similar in plan to
trap nets. Similar to these are the " madragues ' or tunny
nets of the Mediterranean coasts, and the bamboo trap nets of
Japanese fishermen.

The most important herring fishes caught in American
waters, however, are the ale wife or river herring (Pomolobus
pseudoharengus) , the shad ( Alosa sapidissima) , both of which
migrate far up the rivers of Eastern North America, and the
menhaden (Brevoortia tyr annus), a coastal herring captured in
large numbers for the oil which it yields.

The pilchard or sardine of Atlantic waters is more southerly
in its range than the herring, being restricted to the Mediter-
ranean Sea and the coastal waters of the Atlantic from Madeira
to Southern Ireland and Devon. There are two races or
varieties, namely, Sardina pihhardus pilchardus of the Atlantic,
the basis of the French and Portuguese sardine fisheries, and
Sardina pilchardns sardina of the Mediterranean.

There is apparently a spawning area in the northern portion
of the Bay of Biscay, for the first named of these races, from
which spent fish travel towards the English Channel and form
the basis of the Cornish pilchard fishery, and from which young
pilchards eventually appear in the inshore waters of the
Biscayan and Portuguese coasts to be caught in seine nets and
canned as sardines (Fig. 47).

Along the western coast of America, from Peru northwards
to Mexico, occur two other closely allied races or species, namely,
Sardina sagax and Sardina ccerulea. Upon these depends the
extensive Calif ornian sardine fisheries. On this coast the fish
are caught in a peculiar circular type of seine net termed the
" lampara net " (Fig. 45).

324 THE PRINCIPLES OF APPLIED ZOOLOGY

On the other side of the Pacific occur the Japanese sardine
Sardina melanosticta and the Australian sardine Sardina
neopilchardus. In the waters off the Cape of Good Hope occurs
Sardina ocellata. The interrelationships of these various species
and their morphological characteristics are insufficiently known.

The sprat (Clupea sprattus), a smaller fish than the herring,
is confined to the North Sea region. Like the herring, it occurs
in schools or local races, which appear at certain places along
the North Sea coastline, especially in the Channel, the South-
western North Sea, the Baltic, and Western Norway.

The anchovy (Engraulis encrasicholus) has a range similar
to that of the pilchard, although it migrates as far north as
Norway. There is a spawning area in the Zeider Zee, where
the principal anchovy fishery is carried on.

It is of interest to note that the pilchard and the sprat are
comparable in many respects to coastal herrings ; they are small
Clupeoids, they are winter spawners, they come well into in-
shore waters, and their young forms may be carried into river
estuaries.. Like coastal herrings, therefore, they may be
captured not only by drift nets, but in many cases by seine
nets.

A seine net or drag net is a long shallow net supported by
cork floats and weighted by lead sinkers, one end of which is
fixed on shore, the other end being carried out by a rowing boat
along a course which forms a semicircle to the coastline. The
boat finally returns to shore and the net is gradually dragged
to the shore, thus sweeping a considerable area of water (Fig. 45).

Another type of seine net is the purse seine, used in deep
water or out at sea. This net is drawn round a shoal of herring
or mackerel by two boats, and the circular enclosure thus
created is hauled alongside a steamer and the catch bailed by
means of a net bag into the hold. This type is extensively
used in the herring fisheries of the Scandinavian fiords and
Scottish lochs.

Some type or other of trap net or seine net is in use all over
the world, since in the development of fishing industries in every
area, inshore fishing has preceded the more difficult offshore
methods of fishing. As boats and gear improve, the tendency
is always to seek fish farther out at sea.

Mackerel Fisheries. — The mackerel fishery is, so to speak,
the younger sister of the herring fishery. The mackerel
(Scomber scombrus) is common in the Mediterranean, in the east
Atlantic from the Canaries to West Scotland, and in the North
Sea, along the West Atlantic from Cape Hatteras to Labrador.

INSHORE FISHERIES 325

Like the herring, it migrates into coastal waters to spawn,
and during the period May to July can be caught in drift nets.
In the winter it retires to deep water, and in the North Sea is
very often taken in trawls. The migrations of the mackerel
are not fully known, and our ignorance of the question has led
to considerable dispute between Canada and the United States
concerning the rights of fishery in the Gulf of St Lawrence.
The Canadian opinion regards the mackerel as a local fish,
moving between shore and deep water in the immediate vicinity.
On the other hand, the United States authorities hold the view
that the migration is from deep Atlantic water to the coast.
Further, the mackerel catches on the American coast have
steadily decreased, and the suggestion has been made that
the mackerel are leaving the West Atlantic and migrating
permanently to the other side. This decline is a matter of
immense importance since the Massachusetts and Maine mackerel
fisheries have been always the most important fisheries of Eastern
North America, and the largest mackerel fisheries in the world.

Another of the Scombridse, the tunny, is the object of
important fisheries in the Bay of Biscay and off the coast of
Tunisia. The term " tunny' refers variously to the albicore
( Thunnus germo), to the gigantic true tunny ( Thynnus thynnus),
and to the bonito (Sarda sarda).

It must not be assumed that Clupeoid and Scombrid fishes
are the be-all and end-all of inshore fisheries. In every area
of the world where fishing is carried on there are hosts of edible
inshore forms whose capture forms the object of important
local fisheries. Thus along European coasts there are consider-
able captures of dab, plaice, whiting, pollack, hake, conger,
mullet, sand eels, wrasse, bream, bass, sea perch, gurnards, dog-
fishes, and so forth.

Every coast, in fact, has hordes of edible animal products
peculiar to that particular area.

CHAPTER XXIX

OFFSHORE FISHERIES

Offshore fisheries do not necessarily imply deep - water
fishing, although the misleading term of deep-sea fisheries
is often applied to them. Many of the offshore fishing grounds,
in fact, are in water as shallow as the coastal fishing grounds.
The term refers rather to fishing grounds which are at such a
distance from the landing centres as to necessitate the boats
remaining out for a period of days or even weeks. Such a
mode of fishing therefore requires boats of considerable size,
preferably steam powered, provided with fishing gear adapted
to catch fish rapidly and in quantity, and requires the pro-
vision of some system of preserving the catches or of rapidly
bringing them to market. Offshore fishing, on a commercial scale,
is therefore chiefly carried out by joint-stock companies owning
fleets of steam trawlers or liners, and possessing headquarters
at some particular landing centre where the vessels can be
rapidly unloaded and can be rapidly provided with coal and
ice, and where arrangements for marketing or preserving the
catches are available.

The offshore fishing industries are confined almost entirely
to countries bordering upon the North Atlantic, and centre
around such ports as Grimsby, Aberdeen, Hull, London,
Lowestoft, Yarmouth, Fleetwood in Great Britain ; Esjberg
in Denmark ; Geestemunde, Cuxhaven, Bremerhaven, Altona
in Germany ; Aalesund, Bergen, and Stavanger in Scandinavia ;
Boulogne, Fecamp, Arcachon in France ; Ijmuiden in Holland ;
Gloucester, Boston in the United States ; Halifax, Yarmouth,
Luxembourg, Canso in Canada ; St John, Newfoundland.

The Atlantic Fishing Grounds. — Surrounding the coastline
of the continental land masses there is a belt of sea whose depth
rarely exceeds 100 fathoms ; that is to say, between the coast
and the oceanic depths there is a broad ledge which slopes
gradually from the coast to the 100 fathoms line, beyond which
the depth of the sea bottom becomes suddenly very great.
This submarine ledge is termed the Continental Shelf.

The belt of sea which covers this shelf is far richer in marine

326

OFFSHORE FISHERIES 327

life than are the waters covering the oceanic depths, owing to
certain favourable physical factors — light, low salinity, greater
content of dissolved nitrogen, greater oxygen content, and so
forth — which encourage the growth of minute floating plant
organisms and minute floating animal organisms, and indirectly
encourage the presence of the vast variety of marine creatures
which depend for sustenance upon this plankton or minute
marine life. This richness in marine life is particularly the case
in polar and temperate waters, and the most productive fisheries
are situated in such latitudes.

At certain points along the continental shelf there occur
areas where conditions seem exceptionally favourable to fish
life. These areas are generally marked by the occurrence of
sandy or rocky plateaux, and termed in fishing parlance
banks ; they are generally characterised by a mingling or
a contact of cold Polar currents with warm Equatorial currents
and by numerous vertical currents (Fig. 48).

Many such banks probably exist, but the fishing value of
many of them has yet to be explored, and others are either too
far from the commercial fish-landing centres or they are unsuit-
able owing to depth, or to the nature of the bottom, for present-
day fishing methods.

The greatest offshore fishery sites of the world are, in fact,
very few in number and comprehend the following localities : —
The North Sea Banks ; the Iceland Banks ; the Newfoundland
Banks ; the Atlanto-Saharan or Morocco Banks ; the Lofoten
Banks ; the Barents Sea and White Sea Banks ; and the Korean
Banks of the Pacific Ocean.

These fishing grounds may now be discussed in more detail.

The North Sea Banks was the birthplace of modern trawling
methods. The discovery of the potentialities of the Dogger
Bank by Brixham trawlers in the nineteenth century, and of
those famous haunts of the sole — the Silver Pits — in 1837,
led to the development of the British East Coast fisheries and
to the predominance of Grimsby and Hull among the fishing
ports of the world. After the Silver Pits were discovered, the
Dutch, Schleswig-Holstein, and Danish coasts were in turn
exploited, and ultimately the Great Fisher Bank to the north-
ward of the Dogger. The extraordinary value and fertility
of the North Sea as a fishing ground are due to the extreme
shallowness, the average depth being sixty fathoms, the con-
sequent abundance of plankton, added to by the abundance
of organisms brought in by the Gulf Stream, the high nitrogen
content and low salinity produced by the large volume of fresh

328 THE PRINCIPLES OF APPLIED ZOOLOGY

Fig. 48. — The Atlantic Fishing Banks.

1, North Sea. 2, Newfoundland. 3, Iceland.

4, Atlanto-Saharan. 5, Lofoten.

(Map taken from Fowler.)

OFFSHORE FISHERIES 329

water entering the area from the Baltic and North Sea rivers,
and the favourable geographical situation amidst countries of
dense population. There is a greater variety of edible fish
in the North Sea than in any other fishing area.

Cod-fish, herring, and haddock predominate, and make up
90 per cent, of the supply. The sole, turbot, and brill occur
there but are unknown farther north. Different banks are
characterised by different kinds of fishes.

The Newfoundland Banks cover an area exceeding that of
Italy, lying 50-150 miles off the estuary of the St Lawrence,
and marked by a contact between the Gulf Stream and the
Labrador current. The suspended matter deposited by melting
icebergs, by the meeting currents and by the emerging St
Lawrence, has built up in course of time a number of sand
banks, extending from Brown's Bank off the western end of
Nova Scotia to the " Grand Bank " south of Newfoundland.

Cod are the principal fish taken, but haddock, hake, pollack,
and halibut are plentiful. The banks are worked by Nova
Scotians, by New Englanders, by the Bretons, and to some
extent by English.

The Iceland Banks were discovered in 1891, and now supply
a great proportion of the trawl-caught fish landed at East
England ports. The sandy banks in the shallow water adjacent
to the Faroe Isles and on the continental shelf surrounding
Iceland, supply large quantities of cod, haddock, lemon soles,
plaice, and halibut. The fish from the Faroe Banks are light
coloured ; those from the Iceland Banks are much darker.
The shallow waters between Iceland and Greenland offer great
future possibilities.

The Lofoten Banks occur parallel to the Scandinavian coast,
but separated from it by a deep channel, too deep for trawling.
Great shoals of migrating cod visit these banks in spring in
order to spawn, and are extensively fished.

The Barents and White Sea Banks lie north of the Scandi-
navian peninsula. Though exceeding in extent the Mediter-
ranean Sea, they can be fished only in late summer and early
autumn, when the invasion of the Gulf Stream causes the ice
to retreat and brings in large quantities of plaice, cod, and
haddock. In late autumn the Arctic water predominates and
the region becomes icebound.

The Korean Banks, which lie on the north-eastern coast of
Asia, have great possibilities but are accessible only to Japan
among fishing nations.

The Edible Fishes Concerned. — The commercial value of

330 THE PRINCIPLES OF APPLIED ZOOLOGY

offshore fisheries depends upon the capture and marketing of
the members chiefly of two important families of fishes, namely,
the Gadidae or cod family, and the Pleuronectidae or flat-fish
family.

The Gadidae is a family of fishes characterised by a general
resemblance to the North Atlantic Cod-fish, Gadus callarias,
one of the best known of food fishes and the subject of economic
fisheries of the greatest importance. The family includes also
Gadus ceglefinus (the haddock), Gadus merlangus (the whiting),
Gadus virens (the coal-fish), all of similar distribution to the cod ;
and Gadus pillachois, the pollack of the North-east Atlantic.

These fishes do not migrate inshore to spawn as was formerly
thought to be the case, but spawn well offshore in those areas
which constitute fishing banks, and the floating eggs and newly
hatched larvae are carried towards the inshore waters by the
prevailing currents. Thus the Atlantic cod spawns between
February and May, when the waters are coldest, principally
off Newfoundland, the south and west coasts of Iceland, the
Norwegian coast, especially the Lofoten and Romadal banks,
and in the North Sea, but not south of that.

The Pleuronectidae or Flat-fishes also comprise many well-
known food fishes. The family falls naturally into four tribes,
namely : —

(a) The Halibut tribe ( Rippoglossinm) , nearly altogether
Pacific in distribution and nearly all northern. The Halibut
(Hippoglosses vulgaris) and the Long Rough Dab (Hippo-
glossoides limanoides), however, occur in Atlantic waters.

(6) The Plaice tribe (Pleuronectinai) predominantly northern
in distribution. The Atlantic species include the Plaice (Pleuro-
nectes platessa), the Flounder (P. flesus), the Dab (P. limanda),
the Lemon Dab (P. microcephalus) , and the Witch (P.
cynoglossus).

(c) The Sole tribe (Soleince), tropical in distribution,
abounding on sandy bottoms in the warm seas along the
continents. The Common Sole (Solea vulgaris), however, occurs
in the Atlantic as far north as the North Sea up to the Skager
Rack.

(d) The Turbot tribe (Psettince), typically tropical, but
occurring in the Atlantic, especially the Turbot (Psetta
maximus) and the Brill (Psetta Icevis). Turbot and brill are
without doubt the most delicious of flat-fishes, and together
with sole are classed by the English fishermen as " prime fish."

All the members of the flat-fish family agree in the habit of
lying on the sea bottom on one side. Associated with this

OFFSHORE FISHERIES 331

habit is the lateral compression of the body, the lack of pig-
mentation of the concealed side, and the occurrence of both
eyes and the mouth upon the upper side, owing to a twisted
condition of the head. That these morphological features are
a secondary result of the sedentary habit seems indicated by the
fact that larval flat-fishes are always bilaterally symmetrical
and undergo, each in its life -cycle, the twisting of the head,
which brings eyes and mouth to a unilateral position. As a
rule the pigmented side, which bears the eyes, is the left side ;
that is to say, the fish are sinistral. The members of the halibut
tribe, however, have pigmentation and eyes on the right
side ; they are dextral. In spawning habit, flat-fishes are
katadromous, that is to say, they move towards deeper water
to spawn. The eggs and fry, however, become carried into
inshore water, and young plaice are found particularly in shallow
waters lying over coastal banks. As they become larger,
however, they tend to frequent deeper and deeper water, where
they mature. In cold weather, when deep water gradually
becomes somewhat warmer than the shallows, they tend to
creep into the lower depths or " pits " of the fishing banks.

Offshore Fishing Methods. — The commercial methods of
obtaining offshore fishes are two, namely, trawling and lining.

The principle in trawling is of course the dragging of a
conical net with a widely open mouth over the bottom of
shallow waters. Present-day trawling is generally carried out
by one or other of two types of such net, namely : (1) the otter
trawl ; (2) the beam trawl.

The otter trawl consists essentially of a conical bag of
netting (2-2 J inch) about 130 feet long and 90-100 feet wide at
the mouth. The tail end, or cod end as it is termed, is of finer
mesh and its upper and lower surfaces are laced together except
for a passage in the centre which has a valve or flap of netting
to prevent the escape of the fish netted.

This cod end is separate from the " belly " of the net but
laced to it, and so readily removed when the whole net is hauled
up into the hoisting tackle. The mouth of the net is kept open
by a large iron-edged board on each side, in shape and size
comparable to the top of a billiard table. It is known as
the otter board. To these boards the drag ropes are attached
and so arranged that the pull upon them, combined with the
resistance of the water, separates the boards and keeps the
mouth of the nets open. The deadliness of the otter trawl
results from the fact that the upper edge of the net may be as
high as twenty-five feet or more above the sea bottom, and is

332 THE PRINCIPLES OF APPLIED ZOOLOGY

thus liable to enclose fish which swim a considerable height
from the bottom. The upper edge of the trawl may be
supported by a series of glass globes, a recent French invention,
which makes the edge of the trawl skim the bottom rather than
dig into it. In addition, there is a heavy ground rope provided
with wooden rollers to stir up fishes lying flat on the bottom
and make them rise into the mouth of the net.

The beam trawl, which is the older type of trawl, has a net
similar in shape to that of the otter trawl but with a mouth
about seventy feet width. The mouth is kept open horizontally
by a long beam of oak and vertically by a pair of iron runners
or heads.

The modern steam trawler is nowadays a specially designed
steam vessel provided with automatic sounding apparatus, and
with two otter trawls each of about 100 feet width which can be
hauled in by steel ropes wound on the drums of steam winches.
The vessel is provided also with compartments for storing large
quantities of ice.

The beam trawl is carried by the older type of yawl-rigged
smack of about 80 tons register with supplementary engine, a
type which is restricted to home waters and is passing away.

Trawling is carried out in the North Sea principally for cod,
haddock, plaice, and ,to a less extent, for whiting, skates,
rays, lemon soles, etc. Outside the North Sea, trawlers visit
the Iceland Banks, the White and Barents Seas, and the
Morocco banks for cod, haddock, and plaice, and in deep water
for the hake (Merlucius vulgaris).

Lining, although not so commercially important as trawling,
is nevertheless employed to a considerable extent in offshore
fishing where, owing to an unfavourable sea bottom, or for
other reasons, trawling is impracticable. It is the chief method,
for example, used in the Newfoundland Banks cod fisheries,
because the nature of the bottom there is imperfectly known,
and because there is not a large and ready outlet in Eastern
Canada and New England for all kinds of fresh fish at good
prices such as is required for the profitable pursuit of a steam
trawling industry. The bulk of the Newfoundland Bank
product is salted and dried and exported largely to Southern
Europe at low prices. Fears as to the effect of a steam trawling
industry upon the abundance of fish in this area are probably
ungrounded, since climatic conditions alone enforce a non-
fishing period for three or four months of each year that
coincides with the spawning season of cod, haddock, hake, and
such fish.

OFFSHORE FISHERIES 333

The lining is carried out from dories, small, peculiar, flat-
bottomed boats, each with two men, the daily catches being
taken to a parent vessel to be split and salted down. Hand-
lines are used occasionally, but the more usual practice is the
employment of the "trawl," which is a long line, a mile or
more in length, supported at one end by a small cask or similar
buoy, and carrying at intervals of six feet a number of short
lines of about three feet in length hooked and baited with
pieces of frozen herring.

In some fishing areas line fishing is carried out by lines
dragged through the water by a slow-moving vessel.

Problems of the Fishing Industries. — The chief problems
of the commercial fishing industries centre around the arbitrary
fluctuations in the numbers of fishes that are caught. That is to
say, they are problems of scarcity and glut. The difficulty
of deciding whether a scarcity, in the numbers of marketable
individuals of any particular food fish, arises from natural
causes outside the control of man, or whether such scarcity
arises from artificial factors which can be controlled, is particu-
larly acute in the case of an industry such as fishing where the
annual statistics of catches landed cannot, owing to the inter-
ference of other factors concerning markets' demand, efficiency
of gear, labour troubles, and so forth, be considered accurately
to represent the variations in occurrence of marketable fishes
over a period of years.

That there exists an irregular fluctuation in the annual
abundance of available food fishes is of course undeniable.

The occurrence of ' rich and poor years ' ' has already been
remarked upon in the case of the Ceylon pearl oyster. Similar
fluctuations have always characterised the herring fishery. It
seems almost indisputable that fluctuations in the appearance
and numbers of extremely migratory fishes such as cod and
herring, are bound up intimately with variations in the appear-
ance of plankton, and so indirectly with variations in the
annual or cyclical movements of temperatures and currents,
and are not produced to any serious extent by local agencies.
The productiveness of fish is influenced to such a great extent
by widespread climatic fluctuations that it may be regarded
as independent of the interference of man. The conclusions
derivable from the results of modern fishery research seem to
show that the fluctuations in the numbers of Clupeoid and most
Gadid fishes, at any rate, are not affected by the intensity nor
by the methods of fishing.

On the other hand, however, fishing methods would appear

334 THE PRINCIPLES OF APPLIED ZOOLOGY

in certain waters to have reduced considerably the numbers
of plaice and haddock.

It is of course only to be expected that a virgin fishing
ground, abounding in large and aged flat-fishes, will show after
a period of intensive trawling a reduction in the average size
and age of the fishes captured. That is to say, intensive
steam trawling can reduce the number of exceptionally large
and aged flat-fishes that occur in an undisturbed fishing area.

Recent exploitation of the Iceland Banks seems indicative
of this. It would not appear justifiable, however, to attribute
altogether to intensive steam trawling the gradual diminution
in size and numbers of marketable flat-fishes from the North
Sea Banks during the years prior to the Great War, since there
is undoubtedly an enormous mortality of larval and immature
food fishes in inshore waters through the operations of coastal
fishery methods and through predatory birds and fishes.

At the same time it must be remembered that fishery
research tends more and more to show that the more important
kinds of fishes, especially the plaice and haddock, are always
receiving enormous accessions of young individuals and that,
as the Danish scientist Petersen has maintained and demon-
strated, proposals for preserving the fish supply should aim
rather at the protection of older fishes than of the young
year classes.

The cessation of fishing in the North Sea caused by the war
undoubtedly gave the flat-fish jjopulation a great chance of
recuperation.

This contention seems supported by the marked improve-
ment in the numbers of marketable sizes of North Sea flat-fish
during the last few years. During the war there was almost a
complete cessation of bank trawling in the North Sea, but the
amount of inshore fishing and consequent mortality of young
fishes were probably not greatly affected. That this recupera-
tion of the North Sea Banks has resulted from the restriction of
fishing during the war years seems to admit of little doubt.
That is to say, the value of fishery replenishment by the libera-
tion of young fishes bred in coastal hatcheries is doubtful, and
legal restrictions concerning the prohibition of inshore trawling,
the enforced use of definite sizes of mesh, the prohibition of the
sale of undersized fish, the closure of areas, and so on, probably
make little difference to the numbers of marketable flat-fishes.
So long as intensive trawling continues, since any restriction of
trawling activity is uneconomic and impracticable, the diminu-
tion in numbers of marketable sizes of flat-fishes upon the present

OFFSHORE FISHERIES 335

fishing banks is inevitable. It can only be met by the exploita-
tion of virgin areas, and by developing a market for kinds of
fishes which at present are plentiful but unmarketable, owing
largely to the caprice of custom.

The small species of shark which are comprised under the
colloquial terms of dog-fish and cat-fish were, for example, almost
unsaleable before the war, despite the fact that they are excellent
food fishes.

The increased prices, however, of haddock and plaice forced
the British fish - frying trade to experiment with other food
fishes, and dog-fish and cat-fish are now extensively marketed and
consumed as " white salmon."

The wastage and confusion caused by a temporary glut of
food fish catches has been minimised very considerably in recent
years by a better organisation of rail transport and of marketing
facilities ; by improvements of fish preservation methods ;
by the establishment of curing and canning industries ; by the
establishment of fish meal factories, and so on.

CHAPTER XXX

WHALING AND SEALING

The Whaling Industry. — The order of mammals termed Cetacea
or whales comprise two somewhat different groups of animals,
namely, the whalebone whales (Mystacoceti), which lack teeth
and in which the palate carries two longitudinal series of trans-
verse horny plates with fringed edges, and the toothed whales
(Odontoceti), in which calcified teeth are always present after
birth. The whalebone whales, from the point of view of
commercial exploitation, comprise : —

(a) Right whales ( Balcena) with smooth throat and no dorsal
fin, comprising particularly the Greenland whale (B. mysticetus),
the Biscayan whale (B. biscayensis) , or Nordcaper, and the
Southern whale (B. australis) with several varieties.

(6) Humpback whales (Megaptera) with plicated throat,
low hump-like dorsal fin, and long fore flippers ; they include
particularly Megaptera boops, the Humpback.

(c) Rorquals (Balcenoptera,) with plicated throat, small
forelimbs, and slender shape ; they are active whales and
include the Blue Whale (B. sibbaldi), the largest living creature,
the Pinner (B. musculus), the commonest whale of British
coasts, and Rudolphi's Rorqual or the Sei Whale (B. borealis).

The Odontoceti include the Sperm Whale (Physeter macro-
cephalous) or Cachalot, one of the largest creatures, the Bottle
Nose (Hyperoodon rostratus), the various species of small
whales popularly termed porpoises and dolphins, and the
narwhal.

The chief commercial products supplied by the whaling
industry are : —

Oil, which is obtained by boiling every part of the animal
except the whalebone or the teeth for twenty-four hours under
steam pressure. The lower grade oils are used chiefly for soft
soap manufacture, but the neutral, odourless, fatty substance
which occurs in the head of the sperm whale, and is termed
spermaceti, is used in the manufacture of candles. The bulk
of the whale oil is obtained from the blubber, a layer of fat,
twelve to eighteen inches thick and of the consistency of hog's

330

WHALING AND SEALING 337

lard, which lies immediately underneath the skin and yields,
on boiling, its own weight of thick, viscid " train oil."

Whalebone, the horny substance which occurs in thick
parallel plates attached to the upper jawbones and was, during
the crinoline epoch of ladies' fashions, the chief product for which
whales were hunted ; its use has declined considerably and is
now limited chiefly to the preparation of certain stiff silk
fabrics, the baleen being shredded and mixed with the carded
silk.

Products of lesser importance are the meat, usually dried
and ground for cattle food, but canned by some United States
factories for human food.

Bone meal ; and ambergris, a fatty secretion from the
intestines of the sperm whale, much used as a diluent for
perfumes. Ambergris is rare and thus of very considerable
value.

The history of the whaling industry may be said to comprise
four phases, each of which was marked by the abundance of
some particular kind of whale, and each of which declined as
the object became scarcer.

The first of these phases lasted probably from the eleventh
to the sixteenth century, and had as its chief object the Nord-
caper (Balcena biscayensis). This whale was hunted originally
by the people of the Bay of Biscay, Basques chiefly, probably
in inshore waters at first but later as far afield as the Norwegian
coast or even possibly the coast of Newfoundland.

The second great whale fishing phase centred round the
Greenland Right Whale (Balcena mysticetus) . The fishing
was carried out in the sixteenth and seventeenth centuries
chiefly by English and Dutch ships, and to a lesser extent the
Danes and French, and in the early eighteenth century by the
New England whalers. There was continual friction and
quarrelling between the different nationalities. The fishery
was at first an inshore fishery along the coast of Spitzbergen,
but in 1623 this bay fishery was exhausted, and whaling ships
began to exploit the waters between Spitzbergen and Green-
land, and afterwards fished in the waters of Davis Strait and
Baffin Bay. Then from about 1820-80 the Greenland Right
Whale was hunted by United States whalers in the extreme
North Pacific and adjacent parts of the Arctic Ocean. By the
end of the nineteenth century this whale was almost extinct
in all three of the regions where it formerly flourished.

The third phase of the industry was the so-called Southern
Fishery of the British, the Pacific Fishery of British and American

22

338 THE PRINCIPLES OF APPLIED ZOOLOGY

whalers, and its chief object was the Sperm Whale. This phase
commenced about the middle of the eighteenth century and
lasted about 100 years. The fishery was conducted off the
coasts of Chili, Peru, and California, in various parts of the

Blue Rorqual ( Balcenoptera sibbaldi). (After Lydekker.)

Humpback Whale (Meyaptera boops). (After Lydekker.)

Sperm Whale (Physeter macrocephakis) . (After Daniels.)

North Atlantic Black Right Whale {Bahvna ylacialis). (After Lydekker.)

Fig. 49.— Types of Whales.

Pacific around the Galapagos and Marquesas Islands, in the
Indian and China Seas, particularly around the Island of
Timor. In addition to the sperm whale, the Southern Right
Whale (Balcena australis) and the Elephant Seal were also
hunted. The American whalers alone between 1804 and 1817
captured 193,522 Southern Right Whales.

WHALING AND SEALING 339

Many of the American whalers of the fifties and sixties of
the nineteenth century used Honolulu as a base, and from there
fitted out in March for a summer season in the Behring Sea and
the Sea of Okhotsk, and in November for a winter season in
tropical and sub-tropical waters. This sperm whale phase
of whale fishing lingered up to the beginning of the present
century. So late as 1898 there were no less than twenty-nine
whaling companies working at the Azores, and this whale is
by no means extinct yet, a few individuals being captured
every year.

Now from the early days of whaling until about 1880,
methods did not change greatly in principle. Strongly built
sailing vessels, chiefly of the brig and schooner type, were used
and were provisioned for a three years' cruise. The ship was
provided with four to six boats, about twenty-seven feet long
by four feet wide, known as whale boats. When the prey was
sighted, these boats were lowered and went in pursuit. The
whale was lanced by one or more harpoons, six foot wooden
lances, each with a loose steel head to which a long line was
attached. The line was long enough to allow for the stricken
whale diving to a great depth. These boats were towed hither
and thither by the dying animal until it could be given the
coup de grace, towed to the parent ship, and roughly stripped
of blubber and whalebone. The blubber was rendered down
after the ship returned to the home port.

Obviously with such crude fishing methods, no attempt
could be made to utilise the active rorqual type of whale, nor
was it worth while to kill whales less than forty feet long.
There was, in addition, an enormous wastage of whale products.

The fourth and present-day phase of whale hunting may be
said to have been ushered in by the adoption of the harpoon
gun about 1880.

The term harpoon gun is somewhat of a misnomer, the
apparatus being really a sort of explosive bomb attached to
a line and fired from a gun fixed in the bows of a small steamer.
This gun has rendered possible the capture of the smaller and
more active species of whale in such numbers that their small
weight of oil is made up for by the quantity of whales
secured. Further, many of these Finners and Rorquals can
be captured fairly near land and can thus be towed ashore
to a factory, where the whale can be completely utilised.

Modern whaling is almost entirely carried on by Norwegian
companies working from coastal bases with small steamers.
In northern waters such bases occur in Iceland, the Faroes,

340 THE PRINCIPLES OF APPLIED ZOOLOGY

the Hebrides, and the Shetlands. The whales captured are
chiefly the common Finner (Balcenoplera musculus) which
follows the herring shoals inshore, the Sei whale (Balcenoptera
borealis), and occasional Sperm, Blue, Bottlenose, Humpback,
and Nordcaper whales. Similar bases occur in southern waters
in South Georgia, Kerguelen, the South Shetlands, the South
Orkneys, and the Falklands.

A certain amount of whaling is carried out also in the
Behring Sea, off the Australian coast, the coasts of Chile, West
Africa, East Africa, and North Japan. The majority of whales
killed in southern waters are Humpbacks.

There can be little doubt that owing to the gradual decline
in the numbers of whales, and owing to the competition of
vegetable oils with whale oil in the markets, the whaling
industry is a decaying one, so that schemes for the preservation
of the whales yet remaining will probably in the future be
scarcely necessary. The extinction of finners in any case seems
hardly possible, although their numbers are diminishing rapidly.
Right whales and sperm whales are already too scarce to be
worth the fitting out of vessels for their capture. In any case,
under modern conditions, when the number of whales captured
per steamer falls below a minimum number, whaling in that
locality must be abandoned, and the whales would presumably
have a chance to recuperate.

Such recovery, however, is slow, and whales are not as a
rule locally restricted in distribution, so that any increase in
numbers is not readily apparent. Past experience has shown
that once the numbers of a particular species of whale begin
to diminish, no amelioration measures have yet succeeded in
bringing about an increase.

There car be no doubt, therefore, that if only for the sake
of the industry itself, whaling should be restricted. Measures
towards this end, which have been suggested and in some
cases put into operation, comprise : annual licensing of whaling
steamers ; prohibition of whaling in territorial waters ; prohibi-
tion of whaling during herring fishing seasons ; establishment of
closed seasons ; protection of whales accompanied by calves.

The closing of overfished areas is apparently impracticable,
owing to the vast area over which most species of whale are
known to range. The protection also of gravid females is
also out of the question, since it is impossible to distinguish
such females from the others when swimming.

The Sealing Industry. — The term " seal ' will be used in
this chapter in the commercial sense as applying to members

WHALING AND SEALING 341

of three distinct families of aquatic carnivorous mammals,
namely, the Sea Lions (Otariidce), the Walrus family (Tri-
chechidce), and the true Seals (Phocidce).

These animals agree in being adapted to a partially aquatic
mode of life. Thus their shape is fish-like and their hands and
feet are webbed.

The sea lions are the least modified in this respect, since
their hind limbs are still capable of assisting the animal to
shuffle about on land, the external ear, though small, is present,
and the nostrils are at the end of the snout as in terrestrial
animals.

The walrus can progress on land like a sea lion, but there
are no external ears.

The seals have the hind limbs bound up with the tail and
quite useless for progression on land ; they have no external
ears ; and the nostrils are quite dorsal in position, as in other
aquatic animals such as whales and crocodiles.

