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THE CONTEMPORARY SCIENCE SERIES.

Edited by HAVELOCK ELLIS.

EVOLUTION AND DISEASE

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1

2.

Evolution
and Disease

BY

J. BLAND SUTTON.

With 136 Illustrations.

SCRIBNER & WELFORD,

743 & 745 BROADWAY,

NEW YORK.

1890.

Si. H,

CONTENTS.

PAGE

Introduction ... ... ... ... ... i

CHAPTER I.

The Enlargement of Parts from Increased Use,

Overgrowth and Irritation ... ... ... 14

CHAPTER II.
Disuse and its Effects... ... ... ... 35

CHAPTER III.
Vestigial Parts ... ... ... ... ... 60

CHAPTER IV.
Vestigial Parts (continued) ... ... ... 79

CHAPTER V.
Dichotomy ... ... ... ... ... ... 102

CHAPTER VI.
Atavism or Reversion ... ... ... ... 134

viii CONTENTS.

CHAPTER VII.

Atavism {continued) — Supernumerary Digits, Limbs,

Mammary Glands ... ... ... ... 158

CHAPTER VIII.

PAGE

The Transmission of Malformations and Acquired

Defects ... ... ... ... ... 176

CHAPTER IX.

Anatomical Peculiarities of the Teeth in Relation

to Injury and Disease ... ... ... ... 199

CHAPTER X.
Causes of Disease— Inflammation and Fever ... 213

CHAPTER XI.
Tumours and Cancers ... ... ... ... 228

CHAPTER XII.
The Zoological Distribution of Disease ... 250

INDICES 279

LIST OF ILLUSTRATIONS

golden hen-pheasant in cock's plumage ... Frontispiece

FIG. PAGE

1. A DACE WITH SPOTS OF BLACK PIGMENT DUE TO

THE IRRITATION OF A PARASITE ... ... 4

2. HEAD OF FEMALE MOOSE WITH ANTLERS ... 5

3. ANTLERS OF ROE-DEER WITH NODE ... ... 7

4. HEAD OF COW WITH AN ABNORMAL HORN .-. 8

5. HEAD OF RHINOCEROS... ... ... ... 9

6. THE LEG OF AN OYSTER-CATCHER WITH HORN IO

7. HEAD OF THE HORNED PUFFIN... ... ... II

8. SECOND TOE ENLARGED FROM EXCESSIVE USE... 15

9. FINGER OF HORSE AND MAN ... ... ... 1 8

10. OVERGROWN HOOF OF GOAT ... ... 20

11. HEAD OF COCK WITH SPUR ... ... ... 22

12. SPINA BIFIDA OCCULTA ... ... ... 23

13. HEAD OF POLISH FOWL ... ... ... 24

14. HEAD OF DUCKLING WITH FOOT ... ... 25

15. STOMACH OF DARTER ... ... ... ... 27

16. A FISH EMBEDDED IN PEARL ... ... 30

17. THE OWL-PARROT ... ... ... ... 36

18. HEAD AND SUCKING DISC OF LEPIDOSTEUS ... 37

19. ASCIDIAN AND ASCIDIAN TADPOLES ... ... 39

20. THE HEAD OF VARANUS ... ... ... 42

x LIST OF ILL USTRA TIONS.

FIG. PAGE

21. BRAIN OF HATTERIA ... ... ... ... 43

2 2. A SECTION OF THE PINEAL EYE OF HATTERIA,.. 44

23. OVIDUCT IN A MALE SKATE ... ... ... 47

24. THE EMBRYONIC ALIMENTARY CANAL ... 49

25. DIAGRAM OF THE ALIMENTARY CANAL AND NERVOUS

SYSTEM ... ... ... ... ... SO

26. AN AFRICAN CHILD WITH A TUMOUR ... S3

27. A FAUN ... ... ... ... ... 54

28. AN iEGIPAN AND FAUN ... ... ... 55

29. OVERGROWN NAIL IN A SLOTH ... ... ... 57

30. HEAD OF A PARROT WITH OVERGROWN BEAK... 58

31. A HORNED SHEEP WITH CERVICAL AURICLES ... 63

32. THE CLOACA OF A HEN ... ... ... 64

33. VERMIFORM APPENDIX OF A GIBBON ... ... 66

34. FOLLICULAR CYST IN A PORCUPINE ... ... 72

35. AN ODONTOME IN A HORSE ... ... ... 73

^6. AN ELASMOBRANCH FISH WITH ITS YOLK-SAC ... 76

37. DIAGRAM OF THE ALIMENTARY CANAL AND YOLK-SAC 77

38. AN EARLY HUMAN EMBRYO ... ... 8l

39. DIAGRAM INDICATING SITUATIONS OF BRANCHIAL

SLITS... ... ... ... ... 82

40. GIRL WITH CERVICAL AURICLES... ... ... 8^

41. A CHILD WITH CERVICAL AURICLES ... ... 83

42. A COMMON GOAT WITH CERVICAL AURICLES ... 84

43. AN EGYPTIAN GOAT WITH CERVICAL AURICLES... 85

44. MICROSCOPIC STRUCTURE OF A CERVICAL AURICLE 86

45. SECTION OF CERVICAL AURICLE FROM A GOAT... 87

46. HEAD OF A SEAL ... ... ... ... 89

47. HEAD OF AN jEGIPAN WITH CERVICAL AURICLE 90

48. FAUN AND GOAT FROM THE CAPITOL ... ... 9 1

49. CONCRETION FROM THE GUTTURAL POUCHES OF A

HORSE ... ... ... ... •••95

LIST OF ILLUSTRATIONS. xi

FIG. PAGE

50. MALLEOLI OF MAN AND CHIMPANZEE ... 99

51. SUPERNUMERARY RAYS IN STAR-FISH ... ... 103

52. FEATHERS AND AFTERSHAFTS ... ••• 105

53. GEMINATED TEETH ... ... ... ••• 106

54. REDUPLICATED ANTLER OF MOOSE ... ... 10 7

55. SUPERNUMERARY DIGITS IN A CHILD ... ... 108

56. SUPERNUMERARY DIGITS IN A GIBBON ... 109

57. A DOUBLE HAND ... ... ... ••• HO

58. MUD-FISH WITH DICHOTOMIZED LIMB ... HI

59. SUPERNUMERARY HIND-LEG IN A TOAD ... ... Ill

60. SUPERNUMERARY FORE-LEG IN A FROG ... 1 12

61. SUPERNUMERARY LEG IN A CHICK ... •• H3

62. SUPERNUMERARY WING IN A DOVE ... ... H4

63. SUPERNUMERARY FORE-LEG IN A SHEEP ... ... 1 15

64. SECTIONS OF EMBRYO WORMS ... ... 1 17

65. A TWO-HEADED COLT ... ... ... ... H9

66. A DOUBLE SHARK... ... ... ... 121

67. A DOUBLE-HEADED SNAKE ... ... ... 122

68. A MONSTROUS CALF ... ... ... 123

69. A TWO-TAILEDED LIZARD ... ... ... 1 24

70. A SIX-LEGGED FROG ... ... ... 1 26

71. A SIX-LEGGED LAMB ... ... ... ... 127

72. A FOUR-LEGGED CHICK ... .., ... 1 28

73. A FIVE-LEGGED FROG ... ... ... ... 1 29

74. A FOUR-LEGGED DRAKE ... ... ... 13°

75. A MITRAL VALVE CONTAINING MUSCLE ... ... 1 36

76. A HAIRY MAN ... ... ... ... 1 3**

77. A ROCK LOBSTER (CEPHALON) ... ... ... 140

78. PILIFEROUS CORNEA OF OX ... ... I42

79. PATAGIUM IN THE LEG OF A GIRL ... ... 143

80. WEBBED FINGERS IN A MONKEY ... ... 145

Si. HOUR-GLASS CONTRACTION OF THE STOMACH ... 147

xii LIST OF ILL USTRA TIONS.

FIG. PAGE

82. FEMALE ROE-DEER WITH ANTLERS ... ... 155

&$. HEAD OF A FEMALE MOOSE WITH ANTLERS ... 156

84. MANUS OF HIPPARION ... ... ... 160

85. DICHOTOMY OF A HORSE'S DIGIT ... ... l6l

86. DWARF LEMUR ... ... ... ... 164

87. BRACHIAL MAMMA OF HAPALEMUR ... ... 1 65

88. LEMUR MACACO AND YOUNG ... ... 166

89. SUPERNUMERARY NIPPLES IN MAN ... ... 1 68-

90. SUPERNUMERARY NIPPLES IN A MONKEY ... 169

91. INGUINAL RECESSES IN A LAMB ... ... 1 73

92. MARSUPIUM AND NIPPLES OF A PHALANGER ... 1 74

93. THE HUMAN PINNA ... ... ... ... 177

94. A MALFORMED AURICLE ... ... ... 1 78

95- SO-CALLED SUPERNUMERARY AURICLES ... ... 180

96. DEVELOPMENT OF THE AURICLE ... ... l8l

97. DEFECTIVE PINNAE ... ... ... .-.183

98. SO-CALLED TAILLESS TROUT OF ISLAY ... 1 86

99. TAIL OF A NORMAL TROUT FOR COMPARISON ... 1 86

100. THE NOSE OF A HARE ... ... ... 189

101. THE NOSE OF A DOG... ... ... ... 189

102. CLEFT LIP AND NOSE OF A DOG ... ... 190

103. PART OF THE SKULL OF A DOG WITH A CLEFT

PALATE... ... ... .., ... 191

104. HEAD OF A HUMAN EMBRYO OF THE FIFTH WEEK 192

105. AN EXOSTOSED RAY FROM CH^ETODON ... ... 195

106. HORNED MAN (SO-CALLED) ... ... 1 97

107. INCISORS OF THE KANGAROO .... ... ... 20O

108. INCISORS OF KANGAROO SHOWING EFFECTS OF

INJURY ... ... ... ... 20O

109. OVERGROWN TUSKS OF BOAR ... ... ... 203

1 10. ERRATIC INCISORS OF BABIRUSSA ... ... 204

111. BULLET IN AN ELEPHANT'S TUSK ... ... 207

LIST OF ILL USTRA TIONS. xiii

FIG. PAGE

112. THE ROSTRUM OF MESOPLODON ... ... 2IO

113. SECTION OF A PYTHON'S TOOTH .. ... 211

114. LEUCOCYTES ATTACKING BACILLI ... ... 2l8

115. LEUCOCYTES INGESTING BACILLI ... ... 219

116. CYSTIC KIDNEY OF A TERRIER ... ... 229

117. THE CLOACA OF A HEN WITH CYST ... .-.231

118. TRACHEAL POUCH OF THE EMU ... ... 232

119. AN ACTINOMYCES TUFT ... ... •••235

120. SARCOMA IN THE NECK OF A FOWL ... 237

121. MICROSCOPICAL CHARACTERS OF A SARCOMA ... 239
12 2. MICROSCOPICAL CHARACTERS OF AN EPITHELIAL

TUMOUR ... ... ... ... 243

123. CANCER IN A PHALANGER ... ... ... 247

124. ARTICULAR CARTILAGE OF A PIG WITH GUANIN

GOUT ... ... ... ... 257

125. GOUTY FOOT OF A PARROT ... ... ... 258

12 6. AN ENDEMIC CRETIN ... ... ... 260

127. A SPORADIC CRETIN ... ... ... ... 261

128. A CALF-CRETIN ... ... ... ... 262

129. PTAH ... ... ... ... ... 264

130. MOUSE WITH CUTANEOUS HORN ... ... 267

131. SECTION OF HORN ... ... ... ... 267

132. HEAD OF A MOUSE WITH WART HORN ... 268

133. HEAD OF A SHEEP WITH WART HORN ... ... 269

134. HEAD AND LEG OF A THRUSH WITH WART HORN 270

135. HEAD OF A LEPER ... ... ... ... 272

PREFACE.

My object in writing this book is simply to indicate
that there is a natural history of disease, as well as of
plants and animals. I have not attempted to deal with
the subject at great length, far less exhaustively, but
merely to illustrate general principles by a few carefully
selected examples.

The subject is a novel one, and doubtless a more
extended study will serve to show that many of my
conclusions are fallacious. I trust that such errors may
be speedily rectified by any person who has opportu-
nities of testing my opinions practically. It must be
borne in mind that it is a much easier task to write
concerning the habits of animals than to describe their
diseases ; nevertheless, the facts at our disposal clearly
indicate that disease is controlled by the same laws
which regulate biological processes in general.

J. B. S.

EVOLUTION AND DISEASE.

INTRODUCTION.

MOST persons believe Pathology, as the Science of
Disease is called, to be so outside the comprehension
of ordinary individuals, and even in its general bearings
so utterly devoid of interest to all but medical men, that
much misconception prevails in the minds of even
educated persons in regard to its fundamental principles.
As a matter of fact Pathology is only a department of
Biology, and it is very important to bear this in mind if
we wish to study successfully the origin, cause, and
spread of disease. Yet paradoxical as it seems, whilst so
many regard Pathology as occupying an isolated position
among sciences, medical writers always point out the
difficulty they find in framing a definition of disease, and
indeed the impossibility of stating where health ends and
disease begins.

V It is not my object in the present work to attempt the
framing of a definition of disease, or even to offer a
suggestion as to the borderland between it and health*
This difficulty is frequently illustrated in a striking
manner in a law court ; it is not uncommon for a judge

a E VOL UTION AND DISEASE.

in the course of a criminal trial to ask a medical witness,
when the plea of insanity is urged on a prisoner's behalf,
either to define insanity, or to state his opinion where
sanity ends and insanity begins. The judge knows full
well the difficulty, indeed the impossibility of even a
skilled witness making a satisfactory reply to such a
question.

As with mental so with bodily conditions, it is im-
possible to state definitely the borderland between health
and disease, either in relation with functional aberration
or textural alteration. And in many instances we shall
find conditions which we regard as abnormal in man,
presenting themselves as normal states in other animals.

If it be difficult to define disease when our remarks
are restricted to the human family, it becomes obviously
more difficult when we attempt to investigate disease on
a broad zoological basis. As the great barrier which
exists between man and those members of his class most
closely allied to him consists, not in structural characters,
but in mental power, it necessarily follows that there
should be a similarity in the structural alterations in-
duced by diseased conditions in all kinds of animals,
allowing, of course, for the differences in environment.
This we now know to be the case, and it is clear that as
there has been a gradual evolution of complex from
simple organisms, it necessarily follows that the principles
of evolution ought to apply to diseased conditions if
they hold good for the normal, or healthy, states of
organisms : in plain words there has been an evolution
of disease pari passu with evolution of animal forms.
For a long time it has been customary to talk of physio-

INTRODUCTION. 3

logical types of diseased tissues, and my earlier efforts
were directed in searching among animals for the
purpose of detecting in them the occurrence of tissues,
which in man are only found under abnormal conditions.
The search was of great value to me, for the statement
proved to be true in only a limited sense ; at the same
time the truth of an opinion held by nearly all thoughtful
physicians, that disease may in many instances be re-
garded as exaggerated function, was forcibly illustrated,
and I quickly saw that the manifestations of disease
were regulated by the same laws which govern physio-
logical processes in general, and that many conditions
regarded as pathological in one animal are natural in
another. It will be useful to illustrate this by some
concrete examples. To take a simple case. The inside
of our cheeks has a soft lining known as mucous mem-
brane. In very rare instances children have been born
with tufts of hair growing in this situation. Such a
condition is truly abnormal. A physiological type for
such a phenomenon is found in the mouths of rodent
mammals ; the inside of the cheeks of rabbits, hares,
porcupines, and the like, present naturally patches of
hairy skin. Pigment is widely diffused in animal bodies,
both under natural and unnatural conditions, using the
term unnatural as equivalent to disease ; this explana-
tion is necessary, for disease being controlled by
natural conditions cannot logically be regarded as un-
natural.

In the dace (fig. i) we notice sundry collections of
black pigment dotted among the scales. When ex-
amined critically the centre of each dot contains a white

4 EVOLUTION AND DISEASE.

speck. These collections of pigment are due to the
irritation caused by the presence of a parasite. In
tigers, lions, monkeys, and sheep, similar pigmented
spots are occasionally found in the lungs around
parasites. In man, horses (especially grey horses),
and dogs, tumours of an inky-black colour, called in
consequence melanotic, are occasionally met with. All
these formations of pigment are purely pathological.
Under normal conditions, however, cuttle-fish {Octopus,

Fig. i. — A Dace with spots of black pigment due to the irri-
tation of a parasite (Mus. Royal College of Surgeons).

and Sepia), possess an ink-bag from which, when these
animals are irritated, an ink-like pigment, sepia, can be
ejected in such abundance as to colour the surrounding
water to the extent of a cubic yard or more, and under
cover of this dark cloud the cuttles escape from their
enemies.

The close relation existing between physiological and
pathological processes is shown in an interesting manner

INTR OD UCTION. 5

by a study of the development and fall of the antlers
of deer when compared with changes which occur in
bone as a result of injury.

Bones are clothed externally by a membrane termed
periosteum ; this membrane serves as a matrix in
which blood-vessels ramify before entering the compact
tissue of the bone. It must be remembered that bone

Fig. 2. — The head of a female Moose (Alces machlis) ; the antlers
are in " velvet."

is not only dependent on the periosteum for nutrition, but
the deeper layers of this membrane have bone-forming
properties ; the increase in thickness of a long bone is
due entirely to the periosteum. Should the periosteum
be injured and inflammation established, a local increase
in its bone-forming function is the result, producing a

6 E VOL UTION AND DISEASE.

rounded or irregular swelling termed a node. In some
cases the periosteum is so damaged that it becomes
detached, and as a consequence the bone beneath dies.
As soon as a piece of bone is dead those parts of the
living bone adjacent become unusually active, leucocytes
or white-blood cells begin to devour and finally succeed
in detaching the dead portions when large, or digest
them completely when small. Dead bone is known
by the following features — it has no sensation, emits a
sound when struck with a metallic instrument, and does
not bleed when cut.

The antlers of deer when young and growing are
covered with a soft vascular membrane, beset with
delicate downy hair and glands, termed the " velvet/'
which bears the same relation to growing antlers that
periosteum holds to bone (fig. 2). As long as the
antlers retain this velvet in a living condition they
increase in length and thickness ; when the antlers are
actively growing they feel warmer to the hand than the
rest of the body, resembling in this respect an in-
flamed part. When in " velvet " a stag is particu-
larly careful not to knock the antlers, for they are very
sensitive, and when so unfortunate as to bruise them,
a node or swelling forms upon them in every way
resembling nodes on other bones when injured. I have
seen nodes on antlers, caused by blows, as large as
oranges. This is illustrated in fig. 3, which is a drawing
of a pair of antlers of a roe-deer preserved in the
museum of the Royal College of Surgeons. The left
antler is shorter than the right one and has an ossified
node upon it as large as a Tangerine orange. After the

INTRODUCTION, 7

antlers have attained full dimensions it is difficult for
the circulation to be maintained through so thin a mem-

Fig. 3. — A pair of antlers from a Roe-deer [Caprcolus capr<za) with an
ossified node upon them (Mus. Royal College of Surgeons).

brane as the " velvet," and as a consequence it shrivels
and peels off; the bone beneath is deprived of blood

8 E VOL UTION AND DISEASE.

and dies. The branches suffer first and then the
beam. At this stage the antlers become formidable
weapons, and the stag, instead of taking every precau-
tion not to knock or bruise them, now fears nothing,
for they are like dead bone, devoid of sensation. In
time the necrosis extends along the antler until it
reaches the pedicle, that part which is covered by the
natural hairy skin of the deer ; in due course a line of
demarcation is formed by leucocytes, and the antler falls

Fig. 4. — The head of a Cow with a large cutaneous horn.

by a process exactly analogous to that by which a piece
of dead bone is separated. *

We may turn to the consideration of processes in
disease which are dominated by the physiological pro-
cesses peculiar to a particular aninjal, and illustrate
this by reference to cutaneous horns, especially that form
which arises from the modification of warts. Not in-
frequently in mammals and birds the free portions of

INTRODUCTION. 9

warts become transformed into a tissue identical with
horn. Such a specimen is represented in fig. 4. It
shows a large horn projecting from the forehead of
a cow, the horn is fifty centimetres in length. It
was obtained by the celebrated John Hunter, and
is preserved in the museum of the Royal College of
Surgeons. A careful examination of the horn and the

Fig. 5. — The head of the Rhinoceros, showing the nasal horns,
physiological type of wart-horn.

material which occupied the cavity in the horn, indicate
that it originated in a wart. Such horns are common
in man, and have been known to^attain a large size.
A physiological type of such horns is furnished by the
nasal horn of the rhinoceros which in its structure, con-
nections, and mode of origin resembles in its main par-
ticulars the pathological horn on the head of the cow ;

io E VOL UTION AND DISEASE.

indeed we are fully justified in stating that this nasal
horn of the rhinoceros is a gigantic wart (fig. 5). Pro-
fessor Flower recently exhibited at the Zoological
Society the skin from the head of a rhinoceros shot
in Central Africa with three nasal horns. The accessory
one measured twelve centimetres in height and more than

forty-two in circumference. It
was situated in the same line
posteriorly to the normal horns.
It was structurally a wart. That
cutaneous horns should arise in
oxen and other hollow-horned
ruminants {Cavicomid) need not
surprise us when we reflect that
the corneous caps of their natural
horns are modified portions of
the integument.

Birds not infrequently exhibit
wart-horns of this character, and
an example growing from the leg
of an oyster-catcher is shown in
fig. 6. Such horns, whenever

Fig. 6.— The leg of an Oyster &

Catcher (Hcematopus ostra- they have been observed in birds,
Ugus) with a large wart-horn. fojjow ^ usual CQurse of ayjan

dermal organs in general, and are shed with each
moult and reproduced with the new feathers. The
horn on the leg of the oyster-catcher when compared
with the size of the bird is very large. It is represented
one-fourth its natural size.

The shedding of pathological cutaneous horns and
their subsequent reproduction has more than one

INTRODUCTION.

ii

physiological type. Among birds the horned puffin
{Fratercula corniculatd) will be selected.

Growing from the upper eyelid of this bird is a
slender, pointed, black-coloured horn, which in the
specimen from which the drawing (fig. 7) was made,
measured eighteen millimetres in length : there is also
a thin horny scale connected with the lower lid. In
the adult bird it is stated that these horns are shed and
reproduced annually.

Fig. 7. — Head of the Horned Puffin {Fratercula comiculata)
to show the horn growing from the upper eyelid.

It has already been mentioned that the corneous cap
of the cavicorn ruminants is merely modified portions
of the integument. In the Prongbuck (Afttilocarpa
americand) the hard cap of the horn is annually shed, an
observation first made in 1865 in the Zoological Gardens,
London. Subsequently, doubt was thrown on the
matter, but it has been definitely settled by the observa-
tions of Mr. W. A. Forbes. Thus we are able to furnish

1 2 E VOL UTION AND DISEASE.

types among normal cutaneous horns, not only in birds
but among mammals, as parallels to the annual shedding
of the pathological cutaneous horns of birds.

Not infrequently tumours are found in certain abdo-
minal organs and in the subcutaneous tissues of man
and other mammals, possessing skin and its appendages
such as hair, wool, and glands. Such tumours contain
in man, horses, and oxen, hair ; in pigs, bristles ; in
sheep, wool ; and in birds, feathers ; thus harmonizing
with the physiological characters special to the animal in
which such tumours occur. Further, the hair in such
tumour becomes grey as age advances, and like that on
the exterior of the body is shed, so that such tumours
may in the long run become literally bald.

Without attempting to multiply instances, such facts
as these were sufficient to induce me to pursue the
inquiry into Zoological Pathology, or General Pathology
in the fullest sense, and the latest views and investiga-
tions in this wide, but little cultivated, field are sum-
marized in the ensuing pages.

Wherever possible, physiological types of diseased
(pathological) processes are described ; the illustrations,
whenever practicable, have been selected from animals
other than man, for in him they have been too exclusively
studied ; indeed, by restricting our inquiries to man it
is impossible to frame any generalizations concerning
disease upon a sound basis. It has been stated that " a
knowledge of human anatomy is sufficient for the mere
art of the surgeon." This may be correct, but it is quite
certain that if we restrict our observation of the processes
of disease as they occur in man, our notion of them

INTRODUCTION. 13

would be as crude as if we attempted to form conclusions
as to his zoological position without reference to other
species of animals.

In the ensuing chapters the following plan has been
adopted : The effects of increased use and disuse of
parts is considered in connection with the gradual change
in the function of organs, and the part played by the
transmission of the effects of increased use and disuse in
producing vestigial structures in complex organisms.
The tendency of vestiges to become diseased or to give
rise to conditions disadvantageous to the individual is
fully dealt with. The important and interesting subject of
the transmission of acquired characters and malforma-
tions is briefly discussed, and a chapter is devoted to
causes of disease arising without the organism and the
relation they bear to the remarkable processes, inflamma-
tion and fever. Tumours are considered in connection
with general morbid processes, and the scanty knowledge
we possess of the zoological distribution of disease is
summarized.

CHAPTER I.

THE ENLARGEMENT OF PARTS FROM INCREASED USE,
OVERGROWTH, AND IRRITATION.

It is well established that the increased use of a part
tends to enlarge and strengthen it, that disuse on the other
hand often leads to its diminution and enfeeblement :
structural modifications thus induced are inherited.

The truth of the first part of this statement may be
demonstrated by a simple experiment : Let the arm of a
healthy person be firmly strapped for several consecutive
days upon a splint — in a few days the muscles will be
softer than usual and actual measurements will show
that the limb has diminished in size. Allow the arm to
resume its function ; the lost ground will be quickly
recovered.

When a young and vigorous person has the mis-
fortune to lose an arm the remaining limb, being used
for all purposes, will rapidly increase in size and strength.
The same facts may be observed in dogs and cats which
have lost a limb or part of a limb. A woman, aged fifty,
had her big toe, including the metatarsal bone, ampu-
tated ; six months after she had regained the use of the
foot, the second toe had enlarged, and stood out from its
fellows in such a way as to resemble in size and general
appearance the lost toe — indeed, when the foot was

ENLARGEMENT OF PARTS FROM USE. 15

exhibited to a class of students, this large second toe was
mistaken for the hallux (fig. 8). This observation is of
interest, the large size of the first toe and the great
development of its muscles are owing to the greater use
and importance of the hallux in mammals which main-
tain an erect, or semi-erect, position when walking along
the ground as in man, or climbing trees as in monkeys
and phalangers. Humphry, in reference to the large
development of this toe, says, " Man literally stands in
the animal world on his great toe."

Fig. 8. — Enlargement of the second toe subsequent to
amputation of the hallux.

The same remarks apply to the thumb : in man
increased function develops its special muscles, thickens
the bone, and toughens the nail. Even among quadru-
mana the pollex may be absent (Ateles) ; in such a high
form as the chimpanzee the thumb is slender, short, and
insignificant. In man we may attribute the dispropor-
tion of the hallux and pollex, in comparison with the
neighbouring digits, to inheritance through a long line of
ancestors of gradual increments of size induced by

1 6 E VOL UTION AND DISEASE.

excessive use. Such gradual enlargement of a digit and
its hereditary transmission may be demonstrated in
Equidce. The modern horse walks upon the greatly
enlarged third digit of the hand and foot respectively,
the hoof representing the nail. Hidden in the tissues on
each side of this functional toe we find vestiges of the
second and fourth ; these are familiar to veterinarians as
splint bones.

The researches of palaeontologists have furnished an
excellent array of evidence in support of the opinion
that the horse has descended from ancestors which
possessed five functional digits; the first and fifth
gradually disappeared, the second and fourth still persist
but are functionless, whilst the middle one has from
increased use attained an extraordinary size.

In the drawing (fig. 9), a longitudinal section through
this large digit of the horse is represented beside the
corresponding finger of a man similarly bisected. The
homologous parts are indicated by the same letters. In
the horse's finger a bone is shown, in section, at the
junction of the second and third phalanges ; this is called
the navicular bone or small sesamoid. Such bones
are frequently found in the tendons of man, especially
where they glide over bony prominences ; usually they
are small, rarely exceeding a split pea in size. In the
horse such bones are large and important ; not in-
frequently, when the foot is brought violently in contact
with hard ground, the navicular bone in one or both feet
is broken by the concussion ; the result is permanent
lameness, a fractured navicular bone rarely, if ever, unites
by bone. In this respect it resembles the great sesamoid

ENLARGEMENT OE PARTS FROM USE. 17

bone in man, the patella or knee-cap ; when the patella is
broken by muscular violence it is rarely repaired by
bone, but by yielding fibrous tissue.

In the navicular bone of the horse and the knee-cap of
man, analogous conditions prevail, viz., bones which in
many mammals are small and insignificant have become
by excessive use enlarged and of such importance that,
when damaged, permanent lameness in man, and useless-
ness in the horse, ensue.

When parts are enlarged in this way from increased
use, they are said to be hypertrophied ; in the case of the
horse's foot the hypertrophy is said to be functional^ in
that of the big toe figured on page 15, pathological^ as it
arises in consequence of abnormal conditions.

The most striking examples of hypertrophy may be
studied in the muscular system and in paired organs.
For instance, should one kidney from any cause be
slowly destroyed, the other will gradually enlarge and
often double its size, thus compensating the animal and
often preserving it from disaster. Many such cases
have been reported in man and I have met with kidneys
enlarged from this cause in horses, sheep, oxen,
pheasants, and in a hen. Enlargement of a part from
such causes is said to be compensatory ; conspicuous
examples of this form of hypertrophy occur in the
animal kingdom. Variations in the size of a part
according to the amount of work performed by it is
illustrated by the gizzards of birds. In flesh- or fish-
eating birds the muscular walls of the gizzard are
relatively thin ; in grain-eaters they are exceedingly
thick. Hunter fed a sea-gull for a year on barley

3

i8

EVOLUTION AND DISEASE.

and found the muscular coat increased in thickness.
This simple experiment has been varied by other
observers with similar results.

The large breast muscles (pectorals) of birds associated
with and varying according to the expanse of wing,
furnish a good example of the relation of increased size
with augmented use ; these may be compared with the

M

Fig. 9.— A medium longitudinal section through the third
finger of a horse, and man. M, metacarpal bone ; 1, 2, 3,
phalanges. The ossicle, N, situated at the junction of the
second and third phalanges is the navicular.

powerful leg muscle of the frog (known as the gastro-
cnemius) so important in the act of swimming, and the
large muscles of the human buttock, useful in helping
man to maintain the erect position. These are striking
instances of the inherited effects of increased use of a
part.

ENLARGEMENT OF PARTS FROM USE. 19

Enlargement of parts may arise from increased blood
supply due to irritation ; thus a bone, the tibia, has been
known to increase in length when long inflamed, to the
extent of an inch and a half as compared with its
fellow.

Skin supplies many curious and instructive instances
under the names of corns and callosities. Those
troublesome thickenings of the skin covering the toes,
caused by ill-fitting boots, known as corns, or on the
palms of the hands due to the use of tools in particular
occupations, consist anatomically of a raised hard patch
of thick epidermis ; beneath it is a small sac containing
fluid, termed a bursa. When a thickened patch of
skin exists without a bursa it is usually called a
callosity. Corns, as most are aware, occur most
frequently on the toes, whilst callosities form on the
sole of the foot and in the neighbourhood of the heel.
Callosities are inherited, as is shown by the fact that the
skin on the sole of the foot of a peasant's infant is
thicker than that on the foot of the parson's offspring
at the moment of birth. We may not unreasonably
attribute the readiness with which a badly fitting boot
will produce corns to a tendency we inherit from our
parents and grandparents. In the same way the
callosities on the breasts of camels, on the knuckles
of the gorilla's fingers, and the ischial callosities of
baboons, may be regarded as inherited local cutaneous
thickenings, induced by the intermittent pressure to
which the skin of these parts is subject ; in the case
of the camel when lying down, the gorilla when walk-
ing, and the baboon when sitting on its haunches,

20

E VOL UTION AND DISEASE.

Increase in the size of a part may arise from diminished
use co mbined with irritation. For instance, nails, hoofs,
and claws grow throughout life, and the wear and tear
consequent on continued use is thus compensated.
Should such parts be used less than usual, growth
continues at the normal rate and the nails or hoofs
become abnormally large and inconvenient. This form
of enlargement is termed overgrowth, and is more liable

to occur when diminished
use is accompanied by
irritation, as illustrated by
the following specimen.
It was a goat, confined for
many weeks in a muddy
paddock ; on examining
its feet I found them fur-
nished with hoofs of great
length, one measured
thirty-six centimetres fol-

Fig. 10. — An overgrown hoof in a lowing the Curve, and its
goat, which had lived many weeks . _

in a muddy paddock. It measures fellOW twenty - five Centl-

thirty-six centimetres following the metres (fig. IO). The hoofs
curve.

of cows, horses, sheep, and
deer become similarly overgrown when enclosed on
marshy ground, dirty paddocks, or damp sheds. Similar
conditions are not rare in our own species, for old,
bedridden persons often have long toe-nails, some of
them two or three inches long, thick and twisted like a
ram's horn.

The relation between increase in the growth of nail
or hoof in consequence of additional blood supply, is

ENLARGEMENT OF PARTS FROM USE. 21

shown in a striking manner in the foot of the horse.
When inflamed the hoof will sometimes become much
longer than usual, and the softer part, known as the frog,
will enlarge and form a spongy mass, filling up the sole.
This cannot be attributed to disuse as the remaining
hoofs are also idle, for the horse is unable to work on
account of lameness, and we can assure ourselves of the
existence of inflammation in the affected foot by ob-
serving its increased heat.

In the next chapter I shall have occasion to demon-
strate that overgrowth may occur from diminished use
alone ; nevertheless, the most striking examples are
associated with increased blood supply consequent on
irritation, and as this assists in explaining some interest-
ing normal conditions it will be advantageous to consider
some additional instances. It has long been known that
when the skin is irritated, especially in young people, by
long continued discharges from wounds, or by the per-
sistent application of poultices, the hairs of the part
grow thick and long : when the irritation subsides the
hairs gradually return to their normal condition. This
overgrowth of hair may be attributed to a local increase
in the blood supply, for it is a fundamental principle in
Pathology that irritation produces redness of the skin ;
the heightened colour is a consequence of additional
supply of blood to the part. Hunter demonstrated the
relation between blood supply and overgrowth in an in-
genious way : he transferred the spurs of cocks to the
vascular tissue of the comb ; here they took root and, in
consequence of the extra supply of blood, and in part no
doubt from disuse, grew inordinately. These specimens,

22

EVOLUTION AND DISEASE.

in company with several others, are preserved in the
museum of the Royal College of Surgeons (fig. n).

The additional supply of blood to a part abnormally
functional or irritated seems to be largely due to nervous
influence, as the following experiments show. Bidder
excised a piece of the sympathetic nerve in the neck of
a young growing rabbit. This was followed by over-

Fig. ii. — The head of a cock with its spur transferred
to the comb.

growth of the ear of the same side. The experiment
has been repeated by Sterling on young and growing
rabbits, and on dogs. A piece of the vagus and sym-
pathetic— for in dogs both nerves are contained in the
same sheath — was excised. In all cases the ear on this
side became distinctly longer, broader, and somewhat
thicker than its fellow. The hair was longer and

ENLARGEMENT OF PARTS FROM USE. 23

;-t*4iiik -

stronger on the side operated upon, and the ear remained
distinctly warmer.

The relation of irritation upon nerves in connection
with overgrowth of dermal structures may be illustrated
by the curious defect known as spina bifida occulta. In
this malformation the bony arches covering the spinal
cord are defective, and the
nerves issuing from the cord
at this spot are involved in
fibrous tissue or compressed
by an accumulation of fat.
It is no uncommon event
to find the skin covering the
defective parts of the spine
presenting a tuft of hair often \
many centimetres in length, j
or the lower limbs may be
covered with a crop of thick
hair. The common form is
shown in fig. 12.

These facts have been
used in a subtle way by Vir-
chow. The heads of Polish

fowls are Surmounted by a Fig. 12.— A hairy tuft in the loin, due
1 . r, r r , 1 to a defect in the arches of the spine

luxuriant tuft of feathers and irritation of the cord or nerves.

(fig. 13). Underlying this (After Fischer.)

feathery crown in many Polish hens is a defect in the
roof of the skull, resembling in many respects the con-
dition known in man as meningocele. A study of the
effects of spina bifida in man has led Virchow to regard
the crown of feathers as the result of irritation, in the

24

EVOLUTION AND DISEASE.

same way that the hairy tuft may be accounted for in
the back of those with spina bifida occulta. These
fowls are extremely uncertain in their gait, given to
performing circular movements, and walking sideways if
excited, as though they possessed an unstable nervous
system. Darwin was assured that we had here to deal
with a character first acquired and transmitted by the
hen.1

Fig. 13. — The head of a Polish fowl to show the feathery tuft.
(After Darwin.)

A somewhat similar condition is seen in ducks. Pre-
served in the museum of the Royal College of Surgeons
is a duckling with a small tumour projecting from the
top of its head ; hanging from the side of the tumour is
a miniature but well-developed foot (fig. 14). The
swelling is connected with the duckling's brain by means
of a small rounded hole in the summit of the cranium.

1 " Animals and Plants under Domestication."

ENLARGEMENT OF PARTS FROM USE. 25

Isidore Geoffroy Saint-Hilaire x describes and figures
the head of a duck with a tuft of feathers on the occiput
and a foot. In describing the foot Saint-Hilaire states
that the cranium underlying the tuft was defective, and
especially notes that the cranial opening was similar to
that found in " les poules a tete huppee»"

Fig. 14. — Head of a^duckling with a tumour and abnormal foot
growing from the occiput.

During life this foot, like the normal pair, was of a
beautiful orange-yellow colour. Some who saw the duck
were suspicious that the foot had been engrafted on to the
occiput accidentally : such an opinion had no foundation.

t a

Des Anomalies de reorganisation chez Thomme et les Ani-

maux, tome 111. p. 194.

2 6 E VOL UTION AND DISEASE.

Tiedemann * in 1831 described and figured the skull
of a duck with a foot growing from its occiput. There
is a fancy breed of ducks in which the distinguishing
feature is the presence on the occiput of a rounded knob
or swelling covered with feathers.

The acquisition and transmission of such characters
shed light on some rather puzzling conditions. Ab-
normal growth of hair induced by contact with irritating
substances may explain the presence of hair in such a
curious situation as the stomach of a crayfish and the
hairs which form the remarkable plug around the pyloric
orifice of the darter's stomach (fig. 15). This bird feeds
on fish, and as Garrod, in his excellent account of the
anatomy of the darter's stomach, puts it, " This peculiar
hairy mat acts as an excellent sieve to prevent the
entrance of solid particles, fish-bones, &c, into the
narrow intestines." 2 From what we know concerning
the effects of irritation upon the skin it is quite con-
ceivable that the contact of fish-bones and scales would
act as irritants and induce a crop of hairs which, being
advantageous to the bird, have been inherited. It in no
way invalidates the argument by urging that skin, not
mucous membrane, is furnished with hairs. Even the
complex intestinal mucous membrane may, under ex-
ceptional circumstances, become converted into pilose
skin. Such abnormal skin is more likely to possess hair
if it be irritated. Abnormal growth of hair from irrita-
tion is paralleled by the elongation of the cutaneous
papillae under similar circumstances. This may be studied

1 " Zeitschrift fur Physiologic/' Bd. iv. p. 121.

2 " Proceedings of the Zoological Society," 1876, p. 335.

ENLARGEMENT OF PARTS FROM USE. 27

in lambs. In Britain sheep and lambs are often turned
out to feed on clover grown in fields with the stubble
from a previous crop of wheat remaining ; the short,
stiff, hard ends of the straw irritate the mouth and nose
as well as the tender part of the feet above the coronet,

Fig. 15.— The stomach of the Darter (Plot us anhingd), showing
the hairy pyloric plug (Mus. Royal College of Surgeons).

and produce a crop of warts. The relation of such
irritation to warts is demonstrated by the fact that when
the lambs are removed from the stubble the warts dis-
appear. Similar warts grow on the hands of children

28 E VOLUTION AND DISEASE.

when not kept clean ; grubbing about in dirt and
muddy, stagnant pools incidental to farmyards will
produce warts on the noses of lambs.

The hairless pads on the feet of carnivorous mammals
are made up of closely packed enlarged papillae. When
confined in cages and not kept scrupulously clean, the
combined effects of dirt and limited use often induces
a growth of warts. Sometimes, especially in the coati-
mundi, the whole of the pad will be covered with
elongated papillae, the appearance of such feet reminding
us of the pad on the plantar aspect of the ostrich's toes.

The way in which skin responds to external stimuli
explains the manifold modifications it presents in the
various classes of animals, and it is highly probable that
dermal structures of great utility to individual animals
have arisen under circumstances such as produce them
in man under abnormal conditions.

