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THE PRIMARY FACTORS OF
ORGANIC EVOLUTION

THE PRIMARY FACTORS

Qa“

ORGANIC EVOLUTION

E. D. COPE, PH. D.

MEMBER OF THE U. S., NATIONAL ACADEMY OF SCIENCES; PROFESSOR
OF ZOOLOGY AND COMPARATIVE ANATOMY IN THE
UNIVERSITY OF PENNSYLVANIA

CHICAGO

THE OPEN COURT PUBLISHING COMPANY
(LONDON: 17 Jounson’s Court, FLEET St., E. C.)

1904

(® JH4 07

Tue Open Court PUBLISHING Co,
CHICAGO, ILL., 1896.

The Lakeside Press
KK. K. DONNELLEY & SONS CO., CHICAGO.

PREFACE.

HE present book is an attempt to select from the mass of
facts accumulated by biologists, those which, in the author's
opinion, throw a clear light on the problem of organic evolution,
and especially that of the animal kingdom. As the actual lines of
descent can be finally demonstrated chiefly from paleontologic re-
search, I have drawn a large part of my evidence from this source.
Of course, the restriction imposed by limited space has compelled
the omission of a great many facts which have an important bear-
ing on the problem. I have preferred the paleontologic evidence
for another reason. Darwin and the writers of his immediate
school have drawn most of their evidence from facts which are
embraced in the science of cecology. Weismann and writers of
his type draw most of their evidence from the facts of embryology.
The mass of facts recently brought to light in the field of paleon-
tology, especially in the United States, remained to be presented,
and the evidence they contain interwoven with that derived from
the sources mentioned.

Many of the zodlogists of this country, in common with many
of those of other nations, have found reason for believing that the
factors of evolution which were first clearly formulated by La-
marck, are really such. This view is taken in the following pages,
and the book may be regarded as containing a plea on their behalf.
In other words, the argument is constructive and not destructive.
The attempt is made to show what we know, rather than what we
do not know. This is proper at this time, since, in my opinion, a
certain amount of evidence has accumulated to demonstrate the
doctrine here defended, and which I have defended as a working
hypothesis for twenty-five years.

In the following pages I have cited many authors who have
contributed to the result, but it has been impossible to cite all who

vi PRIMARY FACTORS OF ORGANIC EVOLUTION.

have written on one part or another of the subject. If some very

meritorious. essays have not been cited, it has been generally be-

cause I have confined myself to those in which facts or doctrines

were first presented, and have not had so much occasion to refer to
‘ those of later date.

Mr. Romanes, in his posthumous book, Volume II. of his Dar-
win, and After Darwin on Post-Darwinian Questions, expresses
the following opinion of the position which has been taken by the
Neo-Lamarckians of this country. He says that they do not dis-
tinguish between the ‘‘statement of facts in terms of a proposition,
and an explanation of them in terms of causality.” Had Mr. Ro-
manes been acquainted with the literature of the subject published
in America and elsewhere during the last three years, he would
have had reason to change this view of the case. I think he would
have found in it demonstration ‘‘in terms of causality."’

At the outset it must be stated that a knowledge of the history
of organic evolution rests primarily on the science of morphology,
and secondarily on the kinematics of the growth of organic struc-
tures. The phenomenon to be explained is the genealogical suc-
cession, or phylogeny of organisms ; and the access to this subject
is through the sciences of paleontology and embryology. The phe-
nomena of the functioning of the organism, or physiology, are only
incidentally referred to, as not the real object of inquiry. Since
organic species are much more numerous than the tissues of which
they are composed, organogenesis must claim attention more largely
than histogenesis. It is true that histogenesis is fundamental, but
it is a science as yet in its early infancy, and little space can be
given to it. The exact ow of organic evolution will never be
finally solved, however, until our knowledge of histogenesis is com-
plete. ;

The research depicted in the following pages has proceeded on
the assumption that every variation in the characteristics of organic
beings, however slight, has a direct efficient cause. This assump-
tion is sustained by all rational and philosophical considerations.
Any theory of evolution which omits the explanation of the causes
of variations is faulty at the basis. Hence the theory of selection
cannot answer the question which we seek to solve, although it
embraces an important factor in the production of the general re-
sult of evolution.

In the search for the factors of evolution, we must have first a
knowledge of the course of evolution. This can only be obtained

PREFACE, vii

in a final and positive form by investigation of the succession of
life. The record of this succession is contained in the sedimentary
deposits of the earth's crust, and is necessarily imperfect. Advance
in knowledge in this direction has, however, been very great of re-
cent years, so that some parts of the genealogical tree are tolerably
or quite complete. We hope reasonably for continued progress in
this direction, and if the future is to be judged of by the past, the
number of gaps in our knowledge will be greatly lessened. In the
absence of the paleontologic record, we necessarily rely on the em-
bryologic, which contains a recapitulation of it. The imperfections
of the embryonic record are, however, great, and this record differs
from the paleontologic in that no future discovery in embryology
can correct its irregularities. On the contrary every paleontologic
discovery is an addition to positive genealogy. If the present work
has any merit, it is derived from the fact that the basis of the argu-
ment is the paleontologic record.

E. D. Cope.
PuHILapELpuHIA, November 1, 1895.

CONTENTS.
PAGE
PREFACE 5 RU F v
TABLE OF Gesu 5 Bes ‘ 2 ix
LisT oF ILLUSTRATIONS ‘ : xiii
INTRODUCTION Fi $ I

PART I. THE NATURE OF VARIATION.

PRELIMINARY ea F es 19

CHAPTER I. VARIATION.

pees ‘ ‘ q 21
. Variations of Specria’ Characters. . F #3 25
a. Variations in Cicindela . - 25
6, Variations in Osceola doliata ‘ 29
¢. Color-Variations in Cnemidophorus . 41

d, Variations in North American Birds and Mam-
mals in Relation to Locality. . ‘ i 45
2. Variation of Structural Characters . . r 58
3. Successional Relation . .. . z 62

CuaAPTER II. PHYLOGENY.

1. General Phylogeny PhS Se BCS 74
2. Phylogeny of the Vertebrata . . . : 83
«, Phylogeny of the Classes ee ee ee ee 83
6. The Line of the Pisces . 3 ; 99
c. The Line of the Batrachia ‘ 108
d. The Line of the Reptilia. ; Hows oe ETS
e. The Line of the Aves: . 123
f. The Line of the Mammalia. ; + « $26
g. Review of the Phylogeny of the Mammalia 138

x PRIMARY FACTORS OF ORGANIC EVOLUTION.

PAGE
hk, Phylogeny of the Horse . fa a 2 146
z. The Phylogeny of Man & eS 150
3. The Law of the Unspecialized . . . 172
CHAPTER III. PARALLELISM.
Preliminary . : 175
1. Parallelism in the Bisehionaa 3 176
2. Parallelism in the Cephalopoda 182
3. Parallelism in the Vertebrata. . 192
4. Inexact Parallelism or Czenogeny. 3 200
5. Objections to the Doctrine of Parallelism . 205
CHAPTERIV. CATAGENESIS. . . . ; 211
PART II. THE CAUSES OF VARIATION.
PRELIMINARY. . fe 2 Os 225
CHAPTER V. PHYSIOGENESIS.
Preliminary . z ‘ ‘ 227
a, Relation of Size of Mollusca to Environment. . 229
6. The Conversion of Artemia into Branchinecta 229
c. Production of Colors in Lepidopterous Pupz . 230
@. Effect of Light on the Colors of Flatfishes . 238
e. Effect of Feeding on Color in Birds . 238
f. Blindness in Cave Animals. . . . . 241
CHAPTER VI. KINETOGENESIS.
ae tags 3. yi Sahay ola 246
. Kinetogenesis of Miusevlas Sirnetane ge ok : 249
z. Kinetogenesis in Mollusca. . . 255
a, Origin of the Plaits in the Cidlatmmatts of the Gas-
teropoda 255
. Mechanical Origin of Ghantens | in the Lamelli-
branchiata . 261
c. Mechanical Origin of fie. impressed Fite in
Cephalopoda. . . ‘ 268
3. Kinetogenesis in Vermes and Artheopoda ga Sy . 268
4. Kinetogenesis in Vertebrata . . . a a te 275.
i. Kinetogenesis of Osseous Tissue . a TS

«, Abnormal Articulations . . . + 275

CONTENTS. xi

PAGE
6. Normal Articulations. . . . = 6 3 « 283
. The Physiology of Bone Mantding toe ee 285
ii. “Moulding of the Articulations. . . . . . . . 287
a, The Limb Articulations . Ms oe, . . 287
6. The Forms of Vertebral Centra . 6 a & « 362
iii. Increase of Size Through Use. . . . + 304
a, The Proportions of the Limbs and their Seamenle 305
6. The Number of the Digits . . . . . . 309
ce. The Horns . . . « = 314
iv. Mechanical Origin ot Dental Types, : . . 318
Preliminary . . ae ocae, et cai A Ca SLe
a. The Origin of Canines Teeth Bh far oat be +. 327
6. The Development of the Incisors. . . . . . 328
c. The Development of Molars fot. Hot - 331
d, Origin of the Carnivorous Dentition el ge 932
e. Origin of the Dental Type of the Glires. . . . 345
v. Disusein Mammalia. . . . .... , 352
a, Natatory Limbs. . . Hi gs, “gp Ak 352
6, Abortion of Phalanges in Uawalats ie gear + 353
c, Atrophy of Ulnaand Fibula . .. . » . 355
d, Atrophy of Incisor Teeth . . . . . . . . 356
vi. Homoplassy in Mammalia. . . . . . . . . 357
vii. Origin of the Divisions of Vertebrata . . . . . 362
5. Objections to Kinetogenesis . . . . . . . « «375
CuapTER VII, NatTuRAL SELECTION. . . . 1. «© « © 385

PART III. THE INHERITANCE OF VARIATION.
PRELIMINARY. . «©. . s ee ee ee 2 & ee BOT

CuHapTerR VIII. HeEreEpitTy.

1. The Question Stated . 7 ne eee . . 398
2. Evidence from Embryology . . Sica + + 401
a, Vertebrata . . . . . eos . » . 40I
6. Arthropoda. . . ee ee ke GOR
3. Evidence from Paleontology . . 2 & = #405
«a, The Impressed Zone of the Nauiiloids é » 405
4. Evidence from Breeding . . . i, Mili Te wees nd Se
«, Of Characters Due to Nutrition pe . 6 423
4. Of Characters Due to Exercise of Function . . 426

c. Of Characters Due to Disease. . . . . . 430

xii PRIMARY FACTORS OF ORGANIC EVOLUTION.

PAGE
d. Of Characters Due to Mutilation and Injuries . 431
. Of Characters Due to Regional Influences . 435
5. The Conditions of Inheritance ; . 438
6. Objections to the Doctrine of Tatlevitaned of Mcieleea
Characters; « « « 4 © «& © ® * @ «» & « «© 458
CuHaPTER IX. Tue ENERGY oF EvoLuTIon.
Prelimifiary,, s. ae. we Ok ee a a ZS
1. Atiageniesis’ 6.2 4 i) Seow Sa A HR cae 475
2. Bathmogenesis. we ap Pdin Ts) odds) 28g) g - 484
CHAPTER X. THE FUNCTION OF CONSCIOUSNESS.
1. Consciousness and Automatism fu z A 495
2. The Effects of Consciousness . , 509

CHAPTER XI. THE Opinions oF NEO-LAMARCKIANS . 2 518

Fig.

LIST OF ILLUSTRATIONS.

- Horn on Cicindela .

. Osceola doliata triangula .

. Osceola doliata clerica .

. Osceola doliata collaris.

. Osceola doliata temporalis.

. Osceola doliata doliata .

. Osceola doliata syspila .

. Osceola doliata parallela .

. Osceola doliata annulata .

. Osceola doliata coccinea

. Cnemidophorus tessellatus .

. Cnemidophorus gularis .

. Lacerta muralis ‘

. Shoulder-girdle of Pigilomidiica cota: :

. Do. of Rana temporaria, tadpole with budding itmbe:
. Do., adult . © eos
. Bufonide

. Scaphiopidz and Pelobatidze

. Hylide. nah

. Cystignathidze

. Ranide.

. Feet of Uma sbpparts Cape, atl Plonnpass garrulus

Smith

. Eusthenopterum ‘foowds Whiteaves

. Paired fins of Cladoselache Dean

. Extremities of skeletons of caudal fins of fates
. Cricotus crassidiscus Cope, head and belly

. Cricotus crassidiscus Cope, vertebral column and pelvis 112

PAGE

27
32
32
34
34
36
38
38
40
40
42
43
44
64
64
64
66
66
67
67
67

72
go
92
96

. Iii

xiv PRIMARY FACTORS OF ORGANIC EVOLUTION,

PAGE
Fig. 29. Crania of Stegocephalia and Cotylosauria . . . . 117
30. Diagrams of crania of Reptilia. . . . .. . 118
31. Do. . ee 119
32. Archaeopteryx Behograpibien Waipu. ae stie, 22 125
33. Ungulata, anterior feet 129
34. Ungulata, posterior feet . . . . . .. . 130
35. Ungulata, anterior and posterior feet . é 131
36. Phenacodus vortmanii Cope. . . . 134

37. Fore and hind limbs of Phenacodus prima and
Homo sapiens . 137

38. Skull of Anapionephais Hoomnentus Cope. Lower
jaw of Anaptomorphus emutus Cope be oe I51
39. Tomitherium rostratum Cope, mandible . 156
40. Tomitherium rostratum Cope, fore arm ‘ 157
41. Tomitherium rostratum Cope, ilium and femur 158
42. Megaladapis madagascariensis Forsyth ae 160
43. Skullofthe manof Spy ... . 161

44. Outlines of calvaria of the Meandecthal man, of the
Spy men. 162

45. Vertical sections of symphysis mandibull of govilla’

of orang; of chimpanzee; of Spy men . 164

46, Sections of symphysis mandibuli of modern Liégois
and of an ancient Parisian. ae 166
47. Molar teeth of man. . . . : 167
48. Parallelism in Brachiopoda . . , 181
49. Circulatory systems. . 194
50. Succession of horns of Cervzs shapes L. : 197
51. Shoulder-girdles of Anura ba oho Ae 198
52. Lernea branchialis dos div, ie 212
53. Entoconcha mirabilis Mill. ; 214
54. Mycetozoa. . . ‘ ; 220
55. Typhlogobius eben miensis Stead. » 245

56. Fusus parilis Con., displaying non-plicate édtowielte. 257
57. Mitra lineo/ata Heilprin, showing the plications of the

columella - 259
58. Siphocyprea prbliaie. Heilaein, showing plica-

tions of lips ‘ ‘ : : 260
59. Ostrea edulis, embryo . . . . 262
60. Myaarenaria . . play! der! gh. B 263

61. Modiola plicatula . . . . . ae 264

LIST OF ILLUSTRATIONS. xv

PAGE
. Ostrea virginiana . . : 264
: Diagrammatic representation of the segiaents of the
leech. . . , . 270
. Diagrammatic se peesentstion se the rings age a pam:
tive crustacean. . y a « 2975
. Diagrams of hand of Grangois ane of Astana . 274
. Elbows of man and horse rae : 280
. Elbow of horse . . . 281
. Periptychus rhabdodon Cops; slowing Do ee 5 288
. Hind foot of Poébrotherium labiatum Cope. . 290
. Hind foot of three-toed horse F 290
. United first bones of two middle toes of deer: auldiope 291
. Wrist-joints at distal extremity of forearm . . . 292
. Elbow-joint of Crocuta maculataL. . . . - 294
. Elbow-joint of chimpanzee . . be Gr wee. SBOE
. Elbow-joint of Cervus elaphus . . . . . > 296
. Cervus canadensis in motion a @ Ss te 4 9 207
. Cervus elaphus . . . . 298
. Diagram of carpus of a Taxcopoi, a a diplerthrons
ungulate ‘i ’ . 299
. Raccoon pacing. . . .... . 299
. Rhinocerus unicornis carpus. . 5 . 300
. Equus cabatlus fore foot ‘ 300
. Gazelladorcas . . . 301
. Pes of Marychochavasn montanus and Bos taurus . 307
. Anterior feet of primitive Ungulata : . 308
. Right posterior foot of Prothippus and Hesbeotheniiis 310
. Manus of Artiodactyla. . 4 312
. Burrs on antlers of Cosoryx necatus Leidy 316
. Diagram of excursion of lower jaw in mastication 320
. Cervus, molars . ; : 321
. Cusps of superior peal aad ieee So a 322
. Two true molars of both jaws of a ruminant 323
. Sections of superior molar teeth . . 323
. Chirox plicatus Cope, palate and molar teeth 324
. Meniscoéssus conguistus Cope, last two superior mo-
lars. je eS : : be » 325
. Lemur collaris, dentiGion i ‘ . 326
. Esthonyx burmeisterti Cope, dentition ; . . 328

xvi PRIMARY FACTORS OF ORGANIC EVOLUTION.