Of the Otariidce, two genera, namely Callorhinus and
Arctocephalus , are generally referred to as fur seals. The
remaining genera may be termed sea lions.

Callorhinus is the fur seal of the North Pacific waters and
comprises G. alaslcanus of the Pribylov Islands, C. ursinus of the
Commander Islands, and 0. curilensis of Robben Island.

Arctocephalus is the fur seal of the Southern Pacific waters,
and comprises A. townsendii of Guadaloupe, and A. philippii
of Juan Fernandez, the coast of Chile, the Galapagos, etc.,
both genera being now, from a commercial standpoint, extinct.
A. australis occurs off the coast of South America from Brazil
and Chile downwards, the Falkland Islands, Tierra del Fuego,
and South Georgia. A. delalandi inhabits the shores and
islands of South-west Africa, and Tristan da Cunha.

A. gazella inhabits Kerguelen, St Paul and Amsterdam
Islands, and is protected by the Government of New Zealand.

Of the true sea lions, Steller's sea lion (Eumetopias stelleri)
inhabits the Pacific between Behring Strait and California ;
the Californian sea lion (Zalophus californianus) ranges from
lower California to San Francisco ; the Southern sea Hon
( Otaria byronia) ranges along the western coast of South America
as far south as the Falkland Islands ; the Auckland sea lion
(Phoarctos hookeri) inhabits the Auckland Islands ; the Gray
sea Hon (Zalophus lobatus) inhabits the coastal waters of
AustraHa and New Zealand.

The habitat of sea Hons is usually small coastal islands,
on which the young are reared and from which the adults take

342 THE PRINCIPLES OF APPLIED ZOOLOGY

long trips out to sea. The food, judging from an examination
of stomachs of sea lions along the western American coast,

Seal
Fig. 50. — Types of Seals and Sea Lions. (Not to scale.)

seems to be chiefly squid or other cuttle-fish, in spite of the
large quantities of rock cod, salmon, and other fishes in the
vicinity of the sea lion rookeries.

WHALING AND SEALING 343

The walrus (Odobenus) is Arctic and circumpolar, and is
characterised by the enormous canine tusks of the upper jaw,
by the help of which the animal digs up the shellfish and
Crustacea on which it feeds, and by the help of which it clambers
from the water on to the ice floes on which it rests.

The seals include a number of commercially important

species.

The commonest species is Phoca vituli?ia, four to five feet
in length, the coastal or Harbour Seal of Arctic, North Pacific,
American, and North European shores ; on some coasts this
seal is becoming comparatively rare owing to persecution by
fishermen who consider, rightly or wrongly, that this seal takes
an undue share of food fishes.

The Ringed Seal (Phoca hispida) is a circumpolar species
of very great importance as the main source of food for Eskimo

tribes.

Occurring with this seal, in the southern part of its range, is
the Greenland or Harp Seal (Phoca groenlandica) with its harp-
shaped black bar on the back of the males ; this is the most
important, economically, of the true seals.

Along with the Harp seal occurs the Hooded Seal (Cystophora
cristata) of the Greenland coasts, the male of which has a
peculiar inflatable bag on the muzzle.

In Antarctic waters occur the Leopard Seal (Ogmorhinus
leptonyx), the Ross Seal (Ommatophoca rossi), and the Crab-
eating Seal (Lobosa carcinophaga), the first of which preys
chiefly upon penguins.

In tropical waters, an exceptional habitat for seals, occur
species of the genus Monachus, notably the Caribbean Seal
(Monachus tropicalis), the first animal to be described from the
New World, having been noted on the second voyage of
Columbus in 1494.

The Monk Seal (Monachus monachus) inhabits the Medi-
terranean and Adriatic and Black Seas.

The largest of the seal family are the Elephant Seals
(Mirounga), with two species, the Guadaloupe or Northern
Elephant Seal (M. angustirostris) and the Kerguelen or Southern
Elephant Seal (M. leoninus).

These animals are gigantic, reaching a length of twenty
feet, and the males possess a ten-inch trunk or proboscis at the
end of the snout. This trunk, despite the statements of earlier
observers, cannot, according to Townsend, be inflated as can
the trunk of Cystophora, but can be drawn back by muscular
action to form a series of heavy folds on top of the head.

344 THE PRINCIPLES OF APPLIED ZOOLOGY

Commercial Value of Seals. — Seals are hunted commercially
either for their pelts or for their oil.

The finest sealskins have always been obtained from certain
islands in the North Pacific Ocean, notably St Paul and St
George, Pribylov Islands, Copper Island, Robben Islands,
and the islands of North Japan. Other species of fur seal
occur in the South Pacific and South Atlantic around Cape
Horn, the Falkland Islands, up to Lobos Island at the entrance
of the River Plate, off the Cape of Good Hope, and the Crozet
Islands ; but only the pick of the Lobos Island skins come
anywhere near the quality of northern sealskins.

When Alaska and the Aleutian Islands were purchased from
Russia by the United States Government in 1867 for seven
million dollars (£1,400,000), the value of the fur seal pelt was
scarcely known or appreciated. The activities of Russian
fur hunters had been concentrated on the sea otter. On St
George and St Paul the number of seals in 1872-73 was estimated
at three to four millions. In 1870, the islands were leased to the
Alaska Commercial Company for twenty years, not more
than 100,000 seals per year to be killed. A vigorous advertising
campaign undertaken by this company in London brought
sealskin into great popularity, and the value of skins rose
accordingly. The result was that hordes of poachers were
attracted to the seal area, and by 1880, by the so-called " pelagic
sealing " methods, namely the use of long range rifles fired
from ships, poachers were capturing more seals then the
company, whose annual catch had fallen to 8,400.

The habits of the seal are peculiarly favourable to this
method of destruction. From September to May the animal
is almost wholly aquatic, cruising in a 6,000 mile circuit from
Alaska to the Californian coast and northwards to the Aleutian
Islands, where during the first fortnight in May the seals land,
the young are born, and the surplus males fight fiercely for the
privilege of a harem of six to ten females. The young remain
on the islands until October, the parents putting out to sea
daily and returning at night.

It is during this period that the method of pelagic sealing
was bound to inflict enormous damage. Such a method allowed
of no discrimination between the superfluous male and a female
seal with one or two pups to support. In the dense fogs, too,
which occur frequently around these islands, poachers were able
to evade the patrol vessels, to land on the islands, and to club
and hurriedly skin hundreds of seals, the skinning of seals
which were only stunned being a common occurrence.

WHALING AND SEALING 345

In spite of patrols, in spite of the closing of the Behring
Sea, pelagic sealing continued and the number of seals steadily
diminished. In 1895, almost 60,000 sealskins were marketed
by poaching vessels, as against 15,000 taken legally by the
North American Company which had succeeded the Alaska
Company, and some 30,000 pups were estimated to have perished
of starvation. In 1910, the total number of living seals probably
did not exceed 200,000. Then an extensive campaign of
propaganda was instituted, chiefly at the instigation of the
American naturalist Hornaday, supported by the Camp Fire
Clubs of the United States. Pressure upon the Government
brought about an international treaty in 1911 between Japan,
Russia, Great Britain, and the United States, and sealing
became a monopoly of the United States, compensation being
arranged for with other countries concerned. Pelagic sealing
was stopped. A close season of five years was declared. To
protect the females and young, however, it has been necessary
to kill a certain number of surplus males each year. The result
has been quite successful, the estimated number of seals in
1918 being 496,432, and in a few years time the annual surplus
of male seals should be as high as 100,000, and there will be
no loss of females nor young.

It may be added that it has been definitely ascertained
that the principal food of the fur seal is not fish, and that the
same may be true with regard to the other sea Hon, Steller's
sea lion (Eumetopias stelleri) of the same region, despite the
statements made by salmon canning interests in that area.
At any rate the Federal Department of Fisheries of the United
States Government has refused to sanction the indiscriminate
and promiscuous killing of this sea lion.

The present demand for fur of any sort has stimulated the
commercial hunting of the Harp Seal off the coasts of New-
foundland, although its coat cannot compare in quality with
that of the true Fur Seal.

This species at breeding time assembles on the ice
floes, and drifts southwards to be clubbed in thousands
during the summer by the Newfoundland sealers. Sealing
is impossible on these coasts in winter, or this seal would have
been exterminated long ago. As it is, however, an average of
125,000 seals are taken yearly, the smallest catch on record
being just under 34,000 and the largest 350,000.

The newly-born seal has a white coat of thick woolly fur,
and is termed a ' white coat " ; at the end of two weeks this
coat is shed and the colour of the animal is steel-grey ; it is

346 THE PRINCIPLES OF APPLIED ZOOLOGY

termed a " grey coat " ; from one to three years old the coat
is spotted and the hair short ; this animal is termed a ' ' bed-
lamer," a corruption of the French bete de la mer.

The pelts of white coats and grey coats are placed on the
fur markets ; the skins of bedlamers and old seals are com-
mercially valuable for the manufacture of belts, pocket books,
and so forth ; the fat or blubber can be reduced to a tasteless
clear oil which is valuable for many purposes.

The value of large seals has brought about the almost
complete extinction of many forms.

Thus the sea elephants were almost extinguished by the
middle of the last century by sealers and whalers for their oil
and hides, although a few of the southern species survive on
Kerguelen Island, and a few of the northern forms survive on
the Island of Guadaloupe, now a Mexican Government reserva-
tion, which lies in the Pacific Ocean, 140 miles from the northern
part of the peninsula of Lower California.

Similarly, the Caribbean seal (Monachus tropicalis) has been
almost exterminated by sealers for its oil and hide.

The southern fur seals were ruthlessly and wastefully
slaughtered by American sealers long before the Antarctic
was charted, the only protected breeding grounds of these
seals being Lobos Island in the La Plata, belonging to the
Argentine Republic, which yields several thousand skins yearly.
The Guadaloupe fur seal ( Arctocephalus townsendi) has not
been seen since 1894. In the case of the Alaska fur seal, only
timely conservation measures saved it from a similar fate.

CHAPTER XXXI

FUR-BEARING ANIMALS

The greater bulk of the world's supply of furs originates from
areas north of the fiftieth parallel north. A considerable
number of rabbit, kangaroo, fox, wallaby, wombat, and opossum
skins come from Australia ; South America sends pelts of the
coypu rat, chinchilla, vicuna, kit fox, and raccoon ; the bulk
of the trade, however, is based on skins from Alaska, Northern
Canada, and Siberia.

That is to say, the greatest quantities of choice furs come
from areas which are cold, damp, and well wooded. For this
there are very definite reasons.

The type of mammal whose pelt is suitable for the fur trade
has two kinds of hairy covering. There is an overcoat of
long, stiff overhairs and an undercoat of short, thick, soft, and
somewhat silky hairs — the pelage or fur. The pelage hairs
are barbed, and so can be felted ; in the living animal felting
does not occur, as the pelage is protected by the overhairs. In
a prime skin the pelage is not visible unless the overhairs are
blown apart, the overhairs being particularly dense and long
in animals which lie out in the open exposed to severe weather.
In fox skins, for example, they are between three and six inches
in length. Strictly speaking, therefore, the term fur implies
the undercoat, as in the prepared skins of seal and beaver where
the coarse upper hairs have been removed ; but the term is
applied popularly to skins where the overhairs are allowed to
remain, such as fox, sable, mink, or skunk.

Now both overhairs and pelage are longest and thickest in
animals exposed to intensely cold or intensely damp conditions.
Aquatic animals such as seals, beavers, coypu rats, and musk-
rats have very close and thick pelage but somewhat coarse, un-
beautiful overhairs. Dry cold seems to stimulate the growth
of overhairs. The shade of dense forests apparently develops
a lustre or sheen upon the overhairs. Tropical or sub -tropical
mammals have little or no pelage and have somewhat short or
brittle overhairs, unless their habitat is of high altitude.

Fur-bearing Animals. — The more important types of furs

347

348 THE PRINCIPLES OF APPLIED ZOOLOGY

are drawn mainly from two families of mammals, namely the
Mustelidm or weasel family and the Canidce or fox family ;

Mink

Fig. 51. — Types of Fur-bearing Animals. (After Hornaday.) (Not to scale.)

from certain other Carnivora, notably the otter and skunk ;
and from certain rodents, notably the beaver, coypu rat, squirrel,
musk-rat, and rabbit.

FUR-BEARING ANIMALS 349

The Mustelidse is a sub-family of carnivorous mammals,
popularly termed martens, polecats, and weasels, and limited
in distribution to the temperate regions of North America,
Europe, and Asia. There are about sixteen species, varying
in size and colour, but similar in habits, being arboreal
frequenters of woods and rocky places, their snake-like bodies
giving them great grace and agility of movement ; they are
intensely blood-thirsty and feed chiefly upon small birds and
eggs, and upon small mammals of the mouse-like types. The
family may be divided into four groups of species — the martens,
minks, polecats, weasels, and stoats (Fig. 51).

The choicest fur bearer of the Mustelidse is undoubtedly
the Sable, one of the marten group. The true sable (Mustelus
zibellina) is a native of Russia and North China, the finest
specimens coming from the Okhotsk district of Siberia. After
the sable, the choicest member of the family is the Fisher or
Pekan (Mustelus pennanti), a North American animal about
the size of a cat, with a bushy tail, and of a greyish-black colour.
The great standby, however, of the fur trade is the American
Mink (Mustelus vison), some 600,000 of which are estimated
to be captured annually. The animal somewhat resembles a
long, thin rat with brown fur and a hairy tail, and is about
two feet long. The fur is close, strong, and of great durability,
and is of an amber-brown colour, darker and glossier on the
back. The dyers usually accentuate the colour by brush
dyeing. The animal extends over a large portion of North
America, the finest specimens, however, coming from Quebec
and the maritime provinces of Canada. The animal haunts
the banks of streams, swims freely, and lives chiefly on fish
and musk-rats.

The European or Marsh Mink (Mustelus lutreola) does not
fetch the price of the Canadian species, but the Siberian Mink
has become very popular under the name of Kolinsky, and is
particularly prevalent in the Kola district of Siberia. The
finest specimens come from Kusnetsk, the largest quantity
from Yakutsk. The animal is about eighteen inches long,
almost orange in colour, and has therefore to be dyed. A good
skin, well dyed, will pass almost for sable. The rest of the
Mustelidse are rated less highly. The Ermine, which is the
winter phase of the Stoat (M. erminea), no longer fetches the
fabulous prices that were given in the eighteenth century.
Most of the present-day ermine is derived from the American
Short-tailed Weasel (M . cicognanti Bonaparte).

Very closely allied to the martens and weasels, though not

350 THE PRINCIPLES OF APPLIED ZOOLOGY

actually members of the same sub -family, are two animals
whose fur value is sufficiently important to merit attention
here ; they are the Otter (Lutra) and the Skunk (Mephitis).

Otter skin has always been regarded as a desirable and
valuable fur. Of the many species of otter ranging over the
northern hemisphere, the largest and most valuable from a
fur value standpoint is the Canadian otter (Lutra catiadensis) ,
whose sub-species range from Labrador to Alaska, from Florida
to the Arctic. Advancing civilisation, however, has driven
the otter from his southern haunts, and the majority of American
skins come from Labrador, particularly the district of East Main,
Athabasca, the Rocky Mountains, and Alaska. The mode of
life is uniform for all sub-species, and little variation in size
or quality of the pelts is to be noted, although the pelts from
Labrador and Newfoundland are somewhat darker, those from
British Columbia somewhat larger, than in the case of other
sub-species. The animal is semi-aquatic, living chiefly upon
fish, and is about a yard in length. The pelage, as is usually
the case in aquatic animals, is very close and deep and of a
mahogany brown colour ; the overhairs are long and coarse,
and somewhat darker in shade than the pelage.

Otter is probably the most durable of all furs, but being some-
what heavy is suitable for countries where long cold winters
are the rule.

Before the Great War, Canada and Russia provided the best
markets, and something like 30,000 pelts a year were placed
on the market, chiefly from Canada and Kamschatka. Since
then the annual number has steadily dwindled, and the price,
in spite of the closure of the Russian market, has steadily
advanced, until otter now ranks in value only after sable,
marten, mink, chinchilla, and mole.

The Skunk (Mephitis) is purely American in distribution,
its several species ranging from Southern Canada to Central
America ; very few come from Alaska and Labrador. The
common species is M. mephitica, which is about the size of a
cat, possesses a bushy tail about twelve to eighteen inches in
length, generally carried erect, and a coat of stiff black hairs
with a dorsal V-shaped white stripe, the point of the V being
just behind the head. The animal is a burro wer and feeds
largely on insects, particularly grasshoppers, on mice,
and even on poultry when obtainable.

It is exceptionally fearless, and with good reason, since
scarcely any other animal will run the risk of receiving in its
eyes a blinding spray of foetid fluid from the skunk's anal glands.

FUR-BEARING ANIMALS 351

Thirty years ago skunk fur had scarcely any market value.
Better methods of dressing and deodorising the skin, however
increased its value, but for a long time the skin had to be sold
under an assumed name, black marten or Alaska sable. The
pelts, however, are to-day in eager demand under their true
name, and skunk fur is even imitated. The annual catch of
skunks is estimated at a million and a half, and is far short
of the demand. The skins are graded in value according to
the sizes of the white stripe. Grade I. pelts are jet black with
small white patches behind the neck ; Grade II. have the white
V as far as the shoulders ; in Grade III. the V extends along
the back, but the stripe is narrow ; in Grade IV. the stripe is
wide. The white parts of the skins are machine sewn into
strips or plates and dyed black.

A smaller species of skunk, the Little Spotted Skunk (M.
interrupts) , is also trapped for fur, but the pelt is known
commercially as civet.

The Foxes. — Next in value after the mustelid fur bearers,
in aggregate value at any rate, ranks the group of fox species.

The fox is one of the most widely distributed animals in
the world. Few areas of the world, whether arctic, temperate,
or tropical, are without some species of fox. There are foxes
in the remotest deserts of Africa and Asia, foxes in the in-
hospitable wastes of the Arctic, foxes in the vicinity of industrial
cities in civilised Europe and America. From a fur value
standpoint, however, only such foxes as inhabit North America
and Northern Eurasia need be considered, and of these only
the following examples : —

The Common Fox ( Canis vulpes) of Europe and Asia ; the
North American Red Fox (C.fulvus) ; the Kitt Fox (C. velox)
of North America ; the Grey Fox ( Urocyon cinereus) of the
Southern United States; and the Arctic Fox (Canis lagopus).
The Asiatic, African, and South American species are, except
for Alpine varieties, poorly furred.

The Common Fox is widely distributed across Europe and
Asia. There are few animals more variable in size and colour-
ing than a fox, few animals more puzzling to a taxonomist,
and the Common Fox is no exception to this.

There are a large number of sub-species or varieties. The
colour may vary through many shades of red and grey. The
fur is not of great commercial value individually, but in the
aggregate has considerable value, for some hundreds of
thousands are trapped annually in Scandinavian, German,
and Russian districts, and used not only for home use but for

352 THE PRINCIPLES OF APPLIED ZOOLOGY

exportation to the United States, although the quality is
inferior to that of American foxes.

The American Red Fox may represent merely some ten
American sub-species of Canis vulpes, but seems more likely
to be a separate species (Canis fulvus) subdivided into ten
sub-species, since its range is not confined to North America
but extends into China and Siberia. In North America its
extreme southerly range is probably North Carolina, Tennessee,
and Pennsylvania ; in the southern states its place is taken
somewhat by the Grey Fox.

The general colour ranges from yellow to a deep red,
the Kamschatka varieties being particularly deep in colour.
The finest skins are probably those from the Esquimau district
of Labrador.

There are two colour varieties which, owing to their beauty
and scarcity, fetch very high prices. These are : —

(a) The Silver Fox or Black Fox, which at its finest is jet
black with a white tail tip, but may have silver hairs scattered
among the black ones. There is no trace of red.

(6) The Cross Fox, which is a partially melanistic variety,
the black or silver hairs being present on back and shoulders,
so as to give the appearance of a cross, the sides, neck, and
ears being yellowish.

The Kit Fox (Canis velox) or Swift Fox ranges from
Saskatchewan southwards through the Great Plains to New
Mexico, where it overlaps with the Calif ornian and Texan
foxes ( V. nacrotes, V. multicus, V. arsipus).

It is typically a prairie animal, is no larger than a house
cat, and of a yellowish ground colour with silver-grey overhairs
on back, overlying a grey-brown under fur.

The Grey Fox ( Urocyon cinereus) or Virginian Fox of Cali-
fornia, Texas, and Mexico is in less demand than the foxes
described above, the fur being very much coarser.

The Arctic Fox (Canis lagopus) is circumpolar in range.
There are two varieties. In the extreme north the colour is
white in winter and brown in summer (the so-called ' stone
fox "). In more southerly latitudes, such as Greenland and
Alaska, the animal is a grey ash or bluish-brown colour all the
year round, and is known as the ' blue fox." It must be
emphasised that the Blue Fox is not, therefore, the summer
phase of the White Fox ; it is quite a distinct variety of Canis
lagopus. This variety is distinctly rarer than the white and
fetches higher prices.

Statistics as to the number of fox skins that pass through

FUR-BEARING ANIMALS

353

the fur dealers' hands annually are difficult to come by. Emil
Brass, a German commercial agent who for many years com-
piled fur trade statistics, estimated an annual number of
2,952,300, a figure based on the period 1907-09, and divisible
as follows : —

Source.

Red.

Cross.

Silver.

Kit.

Grey.

White.

Blue.

Europe
America
Asia
Australia

775,000

200,000

160,000

30,000

15,000
3,000

4,000
300

4,000
60,000

50,000

5,000
30,000
70,000

1,000
6,000
4,000

• • •

Along with some 260,000 skins of raccoon dog from Japan
and Mongolia, and some 15,000 skins of South American foxes.

Fur trade statistics are notoriously untrustworthy, however,
the number of skins that figure in auction sale lists in any year
rarely corresponding to the actual number of animals caught,
since skins unsold at one auction may appear subsequently
at another auction. During the period 1820-1905, the Hudsons
Bay Company collected 1,536,420 skins of Red Fox, in all
probabilhty the true American red fox, which is a yearly average
of 18,075. In the period 1820-91, the other American com-
panies collected 3,831,516, an annual average of 53,965 ; a
total annual average of American red foxes of 72,040 skins,
which differs somewhat from Brass's estimate. In any case
Brass's estimate is almost certainly too low for recent years.

Other Fur Bearers. — During the first 100 years of its history
the American fur trade may be said to have depended largely
upon the supply of fisher, marten, otter, mink, and beaver.
Sealskin was hardly known before 1870. Beaver in particular
was for a long time the staple fur of the American trade.

The American beaver {Castor canadensis) is the largest,
with one exception, of that order of mammalia termed Rodentia,
being in length from fourteen to thirty-two inches. It is a
thoroughly aquatic animal, a feeder on soft barked trees
(aspen, willow, poplar), and is extremely sociable, living in
colonies of so-called ' lodges," dome-shaped dwellings half
submerged in water, and constructed of timber and mud.

As is usual with semi-aquatic mammals, the pelage is intensely
close and soft, and was formerly in extensive demand for hats ;
but since the beaver hat was ousted from popularity by the
silk hat, the fur has been in request for coats, ties, and muffs.
No animal did more than the beaver to effect the opening up of

23

354 THE PRINCIPLES OF APPLIED ZOOLOGY

North America. In search of beaver, trappers explored the
remotest corners of North America, relied upon it for food and
clothing, and exchanged the skins for the civilised products
of Europe. Unfortunately, owing to its dependence upon
well-watered and well-wooded country, the range of this
interesting animal is rapidly restricted by agricultural settle-
ment. In Europe the animal became practically extinct two
centuries ago, although about 12,000 specimens exist in Southern
Norway, along the River Nidelven, and in North America its
extinction has been barely averted by national conservation
measures. It is now limited in range to the Great Lakes,
Labrador, around Hudson Bay, North Ontario, Athabasca, and
British Columbia.

In 1907-08 Brass estimated the annual output of beaver as
80,000, a considerable reduction from the hundreds of thousands
of skins that were shipped to Europe annually a hundred years
before. In 1912 the annual catch was 17,000 and the beaver
seemed doomed, but vigorous protective measures and the
swing of the pendulum of fashion to fox and mink gave the
animal a chance to recuperate. In the spring sales of 1920,
for example, some 800,000 skins were again on offer.

The scarcity of beaver brought into vogue the pelt of the
Coypu Rat (Myopotamus), an aquatic rodent from South America,
whose skin, under the trade name of " nutria," is very similar,
if inferior, to beaver.

The fur is not so thick and heavy as that of beaver, and is
of a dull sepia brown as compared with the lustrous greyish-
brown of beaver, and has to be dyed, a process which of
course detracts from the value.

The beaver and coypu rat are not the only fur-bearing
representatives of the rodents.

The Musk-rat (Fiber zibethicus) is a rodent about the size
of a vole or meadow mouse, that is to say about eight to ten
inches long. It is aquatic in habit, an inhabitant of the salt
marches around Delaware and Chesapeake Ba}^s of the Atlantic
Coast of the United States, and the swamps in the Cumberland
Lake region of the upper Saskatchewan river of Canada, and
it feeds chiefly upon bulbous roots, wild rice, and wild lilies,
but in some areas feeds upon mussels and carp. The burrows
are either just above the water-line in the banks of streams, or
in built-up nests in shallow water.

The living quarters are always well above water-line, the
entrance below the water-line. The animals are very prolific,
two or three litters of six to twenty being produced each year,

FUR-BEARING ANIMALS 355

and sometimes five litters are produced. About ten million
musk-rats are captured annually in Canada and the United
States, and the supply shows very little sign of diminishing.
The flesh and musk-bags are all saleable. The flesh is sold
in large quantities in Baltimore and Washington as marsh
hare.

The raw pelt is dense and soft, very much like beaver in
appearance, but shorter and less close. The colour varies with
the locality and season. Northern skins, though heaviest in
fur, are lightest in colour, possibly because they are taken in
summer pelage ; very dark skins come from New Jersey,
Delaware, and Maryland. The first demand for musk-rat was
for the manufacture of so-called beaver hats, and when such
hats went out of fashion the demand for musk-rat fell off.
Then it became used for linings. Then improved methods of
dressing and dyeing, and its use as ' Hudson Bay Seal ' in-
creased its market value greatly, and in quantity it is now one
of the biggest items in any fur auction.

The Chinchilla, a jumping mouse of the South American
pampas (Chili, Bolivia, Peru), has a fur of great delicacy and of
a dark blue-slate and pearly appearance. Its pelt brings very
high prices. The Viscacha is a similar animal with a fur, how-
ever, larger, coarser, yellower than that of the chinchilla. The
demand for chinchilla is met by 50,000-80,000 skins a year,
although Bolivia in particular has declared a close season for
some years.

Scarcity of chinchilla has given a stimulus to the production
of mole skins, but the plentitude of these is offset somewhat
by the expense and trouble of dressing them, so that
comparatively high prices are necessitated for what is really
common skin.

Another rodent with a fragile but beautiful fur is the Squirrel,
of which enormous numbers (15,500,000 according to Brass)
are marketed annually, the greater bulk being chiefly provided
by Russia and dressed around Leipzig.

CHAPTER XXXII

THE FUR TRADE

The fur trade is one of the oldest industries in the world, since
the prime article of barter between civilisation and savagery
has generally been the animal skin. In the Middle Ages a
considerable commercial intercourse went on between the
natives of Scandinavia, of North Russia, and of Siberia and
the fur traders of Nijni Novgorod, Moscow, and the Hanseatic
ports of the Baltic. Venice and Genoa distributed these
products of the European forests to the Mediterranean countries,
to France, and probably to Great Britain. Furs were scarce
and dear. Most countries regulated the supply by means of
Sumptuary Laws. Thus in Great Britain, mediaeval law
restricted the wearing of furs to royalty, to the nobility, and
to clerical dignitaries. Ermine was a prerogative of royalty,
just as, up to quite recent times, the use of sea-otter fur was
restricted in China to mandarins.

The history of modern commercial fur trading, however,
may be divided, just as in the case of the whaling industry,
into a number of phases. Unlike the latter industry, these
phases have been influenced to a considerable extent by the
vagaries of fashion.

The first phase was ushered in by the discovery of the vast
animal resources of the North American forests, and was
based upon the skin of the beaver, vast quantities of which were
sent to Europe during the seventeenth and eighteenth centuries
to supply the demand for beaver hats. The exploration of
North America owes much to the fur trader.

Canada, after the French had been ousted, became the
huge preserve of the " adventurers of England trading into
Hudson Bay," who, by a charter granted in 1670 by Charles II.
to his cousin Prince Rupert, acquired a monopoly which
endured, apart from a hectic decade (1811-20) of competition
with the North-Western Fur Company of Montreal, until 1859.
The New England area was exploited by the Dutch West India
Company, perhaps the earliest fur trading company of America,
with posts at New Amsterdam (New York), Beaverwick

356

THE FUR TRADE 357

(Albany), along the Delaware, and along the coast of Maine.
From 1621 onwards this company was sending 60,000 beaver
skins annually to Europe.

The south-eastern area of the United States was exploited
similarly by the Missouri Fur Company and the American Fur
Company, both founded by an enterprising German fur trader
named John Jacob Astor.

The emissaries of these various companies, the voyageur
and the coureur du bois, followed the beaver through the swampy
labyrinths and trackless forests of almost all North America.

Astor even founded a post at the mouth of the Columbia
river, in spite of almost incredible difficulties, but later
abandoned the scheme.

The raw pelts were sent by flotillas of boats from Ottawa
down the St Lawrence to Montreal, or down the Mississippi
and Missouri to St Louis, or they came from Winnipeg to St
Paul in long trains of creaking ox wagons across the prairies.
At St Paul or St Louis the furs were sorted and despatched to
New Orleans, to New York, to London and Hamburg.

During the latter half of the seventeenth century some
40,000 skins, chiefly beaver, were sent to London alone every
year. Twenty beaver skins was the price of a musket along
the Mohawk river, but in more unsophisticated regions a musket
was worth as many beaver skins as could be piled up, one
on top of the other, to its height, and especially long barrelled
muskets were imported. Values of goods all over North
America were computed in beaver skins, the Hudsons Bay
Company issuing a lead coinage stamped with IB, JB, JB,
and with the district of issue — Y.F. (York Factory), E.M.
(East Main), and so on — which was current all over Canada.
Vast fortunes such as the Astors were founded almost entirely
on beaver skins.

The second phase was brought about by the ousting of the
beaver hat from popularity by the silk hat, and the adoption
of ornamental fur garments as fashionable wear. It may be
termed the phase of choice furs, since owing to the absence of
technical methods of fur dyeing and shearing, only such furs
as beaver, sable, otter, ermine, silver fox, sea otter, and chin-
chilla were acceptable. The choicest sable skins came always
from Siberia and North China.

The third phase was that of substitute furs, and commenced
about 1870 when the growing scarcity of sable brought on the
market the American marten and fisher as substitutes. An
advertising campaign about the same time, in London, brought

358 THE PRINCIPLES OF APPLIED ZOOLOGY

sealskins into fashion. Mink, used formerly as a coat lining,
became a choice substitute for fisher and marten. Cross fox
and blue fox replaced the scarce silver fox. Beaver became
replaced by coypu (" nutria "). Persian lamb came into
fashion.

The fourth and present phase is that of imitation furs. The
growing scarcity and dearness even of substitute furs, and
improved methods of dyeing and dressing, brought other kinds
of furs into the market. Skunk, unsaleable as skunk, sold
readily as Alaska Sable ; musk-rat was dressed and dyed until
almost indistinguishable from sealskin, and fetched good prices
as Hudson Bay Seal ; raccoon became fashionable as Silver
Bear and Blue Fox ; then came the later years of the Great War,
and an enormous boom in furs, whose prices soared to fantastic
heights. Almost any kind of skin could be sold as fur. Even the
Hair Seal became sought after. Skunk, which could now be sold
unashamedly under its own name, became fashionable and
dear, and the humbler opossum became its handmaiden under
the name of Skunk Opossum. Musk-rat, no longer under the
necessity of masquerading under an assumed name, sold boldly
as musk-rat or musquash. The rabbit came into its own.
Millions found their way to America via California, were clipped,
dyed and doctored, and appeared, and still appear, as Electric
Seal, Coney Seal, Coney Beaver, Squirrel Coney ; white hares
masquerade now as White Foxes ; grey foxes, dyed black and
with the silver tipped hairs of badger glued in, imitate very well
the beauty of Silver Fox ; Chinese goat is transmogrified by
bleaching into Iceland Fox.

There is, in fact, quite a list of animals whose real names
are not found among trade terms of the fur industry : thus the
Siberian Mink (Mustelus siberica) is always termed Kolinsky ;
the Polecat (Mustelus putorius) is Fitch ; the Common Cat is
Genet ; the Coypu Rat (Myopotamus coypu) is Nutria ; the
Koala (Phascolarctus cinereus) is Wombat ; the Little Spotted
Skunk (Mephitis interrupta) is Civet.

The Procuring of Furs. — Although fur companies no longer
enjoy a monopoly and trapping is free to anyone, subject to
legislative restrictions, yet the great majority of furs obtained,
in North America at any rate, pass into the hands of several
big fur trading companies. There are : The Hudsons Bay
Company, Russian Fur Company, Alaska Fur Company, North
American Fur Company, Russian Sealskin Company, Harmony
Fur Company (Labrador), Royal Greenland Fur Company,
American Fur Company, Missouri Fur Company, and the Pacific

THE FUR TRADE 359

Fur Company. To this list may be added such companies as the
French firm of Revillon Freres, competitors with the Hudsons
Bay Company, who, however, do a wholesale and retail business
and offer no skins at public auction.