This response of the skin to irritation or abnormal
stimulus is not confined to vertebrates ; the lamelli-
branchs illustrate it in a striking way.

Lining the concavity of the shells is a membranous
structure, which may be regarded as the integument,
and is known as the pallium or mantle. The shell itself
is the direct result of the excretory efforts of the lobes
of the mantle, and is composed of animal matter
hardened by deposits of carbonate of lime.

Occupying the space between the mantle of opposite
sides, we find the animal proper, consisting of branchiae,
intestines, foot, nervous system, heart, reproductive
organs, &c.

These animals obtain their food in a somewhat lazy

ENLARGEMENT OF PARTS FROM USE. 29

fashion. The margins of the gills are covered with
cilia, which, by their constant movements, set up in-
halent currents, which not only serve to oxidise the
blood in the branchiae, but convey concrete particles,
many of which are seized upon by the mussel and
utilised as food.

Some lamellibranchs have animals commensal upon
them. Commensalism differs from parasitism in the
important fact that an animal commensal on another
lives upon the food of its host, whereas a parasite lives
in the cavities or tissues of, and draws nourishment
from, the blood of its host. It would seem that as long
as the animals commensal on a lamellibranch keep
within the space between the mantle they are safe
enough, but occasionally they are rash enough to enter
the space between the shell and the mantle. This
trespass is resented by the lamellibranch, and the tres-
passer is punished by being entombed in shell-tissue,
and in some cases by pearl.

A very beautiful example of this has been recorded
by Dr. Gunther.1 The specimen is represented in the
accompanying woodcut (fig. 16). It had been in Dr.
Glinther's possession for many years. It is an old shell
of Margarita margaritifera, in which there is embedded,
behind the impression of the attractor muscle, a perfect
individual of a fish belonging to the genus Fierasfer.
The fish is covered by a thin layer of pearl-substance,
through which not only the general outlines of the body,
but even the eye and mouth, can be seen.

In this case the fish, instead of keeping between the
1 " Proceedings of the Zoological Society," 1886.

3°

EVOLUTION AND DISEASE.

two halves of the mantle, penetrated between the mantle
and the shell. The irritation thus caused induced the
mollusc to cover the intruder with pearl. The secretion
must have taken place in a very short time, at any rate
before the fish could have been destroyed by decom-
position.

Fig. 16. — A fish embedded in pearl (after Gunther).

Dr. H. Woodward has described some interesting
specimens of the same nature. He exhibited before the
Zoological Society (1886) a Pinnotheres which had been
entombed in a cyst of pearl by a pearl-mussel. In connec-
tion with the specimen Dr. Woodward made the following

ENLARGEMENT OF PARTS FROM USE. 31

remarks : " It seems extraordinary and beyond belief
that the Meleagrina should, of all the Conchifera, be the
one to resent the commensalism of the Pea-crab, which
has been known since the days of Cicero, Pliny, Oppian,
and Aris'totle to inhabit the shell of the Pinna and the
Oyster, and has been recorded from Astarte, Pecttmculus,
and at least some half-dozen other bivalves, with whom
it appears to live on the most friendly terms. It is the
females, however, which constantly reside within the
shells of the Conchifera, whilst the males are said to
avail themselves of favourable opportunities to visit the
females in their retirement."

Whether or not the unlucky male in this case in-
truded himself upon Meleagrina at an unfavourable
period, and, finding no female Pinnotheres, penetrated
so far beneath the mantle of the pearl-mussel as to be
unable to retreat, one thing is quite clear, namely, that
Meleagrina entombed the intruder in a cyst of pearl,
from which the clever pearl-button maker alone liberated
him.

Increased thickness of the shell of an oyster from
irritation is comparable to the formation of thick skin
under similar conditions. The thin shells of " native
oysters'* living in quiet shallow water stand in striking
contrast to the huge, rough, laminated shell of the
"North Sea oyster " which has to contend with the
pressure of a large volume of water and much buffeting
from a tumultuous ocean. So that a native oyster, when
compared with one from the North Sea, resembles the
hand of a courtier when contrasted with that of a
peasant.

32 E VOL UTION AND DISEASE.

That Increased size is not due always to increased
function but may arise from irritation is admirably
illustrated in Solanum jasminoides described by Darwin.
" The flexible petiole of a half or a quarter grown leaf
which has clasped an object for three or four days
increases much in thickness, and after several weeks
becomes so wonderfully hard and rigid that it can hardly
be removed from its support. On comparing a thin
transverse slice of such a petiole with one from an
older leaf growing close beneath, which has not clasped
anything, its diameter was found to be fully doubled
and its structure greatly changed " ("Climbing Plants").

In this example the extra thickness could not be due
to increased function, but to irritation ; the petiole had
less work to perform as the leaf was largely supported by
the object which its petiole had clasped.

The effects of increased use may be observed in the
organs of special sense. When an individual loses an
eye in early life the remaining healthy eye acquires a
greater range of movement and quickness which com-
pensates in no small degree for the loss of its companion.
In persons blind from early life the power of hearing
becomes wonderfully quickened, and their tactile sensi-
bility is so heightened that they make themselves
acquainted with external surroundings in a marvellous
manner. Similar instances are furnished by the mole ;
its sense of hearing is proverbial. Says Caliban to
Stephano and Trinculo : " Pray you tread softly, that
the blind mole may not hear a footfall." The blind
fish of the mammoth cave are said to be abnormally
sensitive to sounds as well as to undulations produced

ENLARGEMENT OF PARTS FROM USE. 33

by various causes in the water. Wyman has attempted
to show that the semicircular canals are unusually large
in the blind fish Amblyopsis.

The study of the examples of enlarged parts arising
from increased use, additional blood supply, and irritation,
teaches clearly enough that the same laws which regulate
these processes under normal conditions are equally
active under abnormal conditions, and indicates that the
thick fur of mammals living in cold climate, or the local
growth of hair on the skin of man when stimulated by
irritants or unusual states of the nerves, are responses to
such stimuli as call up the growth of hair in the stomach
of the darter or crayfish ; the scales of serpents, feathers
of birds, quills of porcupines, and bristles of hogs, are like
hair, epidermis and horn, modifications of the surface
epithelium, probably induced by variations in the nature
of the stimuli, or irritants, and in differences of surround-
ing conditions, such modifications being transmitted to
the offspring.

The inheritance of the effects of increased use of
parts not only manifests itself in enlarged muscles, thick
bones, and stout ligaments, but explains the large
udders and bountiful supply of milk we obtain from
domesticated cows, and, as Wallace rightly remarks,
" almost perpetual egg-laying in poultry."

In a similar manner increased use of the special senses
with the transmission of the extra acuteness gradually
acquired by individuals, explains the wonderful power of
scent in dogs, of sight in hawks, and of cunning in
foxes.

In a similar manner, also, the use of the fingers in

4

34 E VOL UTION AND DISEASE.

particular trades, as those of watchmakers, jewellers,
ivory carvers, &c, or the precision of artists and sculp-
tors, and, in a more marked sense, the keen ear of
musicians, and the wonderful faculty displayed by
mathematicians in their marvellous dealings with num-
bers and calculations, have all been slowly attained by
the persistent transmission of the effects of increased
use.

CHAPTER II.

DISUSE AND ITS EFFECTS.

DISUSE of a part usually leads to its enfeeblement and
diminution, a result conveniently expressed by the term
atrophy ; in many instances the effects of disuse are
transmitted. Atrophy may be induced in a variety of
ways, but in nearly all cases it is attributable to
diminished use and its inevitable consequence, lessened
blood supply. Disuse of a part may be caused by
changed habits of life, or by the increasing importance
of some other organ. Certain parts are only useful for
a brief period in an animal's life ; some appear to have
no function and are present in conformity with the law
of heredity, whilst atrophy from disuse may be the
consequence of injury; and, lastly, an interesting variety
of atrophy is due to continuous pressure. It will there-
fore be instructive as well as conducive to clearness to
describe some typical cases of the various forms of
atrophy.

Atrophy from changed habits. — Among the many
anomalies of animal life in New Zealand must be in-
cluded the remarkable owl-parrot or kakapoe (Stringops
habroptilus). This bird is nocturnal in its habits, feeds
on fern-shoot, roots, berries, and, it is said, occasionally
lizards. It climbs but does not fly, though possessing

36 EVOLUTION AND DISEASE.

what looks like, in so far as shape and size are con-
cerned, an admirable pair of wings. A dissection of
the pectoral muscles is suggestive, for they are thin,
flat, and contain but little contractile tissue. The
prominent keel so conspicuous on the sternum of fly-
ing birds is, in Stringops, a mere ridge. The intrinsic
muscles of the wings are pale, thin, and composed
largely of fibrous tissue (fig. 17).

It has been inferred that these birds have not long
been inhabitants of New Zealand only, but were de-

FjGf 17. — The Owl-parrot, or Kakapoe {Stringops habroptilus).

veloped in other countries where their wings were of
use to them. The disuse of the wings is due to altera-
tion in environment.

The atrophied wing muscles in the owl-parrot recall
the observations of Rengger who attributes the thin legs
and thick arms of the Payaguas Indians to successive
generations having passed nearly the whole of their lives
in canoes with their lower extremities motionless.

Atrophy of parts useful for a brief period. — Very
many organs are useful for a brief period, and later

DISUSE AND ITS EFFECTS

37

atrophy or even disappear. The curious suctorial disc
of the recently hatched embryo of the fish, lepidosteus,
is a case in point. In the adult fish the upper jaw ends
in a fleshy globular projection ; this, in the embryo, is
a large disc, as in fig. 18. Agassiz, to whom we are
indebted for much of our knowledge of this structure, has
ascertained that the disc is formed two or three days
before hatching, and the young fish uses it as a sucker,

— Scl B

Fig. i 8. — A, head of a young lepidosteus ; B, the suctorial
disc seen from below ; sd, suctorial disc ; m, mouth.
(From Balfour.)

by means of which it can attach itself to the sides of
the vessel in which it is confined, or to other objects.
The young lepidosteus can fix itself so firmly that con-
siderable commotion in the water is required in order
to make the fish lose hold : it can even remain suspended
after the water has been lowered beyond the level to
which it is attached,

38 E VOL UTION AND DISEASE.

This form of atrophy may be studied in ascidians.
These are marine animals which encrust stones, rocks,
and weeds on the sea-bottom. Sometimes they are
solitary, but often occur combined in masses. In the
adult condition they have an appearance recalling that
of a tough leathern bottle with two openings ; water
enters at one, leaves by the other. The young of some
ascidians have a totally different form, resembling a tad-
pole not only in external configuration but in internal
organization ; the general details of the anatomy of an
ascidian tadpole is shown in fig. 19.

After existing in a free state for some time the
young ascidian fixes itself to a stone by its head ; the
tail, with the notochord and nervous axis, atrophies, the
body changes its shape, the brain remains small and
undeveloped, and the eyes disappear. Finally the
animal increases in size, its outer case becomes tough
and leather-like.

Among other examples of this form of atrophy,
mention may be made of the tail and gills of frog-
tadpoles, the external gills of sharks, and the Alpine
salamander, the yolk sac of vertebrata. Remarkable
instances of the atrophy and disappearance of larval
organs may be studied among invertebrates, especially
in the echinoderms and star-fish. Many marvel at such
things occurring in other animals, and overlook the fact
that similar conditions may be studied in our own
bodies, for the fall of the milk teeth is induced by the
same process which brings about the disappearance
of the tadpole's gills and tail. Puppies are born blind :
this blindness is due to the existence of a vascular

DISUSE AND ITS EFFECTS,

39

membrane occupying the space known as the pupil of
the eye. This membrane rapidly atrophies and the
pups begin to see. In the human offspring a precisely
similar membrane is present during em-
bryonic life, but atrophies a few weeks
before the termination of intra-uterine life.
The mode by which foetal or larval organs
of this character are slowly removed will
be considered in detail in a later chapter.
Suppression of Parts, — It has long been
known that in the embryo of vertebrates

SPIRACLE

EYE MOUTH

ASCIDIAN

NOTOCHORD

Fig, 19. — Ascidian Tadpoles (after Lankester).
adult ascidian.

A, An

many structures and organs are formed and then dis-
appear without attaining, as far as our knowledge allows
us to judge, a functional condition.

40 EVOLUTION AND DISEASE.

The only interpretation which can be put on
this fact is, that these organs or parts have been
functional in the ancestors of such animals, but in
consequence of the increased use of other parts and
change in surrounding conditions, the organs in question
are not so serviceable to the animal and have, in
consequence of diminished use, slowly but gradually
atrophied. This effect may be conveniently referred
to as suppression. It is also a point of some importance
to remember that in consequence of changed con-
ditions in the surroundings and habits of an animal,
organs originally used for one purpose may become
so changed that they fulfil quite a different purpose : for
example, the remora, or sucking-fish, is able to attach
itself to the shark by means of a sucker-like disc on its
head ; in the embryo this disc arises from the anterior
part of the dorsal unpaired fin ; this is indicated through-
out life by the arrangement of blood-vessels and nerves.
Thus a locomotor-organ has become modified for
attaching purposes. Change of function and atrophy is
illustrated in a striking manner by the allantois.

The Allantois. — The embryos of reptiles, birds, and
mammals, differ from those of fish and amphibians by
the fact that at a very early date a vascular dilatation
arises from the posterior end of the developing gut.
This dilatation is known as the allantois, and in birds
and reptiles spreads itself beneath the shell-membrane.
The blood circulating in the membrane is in this way
brought into favourable relations with the atmosphere ;
the air diffusing through the shell, oxidises the blood in
the allantoic capillaries. The allantois is the respiratory

DISUSE AND ITS EFFECTS. 41

organ of the sauropsidian embryo. In the embryo of
placental mammals the work of respiration is considerably
modified, being performed by means of the placenta, an
organ formed of structures derived in part from the
foetus and in part from the mother. Under these
conditions the function of the allantois is limited to
the conveyance of blood-vessels from the embryo in
order to bring them into intimate relation with the
maternal tissues. This work accomplished, the allantois
shrivels, with the exception of the part in relation with
the cloaca ; this becomes permanently useful in mammals
as the urinary bladder ; a portion, however, remains as a
withered cord passing from the summit of the bladder to
the navel and is known as the urachus.

Thus the allantois exhibits what at first sight appears
to be a change from a respiratory organ to a receptacle
of urine, but closer inquiry shows the matter to be some-
what different. Amphibians possess a urinary bladder,
but not an allantois : a critical inquiry into the matter
induces me to accept Balfour's view and to look upon
the allantois as an enormously enlarged urinary bladder
which assumed in the embryo respiratory functions.
This change is coincident with, if not responsible for,
some extraordinary alterations. Fish and amphibia
{Ichthyopsidd) differ from reptiles and birds {Saurop-
sidd) and mammals in that they possess during some
period of their lives, gills, and in the non-possession of a
functional allantois. No vertebrate is known which
possesses gills and a functional allantois. Before the
advent of the allantois, embryonic respiration is carried
on in a variety of ways, sometimes by external gills, as in

42

EVOLUTION AND DISEASE.

sharks and the Alpine salamander, or by means of the

yolk sac forming adhesions to the oviducal wall, as in

Mustelus IcBvis, or even by means of the tail {Cczcilia

compressicandtx).

It is not unjustifiable to hold the allantois responsible

for the abolition of gills in sauropsida and mammalia.

This is much more probable than to attribute the change

to the evolution of lungs from
a swim-bladder, for functional
gills and lungs co-exist in such
forms as the mud-fish {Lepido-
siren) and ceratodus.

The history of the pineal
eye is an instructive instance.
Connected with the vertebrate
mid-brain is a structure known
as the pineal body, which
has long puzzled anatomists.
Many investigators have re-
garded it as vestigial ; that is,
it was of some functional value
in the ancestors of exist-

Fig. 20.— The head of a Lizard ing vertebrata. The truth of

(Varanus), showing the -bright this opinion has been demon-
scale indicating the pineal eye, P. r

strated by the admirable re-
searches of De Graaf and Baldwin Spencer.

On the dorsal aspect of the skull in lizards a
small opening exists, known as the parietal foramen.
In some lizards — as, e.g., Varanus — the situation of
this foramen is indicated by a bright scale (fig. 20).
On making a longitudinal section of the head, so as

?-

DISUSE AND ITS EFFECTS.

43

to include this parietal foramen, we find it occupied
by an organ representing an eye in miniature, con-
nected with the pineal body by nerve-fibres. The
relation of the parts is indicated in fig. 21, represent-
ing a lateral view of the brain and adjoining parts
of the skull in the New Zealand lizard, Hatteria
(Sphenodoii).

When the eye is examined microscopically, it pre-
sents the structural details found in functional eyes,
such as cornea, lens, retina, pigment, &c. (fig. 22).

Fig. 21. — Lateral view of the brain of Sphenodon, showing
the relation of the pineal eye, P ; the cerebrum, C ; and the
medulla, .M. (After Baldwin Spencer.)

Spencer is of opinion that this suppressed eye repre-
sents the unpaired eye of larval Tunicata. There is
good evidence that it was highly developed in extinct
amphibia {Labyrinthodontd)^ and was probably a sense-
organ in animals of pre-tertiary periods.

It is not unreasonable to suppose that the gradual
development and greater utility of the lateral eyes
have led to the suppression of the median eye.

Although the pineal body (regarded by Descartes as
the seat of the soul) in man is clearly vestigial, it is

44

EVOLUTION AND DISEASE,

by no means harmless, for occasionally it enlarges and
becomes occupied by tumours, sometimes of large size
and complex constitution, which cause death from
mechanical interference with the brain.

Darwin has pointed out that rudimentary (vestigial)
parts are apt to be highly variable. This variability
he thought was largely due to uselessness, and there -

Fjg. 22. — A magnified view of a section through the pineal
eye of Hatteria. (After Baldwin Spencer.)

fore to natural selection having no power to check
deviations in the structure of such parts.

It will be interesting to study this view of the matter
in connection with oviducts, which are of frequent occur-
rence as anomalies in the males of unisexual animals,
especially as two reasons can be advanced for their
vagarious conduct. In the first place, I shall endea-
vour to show that they have undergone a remarkable

DISUSE AND ITS EFFECTS. 45

change of function, inasmuch as they are transformed
from urinary to reproductive functions in the female,
whilst in the male they are functionless.

The Oviducts. — The history of the excretory organs
indicates that the kidneys were larger in the an-
cestors of vertebrata than in existing forms, and
the urinary excretion was conveyed by a series of
ducts to the exterior of the body, whereas the kidney
possesses now only one duct, the ureter. Of the once
extensive renal system, the higher vertebrata possess
relics in the form of the Wolffian bodies and their
ducts, structures which are relatively very large in the
embryo, but towards the mid-period of intra-uterine
life dwindle, and are for the most part present in
adults as vestiges. Although the glandular portions
of the primitive renal system atrophy, and are per-
manently replaced by the kidney, the ducts belonging
to them undergo a great change, and become utilized
for reproductive purposes.

In some fish the ova are shed into the abdominal
cavity from the ovary, and then escape to the exterior
by small openings near the anus, known as genital
pores. In many fish the ducts which belonged to the
anterior section of the primitive kidney become modified
into egg-conduits or oviducts.

When dealing with the Laws of Variation, Darwin
states that " a part developed in any species to an
extraordinary degree or manner, in comparison with
the same part in allied species, tends to be highly
variable." This law may be extended beyond the
scope of species, and applied to the reproductive ducts,

46 E VOL UTION AND DISEASE.

for we must regard them as being extraordinarily
modified as well as highly variable. This may be
illustrated by examples from widely separated animal
forms. It will be advantageous to commence with
the oviducts. In male toads and frogs two slender
streaks may generally be detected passing from the
so-called vesiculse seminales forwards to the roots of
the lungs. These thin streaks are the oviducts ; in
the male they are functionless, and normally remain
diminutive. It is by no means uncommon to find,
especially in male toads, the duct on one or both
sides, as well developed as in the female.

Professor Howes has described some well-marked
instances of the persistence of portions of the
oviducts in male specimens of the green lizard,
and in one the entire oviduct persisted as in the
female.

One of the most noteworthy examples of a persis-
tent oviduct in a male is that recorded by Mr. J. D.
Matthews,1 which he met with in a skate dissected in
the Natural History Department of the Edinburgh
University. In this fish a well-developed oviduct was
found on the left side in association with male organs
(fig. 23). An examination of the drawing shows
clearly enough that this oviduct was not a mere rudi-
ment, but was of the same proportion as would be
found in a female skate of corresponding size. The
claspers were present, and about six inches long.

This tendency of the oviducts to persist in the male
is not limited to fish and amphibians, but is manifested
1 Journal of Anatomy and Physiology ', vol. xix. p. 144*

DISUSE AND ITS EFFECTS.

47

OE-

by sheep, deer, oxen, monkeys, goats, and occasionally
in man.

In mammals the oviducts become transformed into a
complex uterus. Other ducts belonging to the Wolffian
bodies are modified in a similar way, serving to convey
the products of the male
generative gland to the ex-
terior.

It is somewhat remark-
able that each vertebrate
embryo possesses male and
female reproductive ducts ;
the adult male of most verte-
brates possesses vestiges of
the female ducts, whilst the
adult female possesses, much
more constantly, easily de-
tected remnants of the male
sperm-ducts. Remembering
that the primitive renal
organs are common to both _ T^ . , .. tA

& Fig. 23.— Ihe male reproductive

sexes, and as the disused
ureters have been utilized
in the male and female for
reproductive purposes, it ren-
ders their temporary co-existence in the embryo, and the
persistence of one or other in a vestigial form accord-
ing to the sex, comprehensible without invoking aid
from the much-disputed question of the existence of
a condition of primitive hermaphrodism.

The history of the reproductive ducts in the female

organs of a Skate, with a fully-
developed oviduct on the left side.
CE, oesophagus ; T, testis ; E,
epididymis (after J. D. Matthews) ;
P, shell-gland.

48 E VOL UTION AND DISEASE.

of vertebrata is certainly very remarkable, but a much
more extraordinary instance of change of function is
manifested in the nervous system now to be considered.

The Central Nervous System. — Vertebrate animals are
distinguished from invertebrate not only in the posses-
sion of a vertebral column, but also by the fact that they
are furnished with a central nervous system known as
the spinal cord and brain. Of late years it has been the
opinion of many biologists that the separation of the
invertebrata from vertebrata is unjustifiable, and many
attempts have been made to bridge the gulf supposed
to exist between these great divisions of the animal
kingdom.

Those invertebrates which approach nearest the verte-
brates are the cephalopods (cuttles, octopods, &c), and
in these forms the central nervous system is represented
by ganglionic masses collected around the oesophagus or
gullet and united by commisural fibres : this arrangement
is known as the oesophageal collar, so that in order to
bring this into harmony with the anatomical disposition
of the vertebrate gullet, some eminent biologists have
maintained that the vertebrate mouth is secondary, and
that the primitive gullet traversed the central nervous
system by way of the third cerebral ventricle and
infundibulum, a diverticulum from the original vesicles
out of which the brain is ultimately developed. This
hypothesis has not found much favour, but recently
some observations and speculations have been announced
which throw much new and important light on the
matter.

The central nervous system is traversed by a canal

DISUSE AND ITS EFFECTS.

49

which is of large relative size in the embryo and lined
by epithelium. The significance of this canal has long
puzzled anatomists. A new interest attached to it
when Kowalevski discovered in the embryo of ascidians
and amphioxus, that this central canal is directly con-
tinuous with the intestine. This temporary connection

Fig. 24. — The U-shaped tube from which the alimentary canal
and central nervous system of vertebrates arise. N,
nervous tube ; V, intestine ; N1, neurenteric passage ;
X, notochord ; Y, yolk sac ; P1, pineal ; and P. Pituitary
diverticulum.

has been observed in all the great groups of vertebrata.
even in the human embryo.

In 1887 I was able to furnish evidence that this central
canal of the cord, and a portion of it prolonged into the
brain, may be regarded as originally a segment of intes-
tine which has become disused for alimentary purposes

5

5°

EVOLUTION AND DISEASE.

and undergone gradual
transformation into a spinal
cord. These facts were
based on the embryological
history of the parts and
from a study of the malfor-
mation exhibited, not rarely,
by this central canal and
the permanent alimentary
canal.

The mode of development
of the parts may be briefly
described. The alimentary
canal and spinal cord of all
vertebrates arise on a com-
mon plan. At a certain
stage it consists of a U-
shaped tube, as in fig. 24,
each limb ends in a cul-de-
sac^ and the ventral limb is
connected by a hollow duct
with the yolk sac.

By a series of secondary
changes the anterior end of
the ventral limb of this tube
is made to communicate
with the exterior by way of
the mouth and pharynx, and

Fig. 25. — A diagram representing the parts in the adult derived from the (J-
shaped tube of the embryo. S, stomodoeum ; I, infundibulum ; Pt, pituitary
body; T, thyroid; L, lung; M, vitello-intestinal duct ; A, allantois ; C,
coccygeal body ; G, post-anal gut ; N, neurenteric passage.

DISUSE AND ITS EFFECTS. 51

by a similar method a nether opening, the anus, is
established. The intermediate section becomes the
permanent alimentary canal. The walls of the dorsal
section of the tube thicken, the cavity becomes restricted,
and the bend connecting it with the ventral tube atrophies,
thus disconnecting the two limbs ; the dorsal portion
finally developes into the brain and spinal cord. The
various connecting parts are represented in the adult by
the following structures, diagrammatically indicated in
fig. 25. The diverticulum, P, is the infundibulum ; this
was closely associated with the primitive gullet. The
connecting limb, Incompletely disappears, but the section
of the gut into which it opens is represented by a small
pedunculated body at the extreme end of the vertebral
column, and known as the coccygeal gland. The dorsal
and ventral limbs of these tubes in the adult are con-
nected in a subtile manner by means of nerves. The
walls of the dorsal tube contain collections of nerve-cells,
from which nerves issue, portions of which are distri-
buted to the body walls, others of peculiar character
ramify in the walls of the intestines and are intimately
associated with its nerve plexuses.

This view as to the intestinal origin of the central
canal of the nervous system receives admirable support
from the investigations of Dr. Gaskell,1 who, from a

1 My conclusions were framed in July, 1887, and briefly stated to
the Pathological Society in October of that year. My manuscript
was sent to " Brain " in August, but owing to the unfortunate illness
of the Editor it was not published till January, 1888. Gaskell
states that he framed his conclusions in the summer of 1887, but
he did not mention them in public till June, 1888, and did not
publish them till April, 1889.

5 2 E VOL UTION AND DISEASE.

different mode of working to that adopted by me, has
come to a similar conclusion. Gaskell's conclusions are
based mainly on the fact that the central nervous system
is composed of two parts, a nervous and a non-nervous
element, especially in the cranial region, and he considers
that the nervous elements have been thrust upon and
thus utilized the alimentary tube as a supporting struc-
ture. Gaskell has entered minutely into details con-
cerning the modification induced by the change in the
position of the mouth.

Which of the views is the correct one — whether the
gut, becoming disused from gradual loss of function,
became utilized for the support and extension of the
surrounding nerve ganglia, or was rendered useless in
consequence of the encroachment of nervous material,
or, what seems equally probable, the change of its intrinsic
elements into nerve-cells, will require further investiga-
tion.1

Apart from such considerations, the view that the
central nervous system is disposed around a modified
piece of intestine, offers an explanation of several
otherwise inexplicable phenomena which will be duly
considered in some of the ensuing chapters.

Tails. — Among suppressed parts, so far as man is
concerned, must be included the tail. That man has
descended from forms furnished with tails cannot be
doubted, for at the end of the vertebral column he still
carries three, four, and occasionally five rudimentary

1 Those interested in this question will find the matter discussed
in my monograph on Dermoids. Gaskell's views are published
in the Journal of Physiology. April, 1889, vol x. part 3.

DISUSE AND ITS EFFECTS. 53

caudal or coccygeal vertebrae. The most constant
number in the adult is three, but in the embryo germs
of five vertebrae can be distinguished. This remnant of
a tail is connected with the sacrum by bands of fibrous
tissue, the degenerate remnants of the muscles which in

Fig. 26. — An African child with a pendulous tumour hanging
from its buttocks ; false tail. (After Virchow.)

a functional tail raise, depress, or move it from side to
side. This is not mere speculation, for these ligamen-
tous bands are not infrequently replaced by muscles
known as curvator coccygis, extensor coccygis, and
agitator caudae. The scepticism regarding the occur-

54

EVOLUTION AND DISEASE,

rence of tails in men is mainly attributable to the
mistakes which have been made by incompetent ob-
servers in reporting, as tails, structures which had no
right to such a title, and it will be useful for us to
consider the various forms of true tails and the appen-
dages which may be mistaken for them.

We may, with Virchow, divide
tails into two classes, true and
false. True tails are of two
varieties : the most perfect tails
are composed of bony segments
directly continuous with the
vertebral column, as in the case
of monkeys, horses, dogs, cats,
lions, &c. The less perfect
variety is like that of the pig,
soft and flexible. That man
has descended from ancestors
which possessed tails there can
be little reasonable doubt, and
that children are occasionally
born with one and even two
extra bony segments to the
coccyx, as man's rudimentary
tail is termed, is 'undoubted. I
have on several occasions seen five rudimentary vertebrae
in a child's coccyx.

It must also be remembered that this portion of the
vertebral column may be more prominent than usual and
project like a tail, yet on dissection contain but the
normal number of bony elements ; whilst in other cases

Fig. 27.— A Faun, to show
the goat-like tail.

DISUSE AND ITS EFFECTS.

55

the number may amount to five, and no abnormal pro-
jection be observable. Thus far a well-developed tail
in an adult human subject containing bony elements
continuing the vertebral series has yet to be detected.
In the new-born child, soft tails about an inch in length
have been observed : these contained cartilaginous tissue
and resembled the flexible tail of pigs.

Fig. 28. — An ^Egipan sporting with a Faun. Bacchus and

Silenus.

Many instances of tailed children when critically
examined turn out to be tumours or tufts of hair in the
loin. A general notion of a false tail may be gathered
from the African child represented in fig. 26. In this
case a large rounded tumour hangs pendulous from the
child's buttocks, and a little imagination would soon

S6 E VOL UTION AND DISEASE.

distort this into a tail. The tumour was removed in
Central Africa and sent to Professor Virchow.1 The
pendulous mass consists of a hollow central cavity sur-
rounded by fat and covered externally by skin, and in
Virchow's opinion it arose as a diverticulum from the
membranes of the spinal cord [spina bifida).

The most interesting false tails are those formed of
tufts of hair. It was mentioned in the last chapter that
certain malformations of the spinal column are associ-
ated with hair-fields and long tufts of hair in the loin.
Sometimes, as in the example on page 23, the hairs are
several inches long, recalling the goat-like tuft of hair
or tail which sculptors represent in the loins of satyrs
(fauns and segipans). In fauns the tail strongly re-
sembles the tuft of hair seen in some human beings.
For instance, compare the back of the faun in fig. 27
and that of the child, fig. 12.

Virchow, in writing on this subject, points out the
possibility that sculptors and artists in representing
these mythical satyrs and "gods of the wood" with
tufts of hair for tails, did not trust entirely to the
imagination, but that such oddities had a certain
amount of foundation in fact. There is much to sup-
port this view. Those sylvan deities, the segipans, had
a man's head and body, pointed ears, and the hind-
quarters of a goat. In some forms of local hairiness
due to spinal defect, the hair extends over the legs and
buttocks as in the aegipans. The cloven hoof admits
of a two-fold explanation. In the first place, malposi-
tion of the foot is a frequent complication of congenital
/ Virchow's Arch. Bd., ci. S. 571

DISUSE AND ITS EFFECTS.

57

defects in the spine, the sole of the foot being turned
upwards and inwards. In some children the middle
toes may be deficient and cause the foot to assume a
cloven appearance.

Recklinghausen has suggested that, as in many cases
of spina bifida, disease of the bones of the foot occurs
as a complication, and often induces
loss of the middle toes, this may
have stimulated in the imagination
the notion of a cloven foot. It is
perhaps not unfair to infer that from
such sources as these originated the
corporeal form of our much dreaded
mystical devil, with hairy body,
cloven feet, and tail (fig. 28).

The relation of fauns, segipans,
and goats is discussed further in
chapter iv. in connection with some
other structural peculiarities they
share in common with goats.

Atrophy of parts when disused
in consequence of injury scarcely
calls for comment (though very
many interesting specimens might claw from a Two-toed
be described) because the effects
of disuse when thus induced are not inherited.

As a general rule, the statement that parts when
disused become reduced in size holds good, but in con-
nection with dermal organs such as nails, horns, and
claws, it is well to point out that disuse leads to en-
largement. In the preceding chapter specimens were

Fig. 29.— An elongated

58

EVOLUTION AND DISEASE.

described to demonstrate the increase in the size of
dermal organs when disuse and irritation from dirt, &c,
were combined. A few specimens will now be con-
sidered in which disuse alone seems responsible for the

Fig. 30. — The head of a Parrot with overgrown beak.

overgrowth. The first is the foot of a two-toed sloth
which lived for many years in the Zoological Gardens,
London. One of its claws, or nails, whereby it hangs
suspended from the branches, is very long and has
almost described a circle. As far as I could learn, the

DISUSE AND ITS EFFECTS. 59

matrix was in no way irritated, and the sloth lived
under admirable sanitary conditions, but spent nearly
the whole of its life suspended by its nails. It is well
known that the beaks of parrots, when confined in cages,
grow very thick and long so as to render it necessary
to give them a piece of rough stone whereon they rub the
beaks to keep them within reasonable proportions. An
unusual beak of this kind is sketched in fig. 30. The
bird was found dead in Australia, and an examination
of the body did not furnish any evidence leading to the
suspicion that it had ever lived in captivity. In this
parrot the upper part of the beak measures sixteen
centimetres following the curve ; it is difficult to imagine
how the bird lived so long.

Conditions similar to this are often detected in the
beaks of partridges, pheasants, peacocks, and fowls.
There now remains for consideration atrophy, the result
of continuous pressure ; this is of importance because
it leads to interesting pathological conditions, and plays
also a part of some interest in connection with the
normal development of complex animals, but as this
subject is beset with technicalities and requires a rather
extensive acquaintance with special anatomy, it will not
be discussed.

CHAPTER III.

VESTIGIAL PARTS.

Under the term vestigial it will be convenient to
consider those parts commonly described as rudimentary,
abortive, atrophied, or useless. On the whole it is
better to refer to these structures as vestigial. In
dealing with such examples as the denticles of the
narwhal, which never cut the gum, the teeth of orni-
thorhynchus, or the splint-bones of horses, we have un-
mistakable evidence that they are remnants of structures
which were functional in the ancestors of these animals.
In many instances it is not easy to decide whether
a diminutive, or feebly grown part, in one animal is the
remnant of an organ better grown in its ancestors, or
the rudiment of an organ which has arrived at a higher
degree of perfection in its descendants.

This is illustrated in the hind limbs of whales. If
we regard cetaceans as living representatives of land
mammals which have taken to water, the hind limbs
are remnants ; on the other hand, if the descendants
of cetaceans have acquired terrestrial habits, then, the
hind limbs which do not project beyond the skin, but
are deeply buried in the blubber, must be considered
rudimentary or incipient structures. The whale is
merely selected as an illustration of the advantage or

VESTIGIAL PARTS. 61

convenience of employing the term vestigial ; there can
be little doubt that its hind limbs are remnants.

The combined effects of enlargement from increased
use, suppression, and change of function, has been to
produce in complex organisms a large number of ves-
tigial parts. Since Darwin considered the matter our
knowledge of such parts has increased greatly, and
in this chapter a few of the more important will be
considered, especially those which lead to pernicious
consequences.

Before entering upon this subject in detail it is neces-
sary to make a few remarks on what are termed useless
parts. It is very essential that care be exercised before
pronouncing any part to be useless, for, as Mr. Wallace
truly remarks, " much of what we suppose to be useless
is due to our ignorance." It also becomes important
to inquire why such supposed useless organs are per-
petuated, seeing that disuse of a part tends to promote
its disappearance. Darwin was ot opinion that what
he termed " rudimentary organs are eminently variable,
and this is intelligible, as they are useless, or nearly
useless, and consequently no longer subjected to natural
selection. They often become wholly suppressed. When
this occurs they are nevertheless liable to occasional
reappearance through reversion." Subsequently Darwin
seems to have changed his opinion somewhat, for in the
fifth edition of the " Origin of Species " he states, in
reference to adaptive changes of structure, " But I am
convinced from the light gained during even the last
few years that very many structures which now appear
to us useless will hereafter be proved to be useful and

62 E VOL UTION AND DISEASE,

will therefore come within the range of natural selec-
tion."

In connection with these remarks it will be well to
note the very small amount of utility which will deter-
mine the persistence of an organ ; take, for instance, the
hind limbs of the python and viper which are only
of occasional use, in connection with procreative function,
yet this is sufficient to preserve them whilst all other
traces of limbs have long disappeared. Mammals
abound in instances of muscles which in some species
are large and important, whilst in others they may sub-
serve such trivial functions that when absent they are not
missed from a utilitarian standpoint, yet even this trivial
amount of service ensures their preservation. This is
well illustrated by the small muscle underlying the
clavicle of man, known as the subclavius. In birds
it is large and powerful, raising the wing in the act of
flying. In man it is small, insignificant, and steadies the
clavicle during movement of the arm. It has been found
as a band of fibrous tissue, and in a few cases absent.

In reference to supposed useless parts, Wallace is of
opinion that the assertion of inutility in the case of any
organ or peculiarity which is not a rudiment or a cor-
relation, is not, and never can be, the statement of a fact
but merely an expression of our ignorance of its purpose
or origin. In the above quotation the term rudiment
refers to such parts as the pineal body, the vermiform
appendix, and teeth which are developed but rarely cut
the gum. These are vestiges of organs probably of great
importance to the ancestors of the forms in which they
now persist as reliquia. It seems highly probable that a

VESTIGIAL PARTS.

63

part which has had important functions in an animal,
and then has had its function gradually abrogated by
another part, is more prone to be persistent in rudiment
than remnants of organs of less importance. Darwin
expresses this view of the matter thus : " Organs nowr
of trifling importance have probably been of high im-

Fig. 31. — A Horned Sheep with cervical auricles.

portance to an early progenitor, and, after being slowly
perfected at a former period, have been transmitted to
existing species in nearly the same state, although now
of slight use." That mere disuse is insufficient to pro-
duce abolition of a part is illustrated in a striking
manner by the cervical auricles in goats, pig, and man.
These ears or auricles, in so far as we know, subserve no

64 E VOL UTION AND DISEASE.

useful purpose, are extremely variable, occur in both
sexes, and often are of large size (fig. 31). These
auricles, as will be shown in detail subsequently, are
enlarged opercula, yet an enormous space of time has
elapsed since the gill-slit they guarded were functional.
Nevertheless they illustrate the view I am advoca-
ting, for gill-slits and opercula were of high functional
importance in the ancestors of mammalia, and are still
conspicuous in the early embryo. As cervical ears or
auricles will occupy our attention at some length

presently, a few examples of
vestigial structures, and the
mischief which they now and
then occasion, will be con-
sidered.

Hen birds possess only one
functional oviduct, the left ;
the chick before hatching has
two, but for some reason at

Fig. 32.— The cloaca of a Hen,

showing the vestigial right ovi- present obscure, the right

duct. C, Cloaca; O, Oviduct. • i . ■ • i

oviduct atrophies, leaving at
most a short tubular stump attached to the right
side of the cloaca (fig. 32). The right ovary is
either vestigial or altogether absent in birds. To the
stump of the right oviduct we may very justly apply
the term vestigial, and as will be demonstrated in the
chapter on tumours, such vestiges are by no means
devoid of danger, and even bring about the bird's
destruction.

The abortion of the right oviduct in birds is in itself
very curious, especially when considered in connection

VESTIGIAL PARTS. 65

with the absence of the right jugular vein and carotid
artery in many birds. This was attributed by Owen to
the habit of birds sleeping with the head under the
wing. This view is not supported by facts.

Man, in common with the four anthropomorphous
apes, has attached to the lower end of the caecum a
small thin tube, which may vary from two to eight
inches in length, known as the vermiform appendix
(%• 33)- This tube agrees in structure with the rest
of the intestine, is covered with peritoneum, possesses
a muscular coat, and is lined with mucous membrane.
In the early embryo it is equal in calibre to the rest of
the bowel, but at a certain date it ceases to grow pari
passu with it, and at the time of birth appears as a thin
tubular appendix to the caecum. In the newly-born
child it is often absolutely as long as in the full-grown
man. This precocity is always an indication that the
part was of great importance to the ancestors of the
human species.