PAGE

Fig. 97. Psittacotherium multifragum Cope, mandibular ra-
mus ; ‘ : . 329

98. Diagrammatic representations of horizontal sections

of tricuspidate molars of both jaws in mutual rela-

tion é » 333
99. Delsathevium fandordeis Cope, Ragmedinty tea 336
100. Centetes ecaudatus, skull and molars 1 « 337

ror. Inferior molar crowns representing transition from
the simple to the quadritubercular vis 338

102. Stypholophus whitie Cope; apposition of inferior
and superior molars . : wi ti . 339
103. Cynodictis geismarianus Cope; skull a - 341

104. Aelurodon sevus Leidy; coadaptation of crowns of
superior and inferior molars in mastitation 342
105. Smilodon neogeus Lund; skull. ' 344
106. Sections of crowns of molars of Ungulata .° 345
107. Castorotdes ohioensis Foster; skull . . . 347
108. Castorotdes ohioensis Foster ; skull from below 350
109. Lschyromys typus Leidy ; cranium and mandible . 351
110. Balena mysticetus ; fore limb ou 353
r11. Feet of Amblypoda . ; ‘ . 354
112. Feet of Proterotheriide ; : » 358
113. Dorsal vertebrz of casnpaadudgiaus ficties 370
114. Vertebral column of Eryops megacephalus Cope 371
114a Sleeve of coat : Bae ‘ 371
115. Metatoceras cavatiformis Hyatt . . 406
116, Do. ; , 407
117. Temnochilus crassus er 407
118. Metacoceras dubium Hyatt . » 408
119. Hyatt on Cephalopoda 410

120. Diagram explanatory of Diplogenesis 441

INTRODUCTION.

‘HE doctrine of evolution may be defined as the
teaching which holds that creation has been and
is accomplished by the agency of the energies which
are intrinsic in the evolving matter, and without the
interference of agencies which are external to it. It
holds this to be true of the combinations and forms of
inorganic nature, and of those of organic nature as
well. Whether the intrinsic energies which accom-
plish evolution be forms of radiant or other energy
only, acting inversely as the square of the distance,
and without consciousness, or whether they be ener-
gies whose direction is affected by the presence of con
sciousness, the energy is a property of the physical
basis of tridimensional matter, and is not outside of it,
according to the doctrine we are about to consider.
As a view of nature from an especial standpoint,
evolution takes its place asa distinct science. The
science of evolution is the science of creation, and is
as such to be distinguished broadly from the sciences
which consider the other operations of nature, or the
functioning of nature, which are not processes of crea-
tion, but processes of destruction. This contrast is
especially obvious in organic evolution, where the two
processes go on side by side, and are often closely in-

2 PRIMARY FACTORS OF ORGANIC EVOLUTION.

termingled, as for instance in muscular action, where
both destruction of proteids and growth of muscular
tissue result from the same acts, or use. Physiology,
or the science of functions, concerns itself chiefly with
destruction, and hence physiologists are especially
prone to be insensible to the phenomena and laws of
progressive evolution. The building of the embryo,
remains a sealed book to the physiologist unless he
take into account the allied biological science of evo-
lution, as resting on the facts of botany, zodlogy, and
paleontology. In his reflections on the relations of
mind to matter he is likely to see only the destructive
functioning of tissue, and not the history of the build-
ing of the same during the ages of geological time.

J. B. P. A. Lamarck! thus contrasts the theories
of direct creation, and creation by evolution. The
former asserts: ‘‘ That nature or its author in creating
animals has foreseen all possible kinds of circumstances
in which they may have to live, and has given to each
species a permanent organization as well as a prede-
termined form, invariable in its parts; that it forces
each species to live in the place and the climate where
one finds them, and to preserve there the habits which
it has.” He then states his own, or the evolutionary,
opinion to be: ‘*That nature in producing succes-
sively all species of animals, commencing with the
most imperfect or simple, and terminating its work
with the most perfect, has gradually complicated their
organization ; and these animals spreading themselves
gradually into all habitable regions of the globe,—
each species has been subjected to the influence of the
circumstances in which it is ; and these have produced
the habits which we observe, and the modifications of

1 Philosophie Zoologique, Paris, 1809, Vol. I., Chap. VII.

INTRODUCTION. 3

its parts.” On an earlier page of the same chapter,
Lamarck thus formulates the laws of organic evolu-
tion, to which his name has been attached.

First law. <‘‘In every animal which has not passed
the time of its development, the frequent and sustained
employment of an organ gradually strengthens it, de-
velops and enlarges it, and gives it power proportional
to the duration of its use; while the constant disuse
of a like organ weakens it, insensibly deteriorates it,
progressively reduces its functions, and finally causes
it to disappear.”

Second law. ‘‘All that nature acquires or loses in
individuals by the influence of circumstances to which
the race has been exposed for a long time, and in con-
sequence of the influence of the predominate employ-
ment of such an organ, or of the influence of disuse of
such part, she preserves by generation, in new indi-
viduals which spring from it, providing the acquired
changes be common to both sexes, or to those which
have produced new individuals.”

We have here a theory of the origin of characters; ,
viz., of the increased development or loss of parts as
a result of use or disuse. We have also the theory
that the peculiarities thus acquired are transmitted to
the succeeding generation by inheritance.

The next formal statement of the efficient cause of
organic evolution was presented by Messrs. Charles
Darwin and Alfred R. Wallace in 1859.1 The cause
assigned is natural selection, and Mr. Darwin thus
states what is meant by this expression in his work
The Origin of Species.? ‘*If under changing conditions
of life organic beings present individual differences

1 Proceedings of the Li: Soctety of London.
2Ed. 1872, p. 102.

4. PRIMARY FACTORS OF ORGANIC EVOLUTION.

in almost any part of their structure, and this cannot
be disputed ; if there be, owing to their geometrical
rate of increase, a severe struggle for life at some age,
season, or year, and this certainly cannot be disputed ;
then considering the infinite complexity of the rela-
tions of all organic beings to each other and to their
conditions of life, causing an infinite diversity of struc-
ture, constitution, and habits, to be advantageous to
them, it would be a most extraordinary fact if no varia-
tions had ever occurred useful to each being’s own wel-
fare, in the same manner as so many variations have
occurred useful to man. But if variations useful to
any organic being ever do occur, assuredly individuals
thus characterized will have the best chance of being
preserved in the struggle for life; and from the strong
principle of inheritance, these will tend to produce off-
spring similarly characterized. This principle of pre-
servation, or the survival of the fittest, I have called
natural selection. It leads to the improvement of each
creature in relation to its organic and inorganic condi-
tions of life; and consequently in most cases, to what
must be regarded as an advance in organization.
Nevertheless, low and simple forms will long endure
if well fitted for their simple conditions of life.”

It is readily perceived that this statement makes
no attempt to account for the origin of variations, but
that it simply formulates, as observed by Mr. Darwin,
the doctrine of survival of such variations as are most
useful to their possessors. This fact is more distinctly
pointed out in the same work (p. 63) where the author
remarks: ‘‘Several writers have misapprehended or
objected to the term natural selection. Some have
even imagined that natural selection induces variabil-
ity, whereas it implies only the preservation of such

INTRODUCTION. 5

variations as arise and are beneficial to the being under
its conditions of life. No one objects to agriculturists
speaking of the potent effects of man’s selection, and
in this case the individual differences given by nature,
which man for some object selects, must of necessity
first occur.” Itis evident then that Mr. Darwin did
not attempt to account for the origin of variations, but
that the service rendered by him and by Mr. Wallace
to the doctrine of evolution consists in the demonstra-
tion of the reality of natural selection. Darwin also
assumes in the statement first quoted above, the in-
heritance of acquired characters.

In 1865 the Principles of Biology of Herbert Spen-
cer appeared. In this work the attempt is made to
set forth the laws of organic evolution, in a way which
represents an advance beyond the positions of his
predecessors. He adopts and harmonizes both the
Lamarckian and Darwinian doctrines, and is at times
more specific in his application of Lamarck’s doctrine
of the stimulus of the environment, and of use, than
was Lamarck himself. Very often, however, Spencer
contents himself with generalities ; or takes refuge in
the ‘‘instability of the homogeneous,” as an efficient
cause. This phrase, however, like his other one, ‘‘the
unknowable,” is but a makeshift of temporary ignor-
ance, and is neglected by Spencer himself, when he
can see his way through it. He approaches the cause
of the varied forms of leaves of plants in this language :!
«And it will also be remembered that these equalities
and inequalities of development correspond with the
equalities and inequalities in the incidence of forces.”
Language of similar significant but rather indefinite
import is frequently used throughout this volume.

1 The Principles of Biology, by Herbert Spencer, Amer. Ed., 1873, II., p. 143.

6 PRIMARY FACTORS OF ORGANIC EVOLUTION,

But in some cases Spencer is more specific. With
reference to the inequality in the basal lobes of the
erect leaves of Tilia and other plants, he says :1 «A
considerable deviation from bilateral symmetry may
be seen in a leaf which habitually so carries itself that
the half on the one side of the midrib is more shaded
than the other half. The drooping branches of the
lime show us leaves so arranged and so modified. On
examining their attitudes and their relations one to
another, it will be found that each leaf is so inclined
that the half of it next the shoot grows over the shoot
and gets plenty of light ; while the other half so hangs
down that it comes a good deal into the shade of the
preceding leaf. The result is that having learned which
fall into these positions, the species profits by a large
deveiopment of the exposed halves ; and by survival
of the fittest acting along with the direct effect of extra
exposure, this modification becomes established.”” In
his discussion of the origin of the characters of ani-
mals, Spencer is also sometimes specific. Respecting
the development of muscular insertions he remarks :?
‘‘Anatomists easily discriminate between the bones of
a strong man and those of a weak man by the greater
development of those ridges and crests to which the
muscles are attached ; and naturalists on comparing
the remains of domesticated animals with those of
wild animals of the same species, find kindred differ-
ences. The first of these facts shows unmistakably
the immediate effect of function on structure, and, by
obvious alliance with it, the second may be held to do
the same, both implying that the deposit of dense sub-
stance capable of great resistance habitually takes

104, cit., p. 143.
2 Loc, cit., p. 200.

INTRODUCTION. 7

place at points where the tension is excessive.” Quite
as specific is his ascription of the forms of epithelial
cells to definite causes, as follows :! « fust the equal-
ities and inequalities of dimensions among aggregated
cells, are here caused by the equalities and inequalities
among their mutual pressures in different directions ;
so though less manifestly, the equalities and inequali-
ties of dimensions among other aggregated cells, are
caused by the equalities and inequalities of the osmatic,
chemical, thermal, and other forces besides the me-
chanical, to which their different positions subject
them.”

In spite of this not infrequent definiteness, Mr.
Spencer occasionally falls into the error of ascribing
the origin of structures to natural selection, as in the
case of the forms of flowers,? and the armor-plates of
paleozoic fishes.? Spencer assumes the inheritance of
acquired characters throughout.

‘In 1866 Haeckel’s Schépfungsgeschichte appeared.
In this work the author presents a mass of evidence
which sustains the doctrine of evolution, and he com-
bines the views of Lamarck and Darwin into a general
system. He says:* ‘“We should, on account of the
grand proofs just enumerated, have to adopt Lamarck’s
theory of descent for the explanation of biological phe-
nomena, even if we did not possess Darwin’s theory of
selection. The one isso completely and directly proved
by the other, and established by mechanical causes,
that there remains nothing to be desired. The laws
of inheritance and adaptation are universally acknowl-

10. cit., p. 260.
2 Of, cit., p. 153.
3 Op. cit., p. 288.
4The History of Creation, Amer. Edition, II., p. 355.

8 PRIMARY FACTORS OF ORGANIC EVOLUTION.

edged physiological facts, the former traceable to prop-
agation, the latter to the nutrition of organisms.”
Apart from the statement that adaptation is traceable
“to the nutrition of organisms,” we find nothing in
Haeckel’s earlier writings which attempts the ex-
planation of the origin of variations, beyond the gen-
eral position assumed by Lamarck. The distinctive
merit of Haeckel is his formulation of phylogeny. Much
of this was speculative at the time he wrote, but so far
as the Vertebrata are concerned, it has been largely
confirmed by subsequent discovery.

Up to this period, the form in which the doctrine
of evolution had been presented, was general in its
application; that is, without exact reference to the
structural definitions of natural taxonomic groups. No
attempt was made to show the modes of the origin of
any particular class, order, or genus, and only in the
most general way in the case of a few species, by Mr.
Darwin. Phylogeny was untried, except by Haeckel;
and this distinguished author did not attempt to ac-
count specifically for the origins of the divisions whose
filiations he set forth.

In the year in which Haeckel’s work above cited
appeared, Professor Hyatt of Boston and myself took
the first step towards the formulization of a rational
theory of the origin of variation, which should accord
with specific examples of taxonomy. Quite indepen-
dently, we selected the simple series presented by the
characters of genera in their natural relations, Hyatt
in the cephalopodous Mollusca, and I in the Batrachia
Salientia. It is probable that Hyatt’s! article was pub-
lished shortly before mine.” He says of the genera of
Cephalopoda: “‘In other words, there is an increasing

1 Memoirs Boston Society Natural History, 1866, p. 193.

INTRODUCTION, 9

concentration of the adult characteristics in the young
of higher species and a consequent displacement of
other embryonic features which had themselves also
previously belonged to the adult period of still lower
forms.””% My own language is:! «*That the presence,
rudimental condition, or absence of a given generic
character can be accounted for on the hypothesis of a
greater rapidity of development in the individuals of
the species of the extreme type, such stimulus being
more and more vigorous in the individuals of the types
as we advance towards the same, or by a reversed im-
pulse? of development, where the extreme is charac-
terized by absence or ‘mutilation’ of characters.” The
phenomena of the aggregation of characters in pro-
gressive evolution, and the loss of characters in retro-
gressive evolution, were termed by me acceleration and
retardation in an essay published in 1869.3 In these
papers by Professor Hyatt and myself is found the
first attempt to show by concrete examples of natural
taxonomy, that the variations that result in evolution
are not multifarious or promiscuous, but definite and
direct, contrary to the method which seeks no origin
for variations other than natural selection. In other
words, these publications constitute the first essays in
systematic evolution that appeared. By the discovery
of the paleontologic succession of modifications of the
articulations of the vertebrate, and especially mamma-
lian skeleton, I first furnished an actual demonstration
of the reality of the Lamarckian factor of use, or mo-

1 Transactions American Philosophical Society, 1866, p. 398; reprinted in
The Origin of the Fittest, p. 92.

2 The expression ‘‘reversed"’ is unfortunate, d/mnished being the proper
word to convey the meaning intended.

8 The Origin of Genera, Philadelphia, 1869.

10 PRIMARY FACTORS OF ORGANIC EVOLUTION.

tion, as friction, impact, and strain, as an efficient
cause of evolution.! This demonstration led me to the
necessary inference that when the agency directive of
motion is consciousness, this also has been an impor-
tant factor of evolution, in demonstration of the sup-
position of Erasmus Darwin.? Hyatt has demonstrated
first on paleontologic evidence, the inheritance of a
mechanically acquired character. Important contribu-
tions to corresponding histories of the Mollusca have
been made by Hyatt,’ Dall,* Jackson,’ and Beecher.®
Many other contributions, into which the paleontologic
evidence does not enter, have also been made by vari-
ous authors in Europe and America.