These companies depend mainly for their supplies upon the
work of licensed trappers and native Indians, the great majority
of whom are at work in the pathless wilderness of the Mackenzie
and Athabasca river areas, and the illimitable stretches of wood-
land between Labrador and Upper Missouri, visiting twice a
day a chain of perhaps thirty traps extending over a circuit
of many miles.

The kinds of traps in use vary. In the main, steel jaw traps
are used ; for marten and for larger animals, dead falls are
arranged so that a tug on the bait brings a heavy log crashing
doAvn on to the animal's back ; small, delicate animals such
as the ermine are preferably taken in box traps ; rabbits are
snared.

There are two ways of removing the skin. There is the
" open method," whereby the skin is incised ventrally and
taken off much as a man takes off his overcoat. There is the
" cased method," in which the skin of the hind legs is slit
along the inner line and the skin peeled off from tail to head
much as a glove can be peeled from the hand.

Pelts of fox, fisher, marten, ermine, otter, skunk, lynx,
and musk-rat are usually cased. Beaver, bear, wolf, and the
large furs are removed by the open method.

After removal, the inside of the skin is carefully scraped
free from fat and muscle with a blunt bone knife, and is stretched
and allowed to dry gradually. Cased skins are stretched, fur
inwards, on a wedge-shaped board with rounded edges about
half an inch thick, the dorsal side of the skin being wholly on
one side of the board, the ventral on another (Fig. 52).

Beaver skins are stretched within an elliptical hoop made
of saplings by twine laced to the skin at intervals of two inches.
Bear skins are similarly laced in a rectangular frame. Other
skins are nailed to a wall or to a pine board by brass tacks,
fur side inwards.

Valuable skins are sewn up in muslin and either sent direct
to the fur broker or handed in at a fur company's trading
post.

The Marketing of Furs. — The skins obtained by the trappers
converge to certain centres : in Canada to Montreal, Winnipeg,
and Edmonton ; in the United States to St Paul, St Louis,
San Francisco, Chicago, and New York ; in Germany to Leipzig

360 THE PRINCIPLES OF APPLIED ZOOLOGY

and Frankfurt on Oder ; in Russia to Nijni Novgorod, Moscow,
Irbit, and Istum.

From these centres the skins go to the great fur brokers of

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London and Leipzig, Montreal and New York, by whom the
skins are graded and sold by auction in lots of varying numbers.
London is still the largest selling centre of the world, and at
the four annual sales — January, March, October, and December

THE FUR TRADE 361

— held by the Hudsons Bay Company, by Messrs C. M. Lampson
& Co., and by Frederick Huth & Co., the vast majority of the
world's output of furs are dealt with. The war, however,
gave a great opportunity to American fur brokers, and very
extensive auctions are now held in Montreal, New York, and
St Louis.

Grading and sorting is a highly skilled and highly paid
occupation, since the methods differ for each kind of fur. As
a rule the " original parcel," as it is called, of raw skins is divided
into a maximum of five grades of quality irrespective of size
and colour. Each grade is then divided into two or three
grades of colour. These are divided into large, medium, and
small sizes. The skins are then made into lots, first quality
lots comprising large, good quality pelts of the correct colour
for the particular skin ; second quality pelts are slightly inferior
in quality, colour, and size ; and so on. With some animals,
fox for example, the place of origin is taken into account also.
A representative sample of twenty-five skins from each lot
is taken out to enable the prospective purchasers to judge the
quality of the bulk.

Fur Dressing. — The final excellence of a manufactured fur
depends very largely upon the dresser and dyer. The secret
of dyeing seal gave London the monopoly of sealskins. The
secret of dressing squirrel similarly gave Leipzig a monopoly
of that class of fur.

Speaking generally, with the exception of seal pelts, the raw
skins, which reach the dresser in a greasy, fleshy, hard condition
are first soaked in or moistened with salt water for twenty -four
hours, to soften them and free them from grease. Then they
are placed in a " hydro," a machine consisting of a large
cylindrical tank containing a revolving perforated basin. The
centrifugal action upon the skin in this perforated basin shakes
out the superfluous moisture. Then the skins are polished
by friction against oak or beech sawdust in a slowly revolving
drum, and are then " fleshed," that is to say, the superfluous
tissues on the inside of the pelt are shaved off by passage over
a sharp knife. Some kinds of pelts can be fleshed by machinery.
The pelts have now to be thoroughly aired in rooms heated by
steam.

The pelts are «till stiff and have now to be made pliable,
the operation being termed " leathering." They are again
moistened with salt water on the inner side, remaining so over-
night. The inside is then thoroughly hand rubbed with seal
oil or butter or tallow. The skins are then placed in pairs,

362 THE PRINCIPLES OF APPLIED ZOOLOGY

hairy sides together, in a machine which pounds and stretches
them until they are thoroughly pliable. This machine has
almost everywhere replaced the old method of " foot tubbing,"
namely, placing the pelts in a huge vat with sawdust and
employing semi-nude men to stamp about on them. Some skins
— mole, for example — are still foot tubbed, however. The
skins are now cleaned by shaking them with dry sawdust, fine
as flour, and a little gasolene, in revolving drums for about three
hours, then beating them with rattan canes and combing them
to eliminate the sawdust.

The dressed skins may now require unhairing and dyeing.

In the case of otter, seal, beaver, and nutria, the coarse
outer hairs are plucked out by hand, the skin being first warmed
and stretched over a smooth log some eighteen inches in
diameter.

Other skins, such as musk-rat, are not plucked but sheared,
the coarse outer hairs being cut down to the length of the pelage
by a shearing machine.

The following table of comparative durabilities, compiled
by Petersen, may be taken as a fair representation of the fur
trade opinion. The otter is taken as the standard, other
durabilities being represented by a percentage of this : —

Otter, natural .

100

Civet, natural .

40

Wolverine

. 100

Fox, natural

40

Otter, plucked

95

Opossum, natural

37

Bear, black and brown

94

Pony, Russian

35

Beaver, natural

90

Mink, dyed

35

Beaver, plucked

85

Marten, stone, dyed .

35

Seal (hair)

80

Musk-rat, seal, dyed .

33

Seal (fur)

80

Wolf, dyed . * .

30

Seal (hair), dyed

75

Ermine ....

25

Leopard

75

Pox, dyed black

25

Seal (fur), dyed

70

Kolinsky

25

Mink, natural .

70

Lynx .

25

Skunk, natural

70

Squirrel, black

25

Marten, baum .

(55

Nutria, plucked

25

Persian lamb .

65

Fox, blue

20

Raccoon, natural

65

Marmot, dyed .

20

Krimmer

60

Mink, Japan

20

Sable, natural

60

Squirrel, black blended

20

Wolf, natural . .

50

Opossum, dyed

20

Skunk, tippets

50

Chinchilla .

15

Raccoon, dyed

50

Goat .

15

Marten, baum, blended

45

Astrakhan-moire

10

Marten, stone .

45

Mole

10

Sable, blended

45

Hare .

10

Musk-rat, natural

45

Rabbit .

10

Opossum, Australian

40

The dyeing of furs is a very delicate and closely guarded
secret of the firms that carry out the work. Speaking very

THE FUR TRADE 363

generally, there are several methods in use. Pelts of rabbit
and musk-rat may be dipped in huge revolving tanks of dyestuff s
until the skins are soaked. More expensive pelts are " topped,"
that is to say, the skin is brushed with the dye so that only the
outer portion of the hair is coloured. A final lustre is often
produced by hand brushing with an application of sulphuric
acid.

Dyeing and plucking, of course, affect the durability of the
fur. Unless the dyeing is extremely well done, even when the
pelt is dyed by hand brushing, the dye will in time soak through
the pelage to the skin and weaken it.

In conclusion, it may be added that the statistics of any of
the fur auction sales are sufficiently imposing to create a feeling
of alarm and doubt not only in lovers of wild life but also in
fur traders themselves as to the conditions of the future. Such
animals as the sable, marten, chinchilla, beaver, and otter are
undoubtedly declining rapidly in numbers, and the sea otter is,
commercially, extinct. Even such prolific animals as musk-rats
and squirrels are being taken in such large numbers that their
relegation to the status of rare animals is only a matter of time.
The chief areas from which furs are taken, notably Alaska,
Northern Canada, and Siberia, are certainly so vast in extent,
so wild and impenetrable, and so, sparsely populated, that the
extinction of any animal to the extent to which the bison was
wiped out in the past is hardly likely to occur. Labrador alone
is 530,000 square miles in extent, twice the area of Germany,
and has a population of 17,000 at the outside. Marten and
mink, fox and musk-rat will always occur somewhere or other.
It should not be difficult, therefore, to devise conservation
measures which, without hampering what is after all a legitimate
and useful industry, will enable animals to maintain a constant
normal level of abundance.

It must be remembered that other causes besides the activity
of man may bring about considerable fluctuation in the number
of fur bearers in any one year. Such animals may, according
to the observations of Macfarlane and of Seton, be divided in
this respect into three groups, namely : —

(a) The herbivorous rodents, mice, rabbits, ground squirrels,
musk-rats, and the like, which are very prolific and increase in
numbers until they reach a high degree of abundance. Then
they either constitute a mouse plague, as described in
Chapter XX., or they are suddenly reduced to a minimum by
an epidemic of some disease. That is to say, they show
periodical abundance and scarcity.

364 THE PRINCIPLES OF APPLIED ZOOLOGY

(b) The various predatory animals which depend upon these
small animals for food, and so fluctuate in numbers in any
particular in correlation with the fluctuations of small rodents.
This category includes the Mustelid animals such as fisher,
marten, mink ; the lynx, which is largely a rabbit feeder ; the
foxes ; and to a lesser extent the skunk. The large predators
such as wolves and coyotes are not so dependent upon the
abundance of small game in any one area, since they can travel
far afield.

(c) Animals which feed on a mixed or exclusive diet of
insects, fruits, and fish, and do not show periodical fluctuations.
This category includes the black and brown bears, the raccoon,
otter, and beaver.

This question requires further and more extensive study,
since a knowledge of the basic causes of such fluctuations may
provide a method of predicting to a large extent the years of
abundance of the larger fur-bearing animals, and so may
influence very largely the framing of legislative measures
designed to conserve these animals.

CHAPTER XXXIII

FUR FARMING

There can be little doubt that the one hope of preserving the
more valuable and the larger fur-bearing animals lies in the
possibility of domesticating them, or at any rate of rearing
them in captivity. There may be said to be two kinds of such
fur farming, namely : —

(a) The production of a new variety of some animal already
domesticated and easily reared, such as the goat, sheep, rabbit,
cat, or dog, with a coat of such quality as to have a value as
fur.

(6) The rearing in captivity of some wild animal whose fur
has already an accepted market value ; such an animal as the
beaver, mink, otter, skunk, fisher, or fox.

The first type of fur farming has been carried out for
centuries. Goats have always had a fur value. Dogs and
cats and rabbits to-day have also a fur value.

Perhaps the most important example of a domesticated
fur-bearing animal is that of the so-called Karakul sheep.

The Karakul sheep is a Central Asiatic breed, the centre of
its distribution being Bokhara, in Turkestan. It derives its
name from Kara-kul, meaning the black lake, a village in
Bokhara.

The Karakul sheep has a fleece which is shaggy and coarse,
and sells commonly as carpet wool. The newly-born lamb,
however, has, when less than five days old, a pelt which is
glossy black, curly, and of high lustre. Such lambskins are
exported at the rate of 40,000-50,000 a year through Persian
and Russian marketing centres to Europe and North America
and sold there as Persian lamb, or broadtail or baby lamb.
A similar but inferior kind comes from Northern Persia and
constitutes Shiraz. A variety from Russia with longer hair,
more open curl, and less lustre sells as Astrakhan. From the
Crimea comes a grey kind, sold as Krimmer.

A good skin should be taken from a lamb less than five days
old, since after that age the curl coarsens and the skin will
fetch the price of a common fur only, whilst after six weeks

365

366 THE PRINCIPLES OF APPLIED ZOOLOGY

old the pelt is not fur at all but wool. Slinks or still-born lambs
provide the most valuable pelts of all.

The average quality of skins from European Russia, Asia
Minor, Trans-Caucasia, and Western Turkestan is declining
rapidly, a larger and larger proportion each year being of the
open curl or Astrakhan quality, a consequence probably of the
crossing of Karakul sheep with mutton or wool sheep such as the
Afghan fine wools, the Achuri and Chulmi fat rumps, and
so on.

Karakul sheep breeding, however, is now established in
North America through the efforts of Dr C. C. Young of Texas,
who managed to import fifteen Afghan Karakul sheep to Texas
in 1908. After great difficulties some Bokhara rams were
obtained in 1912, and in 1914, in the teeth of Russian quarantine
opposition, a herd of twenty-one rams and ewes from Bokhara
was shipped from Libau to Baltimore.

The initial experiments in establishing the sheep were made
in Texas, but later were transferred to Prince Edward Island.
A herd has also been maintained on the British Government
Farm in Inverness-shire, Scotland, and one at the United States
Government Farm at Belts ville, Maryland.

Several years' experience has shown that Karakul sheep are
usually hardier than European breeds and can flourish where
other sheep would starve. Close inbreeding, however, whilst
apparently not physically detrimental to the sheep, makes the
wool finer and induces a more open curl in the lambskin, an
undesirable quality. Future progress of the industry will
depend probably upon successful hybridisation of Karakuls
with native ewes of a coarse class such as Highland Blackface,
Lincoln, Cotswold, Mexican Hairy, Persian Fat-rump, or
similar breeds.

Rabbits. — Rabbit breeding for natural fur, that is to say for
skins which do not require to be dyed or doctored, is a special
industr}^ in which the value of the flesh of the animal is less than
that of the skin. It must be noted, therefore, that the skins
of rabbits killed at four and a half to five months old, or less, for
table purposes are of little value as fur, whatever their size
or colour, and are in demand only by felters and hatters.

Skins which are to command high prices as furs should be
obtained from animals not less than six to nine months old,
not less than 7 lbs. in weight, killed in the middle of winter.

The principal breeds of rabbits with skins of fur value are
Chinchillas, Champagne Silvers, Havanas, Blue Beverens,
Himalayans, and short-coated, self-coloured black, yellow, and

FUR FARMING 367

white rabbits of various breeds, notably Belgian Hares, English,
Dutch, and Polish.

In all cases skins should be as nearly self-coloured as possible,
at any rate between shoulders and tail. Animals with spots
or other marks on the back are of little interset to the fur
producer.

The Chinchilla is a large, light -coloured animal whose coat,
owing to a mixture of black and white hairs, is of a silvery-grey
colour similar to that of the expensive South American chinchilla
which it is intended to imitate. The standard type of coloration
laid down by the British Chinchilla Club is as follows : That
part of the hair next to the skin to be slate-blue, immediately
followed by pearl-grey ; working towards the surface it merges
into white, whilst just at the end of the hair it becomes black ;
scattered over the body are hairs which exceed the length of
the main coat and are entirely black. An exquisitely soft
texture and density of coat are essential, and the coat is to be
no less than one inch in length.

The Chinchilla rabbit is believed to have originated in France
through hybridisation between black and tan, self blue, and the
ordinary wild rabbits. Very young animals, as a matter of
fact, are sometimes coloured somewhat like wild rabbits.

A variety of Chinchilla produced recently is the American
Chinchilla, a product of hybridisation of Standard Chinchilla
bucks with does of the Flemish Giant, a popular general utility
breed. By selection of heavyweight Standard Chinchillas there
has been produced also the Heavyweight Chinchilla in the
United States.

Somewhat similar to the Chinchilla in coloration is the
Champagne Silver rabbit. The colour, however, resembles
more that of platinum or dull silver than the warmer grey of
Chinchilla. The under fur is blue in colour.

The Havana breed is a self-coloured brown or chocolate
variety which originated as a sport in Holland among some
rabbits running loose in a stable. The winter coat is very thick
and close, and its colour makes it a good imitation of the skin
of the marten or the beaver.

The Blue Beveren or Vienna variety comprises two types
of animal, namely : —

(a) The Brabancon, a small aniinal with brown eyes and
short coat of a medium or dark blue colour, and of low fur
value.

(6) The Giant Beveren, created by an Austrian fancier by
hybridising Flemish Giants, blue Lorraine Giants, and the

368 THE PRINCIPLES OF APPLIED ZOOLOGY

French Lop ; it is a large animal with steely blue eyes, long
silky lustrous coat of a lavender-blue colour, and a dense
undercoat ; the coat is twice as long as that of the ordinary
rabbit.

There is a white variety of Beveren, arising probably from
a cross between the Blue Beveren and the White Angora.

The Himalayan variety is thought to have originated in
Northern China. It is white with nose, ears, feet, and tail
black. The fur is of silky texture and makes a good imitation
of ermine.

Other breeds of lesser fur value, however, are Black and
Tans or Blue and Tans, a breed of small rabbits whose coat
colour is brilliant black or clear dark blue with tan markings ;
New Zealand Reds, a self-fawn variety ; Blue Imperials, a
Maltese blue coloured breed created by the English rabbit
fancier, Miss Illingsworth, by the hybridisation of the Lop,
Angora, and Dutch breeds ; American Blues, a large slate-blue
type, probably a mixture of Blue Beveren, Imperial, and
Flemish Giant ; Polish, a small white, short-coated rabbit ;
English, a white animal with spots and markings either of black,
blue, grey, or tortoise ; Dutch, a two colour rabbit, white on the
chest, front, throat, legs, forebody, and lower part of the head,
but black, blue, grey, or tortoise on ears, cheeks, and hind
body ; Flemish Giant, a large, massive animal of various types
of coat colour, steel grey, black, white, blue, and so on ; Belgian
hares, the racehorse of the rabbit class as regards activity and
sprightliness, and a rich red coloured animal.

The Angora breed of rabbit, although not, strictly speaking,
a fur variety, may be mentioned here. It is an animal with a
coat four to five inches long on the back and sides, and of remark-
able density ; the colour may be white, blue, fawn, black, or
smoky, but whatever colour the rabbit possesses, should be
uniform ; the coat is very soft and silky, and can be plucked
off periodically without injuring the animal. This so-called
rabbit wool is in great demand and will fetch from thirty to
forty shillings or eight to ten dollars a pound, and an adult
animal will yield 9-10 oz. yearly.

Rabbits intended for fur production should be reared pre-
ferably in roomy pens in batches of ten individuals of the same
sex. A batch of males will live amicably together if they have
been castrated when three months old. To obtain skins of good
colour and thickness, plenty of shade, cold conditions, and
plentiful food are required.

The domestication or semi-domestication of wild fur-bearing

FUR FARMING 369

animals is a comparatively recent venture, certainly, as regards
large scale domestication, not more than fifteen years old.

A distinction ought to be made between the term fur
farming, which implies the rearing of wild fur bearers in con-
finement, subject to artificial feeding and to a more or less
amount of human handling, and the term fur ranching, which
implies the protection from enemies of some fur-bearing species
within a limited tract of country such as an island, forest,
or marsh, and not characterised necessarily by artificial feeding
nor by human handling.

Obviously, true fur farming is not an economic proposition
unless the selected animal can be reared on a large scale without
any loss of condition due to confinement, and unless the
individual skins command a high market price.

Fur ranching, on the other hand, can be carried out with
animals such as musk-rats, whose individual fur value is low,
but whose aggregate fur value is high, owing to their prolific
breeding habits and the ease with which they can be captured.

True fur farming to-day concerns itself, therefore, chiefly
with the silver fox, mink, skunk, raccoon, marten, fisher, and
beaver in order of importance. Fur ranching concerns chiefly
the musk-rat, and to a lesser extent the blue fox.

Fox Farming. — The original home of silver fox farming is
Prince Edward Island in Canada, and there the business was
started by optimistic individuals who dug their foundation
stock from dens in the woods. For a long time they experi-
mented in secret, but their rapidly increasing revenues betrayed
them, and in 1910 a great boom in fox farming occurred. The
scramble to procure foundation stock sent prices up, and silver
foxes per breeding pair rose from 3,000 dollars in 1910 to 20,000
dollars in 1913, and as much as 35,000 dollars was paid for a
breeding pair. Company after company was floated. Dalton,
one of the pioneers, obtained 34,175 dollars in London for
twenty-five pelts.

The European War disorganised markets, but gradually the
new industry became stabilised, and the days of wild speculation
in breeding stock are over.

At the time of writing, 1927, quality breeding stock can be
obtained at prices ranging around 2,000 dollars the pair, and
good pelts bring from 200-1,000 dollars each. A fox farm
can thus yield good returns for money invested, since a breeding
pair should produce each year a Utter of four pups, and these
pups can be killed and pelted when ten months old.

There are to-day about 2,500 fur farmers in the United States

24

370 THE PRINCIPLES OF APPLIED ZOOLOGY

and Alaska, and about 1,500 in Canada, the majority raising
foxes. Fur farming is also being undertaken in European
countries and in Japan. In Great Britain, up to the end of
1926, there were about ten fox farms, comprising some 500
animals.

The term Silver Fox, as used by furriers, refers to certain
melanic varieties of the American Red Fox, an animal normally
of a rich red or dull yellow colour, but having usually a mixture
of brown or grey hairs, black markings on feet and ears, a white
tipped tail, and certain groups of white hairs on rump and back.

In the so-called Cross Fox variety, black hairs predominate
on the feet, under surface, and legs, and the red hairs occur
chiefly on shoulders and back so as to give the appearance of
a red cross on a dark ground.

In the typical Silver Fox variety there is still more of the
black coloration, and the reddish hairs are replaced by silver
ones so that the animal is black with an admixture of silver
tipped hairs. Silver foxes vary from animals entirely silver to
animals entirely black, save for a few white groups of hairs on
rump and back.

In the Black Fox variety the white hairs are totally absent,
except at the tip of the tail.

Speaking generally, the Black Fox is exceedingly rare and
consequently more valuable, the Silver Fox is scarce, and the
Cross Fox is fairly common.

The most valuable variety of Silver and Black Fox is without
doubt the Prince Edward Island variety, representing melanic
varieties of the geographical sub-species of Red Fox, Cams
vulpes rubicosa ; but Silver Foxes from the Athabasca river,
the Yukon, and Alaska are often of great value. These regions
should provide ideal conditions for fox farming if venison and
fish are procurable readily and cheaply. It may be noted,
however, that silver foxes are being farmed successfully in
practically all of the Northern States of U.S.A., ranging from
New England westwards to Washington and Oregon, and also
in the cooler portions of California, Kansas, Colorado, Iowa,
Ohio, Missouri, Illinois, Pennsylvania, New Jersey, and
Massachusetts.

A fox farm should be located preferably on a knoll or on a
level, well-drained piece of land sloping gently to the south,
and situated in a district where the climate throughout the year
is cool, damp, with snow and frost in winter. There should be
sufficient trees to provide summer shade and to provide seclusion.
The soil should preferably have a hard pan sub -soil in order to

FUR FARMING

371

prevent the animals from burrowing. Each pair of foxes is
kept in a pen of heavy galvanised wire netting of one and a half or

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- 1!

Fox 1 1
jentrancel '

Sill

-Foundation post

Vertical Section of a Fox Kennel

Fig. 53. — A Type of Fox Farm. (After Jones.)

two -inch mesh and sixteen gauge, sunk three feet into the ground
so as to foil burrowing ; the pens may be oblong, square,
octagonal, or circular, but should cover each between 600 and

372 THE PRINCIPLES OF APPLIED ZOOLOGY

750 sq. ft., large enough for the animal to run about in at full
speed ; the height of the pen should be eight to ten feet in
order to prevent the animal from leaping out, but if the pen be
covered, six feet of height is sufficient. Some farmers prefer
a movable pen so that the site can be changed occasionally.

Part of the pen should have good hiding cover, as the fox
is extremely nervous and timid ; female foxes in particular are
liable to fly into hysterics at the approach of human beings
and kill their young.

There should be well-drained and sunny areas of the pen
for the pups to play around, and the ground surface should
be turfy or covered with pine needles.

Inside each pen there is a kennel or den, preferably double
walled. This is a wooden affair entered by a sloping tunnel
termed the chute. There are two types of kennel. The over-
ground or movable kennel is being widely adopted for ranch
purposes as it is drier, better ventilated, and easily cleaned and
moved. On the other hand, the underground kennel is warmer
and more sound proof. Within the kennel itself there should
be a nesting box or bed for the female when suckling her pups ;
such a bed should be about eighteen by twenty inches in area,
by twenty inches high.

A space of two feet is left between pens usually, and the
layout of the pens varies ; they may be in rows or in circles,
the whole layout being surrounded by a high fence of wire
netting.

A necessary structure in a fox farm is the lookout or watch
tower, a conical structure in the centre of the farm from whose
summit a general observation can be kept over the pens, thus
obviating any risk of frightening whelping or sucking females
by going too near the pens.

The diet may consist of horse flesh, butchers' scraps, rabbits,
birds, fish, and so forth, but an excessive meat diet causes
intestinal troubles, and the menu should therefore include eggs,
fruit, and wild berries.

The fox is liable to infection by several kinds of internal
parasitic worm, and much mortality among pups is caused
thereby. Three parasites commonly met with are the round-
worm Belascaris marginata, the hookworm Ancylostoma
caninum, and a lungworm Eucolius cerophilus. Much suffer-
ing may be caused also by the ear mite Otiodectes.

The animals are handled when necessary by gripping them
by the neck in a pair of large tongues, the tongues being held
in one hand, the tail and hind legs of the fox in the other hand.

FUR FARMING

373

Killing is carried out either by crushing the thorax, or by
injecting a quantity of 3 per cent, strychnine sulphate into the
thorax.

Mink Farming. — Mink farming is somewhat in the experi-

---I

D

Fig. 54. — Types of Fox Farm Formations. (After Tufford.)

1, Circular. 2, Semi-circular. 3, 4, Square Types.

5, Split Units. 0, Separate Units.

374 THE PRINCIPLES OF APPLIED ZOOLOGY

mental stage, and the low price of mink skins as compared with
those of foxes has tended to discourage the industry.

A mink farm should be situated ideally in a secluded wood-
land area on the banks of a stream or lake. Usually a separate
pen is required for each animal. Such a pen should be about
eighteen feet long by four feet wide ; one-third should be
covered in, one-third should be open, and the remaining third
should be an enclosed portion of the stream.

On the other hand, many mink farms utilise merely wooden
pens about five or six feet square.

Another system is to rear a Utter, taken from the mother
when six or seven weeks old, in a communal pen with a runway
to an enclosed piece of water.

The usual food is bread and milk, meat, fish, and dog biscuit.
Some breeders use sparrows and rabbits as food. The animals
are fed twice a day.

The chief difficulty in mink farming is that of securing
foundation stock. The wild adult is almost untamable, and
is said to commit suicide when held captive. Young animals,
however, become very tame and are easily handled ; when
mature they breed readily in captivity.

Otter Farming. — The otter thrives in close confinement
and becomes very tame. It can be easily reared in simple
wire mesh pens, enclosing a portion of a stream. The favourite
food is fish and Crustacea, so that in siting an otter farm
due consideration should be given to the possibility of procuring
such food in abundance. Under ordinary conditions, however,
otters do not breed readily in captivity, but possibly this could
be overcome by providing sufficiently normal conditions.

Skunk Farming. — Skunks can be kept in captivity under
conditions similar to those described for mink farming, but as
the animals are less pugnacious, a number may be allowed to
run together. They require, however, a considerable area in
which to roam about, and should have well-insulated or arti-
ficially heated dens, each about a cubic foot in dimension.
A piece of woodland, enclosed by a sunken wire fence about
three feet high and provided with plenty of artificial dens,
would be an ideal situation. There should be at least an acre
of ground for each fifty animals. The young skunks can be
deodorised when about two months old by removal of the anal
scent glands. The methods used are described in detail by
Holbrook. An expert can disarm seventy to one hundred
in a day and not lose a single one.

Fur Ranching. — In the case of otters, skunks, minks, beaver,

FUR FARMING 375

fur ranching is preferable to fur farming when possible. An
extensive range of country is enclosed and a certain amount of
artificial feeding and housing is provided when necessary.
The animals, however, are not handled but are caught, when
required, by trapping.

Ranching on these lines was carried out to a certain extent
in Russia before 1914 with the Sable. To-day it is a method of
fur production confined to two animals, namely the Blue Fox
and the Musk-rat.

For several years Blue Foxes have been successfully pre-
served in this way on several islands off the coast of Alaska,
leased from the United States Government.

It may be added, however, that the idea formerly prevalent
that the Blue Fox could not be reared successfully in confine-
ment has been shown to be erroneous, and every year an in-
creasing number of Blue Foxes are being reared successfully
under conditions similar to those adopted in Silver Fox rearing.

Musk-rats are particularly suitable for rearing under ranch
conditions, since they inhabit marshy country unsuitable for
agriculture and thus cheaply to be rented ; further, they
require no artificial feeding and are enormously prolific, having
from two to five Utters of twelve to twenty young each year.

They can be reared successfully in pens in close confinement,
but the ideal situation for musk-rat raising is a marsh where
there is no running water.

In such a place a large number may be kept in a small area
without fencing, if a sufficiency of natural food such as wild
rice, pond lilies, arums, sedge, and other water plants be present.
If the site be a small lake or marshy basin with water flowing
in and out, a fence will be necessary ; and such a fence requires
a considerable outlay, since it must consist of fifteen-gauge wire
of one and a quarter inch mesh, and must be sunk a foot into
the ground, or even deeper when crossing a stream. In some
localities a fence sunk three feet into the ground, and in height
eight feet above ground, is used in order to exclude coyotes and
minks.

The latter enemies may be prevented from climbing over the
fence by the provision of a strip of galvanised iron, one foot
deep, along the upper edge of the mesh fence. A suitable marsh
should be under four to five feet of water all through the year.

Such musk-rat ranches are operated extensively in Canada.
In New Jersey and Maryland, Delaware and Pennsylvania,
where the best black rats are to be found, the musk-rat marshes
are leased by the owners to trappers, and trappers and owners

376 THE PRINCIPLES OF APPLIED ZOOLOGY

unite to protect the marshes from poachers. Usually the owner
receives half the fur caught, the trapper getting the other
half and the meat, which is sold as marsh hare.

Trapping operations are carried out during the first three
months of the year.

Some of these musk-rat marshes are worth more than
cultivated farms of similar acreage in the same neighbourhood.

CHAPTER XXXIV

ANIMAL CONSERVATION

The basic foundation of any discussion of the wide problem
of animal conservation should be a clear acceptance of the fact
that the indiscriminate encouragement or protection of an
animal may prove to be a policy equally as mischievous as any
policy of indiscriminate destruction.

The relation between associated forms of animal life is a
very close one, and the natural balance may easily be upset.
The following example is given by Fisher : An extensive marsh
in northern New York State was frequented by numbers of
ducks, rails, snapping turtles, frogs, and other aquatic forms.
The turtles' eggs, deposited in the sandy beach around a lake,
attracted large numbers of skunks whose depredations allowed
only a small percentage of eggs and young turtles to survive.
When skunk fur became fashionable and valuable the skunks
were almost exterminated. The snapping turtles multiplied
greatly, and intense competition for food forced them to add
ducklings to their fare, until in turn the ducks and other aquatic
birds went down considerably in numbers. The great aggrega-
tion of turtles attracted the attention of agents of the food
markets and restaurant keepers, and turtles were henceforth
caught in large numbers and shipped away in barrels. Skunk
fur also dropped somewhat in market price. The final result
was that the surviving skunks gathered on the old beach and
devoured the eggs of the surviving turtles, the birds now
remained unmolested, and the marsh reverted to its original
populous condition.

A similar but better known example of the danger of dis-
turbing the indigenous animal association of a locality is the
case of the introduction of the mongoose into Jamaica to cope
with the plague of rats.

The mongooses dealt with the imported rats and the native
cane rats effectively, then turned their attention to ground
birds, lizards, and poultry. As these insect-eating agents
became reduced in numbers, insects and ticks multiplied exceed-
ingly and plants and domesticated animals began to be affected.

377

378 THE PRINCIPLES OF APPLIED ZOOLOGY

Speaking very generally, from the point of view of animal
conservation, wild animals may be grouped in three categories,
namely : —

(1) Animals which should be exterminated or rigidly reduced
in numbers owing to their proved danger to man or to domes-
ticated animals, or to useful animals, or to food crops ; this
category includes a very large number of protozoa, helminthes,
and arthropods ; it includes a large number of graminivorous
and omnivorous birds, notably the English sparrow, and
certain carnivorous birds such, for example, as the New Zealand
kea parrot and certain hawks and owls ; it includes a very large
number of poisonous snakes, of carnivorous mammals, of
graminivorous and herbivorous mammals, notably rats, voles,
and rabbits.

The repression of this category has already been discussed
in previous chapters.

(2) Animals which should be partially protected ; this
category includes, firstly, animals which form the basis of such
industries as whale and seal fisheries, shellfish and food fish
industries, fur trading ; secondly, it comprises the fauna of
areas where native populations support themselves by hunting
or fishing ; thirdly, it comprises many birds and mammals
whose food activities are on the whole a benefit to man during
certain seasons of the year, but which at other times of the
year, or if in excessive numbers, may be distinctly injurious
to crops or livestock. Such is the case, for example, with
rooks, crows, pheasants, and many other birds of omnivorous
habits.

(3) Animals which should be completely protected and, if
possible, actively encouraged ; this category comprises such
wild animals as possess the potentialities of domestication,
animals of food or fur value which are on the verge
of extinction, insect -eating and snake -eating animals, and
animals which possess particular scientific interest and value.

The complete extinction of any animal would seem almost
impossible.