Many mammals, closely allied to the anthropomor-
phous apes, possess very large caeca ; and in some of
these the terminal segment of the caecum, although not
represented as a thin, narrow tube, nevertheless resembles
the vermiform appendix in that it possesses a very large
proportion of the peculiar kind of tissue known as ade-
noid, or lymphatic.

In man the vermiform appendix is a typical example
of a functionless part, and, like an idle person in a
community, is not infrequently a source of considerable
danger and suffering, and is responsible for a number
of deaths annually. The danger may arise in three

6

66

EVOLUTION AND DISEASE.

ways : — The communication with the caecum may
become obliterated, and the tube distend into a cyst
in consequence of fluid accumulating within it ; such a
cyst may rupture, and lead to minor troubles, as local
inflammation or abscess, or induce death by peritonitis.
Adenoid, or lymphatic, tissue is very prone to ulcerate,
and under certain conditions the adenoid tissue lining
the appendix may inflame and lead to fatal perforation.
A much commoner danger is the entrance into it of such
things as fruit-stones and similar indigestible sub-
stances taken with the food ; these
act as irritants, and in the long run
destroy life. A somewhat similar
condition of things may be studied
in lions and tigers. In these hand-
some animals there is no vermiform
appendix, and the caecum is even
more vestigial than in man. This

Fig. -The vermiform smaU Q^cum occasionaUy contains

appendix of a Silvery J

Gibbon {Hyiobates leu- a concretion having a fragment of

bone, a nail, or piece of wood for the
nucleus. Concretions in the vestigial caecum of the
tiger produce similar effects to cherry-stones, &c, in
the human vermiform appendix, and on two occasions I
have been able to connect such concretions with the
fatal illness of tigers.

Although a small and insignificant caecum is not
always an advantage, it is on the other hand a disad-
vantage to have one too large. The horse will illustrate
this : it has a caecum measuring, on an average, one
metre in length, and a capacity equal to thirty-five litres

VESTIGIAL PARTS. 67

This large caecum is a favourite situation for intestinal
concretions. These concretions are of different kinds,
but they all agree in having a foreign body, such as a
button, nail, hair-pin, or stray piece of metal for a
nucleus, around which mineral salts in crystalline form
are deposited in successive layers until the stone attains
great weight — five or six kilograms is not uncommon,
and a stone weighing twenty kilograms is preserved in
the museum of the Royal Veterinary College, London.

Hairs from the animal's skin not infrequently form
the bulk of such concretions, and may be found in the
stomach of many ruminants, especially calves ; but
attention is mainly directed to the caecum. The larger
calculi do not give rise to such dangerous effects as the
smaller, for their weight and size keep them confined to
the caecum, whereas the smaller calculi may leave this
portion of the alimentary canal, and getting into
narrower channels obstruct the bowel and induce death.

Apart from the special inconvenience caused by a
large colon favouring the production of calculi, there is
another aspect under which we may study such a
question. The more remote parts of the body are from
the heart the more likely are they to suffer, if from any
cause the quantity of the blood in the body is dim-
inished, or the power of the heart fails. For instance,
a man suffers severely from typhoid fever, the action of
the heart is weakened, and maintains the circulation
with difficulty ; as a result the toes, situated at the ex-
treme limits of the circulatory system, do not receive
sufficient blood, and mortify in consequence. The
following is an instructive case taken from a young

68 E VOL UTION AND DISEASE.

Sumatran rhinoceros. This animal, like all its kind,
has a large caecum, the distal extremity of which cor-
responds to the vermiform appendix, and derives its
blood-supply from the terminal twigs of a long ileo-
colic artery. The young animal to which these remarks
refer was sent to the Zoological Gardens, London ; at
the end of a few weeks it became sickly, refused food,
and finally died. At the autopsy it was discovered that
the lower jaw was extensively diseased, and a large
abscess had formed. This trouble offered satisfactory
explanation of the loss of appetite and inability to take
food. On examining the viscera, Mr. Frederick Treves
discovered the actual cause of death to be ulceration
and sloughing of the extremity of the caecum. In this
rhinoceros we have a similar condition of things to the
gangrene of the toes after typhoid fever, for the vital
powers being reduced by the trouble in the jaw, and the
inability to take sufficient food, those parts at the end
of the circulatory system suffered first, and the structure
most ready to succumb was the distal end of the caecum.
This case is very suggestive, because it teaches how, in
the process of evolution, so far as individual parts are
concerned, a limit is imposed upon the size attainable
by organs, and indicates the danger to which animals
are exposed in which particular vital organs attain in-
ordinate proportions. For instance, imagine two animals
living under similar conditions and upon the same kind
of food, but one has a moderate caecum, the other an
inordinately large one. Should a time of scarcity or
accident prevent such animals obtaining a proper
supply of nutriment, the one with an average caecum
{cceteris paribus) has the better chance of survival.

VESTIGIAL PARTS. 69

This is merely set forth as an example of the process,
and it may be illustrated by reference to parts far less
vital than the intestines, viz., the antlers of deer.

The antlers when young and growing are covered
with a vascular membrane, the "velvet," which bears the
same relation to the antlers as periosteum bears to
bone. As long as the antlers retain the velvet they live
and increase in length and thickness. After a time the
velvet thins, sloughs, and gradually falls from the bony
portion of the antlers, which gradually dies, and, being
devoid of sensation at this stage, constitutes powerful
weapons of offence or defence. In time the nutrition
fails in them also, and at length the dead antlers fall.
The phenomenon may be explained thus : the antlers
are supplied at a great disadvantage, for the blood has to
travel a long distance to reach them, and is unassisted
by any neighbouring anastomosing vessels such as we
find in other parts of the body ; consequently every inch
added to the antler increases the difficulty of supply and
makes its life more precarious ; finally the length of the
antler exceeds the distributing power of the heart,
nutrition fails, the velvet is shed, and the bony tissue
of the antler dies and falls. We have here conditions
analogous to the caecum of the rhinoceros, and few can
doubt that those enormous antlers which decorated the
head of Megaceros hibernicus have played a part in
bringing about its failure in the great struggle of life
perpetually raging in the organic world.1

1 This view was stongly forced upon my mind during some
observations made on a Wapiti deer (Cervus canadensis) at the
Zoological Gardens. In the course of three or four months this

7o E VOL UTION AND DISEASE.

Teeth furnish much that is interesting in connection
with vestigial structures. The enamel which constitutes
a covering to the crown of teeth in many mammals may
be looked upon as a vestige : no tissue resembling it
occurs in any other part of the body of a mammal.
Teeth are essentially calcified cutaneous papillae ; at one
time in the history of our planet, her seas were peopled
with numerous ichthyic forms furnished with an armour
of enamel ; some of the best specimens being the mailed
ganoids. Under pathological conditions, however, teeth
may spring up in such extraordinary situations as in
cysts of the ovary.

Turning to particular cases, we may study an,
instructive example in the horse. This admirably
specialized animal possesses three incisors and one
canine on each side ; then an interval follows until
we reach the pre-molars : a study of closely allied
fossil forms indicates that this gap, or diastema, was
occupied by well-formed teeth in the ancestors of the
horse, and this view finds support from the circumstance
that the first pre-molar is vestigial and presents itself as
a tiny socketless tooth. This functionless pre-molar is,
as a rule, shed early ; when persistent it is frequently a
source of considerable annoyance to the animal, as every

animal developed antlers weighing from twenty-seven to thirty kilo-
grams. That such rapid growth as this must tax the vital powers of
an animal is clearly shown by the circumstance that during the
growth of the antlers the Wapiti required, and was supplied daily
with, nearly twice the quantity of food consumed by it at the time
when the antlers were fully grown. The bearing of this fact from
an evolutionary point of view is too obvious to need any pointing
out.

VESTIGIAL PARTS. 71

veterinary surgeon knows ; for horses frequently refuse
food, set their coats, and get out of condition simply
from the trouble caused by these teeth : as soon as they
are removed the horse rapidly improves and gets once
more into condition. This vestigial pre-molar of the
horse is often omitted in drawings (even in veterinary
works) of the teeth of the horse.

It has been clearly shown by the researches of

Albrecht that man has a smaller number of teeth than

he formerly possessed. The mouth is often the seat of

a defect known as cleft palate ; not infrequently children

affected with complete clefts are furnished with three

incisor teeth in the jaw which is cleft, and occasionally on

both sides. In rarer cases an extra incisor tooth may

make its appearance taking rank, and being co-equal

with, the normal incisors. This matter has been

inquired into by many competent observers, and its

occurrence is beyond all doubt. The most satisfactory

explanation of the phenomenon seems to be that

offered by Albrecht ; it is to this effect : man normally

inherits in each upper jaw germs of three incisors, one

of these usually becomes suppressed ; in cases of cleft

palate there is more space for the teeth to develop and

a greater supply of blood to the parts adjacent ; these are

circumstances favourable to the full development of the

germ of the third incisor.

The fact related above is of sufficient interest in itself;
it is also of importance in a general way because there is
good reason for the belief that the germs of other teeth
have been suppressed in the mouth of man, and that the
wisdom teeth are slowly undergoing this process. It has

72

EVOLUTION AND DISEASE,

been suggested by Mr. Eve, on very good grounds, that
the germs of teeth which have been suppressed in the
evolution of our species may make themselves ob-
noxious in an unexpected way. Teeth are formed in
part by down-growths of epithelium lining the floor
of the mouth ; these cellular down-growths, known as
enamel-organs, present distinctive features and are
easily recognized by practised histologists. The

Fig. 34. — A follicular cyst developed in connection with an
unerupted tooth of a Porcupine. The upper drawing
shows the effects of the cyst on the jaw.

mouth of man is occasionally occupied by tumours to
which the name epithelial odontomes has been given ;
the peculiar feature of these tumours is that they are
composed of collections of cells in every way resembling
the enamel-organ. The opinion receives considerable
support from the fact that several carefully examined
specimens of this peculiar form of tumour have occurred
in cases where the number of teeth has been below the

VESTIGIAL PARTS.

73

normal, the tumour occupying the position which should
have been filled by the missing teeth.

That imperfectly developed teeth give rise to tumours
is indisputable ; for instance, the teeth before they make
their appearance above the gums are enclosed in a bag, or
follicle, formed partly of fibrous tissue or bone. Occasion-
ally teeth which should normally be cut and take their
position in the dental series, remain hidden beneath the

FlG. 35* — A composite odontome from a Horse, weighing
.700 kilograms.

gums ; in such cases fluid accumulates between the
aberrant tooth and its capsules, forming a tumour known
as a follicular cyst (fig. 34).

Sometimes the germs of several teeth coalesce and
give rise to an ill-shaped mass of dental tissue known as
a composite odontome (fig. 35) : in due course this
abnormal conglomeration of tooth tissue attempts to
rise above the gums, or becomes erupted like an ordinary

7 a E VOL UTION AND DISEASE.

tooth ; this produces severe constitutional disturbance
which may place life in jeopardy.

When dealing with the intestinal origin of the spinal
cord it was mentioned that the central canal of the cord
and the gut communicated with each other around the
caudal end of the notochord. This connecting passage
is known as the neurenteric canal, and the section of the
bowel into which it opens is known as the post-anal gut,
because it is situated posterior to the permanent outlet
of the bowel. In the elasmobranchs this section of the
primitive gut equals a third of its total length. The
coccygeal region is often the seat of congenital
tumours, some of which present peculiar characters.
The examples most interesting to us attain a very large
size — often more than a kilogram in weight — and are
situated anteriorly to the coccyx. Structurally they are
composed of cysts lined with epithelium, the stroma
consists of very young connective-tissue : sometimes
these tumours contain a portion of bowel lined with
mucous membrane, possessing Lieberktihn's follicles
and Peyer's patches.

A study of the development, structure, and relations
of the tumours will serve to convince any impartial
observer that they arise in connection with the post-
anal gut ; they are by no means rare ; few pathological
museums of any pretensions are without a specimen,
or a model of them, and all surgeons of experience
have encountered one or more examples of them. The
large specimens are incompatible with life, but smaller
ones have been successfully dealt with surgically.
Finally every gradation has been recorded, from per-

VESTIGIAL PARTS. 75

sistence of the gut as a simple tube, with an accessory
opening near the coccyx, to large growths exceeding
the weight of the child unfortunate enough to possess
so unwelcome an appendage.

The transformation of a piece of intestine into a
central nervous system has had the effect of rendering
vestigial, structures which not unfrequently behave in
a manner pernicious to the individual.

For instance, the development of a spinal column to
protect the cord is an outcome of this transformation,
and the various defects in the development of the cord
and column, if serious, are incompatible with life. These
defects, known collectively as spina bifida, are of such
frequent occurrence that in a recent careful scientific
report upon this subject, it appears, that in England
alone, six hundred and forty-seven deaths occurred in
1882 from this malformation, of which six hundred and
fifteen were in children under one year of age. It would,
in a work of this kind, be difficult to enter fully into
details of the various forms of this interesting class of
defects, but it may be briefly stated that many of them
are failures in the formation of the bony walls, others
are due to protrusions of the spinal membranes, and a
rarer form arises in consequence of an accumulation of
fluid inducing local dilatation of the central canal of the
cord : an example of the cystic dilatation of a function-
less canal.

That remarkable appendage of the developing ali-
mentary canal, the yolk-sac, with its vitello-intestinal
duct, has already been referred to ; its significance is
not easy to estimate. Although the duct connecting it

76

EVOLUTION AND DISEASE.

with the intestine is pervious, it is not used for the trans-
mission of yolk, for, except in the case of a few fish
(fig. 36), the contents of the yolk-sac have not been
detected in the alimentary canal. The yolk is taken up
by the omphalo-mesenteric vessels circulating on the

walls of the sac. If such is the
case we must regard the vitello-
intestinal duct as a vestigial struc-
ture in the higher mammals, and
as such it is a source of danger to
the individual. In man the duct
should normally disappear long
before birth ; not infrequently it
persists and grows pari passu with
the ileum to which it belongs.
It may be ten centimetres in
length, and remain adherent to
the navel, or form a short, blunted
outgrowth to the bowel. When
it remains adherent to the navel, figT^6
a portion of small intestine may,
during any unusual movement of
the viscera, become twisted over it, obstruction to the free
passage of the contents of the bowel is established, and,
unless quick relief is afforded by art, a fatal issue ensues.
The vitello-intestinal duct leads to disastrous conse-

#

An elasmobranch
fish recently hatched with its
yolk-sac.

VESTIGIAL PARTS.

77

quences in another way. In the ordinary course of
events the duct should shrivel as far as its attachment
to the bowel ; occasionally the process of obliteration
may involve the wall of the ileum and lead to the
formation of a septum, which gradually contracts and
slowly causes death by obstruction of the bowel. In
rarer cases the occlusion of
the duct may extend to the
ileum, and divide it com-
pletely. Such a condition is of
course incompatible with life.

This duct is the source of
other lighter troubles ; those
described above are the most
serious.

The tongue contains a ves-
tigial duct of great interest.
At a very early period in the
life-history of the mamma-
lian embryo a diverticulum
arises from the ventral wall
of the pharynx, and even-
tually gives rise to the
middle portion of that very
puzzling organ— the thyroid
body. For a time this duct retains its connection with
the mouth ; eventually the hyoid bone appears and
divides the duct into two portions. The portion in
relation with the mouth becomes surrounded by the
developing tongue, and finally disappears, leaving
nothing but a small depression on the surface of the

FlG. 37. — A diagram of the alimen-
tary canal showing the yolk-sac
and its duct ys ; c, caecum ; /, lung.

7 8 E VOL UTION AND DISEASE.

organ to indicate its previous existence. A careful
inquiry will reveal the occasional presence in the
tongue of a duct passing from the hyoid bone to the
foramen caecum. This is not a duct which requires a
microscope to distinguish it, but is capable of admitting
a bristle or fine probe. In some cases this duct becomes
obstructed at the upper opening, and the gradual accu-
mulation in its interior of shed epithelium and sebace-
ous matter gradually distends into a large and trouble-
some cyst. In some cases the walls of the cyst are
formed of skin, and hair may sprout from it. These
cysts are not infrequent in the human subject, and have
been found occupying the centre of an ox tongue, under
rather unpleasant circumstances. A gentleman, whilst
carving a tongue at breakfast, unexpectedly came upon
a collection of hairs and fatty material in its midst, and
was in no small measure astonished.

The mammalian tongue should be an organ of great
interest to the morphologist ; unfortunately ks evolu-
tion has not yet been thoroughly unravelled. It has
of course received great attention from anatomists and
surgeons. From anatomical and pathological stand-
points the anterior two-thirds of the tongue differ com-
pletely from the posterior third. The latter part may
be regarded as the more primitive, whilst the tip of the
tongue is of later development and, morphologically,
less important.

CHAPTER IV.

VESTIGIAL STRUCTURES {continued).

THUS far a few clear examples of vestiges of organs and
parts have been briefly considered ; it may, perhaps, be
desirable to trace some such part from as near its
beginning as possible, through its various modifications
and complete disappearance as a part normal to a given
animal. It is also well known that many parts are
present in the embryo which are not represented in the
mature animal. Of this we had many instances in the
preceding chapter, but such parts are often persistent
as abnormalities in the adult ; they are then described
as being reversionary, or atavistic. As this is a subject
of great interest to us, the matter to be considered now
will serve as an excellent introduction to the chapter on
atavism. The next few pages will be devoted to the
description of cervical auricles in man and animals ; the
study is of interest in many ways, and especially from
the circumstance that it clearly shows that disuse is, in
itself, not able to bring about the complete disappear-
ance of parts. It will also serve to illustrate the em-
bryological rule that when parts are precociously
developed in the embryo, but feebly developed in the
adult, it indicates that they were of high importance in
the ancestors of those particular animals.

8o E VOL VTION AND DISEASE.

Embryology is eloquent in furnishing evidence sup-
porting the view that the ancestors of existing vertebrata
were aquatic in their habits, that respiration was carried
on in them by means of gills, and that many structural
peculiarities in mammals result from the transformation
of an aquatic into a terrestrial animal.

The type of respiratory organs in these ancestral
forms is best preserved in elasmobranch fish, such as
the dog-fish, or in a marsipobranch, like the lamprey.
In such forms the water, charged with air, enters the
mouth and is forced through openings in the walls of
the pharynx. The pharyngeal orifices, or branchial slits,
are furnished with vascular processes known as gills. In
the gills, or branchiae, the blood and water are merely
separated from each other by an extremely delicate
layer of tissue. Hence venous blood circulating in the
gills readily gives up the excess of carbon dioxide, and
as readily obtains oxygen from the surrounding water.
The gills of fish and batrachians are supported upon a
cartilaginous or bony framework known as the branchial
bars, and in such fish as sharks a small cutaneous fold
projects from each bar and covers the gill-slit as with a
lid ; these cutaneous lids are named, in consequence,
opercula. The gill-slits, with the opercula, are sketched
in fig. 36, as they are seen in a dog-fish. The first slit
bears no gills in the adult fish, and is known as the
spiracle, or blow-hole. In the embryo it is furnished
with beautiful external delicate vascular tufts. The
neck of a mammalian embryo is furnished with four
similar slit-like orifices, communicating with the pharynx,
as in the dog-fish, but are fewer in number. The gill-

VESTIGIAL STRUCTURES. 81

slits of birds, reptiles, and mammals differ from those of
fish in that they never at any period support gills.
These rudimentary gill-slits further resemble those of
the dog-fish, for they present on their anterior aspect a
small swelling, or tubercle, representing an operculum
In the human embryo four branchial slits present them-
selves (fig. 38).

The first of these represents the spiracle of the shark,
and in mammals becomethe tympano-eustachian passage,
and is subservient to the sense of hearing ; the small
tubercles surmounting it coalesce, and gradually give rise
to the pinna, or external ear, so conspicuous in nearly
all land mammals. Normally the posterior
gill-slits disappear. It is by no means
uncommon to find in the sides of the neck
of a child, along the anterior border of
the sterno-mastoid muscle, small openings
in the skin capable of admitting a thin FlG- 38-— An early

. human embryo

probe. These congenital fistulae, espe- witn the bran
cially when they exist in the upper part chial sllts-
of the neck, communicate with the pharynx. This
in some cases may be demonstrated by allowing the
child to swallow milk ; drops of the milk will find
their way through the fistula and appear in the neck.
Stress must be placed on this simple experiment, for
His, of Leipzic, has urged that branchial fistulae in man
never communicate with the pharynx, and that the con-
nection, in those which were supposed to open into it, was
the result of incautious use of the probe. This view is
erroneous ; I have seen milk issue from such fistulae in
individuals who have never been submitted to sounding

7

82

E VOL UTION AND DISEASE

Those occurring in the lower part of the neck end
blindly. The usual situations of the four branchial slits
are indicated in fig. 39.

Sometimes we find in the situations frequented by
these fistulae instead of openings small rounded white

Fig. 39. — A side view of the neck ; the figures II, III
and IV indicate the common situations of branchial
fistuloe.

patches of skin, natural cicatrices, indicating the points of
obliteration of the clefts. It is by no means infrequent
to find the cutaneous orifice of a persistent branchial slit
surmounted by a cutaneous tag, which often contains a
small nodule of yellow elastic cartilage resembling that
found in the pinna ; these projecting pieces of skin often

VESTIGIAL STRUCTURES.

83

occur unassociated with fistulae, and are most common
in two situations in the
neck, at the spots
marked III and IV in
fig. 39. As a rule they
are symmetrical ; usually
they are short, often
looking like mere pim-
ples on the side of the
neck. In some cases
they may attain a
length of two or three
centimetres. A very
large one is repre-
sented as it grew

Fig. 40.— A Girl with a cervical ear or
auricle.

from the side of a girl's
neck, in fig. 40, and in
a child, fig. 41. These
fistulae and cervical
auricles, or ears, as
they are called, usually
affect many members of
a family ; the mother
maypossesscervical auri-
cles, and one child have
a cervical fistula, whilst
a third may have fistulae
and auricles combined.

The question natu-
rally suggests itself, if
these fistulae and auricles occur in man they should also

Fig. 41. — Child with cervical auricle
and a supernumerary tragus on
each side.

84 E VOL UTION AND DISEASE.

be found in other mammals, especially as the gill-slits are
as marked in them as in the human species. The inquiry
is full of interest. Our knowledge of branchial fistulse
in mammals other than man is very scanty ; this is
not matter for surprise, as it is only of recent years
that information regarding these fistulse in him has
been very exact or abundant.

Fig. 42. — A Goat with cervical auricles.

Heusinger x mentions the occurrence of congenital
fistulse in the horse immediately below the ear, and
near the angle of the jaw. He stated that they are
more frequently recognized in carriage than in draught
horses ; the secretion or discharge which issues from

1 «

Deutsche Zeitschrift fur Thiermedicin," Bd. ii,

VESTIGIAL STRUCTURES.

85

them soils the surrounding skin and draws attention
to their existence.

Cervical auricles have been studied in the goat. In
1876 Heusinger mentioned the frequency with which
pendulous tags of skin occur in the necks of pigs,

-. , -• •• .*.:. ;:-'^

Fig. 43. — An Egyptian Goat (Hircus thebaicus), with cervical

auricles.

goats, and sheep. Yet little has been done to support
his observations. As a matter of fact, these pendulous
bodies are extremely common in the necks of goats ;
few persons seem to notice them until their attention
is particularly drawn to them.

86

EVOLUTION AND DISEASE,

A well-marked specimen of cervical auricle in a goat
is sketched in fig. 42 : these auricles are situated at a
spot corresponding to the external orifice of the third
branchial slit of the embryo.

The auricles are not confined to any particular species
of goat ; the one sketched above is a cross between a

Fig. 44. — Magnified view of a section of a cervical auricle removed
from a baby's neck. C, cartilage ; M, muscle-fibre ; F, fat.

Nubian and a common goat. In fig. 43 a sketch is
given of the head of an Egyptian goat (Hircas tkebaicus),
made from life by Mr. R. E. Holding from a specimen
which was living in the J.ardin des Plantes, Paris.
Their existence in the pig has been recorded, and a
horned sheep with two well-marked cervical auricles
is figured on page 63.

VESTIGIAL STRUCTURES.

87

It has been doubted whether these pendulous bodies
are of the nature of auricles, and it is desirable that
the evidence should be put before the reader which
favours such an interpretation. An auricle, or pinna,
may be defined as an enlarged operculum in a mam-
mal, consisting of a framework of yellow elastic
cartilage covered with skin, simi-
lar to that on the rest of the
body, and containing striped
muscle-fibre.

The cervical auricle, such as
is seen in the neck of the girl
on page 83, agrees with this
definition in every particular ;
it contains yellow elastic carti-
lage, is skin-covered, and has
muscle-fibre attached to it, as
may be seen on reference to the
magnified sketch of a section of
a small cervical auricle removed
from a child's neck, immediately
above the inner end of the
clavicle. In order to complete FlG* 45.-Vertical section of the

r cervical auricle of a Goat. C,

the definition, we require to show

cartilage ; M,
(Nat. size.)

muscle-fibre.

that they are enlarged or persis-
tent opercula. The specimen, from which the drawing,
fig. 44, was prepared was associated with a persistent
branchial cleft, and in the cases where clefts are not
persistent, the auricles are situated at spots exactly
corresponding to the point where such fistulse open ; and,
as has already been mentioned, one member of a family

88 E VOL UTION AND DISEASE.

may have a persistent branchial cleft, another have
a cervical auricle only, and a third a persistent cleft
and auricle. It is also a point of some interest to re-
member that in the human subject the operculum of
the third cleft is that most commonly seen in the adult.

The pendulous bodies in the goat harmonize admir-
ably with these conditions. Professor Charles Stewart
detected in the auricle of the goat figured on page 84,
an axial rod of coarse, yellow elastic cartilage, and
Franck, in his work on the " Anatomie der Hausthiere,"
1883, states that in goats and pigs this rod of cartilage
exists in these so-called bells (Glockchen oder Ber-
locken), and draws attention to the existence also of
striped muscle-fibre in them. The anatomy of a
goat's cervical auricle is shown in fig. 45. As these
bodies occur in goats at the situation of the external
orifice of the third branchial cleft, most anatomists
are of opinion that they are homologous with the
cervical auricles of man.

An impartial consideration of the evidence relative
to the development of the pinna in land mammals
shows, clearly enough, that it is to be regarded as the
confluent opercula of the first and second arch, extra-
ordinarily developed from increased use in connection
with the acoustic functions, which have gradually
arisen in connection with the first branchial cleft.
The remaining opercula have been suppressed partly
from loss of function and partly from the excessive
development of the first and second operculum. That
the gradual development and increased importance of
the external auditory apparatus is in a large measure,

VESTIGIAL STRUCTURES. 89

if not entirely, due to the gradual acquisition of
terrestrial habits by animals originally aquatic, is
largely supported by the condition of the pinna in
aquatic mammalia. The adult whale has no pinna or
external auditory meatus ; Howes has detected vestiges
of the pinna in the embryo of the white whale {Beluga
leucas): the pinna was almost microscopic in size

Fig. 46.— The head of a Seal {Otaria gillcspii), showing the
small pinna. (After Forbes.)

and pointed, resembling in a very striking manner the
small cervical auricles in man.

In most seals the pinnae are wanting, and when
present they are short, pointed, and vestigial, as in the
eared-seals (Otaridce), fig. 46.

If the Cetaceans and Phocidce are to be regarded as
land mammals which have taken to the water— which
is the most consistent manner of studying them — we

9°

EVOLUTION AND DISEASE.

must regard the pinnae as having slowly atrophied from
disuse, but persisting as remnants in a few adult forms,
and present only in the embryos of others. The per-
sistence of the pinna in the Otaridcey and the frequent
presence of cervical auricles in goats are difficult to
account for, especially as we are unable to assign to
them any function.

The consideration of cervical auricles would be in-
complete without reference to their existence on the

Fig. 47. — The head of a Satyr (yEgipan) with a
sessile cervical auricle. (British Museum.)

statues of fauns and satyrs. My talented friend, Mr. S.
G. Shattock, first drew my attention to this matter.
They are not always represented of the same shape or
size, but nearly always occupy the same situation on the
neck : thus in the statue of an aegipan (satyrs with goat-
like legs) in the British Museum, the auricles are sessile
(fig. 47). This is the common form in man.

These appendages are not seen on the statues of

VESTIGIAL STRUCTURES.

9i

modern fauns so constantly as in ancient fauns, and are
usually represented as pendulous structures, admirably
shown in the drawing of a faun in the Capitol (fig. 48).
In all cases these pendulous skin tags in the statues are

Fig. 48. -A Faun and Goat from the Capitol, with
cervical auricles.

placed along the anterior border of the sternb-mastoid
muscle. It is, of course, a matter for discussion whether
the sculptors obtained their notion of the cervical
auricles from human models or from goats. In some

92 E VOL UTION AND DISEASE.

cases they may have obtained them from man, but in
the majority of instances, especially the pendulous
auricles of fauns, the goat furnished the model. This is
illustrated in the faun from the Capitol, for we see by
the side of the faun a goat with cervical auricles clearly
and unmistakably represented (fig. 48), and on the
faun's shoulders a goat's skin is thrown. The goat
element in the composition of these satyrs is evident in
more ways than one ; the segipans are goat-legged and
their tails are excellent copies of that appendage in the
goat. Be this as it may, we are bound to admit that the
old sculptors were close observers of nature.

The grounds for regarding these congenital appen-
dages in man as auricles may be thus summarized : —

1. Embryology teaches that they grow like the normal
pinna from the swollen edge of a branchial cleft, and are
thus homologous with opercula.

2. Frequently such auricles surmount the cutaneous
orifice of a congenital branchial fistula.

3. When no fistulae are present, the situation they occupy
corresponds to that of the third or fourth branchial cleft.
Most frequently it is the third cleft, that is, in the middle
of the neck, corresponding to the anterior border of the
sterno-mastoid muscle. The fourth cleft opens near the
sterno-clavicular articulation.

4. Structurally they correspond to the normal pinna.

5. Not infrequently one member of a family will have
persistent branchial fistulae, whilst another has cervical
auricles, and a third a fistula and cervical auricle.

Before leaving the consideration of the changes which
result from the transformation of aquatic into land

VESTIGIAL STRUCTURES. 93

animals, it may be useful to draw attention to one con-
dition, indirectly associated with this remarkable change,
which produces greater inconvenience than can be attri-
buted to cervical auricles. In many of the situations
where canals open on a free surface, the terminal orifice
of the canal is, as a rule, surrounded with glands and a
collection of tissue, peculiar in structure, termed adenoid.
Such glandular collections are more abundant around
the terminations of functionless ducts. Some of the
more characteristic examples occur in the pharynx
marking the inner orifices of the branchial clefts. Of
these the most conspicuous is named the tonsil.

The tonsils are familiar to all as the sub-globular
shaped structures lodged in the recesses on each side of
the mouth at the spot where the mouth joins the
pharynx, or cavity where the nasal and buccal passages
become directly continuous. The space between the
mouth and pharynx is technically termed the fauces.
The tonsils vary considerably in size ; in some persons
they are large and prominent, in others small and
scarcely recognizable. Structurally they are composed
of adenoid tissue, covered with mucous membrane, beset
with a number of shallow crypts which secrete thick,
tenacious mucus. The niche in which each tonsil is
lodged is termed the tonsillar recess, and indicates the
exact spot where the second branchial cleft in the
embryo communicated with the pharynx ; it is also the
spot where the cleft, when persistent, opens internally.
The connection of the tonsil and its recess with the
second branchial cleft is also indicated anatomically by
the glossopharyngeal nerve and the lingual artery,
which, in the embryo, are distributed to this cleft.

94 E VOL UTION AND DISEASE.

How far the tonsil subserves any useful purpose is
very doubtful : certainly they are often removed, and
persons usually experience relief rather than suffer
inconvenience from the loss. Of course they are only
removed when enlarged from disease ; and it is quite
certain that the tonsils are often the seat of disease
which is not merely troublesome to the individual, but
is at times fraught with great danger to life.

The anatomy of this region in the horse is instructive.
In this mammal veterinarians describe the tonsil as
absent. In that the horse has no collections of adenoid
tissue in the sides of the fauces such as exist in man,
the statement is correct ; but we find on each side a
large cyst occupying the pharynx and constituting a
chamber of communication between each eustachian
tube and the nose. These large sacs are known as the
guttural or eustachian pouches. A careful study of
these pouches has induced me to regard them as dilata-
tions of the pharyngeal ends of the second branchial
clefts ; these are the clefts from which the tonsils of
man arise. It is also of some importance to remember
that in the early human embryo the tonsil is represented
as a sac with a slit-like opening wherewith it communi-
cates with the pharynx. The connection of the guttural
pouches with the eustachian tubes is secondary.

It is not my intention to enter in detail into the
structure and relation of these curious pouches ; but to
point out that, like the tonsils of man, they are sources
of inconvenience, trouble, and occasionally disaster.
Like the tonsils, also, no known function is served by
these pouches.

VESTIGIAL STRUCTURES.

95

It has already been mentioned that they communicate
with the nasal chambers by slit-like orifices ; conse-
quently, when a horse sniffs, air is drawn into the
pouches. Should this occur when horses are feeding in
a manger or nosebag, and the food is dusty, irritant
particles of dust are drawn into the guttural pouches
and set up inflammation. Dust and mucus thus ac-
cumulating in the sac give rise to rounded bodies,

Fig.

49.— Concretions from the guttural pouches of the Horse.
One is shown in section. (Natural size.)

technically known as concretions from the guttural
pouches. Sometimes they are oval, sometimes bean-
shaped, and vary in size from a cherry-stone to a walnut,
and in number from three or four to a hundred. Their
consistence resembles cheese, and on section exhibit a
laminated structure (fig. 49).

96 E VOL UTION AND DISEASE.

When the inflammation is more intense pus forms,
requiring active interference for its relief and cure.
There is reason to believe that millers' horses are more
liable to acquire these concretions than others.

There is a third tonsil in the pharynx which deserves
some attention, although it is not associated with a
branchial cleft.

When discussing the probable mode of origin of the
central nervous system, attention was drawn to a duct
which, in the embryo, traverses the floor of a recess in
the base of the skull (the pituitary fossa) and opens on
the roof of the pharynx. This duct is represented in
fig. 25, page 50, and is now regarded as a remnant of
the ancestral vertebrate gullet. The pharyngeal orifice
of this duct is surrounded by a collection of tissue
which, structurally, is identical with the tonsils, and the
organ has been named in consequence the pharyngeal
tonsil of Luschka, in honour of its discoverer. As far
as is at present known this organ has no function, but it
is often a source of trouble and inconvenience, mainly
in children, inasmuch as it is especially prone to enlarge
and obstruct the eustachian tube, producing deafness.
It also interferes, when large, with the free passage of
air through the nostrils, to such a degree as to require
surgical interference.

As most of the vestigial structures considered in this
chapter are the outcome of modifications induced by
the change from an aquatic to a terrestrial mode of life,
we may conclude it by briefly considering the fibula in
relation to Pott's fracture. Xo bone of the lower limb
of man, excepting the neck of the femur, is so liable to

VESTIGIAL STRUCTURES. 97

fracture as the fibula in its lower fourth. This accident
is attended with certain peculiarities, and is named after
the great surgeon Percival Pott, who first accurately
described them. The chief features of Pott's fracture
are the following : The fibula, or small bone of the leg,
is broken about seven centimetres above the ankle, the
tibial malleolus is splintered off, or the deltoid ligament
ruptured, and the foot everted. The most frequent
cause of this very common accident is a sudden and
violent twist of the foot. In order to study thoroughly
the conditions which predispose to this accident it will
be necessary to briefly review the history of the fibula,
and it is a fact of some interest that no one has ever
described the occurrence of Pott's fracture in any
mammal save man.

An examination of the hind limb of a menobranchus,
or menopoma, will serve to show that the bones of the
leg— the tibia and fibula — are equal in size. In such
animals the legs are used chiefly as paddles, enabling
them to move freely in water. The descendants of
some of these forms changed their mode of life, be-
coming semi-aquatic, or entirely terrestrial animals, and
began to use their limbs for creeping, crawling, or
running habits which led to changes in the bony frame-
work. In the case of the leg it is easy to see that it is
advantageous for the weight of the body to be transmitted
to the ground by one bone rather than two, hence the
bone most used increased in size : this enlargement
would induce a deviation of blood in favour of the bone
most used — the tibia — to the detriment of the companion
bone — the fibula. So truly does the fibula obey the law of

8

98 E VOL UTION AND DISEASE,

heredity, that in the embryo it to some extent maintains
its pristine eminence. This is strikingly shown in birds.
In the chick at the fifth day of incubation the fibula
equals in length, and nearly in thickness, the tibia.
Subsequently it dwindles, and in the adult bird it is
represented as a slender style of bone appended to the
proximal extremity of the tibia. In man the tibia, as
compared with the fibula by weight, is as three to one :
at the third month of embryonic life the fibula has a
transverse section nearly equal to that of the tibia.
Even in adult life if the tibia be broken and fail to
unite, extra work is thrown upon the fibula, and in course
of time this bone will enlarge, and its shaft, as I
have been able to demonstrate, may exceed in thickness
that of the tibia. Darwin refers to some experiments
of Sedillot in which small portions of the shaft of
the tibia were removed in young dogs : the result was
that the fibula, which in dogs is almost as slender
as in birds, became greatly increased in size conse-
quent upon the extra work required of it. As addi-
tional evidence in support of the view that the small
size of the fibula in comparison with the tibia is due,
indirectly, to the change of function of the leg from
a paddle to an organ for land locomotion, it may be
mentioned that in such aquatic mammals as seals the
fibula is not so small in proportion to the tibia as is the
case with terrestrial mammals. It is on these grounds
that we may reasonably believe that the small size of
the fibula, in comparison with the tibia, may be included
as one of the changes resulting indirectly from the
gradual change of an aquatic into a terrestrial animal.

VESTIGIAL STRUCTURES,

99

As the fibula in nearly all mammals is thin, slender,
and almost vestigial, we have yet to inquire how it is
that Pott's fracture is peculiar to human beings. A
comparison of the human malleoli with those of mammals
shows that man differs from them in that the external or
fibular malleolus descends much lower than the tibial
malleolus : even in those mammals which so closely ap-
proach man in anatomical characters as the gorilla, chim-
panzee,orang,gibbon, and macaque, the malleoli are on the
same level. In the accompanying sketches, fig. 50, the

Fig. 50.— A, the malleoli of the Chimpanzee ;
M, the malleoli of Man.

malleoli of man and a chimpanzee are introduced for
comparison.

In 1886 Gegenbaur published the highly interesting
observation that, in the human embryo at the fifth month
of intra-uterine life, the tibial is more prominent than
the fibular malleolus ; at the seventh month they are
equal; from this date onward the fibular exceeds in
length the tibial malleolus. Thus at the fifth month the
human malleoli present a condition common to the
majority of mammals ; at the seventh month they corre-

i oo E VOL UTION AND DISEASE.

spond to the simian type, and subsequently assume the
relation normal only in man. This extra length of the
fibular malleolus gives great firmness to the ankle-joint,
and has probably been acquired concurrently with the
assumption of the erect posture. It is to this extra
length of the outer malleolus, associated with the slender-
ness of the fibula, that the frequency of Pott's fracture
may be largely attributed ; the long fibular malleolus
affording good leverage when the foot is violently and
suddenly twisted laterally, the force applied to the long
distal end causes the fibula to snap at some point in its
lower fourth.

This inquiry, when pushed further, leads to other
points of interest. The foot of an orang, instead of
forming a right angle with the leg, as in man, has its
inner border drawn upwards in such a manner that the
sole of the foot looks inwards, and the back, or dorsum,
of the foot looks outwards. This position of the foot is
associated with a peculiar disposition of the articular
surfaces of the astragalus, or ankle-bone. In the human
embryo, up to the seventh month, the foot has a similar
position, and the articular surfaces are disposed as in the
orang ; after the seventh month the foot gradually
passes into the position characteristic of the adult, but
not infrequently it retains the simian position and the
child is said to be club-footed, or, properly speaking, it
has talipes equino-varus. Messrs. Parker and Shattock
have clearly shown that the articular surfaces of the
astragalus in cases of congenital talipes equino-varus
retain the ape-like disposition, and it occurred to me
that if this is constant, the fibular malleolus in children

VESTIGIAL STRUCTURES. 101

with congenital talipes equino-varus should also retain
the simian type and not exceed in length the tibial
malleolus. Careful dissections of such limbs have shown
this to be the case, and in specimens of congenital
talipes equino-varus in children just born, and in those
who in spite of the deformity have attained mature age,
the tibial and fibular malleoli are equal in length.

Summarizing these facts, we find that in the human
embryo the fibula gives evidence that primitively it was
nearly, if not quite, equal to the tibia in size ; that
during development the malleoli present, in length and
relation to the astragalus, conditions which are perma-
nent in mammals closely allied to man ; that the increased
length of the fibular malleolus firmly fixes the foot in the
standing position ; and that the thinness of the fibula
and its long malleolus is accompanied by the incon-
venience of predisposing him to the occurrence of Pott's
fracture.