The authors quoted up to this point had all as
sumed that the progress of evolution depends on the
inheritance by the offspring of new characters acquired
by the parent, and had believed that such is the fact
in ordinary experience. In 1883, Weismann, in an
essay on heredity, announced the opinion that charac-
ters acquired by the body could not be transmitted to
the reproductive cells, and could not therefore be in-
herited. This doctrine rests on the relation of the
germ-cells to those of the rest of the body, which is
expressed in the following language of his predecessor
Jaeger: ‘‘Through a great series of generations the

1“The Origin of the Hard Parts of Mammalia,” American Journal of
Morphology, 1889, p. 137.

2 Origin of the Fittest, 1887, p. 357.

3 Phylogeny of an Acquired Characteristic,'’’ Proc. Amer, Philosophical
Society, 1893, p. 349; ‘‘ The Genesis of the Arietide," Memocrs Mus. Compar.
Zoblogy, Cambridge, Mass., 1889, XVI., No. 3.

4Dall, W. H., ‘The Hinge of Pelecypods and Its Development, Amer.
Jour, Sct, Arts, 1889, XXXVIIL., p. 445.

5 Jackson, R. T., ‘‘ Phylogeny of the Pelecypoda, the Aviculidz, and Their
Allies,’’ Memoirs Boston Society Natural History, 1890, IV., p. 277.

8American Journal Sei, Arts, 1893.

INTRODUCTION. II

germinal protoplasm retains its specific properties,
dividing in every reproduction into an ontogenetic por-
tion and a phylogenetic portion, which is reserved to
form the reproductive material of the mature offspring.
This reservation of the phylogenetic material I de-
scribed as the continuity of the germ-protoplasm. ...
Encapsuled in the ontogenetic material the phyloge-
netic protoplasm is sheltered from external influences,
and retains its specific and embryonic characters.” In
other words, the reproductive cells are removed from
the influence of those stimuli which affect and effect
growth in the cells of the other parts of the body, so
that no character acquired by the rest of the body can
be inherited. The bearing of this theory on evolution
is thus stated by Weismann:! ‘The origin of heredi-
tary individual variations cannot indeed be found in
the higher organisms, the metazoa and metaphyta, but
is to be sought for in the lowest, the unicellular.” ‘‘The
formation of new species, which among the lower pro-
tozoa could be achieved without amphigony (sexual
union), could only be attained by means of this process
in the metazoa and metaphyta. It was only in this
way that hereditary individual differences could arise
and persist.”” In other words, variation in organic
beings above the unicellular forms, has been and is,
introduced only by sexual reproduction.

The conclusions of Weismann were derived prin-
cipally from embryologic research, and his disciples
have been chiefly recruited from embryologists. These
conclusions have been supported by extensive and ex-
haustive investigations, which have added greatly to
our knowledge of the subject. In order to account for

1£ssays, p. 296. For a complete account of Weismann’s views, see The
Germ-Plasm, 1893.

iz PRIMARY FACTORS OF ORGANIC EVOLUTION,

the appearance of characters in the embryonic succes-
sion, through influences confined to the germ-plasma,
Weismann invented a theory which requires the pres-
ence of distinct molecular aggregates within it, which
represent the potentialities or causes. To these he has
given the names of ids, idants, determinants, etc. As
Weismann’s contribution to evolution has been con-
fined to the department of heredity, I will consider it
more particularly in the third part of this book, which
is devoted to that subject.

Weismann has, however, subsequently modified
his views to a considerable extent. He has always
admitted the doctrine of Lamarck to be applicable to
the evolution of the types of unicellular organisms.
His experiments on the effect of temperature on the
production of changes of color in butterflies, showed
that such changes were not only effected, but were
sometimes inherited. This he endeavors to explain as’
follows.! ‘‘Many climatic variations may be due wholly
or in part, to the simultaneous variation of correspond-
ing determinants in some parts of the soma and in the
germ-plasm of the reproductive cells.” This is an ad-
mission of the doctrine which in 1890 I called Diplo-
genesis,” and which is adopted in the present work. It
appears to have been first propounded by Galton in
1875. In the chapter on Heredity I hope to offer some
reasons for believing that the suggestion of Galton
embraces the true doctrine of heredity.

From what has preceded, two distinct lines of
thought explanatory of the fact of organic evolution
may be discerned. In one of these the variations of
organisms which constitute progressive and regressive

1 The Germ Plasm, Contemporary Science Series, 1893, p. 406.
2American Naturalist, Dec., 1889; published in 1890.

INTRODUCTION. 13

evolution appear fortuitously, and those which are
beneficial survive by natural selection, while those
which are not so, disappear. Characters both benefi-
cial and useless or harmless, which are acquired by the
adult organism, are not transmitted to the young, so
that no education in habit or structure acquired by the
adult, has any influence in altering the course of evo-
lution. This is the doctrine of Preformation. From
this point of view the cause of the variations of organ-
isms has yet to be discovered.

The other point of view sees in variation the direct
result of stimuli from within or without the organism ;
and holds that evolution consists of the inheritance of
such variations and the survival of the fit through nat-
ural selection. This is the doctrine of Epigenesis. To
this I would add that in so far as sensations or states
of consciousness are present, they constitute a factor in
the process, since they enable an organism to modify
or change its stimuli. The position of each of these
schools on each of the questions to which reference
has been made, may be placed in opposition as follows :

1. Variations appear in defi-
nite directions.

2. Variations are caused by
the interaction of the organic
being and its environment.

3. Acquired variations may
be inherited.

4. Variations survive directly
as they are adapted to changing
environments. (Natural selec-
tion.)

1. Variations are promiscu-
ous or multifarious.

2. Variations are ‘‘congeni-
tal” or are caused by mingling
of male and female germ-plas-
mas.

3. Acquired variations cannot
be inherited.

4. Variations survive directly
as they are adapted to changing
environments. (Natural selec-
tion.)

14. PRIMARY FACTORS OF ORGANIC EVOLUTION.

5. Movements of the organ-
ism are caused or directed by
sensation and other conscious
states.

6. Habitual movements are
derived from conscious experi-
ence.

7. The rational mind is de-
veloped by experience, through
memory and classification.

5. Movements of organism
are not caused by sensation or
conscious states, but are a sur-
vival through natural selection
from multifarious movements.

6. Habitual movements are
produced by natural selection.

7. The rational mind is de-
veloped by natural selection
from multifarious mental activ-

ities,

It is not the object of the present book to present all
the available evidence on both sides of each of the ques-
tions above enumerated. I propose merely to submit
certain facts, in support of the doctrines contained in
the left-hand column of the above table. My aim will
be to show in the first place, that variations of charac-
ter are the effect of physical causes ; and second, that
such variations are inherited. The facts adduced in
support of these propositions will be necessarily prin-
cipally drawn from my own studies in the anatomy,
ontology, and paleontology of the Vertebrata. It will
be my aim, moreover, to co-ordinate the facts of evo-
lution with those of systematic biology, so that the re-
sult may be as clearly presented as possible. The fail-
ure to do this by the founders of evolutionary doctrine
has given their work a lack of precision, which has
been felt by systematic biologists. The detailed ap-
plication of the principles of Lamarck and Darwin has
been the work of their successors, and has necessarily
thrown much new light on the principles themselves.
In pursuing the object above stated, I shall be obliged

INTRODUCTION. 15

to consider briefly in the following pages, the validity
of the general propositions on which the doctrine of
evolution rests. Less space will be given, however,
to those which are less relevant, than to those which
are more relevant to the doctrine of neo-Lamarckism.

PART I.

THE NATURE OF VARIATION.

PRELIMINARY.

HE structural relations of organisms may be ex-

pressed in the following canons :}

1. Homology.—This means that organic beings are
composed of corresponding parts ; that the variations of
an original and fixed number of elements constitute
their only differences. A part large in one animal may
be small in another, or vice versa ; or complex in one
and simple in another. The analysis of animals with
skeletons, or Vertebrata, has yielded several hundred
original elements, out of which the twenty-eight thou-
sand included species are constructed. The study of
homologies is thus an extended one, and is far from
complete at the present day.

2. Successional Relation.—This expresses the fact
that species naturally arrange themselves into series in
consequence of an order of excess and deficiency in
some feature or features. Thus species with three toes
naturally intervene between those with one and four
toes. So with the number of chambers of the heart,
of segments of the body, the skeleton, etc. There are
greater series and lesser or included series, and mis-
takes are easily made by taking the one for the other.

1 Origin of the Fittest, p.6, The laws here stated are as expressive of the
relations of plants as of animals.

20 PRIMARY FACTORS OF ORGANIC EVOLUTION.

3. Parallelism.—This states that all organisms in
their embryonic and later growth pass through stages
which recapitulate the successive permanent condi-
tions of their ancestry. Hence those which traverse
fewer stages resemble or are parad/el with the young of
those which traverse more numerous stages. This is
the broad statement, and is qualified by the details.

4. TLeleology.—This is the law of fitness of structures
for their special uses, and it expresses broadly the
general adaptations of an animal to its home and
habits.

The first and fourth of the laws above enumerated
are taken for granted as generally accepted, and are

-not especially considered in the following pages. The
second law, that of successional relation, is discussed
and illustrated under the two heads of Variation and
Phylogeny; the first expressing contemporary relations,
and the second, successive relations in time. The third

-law, or that of parallelism, is considered in a chapter
devoted to that subject.

CHAPTER I—ON VARIATION.

PRELIMINARY.

LL species are not equally variable. Some species
vary little or not at all, even under domestication.

Thus the varieties of the turkey (Aledeagris gallopavo)
and the guinea-fowl (Wumida meleagris) are few, and
are confined to albinistic or melanistic conditions.
The barnyard fowl (Gallus sp.), on the other hand,
varies enormously, as does also the pigeon (Columba
“ivia). Among domesticated Mammalia the variations
of cats (Felis domestica) are few as compared with those
of dogs (Canis sp.). Variability is not peculiar to do-
mesticated animals. A large proportion of animals
and plants are, in a state of nature, variable, and some
of these are much more so than others. The common
garter-snake (Zu¢enta sirtalis) varies exceedingly, while
the variations of the allied ribband snake (Zutenia
Saurita) are minute or none. But little variation has
been observed in the polar bear (Ursus maritimus),
while the common bear (VU. arctos) presents many vari-
eties. Similar conditions are found among fishes. Thus
the larger species of pike, the muskallonge (Lucius nobi-
ior), the pike (LZ. estor), and the pickerel (L. vermicu-
Jatus) are constant in their characters, while the small
pickerel (Z. vermiculatus) presents numerous varieties.

22 PRIMARY FACTORS OF ORGANIC EVOLUTION,

Many of the varieties of the animals referred to in-
habit the same territory, although some are restricted
to particular regions. Of geographical varieties or
races much is known. Asarule, all widely distributed
species present them. Examples are the brown bear of
the Northern Hemisphere (Ursus arctos); the cobra di
capello snake of the warmer parts of Asia (Waja tripu-
dians), and that of Africa (aya haje). In North Amer-
ica the king-snake (Ophibolus getulus) and the milk-
snake (Osceola doliata) are represented by distinct
races in different regions. On the other hand, the
copperhead (Ancistrodon contortrix) and the Eastern
rattlesnake (Crotalus horridus), which have a wide
range, scarcely vary at all. The chub (Aydopsis bigut-
tatus) is an example of a fish distributed everywhere
east of the Rocky Mountains, which presents scarcely
any variation.

Variations are not promiscuous or multifarious, but
are of certain definite kinds or in certain directions.
Thus amid all their varieties, dogs never present black
cross-bands on the back like those of the dog-opossum
(Thylacinus cynocephalus) of Tasmania, nor do they
present ocellated spots like those of the leopard, nor
longitudinal stripes like those of certain squirrels. The
same is true of the many varieties of cattle (Bos tau-
rus), and of numerous other mammalia. Domestic
fowls never vary to blue or green, colors which are
common to many other birds; nor are canaries known
to produce blue or red natural sports. All variations
are in the first place necessarily restricted by the ex-
isting characters of the ancestor; but beyond this it is
evident that other conditions determine the nature of
the variation. It is not supposable, for instance, that
the pale tints of animals which live in dry regions

ON VARIATION. 23

originated by an accident or without a determining
cause. The increased amount of dark pigment ob-
served in animals which dwell in especially humid re-
gions must have a corresponding cause, and it is nat-
urally to be supposed, of a kind the opposite of that
which. produces the pale colors.

I shall adduce some illustrations which show that
color variations in species, as well as structural varia-
tions in higher groups, have appeared in certain defi-
nite series, and observe a successional relation to each
other, which may or may not coincide with geograph-
ical conditions. The same relation is observed in the
order of appearance of variations on the body.

Eimer and Weismann have shown that the grad-
ual modification of color markings has originated in
lizards and in caterpillars at the posterior end of the
body and has gradually extended forwards. This has
been discovered both by comparisons of the variations of
the adults, and by studies of the order of their appear-
ance in ontogenetic growth. Eimer shows that longi-
tudinal bands have been produced in some animals by
the confluence of spots placed in transverse series,
which themselves are the remains of interrupted trans-
verse bands. Thus he believes that the spots of the
leopard group of the large cats were derived from the
breaking up of transverse bands of the character of
those now possessed by the tiger. The uniform colo-
ration of the lion is the result of the obliteration of the
spots. Traces of these spots may be distinctly seen in
lions’ cubs.

In plants variation is said to be equally definite by
Henslow. He says: ‘‘In 1847 Professor J. Buckman
sowed the seed of the wild parsnip in the garden of
the Agricultural College at Cirencester. The seeds

24 PRIMARY FACTORS OF ORGANIC EVOLUTION.

began to vary, but in the same way, though in differ-
ent degrees. By selecting seed from the best rooted
plants the acquired ‘somatic’ characters of an en-
larged root, glabrous leaves, etc., became fixed and
hereditary; and the ‘Student,’ as he called it, having
been ‘improved’ by Messrs. Sutton and Sons, is still
regarded as ‘the best in the trade.’ This is definile
variation, according to Darwin’s definition, for those
weeded out did not differ from the selected, morpho-
logically, except in degree, the variations towards im-
provement not being quite fast enough to entitle them
to survive.”