It probably is impossible if the animal has unrestricted food
habits, has a wide range of distribution, is adaptable to a variety
of environmental conditions, and is a prolific breeder. The
difficulty of even checking the multiplication of such animals
has been already discussed in the case of insect pests and of
such animals as the rat and the rabbit.

On the other hand, where an animal has restricted or peculiar
food habits, is restricted in distribution, is a slow breeder and,

ANIMAL CONSERVATION 379

above all, if it possesses commercial value, then extinction is
certainly possible through human agency.

There are numerous examples of animals, formerly of great
abundance, which have been completely exterminated or have
only been rescued from extermination by conservation
measures.

The Great Auk, a diving bird about the size of a goose, was
formerly abundant in certain islands on the North Atlantic
but was killed in thousands for the sake of the oil it contained,
and is now absolutely extinct. The Dodo, a most interesting
gigantic ground pigeon of Mauritius and Rodriguez, was exter-
minated very soon after the discovery of these islands by the
Dutch, owing to the depredations of vessels' crews and partic-
ularly through the killing of nestlings by the rats, which were
introduced into the islands from European ships. The
Passenger Pigeon, whose flocks of millions of individuals
darkened the skies of Canada and the north-eastern United
States less than a hundred years ago, has been completely
sacrificed to the market and the pot. Not much longer than
fifty years ago, one town alone in Michigan marketed three
carloads of pigeons daily for forty days, a total of nearly twelve
million birds. Another town in Michigan marketed sixteen
million pigeons in two years. To-day not a single individual
survives.

The South African Quagga, an equine animal that might
have proved amenable to domestication, was exterminated by
Dutch farmers early in the nineteenth century because its
hide was useful for whips.

The American Bison formerly blackened the plains between
the Rocky Mountains and the Mississippi River ; so late as
1871 their numbers, in spite of many years of continuous
persecution, were estimated at five millions. The construction
of the Union Pacific Railway cut the bison into northern and
southern herds, and provided marketing facilities for bison
skins. Between 1871 and 1875 the southern herd was wiped
out of existence. By 1883 the northern herd had almost
disappeared ; in 1889 only 645 animals were estimated to
exist in the United States, and to-day the only wild bison are
certain small herds of so-called " wood bison ' in the area
north of the Peace River in Canada. Only the conservation
measures of the Canadian and United States Governments
have saved the bison from complete extinction.

Of the European bison or " wisent," a few still survive in
the forests of East Prussia and of North-western Caucasus.

380 THE PRINCIPLES OF APPLIED ZOOLOGY

In 1741 the Russian explorer Behring was wrecked on
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Pacific, off the mainland of Alaska, and for a year he and his
crew supported themselves on the flesh of a large animal

ANIMAL CONSERVATION 381

about six feet long — later known as the Sea Otter — which
swarmed over the seaweed beds there, and they used its skin,
the most beautiful and valuable in the world, for clothing their
nakedness and for stopping up the chinks of their underground
dens. When they rafted back to Asia they brought back
news of this animal and 1,000 skins, which Chinese merchants
eagerly bought for 30-40 Chinese dollars apiece. The news
was like that of the discovery of a gold field. Four years after
Behring's return there were seventy-seven different private
Russian companies hunting sea otter with the help of a riff-
raff of Siberian convicts and cossacks.

Oonalaska and Kadiak were two main headquarters.
Hundreds of Alaskan natives were brutally coerced into service.
Fifty years later there were at least sixty different fur companies
engaged under many different flags. The takings were
enormous. Skins worth thousands of pounds could be obtained
from the Nootka tribes for a few shillingsworth of old iron.

One ship, a year after Behring's return, sold its cargo of skins
for £100,000 ($500,000). The bulk of the trade became eventu-
ally controlled by one huge company, the Russia- American
Fur Company, whose representative ruled at Sitka like a little
Czar. Gradually the animal became scarce. Islands which
at the end of the eighteenth century had yielded their thousands
of skins each year, by 1830 were yielding in hundreds, and when
Russia sold Alaska to the United States, the otter fishery was
finished and the area in Russian eyes was worthless.

A few animals still exist in the Aleutian and Commander
Islands, and in a few localities along the American and Japanese
coasts, and as the sea otter was included in the Fur Seal Con-
vention of 1911, there is a possibility that it may re-establish
itself.

The foregoing examples will illustrate the ease with which
an animal can be exterminated. The list could be considerably
extended.

The gradual destruction of animal and plant life is to a
certain extent unavoidable. The steady progress of agriculture
brings under human control areas formerly devoted solely to
wild life. The balance of nature is to a large extent destroyed.
The breeding haunts and food supplies of such animals as are
dependent upon forest or marsh or prairie dwindle in extent,
and the interesting tenants of the former wilderness die out or
are driven away. Much as we may deplore the passing of the
bison, his former range extended over an area destined to be
the most valuable wheat-growing region of North America.

382 THE PRINCIPLES OF APPLIED ZOOLOGY

When these vast areas were brought under cultivation, his exist-
ence was bound to become menaced. Railways and the settle-
ments along them were bound to restrict his migrations, and the
end of the bison as a wild animal was only a question of time.

Unavoidable also is the spread of industrial areas and the
consequent destruction of vegetation and pollution of rivers
and streams.

Avoidable, however, should be the depredations of the
market hunter, the fur and feather trader, the hunter of wild
fowl and birds' eggs, the bird trapper. Avoidable also should
be the ravages of the " fool with the gun," the sportsman,
gamekeeper, field naturalist, and ornithologist, the last two
being often mere exterminators of rare birds or rare insects.

The methods by which the extermination of an animal can
be prevented fall into two groups, namely, passive encourage-
ment measures and active encouragement measures. Passive
encouragement can be effected by legislation if such legislation
can be vigorously enforced. Active encouragement can be afforded
by the provision of sanctuaries, varying in size between a huge
tract of wild country, down to a few bird boxes in a city park.

Legislation may be international, national, or local. In
each case laws are passed to prohibit the taking of animals,
or of young stages of animals, during either a certain period of
the year, termed a " close season," or during a period of several
years, or in a particular tract of country.

An example of international legislation is afforded by the
Fur Seal Convention discussed in Chapter XXX.

Another example of international agreement in the enact-
ment of legislation concerning animal conservation is afforded
by the international treaty signed in 1916 between Canada and
the United States for the federal protection of all the migratory
birds of North America north of Mexico.

National legislation may be exemplified by the Wild Bird
Protection Acts of Great Britain, a series of enactments to
protect birds and eggs between 1st March and 1st August in
every year ; by the legislation that many countries have
enacted, or are intending to enact, against the discharge of
refuse oil from oil-burning steamers in coastal waters ; by the
various Game Acts and Game Ordinances of Canada, North
America, and the regions of Africa under British influence.

Such Game Acts are very difficult, of course, to frame in
regions where there is an indigenous population dependent upon
the catching of animals for food or for skins. The usual practice
is to restrict the methods of native hunters — to prohibit, for

ANIMAL CONSERVATION 383

example, the use of poison or of grass burning — and to restrict
the activities of the sportsman by expensive and limited licences.
The activities of the ivory and plumage trade can be curtailed
considerably by limiting the local centres at which such trophies
can be marketed, and by exercising a close surveillance over the
nature of the ivory or plumage or game trophies brought in
for sale or for export.

The African elephant offers an interesting example of the
value of even partial protection of an animal.

Since 1900, elephant hunting in almost every elephant area
of Africa under European influence has been regulated by the
issue of licences, and by the prohibition of the slaughter of
females or of males with tusks of less than 30 lbs. weight the
pair. Of course a considerable number of animals are killed by
poachers and by native hunters in remote districts, and a fairly
large illicit trade in small ivory and female ivory from British
territory goes on through Abyssinia. In spite of this, however,
protection has been successful in arresting the rapid decline
in numbers of elephants which would otherwise have occurred,
and although large tuskers are certainly becoming more
uncommon, there has probably been little numerical decrease
of the animals as a whole during the last thirty years.

As a result of the large herds becoming broken up, small
troops and harried individuals have taken to attacking cultivated
crops in some districts of Africa, and protection, in consequence,
has had here and there to be suspended. Thus in 1908 the
Government of Rhodesia suspended protection in the Lagamundi
district owing to the reported destruction of native crops, but
unfortunately allowed a very large number of animals to be
slaughtered by commercial hunters, whereas the destruction of
the leaders would probably have frightened the elephant troops
away. Similar withdrawal of protection has also been necessary at
times in districts of Kenya and Uganda. In the latter area, for
example, it has actually been necessary to devise control measures.

Measures suggested for Uganda by Swynnerton comprise the
provision of recognised sanctuaries sufficiently provided with food
to encourage elephants to remain within them ; encouragement of
the native population in sparsely populated areas to concentrate
in well-settled districts ; the defence of selected cultivated areas
by salaried European or Sikh shooters with a few well-super-
vised native assistants and a few spare guns for scaring purposes ;
and the gradual herding back of elephants into the sanctuaries
by organised agricultural development of districts.

An example of the difficulty of protecting an animal which

384 THE PRINCIPLES OF APPLIED ZOOLOGY

ranges over a wide area is that of the caribou, or wild reindeer, of
which several species occur in the extreme north of Canada and
in Alaska.

The barren ground caribou (Rangifer arcticus) offers a close
parallel to the bison in its economic status and habits, except that
whereas the bison as a wild animal is extinct, the caribou is one of
the most abundant large mammals of the world. It compares with
the bison in its extraordinary biennial migrations of hundreds of
miles, and in its importance as a provider of meat and clothing
for whole tribes of people who are mainly dependent upon it.

During the summer time the caribou keep to the seacoast
and tundras of Northern Canada between Hudson Bay and
Alaska, feeding on tender grasses and shoots and buds of dwarf
willow and birch. In the autumn the great majority travel south-
wards in large bands for hundreds of miles to the wooded areas,
where they spend the winter feeding on mosses and lichens.

Without the caribou, large tracts of Canada would be prac-
tically uninhabitable, since the animal supplies the Indian and
Eskimo with food, clothing, shelter, and means of obtaining
supplies from the nearest trading post. The migratory move-
ments, though very regular in point of time, are erratic as
regards the route followed, and inability to strike the path of
the migrating masses means very serious hardship for the tribes
dependent upon this animal.

Effective conservation of this animal is therefore of the
utmost importance.

On the other hand, the acquisition of rifles by native tribes
has brought about a wasteful slaughter of the caribou. It
has been already almost exterminated in northern and north-
western Alaska, and is in danger of a similar fate in Canada,
unless effective conservation measures can be devised.

A rational system of animal conservation should not merely
be passive ; it should not confine itself to the enactment of
legislative protection measures that are too often allowed to
become a dead letter, but should include active measures that
still tend toward an increase quantitatively and qualitatively
in animal life. This can only be done by the creation of animal
sanctuaries, definite reservations for animal life ranging in
size from tracts of country down to artificial coppices in the
public parks of urban districts. Within the bounds of such
reservations, animal protection laws can be rigidly enforced.
Outside the bounds the laws can be sufficiently relaxed to
avoid hampering the agriculturist or the marketer of honest
commodities.

ANIMAL CONSERVATION 385

In such sanctuaries, conditions should approximate as closely
as jDossible to those of primeval woodland or prairie or swamp.
Clean forestry is incompatible, for example, with animal
profusion. Decayed and fallen trees, plentitude of brushwood,
standing pools and meres should not merely be tolerated, but
should be supplemented by artificial breeding facilities if
possible. Further, there should be the fullest protection
against the undue increase of wasteful predators.

This method of animal protection is one that is increasing.

The National Parks of the United States and Canada —
Yellowstone, Yosemite, Sequoia, Wichita, Montana, Jasper,
Rocky Mountains, Buffalo, Glacier, and the like — and the
numerous State and Provincial game reserves are the finest
of their kind in the world as regards extent and management.

Africa, once the home of the greatest aggregate of wild
animal in the world, is rapidly losing its larger mammals and
birds. The introduction of firearms, the introduction of such
diseases as rinderpest, which in 1891 killed enormous numbers
of game — particularly buffalo, giraffe, antelopes — in East
Africa, the existence of native tribes dependent largely upon
hunting, have all tended towards the reduction of the larger
fauna. A convention of all the powers owning territory in
Africa drew up regulations in 1900 to prevent unjustifiable
slaughter of game ; the recommendations included the provision
of game reserves, the establishment of closed seasons, restriction
of the export of skins, horns, and tusks of certain forms, pro-
hibition of particularly destructive hunting methods such as
grass fires, pits, snares, and game traps ; many of these recom-
mendations are in force, but the sheer impossibility of policing
such enormous areas with the small forces available renders
the enforcement of legislative measures difficult.

About twenty game reserves, comprising nearly 200,000
square miles, are to be found scattered over the Continent,
mainly in British territories.

The discovery that the trypanosome parasites of sleeping
sickness and cattle trypanosome diseases are harboured by wild
game has, however, done much to strengthen a certain class of
public opinion to whom the preservation of animal life is incom-
prehensible. Thus in 1920 there was an officially authorised
butchery of wild game actually in a game preserve, the Umfalosi
Reserve of Zululand, under the pretext of making the area
" fly proof ' for cattle ; needless to say, this object was not
attained, but about 2,000 zebras, at least 1,000 head of other
game, and four of the twelve much prized and long protected

25

386 THE PRINCIPLES OF APPLIED ZOOLOGY

remaining specimens of the white rhinoceros were slaughtered,
and large numbers of game were scattered and driven further
afield. It is, however, only fair to add that the original intention
of the Zululand Game Drive was to drive the game from a
no-man's land adjacent to European farms into the existing
reserve, and the lack of discipline of shooters who continued
to shoot after the reserve was reached was the reason for the
unfortunate results which ensued.

In India there will be practically no large wild mammals
and birds within a measurable space of time, except in preserves
maintained by native chiefs or in the more inaccessible Govern-
ment Forest Reserves.

India has not suffered much from the fur hunter, since few
Indian animals have valuable fur, but on the other hand the
bird fauna has suffered greatly from the depredations of the
plumage hunter. The white egrets (Herodias alba, intermedia,
and garzetta) have been hunted almost to extinction, and pro-
tective legislation has come into force almost too late to save
them. In Burma the demands of the Chinese for rhinoceros
horns has brought about an alarming decline in the numbers
of the one-horned rhinoceros (Rhinoceros unicornis) and the
Sumatran rhinoceros (Dicerorhinus sumatrensis) ; the Govern-
ment has prohibited the shooting of these animals, but the
difficulties of enforcing the prohibition are probably too great
to render the enactment efficient.

In densely populated countries such as India and Burma,
wild life is almost bound to dwindle in extent before the
encroachments of agricultural settlement and the spread of
cattle diseases.

In Australia vast damage is being done to smaller ground
animals by the multiplication of introduced foxes and domestic
cats. Only the larger kangaroos, the wombat, and the burrow-
ing platypus seem able to hold their own. The demands of
the fur trade, too, are tending to reduce the native fauna.

In Europe there are numerous sanctuaries of a smaller type,
created chiefly for the protection of bird fife. Germany and
Great Britain, in particular, possess many such. In the latter
country a recent movement has created many small bird
sanctuaries, shelter coppices, and nesting facilities in the
public parks of the cities, the Society for the Protection of Birds
and the various Rambling Clubs having done much to influence
public opinion. In the United States and Canada similar credit
must be paid to Hornaday, Hewitt, and others, to the Audubon
Societies, Camp Fire Clubs, and Game Protection Associations.

PART IV
BIBLIOGRAPHY

This bibliography of the more important books and articles and periodicals
which deal with some aspect of Applied Zoology is arranged under the following
headings : —

General Applied Zoology.

Medical and Veterinary Zoology.

Agricultural and Horticultural Zoology.

General Protozoology.

Medico-veterinary Protozoology.

Enteric Protozoa.

Haematophilous Protozoa.

General Helminthology.

Flukes.

Tapeworms.

Roundworms.

Soil Organisms.

General Entomology.

Medical, Veterinary, and Household

Entomology.
Agricultural Entomology.

Forest Entomology.

Insect Control.

Vermin Repression.

Bird Encouragement.

Domesticated Animals.

Horses.

Cattle, Sheep, and Pigs.

Domesticated Birds.

Other Domesticated Animals.

Bee-keeping.

Silk and Lac Culture.

Fisheries.

Whaling and Sealing.

The Fur Trade.

Animal Conservation.

In order to economise space, each reference comprises only the author's
surname, the date of publication, the title, and the town of publication.

References prior to 1906 are omitted, except when of particular historical
interest, and the titles of short articles in periodicals are not included unless
mentioned in the text or unless, again, the article is of particular historical
interest. In these respects the bibliography is incomplete.

GENERAL APPLIED ZOOLOGY

Ainsworth Davis and Others, 1910 : Science in Modern Life, London.
Bigelow and Bigelow, 1911 : Applied Biology, New York. Daugherty
and Datjgherty, 1912 : The Principles of Economic Zoology. Dendy and
Others, 1915 : Animal Life and Human Progress, London. Gruenberg,
1925 : Biology and Human Life, Boston. Hodge and Dawson, 1918 : Civic
Biology, Boston. Hunter, 1914 : A Civic Biology, New York. Kellog
and Doane, 1915 : Elementary Textbook of Economic Zoology and Ento-
mology, New York. Osborn, 1908 : Economic Zoology, New York. Pea-
body and Hunt, 1924 : Biology and Human Welfare, New York.

Periodicals. — American Naturalist, Lancaster, Pennsylvania ; Annals
of Applied Biology, London ; Australian Journal of Experimental Biology and
Medical Science, Adelaide ; British Association for the Advancement of
Science, Annual Report, London ; British Journal of Experimental Biology,

387

388 THE PRINCIPLES OF APPLIED ZOOLOGY

Edinburgh ; Bulletin Biologique de la France et de la Belgique, Paris ; Bulletin
of the Imperial Institute, London ; Comptes Rendus des Seances de la Societe
de Biologie, Paris ; Journal of Zoological Research, London ; Nature, London ;
Philippine Journal of Science, Manila ; Revue d'Histoire Nature! le Applique,
Paris ; Revue de Zoologie Agricole et Applique, Bordeaux ; Science, New
York ; Science Progress, London ; Scientia, Milan ; South African Journal of
Science, Johannesburg ; Zoological Record, London.

MEDICAL AND VETERINARY ZOOLOGY

Blanchard, 1889-90 : Traite de Zoologie Medicale, Paris. Braun, 1906 :

The Animal Parasites of Man, London. Braun and Luhe, 1910 : Handbook

of Practical Parasitology, London. Breinl, 1914 : The Distribution and

Spread of Disease in the East, Stewart Lecture of Univ. of Melbourne. Brooke,

1908 : Tropical Medicine, Hygiene, and Parasitology, London. Brumpt,

1927 : Precis de Parasitologic, Paris. Byam and Archibald, 1921-23 : The

Practice of Medicine in the Tropics, London. Carazzi, 1922 : Parassitologia

Animali, Milan. Castellani and Chalmers, 1919 : Manual of Tropical

Medicine, London. Caullery, 1922 : Le parasitisme et la symbiose, Paris.

Chandler, 1922 : Animal Parasites and Human Disease, New York.

Chavigny, 1924 : Les animaux parasites de l'homme et de l'habitation, Paris.

Cobbold, 1879 : Parasites : The Entozoa of Man and Animals, London.

Davaine, 1887 : Traite des entozoaires et des maladies vermineuses de l'homme

et des animaux domestiques, Paris. Deaderick and Thompson, 1916 : The

Endemic Diseases of the Southern States, Philadelphia. Disselhorst, 1921 :

Die Herdekrankheiten unserer Haustiere, Berlin. Fantham and Porter,

1914 : Some Minute Animal Parasites, London. Fantham, Stephens, and

Theobald, 1916 : The Animal Parasites of Man, New York. Ferroncito,

1901 : I. Parassiti dell'uoma e degli animali utili, Milano. Fiebiger, 1923 :

Die tierische Parasiten der Haus und Nutztiere, sowie des Menschen, Wien.

Gedoelst, 1911 : Synopsis de parasitologic de l'homme et des animaux

domestiques, Lerre; 1911: Synopsis de Parasitologic, Bruxelles. Hall,

1925 : Parasites and Parasitic Diseases of Dogs, U.S. Dept. Agriculture, Bull.

338, Washington, D.C. Hegner, 1920 : The Relation of Medical Zoology to

Public Health Problems, Journal American Medical Association, lxxx.

Hegner and Cort, 1921 : The Diagnosis of Protozoa and Worms Parasitic

in Man, Baltimore. Hegner, Cort, and Root, 1923 : Outlines of Medical

Zoology, New York. Herms, 1913 : A Laboratory Guide to the Study of

Parasitology, New York. Kaup, 1917 : Animal Parasites and Parasitic

Diseases, Chicago ; 1922 : Poultry Diseases, London. Kuchenmeister, 1857 :

On Animal and Vegetable Parasites of the Human Body, London. Leuckart,

1886 : The Parasites of Man, Edinburgh. Macarthur, 1924 : Memoranda

on Medical Diseases in Tropical and Sub-tropical Areas, London. Manson,

1921 : Tropical Diseases, London. Marotel, 1927 : Parasitologic veterinaire,

Paris. Megnin, 1880 : Les parasites et maladies parasitaires chez l'homme,

les animaux domestiques et les animaux sauvages, Paris ; 1906: Medecine des

oiseaux, Vincennes. Mense, 1913: Handbuch der Tropenkrankheiten, Leipzig.

Neumann, 1909 : Parasites des oiseaux domestiques, Paris ; 1910 : Parasites

and Parasitic Diseases of Domesticated Animals, New York ; 1914 : Parasites

du chien et du chat, Paris ; 1914 : Parasites et maladies parasitaires du chien

et du chat, Paris. Neumann and Mayer, 1914 : Atlas und Lehrbuch wichtiger

tierischer Parasiten und ihrer Uebertrager, Munchen. Neveu Lemaire, 1912 :

Parasitologic des animaux domestiques, Paris ; 1921 : Parasitologic humaine,

Paris. Phisalix, 1922 : Animaux venemeux et venins, Paris. Rtley,

BIBLIOGRAPHY 389

1912 : Notes on Animal Parasites and Parasitism, Cornell University Press,
Ithaca, N.Y. ; 1927 : Introduction to the Study of Animal Parasites and
Parasitology, Minneapolis, Minn. Rtvas, 1916 : The Parasitic Diseases in
American Tropical Countries, Proc. Second Pan-American Congress, Washing-
ton, D.C. ; 1920 : Human Parasitology, Philadelphia. Stiles and Hassall,
1912 : Index Catalogue of Medical and Veterinary Zoology, U.S. Dept. Agric.
Bureau Animal Industries, Bull. 39, and U.S. Public Health Service, Hygienic
Lab., Bull. 37, 85, 114, Washington, D.C. Stitt, 1921 : Practical Bacteri-
ology, Blood Work, and Animal Parasitology, Philadelphia. Strong, 1926:
Medical Report of the Hamilton Rice Seventh Expedition to the Amazons,
1924-25, Boston. Theobald, 1896 : Parasitic Diseases of Poultry, London.
Underbill, 1920 : Parasites and Parasitosis of the Domestic Animals,
New York. Van Beneden, 1876 : Animal Parasites and Messmates,
New York. Verdun et Mandoul, 1924 : Precis de Parasitologic Humaine,
Paris. Walton and Rees Wright, 1927 ; Agricultural Parasitology,
London. Ward, 1924 : Present Lines of Attack on Animal Parasitology,
Science, New York ; 1924 : The Needs and Opportunities in Parasitology,
Science, New York. Ward and Gallagher, 1926 : Diseases of Domesticated
Birds, New York. Ztjrn, 1882 : Die tierischen Parasiten unserer Haussaugtiere,
Weimar.

Periodicals. — American Journal of Tropical Diseases and Preventive
Medicine, New Orleans ; American Journal of Tropical Medicine, Baltimore ;
American Journal of Hygiene, Baltimore ; Annales de Parasitologic humaines
et comparees, Paris ; Annals of Tropical Medicine and Parasitology, Liver-
pool ; Archives de Parasitologie, Paris ; Archiv f iir Schiffs und Tropen-Hygiene,
Leipzig ; British Medical Journal, London ; Bulletin de l'lnstitut Pasteur,
Paris ; Bulletin of the Johns Hopkins Hospital, Baltimore ; Bulletin de la
Societe de Pathologie Exotique, Paris ; Canadian Medical Association Journal,
Toronto ; Centralblatt fur Bakteriologie, Parasitenkunde und Infektions-
krankheiten, Jena ; Cornell Veterinarian, Ithaca, N.Y. ; Ectoparasites,
London ; Great Britain Medical Research Council Reports, London ; Indian
Journal of Medical Research, Calcutta ; Indian Medical Gazette, Calcutta ;
Journal of Hygiene, London ; Journal of Medical Research, Boston ; Journal
of Parasitology, Urbana, Illinois ; Journal of the Royal Army Medical Corps,
London ; Journal of Tropical Medicine and Hygiene, London ; The Lancet,
London ; Lister Institute of Preventive Medicine, Collected Papers, London ;
Liverpool School of Tropical Medicine, Memoirs, Liverpool ; Medical Journal
and Record, New York ; Medical Journal of Australia, Sydney ; Medical
Officer, London ; Medical Science, Abstracts and Reviews, London and New
York ; Microbiological Laboratory Report, Sydney ; North American
Veterinarian, Chicago ; Parasitology, London ; Public Health, London ;
Revue d'Hygiene, Paris ; Transactions of the Royal Society of Tropical
Medicine and Hygiene, London ; Tropical Diseases Bulletin, London ; Tropical
Veterinary Bulletin, London ; United States Public Health Service, Hygienic
Laboratory and Public Health Bulletins, Washington, D.C. ; Veterinary
Medicine, Chicago ; Wellcome Tropical Research Laboratory Bulletins,
Khartoum ; Zeitschrift fur Inf ektionskrankheiten, Parasitare Krankheiten und
Hygiene der Haustiere, Berlin.

AGRICULTURAL AND HORTICULTURAL ZOOLOGY

Theobald, 1913 : Agricultural Zoology, Edinburgh and London. Steb-
bing, 1908 : A Manual of Elementary Forest Zoology for India, Calcutta.
Periodicals. — Agricultural Gazette of Canada, Ottawa ; Agricultural

390 THE PRINCIPLES OF APPLIED ZOOLOGY

Gazette, London ; Agricultural Gazette of New South Wales, Sydney ; Agri-
cultural Journal of Egypt, Cairo ; Agricultural Journal of India, Calcutta ;
Agricultural Journal of South Africa, Pretoria ; Agricultural Research Institute,
Pusa, Scientific Reports, Calcutta ; Annales de l'Ecole Nationale d' Agriculture
de Montpellier, Montpellier, France ; Annales de l'lnstitut National
Agronomique, Paris ; Annali della Regia Scuola Superiore di Agricoltura in
Portici, Portici, Italy ; Annali della Regia Stazione Sperimentale di Agrurai-
coltura e Frutticoltura in Acireale, Acireale, Italy ; Annales des fipipbyties,
Paris ; Annales de la Science Agronomique Francaise et Etrangere, Paris ;
Bulletin de la Societe d'fitude et de la vulgarisation de la Zoologie Agricole,
now Revue de Zoologie Agricole et Appliquee, Bordeaux ; Ceylon, Department
of Agriculture, Bulletins and Leaflets, Peradeniya ; Country Gentleman,
Philadelphia ; Country Life, London ; Country Life, New York ; Experi-
ment Station Record, Washington, D.C. ; Farm and Garden, Chicago ; Farm
and Ranch, Dallas, Texas ; Farmer and Stockbreeder, London ; Field, Farm,
and Garden, London ; Gardener's Chronicle, London ; Gardener's Chronicle
of America, New York ; International Review of the Science and Practice of
Agriculture, Rome ; Journal of Agricultural Research, Washington, D.C. ;
Journal of Agricultural Science, London ; Journal d' Agriculture Tropicale,
Paris ; Journal of the Ministry of Agriculture, London ; Journal of the
Scottish Highland Agricultural Society, Edinburgh ; Journal of the College
of Agriculture, Tokyo ; Journal of the Royal Agricultural Society of England,
London ; Philippine Agriculture Review, Manila ; Phytopathology, Lancaster,
Pennsylvania ; Rural New Yorker, New York ; Scottish Journal of Agriculture,
Edinburgh ; Tropical Agriculturist, Peradeniya, Ceylon ; Tropical Agriculture,
St Augustine, Trinidad ; Vie Agricole et Rurale, Paris ; Zentralblatt des
Deutschen Landwirtschaftsrats und der Preussischen Hauptlandwirtschaft-
skammer, Berlin ; Zeitschrift fur das Landwirtschaftliche Versuchswesen in
Osterreich, Vienna ; Zeitschrift fur Pflanzenkrankheiten und Gallenkunde,
Stuttgart.

GENERAL PROTOZOOLOGY

Calkins, 1909 : Protozoology, New York ; 1916 : The General Biology
of the Protozoan Life-Cycle, American Naturalist, 1., Lancaster, Pa. ; 1926 :
The Biology of the Protozoa, New York. Dobell, 1911 : The Principles of
Protistology, Archives fur Protistenkunde, xxiii. Doflein, 1916 : Lehrbuch
der Protozoenkunde, Jena. Dunkerly, 1928 : Protozoa, in Sedgwick's
Textbook of Zoology, London. Hartmann, 1907 : Das System der Protozoen,
Jena. Hartog, 1902 : Protozoa, in Cambridge Natural History, Vol. I.,
London. Hickson, 1903 : The Lobosa : The Infusoria or Corticata Heteryo-
karyota, in Lankester's Treatise on Zoology, Part I., London. Jennings,
1906 : Behaviour of the Lower Organisms, New York ; 1920 : Life and Death,
Heredity and Evolution in Unicellular Organisms, Boston. Kofoid, 1921 :
A Critical Discussion of the Chromidial Formation of Nuclei, of Autogamy,
and of the Multiple Fusion of Polyenergid Nuclei, Anatomical Record, 20.
Minchin, 1912 : An Introduction to the Study of Protozoa, London ; 1915 :
The Evolution of the Cell, Report British Association of Science, 1915, and
American Naturalist, 1. Robert, 1914 : Protozoaires, Paris. Saville
Kent, 1880-82 : A Manual of the Infusoria, London. Schaeffer, 1920 :
Amoeboid Movement, Princeton University Press, Princeton, N.J. Ward and
Whipple, 1918 : Fresh-water Biology, New York. Wenyon, 1926 : Proto-
zoology, London. Wilson, 1925 : The Cell in Development and Heredity,
New York. Woodruff, 1925 : The Physiological Significance of Conjugation
and Endomixis in the Infusoria, American Naturalist, lix.

BIBLIOGRAPHY 391

Periodicals. — Archiv. fur Protistenkunde, Jena ; Review of Bacteriology,
Protozoology, and General Parasitology, London.

MEDICO-VETERINARY PROTOZOOLOGY

Clarke, 1913-15 : Protozoa and Disease, London. Craig. 1926 : The
Parasitic Protozoa of Man, Philadelphia. Crawley, 1912 : The Protozoan
Parasites of Domesticated Animals, U.S. Dept. Agric. Bur. Animal Indust.,
Circ. 194, Washington, D.C. Hartmann and Schilling, 1917 : Die pathogenen
Protozoen, Berlin. Hegner and Taliaferro, 1924 : Human Protozoology,
New York. Kisskalt, 1910 : Praktikum der Bacteriologie und Protozoologie,
II., Jena. Macneal, 1914: Pathogenic Micro-organisms, Philadelphia.
Prowazek, 1921 : Handbuch der pathogenen Protozoen, Leipzig. Stiles
and Hassall, 1925 : Key Catalogue of the Protozoa reported for Man, U.S.
Public Health Service, Hygienic Lab., Bull. 140, Washington, D.C.

ENTERIC PROTOZOA

Cleveland, 1923 : The Correlation between Food and Morphology of
Termites and the Presence of Intestinal Protozoa, American Journal of Hygiene,
3 ; 1923 : Symbiosis between Termites and their Intestinal Protozoa, Proc.
Acad. Natural Science, Philadelphia, ix. ; 1924 : The Physiological and
Symbiotic Relationships between Intestinal Protozoa of Termites and their
Hosts, Biological Bulletin, Woods Hole, Massachusetts. Dobell, 1919 : The
Amoebae Living in Man, London. Dobell and Connor, 1921 : The Intestinal
Protozoa of Man, London. Fantham and Porter, 1912 : The Morphology
and Life History of Nosema apis, Annals of Trop. Med. and Parasitology, 6,
London. Hegner, 1927 : The Host Relations between Man and his Intestinal
Protozoa, New York. Hegner and Hecker, 1920 : The Diagnosis of Intestinal
Flagellates. Hegner and Payne, 1920 : Surveys of the Intestinal Protozoa
of Man in Health and Disease, Scientific Monthly, New York. Kofoid, 1917 :
The Biological and Medical Significance of the Intestinal Flagellates, Proc.
Pan-American Congress, Washington, D.C, 1915-16 ; 1923 : Amoeba and Man,
Univ. of California Chronicle. Kudo, 1919 : Studies on Myxosporidia,
Illinois Biological Monograph, 5 ; 1921 : Microsporidial Parasites in Mosquitoes,
Journal of Morphology, 35 ; Journal of Parasitology, 8. Noller, 1922 : Die
wichtigsten parasitischen Protozoen des Menschen und der Tiere; I. Die
parasitischen Rhizopoden, Berlin. Phillips, 1915 : Amcebiasis and the
Dysenteries, London. Rodenhuis, 1921 : Handleidung bij het onderzoek
naar Protozoen in de menschelijke fseces voorkommend, Kolonial Inst. Amster-
dam Med., No. xvi. ; Afd. tropische Hyg., No. 11. Wenyon and O'Connor,
1917 : Human Intestinal Protozoa in the Near East, London.