CHAPTER V.

DICHOTOMY.

A STRONG tendency exists in the animal and vegetable
kingdoms for parts ending in free extremities to bifurcate
or dichotomize. In many instances partial or complete
dichotomy occurs so constantly that it is regarded as a
normal condition. Many extraordinary and beautiful
forms among animals depend upon its occurrence, as
well as a large number of malformations when dichotomy
occurs abnormally.

The principle may be illustrated by the star-fish. In
many specimens of this invertebrate we find normally
five arms arranged radially around a central disc. It is
not uncommon to find, as in fig. 5 1 (A), an arm redupli-
cated— this is complete dichotomy, and as the two halves
of the bifurcated ray are symmetrical we speak of it as
equal dichotomy. On the other hand, the ray may be
double only at its extremity. In fig. 5 1 (B) is a star-fish
ray drawn upon a larger scale in which the dichotomy is
only partial.

Every supernumerary ray attached to star-fish is not
due to dichotomy. When an arm is lost by accident
and the corresponding segment of the disc is uninjured,
or only slightly damaged, one or more rudimentary rays
may grow from it. Such rays are produced by a process

DICHOTOMY. 103

termed " budding." Very little experience enables an
observer to distinguish between a dichotomized ray and
a bud.

In 1 83 1 Tiedemann * published a brief description of a
star-fish, Asterias equestris Linn, with a partially dicho-
tomized ray, and pointed out that it must be regarded as

Fig. 51. — A, Star-fish with a completely dichotomized ray;
B, a larger ray partially dichotomized.

a malformation and not regeneration, as is so frequently
the case with star-fish.

Dichotomy occurs also in the appendages of the skin.
Few parts seem more distinct than feathers and
teeth, yet a study of the manner in which these

1 " Zeitschtiift fur Physiologie," Bd. iv. p. 121,

io4 E VOL UTION AND DISEASE.

structures are developed, demonstrates conclusively
enough that feathers, hair, and teeth are specialized
papillae of the skin. It is not my intention to discuss
this question, especially as the researches of anatomists
have long established the truth of this generalization.
As a rule feathers and teeth are formed from simple
papillae, but occasionally a papilla will dichotomize ;
should this occur, the result is a bifurcated feather or,
in the case of the dental papilla, two teeth will appear
fused together.

Most of us are acquainted only with single feathers,
such as are used for making pens. If, instead of the
large wing feathers, we select one from those covering
the body — contour feathers, as they are called — we
find in very many birds each quill bearing two vexilla ;
the second is called the aftersliaft or liyporachis, the
part of the feather by which they are attached to
each other is the calamus or quill. In some birds,
such as the emu, the feather and aftershaft equal each
other. The two forms of aftershaft are represented
in fig. 52. A is from the Himalayan Monaul, and B
from the Emu (Dromceus novcB-Jtollandice). These forms
of feathers arise from dichotomy of the feather-papilla.
It is difficult, without specially investigating the matter,
to be sure whether the emu's equal-sized feathers are
due to equal dichotomy of the papilla, and that of the
monaul to unequal dichotomy, or if, in the last case,
the feather grows at a greater rate than the aftershaft
and stunts it.

Hairs grow from cutaneous papillae in the same way
as feathers ; occasionally in hairy men hairs are fur-

DICHOTOMY. 105

nished with an aftershaft exactly resembling, in its

relation to the main hair-shaft, that figured in fig. B.

In the case of teeth it is not unusual in man to

Fig. 52.— A, feather and aftershaft of the Himalayan
Monaul {Lophophorus impeyanus) ; B, feather and
aftershaft of the Emu (Drojnceus novce-hollandice).

find a double incisor or bicuspid tooth. In such cases
the fangs and crowns are usually firmly united together,
but the line of union is indicated by a deep, well-pro-
nounced furrow. Such a condition of the teeth is

1 06 E VOL UTION AND DISEASE.

termed by odontologists, gemination (fig. 53). This
abnormality is not confined to the teeth of man, but
has been detected in those of other mammals, wild
and domesticated.

Typical cases of gemination may be considered as
examples of equal dichotomy. Should the process
only involve a part of the papilla, we should then
have only an extra crown to the tooth if it affect
the incisors or a canine ; but in unequal dichotomy
affecting the germ of a molar we should probably
find it increase the number of the cusps.

Antlers of deer occasionally fur-
nish instructive specimens. Dicho-
tomy may affect the beam or the
tine producing puzzling deviations.
The museum of the Royal College
jj of Surgeons contains a pair of
Fig. 53. —Two geminated antlers of the moose (A/ces ma-

teeth, illustrating equal and Mis\ Jn wh;ch the broad pajm> so

unequal dichotomy.

characteristic of this deer, is redu-
plicated in each antler (fig. 54). The specimen is
Hunterian, and said to come from America.

Dichotomy occurs in the limbs of many vertebrata
from the lowest to the highest, and is the chief cause of
supernumerary fingers and toes, and many examples
of reduplicated limbs. Many simple and uncomplicated
cases of dichotomy are presented by the digits : the
simplest are those in which children are born with a
small fleshy nodule hanging from the finger, usually
the fifth. As a rule the corresponding digit of each
hand is affected. The nodule consists usually of a

DICHOTOMY.

107

terminal phalanx, furnished with a rudimentary nail,
attached by a slender pedicle to a well-formed finger.
These rudimentary digits may be attached to the side
of the terminal phalanx, but sometimes swing from the
side of the first or proximal phalanx. It was this form
of supernumerary digit which Darwin erroneously be-
lieved was reproduced after removal. Dichotomy of

Fig. 54.— The right antler of a Moose with reduplicated palm.

the finger may be equal but incomplete ; it then gives
rise to the malformation shown by the thumb (fig. 55).
When the process is complete, two perfectly distinct
thumbs result. Such reduplication is not necessarily
confined to a finger or a thumb, but may affect several
digits of the same hand or foot. Jonathan, son of
Shimeah the brother of David, slew at Gath a man

T08

EVOLUTION AND DISEASE.

of great stature "that had on every hand six fingers
and on every foot six toes, four and twenty in number/'1
Many such cases have been observed in modern times.
Supernumerary toes and fingers run in families not
merely in man but in cats and dogs. Instances are

Fig. 55. — The hand of a baby, showing two forms of super-
numerary digits (semi-diagrammatic).

known in which cats have six-toed kittens as regularly
as Dorking fowls present five pedal digits.

In some specimens the dichotomy extends beyond
the finger and involves the metacarpal bone. This is
shown in the case of the silvery gibbon (fig. 56) : the
fifth digit was reduplicated and the distal end of the

1 2 Samuel xxi. 20, 21.

DICHOTOMY.

109

fifth metacarpal bone. The opposite hand was simi-
larly affected.

When dichotomy extends beyond the fingers and
metacarpal bones it may involve the terminal segment
and lead to reduplication
of the hand. Accessory
hands or feet due to dicho-
tomy are, in man, of very
great rarity. An excellent
specimen of double hand
has been described by the
late Dr. Jardine-Murray.1
A sketch of the hand is
given on next page (fig. 57).
It may easily be conceived
that should dichotomy in-
volve a greater extent of
the axis of the limb, we
should get an accessory
arm or leg. Accessory
limbs arising in this way
are, in man, very rare ;
indeed no such specimen is
known to me, but it un-
doubtedly occurs in other
vertebrata. Supernumerary
legs are met with in the human subject, but, as will
be seen later, these arise from dichotomy of the trunk
axis. It should be mentioned that all specimens of Poly-
dactyly do not arise from dichotomy. Some are atavistic :
1 " Medico-Chir. Trans." vol. xlvi. p. 29.

Fig. 56. — The left hand of a Silvery
Gibbon (I/ylobates leuciscus), with
dichotomy of the fifth finger and dis-
tal segment of the metacarpal bone.

no

EVOLUTION AND DISEASE.

atavistic Polydactyly can only occur in non-pentadactyl
mammals, but even in them, as will be shown in the
chapter on Atavism, the number of the digits may be
increased by dichotomy.

There is reason to believe that supernumerary digits
and limbs may be produced by cleavage throughout the
vertebrate sub-kingdom. Albrecht has figured a mud-
fish {Protopterns annectans\ with bifurcation of the right
pectoral limb (fig. 58). The specimen is preserved in the

museum at Konigsberg.

Haswell and Howes have
shown and admirably illustrated
the tendency manifested by the
fins of Ceratodus to bifurcate.
This is seen not only in the radii
supporting the fringe of horny
rays, but in the main or support-
ing axis.1

Among amphibians super-
numerary limbs are not rare.
An example from the common
toad is sketched in fig. 59. The
axis of the limb is at right angles to the trunk, and
articulates with the ilium by a perfect ball-and-socket
joint. The additional limb has the usual segments of
femur, cms, and pes. The muscles were well-developed.
This specimen illustrates a condition of frequent
occurrence in such limbs ; it is furnished with an ab-
normal number of digits — the usual number is five,
whereas in this case the pes presents seven.
1 " Proc. Zool. Society," 1887.

Fig. 57. — A double hand.
(After Jardine-Murray. )

DICHOTOMY.

in

Excess in the number of the limbs may occur with the
fore-limbs. The museum of the Royal College of Sur-
geons possesses a specimen of a frog, thus described in

the catalogue : —

Fig. 58. — The Mud-fish (Protopterus annectans),
with partial dichotomy of the right pectoral
limb. (After Albrecht.)

" A frog with a small additional anterior extremity
springing from the posterior and lateral part of the
sternum " (Hunterian).

Fig. 59. — A Toad {Bufo vulgaris iuv.), with
supernumerary hind limb.

A specimen which came under my observation is
sketched in fig. 60. The limb furnished with four
digits was attached to the anterior part of the left
moiety of the shoulder girdle through the intervention

112

EVOLUTION AND DISEASE.

of a bone resembling a supernumerary coracoid. To
judge from published cases it would seem that super-
numerary limbs in amphibia are uncommon, but inquiry
satisfies me that they are, in frogs and toads at least, by
no means infrequent.

We will turn from amphibians to birds. In these
highly specialized and exquisite forms, dichotomy is
very common. The Dorking fowl has long attracted

Fig. 60. — A Frog (Raua iemporaria), with a supernumerary
fore-limb.

attention in that it presents almost constantly a
double digit on the pes, increasing the number to five.
This extra toe is due to dichotomy of the digit attached
to the vestigial first metatarsal ; it possesses three
phalanges, and is furnished with a claw. This deviation
from the number normal among fowls is further interest-
ing in that it is transmitted truly to offspring when the
Dorking is crossed with breeds furnished with four toes.

DICHOTOMY.

113

Dichotomy may, not infrequently, affect other digits ;
thus in fig. 61 a chick is represented with two bifid
toes and partial duplicity of the left leg. Birds with
these accessory parts may live and attain the adult
condition.

Supernumerary legs are very common in birds, indeed

Fig. 61. — A Chick with two dichotomized digits
and a supernumerary leg.

almost every poultry breeder has seen examples, yet
accessory wings are very rare. One specimen only is
known to me, a dove, preserved in the museum of the
Royal College of Surgeons (fig. 62). This bird has an
accessory wing growing from the lower part of the
sternum,

9

ii4

EVOLUTION AND DISEASE.

The apparent rarity of supernumerary fore limbs, in
comparison with hind limbs, will be dealt with when
considering the question of dichotomy as manifested in
the trunk.

In cats and dogs dichotomy of the terminal segments
of the fore and hind-limbs is fairly often seen, and a
five-legged dog is one of the usual exhibits at a penny

Fig. 62. — A Dove with an accessory wing, probably
due to dichotomy.

monstrosity-show. An uncommon example is repre-
sented in fig. 63 ; it is a sheep with an extra fore-limb
attached to the scapula. The terminal segment is re-
duplicated. Dissection of the parts seemed to show that
the abnormal limb was due to dichotomy of the limb
axis, but this explanation is not altogether satisfactory.
From supernumerary limbs we may now pass to the
consideration of what are commonly known as, double

DICHOTOMY.

"5

monsters, and endeavour to show that they arise from
dichotomy, partial or complete, of the trunk-axis of the
embryo. Before describing actual specimens it will be
well to adduce facts in support of the view that double
embryos may arise from a single ovum.

In 1869 Haeckel x showed that it was possible, by

Fig. 63.— A Sheep with supernumerary fore-leg.

dividing artificially the eggs of Crystallodes rigidum to
multiply the number of embryos. The experiments
were very simple, and consisted in taking a Crystal-
lodes larva on the second day, in which the amoeboid
movements were very lively, placing them in a watch-
glass with sea-water, and with the aid of a simple micro-

1869.

Zur Entwicklungsgeschichte des Siphonophoren." Utrecht,

1 1 6 E VOL UTION AND DISEASE.

scope and cataract needle dividing them into two, three,
or four pieces. Detailed accounts of six experiments
are given in which the ova were simply divided, cut into
three portions, or quartered. The results of these experi-
ments were as follows : —

i. Development continued in the divided pieces.

2. The smaller the piece the slower the growth of the
larva.

3. The smaller pieces tended to form incomplete
individuals and inclined towards monstrosity.

These observations are valuable, for it must be borne
in mind that the growth of a morula (segmented ovum),
after artificial division, differs very much from the forma-
tion of a hydra out of a piece cut from an adult hydra.

From SyphonopJiora we may pass to worms. In 1828
Duges1 presented to the Acad£mie Royale des Sciences, a
paper entitled, " Recherches sur la Circulation, la Respira-
tion et la Reproduction des Annelides a Branches,"
which contains the following remarks relative to the eggs
of the worm Ltunbriais trapezoides ; —

"The first of these eggs which I opened embarrassed
me much. I saw escape with a glairy material a living,
white, soft, transversely wrinkled, vermiform animal,
composed of a body terminated by two appendages
marked from right to left by a regular spiral. It was a
monster formed of two individuals joined together, fused
in a part of their length, as I have since observed in
others but with less symmetrical conformation. In each
egg I have constantly found plunged in the same
albuminous jelly, either two germs, two cicatricula, or

1 " Annales des Sciences Naturelles," tome xv. p. 248.

DICHOTOMY.

117

two embryos, except that one of the two germs, though
not aborted, merely left traces of its former existence."

In a foot-note Duges makes a further observation :
" Even in the ovary we perceive that these eggs pre-
sent two distinct cicatricula, in some isolated, in others

1C\

%

Fig. 64. — A, Transverse section of a double embryo
of Lumbrlciis trapezoides.

B, Transverse section of an embryo of L. trape-
zoides. One embryo is suppressed and appears
merely as an excrescence. (After Kleinenberg.)

contiguous." Duges illustrates the phenomena he
describes by some crude drawings, but there can be no
ambiguity about the facts to which he drew attention.

The embryology of the worms concerning which
Duges made the above curious observations has been

1 1 8 E VOL UTION AND DISEASE.

carefully studied by Kleinenberg,1 and he has succeeded
in tracing the development of these worms step by step,
and shows beyond any doubt that it is a normal condi-
tion in L. trapezoides for a single germ to produce two
embryos. For a time the embryos are united and turn
gently in the albumen without at all impeding each
other. The commissure uniting them relaxes gradually,
then breaks, and the embryos are freed. There are
cases not at all rare in which this singular form of
development leads to monstrosity. In fact, among per-
fectly developed worms, double monsters occur pre-
senting all grades of concrescence, from those firmly
united along the whole extent of the body, so that
separation is impossible without breaking the embryo
into pieces, to others which are hatched coupled together,
but only by a thin, frail ligament that the worms easily
effect a separation. These junctions are always confined
to the epithelial layer of the body wall.

Kleinenberg states that he has never found one of
these eggs giving rise to a single embryo. It is true
that a single worm escapes from a capsule, but then
nearly always the remains of its companion are found.
The accompanying sketches exhibit the extreme forms
of these double embryos. In fig. 64 A, they are shown
when of equal size ; in B, one of the embryos has
undergone suppression.

We have direct evidence among vertebrata that two
embryos may arise from a single ovum. It has been
actually witnessed in a batrachian by Clarke.2 In the

1 Quart. Journal of Micros, Science, vol. xix. 1879.

2 "Ann. Mem. Boston Soc. Nat. Hist/' 1880.

DICHOTOMY, 119

spring of 1879 he had in an aquarium two or three
thousand eggs oi Ambly stoma punctatum for the purpose
of studying their development. One day he chanced to
find one with the medullary folds nearly completed, but
they had not united at the cephalic end, and appeared to
be much rounded at their anterior ends, instead of having
the ordinary vague outlines ; he kept it apart, therefore,

tJ

Fig. 65.— A two-headed Foal ; anterior dichotomy.

and watched it. Each free portion of the medullary fold
developed a perfect head, which, at first partly united,
became gradually more so, until they were connected
throughout their entire length. Posterior to the heads
there was no sign of duplicity.

In this case a two-headed monster, with a regular
symmetrical body, was developed from one egg, and

1 20 E VOL UTION AND DISEASE.

the anterior portion of each medullary fold gave rise to
a head.

Double embryos vary greatly, according to the degree
of dichotomy, and the subsequent growth of each half of
the ovum. The cleavage may affect the cephalic ex-
tremity only ; this is conveniently called anterior
dichotomy. Of this the two-headed foal sketched in
fig. 65 will serve as an example.

In many cases the cleavage only involves the facial
portion of the skull, thus producing an animal with two
tongues and four pair of jaws. The supernumerary
jaws are, in such cases, conjoined into a single mass
wedged in between the functional jaws, and not infre-
quently mistaken for congenital tumours. We shall
return subsequently to malformations of this class.

When the cleavage is more extensive than in the case
of the foal it may give rise not only to two heads and
necks, but the thoracic region of the body is reduplicated.
And thus we have a single pair of legs, a common pelvis,
but the anterior part of the embryo double. Several
such cases have been recorded in mammals, even in the
human subject, some of which have been made objects
of careful physiological study, and subsequently carefully
anatomized. The most important case of this kind
was the celebrated Ritta-Christina, born at Sassari, in
Sardinia, 1829, who after surviving the birth eight months
and a half, died in Paris. Isidore Geoffroy Saint-Hilaire I
gives an interesting resume of the chief features of this
case.

When dichotomy is more complete, two individuals
1 " L' Anomalies des Organisation," tome iii. p. 119.

DICHOTOMY.

121

attached only by the pelvis may result, every part of
the body and limbs being reduplicated, as in the case of
the Two-headed Nightingale.

Such specimens occur throughout the vertebrate sub-
kingdoms. Two embryo sharks
are shown in fig. 66. They are
united in the ventral aspect in
the caudal region ; the remains
of a single yolk sac exists
between the pectoral fins, and
serves as additional evidence to
indicate their origin from a
single yolk. These sharks, with
some similar specimens, are pre-
served in the museum of the
Royal College of Surgeons. The
catalogue states that " a female
shark was taken in the Indian
Ocean. When brought on deck
and cut up, about thirty young
escaped from the abdomen. The
specimen lived for two days in a
bucket of sea-water. Several
examples of sharks, trout,
mackerel, and salmon redupli-
cated in this manner have been
recorded. Rauber has contri-
buted some excellent observations on this subject. He
has been successful in detecting many cases of duplicity
of the medullary folds, and the evidence seems to indicate
that, had they continued to develop, double embryos
would have resulted.

Fig. 66. — Two embryo Sharks
joined ventrally.

122

EVOLUTION AND DISEASE.

From examples in which dichotomy gives rise to a
double-headed monster as in the snake (fig. 6j) or the
foal, to more complete forms, such as Ritta-Christina,
the Two-headed Nightingale, or the sharks (fig. 66),
we pass on to instances in which the bond of union is
merely a narrow fleshy band, as in the Siamese Twins.
From these it is but a step to the origin of separate
twin-fcetuses by dichotomy of a single ovum. In all

cases of duplex monsters which have
come under my notice, the individuals
composing a double monster were of
the same sex, and there is good

lriG. 67. — The cephalic
extremity of a double-
headed Snake.

ground for the belief that when twins
are of the same sex and enclosed in
the same membranes they are the
product of a single ovum.

Up to this point we have been con-
sidering duplex forms in which the
body on opposite sides of the cleft
equal each other in development.
We are now in a position to consider
specimens in which the dichotomy is
unequal, or if equal at the outset one half grows at a
less rate or becomes in great part suppressed. Such a
case is shown in the calf (fig. 68). Here we have attached
to the sternum of the healthy calf the headless trunk
and limbs of a second calf. To such specimens the
term parasitic foetus is usually applied, whilst the normal
calf is called the autosite.

Several specimens of this kind have been investigated
in the human subject. A well-known case is that of

DICHOTOMY.

123

the Chinese lad, Ake. He had, like this calf, the trunk
and limbs of a second individual attached to the
sternum.

An instructive individual similar to Ake is the Hindoo

------ > -- • ■ •« ■ • • • •> - >-■ ' \ ^ - ■• - . ■ ■ ■•;'. .-^-v . .:' niL&&\

Fig. 68.— A Calf with a parasitic foetus attached to its
sternum.

lad, Lalloo, recently exhibited in London and various
parts of England. Lalloo is a highly intelligent lad of
seventeen years, and has attached to the sternum near
the xiphoid cartilage the trunk and limbs of a second
male individual. When blindfolded he was able to accu-

I24

EVOLUTION AND DISEASE.

rately localize pricks from a pin made upon the parasite.
Although the parasite seemed to possess independent
reflex centre, it had no power of spontaneously moving
the limbs, neither had the autosite any control over them.

Fig. 69. — A Green Lizard (Lacerta i with dichotomy

of the tail.

Parasitic foetuses similar to Ake and Lalloo and the
calf occur in cats, dogs, and lambs. In such cases the
nature of the abnormal appendage is obvious enough,
but in cases where the growth of the second embryo

DICHOTOMY. 125

is still further arrested, with nothing but a confused con-
glomeration of tissues and organs, without any definite
shape to guide the observer, there is often more difficulty
in coming to a conclusion. Shapeless masses of this
character containing elements of a second embryo in
the form of a tumour consisting of bone, liver, teeth,
intestines, digits, and the like, are known as teratomata.
Many such have been described in human beings. A
few examples have been recorded in calves.

Up to this point we have been concerned with anterior
and complete dichotomy : now posterior dichotomy of
the trunk claims consideration. A simple case is
furnished in the green lizard {Lacerta viridis) shown
in fig. 69. The animal has a bifid tail. To show that the
bifidity is not due to injury and subsequent reproduction
of the tail and consequent budding, it may be mentioned
that reproduced tails are never so perfectly conformed as
in this specimen and do not contain vertebrae ; further,
monstrous lizards have been recorded in which the
cleavage had involved the trunk so as to produce the
bodies and limbs of two lizards but only one head. In
one specimen described and figured by Tiedemann, a
double-bodied monstrous green lizard has a double, but
fused head.

Passing from tailed animals, such as lizards, and
turning to frogs, it must be clear to every one that if
dichotomy occur, it need only be slight to produce re-
duplication of the pelvis with the limbs and associated
parts. This is a matter of interest because many
specimens have been incorrectly interpreted on account
of this fact not being properly appreciated. It is also

126 EVOLUTION AND DISEASE.

clear that if dichotomy lead to reduplication of the
pelvis, four pelvic limbs should result. In typical
specimens such is the case : two of the limbs being
functional, and two usually occupying a median position
on the ventral aspect, much smaller in size.

Fig. 70. — Rana esculenta, with supernumerary hind limbs.

A specimen of this nature was described in 1837 by
Dr. J. van Deen. It occurred in a frog {Rana esculenta),
(fig. 70), and was associated with a bifurcated condition
of the termination of the alimentary canal. Van Deen
gives a carefully detailed account of the dissection of
this frog. It seems to be one of the earliest recorded

DICHOTOMY.

127

cases of this malformation. A much commoner con-
dition is to find the abnormal limb projecting posteriorly
between the normal legs. In such a position the two
legs are as a rule fused together near their attachment
to the trunk, but may retain their individuality in the
distal segments. Such a specimen is sketched in fig.
71. It is a lamb with a supernumerary pair of confluent
hind limbs, as shown by dissection, projecting from the

Fig. 71. — A Lamb with coalesced supernumerary pelvic limbs,
(After Gurlt.)

pelvis. In this case the nether opening of the alimentary
canal is double also.

A much more obvious case than this is represented
in the chick (fig. 72). For some reason or other
supernumerary legs are very common in fowls, ducks,
geese, pheasants, and lambs.

In many cases posterior dichotomy of the axis may
be indicated by one limb only, the other undergoing
suppression. ,

128 E VOL UTION AND DISEASE,

Dr. Tuckerman * has placed on record an account of
such a specimen. The subject was a frog {Rana
palustris) ; it was blown from out a crevice in a ledge
of mica schist during some blasting operations. The
crevice was twelve feet below the surface and measured
only a few lines at its widest point ; flowing into the

Fig. 72. — A Chick with supernumerary legs.

crevice was a small stream of running water, which
undoubtedly conveyed either the eggs, or the frogs in
the larval stage, to the interior of the rock, as the
breach in the ledge was much too small even to admit
the passage of a very young frog. This frog had, as

1 Journal of Anatomy and Physiology, vol. xx. p. 516.

DICHOTOMY. 129

represented in fig. 73, a third hind limb projecting
posteriorly between the normal legs. On dissection it
was found attached by muscle and tendon to the
symphysis pubis : it presented the usual segments of
femur, crus, and pes, and was furnished with two
well - formed digits and the rudiment of a third.
During life it was found that when the skin of the
limb was stimulated the frog would jump quickly
away ; sometimes oft-repeated stimulation would call
forth a muscular contraction
in the limb. Occasionally
movements were observed
in the abnormal limb when
the frog was left entirely to
itself.

It has already been men-
tioned that in parasitic
foetuses, even when the
limbs are well-formed, the
autosite has rarely the power

r . \ • Fig. 73. — A Frog [Rana -palustris).

Of Spontaneously moving with supernumerary hind limb.

the limbs belonging to the (After Tuckerman).

parasite, and this is the rule in supernumerary limbs, so
that the spontaneous movement in the leg of Tucker-
man's frog is interesting. The drake (fig. 74) pos-
sessed the power of moving the abnormal limbs, and
similar specimens have come under my notice in hens.
Such power is, however, exceptional.

Supernumerary pelvic limbs similar to those of
frogs and toads, sheep and birds, occur in the human
subject ; several of the individuals thus affected have

10

130

E VOL UTION AND DISEASE.

lived to twenty, thirty, or more years. Of the more
remarkable cases may be mentioned Jean B. dos Santos
of Portugal, and Blanche Dumas. The mode of origin
of paired pelvic limbs has been especially studied by
Professor Cleland. This anatomist has clearly demon-
strated that many of these are due to posterior

Fig. 74. — A Drake with a pair of supernumerary legs.

dichotomy leading to reduplication of the pelvis. He
further points out that in living specimens of posterior
dichotomy, the functional limbs belong to opposite
pelves. In some it will be right limb of the right
pelvis and the left limb of the left pelvis. In such a
case the adjacent sides of the pelves and the associated

DICHOTOMY. 131

limbs become dwarfed or suppressed. In some the
legs remain separate ; in others they coalesce com-
pletely or partially, and in rarer specimens one leg
may be suppressed. The relation of the suppressed
to the functional pelvis varies greatly. In many
specimens it is represented by an irregular plate of
bone carrying a limb or limbs wedged in the pubic
arch ; in others two fairly-formed pelves may occur on
the same plane. The relation borne by the opposed
halves of these reduplicated pelves is similar to that
which occurs in anterior dichotomy. For instance, we
may have a single body with two perfect heads, or
the dichotomy of the head is so partial that the jaws
in apposition with each other, that is the left one of
the right head and the right jaws of the left head,
fuse together and form a composite pair of jaws
wedged between two functional ones. In cases of
partial posterior dichotomy, it has been already stated
that the functional legs often belong to distinct pelves,
so in many instances of anterior dichotomy the
functional jaws belong to two heads. In anterior
dichotomy, when it extends into the thoracic region,
each individual has a pair of functional arms. In a
few cases the median arms, that is the left arm of the
right body and the right arm of the left body, fuse
together and form a composite median limb.

Although apparently unconnected with the subject
of twin monsters, it is necessary to offer a few remarks
on the subject of transposed viscera. Very many cases
have now been observed and dissected in which the
heart, instead of being inclined to the left side is

132 E VOL UTION AND DISEASE.

turned to the right, the liver is situated in the left
side of the abdomen, thus changing places with the
spleen. This transposition also affects the main
arterial and venous trunks. Mr. Morrant Baker
suggested to me that if double embryos and, in some
instances, twins are produced by dichotomy of a single
ovum, the viscera of one or other embryo should be
transposed — one should be as it were the reflection of
the other vehit in speculo.

There is much to support this view. In many
examples of duplex human children such a trans-
position has been actually found ; in following up the
inquiry it turns out that the hearts in these monsters
are often situated in the median plane of the body,
and not infrequently a composite heart dominates the
circulation of the two individuals. The question
naturally suggests itself, Are all cases of transposition
of viscera associated with twin conceptions ? This
must stand as a question until we know more of the
history of such cases, and it needs careful investigation.

It was formerly believed, and some still maintain the
view, that duplex monsters may arise by the adhesion
of two embryos originally distinct. This view has little
foundation. Without attempting to seriously discuss
the difficulties surrounding this " impaction theory," its
supporters will have to explain the relation of such
foetuses to each other, and why they are united by
homologous parts, such as head to head, back to back,
pelvis to pelvis, &c. Should the second embryo be
represented merely as a teratoma, it usually resembles
the part to which it is attached. By the impaction

DICHOTOMY. 133

theory it is inconceivable that these parts should accu-
rately adapt themselves to each other, that heads should
unite, hearts blend, or the alimentary canals fuse to form
one. On the dichotomy or cleavage theory all this
becomes intelligible, and the fact that reduplicated
digits, limbs, heads, and trunk occur throughout the
vertebrate sub-kingdom and beyond it, is sufficient to
indicate that a common cause underlies these diverse
malformations.

The subject is one of great interest, for the same
tendency which produces dichotomy of the ray in star-
fish, or digits in mammals, will, when it involves the
axis of the limb, produce a supernumerary arm, wing,
or leg; should it affect the axis of the embryo, will lead
to the production of duplex monsters of varying develop-
ment and different degrees of union, or even result in
viable twins. The same tendency to dichotomize is
exhibited in the plant world.

CHAPTER VI.

ATAVISM OR REVERSION.

MUCH that is fanciful and speculative is mixed up with
the subject of atavism ; the widespread acceptance of
the principles of evolution has had the effect of render-
ing us less critical in the examination of suspected cases.
On the present occasion atavism or reversion will be
considered only in relation with structural peculiarities,
and an endeavour will be made to indicate spurious
examples of the process.

Gegenbaur defines atavism as a " reappearance of a
more primitive organization, or a reversion to a primary
state." He is also careful to point out that atavism
does not consist in the existence of a latent germ, but
in its becoming perfected or further developed. This
view may be more clearly expressed thus : —

Atavism consists in the attainment of a functional or,
more or less ', full development of parts which for a given
animal are suppressed during embryonic life, or undergo
great modification,

This definition allows atavistic phenomena to be
arranged in two groups : —

i. The attainment of a functional condition by struc-
tures normally suppressed.

2. Reversion of organs and tissues to an original type.

A TA VISM OR RE VERSION. 135

Examples of each form will now be considered. The
attainment of a functional condition by parts normally
suppressed is well illustrated in the case of man by
supernumerary ribs. Normally the number of ribs on
each side is twelve : not infrequently the number is in-
creased by an additional rib at the cervical or lumbar end
of the series. In many birds and reptiles all the cervical
vertebrae bear ribs ; in mammals the cervical ribs are
represented in a vestigial form, and in man such vestiges
are confined to the fifth, sixth, and seventh vertebrae.
Occasionally the rib attached to the seventh cervical ver-
tebra acquires a length of five to seven centimetres, becom-
ing perceptible, to practised eyes, even in the living body.
Supernumerary ribs attached to the lumbar vertebrae are
more instructive than those in the neck. Each normal
rib has inserted into its angle a fan-shaped muscle which
raises it during inspiration and is known as the levator
costce. In the lumbar region these muscles are repre-
sented by fan-shaped collections of tendons connected
with the transverse processes of the vertebrae. In many
instances, when a lumbar rib is present, the correspond-
ing tendinous levator is replaced by a functional muscle.

This is instructive, as it illustrates a fact which must be
constantly borne in mind when investigating suspected
cases of reversion, viz., atavistic parts do not belong to
forms palceoutologically remote or systematically far dis-
tant. This is particularly insisted upon by Gegenbaur.

In the present case the lumbar ribs are represented by
extra centres of ossification at the extremities of the
transverse processes ; normally they fuse with these
processes, but occasionally attain a functional size

136

EVOLUTION AND DISEASE.

and are recognized as supernumerary ribs. In order
to find mammals with more than twelve pairs of ribs we
need not seek far from man, as the chimpanzee and
the gorilla possess thirteen pairs ; in the American
monkeys there are twelve to fifteen pairs, and in
lemurs twelve to sixteen pairs.

The following specimen illustrates the reversion of

Fig. 75. — The mitral valve of a man's heart containing a
patch of muscle tissue, a. (After Dr. Ogle.)

tissue. Dr. Ogle * has described a man's heart, which
contained a patch of muscle tissue in the anterior
segment of the mitral valve (fig. 75). The patch of
muscle was as large as a fourpenny-piece, and resembled
under the microscope the natural tissue of the heart.
1 " Trans. Path. Soc," vol. ix.

ATA VISM OR RE VERSION. 137

In the embryo these flaps, or valves, arise as outgrowths
from the cardiac walls, and consist of muscle tissue,
which gradually undergoes metamorphosis into fibrous
tissue. In the echidna and ornithorhynchus the valve
of the right ventricle is muscular throughout life : this is
also the case in all birds. Hence a patch of muscle
tissue in the cardiac valves may be regarded as atavistic.

The arch of the aorta, the main arterial trunk, now
and then illustrates this form of atavism. In all mam-
mals the aorta in its normal course should curve over the
root of the left lung ; in birds, with equal constancy, it
curves over the root of the right lung ; in lizards and
frogs an aortic arch crosses the root of each lung and,
subsequently uniting, form a single trunk. In the em-
bryo of birds and mammals both aortic arches exist, but
in mammals the right one becomes suppressed ; occa-
sionally, however, the left arch, from causes quite
unknown to us, undergoes suppression, the right one
becoming the functional vessel. Thus a right aortic
arch in a mammal is a true instance of atavism.

It is well known that in the small amount of hair
upon the body, man differs from all mammals except
the whales and porpoises. He however stands alone in
its unusual distribution. The human foetus is covered
with delicate hair known as lanugo, which is usually
shed shortly before or immediately after birth. This is
clearly an indication of a lost character, the lanugo
representing the hairy covering of closely allied verte-
brates ; it appears in the embryo in obedience to
heredity. Children are often born with pigmented hairy
patches on their bodies known as moles ; these moles

138

EVOLUTION AND DISEASE.

vary in size ; sometimes they are no larger than split
peas, in other cases cover several square inches, and in ex-
ceptional cases nearly the whole of the trunk may be thus
covered ; the hair may even equal in length that growing
on the child's head. Several instances of hairy men of
this sort have been known, and an illustrative case is
shown in fig. 76. The original drawing is preserved in

Fig. 76.— Trunk of a Man with a large hairy mole. (After
Lawson.)

the museum of Middlesex 14ospital. The biblical Esau
was probably a man of this character. These are
examples of reversion, the lanugo instead of being shed
attains full development : we need only descend to those
mammals most closely allied to man, and in his own
order Primates, to find the true significance of the
phenomenon.

A TA VISM OR RE VERSION. 1 39

Some instances of the reversions of organs and tissues
to an original type will now be considered, and it will
serve to simplify matters if the question be illustrated
by a botanical example of this form of atavism. In
1790 Goethe, in his celebrated treatise " On the Metamor-
phosis of Plants," drew the attention of botanists to the
fact that the various parts of a flower may be regarded
as modified leaves. Of course this does not mean that
each part of the flower is a metamorphosed leaf, but that
we are able to trace every structural gradation from
leaves to bracts, from bracts to sepals, and not infre-
quently sepals will be replaced by, or become converted
into, true leaves. The changes from sepals to petals and
from petals to stamens are as gradual as from bracts to
sepals, and the homology is often declared by the
stamens becoming petals, and petals appearing as leaves,
even stamens have been known to revert in this way ;
this is what is meant when we say that the various parts
of a flower are formed upon a common type.

Atavistic phenomena of this character are not un-
known in the animal world, some of which we will now
consider.

One of the most remarkable recorded examples of
this form of atavism occurred in a rock-lobster (Palinurns
penicillatus). It is the specimen originally described by
M. Alphonse Milne-Edwards, and referred to by Darwin ;
the drawing has been published by Professor G. B.
Howes (fig. 77).

Notwithstanding the differences observed in the
various appendages of lobsters, such as the antennae,
eye-stalks, swimmerets, chelae, and the like, morpho-

1 4o E VOL UTION AND DISEA SE.

logists hold the opinion that all these appendages are
modifications of a common type. Normally the eye-
stalk corresponds to the protopodite of an abdominal
limb, consisting of a short basal and a long cylindrical
terminal joint, the distal surface of which is covered with
corneal facets. In A. Milne-Edward's Palmuruswe find
a normal ophthalmite on the right side, but the left one
" has taken on antenniform characters."

Fig. 77. — Cephalon of a Rock-lobster (Palinurus penicillatus),
with an antenniform process growing from the inner
aspect of the eye-stalk. (After Howes.1)

Professor Howes points out that the corneal facets
on the eye-stalk of decapod crustaceans do not in
many instances surmount the whole of the free sur-
face ; frequently the outer free border is destitute of
corneal facets, and often is swollen and well differen-
tiated. This is so in Palinurus, and would serve to
support the view that the facetted portion of the oph-

1 "Proc. Zool. Soc." 1889.

A TA VISM OR RE VERSION. 141

thalmite was exopoditic, whilst the inner portion, which
furnished the antenniform process, was endopoditic in
character.

The interest of this specimen lies in the fact that it is
exactly analogous to the conversion of an element of a
flower, say a stamen, into a leaf. Although I have made
a wide search, nothing in any way comparable to this
specimen can be found recorded in zoological literature,
but there can be little doubt that such cases occur if we
would watch for them. One would also imagine that
similar malformation must occasionally occur in the
appendages of insects, but thus far my inquiries have
not had any material result.

From organs we turn our attention to tissues, and
examine some specimens illustrating the reversion of
mucous membrane to skin.

The exterior of our bodies is covered by a membrane
called skin, which differs in many points from that
lining the internal cavities — the mouth, stomach, and
intestines — and known as mucous membrane. The
contrast between skin and mucous membrane is well
illustrated in the case of the conjunctiva, the delicate,
sensitive membrane covering the eyeball and ocular
aspect of the eyelids. The conjunctiva is really modified
skin, and not infrequently declares its ancestry by
reverting to its original form. Indeed, it is no unusual
event to find a patch of hair-covered skin growing upon
the ocular conjunctiva. Such cases are far from rare.
Mr. T. Collins is of opinion that about twelve cases of
this abnormality are seen annually at the Ophthalmic
Hospital, Moorfields. These dermoid patches are most

142

EVOLUTION AND DISEASE.

frequent on the outer side of the eye near the junction
of the cornea and sclerotic.

Similar hairy patches have been recorded as occurring
on the conjunctivae of dogs, oxen, and sheep ; in the
latter animals these abnormal pieces of skin are fur-
nished with wool. The specimen sketched in fig. 78
represents a large patch of skin growing on the con-

Fig. 78. — The cornea of an Ox with a patch of piliferous skin
growing from it. (After Partridge.)

junctiva of an ox. Some of these patches of skin
have been examined microscopically and found to
contain parts which are characteristic of skin in other
situations of the body such as pigment, sebaceous,
and sweat-glands. The developmental details of the
conjunctiva indicate most conclusively that it is a
modified piece of skin, and though in the individual

A TA VISM OR RE VERSION.

H3

it does not pass from skin to mucous membrane, never-
theless, as in the case of the flower, it now and then
indicates its ancestry by reverting to its original type of
structure.

Spurious Atavism. — It is so important not to con-

FiG. 79. — A congenital fold of skin stretching from the thigh
to the heel of a girl. (After Wolff.)

found spurious instances with examples of genuine
reversion or atavism that, even at the risk of being
tedious, it is necessary to consider briefly a few in-
teresting cases likely to be misinterpreted on superficial
examination.