Finally I wish especially to point out that variation
in animals, and probably in plants, (with which I am
not so familiar,) gives no ground for believing that
‘«sports’’ have any considerable influence on the course
of evolution. This is apparent whether we view the
serial lines of variations of specific, generic, or higher
characters ; or whether we trace the phylogeny of the
animal and vegetable types by means of the paleonto-
logical record. The method of evolution has appar-
ently been one of successional increment or decrement
of parts along definite lines. More or less abruptness
in some of the steps of this succession there may have
been ; since a definite amount of energy expended in
a given direction at a given point of history might pro-
duce a much greater effect than the same amount ex-
pended at some other period or point of evolution.
This might be due to the release of stored energy,
which could only be accomplished by a coincidence of
circumstances. A simple illustration of the phenome-
non of abrupt metamorphosis is to be found in the
passage of matter from the gaseous to the liquid, and

ON VARIATION. 25

from the liquid to the solid state. I have stated the
case in the following language:}

‘As one or more periods in the life of every spe-
cies is characterized by a greater rapidity of develop-
ment ” (ontogenetic) ‘‘than the remainder ; so in pro-
portion to the approximation of such a period to the
epoch of maturity or reproduction is the offspring
liable to variation. During the periods corresponding
to those between the rapid metamorphoses, the char-
acters of the genus would be preserved unaltered,
though the period of change would be ever approach-
ing. Hence the transformation of genera may have
been rapid and abrupt, and the intervening periods of
persistency very long. Thus, while change is really
progressing, the external features remain unchanged
at other than those points, which may be called ex-
pression points. Now the expression point of a new gen-
eric type is reached when its appearance in the adult
falls so far prior to the period of reproduction as to
transmit it to the offspring and their descendants.”

1. VARIATIONS OF SPECIFIC CHARACTERS.
a. Variations in the Coleopterous Genus Cicindela.

Dr. George H. Horn has traced the variations in
the color patterns of the elytra of the North American
species of this abundant and well-known genus. He
shows that they form series, in the following language :?

‘‘Any one in glancing over this series will perceive
that there is a great similarity of marking between
many species. This similarity, which may be con-
sidered as the type of marking, and is illustrated by

l Origin of the Fittest, p. 79.
2 Extomological News, Philadelphia, Feb., 1892, p. 25.

26 PRIMARY FACTORS OF ORGANIC EVOLUTION,

No. 1 of the accompanying plate (Fig. 1) is the under-
lying pattern from which all the forms observed in our
Cicindela have been derived.

“Before going further it is well to present the fol-
lowing propositions that the argument ard the illus-
trations may be understood.

‘<1, The ¢ype of marking is the same in all our spe-
cies.

«¢2, Assuming a well-marked species as a central
type the markings vary,

a, by a progressive spreading of the white,

4, by a gradual thinning or absorption of the white,

c, by a fragmentation of the markings,

d, by linear supplementary extension.

«¢3, Many species are practically invariable. These
fall in two series,

a, those of the normal type, as vulgaris, hirticollis,
and fenutsignata,

4, those in which some modification of the type
has become permanent, probably through isolation, as
marginipennis, togata, and lemniscata.

‘¢4. Those species which vary, do so in one direc-
tion only. That is, supposing a species begins typ-
ically with markings similar to vudgaris, the variation
may be either in the direction of thickening and in-
crease of white, as in hyperborea, generosa, and others,
or in the direction of thinning or fragmentation of the
white with perhaps an entire loss of markings as in
hemorrhagica, splendida, or obsoleta.

«The first two propositions must be considered as
applying to the species of the genus collectively, the
last two to the species separately.

‘“«The accompanying plate has been prepared to
illustrate these propositions. It must, however, be

ON VARIATION.

a
~
o
ss)
&
BS
3)
id
oO
sj
ro)
‘=|
i)
io}
|
4
a
wt
&

28 PRIMARY FACTORS OF ORGANIC EVOLUTION.

understood that, in tracing the derivations from the
typical, it is not possible to use one species, as these
modifications go on gradually through a number of
species, one sometimes beginning where another ends.

‘In the plate, No. 1 represents vu/garis, which is
a fairly typical species, following through generosa
(2-3), pamphila (4), hyperborea var. (5), togata (6), gra-
tiosa (7), canosa (8), we finally arrive at a perfect white
elytron as seen in some varieties of dorsalis.

“‘Following in the other direction through ¢enuz-
Signata (9), marginipennis (10), hentztd (11), sexguttata
(12), hemorrhagica (13), and splendida var. (14), it will
be observed that through a gradual thinning or ab-
sorption of the markings, or by their fragmentation
and obliteration, we arrive at the opposite result of
elytra without any white markings whatever, as in
many forms of odsoleta, scutellaris, punctulata, and he-
morrhagica.

‘« Those species which vary from the type in hav-
ing the markings broken into spots, as in 12-gutta/a
or hentzit, may lose the spots by a gradual decrease of
size, so that they all seem to disappear nearly at the
same time; or the spots may disappear successively,
those on the disc being the first to go, while the mar-
ginal spots remain.

«‘From our series it would be difficult to say which
spot is the most persistent, but it is probably the lu-
nule, as there are more with entirely dark elytra with
slight traces of this spot than with any other, as shown
in abdominalis and punctulata.

‘¢Forms like Zemniscata (16) seem very far removed
from the type, but many forms of zmperfecta (15) show
how the markings gradually leave the margin and tend

ON VARIATION. 29

by fusion to form a vitta at first somewhat oblique,
but finally becoming nearly median.

‘« The last two figures on the plate represent the
markings of gaddci (17) and saudcy? (18), in which the
ends of the bands or lunules are greatly prolonged.
The latter form, which represents dorsalis as well, is
but rarely seen so perfectly marked, the tendency being
toward a greater extension of the white. The other
species is scarcely variable, although equally a coast
form.

‘Those species which retain a permanent diver-
gence from the normal standard, such as /ogata (6) or
lemniscata (16), are doubtless descendants from a nor-
mal type which has varied, and in which a variety has
become isolated and perpetuated itself.”

The accompanying plate is copied from the original
drawing by Dr. Horn, and which accompanies the
paper now cited.

&. Variations tn the Osceola doltata.

The Milk-Snake, Osceola doliata Linn., ranges in
North America over the Eastern, Central, and Austro-
riparian districts, and is absent from the Sonoran
and Pacific districts. It is found also in the humid
regions of Mexico and Central America, as far as the
Isthmus of Darien. Beyond this point it does not oc-
cur, but a very similar snake (Opheomorphus mimus) is
found in New Grenada.

I have called attention to the color variations of
this species in a brief paragraph in the introduction to
my check list of Batrachia and Reptilia in North
America, 1875,) and have given the characters of the

1Bulletin of the U. S. National Museum, No. I, p. 4.

30 PRIMARY FACTORS OF ORGANIC EVOLUTION.

color types, or subspecies, in an analytical key, ina
‘‘Review of the Characters and Variations of the
Snakes of North America,” 1892.! I have also given a
series of figures representing the North American color
forms, for which I am indebted to the United States
National Museum, which are here reproduced.

Before going further into the patterns of the Osce-
ola doliata, 1 give a synoptic key of them.

I. No yellow band posteriorly from orbit (a yellow half-collar).
a. Dorsal spots or saddles (red) open at the side, the borders of
adjacent spots forming pairs of black rings.

Interspaces between red saddles open below ; scales not
black-tipped ; front more or less black ; first black ring
on nape only : O. d. coccinea,

Interspaces between red saddles closed by black spot be-
low ; scales black tipped ; front black; first black ring
complete : O. a. polyzona.

Interspaces not closed; rings, including first, complete on
belly; first yellow band crossing occipital plates; front
black ; scales not black-tipped : O. d. conjuncta,

aa. Dorsal spots closed at the sides below, forming saddles.
6, Saddles closed by a single black tract on the middle of the
belly; no spots between the saddles.

Dorsal spots undivided medially; front black ; first black

ring complete : O. d. annulata,

Dorsal spots divided longitudinally by a median black

connection ; front black : O. d. gentilis.

46. Inferior borders of saddles separate and not confluent with
each other.

Saddles completed on gastrosteges; no alternating spots ;

no black collar : O. d. parallela.

Saddles completed on gastrosteges ; spots opposite inter-
vals forming a single series on the middle line of the
belly : O. d. syspila,

Saddles completed above the gastrosteges; alternating
spots which do not meet on the middle line of the belly:

O. d. doliata.

1 Proceedings of the U.S, National Museum, XIV, p. 589-608.

ON VARIATION, 31

II. A yellow band posteriorly from orbit, bounded below by a black
or brown one.
a, Saddle spots closed laterally on gastrosteges ; alternate spots
entirely on gastrosteges.
A half collar behind parietal plates, no superciliary

stripe : - O. d. temporalis.
aa. Saddle spots closed above gastrosteges ; alternate spots on
scales. :

A half collar nearly or quite touching occipital plates, no
bands ; alternate spots partly on gastrosteges:
O. d, collaris,
Neck with longitudinal bands ; alternate spots partly on
gastrosteges . O. a. clerica.
Neck with bands ; alternate spots entirely on scales:
O. d. triangula.

In Fig. 2 are represented vertical, lateral, and in-
ferior views of parts of the body of the subspecies ¢77-
angula, taken from a specimen in my collection from
Westchester County, New York, which I owe to the
kindness of my friend, Mr. T. H. Mead.

The characters of this form are seen in (1) the
presence of a light band extending from the posterior
angle of the eye downward and backward, which is
bounded by a black border above and below; (2) a
black cross-band on the posterior border of the pre-
frontal plates; (3) chevron shaped mark with the apex
on the posterior part of the frontal plate, whose limbs
extend posteriorly as a band on each side of the neck,
where they are fused together, and continue as a sin-
gle, broad band for a short distance; (4) a series of
lateral spots which do not extend beyond the scales on
to the gastrosteges, and which alternate with the dor-
sal spots; (5) a series of spots on the ends of the gas-
trosteges which alternate with the last mentioned;
(6) a series of spots on the centers of the gastrosteges
which alternate with the spots mentioned under (5).

32 PRIMARY FACTORS OF ORGANIC EVOLUTION.

an
SS. %,
ee eatnt

ee,
See
oe
C

Osceola doliata triangula.

Ke
| iy
A ini

SC)

Fig. 2.

Osceola doliata clerica.

Fig. 3.

ON VARIATION. 33

The ground color in this form is gray, and the spots
are a rich brown with black borders. The belly has a
white ground color.

In Fig. 3 we have the subspecies clerica, where
the following modifications appear. The fusion of the
limbs of the chevron is more complete, and the dorsal
spots are more expanded transversely. They extend
to within two or three scales of the gastrosteges, while
in the form ¢rzangulus they are five scales distant. The
alternate spots touch the gastrosteges. This figure is
taken from a specimen in the Museum of the Phila-
delphia Academy from southern Illinois.

In Fig. 4 we have an individual from Elmira, IIli-
nois, which illustrates the characters of the form co/-
laris. Here the chevrons are distinct from the first
dorsal spot, whose anterior black border forms a half
collar on the neck. This specimen is instructive, as
it displays the last connection between the chevron
and the first spot, in a black line on each side. This
is wanting in the typical ce/aris.

The collar of ground color is complete in its an-
terior border, as well as the posterior in the form ¢em-
poralis (Fig. 5), owing to the disappearance of the
chevron. ‘The transverse band on the prefrontals has
also disappeared. The anterior extremity of the post-
orbital stripe is cut off, and consists of a spot of ground
color. The dorsal saddle spots are wider, reaching the
gastrosteges, while the intermediate spots are exclu-
sively gastrostegal. The spots whichealternate with
them, have fused on the middle line. Fig. 5 is from
a specimen from the State of Delaware.

In subspecies do/iata the postocular stripe has dis-
appeared, and the chevron:is replaced by a black patch
on the parietal and temporal plates. In other respects

34 PRIMARY FACTORS OF ORGANIC EVOLUTION.

i r)
xX Se
tear

Osceola doliata collarts.

Fig. 4.

Osceola doliata temporalis,

Fig. 5.

ON VARIATION. 35

this form is more like the form co//aris. The dorsal
saddle spots are separated by a row or two of scales
from the gastrosteges, and their alternating spots are
partly on the scales. The ground color in this form,
as in the zemporalis, approaches red. This is the form
of the tier of states between latitude 4o° and the Gulf
States.

The subspecies sysfiJa is represented in Fig. 8.
The head pattern is like that of doliata with the black
patch more or less reduced—in the specimen figured
being represented by a cross stripe. The dorsal saddle
spots are more expanded than in any form yet encoun-
tered, their lateral borders being completed below the
scales and entirely on the gastrosteges. The alternate
spots now meet and fuse on the middle line of the ab-
domen, and the second series of alternating spots has
disappeared. This is distinctively a southern form,
extending west to central Oklahoma.

The dorsal saddles are so far extended in the next
subspecies, parallela, as to form two parallel stripes
with a narrow strip of ground color between, on the
middle line of the abdomen. The alternating spots
have disappeared. In the specimen figured, which is
from Florida, and is in the United States National
Museum, the supraocular spots seen in /emforalis, are
indicated. The ground color is red. Black begins to
appear on the head.

From the form syspz/a two types of color modifica-
tion may be traced. One of these brings the borders
of the saddle spots together on the median line, form-
ing a median black stripe; this is the subspecies annw-
Jata, which belongs to western Texas and the adjacent
parts of Mexico. The top of the head is black (Fig.
10). In the other, the lateral borders of the saddle

36 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Figs. 6-7. Osceola doliata doliata,

ON VARIATION. 37

spots have disappeared altogether, so that the body is
more or less completely encircled by pairs of black
rings, the alternating spots having disappeared. This
might be supposed to have resulted from a continua-
tion of the process by which the alternating spots have
disappeared, and the edges of the saddles been brought
closer and closer together. The continued transverse
extension of the spot color would finally obliterate the
lateral borders completely, as actually occurs in this
last form, the coccinea of authors, which is the com-
mon type of the Gulf Coast. But the black has not
covered the head and muzzle of this form as in the an-
nulata. ‘These regions are on the contrary red, as is
the spot color generally, while the ground color is pale
yellow.

A tendency to a development. of black pigment in
the saddle spots is seen in two other forms. The sub-
species gentilis resembles annulata, but has a black
longitudinal dorsal band which divides each saddle
spot in two equal halves. This is a rare form, only
known from the Indian Territory. The common Mex-
ican form (folyzona) has the paired rings of coccinea,
the black head of annulata, but each scale of the red
intervals is tipped with black.

The relations of these forms may be expressed ina
tabular form, given on page 39.

The main series corresponds with a distribution in
latitude, commencing with the ¢riangula of New Eng-
land and New York, and passing gradually to the coc-
cinea of the Gulf Coast regions, and Jolyzona of Mex-
ico and Central America. The forms of the right-hand
column are (except the paradllela) from the central
warmer parts of the continent.

This series of color-forms of the Osceola doliata

38 PRIMARY FACTORS OF ORGANIC EVOLUTION.

i»

10,

Osceola doliata syspila.

Fig. 8.

PA
este

Osceola doliata parallela,

Fig. 9.

ON VARIATION. 39

demonstrates the following points. First: the color-
variation is determinate and not indeterminate. It
consists in, a, the successive enlargement of the dorsal
spots toward, to, and across, the belly; 4, the diminu-
tion and extinction of the longitudinal stripes on the
head ; ¢, do. of the spots of the inferior surface of the
body; @, in the increase of red in the color of the
dorsal spots, coincidentally with the changes men-
tioned. Second: these color-changes follow parallels

gentilis
polyzona

annulata
conjuncta

parallela
coccinea

syspila /

doliata

“~~_temporalis

collaris
clerica
triangula

of latitude, the red color and accompanying changes
developing from north to south. Third: so far as re-
gards eastern North America, there is a diminution of
size in passing from north to south; the O. @. coccinea
being the smallest of the subspecies. In Mexico, the
size is recovered, as the O. @. polyzona equals in di-
mensions the O. d. triangula.