ELEMATOPHILOUS PROTOZOA

Blacklock and Yorke, 1922 : The Trypanosomiases, in Byam and
Archibald ; The Practice of Medicine in the Tropics. Boyce, 1911 : Yellow
Fever and its Prevention, London. Brahmachari, 1920 : Kala Azar and
its Treatment, Calcutta. Bruce, 1895 : Preliminary Report on the Tsetse
Fly Disease or Nagana in Zululand, Umbobo ; 1897 : Further Report on Same,
Umbobo ; 1903 : Appendix to Further Report on Same, London ; 1915 :
The Croonian Lectures on Trypanosomes causing Disease in Man and Domesti-
cated Animals in Central Africa, The Lancet, London. Bruce, Hammerton,
Bateman, and Mackie, 1909 : The Development of Trypanosoma gambiense
in Glossina Palpalis ; Report Sleeping Sickness Commission Royal Society, x. ;

392 THE PRINCIPLES OF APPLIED ZOOLOGY

Proc. Royal Soc, B., lxxxi., London. Chagas, 1921 : Resume of the ^Etiology
and Clinical Aspects of American Trypanosomiases, Printed Copy of Lecture
given in Various Institutions in U.S.A. Clark, 1903-16 : Protozoa and
Disease, London and New York. Craig, 1920 : The Malarial Fevers, Hsemo-
globinuric Fever, and the Blood Protozoa of Man, New York. Grassi, 1900 :
Studi di uno zoologo sulla malaria, Rome. Grassi, Bignani, and Bastianelli,
1898: Ulteriore ricerche sul ciclo dei parassiti malarici umani nel corpo del
zanzaroni (Nota preliminare), Atti R. Accad. Lincei Rendic, viii. ; 1899 (a)
Resoconto degli studi f atti sulla malaria, durante il mese di gennaio, Ibid., viii. ;
1899 (b) Ulteriore ricerche sulla malaria, Ibid., viii. James and Christophers,
1922 : Malaria, in Byam and Archibald. Koch, Beck, and Kleine, 1909 :
Bericht ueber die Tatigkeit der zur Erforschung der Schlafkrankheit im
Jahre 1906-07 nach Ost-Afrike entsandten Kommission, Berlin. Kolle and
Wassermann, 1913 : Handbuch der Pathogenen Mikro-organismen, Band vii.,
Protozoa, Leipzig. Laveran, 1880 : Note sur un nouveau parasite trouve
dans le sang de plusieurs malades atteint de fievre palustre, Bull. Acad. Med.,
ix., Paris ; 1917 : Leishmanioses, Paris. Laveran and Mesnil, 1912 :
Trypanosomas et trypanosomiases, Paris. Lewis, 1879 : Flagellated Organ-
isms in the Blood of Healthy Rats, Quart. Jour. Microscop. Science, xix., London.
Lloyd and Johnson, 1925 : Notes for the Demonstration of Properties
illustrating the Diagnostic Characters of the Flagellate Parasites of Tsetse
Flies, Trans. Roy. Soc. Trop. Med. and Hyg., xviii., London. Manson, 1894 :
On the Nature and Significance of the Crescentic and Flagellated Bodies in
Malarial Blood, Brit. Med. Jour., London ; 1898 : The Mosquito and the
Malarial Parasite, Ibid. ; 1900 : Experimental Proof of the Mosquito Malarial
Theory, Ibid. Noguchi, 1919-20 : ^Etiology of Yellow Fever, Jour. Exp. Med.,
xxix., xxx., xxxi., xxxii. ; 1925 : Yellow Fever Research ; 1918-24 : A
Summary, Jour. Trop. Med. and Hyg., xxviii. Ross, 1895 : The Crescent-
Sphere-Flagella Metamorphosis of the Malarial Parasites in the Mosquito,
Trans. South Indian Branch, Brit. Med. Association, vi. ; 1897 : On some
Peculiar Pigmented Cells found in two Mosquitoes fed on Malarial Blood,
Brit. Med. Jour., ii. Ross, 1910 : The Prevention of Malaria, London.
Smith and Kilborne, 1893 : Investigations into the Nature, Causation, and
Prevention of Texas or Southern Cattle Fever, U.S. Dept. Agric. Bureau
Animal Industry, Bull. 1. Stephens and Christophers, 1900 : The
Malarial and Blackwater Fevers of British Central Africa, Reports of Malaria
Committee Royal Society Series, 1-12, London ; 1908 : The Practical Study of
Malaria and other Blood Parasites, University Press, Liverpool. Thtmm,
1909 : Bibliography of Trypanosomiasis, Sleeping Sickness Bureau, London.
Thomson and Woodcock, 1922 : The Parasites of Malaria, in Byam and
Archibald . Wen yon, 1922 : Leishmaniasis : A Review of Recent Literature,
Tropical Diseases Bulletin, 19, London. Woodcock, 1909 : The Hsemo-
flagellates and Allied Forms, in Lankester, Treatise on Zoology, Part I., London.
Ziemann, 1918 : Die Malaria, in Mense, Handbuch der Tropenkrankheiten.
Zuelzer, 1925 : Die Spirochseten, in Prowazek, Handbuch der pathogenen
Protozoen.

GENERAL HELMINTHOLOGY

Beneden, 1877 : Memoires sur vers intestinaux, Paris. Coet, 1923 :
Worms Parasitic in Man, in Hegner, Cort and Root Medical Zoology. Diesing,
1850 : Systema Helminthium, Vindobonae. Dujardin, 1842 : Histoire,
naturelle des helminthes, Paris. Faust, 1925 : Parasitism among the
Helminthes, American Naturalist, lix. Gamble, 1896: Platyhelminthes, Cam-
bridge Natural History, Vol. 2, London. Hall, 1912 : A Comparative Study

BIBLIOGRAPHY 393

of Methods of Examining Faeces for Evidence of Parasitism, U.S. Dept. Agric.
Bur. Animal Industry, Bull. 135. Koegel, 1925 : Die wichtigsten gesund-
heitschadlichen Wurmer der landwirtschaftlichen Nutztiere in Deutschland,
Stuttgart. Linstow, 1879-89 : Compendium der Helminthologie, Hannover.
Petrunkevitch, 1924 : Environment as a Stabilising Factor, in Thorpe,
Organic Adaptation to Environment, Yale University Press, New Haven,
Conn. Rudolphi, 1808-09 : Entozoorum sive vermium intestinalium, historia
naturalis, Amsterdam. Stiles, 1898 : The Flukes and Tapeworms of Cattle,
Sheep, and Swine, U.S. Dept. Agric. Bur. Animal Industry, Bull. 19. Stiles
and Hassall, 1926 : Key Catalogue of the Worms reported for Man, U.S.
Pub. Health Serv. Hyg. Lab., Bull. 142. Shipley, 1909 : On the Relation of
Certain Cestode and Nematode Parasites to Bacterial Disease, Jour. Econ.
Biol., London. Ward, 1917 : On the Structure and Classification of North
American Parasitic Worms.

Periodicals. — Journal of Helminthology, London ; Journal of Para-
sitology, Urbana ; Centralblatt fur Bakt. Paras, und Infekt., Jena ; Para-
sitology, London ; etc.

FLUKES

Braun, 1889 : Trematodes, Bronns Klassen und Ordnungen des Tierreichs,
Bd. 4, Abt. 1, Berlin. Leiper, 1918 : Researches on Egyptian Bilharziosis,
London. Loess, 1894 : Die Distomen unserer Fische und Frosche, Stuttgart ;
1905 : The Anatomy and Life History of Ancylostoma Duodenale, Records of
the Egyptian Govt. School of Medicine, Cairo. Luhe, 1909 : Parasitische
Plattwurmer, I. Trematodes, Die Siissivasser Fauna Deutschlands, 17, Jena.
Miller, 1926 : Comparative Studies on Furcocercous Cercariae, Univ. Illinois
Biol. Monograph, x. 3, Urbana. Seymour Sewell, 1922 : Cercariae Indices,
Ind. Jour. Med. Research, x., Calcutta. Steles, 1904 : Illustrated Key to
the Trematode Parasites of Man, U.S. Pub. Health Serv. Hyg. Lab., Bull. 17.
Thomas, 1883 : The Life History of the Liver Fluke, Quart. Jour. Micr. Sci.,
London. Loess, 1899 : Der Trematode Fauna iEgyptens, Zool. Jahrbuch.
Abt. Syst., Heft, v.-vi., Jena.

TAPEWORMS

Braun, 1894-1900 : Cestoda, in Bronns Klassen und Ordnungen des
Tierreichs, Bd. 4, Berlin. Cooper, 1919 : North American Pseudophyllidean
Cestodes from Fishes, Univ. Illinois Biol. Monograph, iv., No. 4, Urbana.
Douthitt, 1915 : Studies on the Cestode Family Anoplocephalidae, Ibid., i.,
No. 3. Fuhrmann, 1908 : Die Cestoden der Vogel, Jena. Hall, 1919 : The
Adult Teenioid Cestodes of Dogs, Cats, and Related Carnivores in North America,
Proc. U.S. Nat. Museum, Vol. 55, Washington, D.C. Luhe, 1910: Para-
sitische Plattwurmer, II. Cestodes, Die Silsswasser Fauna Deutschlands, Jena.
Mayhew, 1925 : Studies in the Avian Species of the Cestode Family Hymeno-
lepidae, Univ. Illinois Biol. Monograph, x., No. 1, Urbana. Meggitt, 1924 :
The Cestodes of Mammals, London. Ransome, 1909 : The Taenioid Cestodes
of North American Birds, U.S. Nat. Museum, Bull. 69, Washington, D.C.
Southwell, 1925 : A Monograph of the Tetraphyllidea, University Press,
Liverpool. Stiles, 1896 : A Revision of the Adult Tapeworms of Hares and
Rabbits, Proc. U.S. Nat. Museum, Vol. 19, Washington, D.C. ; 1906 : Illus-
trated Key to the Cestode Parasites of Man, U.S. Pub. Health Serv. Hyg. Lab.,
Bull. 25. Stiles and Hassall, 1912 : Index Catalogue of Medical and
Veterinary Zoology : Cestodes and Cestodaria, U.S. Hyg. Lab., Bull. 85.

394 THE PRINCIPLES OF APPLIED ZOOLOGY

ROUNDWORMS

Anonymous, 1922 : Bibliography of Hookworm Disease, Intermit. Health
Board, Rockefeller Foundation, Publication No. 11, New York. Bastian,
1866 : On the Anatomy and Physiology of the Nematodes, London. Bayliss,
1924 : Some Consideration of the Host Distribution of Parasitic Nematodes,
Annals Mag. Nat. History, London. Bayliss and Daubney, 1926 : A
Synopsis of the Families and Genera of Nematodes, Brit. Mus. (Nat. Hist.),
London. Cobb, 1914 : Nematodes and their Relationships, Year-book U.S.
Dept. Agric, Washington, D.C. Ferrell, 1915 : Hookworm Disease, Internat.
Health Commiss., Rockefeller Foundation, Publication No. 2, New York.
Hetherington, 1923 : Comparative Studies on Certain Features of Nematodes
and their Significance, Univ. Illinois Biol. Monograph, viii., No. 2, Urbana.
Howard, 1919 : The Control of Hookworm Disease, Internat. Health Board,
Rockefeller Foundation, Publication No. 11, New York. Manson, 1903 : The
Life Span of Filaria medinensis, Brit. Med. Jour., London. Ransom and
Foster, 1917 and 1919 : Life History of Ascaris lumbricoides, Jour. Agric. Res.,
Washington ; Jour. Parasitology, Urbana. Riley, 1921 : A Provisional Key
to the Adult Nematode Parasites of Equines, Cornell Veterinarian, Vol. iii.,
Ithaca, N.Y. Schneider, 1866 : Monograph der Nematoden, Berlin.
Shipley, 1896 : Nemathelminthes, Cambridge Natural History, Vol. 2, London.
Stewart, 1916-18 : Life History of Ascaris lumbricoides, Brit. Med. Jour.,
1916 ; Parasitology, 1917 ; Ind. Med. Gaz., 1918. Stiles and Hassall,
1920 : Index Catalogue of Medical and Veterinary Zoology : Roundworms and
the Diseases they Cause, U.S. Hyg. Lab., Bull. 114, Washington, D.C. Yorke
and Maplestone, 1926 : The Nematode Parasites of Vertebrates, Philadelphia.

SOIL ORGANISMS

Alexander, 1920 : The Crane-flies of New York, Cornell Univ. Exp. Station,
Mem. 38, Ithaca, N.Y. Baequart, 1922 : Ants in their Relations to the
Plant World, Bull. American Museum Nat. Hist., xlv. Banks and Snyder,
1920 : A Revision of the Nearctic Termites, U.S. Nat. Museum, Bull. 108,
Washington, D.C. Blanck and Giesecke, 1924 : Ueber den Einfluss der
Regenwurmer auf die physikalischen und biologishen Eigenschaften des
Bodens, Zeitschr. Pflanzenerndhrung, Bd. iii., Berlin. Btjgnion, 1913 :
Differentiation des castes chez les termites, Bull. Soc. Ent. Fr., Paris.
Cameron, 1925 : Soil Insects, Science Progress, 11, London. Cook, 1923 :
Studies in the Physical Ecology of the Noctuidee, Univ. Minnesota Agric.
Exp. Sta. Tech., Bull. 12. Criddle, 1918 : Habits and Control of White
Grubs in Manitoba, Agric. Garette, 5, Canada. Cutler, 1926 : Methods for
the Study of Soil Protozoa, in Abderhalden, Handbuch biologischen Arbeits-
methoden, Abt. xi. Darwin, 1881 : Vegetable Mould and Earthworms,
London. Da vies, 1918 : Common White Grubs, U.S. Dept. Agric. Farmers,
Bull. 940. Donisthorpe, 1915 : British Ants, Plymouth. De Man, 1922 :
Nouvelles recherches sur les nematodes libre terricole, Hague. Desneux,
1904 : Isoptera, Genera Insectorum, 25. Escherich, 1909 : Die Termiten,
Leipzig. Friend, 1923 : British Earthworms, London. Froggatt, 1895-97 :
Australian Termitidse, Parts I. -III., Proc. Linn. Soc. N.S. Wales. Grinnell,
1923 : The Burrowing Rodents of California as Agents in Soil Formation,
Jour. Mammalogy, 4. Kopeloff, Lint, and Coleman, 1917 : A Review of
Investigations in Soil Protozoa and Soil Sterilisation (complete bibliography
up to 1917), Soil Science, 3. Michaelsen and Johansson, 1909 : Oligo-
chseten und Hirudinen, Die Siisswasserfauna Deutschlands, Heft. 13, Jena.
Micoletzky, 1922 : Die freilebenden Erd-Nematoden, Archiv. Naturgeschichte,

BIBLIOGRAPHY 395

Abt. 87. Morris, 1922 : The Insects of Arable Land, Ann. App. Biol., ix.
Percy, 1923 : Les protozoaires du sol, Ann. Sci. Agronome, 39. Rensch,
1925 : Zur Frage der Nematoden Bekampfung, Ziickerrubenbau, vii. ; abstract
in Centralblatt Bakt. Paras. InfeJct., Abt. lxv. Roberts, 1922 : Life History of
Wireworms of Genus Agriotes, Ann. App. Biol., ix. Russell, 1915 : Soil
Protozoa and Soil Bacteria, Proc. Roy. Soc, B., 89, London; 1921: Soil
Conditions and Plant Growth, London. Russell and Hutchinson, 1909 :
The Effect of Partial Sterilisation of the Soil on the Production of Plant Food,
Jour. Agric. Sci., 3. Russell and Others, 1923 : The Micro-organisms of the
Soil, London. Sandon, 1927 : The Composition and Distribution of the
Protozoan Fauna of the Soil, Edinburgh. Sjostedt, 1900-04, Monographie
der Termiten Afrikas, Kungl. Vet. Akad. Handl., 34 and 38, Stockholm.
Steiner, 1924: On some Plant Parasitic Nemas and Related Forms, Jour.
Agric. Res., 28. Strickland, 1916 : The Army Cutworm (Euxoa auxiliaris),
Canadian Dept. Agric. Ent. Branch, Bull. 13. Snyder, 1915 : Biology of the
Termites of the Eastern United States with Preventive and Remedial Measures,
U.S. Dept. Agric, Bull. 94 ; 1924 : Adaptations to Social Life : The Termites,
Smithsonian Miscellaneous Collections, Vol. 76, Washington, D.C. ; 1926 :
The Biology of Termite Castes, Quarterly Review Biology, i., No. 4. Theobald,
1927 : Some Soil Insects and their Treatment, S.E. Agric. College Res. and
Adv. Dept., Bull. 5, Wye, Kent. Waksman, 1926 : Principles of Soil Micro-
biology, Baltimore.

Periodicals. — Annales de Science Agronomique, Paris ; Journal of Agri-
cultural Research, Washington, D.C. ; Journal of Agricultural Science, Cam-
bridge ; Soil Science, Baltimore ; Internationale Mitteilungen fur Boden-
kunde, Berlin ; Zeitschrift der Gesellschaft fur Erdekunde zu Berlin, Berlin.

GENERAL ENTOMOLOGY

Adler, 1894 : Alternating Generations (trans, by Straton), Oxford.
Bachmetjew, 1901 : Experimentelle Entomologische Studien, Part L,
Leipzig ; 1907 : Part II., Sophia. Banks, 1898 : Bibliography of American
Economic Entomology, 1888-96, Washington ; 1925 : Bibliography of
American Economic Entomology; 1905-24: Melrose Highlands, Massachusetts.
Berlese, 1909 : Gli Insetti, Milan. Bischoff, 1927 : Biologie der Hymen-
opteren, Berlin. Blunck, 1925 : Syllabus der Insektenbiologie, Berlin.
Bouvier, 1922 : The Psychic Life of Insects (trans. Howard), New York.
Brues, 1920 : Insects and Human Welfare, Harvard Univ. Press, Cambridge,
Massachusetts. Burmeister, 1832 : Handbuch der Entomologie, Berlin.
Carpenter, 1924 : Insects, their Structure and Life, London ; 1928 : The
Biology of Insects, London. Comstock, 1917 : A Manual for the Study
of Insects, Ithaca, N.Y. ; 1925 : An Introduction to Entomology, New
York. Chapman, 1925 : Animal Ecology, with Special Reference to
Insects, Minneapolis. Donge et Esttot, 1921 : Les insectes et leurs
degats, Paris. Ealand, 1915 : Insects and Man, London ; 1921 : Insect
Life, London. Ellis, 1924 : Insect Pests, London. Essig, 1926 : Insects
of Western North America, New York. Fabre, 1911 : The Life and
Love of the Insect (trans, from Souvenirs Entomologiques by N. T.
de Mattos), London ; 1917 : Social Life in the Insect World (trans, from
Souvenirs Entomologiques by B. Miall), New York. Fernald, 1925 : Applied
Entomology, New York. Fletcher, 1914 : Some South Indian Insects,
Madras. Folsom, 1923 : Entomology, with Reference to its Biological and
Economic Aspects, Philadelphia. Forel, 1908 : The Senses of Insects,
London. Froggatt, 1907 : Australian Insects, Sydney. Henneguy, 1904 :

396 THE PRINCIPLES OF APPLIED ZOOLOGY

Les insectes, Paris. Howard, 1904 : The Insect Book, New York. Howes,
1920 : Insect Behaviour, Boston. Imms, 1925 : A General Textbook of
Entomology, London. Kellogg, 1908 : American Insects, New York. Kirby
and Spence, 1818 : An Introduction to Entomology, London. Lefroy,
1909 : Indian Insect Life, Calcutta ; 1923 : A Manual of Entomology, London.
Lutz, 1921 : Field-book of Insects, New York. Packard, 1898 : A Textbook
of Entomology, New York. Payne, 1926 : Freezing and Survival of Insects
at Low Temperatures, Quarterly Review of Biology, Vol. i., No. 2. Pierce,
1921 : Lectures in Applied Entomology, Denver. Sanderson and Jackson,
1912 : Elementary Entomology, New York. Schoenchen, 1921 : Praktikum
der Insektenkunde, Jena. Schroder, 1912-26 : Handbuch der Entomologie,
Jena. Sharp, 1899 : Insects, Cambridge Natural History, Vols. v. and vi.,
London. Shelford, 1913 : Animal Communities in Temperate America,
University Press, Chicago. Shipley, 1917 : Studies in Insect Life, New York.
Sorauer, 1925 : Handbuch der Entomologie, Jena. Swammerdam, 1737-38 :
Bybel der Natuure, Leyden. Taschenberg, 1879 : Einfuhrung in die Insec-
tenkunde, Bremen. Till yard, 1926 : The Insects of Australia and New
Zealand, Sydney. Uvarov, 1921 : Periodicity and Migrations of Locusts,
Bull. Ent. R., xii. Wellhouse, 1926 : How Insects Live ; an Elementary
Textbook of Entomology, New York. Westwood, 1839 : An Introduction
to the Modern Classification of Insects, London ; 1845 : Arcana Entomologica,
London. Wheeler, 1923 : Social Life among the Insects, New York.

Periodicals. — American Entomological Society, Transactions, Phila-
delphia ; Annales de la Societe Entomologique de France, Paris ; Bulletin
de la Societe Entomologique de France, Paris ; Bolletino della Societa Ento-
mologica Italiana, Florence; Bulletin de la Societe Royale Entomologique
d'^gypte, Cairo ; Canadian Entomologist, Guelph ; Entomological Society
of London, Transactions, London ; Entomologisk Tidskrift, Stockholm ;
Entomological Society of Washington, Transactions, Washington, D.C. ;
Journal of Entomology and Zoology, Claremont, California ; Journal of
Economic Entomology, Geneva, N.Y. ; Journal of the New York Entomological
Society, New York ; Memoirs of the American Entomologica] Society, Phila-
delphia ; Russkoe Entomologicheskoe Obozrienie, Leningrad ; Stettiner
Entomologische Zeitung, Stettin ; Tijdschrift voor Entomologie, The Hague ;
Wiener Entomologische Zeitung, Vienna ; Zeitschrift f ur angewandten
Entomologie, Berlin; Zeitschrift fur Wissenschaftliche Insektenbiologie,
Berlin-Lichterfelde.

MEDICAL, VETERINARY, AND HOUSEHOLD ENTOMOLOGY

Advisory Committee of Royal Society on Plague, 1905-09 : Reports
on Plague Investigation in India, Jour. Hygiene, v., vi., vii., viii., x., London.
Alcock, 1920 : Entomology for Medical Officers, London. Austen, 1903 :
Monograph of the Tsetse Flies, Brit. Mus. (Nat. Hist.), London ; 1909 :
African Blood- sucking Flies, Ibid. ; 1920 : The House-fly, Ibid. Austen and
Hegh, 1922 : Tsetse Flies : Characteristics, Distribution, and Bionomics,
London. Bacot, 1916 : Report of the Entomological Investigations Under-
taken for the Commission during the year August 1914 to July 1915, Yellow
Fever Commission (West Africa), Colonial Office, London; 1917: The Louse
Problem, Proc. Roy. Soc. Medicine, London. Banks, 1904 : A Treatise on
the Acarina or Mites, Proc. U.S. Nat. Mus., xxviii., Washington, D.C. ; 1908 :
A Revision of the Ixodoidea or Ticks of the United States, U.S. Dept. Agric,
Tech. Bull. 15 ; 1912 : The Structure of Certain Dipterous Larvae with Par-
ticular Reference to those in Human Foods, U.S. Dept. Agric, Tech. Ser. 22.

BIBLIOGRAPHY 397

Baker, 1904 : A Revision of the American Siphonaptera, Proc U.S. Nat.
Mus., 27. Berlese, 1882-97 : Acari, Myriapoda et Pseudoscorpiones,
Patavii et Porticis ; 1912 : Trombidiidae, Redia, Vol. viii. ; 1917 : Insetti
delli Case et dell'Uomo e Malattie che diffondono, Milano. Bishop, 1915 :
Fleas, U.S. Dept. Agric, Bull. 248. Bishop and Wood, 1917 : Mites and Lice
on Poultry, U.S. Dept. Agric, Farmer's Bull. 801. Bishop, Laake, and
Brundrett, 1926 : The Cattle Grubs or Ox Warbles, Ibid., 1369. Bishop,
Mitchell, and Parman, 1917 : Screw worms and other Maggots affecting
Animals, Ibid., 857. Blanchard, 1905 : Les moustiques, Paris ; 1909 :
L'insecte et 1' infection, Paris. Boyce, 1909 : Mosquitoes or Man ; the
Conquest of the Tropical World, London. Brauer, 1863 : Monographic der
GEstridse, Vienna. Canestrini and Framer, 1899 : Demodecidse and
Sarcoptidae, Das Tierreich, Berlin. Comstock, 1912 : The Spider Book,
New York. Cooper and Laws, 1915 : Some Observations on the Theory and
Practice of Dipping, Parasitology, London. Cory, 1917 : The Protection of
Dairy Cattle from Flies, Jour. Econ. Ent., Geneva, N.Y. Cummings, 1918 :
The Bed-bug, Brit. Mus. (Nat. Hist.), Econ. Ser. 5, London. Carpenter,
1908-20 : Reports of Experiments with Warble Flies, Jour. Dept. Agric. Ireland,
8, Dublin. Crawford and Chalam, 1926 : Mosquito Reduction and Malarial
Prevention : A Precis, Oxford University Press. Doane, 1910 : Insects and
Disease, New York. Edwards, 1920 : Mosquitoes and Disease, Brit. Mus.
(Nat. Hist.), London. Ellenberger and Chapin, 1919 : Cattle Fever
Ticks and Methods of Eradication, U.S. Dept. Agric, Farmer's Bull. 1057.
Ewing, 1926 : A Revision of the American Lice of the Genus Pediculus,
Proc. U.S. Nat. Mus., lviii., Washington, D.C. Fox, 1925 : Insects and
Diseases of Man, Philadelphia. Giles, 1900 : A Handbook of the Gnats or
Mosquitoes, London. Girault, 1914 : Studies of the Biology of the Bed-bug
Cimex lectularius, Jour. Econ. Biol., London. Goeldi, 1913 : Die Sanitarisch-
pathologische Bedeutung der Insekten und verwandten Gliedertiere, Berlin.
Graham Smith, 1914 : Flies in Relation to Disease : Non-blood-sucking Flies,
Cambridge University Press. Grayeill, 1914 : Repellents for Protecting
Animals from the Attacks of Flies, U.S. Dept. Agric, Bull. 131. Greenway,
1908 : Artropodos Parasitos, Buenos Aires. Gruenberg, 1907 : Die blut-
saugenden Dipteren, Jena. Hadwen, 1912 : Warble Flies, Dept. Agric.
Canada, AnimaVs Bureau, Bull. 16. Hadwen and Cameron, 1918 : Contribu-
tion to the Knowledge of the Bot-flies Gastrophilus intestinalis, G. hcemor-
rhoidalis, and G. nasalis, Bull. Ent. Res., 9. Hardenburg, 1922 : Mosquito
Eradication, New York. Herms, 1915 : Medical and Veterinary Entomology,
New York. Herrick, 1926 : Insects Injurious to the Household, New York.
Hewitt, 1909 : Structure, Bionomics, and Development of the House-fly
Musca domestica, Quarterly Journal Microscopical Science, London ; 1910 :
The House-fly, Manchester University Press ; 1912 : The House-fly, Cambridge
University Press. Htldebrand, 1923 : Fishes in Relation to Mosquito
Control in Ponds, U.S. Pub. Health Report, 527 ; 1925 : A Study of the Top
Minnow Gambusia holbrooki in its Relation to Mosquito Control, U.S. Pub.
Health Service, Bull. 153. Hindle, 1914: Flies in Relation to Disease : Blood-
sucking Flies, Cambridge University Press. Hirst, 1917 : Species of Arachnida
and Myriapoda Injurious to Man, Brit. Mus. (Nat. Hist.), Econ. Ser. 6, London ;
1922 : Mites Injurious to Domestic Animals, Ibid., 13 ; 1923 : On the
Transmission of Plague by Fleas of the Genus Xenopsylla, Indian Jour. Medical
Research, x., Calcutta. Howard, 1911 : The House-fly : Disease Carrier,
New York. Howard, Dyar, and Knab, 1912 : The Mosquitoes of North
and Central America and the West Indies, Carnegie Institute, Vol. i., Washing-
ton. Huber, 1899-1903 : Bibliographie der klinische Entomologie, Jena.

398 THE PRINCIPLES OF APPLIED ZOOLOGY

Huntek, 1915 : Some Observations on Medical Entomology, Proc. Entom.
Soc, Washington, Baltimore. Imes, 1916 : Sheep Scab, U.S. Dept. Agric,
Farmer's Bull. 713 ; 1918 : Cattle Lice and how to Eradicate them, Ibid.,
909 ; 1918 : Cattle Scab and Methods of Control and Eradication, Ibid., 1017 ;
1920 : Hog Lice and Hog Mange : Methods of Control and Eradication, Ibid.,
1085. Kanngiesser, 1911 : Vergiftungen durch Tiere und animalische
Stoffe, Jena. Klrkpatrick, 1925 : The Mosquitoes of Egypt, Egypt. Govt.
Anti-Malaria Commiss., Cairo. Lang, 1920 : Handbook of British Mosquitoes,
London. Larrousse, 1921 : Etude systematique et medicale des Phlebotomes,
Paris. Le Prince and Orenstein, 1916 : Mosquito Control in Panama,
New York. Lloyd, 1919 : Lice and their Menace to Man, London. Martini,
1923 : Lehrbuch der Medinizischen Entomologie, Jena. Marchoux, 1926 :
Paludisme, Paris. Megnin, 1875 : Les Parasites Articules, Paris. Ministry
of Agriculture and Fisheries, Great Britain, 1926 : Report of Depart-
mental Commission on the Warble Fly Pest, London. Moore, 1922 : Use of
Fishes for the Control of Mosquitoes in the Northern Fresh Waters of the
United States, U.S. Dept. Commerce, Bureau of Fisheries, Document 923.
Newstead, 1925 : Guide to the Study of Tsetse Flies, Liverpool University
Press. Nuttall, 1917 : Bibliography of Pediculus and Phthirius, Parasitology,
Cambridge ; 1918 : The Biology of Pediculus humanus, Ibid. ; 1918 : The
Biology of Phthirius pubis, Ibid. ; 1918 : Combating Lousiness among Soldiers
and Civilians, Ibid. Nuttall, Warburton, and Robinson, 1908-26 : Ticks :
A Monograph of the Ixodoidea, Cambridge University Press. Patton, 1921 :
Notes on the Myiasis producing Diptera of Man and Animals, Bull. Ent. Res.,
xii. Patton and Craig, 1928 : Textbook of Medical Entomology, Madras.
Pawlowsky, 1927 : Gifttiere und ihre Giftigkeit, Jena. Pierce, 1921 :
Sanitary Entomology, Boston. Riley and Johannsen, 1915 : A Handbook
of Medical Entomology, Ithaca, N.Y. Russell, 1913 : The Flea, Cambridge
University Press. Oudemanns, 1910 : A Short Summary of the More
Important Families of Acari, Bull. Ent. Res., ii.

Periodicals. — Bulletin of Entomological Research, London ; Review of
Applied Entomology, Series B., Medical and Veterinary, London.

AGRICULTURAL ENTOMOLOGY

Chittenden, 1907 : Insects Injurious to Vegetables, New York. Crosby
and Leonard, 1918 : Manual of Vegetable Garden Insects, New York.
Escherich, 1913 : Die angewandte Entomologie in den Vereinigten Staaten,
Berlin. Essig, 1915 : Injurious and Beneficial Insects of California, Sacra-
mento. Fernald, 1925 : Applied Entomology, New York. Froggatt,
1909 : Fruit-flies : A General Account of the Family Trypetidse, Sidney.
Gowdey, 1917 : Agricultural Pests of Uganda, Kampala, Uganda. Guenaux,
1922 : Entomologie et Parasitologic agricoles, Paris. Hess, 1906 : Die'Feinde
des Obstbaues, Hannover. Herrick, 1920 : Insects of Economic Importance,
New York ; 1925 : Manual of Injurious Insects, New York. Kaltenbach,
1873 : Die Pflanzen-feinde aus der Klasse der Insekten, Stuttgart. Kuster,
1911: Die Gallen der Pflanzen, Berlin. Lefroy and Lean, 1924: Insect
Pests of Cotton, Empire Cotton Growing Review, i., London. Lochhead,
1919 : Economic Entomology, Philadelphia. Marchal, 1916 : Les Sciences
biologique appliquees a 1' Agriculture et la lutte contre les enemis des plant es
aux l^tats Unis, Ann. Service des Epiphyties, iii., Paris. Morstatt, 1926 :
Bibliographie der Pflanzenschutz Literatur, published annually, Biol. Reich-
sanst. Land-u. Forstwirtschaft, Berlin. O'Kane, 1912 : Injurious Insects,
New York. Ormerod, 1877-1900: Reports on Injurious Insects, London;

BIBLIOGRAPHY 399

1898 : Handbook of Insects Injurious to Orchard and Bush Fruits. London ;
1890 : A Manual of Injurious Insects, London. Osborn, 1916 : Agricultural
Entomology, Philadelphia. Palmer and Westell, 1922 : Pests of the Garden,
Orchard, Farm, and Forest, London. Pethekbridge, 1916 : Fungoid and
Insect Pests of the Farm, Cambridge University Press. Pierce, 1918 : Manual
of Dangerous Insects liable to be Introduced into the United States, Washing-
ton. Sanderson, 1911 : Insects Injurious to Staple Crops, New York.
Sanderson and Peatrs, 1921 : Insect Pests of Farm, Garden, and Orchard,
New York. Sllvestri and Grandi, 1911 : Dispense di Entomologia agraria,
Portici. Sltngerland and Crosby, 1914 : Manual of Fruit Insects, New York.
SoRAUER, 1925 : Handbuch der Pnanzenkrankheiten, Vol. 3, Jena. Smith,
1896 : Economic Entomology, Philadelphia. Smith and Gardner, 1922 :
Insect Pests of the Horticulturist, London. Stehli and Others, 1924-26 :
Feinde der Land-und Forstwirtschaft, Hire Biologie und Bekampfung,
Stuttgart. Theobald, 1909 : Insect Pests of Fruit, Wye, Kent, England.
TRiNCHrNEERi, 1916 : La lutte contre les Sauterelles dans les divers Pays,
Inst. Intemat. Agric. Bureau des Renseignements Agricoles et des Maladies des
Plantes, Rome ; 1926 : Etat actuel de 1' organisation de la lutte contre les
sauterelles dans divers pays ; Resultats d'une enquete internationale, Ibid.
Washburn, 1918 : Injurious Insects and Useful Birds, Philadelphia. Will-
cocks, 1916 : The Insects and Related Pests of Egypt, Sultanic Agric. Society,
Cairo.