In 1888 Dr. Julius Wolff, of Berlin, published a

1 44 E VOL UTION AND DISEASE.

description of a remarkable anomaly in the leg of a
girl. Among other defects she had a broad triangular
fold of skin stretching from the thigh to the heel, as
shown in fig. 79. The malformation was congenital
and is in all probability unique ; at any rate, it is very
rare, for such exhaustive writers on the subject of
malformations in general as Forster, St. Hilaire, Alhfeld,
and Albers furnish no parallel case.

On superficial examination a zealous evolutionist
might be induced to argue that we have here an
attempt to produce a wing, or regard it as a reversion
to the parachute-like folds of skin seen in phalangers,
flying squirrels, or even the wings of birds. Wolff,
however, judiciously disposes of fanciful speculation in
this direction by correctly pointing out that, in the
so-called flying mammals, the cutaneous folds, or para-
chute, extends from the fore to the hind limbs, and this
was the condition in those extraordinary extinct forms
the pterodactyls ; indeed, no mammals, are known with
skin-folds passing from the two segments of the hind
limb. In birds we find a cutaneous fold passing from
the humerus to the carpus and known as the patagium,
which in its general appearance resembles the fold in
the girl's leg. Beyond this superficial resemblance these
patagii have nothing in common, for the wing-fold in
the bird is traversed by tendons some of which are
remarkable for their elasticity. Thus we cannot find
among mammals, birds, or lizards, living or extinct, any-
thing corresponding to this curious wing-like expansion.
We must therefore regard this skin-fold as a spontaneous
variation, or " sport." Even if an animal were known

ATAVISM OR REVERSION.

MS

to possess such a web, there would be another strong
argument against its reversionary character, viz., that
in the embryo the two segments of the limb are not
united or in any way connected by a cutaneous fold ; thus
we have not to deal with a persistent foetal structure.

Whilst dealing with skin-folds it may be of interest
to draw attention to a
not infrequent example of
webbing. In the human
subject it is not uncommon
to meet with individuals
possessing two or more
fingers united to an abnor-
mal degree by a web. Nor-
mally our fingers are webbed
as low as the middle of the
first phalanx. The gorilla
has a web extending to the
first joint of the index and
middle finger, and the Sia-
mang gibbon has its second
and third toes webbed as far
as the distal end of the first
phalanx ; the seal and orni-
thorhynchus have a broad
web to the digits of manus
and pes. Abnormally webbed fingers and toes are not
peculiar to man ; they occur in monkeys, and a good
specimen of this malformation which occurred in a
monkey {Pithecus satanus) is drawn in fig. 80. In this
instance the corresponding fingers on each hand were

Fig. 80.

-Webbed finger in a Monkey
( Pithecus sat an us) .

II

1 46 E VOL UTION AND DISEA SE.

similarly affected. In such cases as this it is easy to
argue that such conditions are reversions to the webbed
feet and hands of aquatic mammals, but careful con-
sideration leads me to take an opposite view. If all
the fingers and toes were furnished with a web we
should be justified in regarding the phenomenon as
atavistic, for in their early stages our fingers are com-
pletely webbed, but later the digits grow at a greater
rate than the web, until the skin-fold reaches no lower
than the middle of the first phalanx. This would lead
me to regard the abnormal union of fingers and toes by
skin-folds as a sport or spontaneous variation, and not
atavistic ; and this opinion is strengthened by the cir-
cumstance that, as we have just seen, a patagium may
form between the thigh and leg, a situation where such
a web cannot by any possible means be classed among
atavistic phenomena.

In order to show to what absurd conclusions loose
modes of reasonings lead, reference may be made to
the abnormality of the stomach known as congenital
or hour-glass contraction. In such cases the human
stomach is divided by a constricted or narrow portion
into two compartments (fig. 81), and this has induced
a few observers to regard this as a reversion to the
complex stomach of the ruminant, especially the two-
chambered stomach characteristic of the genus Cervulus.

There is, however, the following difficulty in accepting
this explanation. All such deformed stomachs have
been observed in adults ; no one has ever found a
double-chambered stomach in a child. Again, in many
of the specimens evidence of disease, such as ulcers,
old and recent, or scars have been detected in the

A TA VI SM OR RE VERSION. 147

neighbourhood of the contracted portion. During its
development the human stomach never presents itself
otherwise than as a single-chambered viscus. This is
in itself an important fact, for if in the embryo the
stomach presented a median contracted portion it could
easily be conceived that in some cases the contraction
would persist. It must also be borne in mind that
the ruminant's stomach is highly specialized ; there-

Fig. 81. — A Human Stomach with hour-glass contraction.

fore, as reversion consists in the reappearance of a lost
character we shall have to show that mammals closely
allied to man possess such a stomach : this is not the
case. Thus embryology and comparative anatomy are
eloquent in denying the reversionary nature of hour-
glass contraction of the human stomach.

Having attempted to indicate the general grounds
upon which suspected atavistic phenomena, in so far
as malformations are concerned, should be analyzed,
it will perhaps be interesting to discuss reversionary
phenomena as they manifest themselves in relation
with a particular organ or group of organs ; it will in
this way be possible to display, in a striking manner,
the large amount of misconception which prevails in
regard to atavism in general. This will serve to show
that reversion of organs or tissues, and the assumption
of function by suppressed parts, is not so frequent as

1 48 E VOL UTION AND DISEASE.

many suppose, especially when each suspected case is
submitted to rigid analysis. I shall, however, first of
all consider atavism in relation to secondary sexual
characters, and then proceed to the study of super-
numerary digits and limbs, and supernumerary mammae
and nipples. It will be to the reader's advantage
before perusing those sections to study carefully
the remarks made on dichotomy, for of all examples
mistaken for atavism, dichotomy claims by far the
greatest number.

Atavism in relation to Secondary Sexual characters, —
As Darwin points out, two distinct elements are in-
cluded under the term " inheritance " — the transmission
and the development of characters. The distinction is
so important, especially in its bearing on the question
of atavism, that the two conditions will be illustrated
by concrete examples.

In most species of the deer tribe it is the rule for the
male alone to possess antlers, yet it is a well attested
circumstance that under certain diseased conditions of
the sexual organs, especially atrophy or degeneration
of the ovaries, rudimentary horns which are never shed
appear in the female.

This shows us that the female is in possession
of secondary sexual organs in virtue of transmission,
yet they remain latent as a rule, and only become
developed under extraordinary circumstances. The
same holds good for those cases of hens who for years
lay eggs, yet eventually cease to do so, put on one side
the plumage proper to their sex, and adopt more or less
completely that of the cock.

A TA VI SM OR RE VERSION. 1 49

Hunter1 recorded some examples of this ; the following
is one of them : —

" Lady Tynte had a favourite pyed pea-hen which had
produced chickens eight several times. Having moulted
when about eleven years old, the lady and family were
astonished by her displaying the feathers peculiar to the
other sex, and appeared like a pyed peacock. In this
process the tail, which became like that of a cock, first
made its appearance after moulting ; and in the following
year, having moulted again, produced similar feathers.
In the third year she did the same ; and, in addition,
had spurs resembling those of a cock. She never bred
after this change in her plumage, and died in the
following winter during the hard frost, in the year
1775-6."

The change here described, and now seen in a
large number of birds — indeed, I know of no game-
keeper of experience who has not seen such speci-
mens— has been shown conclusively to be associated
with atrophy or non-development of the ovary.
The best marked case that has come under my
observation occurred in a hen golden pheasant. I
watched the bird for two years. She presented the
resplendent dress of the cock, but her plumage
was not quite so brilliant, had no spurs, and the iris
was not encircled by the ring of white so conspicuous
in the male. Coincident with the change of plumage
she ceased to lay eggs. After this transformation she
lived happily with her mate for two years, and in spite

1 An Account of an Extraordinary Hen Pheasant (" Observation
on the Animal (Economy ").

iSo E VOL UTION AND DISEASE.

of the deceit of feathers I have seen a pheasant in the
next cage making her overtures. Two years later (the
spring of 1885) she would not yield to the solicitations
of her mate, and he savagely killed her. The ovary
was of the size of a split pea. A drawing of this bird,
with the assumed plumage, is given as a frontispiece,
and the hen golden pheasant in the proper sober
plumage is sketched for comparison.

These specimens are of interest in many ways, but they
are especially instructive in showing how limited our
knowledge is concerning latent characters ; although
this comes out in a clear manner in the case of the
golden pheasant, it is even more forcibly illustrated in
an example mentioned by Darwin. It is to this effect : —
" Mr. Hewitt possessed an excellent Sebright gold-laced
hen bantam which, as she grew old, became diseased in
her ovaria, and assumed male characters. In this breed the
males resemble the females in all respects except in their
combs, wattles, spurs, and instincts, hence it might have
been expected that the diseased hen would have assumed
only those masculine characters which are proper to the
breed, but she acquired in addition well arched tail, sickle
feathers quite a foot long, saddle feathers on the loins, and
hackles on the neck — ornaments which,'' as Mr. Hewitt
remarks, " would be held abominable to her breed."
The Sebright bantam is known to have originated about
the year 1800 from a cross between a common bantam
and a Polish fowl, re-crossed by a hen-tailed bantam,
and carefully selected ; hence there can hardly be any
doubt that the sickle feathers and hackles which ap-
peared in the old hen were derived from the Polish fowl or

A TA VISM OR RE VERSION. 1 5 1

common bantam, and there we see that not only certain
masculine characters proper to the Sebright bantam,
but other masculine characters derived from the first
progenitors of the breed removed by a period of above
sixty years were lying latent in this hen-bird ready to
be evolved as soon as her ovaria became diseased.'*
(Animals and Plants under Domestication.)

These examples open up the subject of secondary
sexual characters. The question of primitive herma-
phroditism has been already discussed in a preceding
chapter, and an attempt was made to show that, for a
brief period at least, the embryo presents sexual parts
common to the male and female, so that for a time it is
absolutely impossible to determine the sex. What is
true of the embryo applies equally to animals normally
hermaphrodite : no distinctive characters are displayed
externally. Also in cases of hermaphroditism occurring
in animals normally bisexual, the secondary sexual
characters are intermediate to those of the functional
male and female. It is therefore fairly evident that the
female, though she differs from the male in the non-
development of secondary sexual characters, yet pos-
sesses them in a latent condition ; or, to put the matter
briefly, they are transmitted, but not developed.

We must now inquire how it is, that if the female
possesses all the secondary sexual characters of the male
in a latent manner, they arc prevented manifesting
themselves.

When differentiation of sex occurs in animals pre-
viously hermaphrodite, it involves either the loss of certain
characters on the part of the female, or the acquisition

iS2 E VOL UTION AND DISEASE.

of new characters by the male, or at any rate increased
functional importance of certain organs possessed, when
in the state of hermaphroditism, by all the forms. By
natural selection the male would acquire (or, if already
in his possession in a functional condition, would
gradually develop) means for seizing and retaining
the female, such as the claspers of sharks, the callous
pads of frogs, &c. Paternal duty requires the male to
protect the young and defend the females from harm ;
hence horns, teeth (as in the musk-ox), spurs, tusks, &c,
become more developed in him.

The duties of the female require her not only to furnish
the material out of which the young are to be formed,
but in many cases she is required to provide them with
nutrition long after they enter the world. The material
which the female thus provides is of the very kind neces-
sary, in many instances, to build up such structures as
horns, tusks, teeth, and the like. Further, this material
is required by the female at the corresponding period of
life in which these structures become developed in the
male, viz., on the advent of puberty. We may state with
certainty, that a distinct correlation exists between the
generative organs of the female and the development of
the secondary sexual male characters. The more de-
veloped and functional the female reproductive organs
become, the less likely is she to manifest the secondary
characters of the male. It may be argued, that in some
cases the female simulates the male, as in the few
examples of female deer possessing horns. Quite true ;
but so long as the female is engaged in the duties of
reproduction, these secondary characters are never de-

ATA VISM OR RE VERSION. 153

veloped to the same extent as in the functional male.
It must also be borne in mind, that in cases where sterile
females, or those which have ceased to bear young, put
on external male characters, they rarely attain such pro-
portions or beauty as in the male ; for in the males the
general excitement produced by sexual passion has a
most powerful stimulant effect upon the growth and
development of these structures, which is wanting in
the female. So that in her occasional attempts to
emulate the male she succeeds to a certain degree, but
rarely, if ever, attains to so good a condition.

Hunter has recorded some experiments which have a
bearing on this matter : —

" I wished also to ascertain if the parts peculiar to the
male could grow on the female, and if the parts of a
female, on the contrary, would grow on a male.

Although I had formerly transplanted the testicles
of a cock into the abdomen of a hen, and they had some-
times taken root there, but not frequently, and then had
never come to perfection, yet the experiment could not,
from this cause, answer fully the intended purpose ; there
is, I believe, a natural reason to believe it could not, and
the experiment was therefore disregarded. I took the
spur from the leg of a young cock, and placed it in the
situation of the spur in the leg of a hen-chicken ; it took
root, the chicken grew to a hen, but at first no spur grew,
while the spur that was left on the other leg of the cock
grew as usual. This experiment I have repeated several
times in the same manner, with the same effects, which
led me to conceive that the spur of a cock would not
grow upon a hen, and that they were, therefore, to be

154 E VOL UTION AND DISEASE.

considered as distinct animals, having very distinct
powers. In order to ascertain this, I took the spurs of
hen-chickens and placed them on the legs of young
cocks. I found that those which took root grew nearly
as fast, and to as large a size as the natural spur on the
other leg, which appeared to be a contradiction to my
other experiments. Upon another examination of my
hens, however, I found that the spurs had grown consider-
ably, although they had taken several years to do it ;
for I found that the same quantity of growth in the spur
of a cock, while on the cock, during one year, was as
much as that of the cock's spur on the hen in the course
of three or four years, or as three or four to one ; whereas
the growth of the hen's spur on the cock was to that of
the proper spur of the hen as two to one."

When a female animal belonging to a dimorphic
species assumes male characters, it is truly an example
of atavism, or development of transmitted characters
normally latent.

Before leaving this matter it will be useful to indicate
to some extent our knowledge as to the frequency of
the assumption of male characters by the females of
dimorphic forms. In birds there can be no question
that very many specimens have been seen and carefully
studied, but in the case of female deer putting up antlers
the case is very different. On making inquiries of
persons likely to have seen such specimens I find it
extremely difficult to obtain authentic information, and
many of the statements in circulation on this matter
have very shallow foundations. One of the most acces-
sible specimens is preserved in the museum of the Royal

ATAVISM OR REVERSION. 155

College of Surgeons, London. It is the skull of a doe
roedeer; it was shot by the Earl of Egremont, near
Petworth, Sussex, in 18 10, and presented by him to the
museum. The antlers, as shown in fig. 82, were
evidently covered with "velvet." This specimen is
described by Mr. E. R. Alston.1 One is a simple
curved snag, nearly eight centimetres in length, with
a well-developed burr; the other is a mushroom-
shaped burr without any beam. Lord Egremont, in

Fig. 82. — A female Roedeer {Capreolus caprcua),
with antlers. (After Alston.)

a letter, expressly stated that the deer was " a very
old and uncommonly large female with two young
ones in her." Alston states that in Germany, where
the roedeer is more plentiful than in this country,
many does with antlers have been recorded, no fewer
than forty instances being known to Dr. Altum. Most
of these were barren animals, and the antlers were
always of a more or less abortive character, except one

1 "Proc. Zool. Soc." 1879.

156 E VOL UTION AND DISEASE,

case in which the normal male form was well reproduced ;
but several were fertile and either with young when
killed or had recently given birth to fawns. Such
abnormal antlers appear to be always persistent and
permanently covered with velvet.

Outside the genus Capreolus (excepting, of course, the
genus Rangifer, the females of which are normally fur-

Fig. 83. — Head of a female Moose (Alces machlis), with antlers.

nished with antlers) it is rare to find antlered females.
In fig. 83 a drawing of the head of a female moose {Alces
machlis) is given with velvet-covered horns ; for the details
of this specimen I am indebted to Mr. H. E. Dresser : —
" The female moose was shot by an Indian, on the Upper
Musquash, and taken into Indian Town, St. John's, N.B.,
where it was sold to a butcher ; I was then in charge of

A TA VISM OR RE VERSION. 157

the Musquash estate, and hearing that a cow moose
with horns had been shot I at once drove over to St.
John's, saw the beast which was then unskinned and of
course I could not see that it was a cow, so I bought
the head for a trifle, skinned and stripped it. This was
in November, 1859."

We have authentic evidence of the occurrence of antlers
in female deer — in roedeer {Capreolus caprced), Virginian
deer {Cariacus Virginiamcm)y moose (Alces machlis), red
deer {Cervus elephas). The occurrence of antlered
females in other genera of deer is extremely rare.

The existence of antlers in female deer is not, as far
as I can ascertain, necessarily associated with ovarian
disease or sterility. Again, hen birds which assume
cock plumage regularly moult ; female deer with antlers
do not shed them as is the case with the males which they
mimic.

It may be useful to add a list of birds in which the
hen has been seen in male plumage : pheasants (com-
mon, golden, and silver), the common hen, pea-hen,
partridge, bustard, American pelican, wild and domestic
duck, cuckoo, cotinga or bell-bird, chaffinch, bunting.

CHAPTER VII.

ATAVISM {continued).

Supernumerary Digits \ Limbs , and Mammary Glands. —
Nothing illustrates so forcibly the necessity of critically
examining suspected cases of atavism as those abnor-
malities collectively known as Polydactyly. At the
outset it may be stated, contrary to the prevailing
opinion, that supernumerary digits are very rarely
atavistic.

The various examples of extra fingers, toes, arms, and
legs, described in the chapter on Dichotomy, serve to
show that if all supernumerary parts are to be regarded
as reversions we must find vertebrates provided with an
unlimited number of toes, double hands and feet, and
more than two pairs of limbs.

No vertebrate animals other than fish and the Ichtliyo-
saurii, possess on each limb more than five digits,
therefore when the number of toes or fingers exceed on
each limb this typical number, it must if we, with
Darwin, regard the accessory digit as atavistic, be a
reversion to an Ichthosaurian or a fish form. The
distance is far too great, and in doing so we violate the
rule that atavistic parts do not belong to forms palae-
ontologically remote or systematically far distant.

ATAVISM. 159

Among reptiles, birds, and mammals, our knowledge at
present only warrants us in regarding extra digits as
reversions when they occur in non-pentadactyle animals.
For instance, the spider monkeys have no thumbs ; a
careful dissection of the hand, however, will reveal, in
connection with the trapezium, a band of fibrous tissue
containing nodules of hyaline cartilage, representing the
missing thumb. On one occasion I was surprised to
find in an adult specimen of Ateles panniscus a small
thumb projecting above the web of the finger and
furnished with a nail. This condition is, I understand
from competent zoologists, not infrequent, and as it is
an example of the attainment of a functional condition
by an organ usually suppressed in this species, it comes
within the definition of atavism. Further, those mon-
keys, its closest allies, marmosets, Mycetes, and Callithrixy
possess functional thumbs.

All cases of extra digits in non-pentadactyle mammals
are not necessarily atavistic : let us consider this in
reference to the horse. That the modern horse walks
upon the enlarged third digit, and has a vestigial meta-
carpal or metatarsal on each side of it, is accepted by
morphologists. The comparatively recent ancestors of
the horse had three functional digits. Hensel's investi-
gations on Hipparion mediterraneam indicate the pro-
bability that the inner (second) digit was the last to abort.
Horses are occasionally seen with two functional digits
instead of one, and it is a noteworthy circumstance that
in the majority of cases it is the inner digit which
reappears, that is, the one which we should theoretically
expect to reappear most frequently. Such cases are

i6o

EVOLUTION AND DISEASE.

truly atavistic, and the leading features in the argument
are visually represented in the drawings (fig. 84).

The museum of the Ecole Veterinaire de Lyons con-
tains a very remarkable specimen. It is the skeleton of
an equine manus with two functional digits (fig. 85),
on each side of the metacarpal bone a vestigial
metacarpal exists as in the normal manus. In the
specimen last considered we noted that the super-
numerary digit was articulated with the distal end of
the lateral metacarpal (fig. 85, B). In the Lyons speci-

B

Fig. 84.— A, the manus of Hipparion ; B, the
manus of a horse (Equus) with the inner digit
functional (atavistic) ; C, the normal manus
of Equus, one toe functional, ii. and iv.
vestigial.

men both digits articulate with the main metacarpal ;
and it is clear from even a cursory examination of the
preparation that we have to deal with an example of
dichotomy, or bifurcation of the terminal segments of
the functional digit.

The museum of the Royal College of Surgeons,
England, contains a skeleton of an equine manus with a
supernumerary digit of this character, but it differs from
the Lyons specimen in that the third digit has dich*

ATAVISM. 161

otomized unequally, and is thus more likely to be
erroneously interpreted from a superficial examination.

Bardeleben has recently attempted most strenuously
to prove that the ancestors of modern mammals were
heptadactyle rather than pentadactyle, and he bases this
opinion on a supposed discovery in the human embryo
of some remnants of the missing digits, on the pre- and
post-axial side of the foot respectively. In addition he
draws attention to the existence in some mammals,
chiefly rodents, of an ossicle in the foot, usually regarded
as a sesamoid. This Bardeleben regards as
vestiges of the missing digits on the inner
side of the manus and pes, and terms
prepollex and prehallux respectively. On
these grounds he would urge that super-
numerary big-toes and thumbs are ata-
vistic.

Even supposing the vestiges of such F^^JjJ
digits to exist as Bardeleben believes, it in the manus
would influence but little the views now to dichotomy!
held regarding the nature of bifid thumbs (Modifiedfrom

, . . - . 11. Cheaveau.)

and big toes, for by an overwhelming amount

of evidence it can be shown that in man they arise by

dichotomy of the digits.

A full study of the question of supernumerary digits
in all its bearings, and the examination of a very large
number of specimens convinces me that an excess in
the number of digits, in pentadactyle mammals, is due to
dichotomy, and can in no sense be regarded as reversion.
Supernumerary digits in animals with fewer digits than
five are, in some few cases, due to atavism, but in many

12

162 EVOLUTION AND DISEASE.

instances dichotomy is responsible for the abnormality,
and it is only after careful dissection by an experienced
anatomist that it is possible to determine to which of
these causes the accessory digit or digits can be ascribed.

Supernumerary Manwice and Nipples, — It is so diffi-
cult to distinguish atavistic phenomena from counter-
feit manifestations that the great need for care in
this direction will be further illustrated by discussing
supernumerary mammae and nipples. Up to the present
time accessory mammae, nipples, or teats, have been
reported on reliable authority in the following situa-
tions : — the anterior wall of the chest, abdomen, axilla,
arm, shoulder, the cheek, buttock, and even in ovarian
dermoid cysts. If we accept unreservedly, that super-
numerary mammae are always atavistic, we force ourselves
into the absurd position of imagining ancestors better
supplied with milk-glands than even Diana of Ephesus ;
or if we protect our opinion by stating it in this way : —
When a mamma occurs in an abnormal situation in man,
but corresponds to the normal situation of the mamma
in some lower animal of our class, it is then atavistic, we
save ourselves much trouble.

In a few cases the guess would be correct, but in most
it would be erroneous, and such loose methods of deter-
mining the nature of abnormal organs will in the long
run lead to much confusion. At the outset we are faced
by the question, What is a mamma? A mamma is a
collection of modified sebaceous glands secreting milk,
and having close relation to the function of reproduction,.
As a rule such glands are furnished with a cutaneous
papilla, known as the nipple, or teat, which is either

ATAVISM. 163

traversed by the excretory ducts of the gland, or forms
a conduit whereby the young are enabled readily to suck
the secretion. Mammary glands without ducts occur
normally only in ornithorhynchus and echidna. Milk-
glands are a distinguishing feature of mammalia, being
unknown below this class.

Mammary glands are, as a rule, regularly and sym-
metrically arranged along the ventral aspect of the trunk,
in two rows. When numerous they extend along the
thorax and abdomen into the inguinal region. The teats
usually correspond to the maximum number of young at
a birth, but to this rule there are many exceptions. The
greatest number known is fourteen pairs. When the
number of functional glands is reduced to two, traces of
the suppressed mammae occur as supernumerary or
accessory nipples, with or without rudimentary glands.

The reduction in number may take place in the
thoracic region, leaving the inguinal set functional as in
the cow, mare, sheep, goat, deer, and antelope. The
inguinal glands may abort, leaving the pectoral set
functional as in man, dugong, sloth, manatee, and
monkeys. In marsupials the milk-glands are inguinal
in position, and protected by the remarkable fold of
skin which forms the pouch or marsupium.

The lemurs offer instructive modifications. The ring-
tailed lemur (L. catta\ the black lemur (L. macaco), and
the mongoose lemur (L. mongoz\ possess one pair of
pectoral mammae, as in man and quadrumana. Co-
querel's mouse lemur (Chirogaleus coquereli), and the
dwarf lemur {Microcebus smithi), possess three pair of
mammary glands : one pair in the pectoral, another in

1 64 EVOLUTION AND DISEASE.

the thoracic, and the third pair in the inguinal region
(fig. 86). It is said, but I have had no opportunity of
verifying the statement, that Tarsins spectrum has an
inguinal and a pectoral pair of milk-glands ; the aye-
aye {Cheiromys) has only an inguinal pair ; lastly, the

Fig. 86. — A Dwarf Lemur (Microcebus smilhi), showing the
arrangement of the mammary glands.

gray, or broad-nosed lemur (Hapalemur griseus), has the
mammary glands situated on its arms.1

The above facts (with the exception of those relating
to Hapalemur) seem to indicate that the lemurs have
descended from ancestors possessing two rows of
mammae. In the dwarf lemurs, the abdominal pair

1 Beddard, "[Proc. Zool. Soc."

ATAVISM. 165

have disappeared, whilst in the ring-tailed, black, and
mongoose lemurs the pectoral pair alone persist.

The persistence of the pectoral pair in these lemurs
may possibly be explained by the curious manner in
which they carry the young. Lemur macaco has usually
one at a birth, and this is carried about entwined around
its mother in the manner represented in fig. 88. I have
watched the young lemur, and find that it rarely leaves
its mother, and it is clear that whilst holding on in this

Fig. 87. — The arm of Hapalemur guseus, showing its
brachial mammae.

way it would be difficult for it to use the inguinal teats,
if any existed, whilst it is within easy access of the
pectoral pair. It seems to me reasonable to suppose
that this habit of carrying the young has led to the
pectoral teats being most used, and their gradual
enlargement from increased use would slowly bring
about the suppression of the little used inguinal set.
Usually the nipples are present in the male, and have
a disposition corresponding to that of the female.

A review of the arrangement of the milk glands in
mammals generally indicates that primitively they were

i66

EVOLUTION AND DISEASE.

arranged in two rows, extending along the ventral
aspect of the trunk in both sexes ; and in situation they
correspond to the course of the deep and superior
epigastric arteries, an extraordinary anastomosis effect-

Fig.

-Lemur macaco and young. (After Sclater.)

ing a free communication between the subclavian
arteries at the anterior part of the thorax and the iliac
system of arteries at the groin. This vascular arrange-
ment is peculiar to mammals, and has direct relation
with the mammary glands.

ATAVISM. 167

When the mammae, or nipples, are increased beyond
the number normal to a given mammal, they are said
to be accessory or supernumerary, and occur in three
forms : — ■

i . As nipples or teats.

2. As mammae, furnished with teats.

3. As nipple-less mammae.

Such mammae, or nipples, may be due to atavism, or
arise by dichotomy of a normal gland, or occur as a
spontaneous variation or " sport."

Notwithstanding the scanty evidence at the disposal
of Darwin when he wrote " The Descent of Man," he
regarded supernumerary mammary glands as reversions,
although he considered the opinion weakened by their
occurrence on the thigh and back. Since then our
knowledge on this subject has increased, and has had
the effect of strengthening Darwin's opinion. We will
first discuss those examples which may be safely
regarded as atavistic. From what has been already
stated regarding the ventral disposition of these glands,
their association with the deep epigastric arteries, and
subsequent suppression in the pectoral or abdominal
regions, it would be necessarily inferred that accessory
mammae, or nipples, would reappear in such situations
most frequently ; this is precisely the case. So fre-
quently are supernumerary nipples present in the human
subject that Dr. Mitchell Bruce in three years saw sixty-
five examples. Among 207 men examined consecu-
tively, nine per cent, had an extra nipple, and of 104
women, four per cent. These observations have induced
other observers to look into the question, with a con-

1 68

EVOLUTION AND DISEASE.

firmatory result ; my own experience as to their
frequency coincides with the above statement. As a
rule only one extra nipple is found, but occasionally
two may be detected. A typical specimen is given in fig.
89 : the nipples are situated exactly in the line of the
deep epigastric arteries.

As accessory glands, or nipples, are so frequent in the
human subject, it occurred to me that they ought

Fig.

-Two supernumerary nipples in a Man. (After Licbtenstern.

theoretically to occur in quadrumana. To this end I
examined systematically all monkeys coming under my
observation, and in a short time secured two well-marked
examples. The first was a female macaque {Macacus
sinicus) (fig. 90). On the left side, about an inch below
the normal gland, an accessory and well-formed nipple
was detected ; in size it equalled the normal teats, and
was associated with glandular tissue and traversed by
ducts. The second monkey came to hand a few months

ATAVISM.

169

later. It was a male Cercopit heats patas : in this case
the nipple occupied a similar position to that in the
macaque ; it was unassociated with glandular tissue.
The parts are preserved in the museum of the Royal
College of Surgeons, England.

Among domesticated mammals, cows present one,

Fig. 90.— A female Patas Monkey (Cercopithecus patas) with a
supernumerary nipple.

sometimes two, and even three accessory teats ; such
extra teats are always situated posteriorly to the normal
ones. In some cases they transmit milk, and cows have
been known to furnish milk from seven teats. An in-
stance has been reported to me, from a reliable source,

1 70 E VOL UTION AND DISEASE.

of a cow which had two rudimentary teats in addition to
the normal four. In consequence of an injury one of
the normal teats became obstructed ; this accident was
compensated, as one of the accessory teats enlarged and
was regularly milked. A female zebu {Bos indicus) at
the Zoological Gardens has an extra well-formed teat on
the right side. Goats and sheep are normally furnished
with two teats, but it is not unusual to find a rudimentary
pair posterior, and occasionally anterior, to the normal
teats.

We may now consider supernumerary mammae occur-
ring in the line of the deep epigastric artery which are
not atavistic. In the human female, and occasionally in
the cow, we find mammary glands with bifid nipples ; in
other cases we find two mammae coalesced, but each has
a separate teat. These conditions are not reversions,
but arise by dichotomy from a single gland germ.
Intermediate stages between bifid nipples and two
separate mammae have been recorded.

Aberrant mammary glands, or those arising as spon-
taneous variations, claim careful consideration, for they
may arise on any cutaneous surface which is rich in
sebaceous glands : as a rule they are furnished with
nipples, but not constantly. Among the rarer positions
for such aberrant mammae are the thigh, shoulder, and
cheek. The oft-quoted case of a functional mamma on
the thigh rests upon the authority of a committee of the
French Academy of Sciences. Barth recently gave an
account of a rudimentary mamma connected with the
skin on the cheek of a maiden aged twenty years, it
was situated immediately in front of the right ear, and

ATAVISM. 171

had an areola of pigmented skin ; when removed,
and the parts examined microscopically, glandular
tissue was found beneath it.

The most frequent situation on the exterior of the
body in which to find aberrant mammae is the arm-pit ;
here they appear as glandular masses, communicating
with the free surface of the skin by means of nipple-
less pores, and in parturient women furnish milk and
colostrum. Champneys has particularly investigated
this form of mammae, and finds that they are of frequent
occurrence. Axillary mammae with nipples have been
recorded by several reliable observers.

The tendency of protected cutaneous surfaces to
become glandular is a matter of great interest, not only
in connection with aberrant mammae, for it serves to
explain the abundance of teats lodged within the pouch
of opossums.

It is a noteworthy fact that cutaneous and mucous
recesses are as a rule richly supplied with glands. Take,
for instance, the large glands besetting the ocular aspect
of the eyelids, the crowd of glands lodged in the arm-
pit, in the external ear-passage which secrete ear-wax,
and in many situations which readily suggest them-
selves to anatomists. As far as I have looked into the
matter, no one has suggested any useful purpose served
by glands in these situations worthy a moment's
reflection.

The consideration of cutaneous recesses leads us to
deal with the remarkable pouch of marsupials, which is
neatly described as the bag of the opossum by Paley in
his " Natural Theology " :— " A false skin under the

172 E VOL UTION AND DISEA SE.

belly of the animal forms a pouch into which the
young litter are received at their birth ; where they
have an easy and constant access to the teats ; in which
they are transported from place to place ; where they
are at liberty to run in and out ; and where they find a
refuge from surprise and danger."

On the wall of this pouch formed by the mother's
belly we find nipples and milk glands ; in kangaroos
and phalangers four teats are usually present ; in opos-
sums they are more numerous. Didelphys virginiana
has six on each side and one in the middle ; the crab-
eating opossum {Didelphys cancrivord) has eleven teats,
the odd one occupying the centre, whilst the remaining
ten are disposed in a circle around it.

Such luxuriance of nipples in so limited a space is
unknown in mammals outside the order marsupialia,
and in them is probably due to the protecting influence
of the pouch, as the following evidence indicates : —

Malkmus has recently drawn attention to some points
of interest in the structure of the walls of the cutaneous
recesses which exist in the inguinal region of sheep, or,
as he terms them, rudimentary marsupia. On examining
the inner aspect of a sheep's flank we find it smeared
with an unctuous material not unlike cerumen, or ear-
wax. In the fold of each groin, close beside the dugs, a
shallow recess is seen (fig. 91) usually containing a
quantity of the same brown, unctuous material which
besmears the flanks, and, as far as my observations
extend, it is more abundant when the ewe has a lamb
by its side. The walls of this recess are almost devoid of
wool, but are beset with a number of large sebaceous

ATAVISM.

173

glands, thus furnishing an excellent example of large
and numerous skin glands occurring in a protected
situation.

It has long been established that milk-glands are
modified sebaceous glands, and the difference in the

Fig. 91. — The inguinal region of a Lamb, showing the cutaneous
recesses in its groin.

nature of the secretion is not very great. The sebaceous
variety furnishes a fatty unctuous substance ; mamma?,
a natural emulsion known as milk, consisting of oil
globules suspended in fluid, containing various salts and
a proteid body, casein, with a small but variable propor-
tion of albumen.

174

EVOLUTION AND DISEASE.

As all cutaneous recesses exhibit a marked tendency
to develop glands, the large size and abundance of the
mammary glands within the marsupium of opossums
receives an explanation.

A comparison of the inguinal pouches in the sheep

FlG. 92. — The marsupium of a Phalanger (Phalangista orientalis)
opened to show the number of teats.

with the marsupium of the phalangers, &c, is instructive,
as it indicates in a significant manner the mode by which
a specialized bag, or marsupium, may have originated,
besides throwing light on the number of teats it con-
tains.

ATAVISM 175

By far the most remarkable situation in which milk-
glands arise, is in the interior of some peculiar skin-con-
taining tumours of the ovary. I have traced every stage
from a sebaceous gland to a nippled mamma, furnishing
milk, in such tumours — a situation in which it would
puzzle even Paley to imagine a useful purpose.

These facts indicate clearly enough that a mamma
may make its appearance in any situation of the body
if the favouring conditions exist — Le.% a cutaneous
recess abundantly supplied with sebaceous glands, and
preferably on the ventral or protected aspect of the
body ; warmth and moisture appearing to favour their
development.

The careful consideration of such cases clearly shows
that to attribute such aberrant mammae to atavism
is inconsistent with sound reasoning : it is, however,
obviously erroneous to regard all forms of supernumerary
mammae and nipples as " sports," but I am firmly of
opinion that only those occurring in the line of the
deep epigastric arteries, excepting those clearly due to
dichotomy, can be with any justness considered as re-
versionary. In the section on tumours we shall have to
return to this subject, especially in reference to cancer.

CHAPTER VIII.

THE TRANSMISSION OF MALFORMATIONS AND ACQUIRED

DEFECTS.

IN this chapter it is not proposed to discuss in all its
bearings the question of heredity, or even to propose a
theory to account for the transmission of defects from
parents to offspring. At the present day such an under-
taking is rendered unnecessary, for all thinking persons
are unanimous in believing that malformations of de-
velopment, as well as the tendency to certain diseases,
are inherited, or, as it is familiarly expressed, " run in
families." If anything, perhaps there is a disposition to
ascribe too much to inheritance instead of submitting
suspected cases to critical analysis. My object on the
present occasion is to criticize a few examples of sup-
posed instances of the transmission of characters the
result of mutilation.

I shall commence with an easily observed part of a
mammal's body — the ear, or pinna. In the chapter on
Environment it was pointed out that good evidence
leads us to believe that it is justifiable to regard the
pinna as an enlarged operculum, modified for acoustic
purposes in terrestrial mammals. Before discussing the
malformations of the external ear we may profitably
consider some facts connected with its anatomy.

TRANSMISSION OF MALFORMA TIONS. 1 7 7

The various projections and depressions of the human
pinna have received at the hands of anatomists dis-
tinguishing names ; with these we must make ourselves
acquainted. In the drawing of the pinna (fig. 93), H
indicates the helix, and the prominence X is the anti-
helix ; below the helix we recognize a projection T known
as the tragus. In elderly persons this is furnished with
some stiff hairs, sometimes of
great length ; opposite the tragus
we note another elevation marked
A in the sketch, this is the anti-
tragus. The tragus and anti-
tragus are separated by a deep
notch, the intertragic fissure.
The lower boundary of this fissue
is formed by the lobule L, which
varies considerably in size in
different individuals. The signifi-
cance of the terms helix and
antihelix is easily understood,
but the meaning of the term
tragus, from the Greek, signify-
ing a goat, is not so evident.
Hyrtl suggests the following ex-
planation : — In elderly persons the tragus not infre-
quently has some stiff hairs growing from it, known as
goat's hair. The presence of these hairs was formerly
regarded as indicating a sensual individual. It is pro-
bable that such ears, when the hair on the tragus was
abundant, caused them to resemble the sharp-pointed ears
of the goat-footed satyrs (aegipans). In older works

13

Fig. 93. — The human pinna ;
H, helix ; X, antihelix ; T,
tragus ; A, antitragus ; L,
lobule.

i78

EVOLUTION AND DISEASE.

on human anatomy the tragus is referred to as hircus
or tragus (Latin /iirats = goat), on account of the hairs

growing from it.

It is unnecessary for me to enter into the question of
the vestigial nature of man's pinna ; this has been again
and again pointed out and admits of no doubt. Like

Fig. 94. — A malformed auricle with a sinus in the helix. (After

Paget.)

vestigial organs in general it is very variable. The pinna
may be absent, is often malformed, presents accessory
parts and not unfrequently is occupied by some con-
genital fistulae and recesses.

It is by no means uncommon to find in the helix, at the
spot marked 4 in fig. 93, a small sinus, or recess, capable

TRANSMISSION OF MA LFORMA TIONS. 1 7 9

of admitting a probe sometimes to the extent of an inch,
or even more. Such recesses are known as congenital
auricular sinuses ; they are furnished with glands which
secrete an unctuous material resembling ear-wax, often
troublesome to the individual on account of its amount
These sinuses are usually associated with malformed
ears ; for a typical example see fig. 94. They are here-
ditary, and often appear in several members of a family.
Congenital fistulae occur in the lobule, but they are very
rare, only two or three examples have been placed on
record. One excellent specimen has come under my
observation. In this case the fistula was so complete
that a few days after birth an earring was suspended in
it. Only one pinna was affected. The situation of the
fistula in this case is indicated in the lobule of the pinna,
represented in fig. 93.

If any one possesses the patience to examine a large
number of ears he will find that it is by no means un-
common to see a shallow furrow separating the lobule
from the antitragus, and terminating occasionally in a
slightly marked notch on the posterior rim of the auricle.
The direction of this furrow varies greatly; sometimes it
is nearly vertical, at other times oblique, and in rarer
instances is so pronounced that it seems to divide the
lobule in two parts. Among other variations exhibited
by the pinna is the presence of a supernumerary tragus,
which may or may not be associated with a well-shapen
auricle. Two common forms are shown in the ac-
companying drawings (fig 95). These so-called super-
numerary auricles are probably due to dichotomy of
the tubercle which gives rise to the tragus.

i8o

EVOLUTION AND DISEASE.