The young of the northern O. d. ¢riangula pre-
sents the colors of the dorsal spots nearly as brilliant
as those of the southern O. d. coccinea, and they fade

40 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Be
e:

CoN
™~

Fig. 10. Osceola doliata annulata.

Osceola doliata coccinea,

Fig. 11.

ON VARIATION. 41

with age to the adult character. The pattern in the
young at the period of hatching is the same as that of
the adult.

¢. Color-Variations in Cnemidophorus.

Another illustration of the nature of color-variation
is to be found in certain species of the lacertilian gen-
era Cnemidophorus in America, and Lacerta in Eu-
rope. In both genera the color-markings differ in the
same individual at different ages, and the age at which
the acult coloration ds assumed, differs in different lo-
calities. Some of the species, e. g., Cnemidophorus
sexlineatus, never abandon the coloration of the young
of other species and subspecies. The same condition
is characteristic of the C. deppet of Mexico, the C. Zem-
niscatus of Brazil, and other.species. - The process of
color-modification in the C. Zessellatus and C. gudaris
of North America is, as J have pointed out,! as follows:
The young are longitudinally striped with from two to
four stripes on each side of the middle line. With in-
creasing age, light spots appear between the stripes
in the dark interspaces. Ina later stage these spots
increase in transverse diameter, breaking up the dark
bands into spots. In some of the forms these dark
spots extend themselves transversely and unite with
each other, forming black cross-stripes of greater or
less length. Thus we have before us the process by
which a longitudinally striped coloration i is transformed
into a transversely striped one.

The large number of specimens of the C. ¢essellatus
and C gularis in the National Museum collection show
that the breaking up of the striped coloration appears

1 Proceeds.. Amer. Philos, Soc., 1885, p. 283. Transac, Amer, Philos. Soc
1892, p. 27.

42, PRIMARY FACTORS OF ORGANIC EVOLUTION.

=i) esemmanlly
Pepcid
Om

‘C131

*snqvpjassaz snaoygopruauy ‘y-p

ON VARIATION. 43

first at the posterior part of the dorsal region (i. e., the
sacral and lumbar). The confluence of the spots ap-

- oR

BASES be

ay Aan yy
TU hy aleeatetes r af
A

pears there first; and finally (C. gularis semifasciatus),
where the color markings disappear, leaving a uniform
hue, this also appears first at the posterior part of the

Fr 31g

*$2]DANUL DILIIVT

PRIMARY FACTORS OF ORGANIC EVOLUTION.

MBARBRRKTS
eee ae
<3

SoS rrs
—

ON VARIATION. 45

body. In the C. ¢essellatus rubidus the dark spots dis-
appear first on the anterior regions.

According to Eimer,! among many color-variations
of the Lacerta muralis there exists a series of types
closely similar to those observed by me to characterize
the two species of Cnemidophorus mentioned. I give
figures of these series in all three species. It will be
observed that in the second and third forms (B and C)
of the Z. muralis, the pale portions of the dark stripes
do not assume the very light hue of the ground color
as they do in the corresponding phase of the Cnemido-
phorus tessellatus (C and D, Fig. 12), but this interme-
diate condition is exactly paralleled by the subspecies
mariarum of the Cnemidophorus gularis. The corre-
spondences are represented in the table on page 46.

There are some color forms in the Lacerta muralis
which are not repeated in the North American Cnemi-
dophori, particularly those which result in a strong
contrast between the dorsal colors as a whole and the
darker lateral colors, as a band. The color variety,
No. 7, of the Cnemidophori is not reported by Eimer
as occurring in the Lacerta murals.

The variations from one to four form a direct series,
and so do those represented by Nos. 1, 2, 3, and 5.
Such variations cannot be regarded as promiscuous,
especially when the same process of change is to be
observed in three different species, one of which in-
habits a continent remote from the other two.

@. Variations in North American Birds.and Mammals in
Relation to Locality.

The distinguished zodlogist, Dr. J. A. Allen of New
York, has made a thorough study of this subject with

Lrchiv fir Naturgeschichte, 1881, p. 239.

46 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Cnem. tessellatus,

Cnem. gularis,

Other Cnemidoph't.

Lacerta muralis,

Longitudinally striped. .

Dark interspaces pale spotted .....

Dark interspaces divided by light
ColOM seine ees

Dark spots confluent transversely,

forming crossbars..............

Light spots not confluent; light
stripes broken up; pattern reticu-
Tated a sicaire oones

Dark stripes interrupted by darker
color. .....

Dark spots separate and on a brown

PToUNd sas chee pede hada nian

C. t. perplexus.

C. t. tessellatus a.

C. t. tessellatus B.

C. t. tessellatus y.

(orm

thus.

melanoste-

C. t. rubidus,

C g. gularis a.

C. g. scalaris a.

C. g. scataris B.
C. g.

&. costatus,

C. t, mariarum.,

C. g. semifasciatus,

C. octolineatus.
C. sexlineatus.

C. labialis,
C. septemvitiatus.

C. grahamit.

C. variolosus.

L. m, campestris.

L. m, albiventris.
Lm, striatomacu-
Zata,

L. m.veticulata.
Lim, tigris,

L. m, punctulato-
SJasctata.

L. m. maculostri-

aa,

ON VARIATION. 47

ample material at his disposal. Following lines al-
ready laid down by Prof. Spencer F. Baird, Dr. Allen
has shown that variations in form, size, and color are
directly related to latitude, and that they are not pro-
miscuous or multifarious, but are definite and graded.
I make the following extract from a summary of the
subject published by him in The Radical Review (New
Bedford, Mass.) for May, 1877:

‘¢Geographical variation, as exhibited by the mam-
mals and birds of North America, may be summarized
under the following heads, namely: (1) variation in
general size, (2) in the size of peripheral parts, and
(3) in color; the latter being subdivisible into (a) vari-
ation in color with latitude, and (4) with longitude.
As arule, the mammals and birds of North America
increase in size from the south northward. This is
true, not only of the individual representatives of each
species, but generally the largest species of each genus
and family are northern. There are, however, some
strongly marked exceptions, in which the increase in
size is in the opposite direction, or southward. There
is for this an obvious explanation, as will be presently
shown ; the increase being found to be almost invari-
ably toward the region where the type or group to
which the species belongs receives its greatest numer-
ical development, and where the species are also most
specialized. Hence the representatives of a given spe-
cies increase in size toward its hypothetical center of
distribution, which is in most cases doubtless also its
original center of dispersal. Consequently there is fre-
quently a double decadence in size within specific
groups, and both in size, and numerically in the case of
species, when the center of development of the group
to which they belong is in the warm-temperate or trop-

48 PRIMARY FACTORS OF ORGANIC EVOLUTION.

ical regions. This may be illustrated by reference to
the distribution of the higher classes of vertebrates in
North America. Among the species occurring north of
Mexico there are very few that may not be supposed to
have had a northern origin; and the fact that some
are circumpolar in their distribution, while most of the
others (especially among the mammals) have congeneric
Old World allies further strengthens the theory of their
northern origin. Not only do individuals of the same
species increase in size toward the north, but the same
is true of the species of different genera. Again, in
the exceptional cases of increase in size southward, the
species belong to southern types, or, more correctly,
to types having their center of development within or
near the intertropical regions, where occur, not only the
greatest number of the specific representatives of the
type, but also the largest.

‘‘For more detailed illustration we may take three
families of the North American Carnivora; namely,
the Canidz (wolves and foxes), the Felide (lynxes
and wild cats), and the Procyonide (raccoons). The
first two are to some extent cosmopolitan, while the
third is strictly American. The Canide have their
largest specific representatives, the world over, in the
temperate or colder latitudes. In North America the
family is represented by six species,! the smallest of
which (speaking generally) are southern, and the larg-
est northern. Four of them are among the most widely
distributed of North American mammals, two (the
gray wolf and the common fox) being circumpolar spe-
cies ; another (the Arctic fox) is also circumpolar, but

1 The gray wolf (Canzs Zupus), the coyote (C. latrans), the Arctic fox (Vud-
pes lagopus), the common fox (l, alopfex), the kit fox (V. velox), and the gray
fox (V7. cinereoargentatus),

ON VARIATION. 49

is confined to high latitudes. The three widest-rang-
ing species (the gray wolf, the common fox, and the
gray fox) are those which present the most marked
variation in size. Taking the skull as the basis of
comparison, it is found that the common wolf is fully
one-fifth larger in the northern parts of British Amer-
ica and Alaska than it is in Northern Mexico, where it
finds the southern limit of its habitat. Between the
largest northern skull and the largest southern skull
there is a difference of about thirty-five per cent. of the
mean size’ Specimens from the intermediate region
show a gradual intergradation between these extremes,
although many of the examples from the upper Mis-
souri country are nearly as large as those from the ex-
treme North.

«©The common fox, though occurring as far north
as the wolf, is much more restricted in its southward
range, especially along the Atlantic coast, and presents
a correspondingly smaller amount of variation in size.
The Alaskan animal, however, averages about one-
tenth larger than the average size of specimens from
New England. In the gray fox, whose habitat ex-
tends from Pennsylvania southward to Yucatan, the
average length of the skull decreases from about five
inches in Pennsylvania to considerably less than four
in Central America—a difference equal to about thirty
per cent. of the mean size for the species.

«The Felide, unlike the Canidz, reach their great-
est development, as respects both the number and
the size of the species, in the intertropical regions.
This family has but a single typical representative—
the panther (Fe/s concolor)—north of Mexico, and this
ranges only to about the northern boundary ot the
United States. The other North American represen-

50 PRIMARY FACTORS OF ORGANIC EVOLUTION,

tatives of the family are the lynxes, which, in some of
their varieties, range from Alaska to Mexico. They
form, however, the most northern, as well as the most
specialized or ‘aberrant,’ type of the family. While
they vary greatly in color, as well as in the length and
texture of the pelage, at different localities, they afford
a most remarkable exception to all laws of variation in
size with locality; for a large series of skulls, repre-
senting localities as widely separated as Louisiana,
Northern Mexico, and California, on the one hand, and
Alaska and the Mackenzie River district on the other,
as well as various intermediate localities, reveals no ap-
preciable difference in size throughout this wide area.
The true cats, however, as the panther and the ocelots,
are found to greatly increase in size southward, or to-
ward the metropolis of the family. The panther ranges
from the Northern States southward over most of
South America. Skulls from the Adirondack region of
New York have an average length of about seven and
a half inches, the length increasing to eight and three-
quarters in Louisiana and Texas, from beyond which
points there is lack of data. The ocelot (Felis parda-
Zs) finds its northern limit near the Rio Grande of
Texas, and ranges thence southward far into South
America. The average size of Costa Rican examples
is about one-fifth greater than that of specimens from
the Rio Grande.

Instances of increase in size northward among the
Carnivora of North America are so generally the rule
that further space need not be taken in recounting ex-
amples in detail. It may suffice to state that the
badger (Zaxidea americana), the marten (Mustela ame-
ricana), the fisher (AZ. pennanti), the wolverine (Guo
luscus), and the ermine (Putorius ermineus)—all north-

ON VARIATION. 51

ern types—afford examples of variations in size strictly
parallel with that already noticed 4s occurring in the
foxes and wolves.

“¢To refer briefly to other groups, it may be stated
that the Cervidz (deer family) are mainly rather north-
ern in their distribution; that the largest species occur
in the colder zones, and that individuals of the same
species increase rapidly in size toward the north.
Some of the species, in fact, afford some of the most
striking instances of northward increase in size; among
which are the Virginia deer and its several representa-
tives in the interior of the continent and on the Pacific
Slope. It is also noteworthy that the most obviously
distinctive characteristic of the group—the large, an-
nually deciduous antlers—reaches its greatest devel-
opment at the northward. Thus all the northern spe-
cies, as the moose, the elk, and the caribou, have
branching antlers of immense size, while the antlers
are relatively much smaller in the species inhabiting
the middle region of the continent, and are reduced to
arudimentary condition—a simple, slender, sharp spike,
or a small and singly forked one—in the tropical spe-
cies; the antlers declining in size much more rapidly
than the general size of the animal. This is true in
individuals of the same species as well as of the species
collectively.

“The Glires (the squirrels, marmots, spermophiles
mice, and their affines) offer the same illustrations in
respect to the law of increase in size as the species
already mentioned, the size sometimes increasing to
the southward, but more generally to the northward,
since the greater number of the species belong decid-
edly to northern types. There is no more striking in-
stance known among mammals of variation in size

52 PRIMARY FACTORS OF ORGANIC EVOLUTION.

with locality than that afforded by the flying squirrels,
in which the northern race is more than one-half larger
than the southern; yet the two extremes are found to
pass so gradually the one into the other, that it is
hardly possible to define even a southern and a north-
ern geographical race, except on the almost wholly
arbitrary ground of difference in size. The species,
moreover, is one of the most widely distributed, rang-
ing from the Arctic regions (the northern limit of for-
ests) to Central America.

“Among birds the local differences in size are al-
most as strongly marked as among mammals, and in
the main, follow the same general law. A decided
increase in size southward, however, or toward the
warmer latitudes, occurs more rarely than in mam-
mals, although several well-marked instances are
known. The increase is generally northward, and is
often very strongly marked. The greatest difference
between northern and southern races occurs, as in
mammals, in the species whose breeding-stations em-
brace a wide range of latitude. In species which breed
from Northern New England to Florida, the southern
forms are not only smaller, but are also quite different
in color and in other features. This is eminently the
case in the common quail (Ortyx virginianus), the
meadow-lark (Sturnella magna), the purple grackle
(Quiscalus purpureus), the red-winged blackbird (Age-
lacus phaeniceus), the golden-winged woodpecker (Co-
laptes auratus), the towhee (Pipilo erythrophthalmus),
the Carolina dove (Zenadura macrura), and in nu-
merous other species ; and is quite appreciable in the
blue-jay (Cyanurus cristatus), the crow (Corvus amert-
canus), in most of the woodpeckers, in the titmice,
numerous sparrows, and several thrushes and war-

ON VARIATION. 53

blers, the variation often amounting to from ten to
fifteen per cent. of the average size of the species.

‘‘As a general rule, certain parts of the organisms
vary more than does general size, there being a marked
tendency to enlargement of peripheral parts under
high temperature, or toward the tropics,—hence south-
ward in North America. This is more readily seen in
birds than in mammals, in consequence, mainly, of
their peculiar type of structure. In mammals it is
manifested occasionally in the size of the ears and feet,
and in the horns of bovines, but especially and more
generally in the pelage. At the northward, in individ-
uals of the same species, the hairs are longer and
softer, the under fur more abundant, and the ears and
the soles of the feet better clothed. This is not only
true of individuals of the same species, but of northern
species collectively as compared with their nearest
southern allies. Southern individuals retain perma-
nently, in many cases, the sparsely clothed ears and
the naked soles that characterize northern individuals
only in summer, as is notably the case among the dif-
ferent squirrels and sphermophiles.