Periodicals. — Journal of Economic Entomology, Geneva, N.Y. ; Meddel-
elser fra Statsentomologer Landbrugsdepartementet, Christiana ; Mededee-
lingen van den Phytopathologischen Dienst te Wageningen ; Mitteilungen der
K. K. Landwirtschaftlich-bakteriologischen und Pnanzschutzstation in Wien ;
Monographien fur Angewandten Entomologie : Beihefte zur Zeitschrift f ur
Angewandten Entomologie, Berlin ; Phytopathology, Ithaca, N.Y. ; Review
of Applied Entomology, Series A, Agricultural, London ; Revue de Pathologie
vegetale et d 'Entomologie agricole, Paris ; United States Department of
Agriculture, Bureau of Entomology, Bulletins, Farmers' Bulletins, and Circulars.
An almost complete list of periodicals in which articles relating to Agricultural
Entomology are published may be obtained by reference to the Review of
Applied Entomology, Series A, Vol. I., 1913, List of Publications Examined ;
and by reference to Abbreviations employed in Experiment Station Record for
Titles of Periodicals, United States Department of Agriculture, Department
Bulletin 1330, 1925.

FOREST ENTOMOLOGY

Barbey, 1913 : Traite d'Entomologie Forestiere, Paris. Bechstein, 1829 :
Forst und Jagdwissenschaft, Gotha. Blake, 1925 : Enemies of Timber :
Dry Rot and Death Watch Beetle, London. Boas, 1924 : Dansk Forstzoologi,
Kobenhavn. Dingler, 1927 : Schutz gegen Tiere, in Hessbeck, Forst Schutz,
Neudamm. Eichhoff, 1881 : Die Europaischer Borkenkafer, Berlin.
Escherich, 1914 : Die Forst Insekten Mitteleuropas, Berlin. Felt, 1905-06 :
Insects affecting Park and Woodland Trees, New York State Museum, Mem. 8,
Albany, N.Y. ; 1917 : Key to American Insect Galls, New York Museum,
Bull. 200 ; 1924 : Manual of Tree and Shrub Insects, New York. Fisher,
1907 : Forests and Protection, in Schlich, Manual of Forestry, London.
Froggatt, 1923 : Forest Insects of Australia, Sydney. Gahan, 1920 :
Furniture Beetles, Brit. Mus. Nat. Hist., Econ. Ser. 11. Glllanders, 1908 :
Forest Entomology, Edinburgh. Gtrdwood, 1927 : Worms in Furniture and
Structural Timber, Oxford University Press. Graham, 1922 : Effect of Physical
Factors in the Ecology of Certain Insects in Logs, Minnesota State Ent. Report,

400 THE PRINCIPLES OF APPLIED ZOOLOGY

19 ; 1925 : The Felled Tree Trunk as an Ecological Unit, Ecology, vi.
Henschel, 1895 : Die schadlichen Forst und Obstbaum Insekten, Leipzig.
Hopkins, 1909 : The Genus Dendroctona, U.S. Deft. Agric. Bur. Ent., Tech.
Ser. 17 ; 1911 : Contributions towards a Monograph of the Bark Beetles of
the Genus Pissodes, Ibid., 20 ; 1915 : Preliminary Classification of the Scoly-
toidea, Ibid., 17 ; 1920 : The Bioclimatic Law, Jour. Washington Acad. Sci.,
Washington, D.C. Judeich and Nitsche, 1895 : Lehrbuch der mitteleuro-
pischen Forstinsektenkunde, Berlin. Knoche, 1908 : Uber Borkenkafer-
biologie und Borkenkaferverteilung, Fortwiss. Zentralblatt, xxx. Kuster,
1911 : Die Gallen der Pflanzen, Leipzig. Munro, 1915: The Larvae of the
Furniture Beetle Families, Anobiidse and Lyctidse, Proc. Roy. Phys. Soc,
Edinburgh ; 1926 : British Bark Beetles, H.M. Stationery Office, London.
NiissLEiN and Rhumbler, 1922: Leitfaden der Forst Insektenkunde, Berlin.
Ratzeburg, 1837 : Die Forst Insekten, Berlin. Schierbeck, 1922 : Spruce
Budworm, Bark Beetle, and Borer : The Causes of the Dying of Balsam in
Quebec, Montreal. Stebbing, 1914 : Indian Forest Insects : Coleoptera,
London. Swaine, 1908 : Canadian Bark Beetles, Ent. Branch Dept. Agric,
Ottawa. Tragardh, 1914 : Sveriges Skoginsekter, Stockholm. Wolff and
Krausse, 1922 : Die forstlichen Lepidopteren, Jena.

INSECT CONTROL

Anderson and Roth, 1923 : Insecticides, Fungicides, and Appliances, New
York. Bourcart, 1925 : Insecticides, Fungicides, and Weed-killers, London.
Cockerham, 1923 : A Manual of Spraying, New York. Fryer, 1923 : Suc-
cessful Spraying, London ; 1920 : Insect Pests and Fungus Diseases, London.
Howard and Fiske, 1911 : The Importation into the United States of the
Parasites of the Gipsy Moth, etc., U.S. Dept. Agric. Ent., Bull. 91. Lafont,
1906 : La Lutte contre les Insectes et autres ennemis de rAgriculture, Paris.
Lodeman, 1896 : The Spraying of Plants, New York. Morton, 1926 :
Practical Spraying, London. Vermorel and Dantony, 1914 : La Defense
de nos Jardins, Paris. Vogt, 1926 : Die Chemische Pflanzenschutzmittel, ihre
Anwendung und Wirkung, Berlin. Wardle and Buckle, 1923 : Principles
of Insect Control, Manchester University Press. Winterbottom, 1922 :
Weevil in Wheat, Adelaide.

VERMIN REPRESSION

Bailey, 1908 : Harmful and Beneficial Mammals of the Arid Interior,
U.S. Dept. Agric, Farmer's Bull. 335 ; 1924 : Breeding, Feeding, and other
Life Habits of Meadow Mice (Microtus), Jour. Agric. Res., xxvii., No. 8. Bell,
1920: Hunting Down Stock Killers, U.S. Dept. Agric. Year-book; 1920:
Death to the Rodents, Ibid. Bell and Piper, 1909 : Extermination of Ground
Squirrels, Gophers, and Prairie Dogs in North Dakota, North Dakota Agric
Exp. Stu., Circ 4. Birdseye, 1912 : Some Common Mammals of Montana in
Relation to Agriculture and Spotted Fever, U.S. Farmer's Bull. 484. Boelter,
1909 : The Rat Problem, London. Blake, 1926 : The Protection of Buildings
against Vermin, London. Brooks, 1908 : Notes on the Habits of Mice,
Moles, and Shrews, West Virginia Univ. Agric Exp. Sta., Bull. 113. Burnett,
1918 : Rodents of Colorado, Circ. 25, Office of State Entomologist, Fort Collins,
Colorado. Cleland, 1918 : Rats and Mice, Roy. Soc. New South Wales,
Sydney. Creel, 1915 : The Migratory Habits of Rats, with Special Reference
to the Spread of Plague, Reprint 278, Pub. Health Repts., U.S. Pub. Health
Service ; 1918 : The Rat, Pub. Health Bull. 103, U.S. Pub. Health Service.
Cumming and Others, 1920 : Information Concerning Rat Surveys and

BIBLIOGRAPHY 401

Rat Proofing, Reprint 620, U.S. Pub. Health Service. Dearborn, 1919 :
Trapping on the Farm, Year-book, U.S. Dept. Agric. Dewberry, 1920 : The
Prevention and Destruction of Rats, London. Dixon and De Ong, 1917 :
Control of the Pocket Gopher in California, Bull. 281, Univ. California Agric.
Exp. Sta., Berkeley, Cal. Dunnam, 1924 : The Common Garden Mole in
Iowa, Circ. 88, Iowa Agric. Exp. Sta., Ames, Iowa. Gunther, 1917 : Report
on Agricultural Damage by Vermin and Birds in the Counties of Norfolk and
Oxfordshire in 1916, Univ. Press, Oxford. Hauer, 1921 : Guide to the Proper
Rat Proofing of Buildings, Reprint 655, U.S. Pub. Health Service. Hetser,
1914 : Relative Efficiency of Rat Traps, Reprint 167, U.S. Pub. Health Service.
Hewitt, 1918 : Rats and Mice, Leaflet 7, Dept. Agric. Canada, Entom. Branch,
Crop Protection. Hinton, 1918 : Rats and Mice as Enemies of Mankind,
Brit. Mus. Nat. Hist, Econ. Ser. 8, London. Hisaw, 1923 : Feeding Habits
of Moles, Jour. Mammalogy, iv. Hollister, 1916 : A Systematic Account of the
Prairie Dogs, U.S. Dept. Agric. Bur. Biol. Surv. North American Fauna, No. 40.
Howell, 1914 : Revision of the American Marmots, Ibid., No. 37 ; 1914 :
Revision of the American Harvest Mice, Ibid., No. 36. Jackson, 1915 :
Revision of the American Moles, Ibid., No. 38. Lantz, 1905 : Coyotes in their
Economic Relations, U.S. Biol. Surv., Bull. 20 ; 1907 : An Economic Study
of Field Mice (Genus Microtus), U.S. Dept. Agric. Biol. Surv., Bull. 31 ; 1907 :
The Rabbit as a Field and Orchard Pest, Year-book, U.S. Dept. Agric. ; 1908 :
Use of Poisons for Destroying Noxious Animals, Year-book, U.S. Dept. Agric. ;
1909 : The Brown Rat in the United States, U.S. Biol. Surv., Bull. 33 ; 1909 :
Pocket Gophers as Enemies of Trees, Year-book, U.S. Dept. Agric. ; 1916 :
Destroying Rodent Pests on the Farm, Year-book, U.S. Dept. Agric. ; 1917 :
The House Rat, Year-book, U.S. Dept. Agric. ; 1917 : House Rats and Mice,
U.S. Dept. Agric, Farmer's Bull. 896 ; 1918 : Field Mice as Farm and
Orchard Pests, Ibid., 670; 1918: Rodent Pests of the Farm, Ibid., 932;
1923 : Economic Value of North American Skunks, Ibid., 587 ; 1924 : Cotton-
tail Rabbits in Relation to Trees and Farm Crops, Ibid., 702. M'Coy, 1912 :
Notes on the Bionomics of Rats and Ground Squirrels, Reprint 94, U.S. Pub.
Health Service. Mickel, 1924 : Poisoning Pocket Gophers, Circ. 14, Univ.
Minnesota Agric. Exten. Division. Nelson, 1909 : The Rabbits of North
America, U.S. Biol. Surv. North American Fauna, No. 29. Palmer, 1897 :
The Jack Rabbits of the United States, U.S. Biol. Surv., Bull. 8. Piper,
1909 : Mouse Plagues, Control and Prevention, Year-book, U.S. Dept. Agric.
Rucker, 1913 : Plague, Relation between Traffic and the Spread of Plague,
Reprint 114, U.S. Pub. Health Service; 1915 : Plague, its Geographical Distri-
bution and its Menace to the United States, Ibid., Reprint 274. Scheffer,
1923 : American Moles as Agricultural Pests and as Fur Producers, U.S. Dept.
Agric, Farmer's Bull. 1247. Silver, 1923 : How to Get Rid of Rats, Ibid.,
1302 ; 1924 : Mouse Control in Field and Orchard, Ibid., 1397 ; 1927 : Rat
Control, Ibid., 1593. Stoner, 1918 : The Rodents of Iowa, Iowa Geol. Survey,
Bull. 5. Swene:, 1915 : The Prairie Dog and its Control, Univ. of Nebraska
Agric. Exp. Sta., Bull. 154. Various, 1910 : The Rat and its Relation to
Public Health, U.S. Pub. Health Service. Vorhies and Taylor, 1922 : Life
History of the Kangaroo Rat, U.S. Dept. Agric, Bull. 1091. Zuschlag,
1908 : Le rat migratoire et sa destruction rationelle, Copenhagen.

BIRD ENCOURAGEMENT

Adams, 1908 : The Ecological Succession of Birds, The Auk, xxv. A. L. T.,
1925 : Protection of Wild Birds, Nature, cxv., London. Beal, 1904 : Some
Common Birds in their Relation to Agriculture, U.S. Dept. Agric, Farmer's

26

402 THE PRINCIPLES OF APPLIED ZOOLOGY

Bull. 54 ; 1916 : Common Birds of South-Eastern United States in Relation
to Agriculture, Ibid., 755 ; 1918 : Some Common Birds Useful to the Farmer,
Ibid., 630. Beal and M'Atee, 1922 : Food of some Well-known Birds of
Forest, Farm, and Garden, Ibid., 506. Berry, 1917 : A Chair of Economic
Ornithology, Scottish Naturalist, Edinburgh. Chapin, 1925 : Food Habits of
the Vireos, U.S. Dept. Agric, Bull. 1355. Chapman, 1925 : The European
Starling as an American Citizen, Natural History, xxv., New York. Colltnge,
1910 : Feeding Habits of the Rook, Report to Council Land Agents' Society ;
1912 : Food of Nestling Birds, Jour. Bd. Agric, London ; 1913 : Destruction
and Dispersal of Weed Seeds by Wild Birds, Ibid. ; 1917 : Destruction of House
Sparrows, Nature, London ; 1918 : Some Recent Investigations on the Food
of Certain Wild Birds, Jour. Minist. Agric, London ; 1920 : The Food of the
Nightjar, Ibid. ; 1918 : Sea-birds : Relation to Agriculture and the Fisheries,
Ibid. ; 1920 : The Rook : its Relation to the Farmer, Fruit-grower, and
Forester, Ibid. ; 1921 : The Starling : is it Injurious to Agriculture, Ibid. ;
1922: The Barn Owl, Ibid. ; 1922: The Little Owl, Ibid. Collinge, Dendy,
Johnston, Lefroy, and Maxwell, 1920 : Correspondence re the Plumage
Bill, Nature, cv., London. Coward, 1912 : Note on the Little Owl, Mem.
Proc Manchester Lit. and Phil. Soc Criddle, 1917 : The American Crow
in its Relation to Agriculture, Agric. Gaz., Ottawa. Dearborn, 1912 : The
English Sparrow as a Pest, U.S. Dept. Agric, Farmer's Bull. 493 ; 1914 :
Bird Houses and How to Build Them, Ibid., 609. Fisher, 1907 : Hawks
and Owls from the Standpoint of the Farmer, U.S. Biol. Surv., Circ. 61.
Forbush, 1907 : Useful Birds and their Protection, Mass. State Bd. Agric,
Boston. Frohawk, 1919 : Birds Beneficial to Agriculture, Brit. Mus. Nat.
Hist, Econ. Ser. 9. Gossard and Scott, 1913 : Some Ohio Birds, Ohio
Agric. Exp. Sta., Bull. 250. Gunther, 1917 : Report on Agricultural Damage
by Vermin and Birds of NorfoUs and Oxfordshire, Oxford University Press.
Hammond, 1912 : An Investigation Concerning the Food of Certain Birds,
Jour. Agric. Science. Henshaw, 1907 : Birds Useful in the War against the
Cotton Boll Weevil, U.S. Biol. Surv., Circ 57. Hiesemann, 1912 : How to
Attract and Protect Wild Birds, London. Hewitt, 1921 : The Conservation
of Wild Life in Canada, New York. Hornaday, 1913 : The Federal Migratory
Bird Law, Zool. Soc. Bull., New York ; 1914 : Wild Life Conservation in
Theory and Practice, Yale University Press, New Haven. Judd, 1898 :
Birds as Weed Destroyers, Year-book, U.S. Dept. Agric. ; 1900 : Food of
Nestling Birds, Ibid. ; 1901 : Relation of Sparrows to Agriculture, U.S. Biol.
Surv., Bull. 15 ; 1902 : Birds of a Maryland Farm, Ibid., 17 ; 1905 : The
Bobolink and other Quails of the United States, Ibid., 21. Kalmbach, 1918 :
The Crow and its Relation to Man, U.S. Dept. Agric, Bull. 621 ; 1920 : The
Crow in its Relation to Agriculture, U.S. Dept. Agric, Farmer's Bull. 1102.
Kalmbach and M'Atee, 1925 : Homes for Birds, Ibid., 1456. Kalmbach
and Gabrielson, 1921 : The Economic Value of the Starling in the United
States, Ibid., 868. Kerner and Oliver, 1895 : Natural History of Plants,
London. Leigh, 1916 : Food of Starling, Rook, and Chaffinch, Jour. Bd.
Agric, London. Lincoln, 1924 : Instructions for Banding Birds, U.S. Dept.
Agric Miscell., Circ 18. Lloyd, 1924 : The Protection of Birds : An Indict-
ment, London. Mabbott, 1920 : Food Habits of Seven Species of American
Shoal- water Ducks, U.S. Dept. Agric, Bull. 862. Marriner, 1909 : The Kea :
A New Zealand Problem, London. Mason and Lefroy ; 1911 : Food of
Birds in India, Mem. Dept. Agric. India, Pusa. M'Atee, 1905 : The Horned
Larks, U.S. Biol. Surv., Bull. 23 ; 1906 : Birds that Eat Scale Insects, Year-
book, U.S. Dept. Agric ; 1913 : Index to Papers relating to the Food of Birds
by Members of the Biological Survey in Publications of the United States

BIBLIOGRAPHY 403

Department of Agriculture, 1885-1911, U.S. Dept. Agric. Biol. Surv., Bull. 43 ;
1916 : How to Attract Birds in North- Western United States, U.S. Dept. Agric,
Farmer's Bull. 760 ; 1923 : Community Bird Refuges, Ibid., 1239. M'Atee
and Beal, 1922 : Food of some Well-known Birds of Forest, Farm, and
Garden, Ibid., 506. Meade Waldo, Lloyd, Acland, and Atchison, 1912 :
The Food of the Little Owl, British Birds, Vol. vi., Witherby. Milburn, 1918 :
The Crop of a Wood Pigeon, Jour. Min. Agric, London. Newstead, 1908 :
Food of some British Birds, Jour. Bd. Agric, London. Pellett, 1914 :
The Economic Value of Birds in Horticulture, Missouri State Bd. Hortic
Columbia, Quarterly Bull. 61. Surface, 1908 : Bird Preservation, Zool. Bull.
Pennsylv. Dept. Agric ; 1913 : Some Pennsylvania Birds and their Economic
Value, Bi-Monthly Bull. Zool. Penns. Dept. Agric, 5 and 6. Theobald, 1916 :
Food of Rook, Chaffinch, and Starling, Jour. Bd. Agric, London. Weed and
Dearborn, 1924 : Birds in their Relation to Man : A Manual of Economic
Ornithology for the United States, Philadelphia. Wetmore, 1924 : Food
and Economic Relations of North American Grebes, U.S. Dept. Agric, Bull.
1196.

DOMESTICATED ANIMALS

Antonius, 1922 : Grundzuge einer stammgeschichte der Haustiere, Jena.
Babcock and Clattssen, 1918 : Genetics in Relation to Agriculture, New
York. Bailey, 1922 : Cyclopaedia of Farm Animals, New York. Burkett,
1909 : Farm Livestock, New York. Castle, 1924 : Genetics and Eugenics,
Harvard University Press. Chaveau, 1905 : The Comparative Anatomy of
the Domesticated Animals, New York. Clemen, 1923 : The American Live-
stock and Meat Industry, New York. Craig, 1915: Common Diseases of
Farm Animals, Philadelphia. Crewe, 1925 : Animal Genetics, Edinburgh.
Curtis, 1915 : The Fundamentals of Livestock Judging and Selection, Phila-
delphia. Darwin, 1868 : The Variation of Animals and Plants under Domesti-
cation, London. Davenport, 1907 : Principles of Breeding, Boston ; 1910 :
Domesticated Animals and Plants, Boston. Dietrich, 1917 : Livestock on
the Farm, Philadelphia. East-Jones, 1919: Inbreeding and Outbreeding,
New York. Ellenberger and Others, 1906-11 : Handbuch der ver-
gleichenden mikroskopischen Anatomie der Haustiere, Berlin ; 1920 : Lehr-
buch der vergleichenden Physiologie der Haustiere, Berlin. Finlay, 1925 :
Cattle Breeding, Edinburgh. Fream, 1918 : Elements of Agriculture, Edin-
burgh. Gay, 1915 : Principles and Practice of Judging Livestock, New York ;
1916 : The Breeds of Livestock by Livestock Breeders, New York. Gardner,
1918 : Livestock and Dairy Farming, Philadelphia. Gowen, 1924 : The
Application of the Science of Genetics to the Farmers Problem, Scientific Agric,
v. Harper, 1911 : Manual of Farm Animals, New York. Hauger, 1921 :
Zur romischen Landwirtschaft und Haustierzucht, Hannover. Hays, 1919 :
Inbreeding Animals, Delaware Agric Exp. Sta., Bull. 123. Hehn, 1911 :
Kulturpflanzen und Haustiere in ihrem Uebergang aus Asien nach Griechen-
land und Italien, sowie in das ubrige Europa, Berlin. Hewitt, 1921 : The
Conservation of the Wild Life of Canada, New York. Htjngerford, 1919 :
Tables for the Determination of the Types and Breeds of Domesticated
Animals, Ithaca. Hunt and Burkett, 1914 : Farm Animals, New York.
Jones, 1925 : Genetics in Plant and Animal Improvement, New York.
Keller, 1909-13: Die Antike Tierwelt, Leipzig; 1905: Naturgeschichte
der Haustiere, Berlin. King, 1919 : Studies in Inbreeding, Wistar
Institute, Philadelphia. Kuiper, 1921 : Colour Inheritance in Cattle,
Jour, of Heredity, 12. Low, 1845 : On the Domesticated Animals of the
British Islands, London. Lydekker, 1908 : A Guide to the Domesticated

404 THE PRINCIPLES OF APPLIED ZOOLOGY

Animals other than Horses, British Museum Guide-book. Malin, 1923 :
The Evolution of Breeds, Des Moines, Iowa. Marshall, 1911 : Breeding
Farm Animals, Chicago. Mayo, 1903-13 : Diseases of Animals, New York.
M'Fadyean, 1908 : The Comparative Anatomy of the Domesticated Animals,
New York. Montani, 1917 : Anatomie regionale des animaux domestiques,
Paris. Ministry of Agriculture, Great Britain, Breeds of Livestock,
London. Morse, 1910 : The Ancestry of Domesticated Cattle, 21th Ann. Rept.
Bureau Animal Industries, U.S. Dept. Agric. Mumford, 1917 : Animal
Breeding, New York. Pearl, 1913-18 : Studies on Inbreeding, American
Naturalist, xlvii.-li. ; 1915 : Modes of Research in Genetics, New York.
Plumb, 1916 : Judging Farm Animals, New York; 1920: Types and Breeds
of Farm Animals, Boston. Rice, 1926 : The Breeding and Improvement
of Farm Animals, New York. Rommel, 1920 : Essentials of Animal Breeding,
U.S. Dept. Agric, Farmer's Bull. 1167. Russell Smith, 1919: The World's
Food Resources, London. Scott Elliot, 1912 : Prehistoric Man and his
Story, London. Standard Encyclopaedia of Modern Agriculture,
London. St Hilaire, 1861 : Acclimation et domestication des animaux
utiles, Paris. Torney and Lawry, 1920 : Animal Husbandry, New York.
Vaughan, 1923 : Types and Market Classes of Livestock, Columbus, Ohio.
Voogt, 1907 : Our Domestic Animals, Boston. Wadell, 1911 : Herds and
Flocks and Horses, Chicago. Wallace and Watson, 1923 : Farm Livestock
of Great Britain, Edinburgh. Wilcox, 1906 : Farm Animals, New York.
Wilcox and Smith, 1920: The American Encyclopaedia of Livestock, New
York. Wilson, 1912 : The Principles of Stock Breeding, London. Winters,
1925 : Animal Breeding, New York. Wood and Marshall, 1920 : The
Physiology of Farm Animals, Cambridge University Press. Wright, 1920 :
Principles of Livestock Breeding, U.S. Dept. Agric, Bull. 905.

Periodicals. — American Horse Breeder, Boston and New York ; American
Poultry Advocate, Syracuse, N. Y. ; American Sheep Breeder and Wool-grower,
Chicago ; Breeder's Gazette, Chicago ; Bulletin de la Societe Nationale
d' Acclimation de France, Paris; Canadian National Livestock Records, Ottawa;
Dominion of Canada, Department of Agriculture, Livestock Branch Bulletins
and Poultry Division Reports ; Dairy Farmer, Des Moines, Iowa ; Dairy
Farmer, Hamilton, New Zealand ; Dairy World and British Farmer, London ;
Deutsche Landwirtschaftliche Tierzucht, Hannover ; Duroc Bulletin and Live-
stock Farmer, Des Moines, Illinois ; Farmer and Stock-breeder, London ;
Farmer's Express, London ; Feathered World, London ; Holstein Friesian
World, Syracuse, N.Y. ; Horse Review, Chicago ; India, Memoirs of the
Department of Agriculture, Veterinary Series, Calcutta ; Jahrbuch fur Wissen-
schaftliche und Praktische Tierzucht, Hannover ; Journal of Dairying in
India, Calcutta ; Journal of Genetics, London ; Meat Trades Journal, London ;
National Poultry Journal, London ; Poultry, London ; Pastoral Review,
Sydney, Melbourne, and London ; Poultry Science, Urbana, Illinois ; Revue
Internationale de Genetique, Paris ; Swine World, Des Moines, Iowa ; United
States Department of Agriculture, Bureau of Animal Husbandry, Bulletins,
Washington, D.C. ; Utility Poultry Journal, Newport, Salop, England ;
Veterinary Journal, London ; Veterinary Review, London and Edinburgh ;
Wiener Tierarztliche Monatsschrift, Vienna ; Zeitschrift fur Fleisch und Milch
Hygiene, Berlin; Zeitschrift fur Gestiitkunde und Pferdezucht, Berlin.

HORSES

Barton, 1912 : Horses and Practical Horse-keeping, New York. Biddell
and Others, 1898 : Heavy Horses, London. Blew and Others, 1904 : Light

BIBLIOGRAPHY 405

Horses, London. Busby, 1904 : The Trotting and the Pacing Horse in
America, New York. Carter, 1923 : The Story of the Horse, National
Geographic Magazine, 44. Douglas, 1913 : The Shetland Pony, Edinburgh.
Hayes, 1922 : The Points of the Horse, London. Johnstone, 1908 : The
Horse Book, Chicago. Jones, 1908 : The Surgical Anatomy of the Horse,
London. Loomis, 1926 : The Evolution of the Horse, New York. Lydekker,
1912 : The Horse and its Relatives, New York. Merwtn, 1917 : The Horse,
Chicago. Meysey-Thompson, 1911: The Horse, Chicago. Osborne, 1913:
The Wild Equines of the Zoological Park. Bulletin New York Zoological Society.
Ridgeway, 1905 : The Origin and Influence of the Thoroughbred Horse,
Cambridge University Press. Sanders and Dinsmore, 1917 : A History of
the Percheron Horse, Chicago. Speed, 1905 : The Horse in America, New
York. Trevathan, 1905 : The American Thoroughbred, New York.

CATTLE, SHEEP, AND PIGS

Allen, 1875 : American Cattle, New York. Bruce, 1907 : Fifty Years
Among Shorthorns, London. Coborn, 1909 : Swine in America, New York.
Coffey, 1918 : Productive Sheep Husbandry, Philadelphia. Craig, 1913 :
Sheep Farming in North America, New York. Dawson, 1911 : The Hog
Book, Chicago. Day, 1910 : Productive Swine Husbandry, Philadelphia.
Dietrich, 1910 : Swine Breeding, Feeding, and Management, Chicago.
Doane, 1912 : Sheep Feeding and Farm Management, New York. Eckles,
1923 : Dairy Cattle and Milk Production, New York. Gowen, 1925 : The
Manual of Dairy Cattle Breeding, Baltimore. Hazleton, 1925 : History
and Handbook of Hereford Cattle, Kansas City, Mo. Housman, 1908 : Cattle,
Breeds and Management, London. Johnson, 1925 : Relation of Sheep to
Climate, Jour. Agric. Res., Washington. Kleinheinz, 1918 : Sheep Manage-
ment, Breeds, and Judging, Madison, Wisconsin. Kraemar, 1925 : Das
Schonste Rind, Berlin. Leighton and Loudon, 1910 : The Meat Industry
and Meat Production, London. Lydekker, 1912 : The Ox and its Kindred,
London ; 1912 : The Sheep and its Cousins, London. Mackenzie, 1919 :
Cattle and the Future of Beef Production in England, Cambridge University
Press. Pulling, 1908 : Aberdeen Angus Cattle, London. Richards, 1921 :
Modern Milch Goats, Philadelphia. Russell, 1925 : Swine Production,
U.S. Dept. Agric, Farmer's Bull. 1437. Sanders, 1914 : The Story of the
Hereford, Chicago ; 1916 : Shorthorn Cattle, Chicago. Spencer, 1908 :
Sheep Husbandry in Canada, Ministry of Agriculture, Dominion of Canada,
Bull. 12, Ottawa ; 1915 : Beef Raising in Canada, Ottawa. Spencer, 1910 :
Pigs, Breeds and Management, London ; Storer, The Wild White Cattle of
Great Britain, London. Wagenen, 1922 : The Cow, New York. Wing,
1907 : Sheep Farming in America, Chicago. Wrightson, 1908 : Sheep
Breeds and Management, London. Yapp and Nevens, 1926 : Dairy Cattle,
New York.

DOMESTICATED BIRDS

Beebe, 1918 : A Monograph of the Pheasants, London. Bradley, 1915 :
The Structure of the Fowl, London. Brown, 1906 : Races of Domestic Poultry,
London. Kaupp, 1922 : Poultry Diseases, London. Lamon and Slocum,
1920 : The Mating and Breeding of Poultry, New York ; 1922 : Ducks and
Geese, New York. Lewis, 1919 : Poultry-keeping, Philadelphia. Lippin-
cott, 1916: Poultry Production, Philadelphia. Lovat and Others, 1911:
The Grouse in Health and Disease, London. M'Atee, 1927 : The Propagation
of Game-birds, U.S. Dept. Agric, Farmer's Bull. 1521. Pearl, Surface, and

406 THE PRINCIPLES OF APPLIED ZOOLOGY

Maynie, 1915 : The Diseases of Poultry, New York. Punnett, 1923 :
Heredity in Poultry, London. Rice and Botsford, 1925 : Practical Poultry
Management, New York. Roberts, 1923 : Commercial Poultry Raising,
London. Robinson, 1912 : Principles and Practice of Poultry Culture, New
York ; 1913 : Domestic Birds, New York. Theobald, 1896 : Parasitic
Diseases of Poultry, London. Watson, 1914 : Farm Poultry, New York.
Ward and Gallagher, 1926 : Diseases of Domesticated Birds, New York.

OTHER DOMESTICATED ANIMALS

Ditmars, 1916 : Deer for Parks and Preserves, Bulletin New York Zoological
Society. Had wen and Palmer, 1922 : Reindeer in Alaska, U.S. Dept. Agric,
Farmer's Bull. 1589. Lantz, 1908 : Deer Farming in the United States, U.S.
Dept. Agric, Farmer's Bull. 330 ; 1910 : Raising Deer and other Large Game
Animals in the United States, U.S. Dept. Agric, Bull. 423. Palmer, 1926 :
Progress of Reindeer Grazing Investigations in Alaska, U.S. Dept. Agric.
Biol. Survey, Bull. 36. Speelman and Williams, 1926: Breeds of Dogs,
U.S. Dept. Agric, Farmer's Bull. 1491. Stevenson Hamilton, 1911 : Animal
Life in Africa, London. Townsend, 1922 : The Domesticated Reindeer in
Alaska, New York Zoological Society Bulletin.