In order to appreciate fully the bearing of these facts
and some others which will be mentioned, it will be
necessary to take into consideration the chief points
connected with the development of the pinna as an
illustration of the care requisite in interpreting variations
and abnormalities from the evolutionary point of view.
The details of the development of the human pinna have
been carefully described by Professor His. At the end of
the first month of embryonic life, the first branchial cleft is
surrounded by six rounded, slightly prominent tubercles,

Fig. 95. — Human Ears with so-called supernumerary auricles.

numbered I to VI in fig. 96, and it is by the coalescence of
these six tubercles that the pinna is formed. The details
of their fusion are briefly these : — tubercles I and V
unite across the fissure and form tragus and antitragus,
the gap, or notch, between them is represented in the
adult as the fissura intertragicum ; tubercle VI unites
with these to form the lobule; tubercle II forms the
helix, whilst III lengthens out and forms the conchal
rim and the tail, or cauda helicis, whilst the tubercle
marked IV becomes the antihelix.

These facts explain readily enough the mode of origin

TRANSMISSION OF MALFORMA TIONS. 1 8 1

of the various congenital defects of the pinna. Thus a
fistula in the helix results from incomplete coalescence
of the tubercles II and III, whilst a fistula in the lobule
represents a gap between the tubercles I, V, and VI. The
furrow in the lobule is a fault where the lobule comes
into relation with the tail of the helix. Should any of

Fig. 96. — A, the six tubercles surrounding the first cleft ; B, an
intermediate stage in the coalescence of the tubercles. C, a
still later stage. (After His.)

the tubercles fuse superficially and leave an intermediate
space, this may subsequently dilate and form what is
known as a dermoid cyst — that is, a tumour with a central
cavity lined with skin resembling that covering the
pinna.

These facts are of some importance because, with an

182 E VOLUTION AND DISEASE.

imperfect knowledge of the mode of origin of the pinna,
these conditions might admit of a somewhat different
interpretation. For example, the congenital hole in the
lobule could on superficial examination be interpreted
as the result of piercing the lobe of the ear for the
suspension of ornaments, but the details of the develop-
ment of the pinna offer a much more satisfactory
explanation of the phenomenon. A careful analysis of
the facts at our disposal strongly points to the conclusion
that defects due to mutilations are not inherited.
Recently Dr. Emil Schmidt, of Leipzig, has carefully
argued a case in which he thinks an acquired defect in
connection with the pinna was inherited ; the facts are
briefly these : — In the left ear of a child he noticed a
peculiar congenital fault, consisting of a cleft in the
lobule (fig. 97). The mother also had a similar, defect
in the lobule of the left ear ; in the case of the mother
the cleft was due to an injury. When eight years old,
whilst playing, the earring was torn through the lobe.
The edges of the wound did not completely unite, and
the lobe was subsequently pierced to restore symmetry.
Thirteen years afterwards she married, and gave birth
between 1860-73 to eight children. The second child — a
boy — exhibited the peculiar defect described above : the
remaining children possess pinnae with normal lobules.
A comparison of the ear of mother and son shows that
in the son's ear the cleft is situated more posteriorly and
higher than in that of the mother.

Dr. Schmidt,who is well acquainted with the details of
the mode of formation of the pinna, discusses it at some
length in connection with this case with very great care,

TRANSMISSION OF MALFORMA TIONS. 1 83

and in the end states that he is inclined to regard this
as an example of the inheritance of acquired defect, for
the following reasons : — The limits between the lobule
and the tail of the helix are never so sharply defined as
in this case. The cleft is situated too posteriorly to
correspond to the line of fusion of the fifth and sixth
tubercles, and the tubercle for the antitragus is, in the
embryo, some distance from the external margin of the
ear.

It is unnecessary to discuss the reasons advanced by

A B

FlG, 97.— A, pinna of Mother showing the rent in the lobule
where the earring^was torn away ; B, pinna of Son with
congenital defect. (After Schmidt.)

Schmidt in support of this view, for they are nullified by
some observations made on this case by Professor His,
in a subsequent number of the Correspondenz-Blatt fur
Anthropologic (March, 1889), to the effect that the
defect in the ear of the son not only differs from that
in the mother in its general character, but occupies a
different position in the lobule, as is easily seen in com-
paring the two pinnae.

1 84 E VOL UTION AND DISEASE.

The slit, marked F in the sketch, in the mother's pinna
was made subsequent to the accident, so as to enable
her to wear an ear ornament.

Reference to the drawings in fig. 96, illustrating the
development of the pinna, would show that the defect in
the son may be reasonably attributed to feeble develop-
ment and incomplete union of the tubercles for the
lobule and antitragus.

The facts relative to malformations of the pinna have
been considered in detail, for they serve to indicate the
extreme care it is necessary to exercise before we regard
a defect in the offspring as due to the transmission of an
acquired defect in the parent. In Schmidt's example,
the conclusion at which he arrived, independently of our
knowledge of the mode by which the pinna is developed,
is clearly not in accord with the facts of the case, but in
the example where the child was born with a perforation
in the lobule, without a knowledge of the embryology of
the pinna, it would have seemed unreasonable to doubt
but that we had to deal with the inheritance of an
acquired defect.

The facts considered in relation to acquired defects of
the pinna are of importance in connection with the
subject of the transmission of mutilations. It appears
that, immediately on the announcement of the evolution
theory, those who were antagonistic urged that the
practice of docking the tails of such animals as horses
and sheep for so many generations should have produced
animals with short tails. The Hebrew custom of cir-
cumcision is as necessary now as in the time of Moses.
To these may be added the habit of piercing the lobe of

TRANSMISSION OF MAIFORMA TIONS. 185

the ear, practised early in life, and in most nations of
the world, and even in tribes the most barbaric, yet
there is not the slightest evidence that the result of such
mutilations are transmitted, and the ear is of all parts of
the body the most easily and frequently observed. If
such injuries — for so we must regard them — were trans-
mitted, we ought to find the offspring of wild birds in
confinement, which have been pinioned, lack the bastard
wing ; such is not the case, nor are they in any way
malformed in consequence of the mutilation to which the
parents were subjected. It is inconsistent with the
fundamental principles of evolution that the effects of
removal or injury to parts of the body should be trans-
mitted to the offspring. It may perhaps be interesting
to briefly mention two instances which, in the absence
of more accurate information, have been interpreted as
due to inheritance of acquired conditions.

The first instance concerns the tail feathers of
Momotus ; this bird has the singular habit of picking
away the web of the central feathers of its tail until
they assume a spatulate condition. In consequence of
the constant stripping of the web the feathers, when
they first appear, are naturally narrower in the places
where they are habitually denuded. The habit is
practised by both sexes alike. The matter has been
carefully investigated by Mr. Salvin, who is satisfied
that this plucking process is practised by the motmots.

These observations are interesting, for it is thought
probable that the spatulate or racket-shaped tails in
some other birds may have been brought about in some
such way, so as to become a permanent condition. All

i86

EVOLUTION AND DISEASE.

degrees may be met with, from a broad web to others in
which the rachis of the tail feathers is clean from the first.

Fig. 98.— The tail of the so-called Tailless Trout of Islay.

Fig. 99. — Tail of a normal Trout for comparison. (Aft. r
Traquair.)

The second case is furnished by the so-called tailless
trout of Islay. Professor Traquair has published an

TRANSMISSION OF MAIFORMATIONS. 187

interesting account of the malformation of the tail in
these fish. The most salient peculiarity of these Loch-
namaorachan trout is that the rays of the caudal fin are
abnormally shortened, coarse at the extremities, and
deficient as to the amount of dichotomization and
number of the transverse joints ; besides which, they
also show a tendency to coalesce at their terminations.
By the convergence downwards of the upper long rays,
and upwards of the lower ones, the fin assumes a
rounded form instead of presenting the usual broad fan-
shaped aspect. The abnormal condition of the ex-
tremities of the rays may affect other fins besides the
caudal (fig. 98).

The lake in question is about 1,000 feet above the
level of the sea. It is about an acre in extent, and so
shallow that a man can wade through it ; the bottom is
of quartz rock. Several other lochs near contain trout,
but none are " tailless." So constant is this abnormality
in trout taken from the lake in question, that one keen
fisher, with thirty years' experience of this loch, has never
taken any but docked ones.

It is quite possible, indeed probable, that a more
perfect knowledge of the mode of development of the
spatulate or racket-shaped feathers in the motmots,
and of the tails in the Lochnamaorachan trout would
put a new complexion on the matter. It may be con-
fidently stated that at present there is no satisfactory
case known of the transmission of a defect, the result of
mutilation.

Inherited Malformations. — There can be no reasonable
doubt that defects arising in the course of development

188 E VOL UTION AND DISEASE.

of an individual are in many instances transmitted to
the offspring. Malformations, as such defects are called,
arising in this manner are usually classed as arrests of
development, and as it is clearly established that the
embryological history of a complex individual may be
regarded as an abbreviated history of its evolution, it
necessarily follows that, should the development of a
part be arrested at any particular stage, we should
expect to find, in some less specialized mammal, this
stage represented as a permanent condition. For
instance, children are often born with club feet ; the
commonest congenital form is that which in the sole of
the foot looks inwards and upwards, and the heel is
slightly raised (talipes equino-varus). In the child
before it is born the feet are for several months in this
position, and gradually pass into that assumed normally
in the adult. Not infrequently the foot fails to assume
a position at right angles to the leg, and malformation
is the result. Now it is very instructive to remember
that the orang's foot is in the position typical of talipes
equino-varus, and this is not limited merely to the
position of the foot, but extends also to the disposition
of the articular surfaces on the ankle-bone.

It is far from my intention to enter in a detailed
manner into all forms of malformation which may be
transmitted ; that such characters are inherited is in-
disputable, but it may be useful to describe an instance
in which it has been possible to produce a permanent
variety in which the existence of a malformation is the
distinguishing feature. This is the more important
because as a rule defects of this class appear sporadically

TRANSMISSION OF MAIFORMA TIONS. 1 89

in a family, but do not reappear so constantly to become
as it were, a matter of entail. This may be in part ex-
plained, perhaps, by the fact that attempts are not made
to propagate the malformation, as is done in domesti-
cated animals.

The frequent and familiar malformation known as
hare-lip and cleft palate is not by any means confined to
the human species, but occurs in horses, calves, sheep,
dogs, and even lions. In the human subject it has been

Fig. 100. — The nose and lip of a
Hare, showing the cleft.

Fig. ioi. — The nose of a
Dog, showing the median
furrow.

known to affect several members of the same family, and
to occur in the offspring of the affected members. The
defect takes the name hare-lip because the hare, in
common with a few other mammals, exhibits a median
cleft in its upper lip. This cleft in the hare is an exagge-
ration of the furrow which is present on the upper lip 01
many mammals, and extends on to the nose (figs. 100 and
101). In children affected with hare-lip the cleft is rarely
situated in the middle line, but to one or other side ;

190

EVOLUTION AND DISEASE.

sometimes the lip is cleft on each side, the median piece
standing forward from the nose like a peninsula. An
inquiry into specimens of hare-lip occurring in mammals
generally, discloses the fact that in some the cleft may
be lateral, as in man, but in others it is median in
position. The following facts are interesting in this
direction : —

In the summer of 1886, whilst staying in Paris with
Mr. H. W. Freeman, of Bath, we procured a pug-bitch

Fig. 102. — Cleft-lip and nose in a Dog.

with a peculiar cleft in its nose. At first we thought
that the case was an example of hare-lip, but on making
inquiry we found it to be a distinguishing feature of
this breed of dogs and that it conferred upon them a
high money value. The bitch was brought to Bath, and
Mr. Freeman was successful in crossing her with a
Skye-terrier and obtained some pups. Half the litter
had normal noses like the dog, the remainder had
split noses and lips like the mother. The pups from

TFANSMISSIOA7 OF MALFORMA TIONS. i 9 1

this litter have since had young with cleft noses, and
the malformation seems to be well established. The
deformity consists of a median vertical split in the
upper lip, extending some distance between the nostrils
and involving the hard palate (fig. 102). The ex-
tent to which the bony portion of the palate is in-

Fig. 103. — The hard palate from a Dog with hare-lip, showing
the extent to which the hard palate is involved.

volved may be seen in fig. 103. Apart from its special
interest the malformation is of value as showing that
defects, arising from arrested growth during embryonic
life, are transmitted, and this is clearly the case not only
in connection with the lips, but with the pinna, eye, eye-
lids, and many other parts of the body.

It now becomes necessary to detail briefly the leading

192

EVOLUTION AND DISEASE.

facts connected with the development of the mouth in
order to show that we have here to deal with an arrest
of development, as well as to show the reason why the
cleft in the dog's nose is median, whereas in man and
several other mammals, in which the deformity has
been recognized, the split is, as a rule, lateral. Fortu-
nately the admirable researches of Professor His
remove much of the difficulty which would otherwise

have existed, and the account of
this embryologist will be closely
followed.

The mouth of the human em-
bryo at the fifth week of intra-
uterine life is represented by an
opening from which five fissures
radiate. The upper pair are the
orbito-nasal, the two lower form
the mouth, whilst the median
fissure separates the lower jaws.
As the median process develops

Fig. 104. — Human embryo of _ r , , ,

the fifth week showing the to form the nose, two rounded
parts out of which the lips, prominences make their appear-

mouth, and nose are formed.

ance at each angle. These will
be referred to as the globular processes (fig. 104) ; these
processes furnish the ala^ of the nose and the inter-
maxillae ; later they are joined by the lateral pieces to
complete the lip.

In some mammals, especially rodents, the globular
processes fuse with the lateral pieces but do not fuse
with each other and remain permanently separated, thus
explaining the occurrence of a persistent median cleft in

TRANSMISSION OF MALFORMA TIONS. 193

the hare. Thus the cleft nose in the pug (fig. 101) is due
to the non-union of the globular processes. It is a fact
of some interest that in the embryos of some kanga-
roos (Macropus) the fissures in the lips persist longer
than in any other mammals I have yet had an oppor-
tunity of examining.

These facts concerning the transmissibility of defects
in the dog's nose tend to show that it is probable, if it
were possible to practise selective breeding in the human
species as among dogs, a race of men with hare-lips and
cleft-palates could be produced, and this view is further
strengthened by the knowledge that in some districts
where the inhabitants are not very numerous a sort of
indirect selection goes on with the effect of perpetuating
deformities.

An excellent example of this is given by Professor
Bertram Windle in a paper on " Congenital Malforma-
tions and Heredity." He remarks that a singular
account, given by Devay on the authority of Dr. A.
Potton, seems to show that under favourable circum-
stances, continued for a sufficient length of time, a
separate breed of men, possessed of some malformation,
might be produced, whilst it also shows that the insta-
bility of such a condition, which must persist for some
time, leads to its being easily stamped out by the
introduction of fresh and untainted blood.

In the department of Isere not far from Cote-Saint*
Andre and Rives, there is a small isolated village called
Izeaux, lost, so to speak, in the midst of a plain, called
the plain of Bievre, which, if not completely unculti-
vated, was at least very barren. The roads were difficult,

14

1 94 £ VOL UTION AND DISEASE.

if not impracticable. The inhabitants, thus cut off from
the outside world, intermarried very freely. At the end
of the last century sexdigitism, both of the hands and
feet, suddenly appeared, and in thirty-five or forty years
almost the entire population was thus affected. When,
in 1829 and 1836, says M. Potton, I observed this
strange phenomenon it was present in some subjects
only in a very rudimentary manner ; amongst many it
was only a large tubercle containing a hard osseous body,
and fixed to the side of the thumb, a more or less well-
formed nail terminating it. At this time the influence
of crossing, due to the opening-up of communications,
was making itself felt. In 1847 I had occasion to see
a foreman, originally from this locality, who married and
settled in Lyons. He was affected with the malforma-
tion, but was the father of four normal children. At the
time of writing, he goes on to say, the anomaly has
almost completely disappeared from the district.

This isolation of villages helps to explain the endemic
cretinism of Alpine countries. It has been shown, on
reliable authority, that cretins are most abundant
in villages where intercommunication with towns or
neighbouring villages is difficult, so that the inhabitants
intermarry freely ; since the introduction of railways
freer communications have been opened up, and new
blood introduced in the affected districts ; this has had
the effect of diminishing the number of cretins.

This condition of things is illustrated by the following
example : — There is preserved in the museum of the
Royal College of Surgeons a fish with a large tumour
growing from its side. It was suggested that the pond

transmission of malforma Tiotfs. 1 95

from which this fish was taken should be dragged for

the purpose of ascertaining the existence of other fish

similarly affected. When this was

done several fish of the same

species were taken with tumours

of the same kind growing upon

them.

In this case it is reasonable to
suppose, in the absence of evidence
to the contrary, that the inhabi-
tants of the pond being limited,
the chances of this defect being
transmitted were greatly in-
creased. This view is equally
applicable to the case of the tail-
less trout of Islay.

The curious condition of the
skeleton of the fish Chcetodon,
described by William Bell in the
" Philosophical Transaction," 1 793,
deserves mention in connection
with this subject. He writes: —
" The fish is frequently caught at
Bencoolen and several other parts
on the west coast of Sumatra.
The skeleton is very singular, Fig. 105. -A bone from the fish

Chcetodon with a tumour,
manvof thebones having tumours, shown in section, attached

which in the first fish Mr. Bell saw to [t (Nat' size,)
he supposed to be exostoses arising from disease, but
on dissecting a second found the corresponding bones
had exactly similar tumours, and the fishermen informed

1 96 E VOL UTION AND DISEASE.

him that they were always in this fish ; he therefore
concluded them to be natural to it.

Bones of this kind are not uncommon in osteological
collections. Cuvier explains this by stating that they
are brought home as curiosities by travellers who have
eaten these fish. No one has attempted to explain these
curious bones, which are very characteristic ; at one end
they present a tumour about the size of a chestnut, very
hard, smooth, and as dense as ivory. Articulating with
the tumour by means of a shackle-joint, is one, often
two, small rays. On section the outline of the ray can
be clearly defined running through the midst of the
tumour (fig. 105). The fish on which Bell's original
description was founded is preserved in the museum of
the Royal College of Surgeons, and a drawing of the
specimen is given in " The Transactions of the Patho-
logical Society of London," vol. xxxix.

A consideration of the bones of the Chcetodon is of
interest in connection with what are known as the horned
men of Africa. In 1883 Professor Macalister com-
municated to the Royal Irish Academy a photograph
of one of these men, who came from Akim on the west
coast of Africa (6° N. latitude and i° E. longitude).
From an examination of the photograph, as well as
from the descriptions of those who had examined the
man, the so-called horns appear to be outgrowths from
the malar bone and nasal process of the upper jaw.
This is by no means an infrequent situation for exostoses
in Europeans, and, as a rule, such outgrowths are sym-
metrical, and give a very hideous appearance to the
individual so unfortunate as to possess them. Such

TRANSMISSION OF MALFORMA TIONS. 1 9 7

bony outgrowths are believed by many surgeons to be
hereditary.

In his concluding remarks Macalister says, "That
outgrowths here may be really race characters is not to
be entirely ridiculed, for the neighbouring malar bone
which here, according to O'Reilly's description, partici-
pates in the swelling, certainly shows certain race pecu-
liarities, such as the bigger Tuberositas malaris of the

m

Fig. 106. — A so-called Horned Man of Africa. (After Lamprey.)

Mongolians, and the Processus marginalis, whose race
peculiarities have been pointed out by Werfer."

Some further particulars relative to horned men have
been furnished by J. J. Lamprey,1 of the Army Medical
Staff, who has had opportunities of examining carefully
three persons from different localities in Western Africa,
having peculiarities similar to Macalister's case. In each

1 British Medical Journal^ 1888.

198 E VOL UTION AND DISEASE.

instance there was a clearly defined bony prominence
over the infraorbital ridge of each maxillary bone ; the
skin in each case was freely movable over the abnormal
outgrowth. The ages of the men were 38, 18, and 20
years. The prominences had existed as long as the
men could remember, and caused them no inconvenience
(fig. 106).

CHAPTER IX.

ANATOMICAL PECULIARITIES OF THE TEETH IN
RELATION TO INJURY AND DISEASE,

MANY troubles and disasters arise in animals in conse-
quence of injuries to their teeth, and injuries, trivial in
one mammal, may in another be fraught with serious
results, due to variations in the use and specialization of
the dental organs.

We may commence this subject with the kangaroo.
This mammal has three incisors in the upper jaw, but
only one in the mandible. This lower incisor is procum-
bent and flattened from side to side; the outer surface
is slightly convex, the inner flat, but has a median ridge ;
the margins of the tooth are sharp. The lower incisor,
instead of an-tagonizing the upper teeth by means of its
tip, or crown, meets them along its sharp outer margin
(fig. 107). The lower incisor is provided with a large
persistent pulp ; the pulp chamber, contrary to what is
usual in teeth, extends nearly to the tip. The points of
these teeth, shaped something like a lancet, are exceed-
ingly thin and brittle. As a consequence, the tips are
easily broken, and if only a small piece is detached, the
pulp is exposed (fig. 108). Kangaroos, like mammals of
even high moral pretensions, have domestic differences,
which occasionally lead to unpleasant consequences. In

20C

EVOLUTION AND DISEASE.

the encounter the tips of the incisors are broken, the
exposed pulps inflame, suppurate, and lead to alveolar
abscess, which in some cases terminates in death from
absorption of septic matter. Occasionally the suppura-
tion leads to extensive necrosis of the jaw. Death from

Fig. 107. — The incisors of a Kangaroo [Macropiis major),

Fig. 108. — The anterior portion of a lower jaw of a Kangaroo
showing the effects of alveolar abscess secondary to a
suppurating pulp. M, mental foramen.

such a cause is not uncommon among kangaroos living
in confinement.

In this case the danger depends upon the peculiar
procumbent position of the lower incisor and the
proximity of the pulp to the tip of the tooth. In the

ANATOMICAL PECULIARITIES OF TEETH. 201

majority of mammals the teeth when fully formed cease
to grow ; in some — e.g., the rodents — the teeth continue to
increase in length throughout life : such teeth are said
to possess persistent pulps. This is of great advantage
to the animal, as it compensates for the continual wear-
ing down of the tooth in consequence of the rough work
to which such teeth are subjected. Under abnormal
conditions a persistent pulp may be, and often is, of
great disadvantage. If from accident to a tooth, or
some injury to the jaw, the antagonism of such teeth
be interfered with, the tooth or teeth which fail to
antagonize cannot be used in mastication, and as their
continual growth is not checked by wear, they may attain
a length of several inches. In such cases the enlarged
teeth may prevent the animal feeding, and thus bring
about a fatal result from starvation ; or the elongated
tooth may re-enter the head or mouth, producing pain
or even death, by piercing the brain. This last event is
rare ; the usual mode of death is from starvation — either
the animal cannot bite its food, or the abnormality of
the teeth prevents the mouth being opened. Such cases
are exceedingly frequent in rabbits and rats ; every game-
keeper of experience has met with many examples, and
also those who keep white rats and rabbits as pets.

The study of such aberrant teeth is instructive, as it
serves to throw light on the mode of origin of tusks.
In many mammals it is common to find in the upper
or lower jaw, sometimes in both, one tooth larger and
more projecting than its fellows ; this conspicuous tooth
has a pointed extremity and is known as the canine.
It is exceedingly well developed in most carnivorous

202 E VOL UTION AND DISEASE.

mammals, lions, tigers, bears, cats, dogs, weasels, bad-
gers, and the like. In those mammals with well-formed
canines, the adjacent teeth, more especially those
situated posteriorly to it in the dental series, are either
small in size or absent in the adult animal. This
reduction in size or number of teeth adjacent to those
excessively enlarged occurs, not only in those animals
with enlarged canines, but also when the incisors are
unusually developed, as in the case of rodents, or rodent-
like mammals as the aye-aye and the wombat. This
happens so constantly that in all probability the enlarge-
ment of the incisors, or canines as the case may be, is
directly responsible for this effect, partly by causing
diversion of the blood-supply and partly from disuse.
The combined effects of diversion of the blood-stream
and disuse will be more fully illustrated in the case of
tusks.

When a normal canine or incisor tooth is so long that
it protrudes from the mouth when the lips are closed it
is usual to term it a tusk. In most instances, as in the
boar, walrus, elephant, and narwhal, the tusks protrude
between the lips ; in the babirussa the lower tusks pro-
trude in this manner, but the upper pair make their way
directly through the skin covering the upper jaw.
Tusks, like the teeth of rodents, grow from persistent
pulps, and many interesting pathological conditions arise
in consequence of this peculiarity.

Among boars there is a tendency for the tusks to grow
abnormally and describe circles. An example of this
was described in 1733 by Cheselden ; x the specimen is
1 " Osteographia,'' London, 1733.

ANATOMICAL PECULIARITIES OE TEETH. 203

preserved in the museum of the Royal College of Sur-
geons, England, and is figured below. In this specimen
(fig. 109) the lower canines have grown excessively,
turned backwards, and re-entered the mouth by piercing
the integument and the jaw. The right tusk has tun-
nelled the bone for a distance of three inches and re-
appeared on the floor of the mouth and has described a
complete circle. The left tusk, after re-entering the

Fig. 109. — Abnormal growth of the lower canines of a Boar

mouth, seems to have crossed the buccal cavity so that its
apex rests on the inner side of the right lower jaw.
This is by no means an unique specimen, for on inquiry
I have come across numerous examples of this aberrant
growth of the lower canines of boars. The excellent
museum of the Veterinary School at Alfort has a speci-
men resembling that of Cheselden. I have a canine of
this character from a boar which measures thirty centi-

2o4 E VOL UTION AND DISEASE.

metres round the curve. In the museum of the Odonto-
logical Society of Great Britain the incisor of a hippo-
potamus (a huge pig) is preserved which has described a
complete circle, the point of the tooth re-entering its
own pulp chamber. The circle formed by this overgrown
tooth has a diameter of forty centimetres.

The remarkable tusks of the babirussa, especially
when the animal is confined in zoological gardens, are
exceedingly prone to take an abnormal course, and
instead of forming graceful curves beside the head, may

Fig. iio. — The head of a Babirussa. The upper canines are

re-entering the skull.

deviate towards the middle line and enter the skull.
Such an example taken from life is sketched in fig. 1 10 ;
in order to prevent disaster the babirussa was thrown and
ten centimetres of the tusks removed ; they had, how-
ever, penetrated to the depth of twelve millimetres.

This deviation of the upper canines may be in part
accounted for by the fact that, like tusks in general,
they are slightly movable in their sockets, hence by
rubbing them against the sides of the dens or cages,
a false direction is impressed upon them. Careful

ANATOMICAL PECULIARITIES OF TEETH, 205

consideration of such cases has induced me to believe
that these aberrant tusks may be regarded as arising
in the first instance as overgrowths, and that such
malformations being frequently repeated the tendency
has been transmitted to the offspring and eventually
perpetuated as a normal character of the male.

The various steps of such a process may be studied
in the pig tribe. In the wild boar the upper tusk pro-
jects about an inch from beneath the labial folds and
curves slightly upwards ; in the wart hogs it is much
larger and may attain a length of several inches or
more : in babirussa it is so strongly curved that instead
of emerging from beneath the lips it directly pierces
them. The transfixion of the skin covering the upper
jaw by an abnormal tusk was illustrated in a striking
way in the case of the celebrated African elephant
Jumbo. During fits of bad temper Jumbo often
damaged the tusks by contact with the walls of the
den, and at last the pulp chambers became exposed,
ending in alveolar abscesses of great magnitude. The
constitutional disturbance caused by the suppuration
would in all probability have ended fatally but for the
undaunted bravery, skill, and ingenuity of Mr. A. D.
Bartlett, who successfully attacked the elephant, and
opened the abscesses through the cheek. It was through
the incisions made for this purpose that the damaged
tusks finally emerged, thus explaining why Jumbo's tusks
projected through the cheeks instead of issuing from
beneath the lips, as in elephants generally.

The tusks of elephants, from their large size, are liable
to certain injuries which could scarcely occur in a smaller

2o6 E VOL UTION AND DISEASE.

mammal. The centre of every growing tooth is occupied
by a cavity known as the pulp chamber, which in the
living tooth is filled with connective tissue, blood-vessels,
nerves, and cells known as odontoblasts. The tissues
constituting the pulp are actively engaged in forming
dentine ; in teeth and tusks with persistent pulps this
pulp chamber is always relatively large, and as the tooth
is worn at the apex the pulp adds new material at the
base. In teeth with non-persistent pulps, like those of
primates, carnivora, and the like, the pulp chamber
diminishes with age, and in some the pulp becomes
converted into bony substance known as osteo dentine.
When teeth become inflamed or carious the pulp often
calcifies, and it is no unusual event to find in a carious
tooth extensive ossification of the pulp in the neighbour-
hood of the carious cavity : this is salutary, for by this
means suppuration of the pulp is prevented and often
a tooth remains serviceable much longer than would
otherwise be the case.

Ivory-turners have often found in the tusks of ele-
phants such things as bullets, iron slugs, and spear-heads,
yet on an attentive examination no trace of injury
could be detected on the exterior of the tusk. These
specimens attracted the attention of investigators such
as Blumenbach, Haller, Cuvier, Goodsir, and Owen. The
solution of the mystery was indicated by a study of the
material surrounding the foreign body. Cuvier detected
the irregularity of the dentine immediately surrounding
the bullet, and Goodsir made an elaborate study of the
whole question, and it became clear from the researches
of Goodsir, Nasymth, and Owen, that this irregular

ANATOMICAL PECULIARITIES OF TEETH. 207

tissue is of the nature of secondary or osteo- dentine,
and histologically agrees with that found in the pulp
chamber of human teeth under abnormal conditions.

The presence of bullets may be explained in this
way : — On reference to the section of the tusk in fig. 1 1 1

Fig. hi. — A diagram explanatory of the mode of encystment of
bullets in elephants' tusks.

it will be seen that the walls of the pulp chamber are
thin, hence a bullet fired at an elephant's head will
readily enter the pulp ; and should it lodge in this chamber
inflammatory disturbance is the result, and the pulp
immediately adjacent to the bullet forms irregular bone,

2o8 EVOLUTION AND DISEASE.

or osteo-dentine, thus encysting the missile. In due
course this foreign body moves onward with the segment
of the tusk in which it is embedded, and eventually
comes to lie in the exserted portion of the tusk until it
is liberated by wear or the skill of the ivory-turner.

The entrance of a bullet is readily understood. The
great force by which they are propelled carries them
easily through animal structures, but with spear-heads
it is rather different. Mr. Charles Tomes " gives an
intelligible explanation of this condition in connection
with the head of a spear embedded in an elephant's tusk-
preserved in the museum of the Odontological Society of
Great Britain. It is to be presumed that a heavily-loaded
spear was dropped by a native from a tree, with the
intention of its entering the brain, upon the elephant as
it was going to water. But in this case the spear pene-
trated the open base of the growing tusk, which looks
almost vertically upwards, and then the iron point
appears to have broken off. This did not destroy the
pulp, but the tooth continued to grow, and the iron
point, twenty centimetres long and four in width, became
so completely enclosed that there was nothing upon the
exterior of the tusk to indicate its presence.

The museums of the Royal College of Surgeons,
England, and Odontological Society of Great Britain,
contain many excellent specimens of foreign bodies
embedded in the tusks and molar teeth of elephants, as
well as masses of osteo-dentine removed from tusks
apparently healthy. Osteo-dentine, in all respects
similar to that formed in tusks under diseased con-

1 " Dental Anatomy," ist ed., p. 322.

ANATOMICAL PECULIARITIES OF TEETH. 209

ditions, makes up a large proportion of the tooth in
some whales. This identity of tissue, arising in con-
sequence of disease, in one animal with that which is
normal in another, called forth the remark from Goodsir,
that it " must be looked upon as another instance indi-
cating the existence of a system of laws regulating the
relations between healthy and morbid tissues.''

In this connection a short reference to a curious
affection of the teeth of whales may be made.. In the
grampus and sperm-whale the teeth consist of a hollow
cone of dentine coated by cementum ; the pulp chamber
is very large and contains a quantity of osteo-dentkie.
In one species, Orca, Eschricht found a complete covering
of enamel to the free portion of the tooth. In Orca,
as in the porpoise, the teeth interdigitatc when the
mouth is closed, and as the teeth wear, owing to the
friction, their broad bases come more into apposi-
tion. This wearing of the contact surfaces must, in
the long run, inevitably open up the pulp chamber ;
as a rule it is prevented in consequence of the formation
of osteo-dentine by the pulp. In some cases the de-
velopment of osteo-dentine does not take place with
sufficient rapidity, and the pulp becomes exposed and
subsequently destroyed. A case of this nature has been
minutely described by Eschricht and by Tomes.

No order of mammals exhibits so many deviations
from the ordinary conditions of teeth as whales : not
the least interesting abnormality in connection with our
present purpose is the remarkable overgrowth of the
teeth of Mesoplodon, secured by the naturalists of the
Challenger Expedition, and carefully described by Pro-

*5

2IO

EVOLUTION AND DISEASE,

fessor Sir W. Turner. The illustration (fig. 112), which
was prepared from a model of this specimen, represents
the anterior part of the rostrum and lower jaw with two
teeth of Mesoplodon layardi. This whale has only one
tooth in each mandible (at least, as far as we know). In
the present case the fangs of these teeth had become
greatly elongated, and after emerging from the gum had
curved backwards, upwards, and inwards, so as to cross
each other on the dorsal surface of the whale's beak.
The anterior border and inner surface of each tooth was

Fig. 112. — The rostrum of Mesoplodon layardi, %&\\ovimg the curved
and elongated mandibular teeth.

smooth where they rubbed together during the move-
ments of the mouth. The size of these teeth is as
follows :— The extracted tooth measures 35 centimetres,
16 of which were embedded in the alveolus, or surrounded
by the gum. The breadth of the tooth where it emerged
from the alveolus was 9 centimetres. At the time this
specimen was submitted to Turner, he was fortunate
enough to receive a young specimen of Mesoplodon
which enabled him to determine the nature of the
various parts of this abnormal tooth, and he came to

ANATOMICAL PECULIARITIES OF TEETH 211

the conclusion that its peculiar form was due to changes
in the fang.

From mammals we may turn our attention to snakes.
In toothed reptiles the teeth are attached to the jaw-
bone in a manner differing from that which pertains to
mammals. In the latter the teeth, as they develop,
become surrounded by walls of loose porous bone, forming

Fig. 113.— Section through the jaw and tooth of a Python,
showing bone of attachment.

an alveolus ; when the teeth are erupted the roots or
fangs remain embedded in this imperfect kind of bone ;
hence, when a tooth is extracted, a socket, or empty
space remains, resembling that left by withdrawing a
nail from a piece of wood into which it has been driven.
On this account this mode of lodgment of teeth is
termed gomphosis.

212 E VOL UTION AND DISEASE.

In snakes the teeth do not come directly in contact
with the osseous tissue of the jaw ; but, coincident with
the development of the teeth, a formation of loose, bony
matter occurs, whereby the base of each tooth is firmly
cemented to the jaw-bone. Charles Tomes aptly de-
scribes this intermediate tissue as " bone of attachment";
it is of loose and open texture, resembling the alveolus.
If from any cause this bone of attachment is softened or
absorbed the teeth fall. It happens that snakes living
in confinement are liable to a disease which induces
softening of the bones of the skull, and as the bone
which attaches the teeth to the jaw is, especially when
compared with the bones of the skeleton generally —
which are of almost ivory-like hardness — soft, and easily
absorbed, the snake in consequence loses its teeth.
The relation of tooth, jaw, and bone of attachment is
represented in fig. 113. Premature shedding of teeth
from this cause is not infrequent in snakes living in
captivity ; but I am unaware of its occurrence in snakes
living wild.

Absorption of the alveolus occurs in mammals as age
advances, leading to the edentulous condition of the
gums which is one of the concomitants of advanced life ;
but the fall of teeth referred to in the case of the snake
is due to constitutional defects, and not old age.

CHAPTER X

CAUSES OF DISEASE,

Inflammation and Fever. — Thus far we have been con-
cerned with diseases and malformations arising mainly
from structural alterations due to the combined effects
of variability and inheritance. We will now consider
some examples of disease due to other causes.

Biological researches of the last few years have shown
that many diseases of animals are due to the entrance,
and subsequent multiplication in the system, of micro-
scopic bodies known collectively as bacteria, or micro-
organisms. It has been clearly established by an
overwhelming amount of evidence that such conditions
as tuberculosis, glanders, actinomycosis and other
contagious diseases are due to the action of these
minute bodies.

For our purpose bacteria may be divided into two
groups — those which when introduced into the body
cause no harm, and those which produce disturbance
either local or general. The latter are said to be
pathogenic, or disease-producing. A study of the
relation of bacteria to disease is of great interest, and
sheds abundant light, not only on the nature of specific
diseases, but also on the nature of a very remarkable
condition known generally as inflammation.

2i4 E VOL UTION AND DISEASE.

Bacteria — using this term in a general sense — require
high powers of the microscope and suitable methods of
preparation for their satisfactory detection and identifica-
tion : they appear as minute rods, or small rounded
bodies ; the latter are usually termed micrococci. In
order to prove that any given bacterium is the cause of
a particular disease, it is necessary to ascertain its
constant presence in the blood or tissues of animals
suffering from the disease, and then to cultivate it in
media apart from the living body through several
generations ; on introducing the product of such cul-
tivations into an animal, the disease should make its
appearance and the micro- organisms occur in the
lesions.

Pathogenic bacteria, when introduced into an organism
either accidentally or designedly, give rise to trouble
whicli may be either local or general. The local signs
are peculiar, for the disease may in some cases be
restricted to the part at which the morbid agents were
introduced, or the tissues at the seat of inoculation may
serve as a focus in which the bacteria germinate and are
subsequently disseminated through the system generally,
producing profound disturbances and not infrequently
death.

Before studying in detail the effects of the introduction
of bacteria into an organism, it will be necessary to
review the leading facts connected with the evolution of
the inflammatory process as manifested by a complex
organism.

The simplest animal known — the amoeba — is a
microscopic mass of nucleated protoplasm capable of

CA USES OF DISEASE. 2 1 5

spontaneous movement and possessing the power of
ingesting, and digesting when suitable, particles of
matter presented to it. The essential difference between
the simple amoeba and the most complex animals is
that the latter are compound amoebae in which individual
cells perform separate duties ; there is a differentiation
of labour ; some persist in virtue of their contractility,
others for digestive functions ; some secrete, others
serve for reproduction, and so forth. Most complex
organisms are pervaded by a corpusculated fluid, which
may circulate throughout the organism by travers-
ing lacunar spaces, or by means of narrow tubular
passages possessing distinct walls. This circulating
fluid, named blood, serves as a living medium of com-
munication between the various parts of an organism.
The blood in higher metazoa contains two kinds of
corpuscles ; the more numerous are circular or elliptical
microscopical discs, tinged of a pale red colour, and, in
some vertebrates, furnished with a nucleus. The second
variety are nucleated, irregular, colourless, and exhibit
amoeboid movement ; they change their shape, and can
escape from the confines of the capillary vessels when
such are present. Like an amoeba they can ingest, and
when suitable digest, particles of matter presented to
them. In all vertebrata, with the exception of amphi-
oxus and ascidians, red and colourless corpuscles are
present. The invertebrata possess, with very few
exceptions, only the colourless corpuscles. These
corpuscles, or leucocytes as they are called, fulfil some
very extraordinary functions. Should a portion of an
animal die, the leucocytes will attack it and, if it be

2 1 6 E VOL UTION AND DISEASE.

small, will cluster around and by a process of intracellular
digestion devour it. When the part to be removed is
large, the leucocytes will effect a separation between
it and the living body. Not only dead or damaged
portions of tissue are thus removed by leucocytes, but
useless parts, such as the tails and gills of tadpoles,
remains of larval organs, and the tails of ascidians, are
thus slowly removed. No animal tissue is capable of
resisting an attack of leucocytes. For instance, an ex-
amination of the milk-teeth of children or puppies at
the time they are shed, well attests the digestive powers
of these cells. Surprise is often expressed that when
such teeth tumble, or are dislodged, from the gums
only the crown is present, the root, or fang, is usually
absent. That portion of the tooth in contact with the
gum is irregular, and an ordinary magnifying-glass shows
it to be full of bays and recesses. When such a tooth
is decalcified and suitably prepared for microscopical
scrutiny these bays are found filled with leucocytes
which, during life, were busily engaged in destroying the
fang of the tooth and have slowly induced its fall. The
shedding of milk-teeth in mammals, like the disappear-
ance of the tadpole's tail, is due to the persistent attacks
of leucocytes. Introduce into the tissues of a cat, a dog,
or a man, small pieces of clean sponge. In the course of
a few days the fragments of sponge will have disappeared.
Vary the experiment by removing the sponge two days
after its insertion, cut sections and examine under the
microscope, the interstices will be found occupied by an
army of leucocytes. Introduce some indigestible object
such as glass, a needle, or a fragment of metal. When

CA USES OF DISEASE. 2 1 7

these are free from any dirty particles and are not
lodged in a vital organ, the leucocytes at once attack
them, but find such intruders unconquerable ; the result
is that very large numbers of these cells surround them
and gradually become transformed into neutral tissue,
thus isolating the intruding bodies from neighbouring
parts. The tissue thus formed is known as fibrous-tissue,
and the process is termed encystment. Should the
intruded body contain particles of dirt offensive to the
leucocytes, the action becomes intensified and often
disastrous to the cells, for they die in the conflict, and in
a few hours the foreign body is surrounded by fluid
containing the dead cells. This fluid is usually of a
yellowish colour and is known technically as pus ; a
collection of pus is termed an abscess. As long as an
offensive foreign body remains in the organism the
abscess enlarges until it finds its way to a free surface
and discharges itself: with the evacuation of the pus the
cause of the disturbance often escapes.