‘¢In mammals which have the external ear largely
developed—as in the wolves, foxes, some of the deer,
and especially the hares,—the larger size of this organ
in southern as compared with northern individuals of
the same species is often strikingly apparent. It is
more especially marked, however, in species inhabit-
ing extensive open plains and semi-desert regions.
The little wood hare, or gray rabbit (Lepus sylvaticus),
affords a case in point. This species is represented,
in some of its varieties, across the whole breadth of
the continent, and from the northern border of the
United States southward to Central America, but in

54 PRIMARY FACTORS OF ORGANIC EVOLUTION.

different regions by geographical races or subspecies.
In addition to certain differences of color and general
size, the ears vary still more strongly. In the form
inhabiting the Great Plains, commonly known as the
little sage-brush hare (LZ. sylvaticus nuttall?), the ears
are considerably longer than in the eastern variety,
and increase in size from the north southward, reach-
ing their greatest development in Western Arizona and
the desert region further westward and southward,
where the variety is characterized mainly by the large
size of its ears, which are in this race nearly twice the
size they attain in the eastern variety. In the long-
eared ‘jackass’ hares of the plains, the ear likewise
increases in size to the southward. In Lepus callotis,
for example, which ranges from Wyoming southward
far into Mexico, the ear is about one-fourth to one-
third larger in the southern examples than in the north-
ern. The little brown hare of the Pacific Coast (Z.
trowbridge’) presents a similar increase in the size of
the ear southward, as does, to a less extent, the prairie
hare (LZ. campestris). Not only are all of the long-
eared species of American hares confined to the open
plains of the arid interior of the continent, but over
this same region is the tendency to an enlargement of
the ear southward stronger than elsewhere. It is also
of interest in this connection that the largest-eared
hares of the Old World occur over similar open, half-
desert regions, as do also the largest-eared foxes. On
our western plains, the deer are represented by a large-
eared species. Among the domestic races of cattle,
those of the warm temperate and intertropical regions
have much larger and longer horns than those of north-
ern countries ; as is shown by a comparison of the
Texan, Mexican, and South American breeds, with

ON VARIATION. 55

the northern stock, or those of the South of Europe
with the more northern races. In the wild species of
the Old World, the southern or sub-tropical are re-
markable for the large size of their horns. The horns
of the American prong-horn (Antilocapra americana) are
also much larger at southern than at northern locali-
ties.! Naturalists have also recorded the existence of
larger feet in many of the smaller North American
Mammalia at the southward than at the northward,
among individuals of the same species, especially
among the wild mice, in some of the squirrels, the
opossum and raccoon, as well as in other species.
‘<In birds, the enlargement of peripheral parts, es-
pecially of the bill, claws, and tail, is far more obvious
and more general than in mammals. The bill is par-
ticularly susceptible to variation in this regard,—in
many instances being very much larger, among indi-
viduals of unquestionably the same species, at the
southward than at the northward. This accords with
the general fact that all the ornithic types in which the
bill is remarkably enlarged occur in the intertropical
regions. The southward enlargement of the bill within
specific groups may be illustrated by reference to al-
most any group of North American birds, or to those
of any portion of the continent. As in other features
of geographical variation, the greatest differences in
the size of the bill are met with among species having
the widest distribution in latitude. Among the species
inhabiting eastern North America we find several strik-

1The deer tribe, in which the antlers increase in size toward the north,
offer an apparent exception to the rule of increase in size of peripheral parts
toward the tropics. The antlers of the deer, however, are merely seasonal
appendages, being annually cast and renewed, and are thus entirely different
physiologically from the horns of bovines, which retain a high degree of
vitality throughout the life of the animal.

56 PRIMARY FACTORS OF ORGANIC EVOLUTION.

ing examples of this enlargement among the sparrows,
black-birds, thrushes, crows, wrens, and warblers, in
the quail, the meadow-lark, the golden-winged wood-
pecker, etc. Generally the bill, in the slender-billed
forms, becomes longer, more attenuated, and more de-
curved (in individuals specifically the same) in pass-
ing from the New England States southward to Flo-
rida, while in those which have a short, thick, conical
bill there is a general increase in its size so that the
southern representatives of a species, as a rule, have
thicker and longer bills than their northern relatives,
though the birds themselves are smaller. There is
thus not only generally a relative, but often an abso-
lute, increase in the size of the bill in the southern
races. The species of the Pacific Coast and of the in-
terior afford similar illustrations, in some cases more
marked even than in any of the eastern species. More
rarely, but still quite frequently, is there a similar in-
crease in the size of the feet and claws.

“The tail, also, affords an equally striking exam-
ple of the enlargement of peripheral parts southward.
Referring again to the birds of the Atlantic Coast,
many of the above-named species have the tail abso-
lutely longer at southern localities than at northern,
and quite often relatively longer. Thus while the gen-
eral size decreases, the length of the tail is wholly
maintained, or decreases less than the general size;
but, in some cases, while the general size is one-tenth
or more smaller at the south, the tail is ten to fifteen
per cent. longer than in the larger northern birds.
Some western species are even more remarkable in
this respect ; and in consequence mainly of this fact
the southern types have been varietally separated from
the shorter-tailed northern forms of the same species.

ON VARIATION. 57

‘«Variations in color with locality are still more ob-
vious, particularly among birds, in which the colors
are more positive, the contrasts of tints greater, and
the markings consequently better defined than is usu-
ally the case in mammals. The soft finely-divided
covering of the latter is poorly fitted for the display
of the delicate pencilings and the lustrous, prismatic
hues that so often characterize birds. Mammals, how-
ever, present many striking instances of geographical
variation in color.

“‘As already stated, geographical variations in color
may be conveniently considered under two heads.
While the variation with latitude consists mainly in a
nearly uniform increase in one direction, the variation
observed in passing from the Atlantic Coast westward
is more complex. In either case, however, the varia-
tion results primarily from nearly the same causes,
which are obviously climatic, and depend mainly upon
the relative humidity, or the hygrometric conditions
of the different climatal areas of the continent. In re-
spect to the first, or latitudinal variation, the tendency
is always toward an increase in intensity of coloration
southward. Not only do the primary colors become
deepened in this direction, but dusky and blackish
tints become stronger or more intense, iridescent hues
become more lustrous, and dark markings, as spots
and streaks or transverse bars, acquire greater area.
Conversely, white or light markings become more re-
stricted. In passing westward a general and gradual
blanching of the colors is met with on leaving the
wooded regions east of the Mississippi, the loss of
color increasing with the increasing aridity of the cli-
mate and the absence of forests, the greatest pallor
occurring over the almost rainless and semi-desert re-

58 PRIMARY FACTORS OF ORGANIC EVOLUTION.

gions of the Great Basin and Colorado Desert. On
the Pacific Slope, north of California, the color again
increases, with a tendency to heavy, sombre tints over
the rainy, heavily-wooded region of the Northwest
Coast.”

2. VARIATION IN STRUCTURAL CHARACTERS.

Modifications of structural characters may appear
quite independently of variation of specific ones. In-
deed, generic characters have at times changed
completely without the appearance of corresponding
changes in the more superficial characters which de-
fine the species. Thus changes in the dentition of
some of the Mammalia appear within the limits of
species, which, should they become permanent, would
entitle the two sets of individuals which display the
different dentitions to be placed in different genera.

Some striking examples of how generic characters
may undergo metamorphosis without corresponding
changes in specific characters, have been brought to
light by Dr. William H. Dall among the Brachiopo-
dous Mollusca. Some of the species of different gen-
era can scarcely be distinguished, except by compari-
son of their generic characters. I have cited the
axolotls as illustrative of this phenomenon. Here the
same species may reproduce as a permanent larva, or
as an adult. Duméril has shown that the North Amer-
ican salamander (Amélystoma tigrinum) can lay and
fertilize eggs before the metamorphosis is passed. I
have since observed that the females of the allied spe-
cies of Amblystomide, the Chondrotus tenebrosus B. and
G., of California contain mature eggs ready for de-

1 The Radical Review, May, 1877.

ON VARIATION. 59

posit, and have supposed that this species has also the
same power.! The difference between such larve and
the adult which has passed the metamorphosis is great.
It extends not merely to the branchial processes, but
to the splenial teeth, which are shed, and to the palato-
pterygoid arch, which is absorbed, and to the pos-
terior ceratobranchial and epibranchial cartilages, which
are absorbed. In the larva of the C. tenebrosus the
palatopterygoid arches and epibranchials are ossified,
so that the probability of its being able to maintain an
independent existence as a larva is greater than in the
case of the 4. tigrinum. In this type, then, each spe-
cies displays variations concomitant with reproductive
maturity, which are not only of generic, but of family
significance. In a third species, the Sivedon mexica-
num, no metamorphosis has yet been shown to take
place, so that it is probable that it reproduces ordina-
rily while in the branchiferous stage. Yet it is only
specifically different from the larva of the Amélystoma
tigrinum.

Excellent illustrations of the serial appearance of
generic characters may be seen in the family of the
dogs (Canidae). In the true genus Canis, the dental
formula is, I. 3; C.4; P. m. $; M.2. The inferior sec-
torial (m. 1) has a metaconid, and the second inferior
true molar has two roots. It not unfrequently hap-
pens, however, that the last inferior molar (m. 3) is
wanting; and in some cases the inferior m. 2 has but
one root. When in addition to this, as in some of the
black-and-tans, in the Mexican naked dog, and in the
pug, the inferior m. 1 loses its metaconid, we have the
genus Synagodus. Occasionally the pug dog, and fre-
quently the Mexican dog, loses one of its premolars

1Batrachia of North America, 1888, p. 113, Pl. xxii, xxiii,

60 PRIMARY FACTORS OF ORGANIC EVOLUTION,

from both jaws. The Japanese spaniel goes still fur-
ther, and usually loses also its second superior true
molar and frequently another premolar from each jaw;
and we then have a dentition which indicates a third
genus, which has been called Dysodus. Its dental
formula is I. 3; C.4; P.m. 2-8; m.4. Transitions
between this and the normal dentition of Canis, in all
respects can be found in the smaller domesticated
dogs. And these modifications are not pathological,
but simply express a rapid metamorphosis of the den-
tition towards the reduced formula which is charac-
teristic of the cats. And while the most characteristic
dentitions belong to particular species (or races) of
dogs, many of the single modifications are both absent
and present in dogs of the same species or race. And
these are the kind of characters which are observed
to mark the slow progress during long geologic
ages, of mammals of various other groups. These
modifications are not promiscuous, but are in the di-
rect line of change which has characterized all Mam-
malia during geologic time; 1. e., the reduction of the
numbers of the molar teeth. And in greater detail,
the loss of metaconid of the inferior sectorial, and loss
of posterior true molars, are the exact losses which the
carnivorous type has undergone in the evolution of
the cats.

A significant modification of the third superior pre-
molar has been observed by Dr. Horace Jayne to be
occasionally met with in the domestic cat. Sometimes
an internal cusp (deuterocone), with a corresponding
root is developed, giving rise to a tritubercular crown.

Similar observations have been made on the denti-
tion of man, which presents two phenomena of varia-
tion of opposite phylogenetic significance. I have

ON VARIATION. 61

shown! that most of the Indo-European race, together
with the Esquimaux, present a reversion to a lemu-
rine form in the second and third superior molars, and
sometimes, in the case of the Esquimaux, in the first
superior molar also. I have also shown,’ after a study
of the dentition of the extinct Mammalia, that the more
complex molars of later placental orders, have been
derived from a tritubercular type, which prevailed
throughout the earth just before the opening of the
Eocene period. In the line of human and quadruma-
nous phylogeny, the lemurs of the Eocene period pre-
sented this type of molar in the upper jaw, and mostly
continue to do so to the present time. The true mon-
keys, however, added the fourth tubercle or hypocone,
in accordance with the developmental law in Mamma-
lia generally, and the apes and men of the lower races
present the same characteristic. Now, in the yellow
race the hypocone of the last molar is generally want-
ing, while in the white race it is usual to find it absent
from both the second and third molars. In this we
have a case of reversion.

The reduction of the third (last) superior molar,
and of the inferior as well, has gone further in the
white race, since the tooth is frequently abnormally
small, abortive, or totally wanting. The external su-
perior incisor has a similar history, although its reduc-
tion and loss is not nearly so frequent as that of
the last molars. These losses from the dental series
are not of the nature of reversions, since the number
of teeth is more and more numerous as we recede in
time along the line of human ancestry. It is, on the
contrary, the continuation of a process which has been,

lLAmerican Journal of Morphology, 1888, p. 7.
“2 American Naturalist, 1884, p. 350; Origin of the Fittest, 1887, p. 347.

62 PRIMARY FACTORS OF ORGANIC EVOLUTION.

as already remarked, common to all the Mammalia, of
reduction in the number of teeth. Thus men with fewer
teeth are more advanced than those with more numer-
ous ones; while people with tritubercular superior
molars have reverted to an ancient type; and both re-
sults are probably attained by the same physiologic
process, i. e. defect of nutrition. It is to be remem-
bered also, in connection with our argument, that these
dental variations are modifications of generic charac-
ters, and that they are in definite directions, and are
not promiscuous. With regard to the question as to
whether dental variations in man are promiscuous or
not, we have better opportunities of investigation than
in the case of the lower animals generally. It may be
safely asserted that the dental variations above cited
are by far the most frequent in man, and that all others
put together are relatively insignificant.

3. SUCCESSIONAL RELATION.

As the biologic types are variations become perma-
nent, it is important to examine how the former stand
related to each other. These relations express the
direction which variation has taken, and throw a great
deal of light on the nature of the process. That exist-
ing types of all grades are the result of the isolation of
variations of species, is shown by the frequent exam-
ples of incomplete isolation, which follows inconstancy
of the definitive characters. Groups of individuals
which display this partial isolation are termed sub-
species. ;

As an illustration of the mingling of isolated groups
of individuals (species) with imperfectly isolated groups
(subspecies), in a single genus, I refer to the American

ON VARIATION. 63

garter-snake (genus Eutaenia B. andG.). An exami-
nation of several hundred individuals of this genus
yielded the following results: I found seventeen groups
of individuals, which could be said to be completely
isolated in characters, with very few exceptions. Eight
other groups (species) are probably isolated, but they
are not represented by a sufficiently large number of
specimens to yield a satisfactory demonstration. Of
the seventeen, four species embrace fifteen non-isolated
geographical forms (subspecies), besides the typical
forms (eight of which are included under the £. szrta-
Zs); and two others include three color forms easily
recognizable, besides the typical ones. Similar phe-
nomena are presented in every part of the animal and
vegetable kingdoms.

One of the most instructive natural divisions for
the study of taxonomic relations as the result of varia-
tion, on account of the simplicity of the relations pre-
sented, is the Batrachia Salientia, or the order of Ba-
trachia to which belong the toads, frogs, etc. Omitting
the very restricted suborders of the Aglossa and Gas-
trechmia, the Batrachia Salientia fall into two divi-
sions, which differ only in the structure of the lower
portion of their scapular arch, or shoulder-girdle. In
the one the opposite halves are capable of movements
which contract or expand the capacity of the thorax ;
in the other the opposite halves abut against each
other so as to be incapable of movement, thus pre-
serving the size of the thoracic cavity. But during the
early stages, the frogs of this division have the mova-
ble shoulder-girdle which characterizes those of the
other division, the consolidation constituting a modifi-
cation superadded in attaining maturity. Further-
more, young Salientia are toothless, and one section of

64 PRIMARY FACTORS OF ORGANIC EVOLUTION,

the species with embryonic shoulder-girdle never ac-
quire teeth. The suborder with embryonic shoulder-
girdle is called the Arcifera, and that which is ad-
vanced in this respect is the /irmisternia. Now the
frogs of each of these divisions present nearly similar
scales of development of another part of the skeleton,
viz., the bones of the top of the skull. We find some
in which one of these bones (ethmoid) is represented

Fig. 16.

SHOULDER-GIRDLES OF ‘‘ANURA."'