BEE-KEEPING

Anderson, 1923 : Isle of Wight Disease in Hive Bees, Scott. Jour. Agric,
vi. Betts, 1923 : Practical Bee Anatomy, Oxford. Buttel-Reepen, 1906 :
Leben und Wesen der Bienen, Braunschweig. Cheshire, 1886 : Bees and
Bee-keeping, London. Dad ant, 1919 : Outapiaries and their Management,
Hamilton, Illinois. Edwardes, 1911 : The Lore of the Honey-bee, New York.
Ellinger, 1923 : Die Erkrankungen der Honigbiene, in Ludwig, ' Unsere
Bienen." Ghosh, 1915 : Bee-keeping, Agric. Res. Inst. Pusa, Bull. 46,
Calcutta. Hewitt, 1912 : The Honey Bee, Dept. Agric. Canada Div. Ent.,
Bull. 2, Ottawa. King, 1918 : The Production of Honey, Sudan Ent. Service,
Bull. 11, Khartoum. Langstroth and Dad ant, 1922 : The Honey Bee,
Hamilton, 111. Ludwig, 1923 : Unsere Bienen, Berlin. Lyon, 1910 : How
to Keep Bees for Profit, New York. Lubbock, 1917 : Ants, Bees,
and Wasps, New York. Mace, 1927: Modern Bee-keeping, London.
Maeterlinck, 1917 : The Life of the Bee, Trans, by Sutro, New York.
M'Cray and White, 1918 : The Diagnosis of Bee Diseases by Laboratory
Methods, U.S. Dept. Agric, Bull. 671. Nelson, 1915: The Embryology
of the Honey Bee, Princeton University Press. Otanes, 1926 : Honey
Bees and How to Rear Them, Philippine Agric. Rev., xix., Manila.
Pellett, 1916 : Productive Bee-keeping, Philadelphia ; 1923 : American
Honey Plants, Hamilton, 111. Phillips, 1910 : Bees, U.S. Dept. Agric,
Farmer's Bull. 397 ; 1911 : The Treatment of Bee Diseases, Ibid., 442 ; 1915 :
Bee-keeping, New York ; 1922, 1923 : The Occurrence of Diseases of Adult
Bees, U.S. Dept. Agric, Circs. 218, 287. Rennie, 1921 : Isle of Wight Disease
in Hive Bees : Acarine Disease ; (4) The Organism Associated with the
Disease, Tarsonemus woodi n. sp., Trans. Roy. Soc Edinburgh, v. ; 1923 :
Acarine Disease Explained, Bee Disease Investigation Memoir 6, North of
Scotland College of Agric. ; 1924 : The Control of Acarine Disease, Oxford.
Rennie, Bruce, and Harvey, 1921 : Isle of Wight Disease in Hive Bees ;
(1) The ^Etiology of the Disease, Trans. Roy. Soc. Edinburgh, v. Root,
1923 : A.B.C. and X.Y.Z. of Bee-keeping, Medina, Ohio. Sladen, 1912 :
The Humble Bee, London. Snodgrass, 1925 : The Anatomy and Physiology

BIBLIOGRAPHY 407

of the Honey Bee, New York. Sturges, 1926 : The Present Position regard-
ing Adult Bee Diseases in Great Britain, Bee World, viii. ; 1924: Practical
Bee-keeping, London. Sturtevant, 1920 : A Study of the Behaviour of Bees
in Colonies affected by European Foul Brood, U.S. Dept. Agric, Bull. 804.
White, 1912 : The Causes of European Foul Brood, U.S. Dept. Agric, Girc.
157; 1917: Sac Brood, U.S. Dept. Agric, Bull. 431. White, 1921 : Isle of
Wight Disease in Hive Bees ; (2) The Pathology of Isle of Wight Disease in
Hive Bees, Trans. Roy. Soc Edinburgh, v. Zander, 1919-23 : Handbuch der
Bienenkunde, Stuttgart.

Periodicals. — Archiv. fur Bienenkunde, Leipzig ; American Bee Journal,
Hamilton, Illinois ; British Bee Journal, London ; Bee World, Oxford ;
British Bee-keeping, London ; Dominion of Canada, Department of
Agriculture, Bee Division Reports, Ottawa ; Gleanings in Bee Culture, Medina,
Ohio ; Schweizerische Bienen Zeitung, Aarau, Switzerland.

SILK AND LAC CULTURE

Silk

Banks, 1911 : A Manual of Philippine Silk Culture, Entom. Sect. Biol. Lab.
Bur. Sci., Manila. Dudgeon, 1908 : Silk-producing Insects of West Africa,
Nature, lxxix., London. Fabre, 1923 : La sericiculture au Cambodge, Bull.
Econ. Indo-chine, xxvi., Hanoi-Haiphong. Howard and Buswell, 1925 :
A Survey of the Silk Industry of South China, Bull. 12, Dept. Sericiculture,
Ling Nan Agric. Coll., Canton. Jamieson, 1922 : Report on the Diseases of
Silkworms in India, Calcutta. Kellogg, 1908 : Inheritance in Silkworms,
Leland Stanford Junior Univ. Publications, Univ. Ser. 1. Lefroy and Ghosh,
1908 : Eri Silk, Mem. Dept. Agric. India, Pusa. Lefroy, 1912 : A Possible
New Industry for the West Indies, West Ind. Comm., Pamphlet No. 16, London.
Watson, 1908: The Wild Silk Moths of the World, Manchester. Watt,
1908 : Commercial Products of India, London.

Periodicals. — The American Silk Journal, New York ; Bulletin de
l'Association Sericicole du Japon, Tokyo ; Bulletin of the Imperial Sericicultural
Experimental Station, Tokyo ; Bulletin of the Imperial Sericicultural College,
Tokyo.

Lac

Chamberlin, 1923 : A Systematic Monograph of the Tachardinae or Lac
Insects, Bull. Ent. Res., xiv. ; Imms and Chatterjee, 1915 : The Structure and
Biology of Tachardia Lacca, Indian Forest, Memoirs, Vol. iii., Calcutta.
Mahdihassan, 1923 : Classification of Lac Insects from a Physiological Stand-
point, Jour. Sci. Ass. Maharajah College, Vizianagaram ; 1923 : Observations
on the Life-Cycles of South Indian Lac Insects, Indian Forester, xlix.,
Allahabad ; 1924 : Statics of Lac Production, Jour. Sc. Ass. Maharajah's
College, Vizianagaram. Srintvasayya, 1924 : The Fundamentals of Intensive
Lac Production, Ibid.

FISHERIES

Adams, 1906 : Mussel Fishing and the Pearl Button Industry, Journal of
Conchology, ii. Aflalo, 1904 : The Sea Fishing Industry of England and
Wales, London. Armistead, 1908 : Trout Waters : Management and
Angling, London. Atkins and Others, A Manual of Fish Culture, U.S.
Commission of Fish and Fisheries, Washington. Baievsky, 1926 : Fisheries
of Siberia, U.S. Dept. Commerce, Bur. Fish., Doc. 1006. Borley and Russell,
1922 : Report on Herring Trawling, Fishery Investigations, Minist. Agric and

408 THE PRINCIPLES OF APPLIED ZOOLOGY

Fisheries, London. Boulenger, 1916 : Catalogue of the Fresh-water Fishes
of Africa in the British Museum (Natural History), London. Bower, 1926 :
Alaska Fishery and Fur Seal Industries in 1925, U.S. Dept. Commerce, Bur.
Fish., Doc. 1008. Calderwood, 1908 : Life of the Salmon, London. Clark
and Almy, 1918 : The Commercial Freezing and Storing of Fish, U.S. Dept.
Agric, Bull. 635. Cobb, 1921 : Pacific Salmon Fisheries, U.S. Dept.
Commerce, Bur. Fish., Doc. 902 ; 1927 : Pacific Cod Fisheries, Ibid.,
Document 1014. Cunningham, 1896 : The Natural History of the Marketable
Marine Fishes of the British Islands, London. Dahl, 1909 : The Scales of
the Herring as a means of Determining Age, Growth, and Migration, Norwegian
Fish. Investigations; 1911 : The Age and Growth of Salmon and Trout in
Norway as shown by their Scales, London. Damas, 1909 : Contribution a la
biologie des Gadides, Rapports Conseil Berm. Internat. Exp. Mer. Dean,
1895 : Fishes : Living and Fossil, New York ; 1923 : A Bibliography of Fishes,
New York. Ehrenbaum, 1912, 1914, 1923 : The Mackerel and the Mackerel
Fishery, Rapports et Proces Verbal du Conseil Permanent Internationale pour
V Exploration du Mer, Copenhagen. Fearnow, 1925 : Goldfish, U.S. Dept.
Commerce, Bur. Fish., Doc. 980. Ford, 1920 : The Economic Value of
the Dog-fish, Fish Trades Gazette, London. Fowler, 1912 : The Science of
the Sea, London. Gardiner, 1923 : The Application of Science to the
Fishing Industry, Cambridge University Press. Garstang, 1900 : The Im-
poverishment of the Sea, Jour. Marine Biol. Ass., Plymouth. Gibbs, 1922 :
The Fishing Industry, London. Grassi, 1913 : Metamorphose der Murse-
noiden, Jena. Green, 1918 : Fisheries of the North Sea, London. Guenaux,
1909 : Pisciculture, Paris. Hardy, 1924 : The Herring in relation to its
Inanimate Environment, Fishery Investigations, Minist. Agric. and Fish.,
London. Herdman, 1914-18 : An Intensive Study of the Marine Plankton,
Reports, Lancashire Sea Fish. Lab. ; Spolia Runiana, iii. ; Jour. Linn.
Soc, London ; 1907 : Report on the Pearl Oyster Fisheries of the Gulf of
Manaar, 1903-06, Proc. Roy. Soc, London. Herubel, 1912 : Sea Fisheries,
London. Higgins and Holmes, 1921 : Methods of Sardine Fishing in Southern
California, California Fish and Game, Sardine Number VII., No. 4. Hilde-
brand and Hansel, 1926 : Diamond Back Terrapin Culture at Beaufort,
N.C., U.S. Dept. Commerce, Bur. Fish. Econ., Circ. 60. Hjort, 1908-10 :
Reports regarding the Herring, Cons. perm, internat. explor. de la mer ; 1909 :
Review of the Norwegian Fishery and Marine Investigations, 1900-08, Rept. on
Norweg. Fish, and Marine Investigations, Vol. ii. ; 1908 : Some Results of the
International Ocean Researches, Publication, Scott. Oceanogr. Lab., Edinburgh ;
1914 : Fluctuations of the Great Fisheries of Northern Europe, viewed in the
Light of Biological Research, Rapport et Proces Verbale, xx., Con. Perm.
Internat. Explor. Mer, Copenhagen. Hofer, 1914 : Handbuch der Fisch-
krankheiten, Munich. Holder, 1913 : The Game Fishes of the World,
London and New York. Horton, 1926 : The American Slipper Limpet,
Nature, London. Howell, 1926 : Ocean Research and the Great Fisheries,
London. Issel, 1918 : Biologia Marina, Milano. Jamieson, 1912 : An
Examination of the Causes which have Led to the Failure of the Biological
Work recently undertaken on the Ceylon Pearl Fisheries, Jour. Econ. Biol.,
vii. ; 1912 : Studies on Pearl Oysters and Pearls, Proc. Zool. Soc, London.
Jenkins, 1920 : The Sea Fisheries, London ; 1921 : A Textbook of Oceano-
graphy, London ; 1925 : The Fishes of the British Isles, both Fresh Water
and Salt, London ; 1927 : The Herring and the Herring Fisheries, London.
Johansen, 1924 : On the Summer and Autumn Spawning Herrings of the
North Sea, Meddelelser fra Kommissionen for Havu under sogelser, Serie
Fisherei, Band, vii., Kobenhavn. Johnstone, 1905: British Fisheries,

BIBLIOGRAPHY 409

London; 1906-12: Internal Parasites and Diseased Conditions of Fishes,
Reports, Lancashire Sea Fish. Lab., 1905 ; Trans. Liverpool Biol. Soc, xx. ;
1912 : Life in the Sea, Cambridge University Press ; 1918 : The Dietic Value
of the Herring, Reports, Lancashire Sea Fish. Lab., Liverpool; 1924 : Malignant
Tumours in Fishes, Jour. Mar. Biol. Ass., Plymouth. Johnson and Staple-
ton, 1921 : Fish Ponds on Farms, U.S. Dept. Commerce, Bur. Fish., Doc. 826.
Jordan, 1902 : American Food and Game Fishes, New York ; 1925 : Fishes,
New York. Kellogg, 1910 : Shellfish Industries, New York. Koelz,
1926 : Fishing Industries of the Great Lakes, U.S. Dept. Commerce, Bur.
Fish., Doc. 1001. Kyle, 1921: The Asymmetry, Metamorphosis, and Origin
of Flat-fishes, Phil. Trans. Roy. Soc, London ; 1926 : The Biology of Fishes,
London and New York. La Gorce, 1923 : Fish and Fisheries of our North
Atlantic Seaboard, Nat. Geog. Mag., xliv. Leach, 1919 : The Artificial Propa-
gation of Carp, U.S. Dept. Commerce, Bur. Fish., Doc. 39 ; 1923 : Artificial
Propagation of Brook Trout and Rainbow Trout, Ibid., 955 ; 1923 : Artificial
Propagation of White-fish, Grayling, and Lake Trout, Ibid., 949 ; 1926 : Co-
operative Fish Culture, Ibid., Econ. Circ. 59 ; 1927 : Artificial Propagation of
Pike, Perch, Yellow Perch, and Pikes, Ibid., Econ. Circ. 1018. Lebour, 1921 :
The Food of Young Clupeoids, Jour. Mar. Biol. Ass., Plymouth ; 1924 : The
Food of Young Herrings, Ibid. Lee, 1912 : An Investigation into the Methods
of Growth Determination in Fishes, Cons. Perm. Internal. Explor. Mer. Pub.
de Circ. 63 ; 1920 : A Review of the Method of Age and Growth Determination
in Fishes by Means of the Scales, Fishery Investigations, Pub. 4, Minist. Agric.
and Fish. Great Britain, London. Le Danois, 1924 : Les Conditions de la Peche
a la Morue sur les Blancs de Terre Neuve, Notes et Memoires, 35 ; Off. Sci. et
Tech. des Peches maritimes, Paris. Le Danois and Belloc, 1923 : Recherches
sur la Regime des Eaux Atlantiques et sur la Biologie des Poissons comestibles,
Ibid., 34. Malloch, 1910 : Life History and Habits of the Salmon, Sea
Trout, Trout, and other Fresh- water Fish, London. Malpas, 1924 : The
Fishing Industries, Ceylon Handbook, Brit. Empire Exhibition, London.
Matsubara, 1908 : Goldfish and their Culture in Japan, Proc. 4&h Internal.
Congress, Washington. M'Farland, 1911 : A History of the New England
Fisheries, University of Pennsylvania Press. MacFarlane, 1923 : Evolution
and Distribution of Fishes, New York. M'Intosh, 1899 : Resources of the
Sea, London. MTntosh and Masterman, 1897 : The Life Histories of the
British Marine Food Fishes, London. Meek, 1916 : The Migrations of Fishes,
London. Mellen, 1923 : The White-fishes, Zoologica, New York. Mitsukuri,
1905 : The Cultivation of Marine and Fresh- water Animals in Japan, U.S.
Dept. Commerce, Bur. Fish. Bull. Moore, 1923 : Diseases of Fish in
State Hatcheries, 12^ Ann. Rept. N. York Conservation Commission for 1922,
Albany. Murray and Hjort, 1912 : The Depths of the Ocean, London.
Nicholson, 1907 : Notes on Some Fisheries in Japan, Madras. Osborn,
1914 : The Increased Utilisation of Carp, Bulletin New York Zoological Society.
Petersen, 1918 : The Sea Bottom and its Production of Fish Food, Rep.
Danske Biol. Sta. Plehn, 1924 : Praktikum der Fischkrankheiten, Stuttgart.
Prince, 1924: The Fisheries of Canada, Handbook of Canada, Toronto Uni-
versity Press. Prypterch, 1924 : The Ichthyophthirius Disease of Fishes
and Methods of Control, U.S. Dept. Commerce, Bur. Fish., Doc. 959.
Regan, 1911: Fresh- water Fishes of the British Isles, London; 1916:
The British Fishes of the Sub-family Clupeinse and Related Species in
other Seas, Ann. Mag. Nat. Hist., xviii. Rotjle, 1914: Traite de la
Pisciculture et des Peches, Paris. Samuel, 1918 : The Herring, London.
Schmidt, 1909 : The Distribution of the Fresh-water Eels (Anguillula)
Throughout the World, I. Atlantic Ocean and Adjacent Regions, Copenhagen ;

410 THE PRINCIPLES OF APPLIED ZOOLOGY

1914-22 : Various Papers concerning Breeding Grounds of Fresh-water
Eels, in Publications of Conseil permanent international pour V exploration de
la Trier, Copenhagen ; Meddelelser fra Kommissionen for Havundersogelser,
Kobnhavn ; Philosophical Transactions Royal Society, London. Schofield,
1924 : The Lampara Net, California Fish and Game, x. Seite, 1926 : Fishing
Industries of the United States in 1925, U.S. Dept. Commerce, Bur. Fish., Doc.
1010. Smith, 1919 : The World's Food Resources, London. Southwell,
1906-12 : Reports on the Ceylon Pearl Oyster, in Ceylon Marine Biol. Repts. ;
Spolia Zeylandica ; 1913 : Brief Review of the Scientific Work done on the
Ceylon Pearl Banks since the Year 1902, Jour. Econ. Biol., viii. Supino,
1917 : Piscicoltura Pratica : Legislazione sulla Pesca d'Acqua Dolce, Milano ;
1926 : L'Acquario Manutenzione Funzionamento, Milano. Taylor, 1925 :
Pearl Essence : Its History, Chemistry, and Technology, U.S. Dept. Commerce,
Bur. Fish., Doc. 989. Thompson, 1919 : The Conservation of our Fisheries,
California Fish and Game, Vol. v. ; 1926 : The California Sardine, Bulletin 11,
Fish and Game Commission California, Sacramento. Tressler, 1923 :
Marine Products of Commerce, New York. Veratti, 1926 : Acque dolci
incolti Carpicoltura e Trutticoltura, Memoria No. 1, Ministero delV Economie
Nazionale, Rome. Weymouth, 1921 : The Edible Clams, Mussels, and
Scallops of California, Bull. 4, Fish and Game Commission California, Sacra-
mento. Wolf, 1908 : Goldfish Breeds and other Aquarium Fishes, Phila-
delphia.

Periodicals. — Annual Reports of the Fishery Board for Scotland,
Edinburgh ; Annual Reports and Reports on Fishery Investigations of the
Ministry of Agriculture and Fisheries, Great Britain ; Bulletins, Circulars, and
Documents of the Bureau of Fisheries, United States Department of Commerce,
Washington, D.C. ; California Fish and Game, Sacramento ; Canadian Fisher-
man, Gardenvale, Quebec ; Contributions to Canadian Biology, Ottawa ;
Fauna und Flora des Golfes von Neapels ; Fish Trades Gazette, London ;
Fish and Game Commission of California, Biennial Reports, Sacramento ;
Journal of the Marine Biological Association, Plymouth ; Lancashire Sea
Fisheries, Laboratory Reports, Liverpool ; Lancashire Marine Biological
Committee, Reports and Monographs, Liverpool ; Madras Dept. of Fisheries,
Bulletins, Madras ; Mitteilungen aus der Zoologischen Station zu Neapel ;
Oregon Fish and Game Commission, Bulletins, Salem ; Rapports et Proces
Verbaux des Reunions du Conseil permanent international pour 1' exploration
de la mer, Copenhagen ; Reports on Fisheries, Department of Trade and
Commerce, Australia ; Reports of the Fishery Branch of the Department of
Agriculture and Technical Instruction for Ireland, Dublin ; Svenska Hydro-
grafisk Biologiska Kommissionens, Skrifter, Stockholm.

WHALING AND SEALING

Allen, 1916 : The Whalebone Whales of New England, New York.
Andrews, 1916 : Whale Hunting with Book and Camera, New York. Bear-
park, 1921 : The Whaling Industry, The Statist, xcviii., London. Beddard,
1900 : A Book of Whales, London. Bower, 1926 : Alaska Fishery and Fur
Seal Industries in 1902, 1925, U.S. Dept. Commerce, Bur. Fish., Doc. 1008.
Chatterton, 1925: Whalers and Whaling, London. Fishery Board of
Scotland, 1920 : Report of Committee appointed to Inquire into the
Scottish Whaling Industry, Edinburgh. Hawes, 1924: Whaling, London.
Jenkins, 1921 : A History of the Whale Fisheries, London. Lydekker,
1909: Guide to the Whales, Porpoises, and Dolphins, Brit. Mus. Nat.
Hist., London. Morley and Hodgson, 1927: Whaling North and South,

BIBLIOGRAPHY 411

London. Murdoch, 1917: Modern Whaling and Bear Hunting, London.
Murphy, 1923 : The Extinction of Sea Mammals, Natural History, Jour.
Amer. Mus. Nat. Hist., New York. Report of Interdepartmental Com-
mittee on Research and Development in the Dependencies of the Falkland
Islands ; 1920 : H.M . Stationery Office, London. Salvesen, 1914 : The
Whaling Fisheries of the Falkland Islands and Dependencies, Scottish
Nat. Antarctic Exped. Rept., Edinburgh ; 1912 : The Whaling Industry of
To-day, Jour. Roy. Soc. Arts, lx., London. Tower, 1907 : A History of the
American Whale Fishery, Univ. Pennsylvania Series in Economics and Public
Law, No. 20, Philadelphia. Townsend, 1899 : The Fur Seals and Fur Seal
Islands of the North Pacific Ocean ; 1912 : The Northern Elephant Seal,
Zoologica, New York ; 1924 : The Northern Elephant Seal and the Guada-
loupe Fur Seal, Natural History, Jour. Amer. Mus. Nat. Hist., New York.
Tressler, 1918 : Sea Lions and the Fishing Industries, Bull. New York Zool.
Soc. Verrill, 1916 : The Real Story of the Whaler, New York.

THE FUR TRADE

Allen and M'Clure, 1926 : The Theory and Practice of Fox Ranching,
Charlottestown, P.E.I., Canada. Arnold, 1921 : Trapping, Guildford, Me.
Ashbrook, 1923: Silver Fox Farming, U.S. Dept. Agric, Bull. 1151; 1926:
Fur Laws for the Season 1926-27, U.S. Dept., Farmer's Bull., 1515. Ashbrook
and Walker, 1925 : Blue Fox Farming in Alaska, U.S. Dept. Agric, Bull.
1350. Austin, 1922 : The Principles and Practice of Fur Dressing and Fur
Dyeing, London. Bailey, 1922 : Beaver Habits, Beaver Control, and Pos-
sibilities in Beaver Farming, U.S. Dept. Agric, Bull. 1078. Coues, 1877 : Fur-
bearing Animals : A Monograph of the North American Mustelidse, Govt.
Printing Office, Washington. Davies, 1918 : Rabbits for Fur and Flesh,
London. Dearborn, 1917 : The Domesticated Silver Fox, U.S. Dept. Agric,
Farmer's Bull. 795 ; 1920 : Rabbit Raising, Ibid., 1090 ; 1920 : The Mainten-
ance of the Fur Supply, Ibid., Circular 135. Dugmore, 1918 : The Romance of
the Beaver, London. Edwards, 1912 : Fur Farming for Profit, New York ;
1925 : Raccoon Raising, Utica, N.Y. Gibson, 1917 : Breeding and Care of
Rabbits, Detroit. Green, 1927 : Rabbit Skins for Fur, U.S. Dept. Agric,
Farmer's Bull., 1519. Harding, 1909 : Fur Farming, Columbus, Ohio.
Hewitt, 1921 : The Conservation of the Wild Life of Canada, New York.
Hodgson, 1924 : Raising Beavers for Profit ; 1925 : Successful Musk-rat
Raising ; 1925 : Fur Farming, the Weasel Family, Oshawa, Canada. Hol-
brook, 1915 : Skunk Culture for Profit, Chicago. Hollister, 1911 : A
Systematic Synopsis of the Musk-rats, U.S. Dept. Agric. Bur. Biol. Surv.
North American Fauna, No. 32. Hornaday, 1921 : The Fur Trade and the
Wild Animals, Bull. Zool. Soc, New York. Hunter, 1920 : Some Problems
of the Fox-raising Industry, Ottawa. Jones, 1914 : Fur Farming in Canada,
Ottawa ; 1914 : Second Report, Commission of Conservation Committee on
Fisheries, Game, and Fur-bearing Animals, Ottawa. Keast, 1925 : Fur
Farming, University of Toronto, Dept. Univ. Extension, Toronto. Kreps,
1909 : The Science of Trapping, Columbus, Ohio. Lantz, 1914 : Economic
Value of North American Skunks, U.S. Dept. Agric, Farmer's Bull. 587 ;
1917: The Musk-rat as a Fur Bearer, Ibid., 869. Laut, 1921: The Fur
Trade of North America, New York. Macfarlane, 1905 : Mammals of the
North- West Territories, New York. M'Dougal, 1926 : The Angora Rabbit,
London. Parker, 1923 : Northern Crusoes Island (Fox Farming), Nat.
Geog. Mag., xliv. Patton, 1925 : Raising Fur-bearing Animals, Chicago.
Preble, 1908 : A Biological Investigation of the Athabasca Mackenzie Region,

412 THE PRINCIPLES OF APPLIED ZOOLOGY

U.S. Dept. Agric. Biol. Surv. North American Fauna, No. 27. Ritchie,
1925: Biology and the Fur Trade, Nature, cxvi., London. Robinson and
Others, 1926 : Principles of Fur Farming, Kansas City, Mo. Rosenberg,
1921 : Furs and Furriery, London. Roth and Cornman, 1916 : Rabbit and
Cavy Culture, Sellersville, Pennsylvania. Sachs, 1922 : Furs and the Fur
Trade, London. Scheffer, 1917 : Trapping Moles, U.S. Dept. Agric, Farmer's
Bull. 832 ; 1922 : American Moles as Agricultural Pests and as Fur Producers,
Ibid., 1247. Seton, 1909 : Life Histories of Northern Mammals : An Account
of the Mammals of Manitoba, London. Smith, 1921 : Food Requirements of
the Ranch Fox, Privy Council Sci. Industr. Res., Ottawa. Tufford, 1926 :
Ranch Construction, American Fox and Fur Farmer, Minneapolis, Minn.
Washburn, 1920 : The Rabbit Book, Philadelphia. Anonymous, The Fur
Trade in Canada, Handbook of Canada, Toronto University Press. Anonymous,
Standard of Perfection for Rabbits, Cavies, Mice, Rats, Skin, and Fur-bearing
Animals, National Breeders and Fanciers Association of America, Cleveland,
Ohio.

Periodicals. — American Breeders' Review, New York ; American Fox
and Fur Farmer, Minneapolis ; Black Fox Magazine, New York ; Bulletin
of the American Game Protective Association, New York ; Canada, Dominion
Bureau of Statistics, Fur Branch, Annual Reports, Ottawa ; Food, Fur, and
Fancy, Chicago ; Fur Journal, New York ; Fur Trade Review, New York ;
Fur Trade Journal, Toronto ; Fur Animals, Kansas City, Mo. ; Game Breeder,
New York ; Journal National Poultry Institute, Newport, Salop, England ;
National Association of the Fur Industry, Year-books, New York ; Outdoor
Enterprises, Kansas City, Mo.

ANIMAL CONSERVATION

Chase, 1913 : Game Protection and Propagation in America, Philadelphia.
Christy, 1924 : Big Game and Pygmies, London. Davis, 1925 : The,
Relation of Animal Pest Control to Conservation, Proc. Indiana Acad.
Sci., Vol. 34. Denmead and Earnshaw, 1926 : Game Laws for the
Season 1926-27, U.S. Dept. Agric, Farmer's Bull. 1515. Donne, 1924 : The
Game Animals of New Zealand, London. Dugmore, 1913 : The Romance
of the Newfoundland Caribou, London. Faunthorpe, 1924 : The Dis-
appearance of the Wild Life of India, Jour. Amer. Mus. Nat. Hist., xxiv., New
York. Fisher, 1908 : The Economic Value of Predaceous Birds and
Mammals, Year-book, U.S. Dept. Agric. Fitzsimons, 1919 : The Natural
History of South Africa, London. Goldman, 1920 : Conserving our Wild
Animals and Birds, Year-book, U.S. Dept. Agric Grinnell and Sheldon
(Editors), 1925 : Hunting and Conservation, Yale University Press, New
Haven, Conn. Gunn (Editor), 1926 : Empire Big Game, London. Gutsell,
1921 : Danger to Fisheries from Oil and Tar Pollution of Waters, U.S. Dept.
Commerce, Bur. Fish., Doc. 1910, Haagner, 1921 : Vanishing South
African Game, Bull. New York Zool. Soc Hewitt, 1921 : The Conservation
of Wild Life in Canada, New York. Holder, 1913 : The Game Fishes of the
World, London. Horn ad ay, 1913 : Our Vanishing Wild Life, Yale University
Press ; 1914 : Wild Life Conservation in Theory and Practice, New York.
Johnstone, 1907 : Big Game Preservation, Nature, lxxvi., London. Lane
and Others, Effect of Oil Pollution on Marine and Wild Life, U.S. Dept. Com-
merce, Bur. Fish., Doc 995. Lang, 1924 : The Vanishing Wild Life of
Africa, Jour. Amer. Mus. Nat. Hist., xxiv. Le Souef, 1924 : The Vanishing
Wild Life of Australia, Ibid. Lucas and Le Souef, 1909: The Animals
of Australia, Melbourne. Lydekker, 1926 : The Game Animals of Africa,

BIBLIOGRAPHY 413

London. Merriman, 1926 : The Bison and the Fur Trade, Queen's Univer-
sity, Kingston, Ontario, Dept. History, Bull. 53. Nelson, 1925 : The
Status of the Prong-horned Antelope in 1922-24, U.S. Dept. Agric, Bull. 1346.
Palmer, 1922 : Game as a National Resource, Ibid., 1049. Shelford, 1912 :
Chronology and Index of the More Important Events in American Game
Protection, 1776-1911, U.S. Dept. Agric. Biol. Survey Bull. 41 ; 1918 : Ways
and Means of Measuring the Dangers of Pollution to Fisheries, Illinois
Nat. Hist. Surv. Bull., Vol. xiii., Urbana, 111. ; 1920 : Preserves of Natural
Conditions, Trans. Illinois State Acad. Science, xiii. St Clair Thompson,
1928: The Protection of Woodlands, London. Stevenson Hamilton,
1911: Animal Life in Africa, London. Swynnerton, 1924: Reports on
Control of Elephants in Uganda, Uganda Govt. Press. Ward, 1919 : Stream
Pollution in New York State, State of New York Conservation Commission,
Albany, N.Y.

Periodicals. — American Museum Journal, New York ; Bulletin of the
American Game Protective Association, New York ; Bulletin of the New York
Zoological Society ; Bulletins and Circulars of the Bureau of Biological Survey,
United States Department of Agriculture, Washington, D.C. ; Journal of the
American Museum of Natural History, New York ; Journal of Mammology,
Washington, D.C; Fins, Feathers, and Fur, St Paul, Minn.; Forest and Stream,
New York ; National Association of Audubon Societies, Bulletins, New York ;
Society for the Preservation of the Fauna of the Empire, Occasional Papers,
London.