In their behaviour to foreign bodies leucocytes remind
us of the resentment of bees to insects intruding into
their hives. When the offender is small it is quickly
stung to death and turned out ; when large, and they
succeed in depriving it of life, it may be too heavy to
admit of removal, and the bees render the dead organism
inocuous by a covering of wax.

This aggressive behaviour of leucocytes to foreign
bodies is extended to such unwelcome guests as
pathogenic bacteria. When micro-organisms effect an
entrance into an animal the leucocytes attack and
attempt to destroy them, and the details of such

2l8

EVOLUTION AND DISEASE.

amoebic warfare may be described from attacks actually
witnessed by Metschnikoff in the water-flea Daphnia.
This observer kept many of these interesting trans-
parent creatures in a tank, and noticed that they became
affected with spores which gained an entrance into the
body of the crustacean, germinated, and were dispersed
by the blood over the body (in Daphnia the blood
circulates in lacunar spaces) and deposited in those
parts where the blood moves slowest, viz., in the cephalic
and hinder portions of the mantle cavity : in these

places heaps of conidia collect.
In the meantime the leuco-
cytes do not remain idle against
the invasion, but attack and
devour the conidia, take them
into their interior and digest
them. If a conidium be too
much for one cell others join

fig. ii4. -White bioocT- cells &. form a giant-cell, and thus
(leucocytes) attacking bacilli, struggle with the invader.

(After Metschnikoff.)

Should the leucocytes over-
power the spores, the daphnia lives ; if not, the conidia
overrun the crustacean and death is the result.

A similar process takes place in animals more highly
organized, and as no disease illustrates more thoroughly
the defending power exercised by leucocytes than that
known as avian tuberculosis, the leading points in this
widespread affection will be briefly considered. Tuber-
culosis in man is unfortunately very prevalent, but in
birds, especially those which live on grain, it is more
common than in human beings. On examining a bird

CA USES OF DISEASE. 219

which has died of this disease we find the liver and
intestines presenting numerous rounded nodules of a
pale yellow colour, varying in size from a pin point to
that of a filbert. On cutting into the larger nodules the
centre is found occupied by pus. The smaller ones are
homogeneous, and on examining them microscopically
we recognize in the centre small circular cells with larger
ones — giant-cells — lodged among them, outside these a
layer of smaller cells with no giant-cells, and lastly a
layer of fibrous tissue.

When such specimens are suitably stained, minute
rod-like bodies — bacilli — are
seen clustered in the centre
of the mass and occupying
the interior of the cells, espe-
cially the giant-cells. In
nodules of moderate size the

Centre is OCCUpied by CaseOUS FIG. 115.— Leucocytes ingesting

material surrounded by a zone aci u

of cells containing bacilli. Adjacent nodules may
coalesce and thus produce large masses. The blood-vessels
connected with the nodules frequently present clusters
of bacilli in their interior. An extensive and prolonged
study of this disease has convinced me that the bacilli,
from whatever source arising, are introduced into the
alimentary canal and find their way into the walls of the
bowel. Here they are attacked by the leucocytes which
surround, ingest, and destroy them. The bacilli may be
too numerous for the leucocytes, and the point where
the bacilli gain entrance into the tissues become a
battle-field, large numbers of leucocytes are quickly on

2 20 E VOL UTION AND DISEASE

the spot, and reinforce their comrades ; as a result of
this encounter many of the leucocytes die, others fuse
together and form giant-cells : the dead leucocytes form
pus cells and give rise to the caseous centre in the
nodules, whilst along its confines, in the bacilliferous
zone, the conflict continues to rage. The giant-cells are
powerful antagonists, for I have seen one contain as
many as fifty bacilli. From these nodules the bacilli are
conveyed by blood-vessels, or even carried away by the
leucocytes, and initiate new struggles in distant parts.
It must also be remembered that after their introduction
into the body the bacilli will, if the conditions of the host
be favourable, multiply very rapidly, and in due course
overrun the whole system ; nodules arise in the liver,
lungs, brain, and skin ; function is interfered with and
death results. In addition to the local troubles the
invasion of an organism by bacteria produces general
disturbances, one of the most important being an
increase of the temperature of the body, usually termed
fever.

It must be borne in mind that local lesions are not
necessary results of the entrance of pathogenic organisms
into the system. In such a disease as anthrax we have
one local sore indicating the seat of inoculation, but
beyond the presence of the bacilli in the blood we have
no special tissue-change enabling us to identify the
nature of the disease, the general disturbance and fever
in anthrax conforming to that characteristic of acute,
specific, contagious maladies in general.

The behaviour of leucocytes to pathogenic bacteria
constitutes the essence of the inflammatory process. It

CA USES OF DISEASE. 2 2 1

has been known since the time of Celsus that the
cardinal signs of inflammation in a warm-blooded
animal are redness, swelling, heat, and pain. The red-
ness is due to afflux of blood, the swelling to an increased
quantity of fluid in the part, the excess of heat is con-
sequent on the extra tissue-change, and the pain to
pressure on the nerves of the inflamed part. The in-
genuity of pathologists has devised plans whereby the
inflammatory process can be actually watched in such
situations as the web of the frog's foot, in the tongue of
the frog, and in the mesentery of the mouse. One of the
most striking events seen on irritating the parts either
by acid, by foreign bodies, or the introduction of bacteria,
is the emigration of leucocytes from the walls of the
vessels. How the leucocytes escape from the capil-
laries is a mystery, but that they make their way through
the vessel-wall is one of the best ascertained facts of
experimental pathology.

The emigrated leucocytes then proceed to attack the
intruding matter, and usually effect its removal, but failing
this may encyst it in the way already explained. When
the invaders are bacilli they may overrun the organism
by gaining entrance into the circulatory system. The
experimental evidence, and our better knowledge of
intra-cellular digestion, shows clearly that, zoologically
considered, inflammation is in essence a local struggle
between irritants and the white cells of the blood. When
the whole of the blood is engaged in the struggle, as in
ague, pyaemia, anthrax, and the like, we have general
inflammation or fever. The different varieties of fever,
when due to micro-organisms, depend on the habits

222 EVOLUTION AND DISEASE.

of the specific bacteria ; some are more virulent, others
are slower in attaining maturity, or are more irritating
to the tissues.

This view of the nature of inflammation is of some
importance, for it shows that the process may take place
in any compound cellular organism, and it certainly takes
place in plants ; for example, the galls on leaves due
to the deposition of eggs in their interstices by insects ;
each insect producing in this way a different variety of
gall, so that one leaf may present at the same time
several varieties of galls.

The modification of the inflammatory process accord-
ing to the nature of the irritant is of interest in its
bearing on the evolution of specific diseases. The course
of a specific contagious disease, whether due to bacterial
infection or to noxious agents produced by bacteria, pre-
sents well-marked stages. The first is known as the
incubation stage, which may vary from a few hours to
days, or even weeks : this is succeeded by a stage of
eruption, in which the body presents manifestations of
the presence of noxious particles, such as a rash in small-
pox, scarlet fever, measles, and the like, or a sore limited
to a small area of the body, as in glanders, anthrax,
syphilis, &c.

These outward signs are accompanied by fever and
general disturbance, marking the maturation of the
poison in the organism. After a variable period the signs
gradually subside, or terminate the life of the individual,
or the bacteria continuing to thrive in the organism may,
with the maturation of successive generations, produce
periodical disturbance at intervals of several hours, or

CAUSES OF DISEASE. .223

days, as is seen in the various forms of malarial
fevers.

The variations in the periods of incubation, eruption,
and crisis, correspond with the life-history of the various
micro-organisms as ascertained by means of experiments.
When bacteria are introduced into cultivation-media,
such as solutions of gelatine, agar-agar, chicken-broth,
and the like, there is always a latent period which varies
with different bacteria. When the micro-organisms com-
mence to grow it is often possible to identify its nature
from the mode of growth and behaviour towards the
medium, independently of its microscopical characters.

Inasmuch as the varieties of bacteria present intrinsic
differences in this respect, it is not unreasonable to sup-
pose that the variations in the period of incubation,
character of the eruption, and effects upon an organism
should vary according to the nature of the parasite intro-
duced.

Bacteria, like other forms of life, present extreme
variety, and the differences between innocent and malig-
nant forms of bacteria, in so far as their effects upon an
organism is concerned, are very great. Nevertheless, we
can pass by insensible gradations from one form to the
other : indeed, the history of micro-organisms shows
clearly enough, as in the case of animal parasites, that
pathogenic bacteria have been slowly evolved from non-
pathogenic forms, and have slowly acquired the power of
flourishing upon living bodies when the environment is
suitable. This, of course, raises the all-important ques-
tion, What is suitable environment? Micro-organisms
exhibit wonderful vitality and seem to be omnipresent.

224 E VOL UTION AND DISEASE.

Let us take yeast for example. Torula spores exist in
countless myriads, and it is necessary merely to expose a
solution of sugar to the air in a warm place and in the
course of a few hours it is filled with torulae ; according
to the amount of sugar present in the solution depends
the degree of fermentation established by them, and the
amount of alcohol resulting from their activity. The
time occupied in producing it depends largely upon
the favouring influence of temperature.

Thus it is clear that in this case the determining condi-
tions are the presence of a solution of sugar exposed to air,
and a suitable temperature. The spores of the yeast
being always around us ready to develop as soon as en-
vironing conditions are favourable. So with pathogenic
organisms, it by no means follows because they gain
entrance into an organism they necessarily flourish.
Pasteur demonstrated in the case of silkworms that the
micro-organisms found in cases otflacherie are only to be
found among the pounded leaves in their alimentary
canal when the worms digested badly ; when the digestive
functions of silkworms are active the germs of the
micro-organisms are either digested or hindered in their
development.

Similar conditions may be studied in man. It is now
clear that the disease known as erysipelas is due to
pathogenic bacteria which gain entrance into the body
through abrasions of the skin. This is more likely to
happen when individuals with wounds are surrounded
by insanitary conditions, are badly fed, and crowded
together. It by no means follows that every wound ex-
posed to the poison of erysipelas necessarily becomes

CAUSES OF DISEASE. 225

affected, and pathologists are ignorant of the actual con-
ditions of wounds favourable to the development of the
micro-organism characteristic of this disease, and it is
equally certain that three or more individuals with open
wounds may be equally exposed to the virus and yet
some of them escape. This immunity may depend on
chemical, or fermentative changes, going on in the wound,
which produce a medium favourable to the growth and
development of the erysipelas-germ. On the other hand
it is possible that atmospheric and thermal conditions
may favour their development.

The more these questions are studied the more we
perceive that the outbreak of infectious diseases depends
not so much upon the presence of micro-organisms —
for, like the torula, they seem to exist everywhere —
as upon the existence of suitable conditions, and as
yeast cannot grow and multiply without sugar, neither
can the poison of erysipelas, typhus, relapsing fever,
and the like, propagate without the presence of some sub-
stance produced in living bodies, of the nature of which
we are ignorant. This is well shown in Pasteur's researches
on fowl cholera : in this instance the microbe would not
live in the ordinary cultivation-media employed by
him, but when introduced into chicken-broth grew
rapidly. On a similar principle relapsing fever is
unknown except in times of famine, when the body-
chemistry is deranged by want of food, privation, and
hardships of every kind.

There is yet another remarkable process which is a
modification of inflammation, viz., the repair of wounds.
When a wound is made in the tissues of an animal, and

16

226 E VOL UTION AND DISEASE.

it survives the injury, a series of events, varying accord-
ing to the extent of tissue damaged, ensues. The
simplest case is when the tissues are severed with a
clean, sharp knife. In this case, unless a large artery is
wounded, if the two surfaces of the wound be brought
together and maintained in strict apposition, the bleeding
will cease, and in the course of a few hours the whole of
the damaged surface will be invaded by leucocytes, these
gradually elongate and become transformed into tissue
and form a uniting medium between the two surfaces
of the wound.

When a wound is thus inflicted, and the surfaces not
brought into contact, the result is different. Exposure
to the air gradually arrests the bleeding, unless large
vessels are cut ; as in the preceding case the damaged
tissue is invaded by leucocytes, and many cells lying
exposed on the surface, being too far removed from the
living tissue, die. The surface of the wound is at first
moist, due to the exudation of fluid from the divided
tissues ; this, in conjunction with the blood clot, dries in
consequence of exposure to the air and forms a scab.
This is of great use, for in many instances it her-
metically seals the wound, preventing the entrance of
micro-organisms. Under the scab the leucocytes unite,
become transformed into tissue of repair, and finally,
completely fill the gap. Should micro-organisms pos-
sessing pathogenic properties gain entrance the leuco-
cytes attack them, the inflammation becomes often
intense, fermentation, due to the growth of micro-
organisms in the juices of the wound, takes place,
products noxious to the individual are produced, and
consequences, often disastrous, arise.

CA USES OF DISEASE. 227

In a general work of this character it is impossible to
describe in technical detail the different stages and
variations displayed in the healing of wounds, but the
principles of this important process are the same as
those which underlie inflammation. It certainly simpli-
fies our notions of morbid processes to find that the
phenomena known as repair of wounds, inflammation,
and fever, are manifestations of the same process by
which a child loses its milk-teeth, the tadpole its tail, or
the stag its antlers, rather than to look upon such con-
ditions as the result of some special law.

CHAPTER XL

TUMOURS AND CANCERS.

TUMOURS are very interesting to the evolutionist, and in
order to obtain a clear notion of them it will be necessary
to classify the various " swellings " to which the term is
applied, and this is more essential as even medical men
use the word in a very indefinite sense. The term
" tumour," which literally signifies " a swelling," com-
prises Cysts, Infective Tumours, Sarcomata, Neoplasms,
and Cancers. Each requires separate consideration.

Cysts. — A cyst is a tumour containing fluid or semi-
fluid contents resulting from the dilatation of a pre-existing
cavity.

Tumours conforming to this definition arise in different
ways. For instance, many organs such as the kidneys,
liver, salivary glands, and the like, are furnished with a
duct, or series of ducts, whereby the fluid secreted by
them is conveniently discharged. If from any cause the
fluid be prevented from escaping after it has been
secreted, it will distend the ducts until they become
dilated into large reservoirs, or retention-cysts, as they
are termed. This is well illustrated in the case of
the kidneys represented in fig. 116. The drawing
shows the kidneys with their ducts (ureters) and the
urinary bladder of a terrier. The bladder contains two

TUMOURS AND CANCERS. 229

large and two small calculi. One calculus is lodged in
the lower end of the left ureter, obstructing it. In con-
sequence of this, the retained fluid has dilated the ureter,
and the pressure has induced absorption of the secreting

Fig. 116. — The kidneys, ureters, and bladder of a Terrier.
The bladder contains calculi, one of which, C, obstructs
the left ureter, and has induced a cystic condition of the
kidney. (Mus. Royal College of Surgeons.)

tissue of the corresponding kidney, which has become
transformed into a hollow bag, or cyst, filled with fluid.
This condition of the kidney will arise from any cause
obstructing the free flow of urine.

23o E VOL UTION AND DISEASE.

The bodies of animals contain cavities unprovided
with ducts : occasionally fluid exudes into such cavities
and dilates them into tumours. Such are termed exuda-
tion cysts. These have little interest for us.

The bodies of complex animals contain many ducts
and passages which were presumably functional in their
remote ancestors, but are functionless in existing forms.
Such are collectively known as obsolete canals. These
canals are occasionally distended with fluid and form
tumours often of large size. This group is of great im-
portance to us, as the germs of such tumours are due to
modifications induced in animal organization mainly by
change in the environment, and inheritance of structural
variations.

A very striking example occurs in connection with the
ovary. In many mammals and reptiles a collection of
vestigial tubular structures has been observed in connec-
tion with this organ. In the higher mammals they con-
sist of a series of short vertical tubules dipping into the
hilum of the ovary ; above, they end blindly in a duct.
This vestigial tubular organ is known as the parovarium,
and in the male it forms an important part of the excre-
tory apparatus of the reproductive organs.

From some cause quite unknown to us, one or other of
these tubules may become distended into tumours hold-
ing many ounces, or even pints, of fluid. Such tumours
may jeopardise life from mechanical reasons or induce
death by reason of secondary changes in their interior.
Cysts of this kind are met with in mammals of all kinds,
in birds, reptiles, and in amphibians.

Hen birds occasionally furnish an admirable example

TUMO URS AND CANCERS. 2 3 r

of this kind of cyst. I have already described the ves-
tige of the right oviduct which may be detected on the
right side of the cloaca (see p. 64). This slender and
apparently innocent tube may now and then dilate to
form a cyst as large as a walnut (fig. 117). As a rule
such cysts are harmless, but at times they inflame and
become filled with pus ; should the cyst rupture the pus
escapes among the intestines and the bird dies from
peritonitis.

Other cystic conditions arising in functionless ducts
are described in Chapter III.

In addition to cystic tumours
arising from retention of fluid,
or in functionless ducts, there
is an interesting class known
as diverticula, or false cysts :
these demand some considera-
tion.

Many of the tubes and pas- FlG> II7._The cloaca of a Hen i
sages of animal bodies possess the stumP of the risht oviduct

is dilated into a cyst.

two walls, an outer one, more or

less rigid, which gives it shape, and an inner one lined with
a soft velvety covering known as mucous membrane. This
differs from the outer tube in being usually distensible and
easily separable from the outer or protecting wall. Not
infrequently from strain, accumulations of fluid or air,
the inner, moveable, elastic mucous membrane lining
such a tube will be forced through a weak or defective
spot in the outer tube and form a soft rounded bulging
or diverticulum ; the cavity of such a diverticulum still
retains its connection with the tube to which it belongs.

232

EVOLUTION AND DISEASE.

One of the most remarkable diverticula known to me
exists in the neck of the Emu (Dromcens novce-liollandice)^
which demands consideration, as it serves as an admir-
able physiological type of diverticula in general.

Fig. 118. — Tracheal pouch of the Emu. (After Murie.)

In the emu there is a natural defect in the trachea at
a spot varying in position between the fiftieth and sixty-
fifth rings. This spot has the form of an oblong slit,
which in the adult bird is about seven centimetres in

TUMOURS AND CANCERS. 233

length ; the width varies from eight to twelve millimetres,
according to the retracted or distended condition of the
windpipe. The mucous membrane lining the trachea
passes through this slit, and forms a large bag or sac,
which lies between the trachea and the skin (fig. 118).
During the breeding season, the birds inflate the sac with
air and produce a peculiar drumming sound which
resembles the booming noise made by blowing forcibly
across the opening of a large but narrow-necked bottle
This cyst is not present in the emu chick, only the slit
in the trachea ; as the bird grows, so the mucous mem-
brane becomes slowly protruded through it. On one
occasion I have found this cyst filled with fluid mucus,
due to inflammation of its walls, and on attempting to
relieve it, the mucus passed into the trachea and literally
drowned the bird.

Among diverticula, analogous to the tracheal pouch
of the emu, should be mentioned the singular pouch of
the Bustard (Otis tarda).

Infective Tumours. — Tumours belonging to this
group are caused by micro-organisms. They demand
close attention, because they are the most generalized
of all tumours and occur in every kind of vertebrate
animal.

Structurally, they consist of small round, or spindle-
shaped cells, intermixed with giant-cells in variable pro-
portions. Infective tumours are of two classes : (a) sar-
comata, (J?) infective granulomata. A sarcoma usually
appears as a tumour, and later infects the system, pro-
ducing secondary nodules in different organs, such as
the lungs, liver, &c. The infective granulomata appear

234 E VOL UTION AND DISEASE.

as small scattered nodules in various parts of the body.
In many cases the micro-organism which produces the
disease, has been satisfactorily isolated. A few tumours
have been placed in this group because their structure,
history, and infective properties correspond to those in
which micro-organisms have been satisfactorily detected.
The consideration of infective tumours belongs strictly
to the evolutionist, for the causative agents may be re-
garded as parasites which have gradually acquired the
power of flourishing in animal bodies. This group may
be illustrated by an account of the remarkable disease
known as actinomycosis.

Actinomycosis is a disease prevalent among cattle.
It commences as a rule in connection with the jaws and
tongue in the form of nodules, which become confluent
and form large masses. After attaining a certain size
these tumours suppurate and discharge pus. When the
jaw is the seat of the disease, the bone becomes eroded
and expanded on account of the growth invading it.
Such tumours were formerly described by veterinary
surgeons as sarcomata, but in 1877 Bollinger detected in
them microscopic organisms of peculiar radiating struc-
ture, termed in consequence actinomyces, or the rayed-
fungus. The matter has received the close attention
its interest and importance deserves. It appears that the
spores of the fungus enter the tissues, either through
ulcers, decayed teeth, or the sockets of teeth, and acting as
irritants establish inflammation. After lodging in the
tissues for a time, the spores develop a mycelium (fig.
119), and the radiated structures thus formed become
surrounded by leucocytes, round cells, and giant-cells,

TUMOURS AND CANCERS.

235

which form perceptible nodules. Many nodules becom-
ing confluent give rise to a tumour in the affected part.
That the actinomyces is the cause of the disease is demon-
strated by the fact that the fungus may be cultivated
artificially, and when introduced into a calf experi-
mentally will produce the disease.

Actinomycosis is interesting pathologically, but is also
important from an economical point of view, and still

Fig. 119. — A tuft of Actinomyces highly magnified, showing the

clubs.

more important in a sanitary respect, as quite a number
of cases have been placed on record in this country, but
more especially in Germany, which have occurred in the
human subject, and it is a noteworthy fact that in many
of the patients the disease seems to have commenced in
the alimentary canal.

Sarcomata. — Those tumours which pathologists term
sarcomata differ from those produced by the ray-fungus

236 EVOLUTION AND DISEASE.

in the following particulars. The micro-organism or
causative agent has not yet been isolated, and we have
no satisfactory evidence that a sarcoma can be inoculated
into another animal. Nevertheless the two forms of
tumours agree in the general principle of structure,
disastrous effects upon the life of the individual, and in
a tendency to infect the system. Careful research will
probably establish before very long a poison or micro-
organism for each of the various types of sarcoma. My
own inquiries into these tumours has long served to con-
vince me that such will be the case, and a few of the
reasons will be briefly detailed. Every day experience
teaches that tumours in the human subject are extremely
common. Attendance at a veterinary infirmary will
soon convince a regular visitor that tumours are frequent
in horses, cattle, sheep, and dogs. A long and careful
personal attendance at many thousand post-mortem
examinations of wild animals, dying in captivity, has
disclosed the fact that such animals are rarely affected
with tumours. A critical analysis of facts further shows
that in man cancer is more common than infective
tumours. In domesticated mammals cancer, in the
sense in which it will be employed later, is unusual,
whilst infective tumours are extremely common. In wild
animals nearly all the tumours belong to the infective
granulomata, only a few cases of cancer being known.
It may be useful to detail one or two typical specimens
of sarcomata from animals.

The first is a round-celled sarcoma growing in the
subcutaneous tissues of the neck of a hen. It is of the
size of a chestnut, and is surrounded by a capsule of

TUMOURS AND CANCERS,

237

fibrous tissue. On section it has a pale yellow colour,
and is elastic to the touch. When portions of the tumour
were hardened, and thin sections prepared for the micro-
scope, it was found to be made up of a multitude of
closely-packed round cells, with here and there slender
fibrillae of delicate tissue passing between them ; occa-
sionally a giant-cell, with many nuclei, was seen. The

Fig. 120. — The head of a Fowl, with a sarcoma growing in
the subcutaneous tissue.

general appearance of the tumour may be inferred from
the drawing in fig. 120. In this case the sarcoma grew
in the subcutaneous tissue, and was of small size ; but
such tumours may grow in any situation of the body,
sometimes in bones, where they attain a very large size ;
in the brain, eye, intestine, limbs, &c. I have examined

238 E VOL UTION AND DISEASE.

tumours in fish, frogs, birds, snakes, marsupials, rodents,
carnivora, quadrumana, and ruminants.

When sarcomata grow from bone, especially from
the interior of a bone, they usually possess large num-
bers of giant-cells. When originating in pigmented
spots such as the black or pigment coat of the eye, or
the pigment layer of the skin, they are of a deep black
colour, and named in consequence melanotic. Grey
horses are especially liable to this form of tumour, yet
we have no reason to believe that the coloured races of
mankind are more or even so prone to them as
Europeans.

Sarcomata do not always remain localized in this
way. After the tumour has been growing for a time,
other nodules make their appearance in different parts
of the body, and not infrequently the secondary forma-
tions are larger than the original tumour. These facts,
and the general effects of such tumours, would alone
cause us to suspect some parasitic agent, and what is of
utmost importance, the early removal of the primary
tumour occasionally prevents general infection.

In the chapter on Inflammation, the relation of the
leucocytes to bacterial invasion was described. Let us
ascertain how it will elucidate the nature of sarcomata.
The classification of these tumours is founded on the
structural characters displayed by thin sections of the
dead tumours under the microscope ; they are then
described as round-cell tumours, spindle-celled, melanotic
or giant-celled. The appearance of a section of a round-
celled sarcoma is exhibited in fig. 121.

When fluid portions of such tumours are examined,

TUMOURS AND CANCERS.

239

whilst they are yet alive, on a suitable stage, these cells
have been found to exhibit amoeboid movements and
change of shape. When such cells die they assume a
rounded form, in the same way that a dead leucocyte
becomes transformed from an irregular shapeless mass
of active protoplasm to a definite rounded cell.

To put the matter in a clear form, a sarcoma is pro-
bably the scene of action of a violent and prolonged

© mm

®

*•• ®fl €S

®®m

•mi

Fig. 121. — The microscopic appearance of a round-celled
Sarcoma.

conflict between irritant micro-organisms and leucocytes.
I say probably, because, as has been already remarked,
bacteriologists have not yet succeeded in isolating a special
bacterium for sarcomata in general ; that such agents
will soon be discovered is in the highest degree probable,
because in recent years each increase in the list of infec-
tive granulomata is made at the expense of sarcomata.
The structure, mode of growth, infective properties, and

24o EVOLUTION AND DISEASE.

manner in which these tumours destroy life, clearly
coincide with what is positively known with regard to
infective granulomata. The fact that sarcomata make
up the greater part of tumours occurring in wild and
domesticated animals has, in my opinion, a very signifi-
cant import in this relation.

NEOPLASMS. — Tumours belonging to this group will
not detain us long. They are innocent in so far as the life
of the individual is concerned, and are composed of fat,
bone, or cartilage ; in some cases they consist of an
aggregation of blood or lymph vessels. Such tumours
may cause inconvenience from their large size, or inter-
fere with vital organs, but they never produce constitu-
tional disturbance or infect the system. In many
instances they occur as local overgrowths of tissues,
resembling in this way the deviations which occur in
the vegetable world and known as " sports ; " this term
being used by gardeners as signifying a bud or off-shoot
which suddenly assumes a new, and sometimes very
different, character from that of the rest of the plant.
The term u spontaneous variation " is sometimes applied
to such conditions. As " sports " occur throughout the
plant world, so simple neoplasms occur throughout the
vertebrate kingdom, and wherever fat, bone, and cartilage
are found, will the tendency to " sports " exist and pro-
duce fatty tumours, bony tumours, cartilaginous tumours,
and the like.

Cohnheim attempted to account for the occurrence of
neoplasms by supposing that during the development of
an animal a certain number of the original cells of a
part remained undeveloped, and that later in life they

TUMOURS AND CANCERS. 241

grew erratically or aimlessly and formed tumours. This
view has been discussed critically by almost all writers
on tumours since Cohnheim expressed it, and it un-
doubtedly accounts for many neoplasms. The great
objection to the view has been that such undeveloped
rudiments have not been shown to exist. More careful
researches show clearly enough that among the great
class of morbid productions generically referred to as
tumours, Cohnheim's theory holds good for cysts, many
neoplasms, and a remarkable group known as dermoids,
and by a careful extension of the definition " tumour
germ," it could be applied to cancer. Restricting the
application of this theory to the tumours indicated, this
view offers adequate explanation of bony and carti-
laginous neoplasms, of some vascular tumours, and those
which have been already referred to as arising in con-
nection with vestigial structures. (See Chapters III.
and IV.)

The full details cannot here be discussed, but any one
exercising patience in such anatomical inquiries will
soon be able to satisfy himself, as I have done, that
" tumour-germs " actually exist in our bodies, and of
such a character as Cohnheim's theory requires. The
erratic growth of such undeveloped portions of tissue
may be well illustrated in a simple way by examples
from the vegetable kingdom. The stems of trees and
woody plants form a large number of buds, most of
which grow into branches. Some of these remain un-
developed for a time, and then, instead of forming a
normal branch, they grow erratically, and form a swelling
or woody tumour of irregular shape, which may attain

17

242 EVOLUTION AND DISEASE,

a large size. Such a tumour of a tree is termed a
xyloma. The bud-like character of such woody tumours
is shown in an interesting series presented to the
museum of the Royal College of Surgeons by Mr.
Stephen Paget. From some of the tumours buds have
formed, and in one case the bud has grown into a
minute branch. Every swelling on a tree, however, is
not a woody tumour or xyloma ; many are due to the
irritation of insects.

CANCERS. — We have now to consider the tumours
whose main structural peculiarity is that they contain
epithelium. The group is of great importance in that it
includes the terrible disease known as cancer. It is only
of late years that the term cancer has come to possess
any strictly scientific significance. In the early days of
pathological anatomy any tumour presenting malignant
characters was termed cancer, but in the present day
the term is restricted to tumours structurally resembling
imperfectly formed glands. In order to appreciate the
nature of cancer it will be advantageous for us to briefly
study the evolution of glands in general. I can only
attempt to give in abstract the large amount of evidence
I have accumulated, in order to show that cancers are
aberrant glandular formations, and may not inaptly be
defined as "biological weeds."

In complex animals the free surface of the body and
the alimentary canal is covered with cells differing from
those found in the underlying tissues. Such cells are
known collectively as epithelium, and though varying in
shape in different situations and under various conditions,
present identifying characters. This epithelium is prone

TUMOURS AND CANCERS.

243

to dip below the surface and invade the underlying
tissues. In their simplest form such downgrowths are
at first solid and club-shaped. Subsequently the central
cells liquefy whilst the peripheral ones arrange themselves
in a definite and regular order, so as to form a lining
membrane to the central chamber, or acinus. The por-
tion of the acinus near the surface from whence the
downgrowth originated is slightly narrowed and consti-
tutes the duct of the gland. This is one of the simplest

Fig. 122. — The microscopical appearance of an epithelial
Tumour (Cancer).

forms of gland, and from it any complex type may be
derived by buddings or outgrowths from the primary
epithelial germ (fig. 122). Secreting glands are arranged
by anatomists into groups according to their structure.
Physiologists give them specific names according to the
secretion furnished, such as mucus, sweat, milk, and the
like. Structurally they form two main groups, tubular
and racemose. The simple tubular gland is met with in
the intestine of man and in any mammals, whilst the
racemose variety is represented by sebaceous glands

244 E VOL UTION AND DISEASE.

usually attached to hairs, but may occur in situations
where hairs are not found normally. A number of tubu-
lar glands may be collected together and give rise to a
compound organ like the kidney ; in the same way a
collection of racemose glands may form a compound
organ, such as the salivary glands, or the poison glands
of snakes. In complex animals like vertebrata, glands
of peculiar character are restricted to definite parts of
the body. Thus sebaceous glands are almost peculiar to
the skin ; mucous glands to mucous membrane, and so
forth. Thus it comes to pass that there are frontier lines,
and as a rule these lines are not violated. For instance,
at the lips the territory of sebaceous glands ends and
that of mucous glands commences. At the termination
of the large bowel or rectum, a similar condition of things
exists, Lieberkiihn's follicles so characteristic of the
bowels terminate. Numerous frontier lines of this nature
exist in our bodies. Another fact of considerable im-
portance is that at birth an animal is not furnished with
all the glands it will require, the germs of many arise
in after-life and even subsequent to the years of active
growth. In the chapter on supernumerary mammae, it
was pointed out that in recesses of skin or mucous mem-
brane glands grow luxuriously, and to this may be added,
especially if the recess is moist.

In young individuals we find occasionally in connec-
tion with a functional gland, a tumour which when
examined microscopically displays all the features pecu-
liar to the gland with which it was connected ; the only
point in which it differs is that the adventitious mass is
impotent, that is, it cannot produce the secretion peculiar

TUMOURS AND CANCERS. 245

to the gland from which it arose. Such a tumour is
called an adenoma, and receives a specific name accord-
ing to the gland it resembles — sebaceous, mammary, renal,
hepatic, &c. Adenomata may attain enormous size and
weigh many pounds. As life advances the mimicry is
crude, the cells, instead of clothing the alveoli in a
regular manner, are tumbled together in confusion. Such
tumours are cancers ; they grow aimlessly, having no
function to keep them in subjection, and being poorly
supplied with blood vessels, undergo degenerative
changes, and the cells being dispersed over the body
may reproduce, in remote tissues and organs, secondary
tumours resembling the original cancer from which they
arose.

The glandular nature of cancers is further illustrated by
the fact that in their intimate structure they resemble
the glands in the immediate neighbourhood. Thus a
cancer of the lip resembles the cutaneous glands ; in the
liver it mimics the liver ; mammary cancer resembles im-
perfectly the secreting tissue of the breast, and so forth.

Many competent pathologists are of opinion that
cancers like the infective tumours are due to a micro-
organism ; this is very probable, although thus far inqui-
ries in this direction have not yet succeeded in identifying
such agents ; nor is cancer inoculable from one animal
to another. Should a bacterium be ultimately found as
the causative agent, it will in no way affect the arrange-
ment of cancers into a group apart from other tumours,
as they exhibit in such a marked degree the glandular
type of structure which alone serves to distinguish them
from sarcomata, with which they were frequently con-

246 E VOL UTION A ND DISEASE.

founded, nor is the distinction always made with the
accuracy that is essential in order to enable us to draw
conclusions from statistical tables as to the frequency of
cancer in comparison with other tumours.

Another circumstance which has never received full
attention is the great frequency of cancer in the white
races of mankind. A careful and extensive inquiry into
this question is very desirable, for we are grossly igno-
rant as to the occurrence of cancer among the natives of
colonies, even of India.

Again, cancer, using the term in the sense in which
it is employed throughout this chapter, is rare among
domesticated mammals, and rarer still among wild
mammals, even those living in captivity. To take one
example, cancer of the uterus, which is responsible for
the death of an appalling number of women every year
in England, is, as far as my inquiries have extended
among veterinarians, as well as from my own observations,
very rare in domesticated and wild mammals.

The cause of the extreme frequency of cancer in one
case, and its absence in another, may be in a measure
explained by certain peculiarities in structure and gland
distribution. The question is far too extensive to be
adequately considered in such a work as this, and
when I have pushed my investigations further I hope to
deal with it in a systematic manner.

Before leaving this subject it will be interesting to
describe a specimen illustrating the close relation which
exists between glands and cancer. In the section de-
voted to supernumerary mammae, I drew attention to the
relation existing between cutaneous recesses and glan-

TUMOURS AND CANCERS. 247

dular organs, and used this as an explanation of the
inordinate number of teats found within the pouch of
some opossums. It is a remarkable fact that one of the
most typical specimens of cancer that has come under
my notice in a wild animal occurred in a short-headed

Fig. 123.— The posterior half of a short-headed Phalanger. The pouch is
occupied by a cancer. (Nat. size.)

phalanger (Belidens breviceps) (fig. 123). In this case the
pouch was occupied by a tumour as big as the kernel
of a filbert, and when we remember that the parts of the
phalanger arc represented of natural size in the drawing,
the tumour was relatively large. In order to appreciate

248 EVOLUTION AND DISEASE.

the significance of this specimen, it should be studied in
conjunction with the remarks on the marsupial pouch
contained on p. 171, et seq.

SUMMARY. — To epitomise the facts briefly considered
in this chapter relative to tumours, from an evolutionist's
point of view, it may be stated that (excluding those
arising from accidental interference with the function of
secreting organs), some tumours arise as a result of
change of function in organs, rendering some part of
them useless ; others arise from the introduction into
an organism of bacteria which have by imperceptible
stages become slowly modified so as to be able to thrive
on or in animal bodies ; some, and these the most inno-
cent forms, arise as "sports" ; whilst the gland tumours and
cancers are due to the epithelial modifications which give
rise to secreting glands. It may be further stated that
animals other than man are liable to tumours, agreeing
in all respects with those which have been so long and
closely studied in him. Of all tumours occurring in the
lower animals, so far as the facts at our disposal show,
the commonest forms are the infective granulomata,
including sarcomata.

With respect to the cancer group there are some
very extraordinary facts which cannot be passed over
in silence. For instance, hair, teeth, feathers, glands
of all kinds and cancers arise on fundamentally the
same plan, — a downgrowth of epithelium into the
subjacent tissues ; it is certainly a suggestive fact that
abnormal irritation will produce a crop of hairs in an
unusual situation, as was shown in an early chapter,
and used to explain the curious hairs at the pyloric end

TUMOURS AND CANCERS. 249

of the darter's stomach. In the same way glands may
be induced to grow by irritation, moisture, and warmth
combined, and a continuance of such conditions will
often provoke an outbreak of cancer.

CHAPTER XII.

THE ZOOLOGICAL DISTRIBUTION OF DISEASE.

A LITTLE reflection soon convinces us that as the habits,
structure, and environment of animals differ very widely,
the manifestations of disease must also vary. Little,
however, has been done in the direction of studying the
zoological distribution of disease, and its consideration in
this work may be regarded as premature. Still it may
be useful to indicate the amount of information we
possess on the subject, and its scanty proportions should
serve as a stimulus for further inquiry in this direction,
and show how necessary it is that those who have had
opportunities of making observations on this subject
should record their experience. The matter is rendered
more difficult from the impossibility of obtaining positive
information concerning the diseases of wild animals in a
state of nature ; even the difficulty of obtaining their
bodies is illustrated, in the case of monkeys, by Dr.
Falconer in explaining the paucity of the remains of
quadrumana in geological strata. " When the monkey
pays the debt of nature his carcass falls to the ground,
and immediately becomes the prey of the numerous
predaceous scavengers of torrid regions, the hyaena and
wolf. So speedily does this occur, that in India, where
monkeys occupy large societies in mango groves around

ZOOLOGICAL DISTRIB UTION OF DISEASE, 2 5 1

villages, unmolested and cherished by man, the traces of
casualties among them are so rarely seen, that the simple
Hindoo believes that they bury their dead by night."

As far as my own investigations have extended I find,
excluding the affections known collectively as the acute
exanthemata (scarlet-fever, measles, small-pox, and the
like), that most diseases known in the human species
occur in mammals. A few affections rare in man are
frequent in mammals ; a limited number of diseases are
peculiar to mankind, whilst others occur only in the
lower animals. The inquiry is of some importance, for
it serves to show that certain diseases give rise to
changes so very different in animals of one class to
those of another class as to be described under a
different name, whilst two distinct affections may pro-
duce in animals belonging to different classes lesions of
such close naked-eye resemblance that they are fre-
quently confounded with each other. Such conditions
raise the all-important question, " How far is it probable
that many of the acute contagious fevers which affect
the human species occur in other animals, but producing
different symptoms receive another name ? " This is
illustrated in a remarkable manner by tuberculosis, a
disease of world-wide distribution. Writing concerning
that common manifestation of this disease, pulmonary
consumption, Hirsch, in his admirable Geographical and
Historical Pathology, states that it has held at all times
and among all civilized peoples a foremost place among
the national diseases, and that it extends over every
part of the habitable globe, and may be designated
ubiquitous in the strictest meaning of the term.