Fig. 15.—Of the Arciferous type (Phyllomedusa bicolor), Fig. 16, Rana
temporaria, tadpole with budding limbs. Fig. 17, do., adult. Figs. 16 and 17
from Parker.

by cartilage only, and the frontoparietals and nasals
are represented by only a narrow strip of bone each.
In the next type the ethmoid is ossified; in the next,
we have the frontoparietal completely ossified, and the
nasals range from narrow strips to complete roofs; in
the fourth station on the line, these bones are rough,
with a hyperostosis of their surfaces ; and in the next
set of species this ossification fills the skin, which is
thus no longer separable from the cranial bones ; in

ON VARIATION. 65

the sixth form the ossification is extended so as to roof
in the temporal muscles and inclose the orbits behind,
while in the rare seventh and last stage, the tympanum
is also inclosed behind by bone. Now all of these
types are not found in all of the families of the Saden-
tia, but the greater number of them are. Six principal
families, four of which belong to the Arcifera, are
named in the diagram below, and three or four others
might have been added. I do not give the names of
the genera which are defined as above described, re-
ferring to the explanation of the cuts for them, but in-
dicate them by the numbers attached in the plate,
which correspond to those of the definitions above
given. A zero mark signifies the absence or non-dis-
covery of a generic type.

Sternum embryonic. Arcifera. Sternum_ complete

Toothless. Toothed. Firmisternia.

Bufonide. Scaphiopide. Cystignathide. Hylide. Ranidz.

= T oO I I oO
2— S 2 2 Oo
3— 3 ° 3 3 3
4— 4 4 4 4 4
5— 5 5 o 5 5
6— 6 6 6 6 6
I— 7 fo) ° ° °

It is evident, ‘from what has preceded, that a per-
fecting of the shoulder-girdle in any of the species of
the arciferous columns would place it in the series of
Firmisternia. An accession of teeth in a species of the
division Bufonide would make it one of the Scaphiopide;
while a small amount of change in the ossification of
the bones of the skull would transfer a species from
one to another of the generic stations represented. by
the numbers of the columns from one to seven.

Fig. 18. Fig. 19.
SCAPHIOPIDA AND PELOBATID.

BuFONID.

Fig. 22.

Fig. 21.
CYSTIGNATHIDE.

Fig. 20,
Hy.ip2.

RANIDA.

68 PRIMARY FACTORS OF ORGANIC EVOLUTION.

That the above generic divisions have been actually
developed from each other is demonstrated by the oc-
currence of occasional intermediate forms. Thus no
generic distinction can be maintained between types
third and fourth in the family of toads (Bufonidz), so
complete is the transition between them. In Hylide
and Cystignathide occasional transitions between types
second and third occur. In the Scaphiopide the sub-
species Spea hammondii intermontana sometimes has the
frontoparietal fontanelle open, sometimes closed. I
have seen some adult specimens of Rana virescens au-
stricola from Central America with the ethmoid bone
unossified above, as in the genus Ranula. The rugose
cranium is only acquired in old age of some of the spe-
cies of Polypedates of India. Yet these genera are as

EXPLANATION OF CUTS OF CRANIA OF SALIENTIA.

The numbers in each column correspond with the types of ossification
mentioned in the text, and are the same as those in the table of families given
in the same connection. The power numbers attached to No. 4, represent the
degree of ossification of the nasal bone, except —1, which signifies unossified
ethmoid, Most of the cuts are original

Fig. 18.—Buronip#.—No. 1, anterior part of skull of Chelydobatrachus
gouldiz Gray, from Australia. No. 4, do. of Schismaderma carens Smith, South
Africa. No.5, top of head of Peltaphryne peltacephala D. and B., Cuba. No.
7, top of head of Ofasfis empusa Cope, Cuba.

Fig. 19.—ScAPHIOPID# AND PELOBATID#£.—No. 2, diagram of top of cranium
of Didocus calcaratus Micahelles, Spain. No. 5, skull of Scaphiopus holbrookti
Harl., United States. No.6, skull of Cultr7pes provincialzs, from France, after
Dugés.

Fig. 20.—Hy.tip&.—No. 1, Thoropa miliaris Spix., Brazil. No. 2, Hypsi-
boas doumercit D.and B., Surinam. No, 21, Hypszboas punctatus Schn., Brazil.
No. 44, Scytopis venulosus Daudin, Brazil. No. 5, Osteocephalus planiceps Cope,
E. Peru. No.6, Trachycephalus geographicus D. and B., after Steindachner.

Fig. 21.--CySTIGNATHID2.—No. 1, Eusophus nebulosus Gir., Chili. No. 2,
Borborocetes tasmantensis Gthr., Tasmania. No.3, Zlosda nasus Licht., Bra-
zil, No. 4, Hylodes oxyrhynchus D, and B., West Indies. No. 6, Calyptocepha-
lus gay? D. and B., Chili.

Fig. 22. Ranip&.—No. 4-1, Ranula chrysoprasina Cope, Costa Rica. No.
41, Rana clamata Daud.,N. America. No. 42, Rana agilis Thomas, Europe.
No. 43, Rana hexadactyla Less., India. No.5, Polyfedates guadrilineatus D.
and B., Ceylon.

ON VARIATION. 69

well defined as closely allied genera in most natural
divisions.

It is seldom that so many stages of developmental
series survive so as to be contemporaries, as in this
case of the Batrachia Salientia. In order to obtain
such series we usually have to explore the ages of the
past. Inthe higher groups this is also the case, but
here we have also occasional examples of the persis-
tence of fairly complete series. Such a one is pre-
sented by the suborder Artiodactyla of the Diplarth-
rous Ungulate Mammalia. I give the definitions of
the succession of the existing families.

I. Molars bunodont (tubercular) ; superior incisors generally pres-
ent. Nocannon or naviculocuboid bones. :
Lateral toes well developed ; Hippopotamide.
Lateral toes rudimental ; Suide,
II. Molars selenodont (crescent-bearing). (Lateral toes rudimental
or wanting).
A. Premolars with one row of lobes.
No naviculocuboid bone ; one superior incisor; a can-

non bone ; Camelide,
A naviculocuboid bone; no superior incisor; (cannon
bone variable) ; Tragulide.

AA. Premolars with two rows of tubercles ; a naviculocuboid
and cannon bones; no incisors above.
Premolar iii with only one row of lobes; canine teeth,

no horns; Moschide.
Premolar iii with two rows of lobes; fixed horns; no
canines above ; Bovide.
Premolar iii with two rows of lobes; horns decidu-
ous; Cervide.

In this suborder we see a gradual complication of
the structure of the molar teeth, and a loss of the in-
cisors. In the limbs we observe the successive loss of
the lateral digits, and the fusion of elements,—as the
metapodials into cannon bones, and the elements of

yo PRIMARY FACTORS OF ORGANIC EVOLUTION.

the tarsus, and, what is not stated in the above table,
of the carpus also. Finally there is the remarkable
development of horns on the head. When we come
to examine the phylogeny of this order we will find
how completely these characters are the result of the
fixation of variations which have appeared in past geo-
logic ages, and how various are the combinations and
modifications presented by the extinct types.

Few natural groups permit of representation of
their subdivisions in linear series. The only correct
representation is in the form of a branching tree, and
this cannot be well done in flat projection on the pages
of a book. Each branch taken by itself, however,
yields itself for a longer or shorter space to linear
treatment.

For an example of such linear series in higher
groups I turn again to the Batrachia Salientia. Here
the two suborders of the Arcifera and Firmisternia pre-
sent the following interesting parallels:

ARCIFERA. FIRMISTERNIA
I. Without teeth.

a. With sacral diapophyses dilated.

Brevicipitide.
Butonidey. + sasvingsetve ss edas soe Meee Reese Engystomidz.
Phryniscide.
aa, Sacral diapophyses cylindric.
Dendrophryniscidze. ......... 00. e cee eee eee ee Dendrobatidze

II. With premaxillary and maxillary teeth only.
«. With sacral diapophyses dilated.

Pelodytidze Dyscophidz.
Pelobatide ee Co h lide
Hylide ee
aa, With sacral diapophyses cylindric.
Cystignathide............ 0. ccc c cc ceeeccenoes Eelostetinds:
Ranide.

ON VARIATION. 71

III. Teeth in both jaws.

a, Sacral diapophyses not dilated.
Amphignathodontidz }

tics Gan meena Ceratobatrachide.”
Hemiphractide ..... Bocas tp Oo

In strict reference to the structure of the hind feet
the following parallels may be drawn:

FIRMISTERNIA. RAnIDé. ARCIFERA.
External metatarsal free :
Aquatic. Rana. Pseudis.
Subfossorial. Hoplobatrachus. Mixophyes.

External metatarsal attached :
Feet webbed—

Burrowing. Pyxicephalus. Ceratophrys.
Arboreal (vom. teeth). Leptopelis. Hyla.
Arboreal (no v. teeth). Hyperolius. Hylella.
Aquatic. Heteroglossa. Acris.

Feet not webbed—
Terrestrial. Cassina. 4 Cystignathus.
Terrestrial, spurred. Hemimantis. Paludicola.

Parallel series like those of the Arcifera and Fir-
misternia I have termed ‘‘ homologous,” and the cor-
responding terms of such series I have called ‘‘ hete-
rologous.”! Such corresponding phylogenetic series
are homologous to each other, while their terms or
genera are heterologous in their relation to correspond-
ing terms of other phyla. In such cases the genera or
terms of a series owe their resemblances to each other
to inheritance; but they owe their resemblances to
their corresponding or heterologous genera, to identi-
cal evolutionary influences. Subsequently to my pro-
posal to use the above terms, Prof. E. R. Lankester
proposed the word ‘‘homogenous” to express what is
conveyed by my term homologous, and ‘‘homoplastic”
to express the sense of heterologous. For the two con-

1“ Origin of Genera,” Proceedings Philadelphia Academy, 1868, p. 281.

72, PRIMARY FACTORS OF ORGANIC EVOLUTION.

ditions he coined the words ‘‘homogeny ” and ‘‘ho-
moplassy.” The terms introduced by Lankester differ
from mine in that they convey implications as to the
origin of the respective conditions.

Anant

Fig. 23.—Feet of (1-2) Uma scoparia Cope, from near Tucson, Arizona,
and (2-3) Plenopus garrudus Smith, from South Africa. No. 1, manus; No. 2,
pes; Nos. 3-4, pes. Nos, 1-2, original; Nos. 3-4, from Boulenger.

An illustration of homoplassy is to be seen in the
spines on the head, tail, and feet of lizards which in-
habit desert regions. The parallelism between Phry-
nosoma of the American dry regions, and the Moloch
of the corresponding climates of Australia has been

ON VARIATION. 73

already noted. In the deserts of Asia, South Africa,
and North America some of the lizards exhibit a great
elongation of the lateral scales of the digits on one or
both extremities. These become fringes of spines,
freely articulated at their bases with the integument.
By penetrating the sand, they increase the hold on its
yielding surface, and greatly improve the speed of
their movements. The genera in which this structure
is conspicuous in the three localities in question, be-
long to as many distinct families. Thus in Asia it is
the genus Phrynocephalus of the family Agamidez; in
South Africa it is Ptenopus of the Gecconide; while
in North America it is Uma of the Iguanide. I give
figures of the feet of Ptenopus and Uma for comparison.
(Fig. 23.) Phrynocephalus is more like Uma than is
Ptenopus.

In the succeeding chapters of this book many illus-
trations of the serial relation of characters will be
given, so that it is not necessary to occupy more space
with the subject here.

CHAPTER II.—PHYLOGENY.

1. GENERAL PHYLOGENY.

HE actual phylogeny or genealogy of organisms
can only be positively determined by paleonto-
logic research. We have been able in this way to ob-
tain numerous lines of descent of animals and some
general results as to the genealogic relations of the
primary types of animals and plants. Many forms of
both animals and plants are and have been without
those hard parts which are susceptible of preservation
in the formations of the earth’s crust, so that no trace
of their existence remains to us. In these cases our
resort is embryologic investigation, since the embry-
onic history is a more or less complete recapitulation
of the types of the past ages, from which the existing
ones are descended. But since many representatives
of the ancient and primitive forms of life still remain
on the earth, we can trace, by the study of their struc-
ture, the larger features of general phylogeny. So far
as we have compared the results derived from these
three lines, it has been found that they coincide in
their indications. We have in this a satisfactory proof
that our conclusions are trustworthy contributions to
the knowledge of the history of life.
The study of phylogeny shows that the evolution

PHYLOGENY. 75

of life-forms has been from the simple to the complex,
and from the generalized to the specialized. These
two forms of expression are not identical. In the
phrase, ‘‘from the simple to the complex,” is implied
an ascending scale of evolution. In the phrase, ‘from
the generalized to the specialized,” we may include
both progressive and retrogressive evolution. Retro-
gressive or degenerative evolution has been a frequent
phenomenon in the past, and scarcely an organism ex-
ists which does not display degeneracy in some detail of
its structure. Progressive evolution has, however, not
been prevented by the frequent occurrence of an op-
posite process; and, indeed, degeneracy of parts, or of
types of life, have been necessary to the advance of
other and better organs or forms.

It is necessary to an understanding of the laws of
evolution to get beforehand some idea of what that
evolution has actually been. I will, therefore, give a
general outline of the phylogeny of plants and animals,
and will thus illustrate the subject in full detail in the
case of the Vertebrata, where our facilities are espe-
cially good.

It is well known that the Protophyta and the Pro-
tozoa are not distinguishable by any sharp line of de-
marcation. Chlorophyll, which is so characteristic of
plants, is absent from many of the lowest forms, in-
cluding the entire class of Fungi, while it is present
in a few of the lowest animals. The capacity for mo-
tion from place to place, so general in animals, at
least in their earlier stages, is present in the earlier
stages of some of the Alge, and is universal, except at
the period of reproduction, in the Myxomycetes. If it
be denied that the latter are plants, then they are ani-
mals which do not reproduce by the ordinary process

76 PRIMARY FACTORS OF ORGANIC EVOLUTION.

of fission, but by spores, which are borne together in
a mass, or in a sporangium distinguished from the rest
of the body. A distinction between the lower animals
and plants is that the former introduce their food at a
definite, though it may be a variable, point of the body;
while plants absorb their nutriment in solution at all
points. It is however demonstrated that some animals
(many parasites) nourish themselves in the same man-
ner as do plants; and in their early stages the Myxo-
mycetes have the feeding habit of the lowest animals
(Ameebz). Both animals and plants from a morpho-
logical point of view have a common origin, in a nucle-
ated, undivided, more or less globular piece of proto-
plasm or sarcode.

From freely moving Protophyta of this form, the
vegetable kingdom took its rise. They first of all as-
sumed a sessile position on the earth, and became
what one may call earth-parasites. This abandonment
of free mobility we cannot hesitate to regard as the
efficient cause of a degenerate line of evolution. There
can be no doubt about this, since fixity of habitat at once
limits enormously the range of active influences which
tend to modify an organism, whether they proceed
from within it or from without it. The subsequent
inclosure of the protoplasm in a structure of cellulose
removes them from many of the stimuli which have so
potent an influence in the life-history of animals, and
the storage of other substances, as proteids, gums,
resins, etc., in their cells, still further emphasizes the
distinction.

From this beginning, progress in plants is seen
chiefly in the modifications of their methods of repro-
duction. This function is the aim of the vegetable
kingdom so far as their own condition is concerned.