INDEX

Abalones, 319

Aberdeen Angus, 271

Acanthoscelides obtectus — effect of

temperature on life cycle, 196
Acarapis woodii, 293
Acarid entomiasis, 110
Acaridiosis, 293
Actinopods, 7
Acipenser, 306
Active encouragement measures,

382
Aedes, 130, 132.

Africa — trypanosomiases, 35, 36
Agamodistomum, 50
Agricultural Zoology, Part II, 145
Albicore, 325
Aleppo button, 33
Alevin, 302
Aleyrodidce, 169
Alkaloids, as insecticides, 219
Allelomorphs, 280
Allolobophora, 148
Alosa sapidissima, 323
Alpaca, 258
Ambergris, 337
Ambrosia, 190
American Bison, 379

Extermination of, Fig. 55 ; 380

Mink, 349

Trotter, 267
Amoebic Dysentery, 24
Amoebae —

Feeding habits, 5

Parasitic, 23

SoH, 147
Amcebiasis, 24
Amphistomid condition, 49
Anachceta, 148
Anadromous fishes, 300
Analogy — definition, 4
Anaphe silk, 297
Anasa tristis, 162
Anchovy, 324
Ancylostoma, 77, 372
Angora rabbit, 368
Angoumois grain moth, 184
Anguillulidce, 149

Animal conservation, Chapter

XXXIV ; domestication, Chapter.
XXII
Anobiidce, 188
Anomala, 152
Anopheles, 132
Anopheline mosquitoes —

Diagnostic features^ 130, opp. Fig. 21

Eggs, 129

Genera, 132

Larvae, 130
Anoplura, 124
Anoplocephalince, 66
Antherea pernyi, 296
Anthomyiidce, 191
Anti-mosquito measures, 133
Anihonomus grandis, 171, 216

pomorum, 173

quadrigibbus, 173

signaius, 173
Antihelminthics, 96
Ants, 57

Anuraphis maidiradicis, 169
Aphelenchus, 150
Aphelinus mali, 229
Aphididce, 166
Aphids — food habits, 217
Aphis, 166, 217
Apiculture, Chapter XXIV
Apis mellifica, 255

dorsata, 285

fiorea, 285

indica, 285
Apodemus, 233
Apple sucker, 109
Apterous, 155
Arab horse, 265
Arcachon, oyster culture, 314
Arcella, 7
Ar otocephalus, 341
Argas, 142
Argasince, 142
Argentine ant, 157
Army worms, 174, 211
Arrow poison, 102
Arsenical insecticides, 219
Arthropoda and Disease, Chapters IX,

X, XI, XII
Artificial pearls, 317

415

416

INDEX

Arvicola, 233

Ascaris, 73

Ascomycetes, 224

Asexual reproduction, in Protista, 6

Asiatic cattle, 254

Aspidiotus perniciosus, 178, 216, and

Fig. 30
Aspidocotylea, 49
Asses, 251
Astrakhan, 365
Atlantic fishing grounds, 326
Auchemia, 250
Auchmeromyia, 106
Audubon Societies, 245
Australia — Sheep maggot flies, 106
Australorp fowls, 262, 275
Autumn mite. See Trombidium
Avicularidce, 98
Axostyle, 9

B

Babesia, 42
Bacon pig, 274
Bacteria, in insects, 222
Bakewell, 276
Balcena, 336

australis, 338

biscayensis, 337
Balcenoptera, 336, 340
Balantidium coli, 31, Fig. 4
Banks, 327
Banting, 254
Barbeiro, 36
Bark beetles, 189
Bartonella, 43
Bates Shorthorns, 277
Beam trawl, 331
Beaver, 353
Bed bug, 123
Bee, Diseases, 291

Hives, Chapter XXIV
Bee-keeping Chapter XXV
Bee Moth, resistance to bacteria, 222
Beef cattle, 270
Bees, stinging powers, 101
Belascaris, 73
Belgian horse, 265
Bezoar, 256
Bilharziosis, 54
Binary fission, 6
Bioclimatic Law, 208
Biological races, 218
Biotic potential, 205
Bird boxes, 249
Bird encouragement, Chapter XXI

Protection, 244
Birds, domesticated, flukes, 53
Bison, 260
Biting arthropods, 98

Black bees, 286

Black flies, 100

Black fox, 370

Blackhead, in turkeys, 27

Black rat, 231

Black scale, 181

Black widow spider. See Latrodectus

Blepharoplast, 9

Blissus leucopterus, 163, and Fig. 27

Blister beetles, 102

mites, 194
Bloodsucking habits —

Bugs, 123

Congo flour maggot, 107

Diptera, 119

Fleas, 120

Lice, 124

Mosquitoes, 126
Blowflies, 106
Blubber, 336
Blue-greys, 272, 282
Bodo, 16, 21, 147
Bollworms, 174
Bombyx mori, 295
Bone meal, 337
Bonito, 325

Bos, 253. Breeds .Fig. 8
Bostrychidce, 188
Bots, 107

Brachypterous, 155
Braulidce, 140
Brazil trypanosomiasis, 36
Brevoortia tyrannus, 323
Brill, 330
Brine flotation, 92
Broad tapeworm, 65
Browntail moth, 176

Poisonous hairs, 101
Bruchidat, 190
Bryobia, 161
Bubonic plague, 121
Buffalo, 254

Hybridisation, 282
Buffalo tree hopper, 165
Buprestidce, 159
Bushman — arrow poison, 102
Byerley turk, 265

Caconema, 150
California —

leery a puchasi, 180

Plague, 122
Callorhinus, 341
Calonymphidai, 28
Camels, 250

Surra, 36
Camel spiders, 98
Cankerworms, 175

INDEX

417

Canning, of salmon, 305
Cantharidin, 102
Capra, 256
Capsidce, 164
Carp rearing, 309
Carriers, 24
Cat-
Liver fluke, 53

Origin, 256
Cattalo, 260
Cattle-
Breeds, 268

Breeding, Chapter XXIV

Origin, 253

Red water fevers, 43

Trypanosomias, 36
Caviare, 306
Cecidomyiidce, 190
Cell Theory, 1
Celtic Shorthorn, 254
Centrifugation method, 92
Gephidce, 193
Cerambycidce, 189
Ceratitis capitata, 192, 199
Ceratopogince, 100, 135
Cercaria, 50
Cercariseum, 50
Cercopidce, 165
Ceresa, 165
Cetacea, 336
Chceromyia, 107
Chagas disease, 36
Chaleis calliphorce, 106
Chemical control of insects, 218
Chermes, 217

CJiilomastix, 30, and Fig. 7
Chilomonas, 16
Chinch bug, 163, and Fig. 27
Chinchilla, 355

Babbit, 367
Chiracanthium nutrix, 98
Chironomidas, 135
Choice furs, 357
Chlorioptes, 113
Chromatoid bodies, 24
Chromidial condition, 3
Chrysomelidce, 170
Chrysomyia, 106
Cicada, 164
Cicadidce, 164
Cilia, 6, 11
Ciliata, 11

Characteristics, 11

Ectozoic, 17

Enteric, 30

Limnobiotic, 16
Cirphus unipuncta, 174, 211
Classification —

Protista, 6

Protozoa, 7
Clear wing moths, 182

27

Cleveland bay, 266

Glonorchis sinensis, 57

Clothes moths, 184, 199

Ghipea sprattus, 320, 324

Clupeidce, 320

Clydesdale horse, 264

Cnemidocoptes, 113

Coal fish, 330

Coastal group, 322

Coat colour, 281

Coates Shorthorn ; Third Book, 277

Cobboldia, 107

Coccidce, 177

Coccidia, 31

Coccidiosus of birds, 31

Rabits, 32

Man, 32
CoccobaciUus acridiorum, 222
Cochliomyia, 106
Cockchafer, 152
Cod family, 330
Codling moth, 184
Coenurus cerebralis, 64, 67
Cold storage, in insect control, 199
Collings Shorthorns, 276
Colorado potato beetle, 170, 203
Conjugation in Protista, 6
Conjunctivitis, 102
Gonorhinus, 100, 123
Contact insecticides, 218
Gontarinia pyrivora, 191
Continental shelf, 326
Contrasted characters, 280
Copper insecticides, 219
Copulatory bursa, 75
Corceidce, 162
Gordyceps, 224
Cordylobia, 106
Corn root aphis, 169
Corriedale sheep, 273
Cossar Ewart's experiments, 283
Cossidce, 183
Costia necatrix, 17, 310
Costiasis, 310
Cotton —

Boll weevil, 171

Bollworms, 174

Flea beetle, 170

Leaf -roller, 186

Oxycaroenus, 163

Pink bollworm, 183, 199

Rat, 234

Seed, heat sterilisation, 199

Stainer bugs, 164

Stem-borer, 189
Gouncilmania Lafleuri, 27
Coypu rat, 354
Craneflies, 154
Crayfish disease, 18
Crepidula, 316
Crithidia, 35

418

INDEX

Cross-breeding, 282

Fox, 352, 370
Cruel worm, 87

Cryptolce?nus Montrouzieri, 180
Culicidce. See Mosquitoes
Culicine mosquitoes —

Diagnostic features, 132, and Figs.
20, 21

Eggs, 129

Genera, 132

Larvse, 129
Culture pearls, 317
Gurculionidce, 170
Custer wolf, 238
Cuterbrince, 109
Cutworms, 154
Cyclical transmission of disease:

Chapter XII
Oyclophyllidea, 65
Cyclops as host of Dibothriocephahis,

65
Gydia pomonella, 185
Gynipidce, 193
Cyst of Protozoa, 14
Cysticercoid, 63
Cysticercus, 64

Cytopyge, 12

D

Dab, 330
Dacus, 193
Dairy Shorthorn, 271
Darley Arabian, 265
Davainea, 68
Death watch beetle, 188
Deer, 261
Delhi boil, 33
Demodex, 114
Dendroctonus frontalis, 208
Dermanyssus, 114
Dermatophilus. 109
Dermatitis, 99
Dermatobia, 109
Dextral, 331

Diamphidia simplex, 102
Diaspinse scales, 179
Diatrcea saccharalis, 186
Dibothriocephalus latus, 65
Dicroccelium lariceolatum, 51
Dictyocaulus filaria, 76
Dientamceba fargilis , 27
Difflugia, 7
Diparopsis, 174
Diplosis tritici, 191
Dipping fluids, 221

of animals, 113
Dipylidium caninum, 70
Disease, transmission by Arthropods,
Chapters IX-XII

Distomid condition, 49
Dodo, 379
Dog-
Cruel worm, 87

Liver fluke, 53

Origin, 256
Domesticated animals —

Birds, 258

Breeding, Chapter XXIV

Breeds, Chapter XXIII

Horse —
Breeds, 262
Origin, 252

Mendelian characters, 281

Origin, 250

Telegony, 283
Dominant, 280
Down sheep, 272
Dranunculus, 87
Dual purpose cattle, 270
Ducks, 258
Durham cattle, 276
Dusky cotton bugs, 163
Dysentery —

Amoebic, 24

Balantidial, 31

E

E arias insularia, 174
Earthworms, 148
East coast fever, 43
Echidnophaga, 110
Echinococcus, 64

granulosus, 68
Echinostomum echinatum, 53
Ecological succession of Protozoa, 15
Ectozoic Protozoa, 17
Edible fishes, 329
Eel fisheries, 306

Fry, 308
Eelworms, 149
Effective humidities, 197

Temperatures, 197
Egrets, 247

Egypt, schistosomiases, 54
Egyptian Bollworm, 174
Eimeria avium, 31

stiedce, 32
Eisenia, 148
Eland, 260
Elephant, 260

Bots, 108
Elephantiasis. 85
Elk, 261

Embryonic Capsule, 61
Empoasca, 165
Empusa muscce, 117, 223
Enchytrazidce, 148
Enchytraius, 148

INDEX

419

Encystment of Protozoa, 14
Eadolimax nana, 26
Endozoic Protozoa, 17
Engraulis encrasicholus, 324
Entamoeba coli, 26, and Fig. 6

gingivalis, 26

histolytica, 23, and Fig. 6

meleagridis, 27
Enteric Amoebae, 23

Ciliata, 30

Protozoa, characteristics, 22

Sporozoa, 31
Enterobius, 14:

Entomiasis, 97, and Chapter X
Ephe-stia Jcuchniella, 186, 199
Equus, 251

Breeds, 262

Mendelian characters, 281

Telegony, 283
Eriococcince, 180
Eriophyidai, 194
Eriosoma lanigera, 167

Parasites, 229
Eri silk, 297
Ermine, 349
Eublemina, 299
Euproctis chrysorrhea ; poisonous

hairs, 101
European corn borer, 187
Eutettix, 165
Evaporative power of air, 206

Faecal examination, 91

Fannia, 116

Farm animals, breeds, 262

Fasciolopsis buski, 57

Filaria, 85

Fin disease, 311

Fish diseases, 310

Hatching, 308

Parasites of, 17

Wheels, 304
Fisher 349

Fisheries, Chapters XXVII-XXIX
Flagella, 6

Flat-headed borers, 189
Flatworms, 46
Flea beetles, 170
Fleas, 120

Entomiasis, 109
Flounder, 330

Flour mills. Heat sterilisation, 200
Flukes, Chapter V
Fluted scale, 180
Fly-free dates, 209
Follicular mange, 114

Food habits —

of birds, 239

of insects, 214
Foraminifera, 7
Forest horse, 252
Foul brood, 291
Fowl. See Poultry
Fox, 35

Farming, 369, and Figs. 53, 54
Foxes, ear mange, 113

Parasites of, 372
Frame hive, 286
Fredericia, 148

Freezing point of insect tissues, 197
Fresh-water fisheries, 300
Frit fly, 193
Fruit flies, 192
Fulgoridoe, 165
Fumigants, 219

Fumigation against rodents, 238
Fungus diseases of insects, 223

Epidemics, 224
Fur-bearing animals, Chapter XXXI

Dressing, 361

Farming, Chapter XXXIIT

Ranching, 369, 374

Trade, Chapter XXXII
Furniture beetles, 188
Furs, marketing of, 359

Procuring of, 358
Fusca group, 137

G

Gadflies, 100, 119
Gadidce, 330
Gadus ceglefinus, 330
Galleria melonella, 293

Resistance to bacteria, 222
Gallmidges, 190

Wasps, 193
Galloway cattle, 272
Gamebirds, gapes, 82

Destruction against trypano-
somiases, 38
Gapes, 82
Gastrophilus, 107
Gaur, 254
Geese, 258
Gelechiadce, 183
Genal comb, 120
General purpose fowls, 275
Genotype selection, 279
Geometridce, 17 5
Gerardinus pceciloides, 228
German coach horse, 268
Giardia, 30, and Fig. 7
Gid, 68
Gill nets, 304
Gipsy moth, 175, 216

2JA

420

INDEX

Glossina, 135, and Fig. 22

palpalis, 36, 139
Goat moths, 183
Goats, origin, 255
Godolphin horse, 265
Goldfish, 310
Grain weevils, 173
Grasserie, 225
Grasshoppers, 159
Grassi, 42

Grass stem maggot flies. 193
Great auk, 379
Oregarinidea, 31
Grey rat. 231
Grilse, 302
Grocers itch, 99
Grouse disease, 77

Tapeworms, 68
Guinea worm, 87
Gvrodactvliasis. 311

Habronema, 117
Hacknev, 266
Haddock, 330
Hcemoflagellata, 33
Hcemonchus contortus, 76
Hcemoproteus, 42
Hcemosporidia, 38
Halibut, 330
Haliotis, 319
Halteridium, 42
Hambletonian, 267
Hamster, 233
Hard ticks, 142
Harlequin bug, 162
Harvest mite, 99

Mouse, 232
Heat, as sterilisation measure, 199
Heliozoa, 7
Helminthes, Chapters V-VIII

Cultivation, 92

Diagnosis, 91

Eggs, Fig. 17
Helminthiasis, 90

Diagnosis, 91

Prophylaxis, 95
Helodrilus, 148
Helopeltis, 164

Hemi-metabolous insects, 195
Hemippus, 251
Hepatic abscesses, 25
Herd books, 277
Hereford cattle, 271
Herpetomonas, 34
Herring, 320

Fisheries, 320
Hessian Fly, 190, 208, 204
Heterahis, 73

Heterocotylea, 49
Heterodera, 150
Heterodynamic insects, 204
Heterozygote, 280
Hibernation, 203
Hippoboscidm, 140
Hippoglossince, 330
HippogJossis vulgaris, 330
Hippoglossoides limanoides, 330
Hog, origin, 258

Breeds, 262, 273
Holometabolous insects, 196
Holophyte, 4
Holostomid condition, 49
Holozoite, 5

Homodynamic insects, 204
Homology, definition, 4
Homozygote, 280
Honev dew, 166

Flow, 290
Hookworm disease, 79
Hookworms, 77
Hoose, 76

Horned lark. Status, 243
Horse, ascaris, 73

Bots, 107

Dourine, 36

Strongyloxis, 82
Horses, origin, 251

Breeds, 262

Mendelian characters. 281

Telegony, 283
Host resistance factors, 215
House-flies, 115

Myiasis, 103

Prophylactic measures, 118
House-fly, 205
Hunter, 266
Hybridisation, 252
Hydatid, 69
Hymenolepus nana, 70
Hypoderma, 108
Hy pod er matinee, 108
Hyperoodon rostratus, 336

I eery a purchasi, 180
Ichthyophthiriases, 311
Imitation furs, 358
Importation of plumage act, 246
Inbreeding, 276

India, transmission of plague, 121
Infantile splenic anaemia, 33
Infusions, protozoa of, 16
Infusoria. See Ciliata
Insecticides, 219
Insectifuges, 220
Inshore fisheries, 313
Intestinal hookworms. 75

INDEX

421

lodamoeba batschlii, 27
Isaria, 224
Isinglass, 306
Isle of Wight disease, 292
Isospora hominis, 32
Itch mites, 110
Ixodidce, 99, 140
Ixodina, 142

Janthinosoma lutzi, 109
Japan, Clonorchis, 57
Schistosomiasis, 54
Japanese silk, 296
Jassidcs, 165
Joint worms, 194

K

Katadromous fishes, 301
Khartoum hives, 288
Kiang, 251
Kinetonucleus, 9
Kolinsky, 349

Lac culture, Chapter XXVI and 297

Lackey moth, 175

Lampara net, 323

Langstooth, 286

Lard hog, 274

Larvicides, against mosquitoes, 133

Laspeyresia, 185

Latrodectus, 98

Laveran, 42

Laying fowls, 274

Leaf -cutting ants, 157

Leaf hoppers, 164

Leather jackets, 154

Lecaniince, 181

Legislation re bird protection, 244

in insect control, 212
Leishmania, 33
Leishmaniasis, 33
Lemming, 233
Lemon dab, 330
Leopard moth, 183
Leptinotarsa decemlineata, 170, 203
Leptocephalns, 307
Leptocorisa, 162
Lice, 124
Limncea, 52

Limnobiotic protozoa, 15
Line breeding, 277
Lining, 331, 332

Liver fluke, 51

Livestock breeding, Chapter XXIV

Llama, 258

Loa loa, 86, 120

Lobster fisheries, 316

Locusta migratoria, 161

Locusts, 159

Disease, 222

Phase Theorv, 210
Longhorn breeding, 276
Long rough dab, 330
Long wool sheep, 272
Lord Morton's mare, 283
Low temperatures and insects, 199
Lucilia sericata, 106
Lumbricus, 148
Lung hookworms, 75
Lutra, 350
Lycosa tarantula, 98
Lyctidce, 187
Lygceidce, 162
Lygus, 164

M

Macaque worm, 109
Mackerel fisheries, 324
Macronucleus, 12
Macropterous forms, 155
Maggot, 104
Malacocotylea, 49
Malacosoma, 175
Malaria, 39
Mallophaga, 124
Manaar pearl fisheries, 318
Man, flukes, 56

Tapeworms, 67
Mange, 110

Manure heaps, anti-fly treatment, 116
Margaritifera, 317
Margaropus annulatus, 144
Markhor, 256
Marmotinaz, 235
Mass migration of insects, 211
Mass selection, 278
Mastigoamceba, 9
Mastigophora, characteristics, 7

Ectozoic, 17

Enteric, 27

Hseniatophilous, 33

Limnobiotic, 16

Phytobiotic, 17

tStructure, 9

Types, Fig. 2
Maternal impression, 284
Mayetiola destructor, 190, 208
Meadow mice, 233, 236
Mechanical transmission of disease,
Chapter XI

422

INDEX

Mediterranean flour moth, 186, 199

Fruit fly, 192, 199
Megaptera, 336
Melipona, 286
Meloidce, 102
Melolontha, 152
Mendelian laws, 279
Menhaden, 323
Mephitis. 350
Merino sheep, 272
Merriam's laws, 206
Metacestode, 62
Mice, 232
Micromys, 232
Micronucleus,
Microsporidia, 18
Microsporidiosis, 293
Microtus, 233
Miesche's tubes, 18
Migratory Bird Convention Act. 245

Locust, 161
Migration of insects, 210
Milch cattle, 270
Millions fish, 228
Mining insects. 182
Mink, 349
Mink farming, 373
Miracidium, 49
M'Lean Federal Migratory Bird Law,

245
Monophagous, 159
Monophlebine scales, 179
Monostomid condition, 49
Mosquito blight, 164
Mosquitoes and filariasis, 86

Classification, 130

Control, 133

Distribution and life evcle, 129

Enemies, 228

Larval habits, 129

Morphology, 126
Moth borersVl86
Mother of pearl, 319
Mouflon, 256
Mountain sheep, 273
Mouse plagues, 236
Muga silk, 296
Mulberv silk, 294
Mule, 282
Multiceps, 67
Multiple fission, 6
Multivoltine, 295
Murgantia, 162
Mus, 231

musculus, 232

norvegicus, 231

rattus, 231

trypanosoma lewisi, 35
Musca domestica, 115, 200
Muscardine fungi, 224
Muscid entomiasis, 103

Musk ox, 259
Musk rat, 233, 354
Mustelidce, 349
Mustelus zibellina, 349
Myiasis, 97, and Chapter X
Mystacoceti, 336
Myxosporidia, 18.

N

Nagana, 35

Nasonia brevicornis, 106
Necator, 77
Nematobothrium, 47
Nematoda, Chapter VII
Nematoda in the soil, 149
Neosporidia, 18

Types, Fig. 5
Neuromotor apparatus, 9
Nezara, 162
Noctiluca, 15
Noctuidce, 154, 174
Noguchi, 45
Non-cellularity. 3
Nosema apis, 18, 293

bombycis, 18
Nostril flies, 108
Notal comb, 120
Notcedrus, 11
Nuclear diseases, 225
Nucleus of Protista, 2
Nun moth, disease, 225
Nutria, 354
Nycteribiidce, 140
Nyctotherus faba, 31, and Fig. 4
Nygmia phceorrhea, 176

Oceanic group, 322
Odobenus, 343
Odontoceti, 336
(Edemagenia, 109
(Estridce, 107
(Estrince, 108
Offshore fisheries, 326

Fishing methods, 331
Oil from whales, 336
Oiling, against mosquitoes, 134
Oldenburger, 268
Onager, 251
Onchocerca, 88
Onchosphere. 61
Oncorhynchus, 302
Ookinete, 39
Ophthalmia nodosa, 102
Opistorchis felincus, 53

INDEX

423

Organelles, 4

Oriental sore, 33

Orloff trotter, 268

Ornithodorus moubata, 44. 142

Oroya fever, 43

Oryctes rhinoceros, 171

Oscinella frit, 193

Osci niche, 193

0 street, 313

Otariidce, 341

Otodectes, 113

Otter, 350

Farming, 374

Trawl, 331
Outbreeding, 278
0 verb airs, 347
Ovibos, 239
Ovis, 256

Breeds, 272

Mendelian characteristics, 281
Owl midges, 135
Oxycarcenus, 163
Oxyuris, 74
Oyster, 313

Fisheries, 313

Pares, 315

P

Pachyrhina, 154
Pacific salmon, 302
Palpalis group, 138
Pappataci fever, 135
Parabasal body, 9, 22
Paradise birds, 246
Paragonimus ringeri, 56

wesfermanni, 53
Parasites, definition, 5

Artificial introduction, 228

of foxes, 372

of insects, 226

of Protozoa, 20
Parr, 302

Partial sterilisation of soil, 145
Passenger pigeon, 379
Passeromyia, 107

Passive encouragement measures, 382
Pear midge, 191
Pearl fisheries, 317

Shells, 319
Peat sheep, 256
Pebrine, 18, 225

Pectinoplura gossypiella, 183, 199
Pediculoides, 99
Pediculus, 124, 218
Pedigree breeding, 277
Pelage, 347
Pentatomidce, 162
Penycuik experiments, 283

Percheron, 265

Perkinsiella, 165

Persian Gulf : pearl fisheries, 318

Persian lamb, 365

Peru : oroyo fever, 43

Phase Theory, 210

Phenotype selection, 278

Pheasants, 246

Phlebotomus, 135

Phoca, 343

Phocidce, 341

Phormia, 107

Phototropism, 214

Phthorimcea operculella, 184

Phyllophagus, 152

Phylloxera vastatrix, 167

Physeter meter ocephalus, 336

Phytobiotic Protozoa, 17

Pieris brassicce, Poison, 102

Pigeons, 258

Pigs —

Breeds, 262, 273

Chiggers, 110

Origin, 250

Parasites, balantidium, 31
Pilchard, 323
Pink bollworm, 183, 199
Piroplasma, 42
Plaice, 330
Plankton, 327
Planorbis, 52

Plasmodium, 39, and Fig. 9
Plateau horse, 253
Plerocercoid, 62
Plerocercus, 52
Plesiocoris, 164
Pleuronectes, 330
Pleuronectidce, 330
Pleuronectince, 330
Plumage trade, 246
Pocket gopher, 234
Poison baits, 161
Poisoning of vermin, 237
Poisonous caterpillars, 101
Polar capsule, 18
Pollack, 330
Polled cattle, 280
Polyhedral diseases, 225
Polymastigina, 21
Polyphagous, 159, 214
Polytoma, 16

Pomolobus pseudoharengus, 323
Ponies, 267

Porthetria dispar, 175, 216
Potato tuber moth, 184
Poultry —

Breeds, 262, 274

Coccidiosus, 31

Filariasis, 87

Gapes, 82

Origin. 258

424

INDEX

Poultry — contd.

Scaly leg, 113

Stick-tight flea, 110
Powder Post Beetles, 187
Prairie dog, 235
Predators of insects, 226
Proglottis, 58, and Fig. 13
Protandrously hermaphrodite, 59
Protista —

Classification, 6

Definition, 7

Life cycle, 6

Mode of life, 4
Protozoa —

Biology and classification, Chapter I

Definition, 7

Distribution, Chapter II
Protozoa —

as insect parasites, 225

Enteric forms, Chapter III

Hsematophilous, Chapter IV

Transmission by insects, Chapter
XII
Protozoan diseases —

of fishes, 17, 18

Insects, 18, 225

Mammals, 18, and Chapters III and
IV
Prowazckia, 28
Przewalskii horse, 253
Psetta Icevis, 330

maximus, 330
Psettince, 330
Pseudococcus citri, 181
Pseudophyllidea, 64
Pseudopodia, 5, 7
Psoroptes, 113
Psychodidce, 135
Psylla, 169
PsyttidcB, 169
Pulex, 122
Punkies, 100
Pupiparid flies, 140
Pycnothrix monocystoides, 20
Pygidium, 120
Pyralidce, 186
Pyrausta nubilalis, 187
Pyrrhocoridw, 164

Q

Quagga, 379
Queen excluder, 291
Quinnat, 304

R

Rabbits —
Breeding, 366
Coccidiosus, 32

Racehorse, 265
Radiolaria, 7
Rambouillet sheep, 272
Rat bite fever, 45
Rats, 231

Trichinosis, 84
Recessive, 280
Redia, 50
Red spiders, 161
Redaviidfe, 123
Reduvius, 100
Red-Avater fevers, 43
Reindeer, 259

Warbles, 109
Relapsing fevers, 44
Reproduction in Protozoa, 6
Reproductive potential, 205
Resistance, vines to phylloxera, 165
Resistance to insect pests, 215
Restriction of spread, 211
Rhizoplast, 9
Rhizopods, 7
Rhogas, 183
Rickettsia, 125
River herring, 323
Rocky Mountain fever, 144

Locust, 213
Rodents, injurious, 230
Rodent plagues, 236
Root maggot flies, 191
Rorquals, 336
Ross, 42

Round-headed borers, 189
Roundworms, Chapter VII, 372
Russell and Hutchinson, 145
Russian trotter, 268

Sable, 349

Sac Brood, 291

Saissetia olecv, 181

Salmo salar, 302

Salmon fisheries, 301

Sanctuaries, 248

Sand-flies, 100

San Jose scale, 178 and Fig. 30, 216

Saperda Candida, 189

Saprobiotie, 5

Saprohgniaceci', 311

Sarcodina, 7

Sarcoptes, 111

Sarcoptidte, 110

Sarcosporidia, 18

Sarda sarda, 325

Sardina ccerulea, 323

Sardine, 323

Saturniid(p, 294

Scale insects, 177

INDEX

425

Scaly leg, 113
Schistocerca, 161

Schistosoma, 53
Schistosomiasis, 54
Schizogony, 11, 38
Schizotrypanwm cruzi, 36
Scolex, 58
Scolytidce, 189
Scomber scombrus, 324
Scorpion, 100
Screw- worm flv. 106
Seal, 343

Commercial value of, 344
Sealing industry, 340
Sea lions, 341
Sea otter, 381
Seed lac, 299
Seine nets, 304, Fig. 45
Sense reaction, 213
Sericiculture. Chapter XXVI
Sesiidre, 182

Silver rat. See Mtjs norvegicus
Sexual reproduction, Protista. 6
Shad, 323
Shantung silk, 296
Sheep —
Breeds, 272
C ceriums cerebralis, 67
Liver fluke, 51
Lung hookworms, 75
Maggot flies, 103, 106
Mendelian characters, 281
Nostril fly, 100
Origin, 255
Scab, 113
Strongvlosis, 76
Shellac, 297, 299
Shell fisheries, 313
Ship fumigation, 238
Shire horse, 264
Shirt wool sheep, 272
Shorthorn breeding, 276
Shorthorn cattle, 270
Shot hole borers. 189
Silk, 294
Silkworms, 294
Silver fox, 352, 370
Simuliidce, 100
Sinistral, 331
Siphonaptera, 120
Sitopkilus, 173

Low temperatures, 198
Sitotroga cerealella, 184
Skunk, 350

Farming, 374
Sleeping sickness, 35
Slipper limpet, 316
Smear method, 91
Smolt, 302
Sock eye, 304
Soft ticks, 142

Soil Fertility, Protozoan Theory, 145
Insects, 151

Organisms, Chapter XIII
Protozoa, 145
Sole, 330

Solea vulgaris, 330
Soleince, 330
Sol pug i da, 98
Southern Pine Beetle, 208
Spanish fly, 102
Sparganum, 65

Sparrow, economic status, 243
Spat, 314
Spermophile, 235
Spiders, 98
Spirochceta, 43
Spirocyst of neosporidia, 18
Spironema, 44
Spore formation, 9
Sporocyst, 50
Sporogony, 11, 39
Sporotrichum, 163, 224
Sporozoa —

Characteristics, 9
Classification, 11
Life evele, 11
Types, Fig. 3

Sprat, 324

Squash bugs, 162

Squirrel, 355

Stable flv, 119

Starling— Food, Fig. 33

Stem sawflies, 193

Steppe horse, 252

Sterilisation in insect control, 199

Stick-lac, 299

Sticktight flea, 110

Stinging insects, 100

Stomach hookworms, 75

Stomach poisons, 219

Stomoxys, 119

Streblidce, 140

Striping in horses, 283

Strobila, 58

Strongylidce, 75

Strongyloides, 83

Strongylus equinus, 81

Stud books, 277

Sturgeon, 306

Substitute furs, 357

Sudan bollworm, 174

Suffolk horse, 264

Sugar beet leaf hopper, 165

Sugar cane frog hopper blight, 165
Leaf hopper, 165
Moth borers, 186

Survival potential, 205

Sus scrofa, 258

Syngamus, 82

Synthetocauhis rufescens, 76

Syphilis, 45

426

INDEX

Tabanidm, 100, 119
Tachardia lacca, 297
Taenia, 66, 67
Tceniorhynchus, 130
Table fowls, 274
Tapestry moth, 184
Tapeworms, Chapter VI
Tarbagan, 122
Tasar silk, 296
Telegony, 283
Termites, 155

Intestinal Protozoa, 28
Temperature — effect on insect meta-
bolism, 197
Tetranychus, 161
Texas cattle fever, 43
Thelohania contejeani, 18
Thermometabolism, 197
Thermotropism, 214
Thoroughbred, 265, 278
Thrips, 169
Thunnus germo, 325
Thynnus thynnus, 325
Thysanoptera, 109
Ticks, 140

Red water fevers, 43

Spirochetosis, 44
Tineidce, 184, 199
Tineola biselliella, 184
Tipula, 154
Tomaspis, 165
Toothed whales, 336
Tortoise scales, 181
Tortricidce, 184

Total effective temperature, 202
Toxic inoculation, Chapter IX
Trapping of vermin, 238

For the procuring of furs, 359
Trawling, 331
Tree-hoppers, 165
Trematoda, 46
Treponema pallidum, 45
Triatoma, 36
Trichechidce, 341
Trichinclla, 84
Trichinosis, 84
Trichocephalus, 74
Trichomonas, 28, and Fig 7
Trichophaga tapetzella, 184
Trigona, 286
Trochosa singoriensis, 98
Trombidium, 99
Tropisms, 213
Trout culture, 308
Trypanosoma, 34, and Fig. 2

brucei, 35

equiperdum, 36

evansi, 36

gambiense, 35

Trypanosoma — contd.

leivisi, 35

pecorum, 36

rhodexsiense, 35

simia?, 36
Trypanosomiasis, human, 35, 36

Bovine, 36
Trypetida', 192
Tsetse fly. See Glossina
Tunny, 325
Turbellaria, 46
Turbot, 330

Tussock caterpillars, 175
Tylenchus, 149
Tyroglyphus, 99

u

Undercooling point, 197
Undulating membrane, 34
Unicellular organisms, 1
Univoltine, 295
Urial, 256
Urodis, 253

Vedalia cardinalis, 180
Venomous biters, 98
Vermin repression, Chapter XX
Vertebrate reservoirs of trypano-

somes, 38
Vine aphis, 167
Vine moths, 185

Viscacha, 355
Voles, 233

w

Walrus, 343

Wapiti, 261

Warbles, 100

Ware, 314

Water buffalo, 254

Water optimum, 201

Wax moths, 293

Weeds, propagation by birds, 240

Weevils, 170

Weils disease, 237

Whalebone, 337

Whales, 336

Whaling industry, 336

Wheat midge, 191

Whipworm, 74

Whirling sickness, 310

White ants, 155

White diarrhoea of poultry, 32

White flies, 169

INDEX

427

White grubs, 152
Whitebait, 323
Whiting, 330
Winter moths, 175
Wire worms, 154
Wohlfartia, 106
Woodchuck, 235
Woolly aphis, 167

Parasites, 229
Workers, 155

X

Xenopsylla, 121

Yaws, 45
Yellow fever, 45
Yorkshire coach horse, 267

Zebras, 252

Telegony in, 283
Zebrule, 282
Zebu, 254

Resistance to disease, 282
Zeuzera pyrina, 183
Zones of metabolic activity, 200
Zoobiotic Protozoa, 17
Zygomycetes, 223

Printed in Great Britain at The Darien Press, Edinburgh

I

SB 805.W3

3 9358 00026795 2

CHEM

SB805
W3

Wardle, Robert Arnoidf 1890-

The principles of applied zoology* bj
Robert A» Wardle* London* New York
[etc*] Longmans* Greem* and co** 1929*

xii* 427 p* front** illust 23 cm*

26795

CHEM BLDG

MBNU

APR 29,«75 1302531 NECbp

29-4436

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3 9358 00026795 2