252 E VOL UTION AND DISEASE.

In man tubercle affects any organ and tissue of the
body, and is due to the entrance and multiplication
in the body of a micro-organism, the tubercle bacillus,
identified by the genius of Koch. Until the discovery
of this bacillus in tubercular lesions it was customary to
apply the term tubercle to almost any disease which was
characterized by the formation of nodules in the tissues,
thus the term came to have a generic rather than a
specific signification. Now that we have a pathological
criterion of tubercle, the term tuberculosis has a definite
meaning, and certain affections formerly included are
now known to be due to other causes, and numerous af-
fections formerly excluded now help to swell the list of
troubles due to this omnipresent micro-organism.
Among other mammals the disease has a peculiar
distribution ; it is very common among cattle under the
name of grape disease, or its German equivalent, Perl-
sucht. Monkeys living in confinement in this country
are occasionally attacked by it, but not so frequently as
was formerly supposed. Among grain-eating birds the
disease is a perfect scourge ; the flesh-eating birds are
not so liable to contract it, and are probably not in-
frequently attacked in consequence of devouring tuber-
cular grain-eating birds. In quadrumana and man the
disease runs a similar course, whilst in cattle the lesions
are so different, that it would be difficult to believe that
it is in any way related to the tuberculosis of Primates^
were it not for the existence of identical micro-
organisms, and this again applies equally to birds in
whom the lesions differ from those in man and cattle.
It is also extremely difficult to understand the immunity
of horses, tuberculosis being rare among Equidce.

ZOOLOGICAL DISTRIBUTION OF DISEASE. 253

Anthrax demonstrates in a remarkable manner why
disease should have a zoological distribution, for slight
physiological differences protect an animal against the
action of the anthrax bacillus, the morbific agent of the
ruinous splenic fever. This disease can easily be com-
municated to the ox, sheep, rabbit, and guinea pig by
injecting into the circulation a small quantity of blood
taken from an animal which has died of splenic fever.
Such injections are rapidly fatal. On the other hand, it
is difficult to inoculate the dog and pig, and fowls never
acquire the disease. The cause of the immunity of
fowls has been cleverly explained by Pasteur. It had
been ascertained that the anthrax bacillus does not
develop when subjected to a temperature of 440 Centi-
grade. The body temperature of a fowl is about 410 C,
whilst that of the horse is 377 C, the dog and
rabbit, 38°-39° C. On immersing the feet of a fowl in
cold water at a temperature of 250 Cent, so as to
reduce its body heat to $7° or 380, and then injecting
it with blood from a case of splenic fever, it was
found at the end of twenty-four hours dead, with its
blood filled with the bacteria of splenic fever. In another
experiment a hen was inoculated and subjected to the
cold-water treatment ; when the fever was at its height
the hen was taken out of the water, wrapped carefully
in cotton wool and placed in an oven at 350 C. In the
course of a few hours it was restored to health. Hens
killed after being experimented upon in this way exhibit
no trace of the bacteria in their blood.

Under ordinary conditions a frog cannot be killed by
injection of anthrax cultures, but if, after inoculating a

254 E VOL UTION AND DISEASE.

frog, its temperature be raised to 360 by carefully warm-
ing the water in which the frog is placed it will succumb.

Such facts as these throw great light upon the re-
striction of diseases to particular groups of animals, and
it explains the readiness with, which the tubercle bacillus
flourishes in man, for experimentally it has been found
to develop most luxuriously at a temperature of 370 to
390 Cent. This would serve to explain the rarity of
tubercular lesions in cold-blooded animals.

Up to the present time tubercle has only twice been
recorded in reptiles. The first specimen I observed in a
large Python {Python molurus). The nodules in the
various organs contained bacilli in large numbers. In
this instance I am of opinion that the reptile contracted
the disease from eating tubercular birds. Mr. W. K.
Sibley reported a case of tuberculosis which he found in
a snake ( Tropidonotns natrix). As the tubercle bacillus
flourishes at a temperature of 37°-39° Cent, it at first
seems difficult to account for tubercular lesions in snakes.
In a valuable series of observations made by Mr.
Forbes1 on an incubating python at the Zoological
Gardens, the temperature of the male was found to
vary from 28°-30° C. ; the temperature of the female
under the same conditions of external warmth was
29°-3i*6° C. These observations were made in July,
and the greatest temperature recorded between the folds
of the male was 320 C. ; for the female, 33*8° C. It is
also of interest to find that the temperature of the
pythons, taken between the folds, was higher than the
surrounding air, sometimes as much as 6*4° C. in the
1 " Collected Papers, 1885," p. 285.

ZOOLOGICAL DISTRIBUTION OF DISEASE, 255

male, and 9*2° C. in the female. Valenciennes, in some
similar observations conducted in 1841 in the Jardin des
Plantes, Paris, found the temperature of the incubating
python as high as 41*5° C.

The observations are of interest, for it indicates the
occasional possibility of the python's body temperature
rising sufficiently high to favour the development of the
tubercle bacillus, and as the python's temperature
appears to be slightly raised above that of the surround-
ing media, it would come very close to the required
370 C. when the snake was exposed to the full glare
of a hot midsummer sun.

Under such conditions a snake when exposed to
tubercular food resembles a European when exposed to
the dangers of malaria on an unhealthy tropical coast.
Vagary, in the liability to or immunity from a special
disease among closely allied families of mammals, is
exhibited in other than infectious diseases. Take, for
instance, gout. No one has ever clearly shown that
this affection occurs in animals other than man. It is
stated that parrots are liable to gout, but this question
assumes a different aspect when studied in relation with
an interesting disease of the hog known as guanin
gout.

In man, apart from the pain and disturbance induced
by an attack of gout, we find deposited in the less vas-
cular parts, such as cartilage, tendinous and fibrous
tissues, masses of a crystalline nitrogenous substance
known as urate of soda. The crystals are needle-shaped,
and in severe cases form collections, familiar to those
who have very gouty relations, as chalk-stones, These

256 EVOLUTION AND DISEASE.

deposits constitute the most constant pathological con-
dition in gout.

There is a parasitic affection common in swine
(and not infrequently found in man), to which atten-
tion has of late years been largely directed, known
as trichinosis. The parasite Trichina spiralis when
hatched finds its way into the voluntary muscles of
man and the pig, there becomes encysted, and in due
course is surrounded by calcareous particles. The
encysted worms are visible to the naked eye in cut
sections of muscle as small dots. In 1866 Virchow
detected in a piece of ham some small white concretions
which were regarded as trichinae ; but on examination
were found to be of crystalline structure, and to furnish
the reaction for guanin, a crystalline nitrogenous body
resulting from chemical changes in animal tissues, first
discovered by Unger in Peruvian guano.

Guanin seems to be very widely distributed in the
animal kingdom ; it occurs in fish, the excrement of
spiders, in the pond mussel, the pancreas and liver of
the horse, and the skins of frogs and lizards. It responds
to easily applied chemical tests. The interest of guanin
for us centres itself in the fact that it produces lesions
identical in their pathological anatomy with gouty
lesions, that is to say, it becomes deposited in cartilage
and fibrous tissue, forming deposits exactly resembling
the urate of soda deposits in man. Such resemblance is
not confined to naked-eye characters, but extends also
to the microscopic details as is shown in the drawing
(fig. 124), taken from Dr. Mendelson's admirable contri-
bution to this interesting subject. When examined in

ZOOLOGICAL DISTRIBUTION OF DISEASE. 257

thin sections under the microscope, the affected tissues
are found impregnated with feathery tufts of crystals,
which respond to the ordinary tests for guanin.

From the hog we may turn to parrots, which frequently
present in their subcutaneous tissues, cartilages, skin,
muscles, and intestines, nodules, which, in their naked-
eye characters, are indistinguishable from gouty nodules

Fig. 124. — Microscopic section of the articular cartilage of a
pig's knee-joint affected with guanin gout. (After Men-
delson.)

as seen in man. Indeed such deposits have been de-
scribed as gout, not only in parrots, but in fowls, falcons,
ostriches, &c. In the drawing (fig. 125), the foot of a
parrot is represented with characteristic nodules, and
when cut into, the centre of such nodules is occupied by
a white mortary-looking substance in every way resem-
bling that known as chalk (urate of soda) in human
gout. The analogy goes beyond mere naked-eye cha-

18

258 E VOL UTION AND DISEASE,

racters, for these deposits consist of a crystalline sub-
stance resembling guanin and urate of soda, and respond-
ing to the murexide test. Guanin and urate of soda are
closely allied bodies, and as far as I can ascertain it is no
easy task to decide between them. Until the subject
has been more thoroughly investigated it will remain
uncertain whether the nodular lesions of parrots and
other birds are really of the same nature as gout in man,
or allied to guanin gout of the hog, and it is very

Fig. 125. — The feet of a Parrot with supposed gouty nodules.

probable that some case of supposed uratic gout in man
may be guanin gout.

This confounding of avian and human gout, and
trichinosis with the guanin gout of the hog, is easy to com-
prehend, as it requires chemical cunning to complete the
identity, but we must remember that true gout was
formerly, and is now, often confounded with a disease
of the articular ends of bone, which, though often referred
to as rheumatic gout, has no relation with gout, except
that both diseases are distinguished by nodules on the

ZOOLOGICAL DISTRIBUTION OF DISEASE. 259

joint ends of bones. Rheumatic gout, or, as it is now
more appropriately termed, osteo -arthritis, is a disease
of great interest, for it has a wide zoological distribution,
and has even been detected in the joints of the extinct
Irish Elk (Megaceros hibernicus). This disease is cha-
racterized by enlargement of the ends of bone, destruc-
tion of the cartilage and synovial membrane of joints,
with calcification of the ligaments. It is no respecter of
persons ; young and old, rich and poor, high and low,
suffer from it. I have detected the disease in the joints
of a snake's backbone, in birds of various kinds, including
the neck of an ostrich, in cats, dogs, leopards, lions,
tigers, horses especially, oxen, sheep, kangaroos, bears,
and many others. It is as far as I can ascertain the
most widely diffused of all the bone diseases to which
vertebrated animals are liable.

In order to show the care necessary in such generali-
zations we may take the recent additions to our know-
ledge of such a long recognized disease as cretinism.
All visitors to Switzerland, the Rhone and Aosta valleys,
are familiar with what is termed endemic goitre and
endemic cretinism. The leading features of cretinism
are briefly these : — The disease" is congenital, and dis-
plays itself in unnatural shortness of the trunk and
limbs, malformations of the skull (as a rule it is unusually
small), and idiocy, combined with abnormal conditions
of the thyroid body. Cretins, as those affected with
this disease are called, present a characteristic appear-
ance ; a typical cretin is represented in fig. 126, taken
from the admirable report, compiled by a Commission,
created by the King of Sardinia, to inquire into this

260

EVOLUTION AND DISEASE.

disease, published at Turin, 1848. The boy is described
as being twenty years old, is one metre in height; he is
deaf and dumb, not comprehending any sign, and spends
his time in turning the small baton between his fingers ;
the intellectual faculties are practically wanting.

Fig. 126. — An endemic Cretin twenty years old : one metre
high. (From the Sardinian Report.)

Until recently it was little thought that cretinism

occurs in our country, although it was known that goitre

is endemic in certain districts. In 1871 Dr. Hilton

Fagge x clearly showed that cretins occurred in England

1 " Medico-Chir. Trans.," 1871.

ZOOLOGICAL DISTRIBUTION OF DISEASE. 261

by publishing descriptions of undoubted examples. One
of Fagge's specimens is drawn in fig. 127, for compari-
son with the endemic cretin on the opposite page. This
boy is sixteen years and a half old, rather less than
a metre in height, and could understand a good deal
of what was said to him, ask for what he wanted, and
the parents could understand what he said.

Fig. 127.— A sporadic English Cretin, rather less than a
metre in height, and sixteen years of age. (After Hilton
Fagge.)

In subsequent investigations Hilton Fagge showed
that, contrary to what he had originally stated, the
thyroid body in some of these children was abnormally
large.

Since the attention of medical men has been drawn

262 E VOL UTION AND DISEASE.

to this matter, a large number of cretins has been
detected in England, and many have been critically
observed, and detailed accounts of their anatomy placed
on record, which remove any doubts as to the identity
of the English sporadic with the Alpine endemic cretin.
It is also significant that since careful accounts of the
leading features of the disease have been circulated,
cretins have been recognized in many parts of England,
and instead of being limited to the small village of
Chiselborough, in Somersetshire, it turns out to be a
far from infrequent condition in many large towns,

Fig. 128. — A Calf-cretin. Length of trunk, thirty centimetres.
Length of limbs, five centimetres.

including London. Cretinism is not confined to the
human species. In 1877 H. Miiller described a cre-
tinous calf, and subsequently Eberth was able, in a
monograph on this subject, to refer to cases which had
been reported in the human subject under different
names. Thus far cretinism has been recorded several
times in the calf, in sheep, and dogs, and the careful
accounts of the anatomy of the specimens leave no
room for doubt as to its identity with the cretinism of
man. Animal cretins occur not only in regions where
the disease is endemic in man, but also in England,

ZOOLOGICAL DISTRIBUTION OF DISEASE. 263

and a typical specimen of a calf-cretin which came under
my observation is sketched in fig. 128. This calf ex-
hibits in a striking manner the leading features of the
affection. For instance, its trunk only measures thirty
centimetres in length, and the legs are five centimetres
long : the head arrests attention on account of its
shortness, resembling strongly the head of a pug-dog.
Cretinism is not unknown among dogs ; the museum of
the Royal College of Surgeons possesses an excellent
specimen in a foetal puppy.

The calf-cretin is of interest especially with regard
to the undue shortness of the head and limbs, for it
has been suggested that the pug-dogs, which are such
favourite pets with many ladies, are cretins, and that
by selected breeding a race of cretinous dogs has been
produced. It has also been suggested that the short-
legged spitze or Dachshund is possibly cretinous. This
however is problematical ; the spitze must be a very
old variety of dog. Dr. Blackmore showed me in the
Salisbury museum some arm bones which clearly
belonged to a dog, and they were curved, or bowed like
the bones of a spitze ; the curves were certainly not due
to rickety changes. These bones were obtained among
others from excavations made in investigating the pit-
dwellings, admirable models of which are exhibited ir
the same museum.

Dr. Parrot has made a careful study of cretinism5
and allied diseases of the skeletons, and goes so far as
to believe that the ancient Egyptians were acquainted
with cretinism, and even had a cretinous god, Ptah,
which was particularly venerated at Memphis. An

264

EVOLUTION AND DISEASE.

examination of the models and figures of this god
preserved in the Egyptian galleries of the British
Museum shows, that in some of the figures Ptah is
represented as a big-bellied, squat divinity, with short

Fig. 129.— The Egyptian God Ptah.

limbs, not unlike a cretin (fig. 129), in others he is
represented as of noble figure, the type of lordly bear-
ing and majesty. The notion that the dwarf models of
Ptah represent cretins is very speculative and improb-
able.

ZOOLOGICAL DISTRIBUTION 01 DISEASE. 265

Cretinism has a wider distribution, geographically and
zoologically, than we were aware even twenty years ago,
and it is not unreasonable to suppose that careful
inquiry will show that many other similar diseases,
supposed to be rare or confined to certain districts, are
as a matter of fact commoner than we suspect.

Rickets is another example of a disease having a
wide zoological distribution. The leading characters
of rickets are, undue softness of bone in young animals,
associated with catarrh of the stomach and intestines,
depending upon, or induced by, unsuitable food and
unfavourable surroundings. The softness of the dif-
ferent parts of the skeleton gives rise to a complicated
series of deformities, some of which are incompatible
with life.

For a long period rickets was supposed to be re-
stricted in its distribution to England, and is, to this
day, often referred to as the English disease. Now, we
know that rickets occurs all over Europe and in other
parts of the world, and recently I had an opportunity
of examining portions of a rickety skull which were
obtained from Lamoo, an island near Zanzibar ; it was
found buried in sand, on the site of an old battle-field,
by Dr. Briscoe.

Rickets is so very common in man that a priori we
should expect it to be frequent in other members of
man's class. On this head we possess but scanty infor-
mation. Mammalian skeletons have been preserved in
museums, and erroneously labelled ; we now know that
most of them are rickety skeletons, for the systematic
inquiry which I have conducted into the diseases of

266 EVOLUTION AND DISEASE.

mammals dying in the Zoological Society's Gardens has
established the fact that rickets is a very common
disease. Indeed, so frequent is it among quadrumana
that half the monkeys and lemurs brought to this
country die rickety. This disease affects, besides men,
chimpanzees, orangs, gibbons, macaques, baboons, capu-
chins, squirrel and spider monkeys, and lemurs. Among
carnivora we find it in lions, tigers, hyaenas, bears of all
kinds, and in the domestic cat, the dog, fox, raccoon,
and seal. Among ruminants it occurs in deer, sheep,
and goats. In rodents, the beaver, porcupine, rabbit,
and coypu rat are affected by it. Among marsupials,
the kangaroos, phalangers, and opossums are most
liable. In birds it has been found in the emu, ostrich,
rhea, and pigeon.

All who have studied the disease are of opinion that
it is due to deficiency of lime salts with the food. Mr.
T. D. A. Cockerell has argued, and I think on good
grounds, that the scalariform shells of some mollusks
may be regarded as arising from the same cause as
rickets in vertebrates. Thus rickets has an exceedingly
wide zoological distribution.

Those singular productions known as cutaneous horns
are interesting in connection with the subject matter of
this chapter. In the Introduction some remarks were
made concerning such horns in relation to physiological
types, but the question was by no means exhausted.

Man, in common with many mammals, possesses
glands in the skin, which secrete an unctuous material
known as sebum. Such glands are termed sebaceous,
and are more abundant in certain regions of the skin,

ZOOLOGICAL DISTRIBUTION OF DISEASE. 267

whilst in other parts they are absent. Not infrequently
changes occur in the interior of such glands causing the
sebum to be retained, and the acini of the glands

Fig. 130. — A Mouse with a cutaneous horn arising in a seba-
ceous cyst.

becoming dilated by the accumulated secretion forms
a perceptible swelling known as a sebaceous cyst. At
times the secretion bursts through
the cyst-wall in the form of a
dark-coloured corneous substance,
which increasing in length, by ad-
ditions at the base, may attain a
length of many centimetres. Such
a horn is shown in fig. 1 30, grow-
ing from a cyst on the back of a mouse, and in order to
show its relation to the sebaceous cyst, the horn is shown
in vertical section in fig. 131.

Cutaneous horns, in their naked eye and even micro-

Fig. 131. — The horn and
cyst in section.

268

EVOLUTION AND DISEASE.

scopical characters agreeing with those formed in seba-
ceous cysts, may arise from the transformation of warts,
and so closely do the two forms mimic each other that
it is not easy to distinguish between them. Thus to
all outward appearance the horn of the mouse in fig.
132 is identical in its structure and naked-eye characters
to that growing from the back of the mouse ; but I

Fig. 132. — The head of a Mouse with a cutaneous horn
arising from a wart. (Mus. Royal College of Sur-
geons. )

have had ample opportunity of demonstrating its origin
in a wart. These specimens illustrate how necessary it
is to exercise care in discriminating between patho-
logical productions apparently r.esembling one another.
Cutaneous horns are very common in man, and have
been known to attain a length of fifteen centimetres ;
they were formerly regarded by ignorant persons as

ZOOLOGICAL DLSTRIBUTLON OF DISEASE. 269

objects for veneration. In addition to the modes of
origin mentioned, horns may arise from the overgrowth
of nails, and also in the scars of burns ; these have no
connection with our present study.

Horns arising in sebaceous cysts, or from warts, have
been recorded in man, oxen, sheep (fig. 133), goats, dogs,

Fig. 133. — The head of a Sheep with a large wart-horn on its

head.

and hare. I have recently seen one growing near the
hock of an eland : in birds they have been recorded in the
parrot, greenfinch, linnet, canary, and oyster-catcher.
The museum of the Royal College of Surgeons, London,
contains an admirable collection of such horns, one of
them which grew from the flank of a ram, and from its
structure is clearly a wart-horn, is the largest on record,

270

EVOLUTION AND DISEASE.

it measures in length nearly one metre, and is twenty-
eight centimetres in circumference at the base.

In birds cutaneous horns grow very rapidly, and are
shed with each moult : in the course of three months
such horns have been known to attain a length of seven

Fig. 134. — The head and leg ot a Thrush : the horns on the
leg arise from warts, that on the head from a sebaceous
cyst.

and even ten centimetres, and to be reproduced for
several consecutive years. An excellent specimen of this
form is shown on the thrush (fig. 134). This bird was
observed by Mr. Roger Williams : it had three wart horns
on the legs, and upon its head a sebaceous cyst with a

ZOOLOGICAL DISTRIBUTION OF DISEASE. 271

cutaneous horn just commencing to protrude from it.
The bird is interesting as illustrating the two modes
by which these horns arise. The statement that birds
have no sebaceous glands except the uropygial gland
requires modification.

Cutaneous horns, due to the hardening of secretion,
occur as normal productions in several animals. Thus
the patch of spines on the fore-arm of hapalemur
(H. griseus) and on the fore-arm of the ring-tailed lemur
(E catta), are of this character. Even more curious are
the wart-like processes formed on the skin of the thigh
in lizards, from the hardening of the secretion furnished
by the femoral glands ; this hardened secretion enables
the male to clasp the female.

Among the few diseases restricted to mankind must
be mentioned leprosy. Elephantiasis grczcorum, as true
leprosy is called, is a very remarkable affection : it has
never been seen in any animal other than man, although
determined attempts have been made to communicate it
to rabbits, monkeys, cats, dogs, and fowls. Neisser
claims to have successfully produced leprous tubercles in
rabbits and dogs, but the results have not been confirmed
by others who have repeated his experiments. The
latest contribution to this subject is by Dr. Beaven Rake,
Superintendent of the Trinidad Leper Asylum. The
possibility of causing leprosy by inoculation has occu-
pied his attention during four years. He has performed
fifty-four experiments, some being the direct introduction
of the diseased tissues from man into the subcutaneous
tissues of guinea-pigs and rabbits, and by feeding fowls
on leprous material. In all cases the experiments failed
to produce constitutional leprosy.

272

EVOLUTION AND DISEASE,

Leprosy is distinguished anatomically by the forma-
tion of nodules or tubercles in the skin, mucous mem-
branes and underlying tissues. When the skin is affected
the hands, feet, and face are most frequently attacked.
The nodules commence as red spots in the skin, which
become gradually of a blue tint, then brown : the sub-
jacent tissue becomes thick and hard. The tubercle

Fig. 135. — The face of a Leper. (After Ziegler. )

increases and forms a sub-globular, soft, pale-coloured
prominence, which, when knocked or rubbed, may
ulcerate. Leprous ulcers are commonest on the inside
of the nose, on the conjunctiva, and mucous membrane
of the larynx. When the nodules form on nerve sheaths
anaesthesia is produced.

Microscopically, leprosy nodules are found to be made

ZOOLOGICAL DISTRIBUTION OF DISEASE. 273

up of round cells, with larger ones known as leprous cells
intermixed. When suitably stained the nodules are
found to contain enormous numbers of bacilli, many of
which crowd the large leprous cells.

It should be borne in mind that in the Mosaic books the
term leprosy is used in a generic sense, for it included
many forms of curable skin disease under this name, as a
careful perusal of that very interesting chapter (Leviticus
xiii.) will clearly show. It was only by isolating and
carefully watching the initial red spots that a confident
opinion could be expressed. The evidence furnished by
the same chapter indicates that even when the disease
was well pronounced, other affections than that which
we now recognize as Elephantiasis grcecorum were classed
together under the term leprosy, but leprosy in animals
is not mentioned once in the whole Pentateuch.

The means described in the Mosaic books of isola-
ting suspected cases, and allowing time to settle the
diagnosis, are admirable. Even in these days of
advanced civilization well-trained and thoughtful
physicians find that the isolation of infectious cases
is the best preventative treatment known. It is more
than probable that this old-established custom explains
the present restriction of leprosy to definite regions, such
as Norway, Finland, and the Baltic provinces of Russia,
Central and Southern America, South Africa, and
Asia.

As far as our knowledge of the zoological distribution
of disease at present extends there are two affections
peculiar to mankind, viz., true leprosy and syphilis. Even
mental affections occur in animals : we have already

19

274 E VOL UTION AND DISEASE.

seen that the form of idiocy known as cretinism is
recognized in calves, dogs, and lambs. Horses are cer-
tainly known to suffer attacks of acute mania, and dogs
become demented and are occasionally imbecile, not
recognizing their master from other persons, and forgetting
their own names. From being keen at sport, they fail to
recognize a hare or partridge, even blunder over them in
a field and take no notice of the game when it rises.
Convulsions caused by troubles during dentition are well
recognized in dogs, as well as a nerve affection, closely
similar to epilepsy. The remarkable affection of human
beings termed locomotor ataxy, and the singular St.
Vitus' dance, or chorea, occur in dogs.

It will, perhaps, be desirable to conclude this chapter
by a brief consideration of the strange disease known as
ElepJiantiasis arabum, the zoological and geographical
distribution of which is limited in an interesting manner
by mosquitoes.

In India, China, Egypt, Arabia, the West Indies, and
Australia this disease is endemic : it is characterized by
enlargement of the parts affected, which may be the
arms, legs, and other parts of the body. The skin cover-
ing the part becomes enormously thickened, forms hard
masses and folds obscuring the toes when the legs are
affected, producing an appearance not unlike an
elephant's leg. One of the most remarkable features in
this extraordinary disease is that very frequently the
blood of individuals with elephantiasis swarms with
minute haematozoa, named by Lewis Filaria sanguinis
hominis ; and recent researches go to show that the
presence of filaria in the blood in association with

ZOOLOGICAL DISTRIBUTION OF DISEASE. 275

elephantiasis is so frequent that they are manifestations
of the same disease.

According to the admirable researches of Dr. Manson
the chief facts connected with this disease are the
following : —

The adult worm is probably taken into the alimentary
canal of man in drinking-water. From the stomach
it bores its way into the thoracic duct or some
lymphatic vessel, and is subsequently joined by one of
the opposite sex. Here they may live for years, dis-
charging their embryos into the lymph stream, to become
distributed by the blood current over the body.

One of the most remarkable phenomena connected
with filarial disease is that the embryos disappear from,
and reappear in, the general blood stream at certain
periods of the day. Under ordinary conditions the blood
of an affected individual presents no filarial between the
hours of nine a.m. and six p.m. ; after six p.m. they begin
to make their appearance and increase in numbers until
midnight, at which hour as many as 260 filaria have
been counted in a single drop of blood : from this hour
they gradually diminish in numbers and at nine o'clock
in the morning they cannot be detected in the blood.
During the night, and whilst the filarial migration is at
its height, mosquitoes visit the body, and Manson has
identified the female, a particular variety of Ciilex which,
by the structure of its oral appendage, abstracts blood
from the filariated individual, be it man or beast. As
the culex selects eight o'clock in the evening as the feed-
ing hour it necessarily follows that the embryo filariae
are taken into the stomach of the mosquito, and Manson

276 E VOL C/2Y0JV AND DISEASE.

by a series of well-planned experiments, has demon-
strated that this insect acts as the intermediate host of
the parasite. During the following four or six days the
embryos complete their metamorphosis, and the friendly
mosquito has completed its life cycle and dies, and its
body probably falls into the water in which the eggs were
deposited. The filaria by this time has developed so far
that it is capable of living independently of the mosquito,
and it seems probable that it remains in the water until
it is captured by some animal in search of food, or
swallowed by man, thus enabling it to complete its
development.

These facts indicate conclusively that this disease
is spread and, in all probability, maintained by mos-
quitoes, and the geographical distribution of the disease
is coincident with that of culex. In this connection it is
a fact of some importance to remember that filariae occur
in other animals as well as in man. Manson states that
half the dogs in China, all the magpies, one-third of the
crows, and many other birds harbour similar haematozoa
in prodigious numbers ; and in South China where the
filarial disease is endemic, if the blood of one thousand
natives, selected indiscriminately, be examined some
time between sunset and sunrise, in about one hundred
the Filaria sanguinis hominis will be discovered.

The point of interest to us in connection with this
disease is that though the filariae occur in dogs, magpies,
and I have detected them in the blood of macaque
monkeys, the enormous enlargement of the legs and
other parts of the body, which is one of the chief cha-
racters of the disease in man, has not been recorded in

ZOOLOGICAL DISTRIBUTION OF DISEASE. 277

these animals. This, again, is another example of the
same cause producing varying effects in different species
of animals, of which we have had several instances in
this chapter, and I can only repeat that if this subject
were carefully and broadly investigated, many diseases
supposed to be distinct in man and the lower animals
would be found to depend upon the same cause.

INDICES

INDEX TO AUTHORS CITED.

Ahlfeld, 144
Albers, 144
Albrecht, 71, 11 1
Alston, 155
Altum, 155
Aristotle, 31

Baker, M., 132
Balfour, 41
Bardeleben, 161
Barth, 170
Bartlett, A. D., 205
Bell, 195
Bidder, 22
Blackmore, 263
Blumenbach, 206
Briscoe, 265
Bruce, M., 167

Champneys, 171
Cheselden, 202
Cicero, 31
Clarke, 118
Cleland, 130
Cockerell, 266
Cohnheim, 240, 241
Collins, 141

Cuvier, 196, 206

Darwin, 24, 32, 45, 61, 98, 139,

148, 150, 167
Deen, Van, 126
Devey, 193
Descartes, 43
Duges, 117
Dumas, Blanche, 130

Eberth, 262
Egremont, Lord, 155
Eschricht, 209
Eve, 72

Fagge, Hilton, 260
Falconer, 250
Flower, 10
Forbes, n, 254
Forster, 144
Freeman, H. W., 190

Garrod, 26
Gaskell, 51
Gegenbaur, 99, 135
Goethe, 139

280

INDICES.

Godsir, 206, 209
Graaf, 42
Giinther, 29
Gurlt, 127

Haeckel, 115
Haswell, no
Hensel, 159
Hensinger, 84
Hewitt, 150
Hilaire, 25, 120, 144
Hirsch, 251
His, 81, 180, 183, 192
Howes, 89, 139
Humphry, 15
Hunter, 17, 21, in, 153
Hyrtl, 177

Kleinenberg, 117
Koch, 252
Kowalevski, 49

Lamprey, 197
Lewis, 274
Luschka, 96

Macalister, 196
Malkmus, 172
Manson, 275
Matthews, 46
Mendelson, 257
Milne-Edwards, 139
Miiller, 262
Murray, Jardine, no

Paget, Stephen, 242

Paley, 171

Parker, 100

Parrot, 263

Pasteur, 224, 225,253

Pliny, 31

Pitt, Percival, 97

Potton, 193

Rake, Beavan, 271
Rauber, 121
Recklinghausen, 57
Rengger, 36

Salvin, 185
Schmidt, 182
Sclater, 166
Sedillot, 98
Shattock, 90, 100
Sibley, W. K., 254
Spencer, 42
Sterling, 22
Stewart, 90

Tiedemann, 26, 103

Tomes, Chas. S., 208, 209, 212

Traquair, 186

Treves, 68

Tuckerman, 128

Turner, 209

Unger, 256

Valenciennes, 255
Virchow, 23, 54, 56, 256

Nasymth, 206

Ogle, 136
Oppian, 31
O'Reilly, 197
Owen, 65, 206

Wallace, 33, 61
Werfer, 197
Windle, 193
Wolff, 143
Woodward, 30
Wyman, 33

INDICES.

281

INDEX TO ANIMALS.

A ices machlis, 5 106, 156
Amblyopsis, 33
Amblystoma, 1 19
Amoeba, 214
Amphioxus, 49
A?itilocarpa americana, 1 1
Ascidians, 39, 49
Astarte, 31

As terms equestris, 103
A teles paniscus, 15, 159
Aye-aye, 202

Babirussa, 204
Baboon, 19

Belideus breviceps, 247
Beluga leucas, 89
Bos indicus, 170
Bufo vulgaris, 1 1 1
Bunting, 157
Bustard, 157, 233

Cce cilia compressicauda, 42
Callithrix, 159
Camel, 19

Capreolus caprasa, 156
Cariacus virgi?iianum, 157
Cavicornia, 10
Ceratodus, 42
Cercopithecus pat as, 1 69
Cervulus, 146
Cervus canadensis, 69
Cervus elephas, 157
Cetaceans, 60, 89
Chcetodon, 195
Chaffinch, 157
Cheiro?nys, 164
Chimpanzee, 99, 136
Chirogaleus coquereli, 163
Cotinga, 157

Crystallodes rigidum, 1 1 5
Cuckoo, 157
Culex, 275

Dace, 4
Darter, 26

Didelphys cancrivora, 172
Didelphys virginianum, 172
Dove, 114
Dorking-fowl, 112
Drake, 130

Dromceus novce-hollandia, 104,
232

Echidna, 137, 163
Elasmobranch fish, 76
Elephant, 204
Emu, 104, 232
Equidae, 16, 252

Filaria sanguinis hominis, 276

Fierasfer, 29

Fratercula cor?iiculata, 1 1

Gibbon, 66, 99
Goat, 20, 84
Gorilla, 19, 99, 145
Grampus, 209
Ground parrot, 35

Hapalemur g riseus, 1 64
Hcematopus osiralegus, 10
Hare, 189
Hatteria, 43

Himalayan monaul, 104
Hipparion, 159
Hircus, 178
Hircus thebaicus, 85
Horse, 16

282

INDICES.

Hylobates leuciscus, 66, 109

Ichthyosauri!, 158

Labyrinthodonta, 43
Lacerta viridis, 1 24
Lamellibranch, 28
Lemurs, 136
Lemur catta, 163,271
Lemur macaco, 163, 165
Lemur mongoz, 163
Lepidosteus, 37, 42
Lizard, 124
Lobster, rock, 139
Lophophorus impeyanus, 104
Lumbricus terrestris, 116

Macaque, 99

Macacas sinicus, 168

Macropus, 193

Margarita margaritifera, 29

Marmoset, 159

Megaceros hibcrnicus, 69, 259

Meleagrina, 31

Menobranchus, 97

Menopoma, 97

Mesoplodon layardi, 209

Metazoa, 215

Microcebus smithi, 163

Mole, 32

Monkeys, American, 136

Moose, 5, 107

Mot-mots, 185

Mustelus, 42

Mycetes, 159

Narwhal, 60

Octopus, 4
Opossum, 172
Orang, 99, 136, 188

Orca, 209

Or?iithorhynchus, 60, 137, 145,

163
Ostrich, 19
Otaria gillespii, 89
Otarida;, 89
Otis tarda, 233
Oyster, 31
Oyster-catcher, 10

Palinurus, 139
Parrot, 59, 258
Patas monkey, 169
Peacock, 157
Pea-crab, 31
Pea-hen, 149
Pearl oyster, 29
Pectuncutus, 31
Pelican, 157
Phalanger, 144
Pheasants, 157
PhocidcE, 89
Pithecus satanus, 145
Pinnotheres, 30
Plotus anhinga, 26
Polish fowl, 23
Primates, 252
Prongbuck, 11
Pterodactyl, 144
Puffin, 11
Python molurus, 211, 254

yvVz;z# esculent a, 126
Rana palustris, 128
Rana temp or aria, 112
Rangifer, 156
Rhinoceros, 9
Roedeer, 7

Seabright bantam, 150
Sea gull, 17

INDICES.

283

Seal, 89, 145

Sepia, 4

Shark, 76, 121

Sheep, 27

Siamang gibbon, 145

Silkworm, 224

Skate, 46

Sloth, 57

Sphcnodon, 43

Spider monkey, 159

Squirrel, flying, 144

Star-fish, 103

Stringops habroptilus, 35

Syphonophora, 116

Tar sins spectrum, 164
Trichina spiralis, 256
Tropidonotus natrix, 254
Trout, tailless, 186

Varanus, 42
Viper, 62

Wapiti deer, 69
Wombat, 202

Zebu, 170

INDEX TO SUBJECTS.

Actinomycosis, 235
^Egipans, 56,90, 177
Aftershaft, 104
Allantois, 40
Anthrax, 253
Antitragus, 177
Antlers, 5, 107, 155
Astragalus, 100
Atavism, 134

„ Spurious, 143
Auricle, 63, 79, 83, 177
Auricular fistula, 178
Autosite, 122

Bacteria, 2T3

„ pathogenic, 213
Big-toe, 14
Bifid tail, 124
Bone, 5

Bone of attachment, 211
Branchia, 80
Branchial fistula, 81
Bullets in tusks, 208

Caecum, gibbon, 66

Caecum, horse, 67
„ man, 65
„ tiger, 66
„ rhinoceros, 68

Calamus, 104

Callosites, 19

Cancer, 242

Cauda helicis, 177

Circumcision, 184

Cleft-palate, 189

Commensalism, 29

Conjunctiva, hair on, 141

Corns, 19

Cretinism, 259

Cretins, 194

Cysts, 228

Defects, acquired, 176
„ transmitted, 176

Devil, 57

Diana of Ephesus, 162

Dichotomy, artificial, 115
„ limbs, 102

„ tail, 124

„ trunk, 119

284

INDICES.

Dichotomy in worms. 116

Disuse, 14, 35

Ducts, functionless, 231

Elephantiasis arabum, 274
„ graecorum, 271

Fauns, 56, 91
Feathers, 105
Fever, 213
Fermentation, 224
Fibula, 97
Fistula, auricular, 177

„ branchial, 81
Flacherie, 224
Fracture, Pott's, 96
Functionless ducts, 231

Giant-cells, 238
Gill-slits, 80
Gizzard, 17

Gods of the woods, 56
Gout, Guanin, 255

„ uratic, 255

„ in parrots, 257
Guttural pouches, 96

Hare-lip, 189
Hearing, 32
Horned men, 197
Horns, 9, 266
Hypertrophy, 17
Hyporachis, 104

Impaction theory, 132
Infective granulomata, 233
Inflammation, 213
Inherited defects, 188
Irritation, 21

Lalloo, 123

Lanugo, 137

Leaves, metamorphosis of, 139

Legs, supernumerary, 127

Leprosy, 271

Leucocytes, 215

Levator costse muscle, 135

Lobule of pinna, 177

Malformations, 188
Malleoli, 99
Mamma, 162

abdominal, 168

axillary, 171

brachial, 165

inguinal, 163

supernumerary, 167

thoracic, 168
Meningocele, 23
Micrococci, 214
Micro-organisms, 217
Milk-glands, 162
Muscle agitator caudae, 53
,, depressor „ 53
,, levator, 52
,, levator costae, 135

Odontome, 7$
Oesophageal collar, 48
Opercula, 64

Organisms, pathogenic, 213
Osteo-dentine, 208
Ovaries, 149
Overgrowth, 20

„ of beaks, 58

„ claws, 57

„ hoofs, 20

„ nails, 57

„ spurs, 22

„ teeth, 199

„ from disuse, 57

Oviducts, 45, 64

INDICES.

285

Parasite, 122

Patagium, 144

Patella, 17

Pigment, 3

Pineal body, 50
„ eye, 42

Pinna, 176
„ of whale, 89

Polydactyly in horses, 159
,, in man, 159

„ monkeys, 100

Pre-hallux, 161

Pre-molars of horse, 70

Pre-pollex, 161

Ptah, 263

Repair, 225
Reliquiae 62
Reversion, 134
Rickets, 265
Right aortic arch, 137
Ritta-Christina, 120
Rudimentary organs, 60

Santos, dos, 130
Sarcomata, 235
Satyrs, 56,90, 177
Sexdigitism, 194
Sexual characters, 148
Solatium jasm inoides, 3 2
Shackle joint, 196
Spina bifida, 23, 56, 75
Spinal cord, 48
Sports, 240
Spurious atavism, 143
Spurs, transplanted, 153
Stomach, hour-glass, 149
Supernumerary antlers, 107
,, arms, 115

,, auricles, 83

., digits, 108

Supernumerary hands, no
„ heads, 122

legs, in
,, mammae, 167

„ nipples, 167

„ rays, 103

„ ribs, 135

,, tails, 124

,, teeth, 106

tragus, 179

Tails, true, 52
„ false, 54
Tailless trout, 186
Talipes, 188
Teeth, overgrown, 199
Teratomata, 125
Tongue, 77
Tonsil, 93
Torula, 224
Tracheal pouch, 232
Tragus, 177
Tumours, 228
Tuberculosis, 251
Two-headed Nightingale, 121

U radius, 41

Use and disuse, 14

Useless parts, 61

Variations, 45

Viscera, Transposition of, 131
Vermiform appendix, 65
Vestigial parts, 60

Warts, 8
Webbed-fingers, 145

„ legs, 143
Wolffian bodies, 45

Yolk-sac, 75

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and juvenile books published within one year) without fine ;
not to^^ren^vgd; to be reclaimed by messenger after 21
dAxs,mb<§v^kc<medE Joofhts be^JewJce gfiia Cjitits a day,
incluAis#ggf|fajs and holidays ; Mi qt w> befij^nt.f)u* of the
borro\vxfrsTWfBWl6td,'«w*d^Dt talbe ffsyjis^rred|^d be re-
turned at this Hall.

Borrowers finding- this book mutilated or unwarrantably
defaced, are expected to report it; and also any undue delay
in the delivery of books.

*** No claim can be established because of the failure of
any notice, to or from the Library, through the mail.

The record below must not be made or altered by borrower.