PHYLOGENY. 77

Incidentally they are, however, essential to the exist-
ence of the animal kingdom, since they alone elaborate
protoplasm and ‘proteids from inorganic nature. In
the simplest plants there is no sexuality, and repro-
duction is effected by spores which are mere fragments
of the parental protoplasm (Protophyta). In the next
stage sexual conjugation is necessary, but the sexes
do not differ from each other in characters (Zygo-
phyta). In the third stage (Odphyta) the sexes are
distinct, and the reproductive elements are distin-
guished as female germ-cell and male antheridium.
In the remaining types of plants a distinct set of indi-
viduals, the prothallia, is produced by cell-division,
whose function is sexual reproduction, thus constitut-
ing an alternation of generations. These plants may
be entirely cellular (Carpophyta), or may be furnished
with vascular canals. Of the latter the male and fe-
male prothallia may be naked and free (Pteridophyta
or ferns, etc.), or may be enclosed in modified leaves,
or flowers, the Phznogamia or flowering plants.

For the reasons already mentioned the order of
“¢successional relation” above pointed out, is likely to
prove to be the order of appearance of plants in time,
and that such is the fact is demonstrated by their pa-
leontology. In the earliest beds in which plants are
positively known to occur, the Ordovician, we have
only Alge (Zygophyta and Oéphyta). In the Siluric
we have a great predominance of the same classes, a
very few species of which appear to have formed great
erect stems. In the next period, the Devonic, prob-
able Carpophyta are present, while the vascular Pte-
ridophyta appear for the first time, and in consider-
able numbers. A few members of the gymnospermous
Phenogamia (Conifere) appear. In the Carbonic pe-

78 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Present
period

Plistocene
Neocene
Eocene
Cretacic
Jurassic
Triassic
Carbonic
Devonic
Siluric
Ordovicic

Cambric

Proto-
phyta

Zygo-
phyta

Odphyta

Carpo-
phyta

Pterido-
phyta

Gymno-
sperms

Monoco-
tyledones

Poly-
petale

Gamo-
petala

PHYLOGENY. 79

riod, the greatest known development of the Pterido-
phyta (Lycopodia, ferns, Equiseta) took place, while
the Gymnosperms were still represented by a few gen-
era. Their period of development or acme arrived in
the Mesozoic ages, and the Pteridophyta underwent a
corresponding reduction of numbers and importance.
Not until the upper Cretaceous epoch did the Angio-
spermous Phanerogams with their attractive flowers
appear, and from that period to the present they have
gained and maintained the ascendency. In accord-
ance with the mode of origin of tubular flowers by the
fusion of the separate petals of polypetalous forms,
we find that the former succeeded the latter in time.
We may review this brief sketch of the paleontol-
ogy of plants in the preceding phylogenetic table.
Turning now to the animal kingdom, its order of
succession may also be perceived in existing species.
As with plants we commence with unicellular asexual
forms (Protozoa). Some of these increase by division
only (Rhizopoda), while others must occasionally con-
jugate, since, according to Maupas, the reproductive
energy is exhausted by continued self-division (Infuso-
ria). Such structural specializations as the highest of
the Protozoa possess, are merely vacuities or processes
of their material, for the purpose of internal or exter-
nal motion. In the second grade of organization ani-
mals are multicellular, or composed of more than one
protoplasmic unit. The simplest of these, as Volvox,
contains no specialized organs, but seems like a colony
of Protozoa, although all its cells are not exactly alike
(Ryder). An appreciable advance of structure de-
fines the next class, the Celenterata. Here the mul-
ticellular mass contains a distinct digestive chamber,
from which usually radiate tubes towards the periph-

80 PRIMARY FACTORS OF ORGANIC EVOLUTION,

ery, which distribute the products of digestion. - The
first nervous threads appear. But there is as yet no
body cavity which should form a sac in which the or-
gans of nutrition and reproduction should be sus-
pended. The Porifera (sponges) appear to be a much
modified form of this type.

This grade of specialization belongs to the greater
number of the five succeeding classes, the Echinoder-
mata, Vermes, Mollusca, Arthropoda, and Vertebrata.
Where it is absent from a few of the three lower
classes, it is supposed to have disappeared by degen-
eracy.: The Echinodermata come first in considera-
tion. In these animals the form inclines to be radiated
and the nervous system presents no single axis, but
consists of branches which radiate from a ring sur-
rounding the oral extremity of the digestive canal. In
the second type, the general form is longitudinal and
may be segmented, and a nervous axis may extend
longitudinally from one or more points on the ceso-
phageal ring.- These are the Vermes (true worms).
Embryology indicates clearly the common origin of
the Echinodermata and the Vermes. No line of de-
scent can be traced from the former, but from the lat-
ter we have traced the remaining branches of animals,
three in number. Lowest of these is the Mollusca.*
The form of the body is sac-like, and the nervous sys-
tem displays, typically, besides the cesophageal ring,
a second ring, consisting of lateral commissures, mak-
ing a single median ganglion of the foot. The body
is not segmented, and there are no jointed limbs. In

the second branch, that of the Arthropoda, the body .

is longitudinal and segmented, and segmented limbs
are present. There is a median nervous axis, proceed-
ing from the cesophageal ring along the inferior axis

PHYLOGENY. 81

of the body, connecting several ganglia, (with some
exceptions where the ganglia are fused or wanting).
There is no internal skeleton. In the last and highest
branch, that of the Vertebrata, the body is longitudi-
nal and is segmented. It has a longitudinal nervous
axis on the superior middle line, which is supported
below by an axis of resistant material, usually bone,
which forms the axis of an internal skeleton. Seg-
mented limbs are present.

The lines of descent of these branches indicated by
embryology are as follows:

Vertebrata.
Arthropoda.
Mollusca.
Echinodermata.
ermes:
Porifera.
Ceelenterata.
Catallacta,
Protozoa.

The above series present a history which is, on the
whole, very different from that already described as
characterizing the vegetable kingdom. Between the
first and last terms of the series, there is exhibited a
great progressive advance in all the higher features of
life. “These are mobility, and such control over the
environment as it gives; and sensibility, through the
development of a nervous system, which gives control
over the movements.” The highest development is
that of mental characteristics, as emotions and intelli-
gence, which are especially seen in the higher Verte-
brata.

82 PRIMARY FACTORS OF ORGANIC EVOLUTION.

This progress has not been accomplished without
much degeneracy by the way. All of the branches
display divisions which have become sessile, and some
of them are almost altogether so. Among Ccelenterata
the Actinozoa are fixed, and often develop a calcareous
skeleton. Many of the Hydroids are sessile. The
great branch of the Echinodermata has its locomotive
powers greatly curtailed, and many of them are per-
manently sessile. The same is true of the Mollusca.
Both divisions are at one side of the line of progres-
sive evolution as a consequence of this tendency. The
Vermes display in their free representatives the condi-
tions of progressive evolution. Being longitudinal
and bilateral, one extremity becomes differentiated by
first contact with the environment, as the seat of spe-
cial senses, the basis having been secured by the loca-
tion there of the nervous centers and ring. The Ar-
thropoda present us with a great development of
locomotive organs, and of special senses. As a whole,
they have not made a considerable advance into the
possession of the higher animal mental capacities, but
display various degeneracies or degenerate tendencies
among themselves. The moderately specialized as to
structure are the most intelligent. These are the Hy-
menoptera, which display mental capacity superior to
that of many Vertebrata. The latter branch, although
presenting one sessile type, the Urochorda, has pro-
duced in its highest class, the Mammalia, the most gen-
eral elevation in this, the highest of animal functions.
This intelligence is in most of the types expended in
preserving themselves from destruction against hostile
environments, and the conquest of nature thus effected
is remarkable from a physical point of view, but is an
end of no great elevation of purpose from a mental

PHYLOGENY. 83

standpoint. It is only in the most intelligent of the
Mammalia, and in man, that we behold social and in-
tellectual qualities which express something more than
a mere routine of material existence.

Since Protozoa are very fragile, even when pos-
sessed of shells of mineral salts, we cannot expect to
discover the actual date of their first appearance on
the earth. Nevertheless they have been recently dis-
covered in the later Archzean (= Huronian) beds of
France. Some of the simplest Ccelenterata, however,
(the Actinozoa), have deposited lime salts in the septa
of their digestive chambers, and in some instances over
their entire surface, so that their preservation has been
assured. Thus we can prove that the simplest coral
animals appear in the oldest rocks of sedimentary ori-
gin, the Cambric. Probably Vermes, and positively
Echinodermata, Mollusca, and Arthropoda (Trilobita),
also appear in the Cambric. Vertebrata appear defi-
nitely in the Siluric ; their supposed appearance in the
Ordovicic being very doubtful. °

The paleontologic history conforms to the syste-
matic order in so far as it shows that the Ceelenterata
appeared first, and the Vertebrata last, in time. A
more complete correspondence between the two his-
tories is found in the divisions of these branches, and
I will take up the Vertebrata as the one of whose be-
ginning we know the most, and are likely to know
more.

2. THE PHYLOGENY OF THE VERTEBRATA.
a. Phylogeny of the Classes.

As the illustrations of evolution in the present work
are mainly drawn from the Vertebrata, I go somewhat
into detail in discussing the phylogeny of that branch.

84 PRIMAKY FACTORS OF ORGANIC EVOLUTION.

They present the advantage, that, since they appeared
last of the animal kingdom in time, we can obtain a
clearer view of their beginnings than in the case of the
other great branches.

Before going into the subject I wish to call atten-
tion to a prevalent source of error in the construction
of phylogenies. This is the confusion of ideas general
among naturalists who are not at the same time com-
petent systematists, as to the subordination of charac-
ters. All correct phylogenetic inference depends on a
correct appreciation of the value of characters. Fail-
ing this, error and confusion result. If, for instance,
it is alleged that such a genus is ancestral to another
genus, it is often forgotten that the descent of generic
character, and not specific character, is meant. The
usual type of critic attempts to contradict such hy-
pothesis by showing some incongruity in specific char-
acters, a matter which is quite irrelevant to the issue.
Thus Madame Pavlov finds that Aippotherium mediter-
raneum is not the ancestor of EZguus caballus, and comes
promptly to the conclusion that the genus Hippothe-
rium is not ancestral to the genus Equus. This is a
non sequitur, for there are perhaps twenty species of
Hippotherium, some of which are almost certain to
have been ancestral to species of American Equus. In
like manner, if it is alleged that the condylarthrous
Mammalia are ancestral to the Diplarthra, if it should
happen that no known genus of the former fits exactly
the position of ancestor to any genus of the latter, in
our present state of knowledge, the contention is not
thereby vitiated, and it is implied that such genus will
certainly be found. If it is also alleged that Condy-
larthra have been the ancestors of the anthropoid line,
if some of the known genera of the former turn out to

PHYLOGENY. 85

have no clavicle, a bone which is possessed by the
latter, it is only to be concluded that the early lemur-
oids were derived from Condylarthra which possessed
a clavicle. And in the discussion of the descent of
one order from another, care must be taken that fam-
ily, generic, and even specific characters are not im-
ported into the discussion.

It is this confusion of ideas on the part of both
phylogenists and their critics, that has brought phylo-
genetic schemes into a discredit in some quarters,
which is sometimes deserved and sometimes unde-
served. Embryologists are especially apt to construct
impossible phylogenies, as they are generally not sys-
tematists, and frequently not anatomists. An excel--
lent illustration of an impossible phylogeny is that of
the fishes published a few years ago by the embryolo-
gist Dr. Beard. As an illustration of clean-cut phy-
logeny without confusion, I cite that of Haeckel; which
I have shown to be, as regards the Vertebrata, mainly
correct.

In attempting to ascertain the course of evolution
of the Vertebrata, and to construct phylogenetic dia-
grams which shall express this history, among the dif-
ficulties arising from deficient information one is espe-
cially prominent. As is well known, there are many
types in all the orders of the Vertebrata which present
us with rudimentary organs, as rudimental digits, feet
or limbs, rudimental fins, teeth, and wings. There is
scarcely an organ or part which is not somewhere ina
rudimental and more or less useless condition. The
difficulty which these cases present is, simply, whether
they be persistent primitive conditions, to be regarded
as ancestral types which have survived to the present
time, or whether, on the other hand, they be results of

86 PRIMARY FACTORS OF ORGANIC EVOLUTION.

a process of degeneration, and therefore of compara-
tively modern origin. The question, in brief, is,
whether these creatures presenting these features be
primitive ancestors or degenerate descendants.

A great deal of light has been happily thrown on
this question, as regards the Vertebrata, by the recent
work done in North American paleontology. The lines
of descent of many of the minor groups have been
positively determined, and the phylogenetic connec-
tions of most of the primary divisions or classes have
been made out. The result of these investigations has
been to prove that the evolution of the Vertebrata has
proceeded not only on lines of acceleration, but also
on lines of retardation. That is, that evolution has
been not only progressive, but at times retrogressive.

The Amphioxus (genus Branchiostoma) is generally
regarded as the ancestral vertebrate. There are many
reasons why this position must be accepted, although
it possesses a few secondary modifications. Whether
Branchiostoma derived its descent from an annelid
worm, or from a tunicate, is a vexed question. Brooks}
remarks as to this, ‘‘Up to this point I believe that
the ancestral history of the tunicates was identical with
that of the vertebrates; for the hepatic ccecum, the
dilated pharynx, the pharyngeal clefts, the hypophar-
yngeal gland, and the peripharyngeal bands, have been
inherited by all the Chordata (Vertebrata), and have
impressed themselves so firmly in their organization
that even the highest vertebrates still retain them,
either as vestiges or as organs which have béen fitted
to new functions. I believe, however, that while they
were acquired before the tunicates diverged from the
chordate (vertebrate) stem, they were acquired by an

1Studies from the Laboratory of the Johns Hopkins University, 1893, p. 175.

PHYLOGENY. 87

organism whose environment and habits of life were
essentially like those of the modern Appendicularia.’
Appendicularia is well known as the tunicate which
retains throughout life, the notochord and tail which
characterize the larve of other Tunicata. ;

Omitting from consideration the two classes above
mentioned (Acrania and Tunicata), whose remains
have not yet been certainly found in a fossil state, there
remain the following: the Pisces, Batrachia, Mono-
condylia, and Mammalia.!

I have traced the origin? of the Mammalia to the
theromorous reptiles of the Permian epoch, and these
to the Cotylosauria. The latter include the Pelycosau-
ria, Procolophonina, Anomodontia, and perhaps other
orders. In the Cotylosauria the temporal region is
roofed over, which roof is reduced in the Pelycosauria
to one postorbital arch of the skull, and this is the zy-
gomatic of the Mammalia. In both Reptilia and Mam-
malia (excepting Prototheria and Procolophonina?) the
coracoid element is of réduced size, and is co-ossified
with the scapula. In both (except Cotylosauria) the
capitular articulation of the ribs is intercentral. In
both the humerus has distal condyles and epicondyles,
and there is an entepicondylar foramen in the Pelyco-
sauria as in the lower Mammalia. The posterior foot

1See The Evolution of the Vertebrata Progressive and Retrogressive; Amer,
Naturalist, 1885, Dohrn, Der Ursprung der Wirbelthiere und das Princip
des Functionwechsels, Leipsic, 1875. ‘‘Onthe Phylogeny of the Vertebrata,”
Cope, American Naturalist, Dec., 1884. See also the following references:
American Naturalist, 1884, p.1136; Proceedings of the Academy of Philadelphia,
1867, p. 234; Proceedings American Philosophical Soctety, 1884, p. 585 ; American
Naturalist, 1884, p. 27; Proceedings American Association for the Advancement
of Science, XIX, 1871, p. 233; Proceedings American Philosophical Society, 1882, p.
447; American Naturalist, 1884, pp. 261 and 1121; Report U.S. Geol, Survey W.
of rooth Mer., G. M. Wheeler, 1877, IV, 2, p. 282.

2 Proceedings American Philosophical Society, 1884, p. 43.

8 Seeley, Philos. Trans. Royal Society, 1889, 269.

88 PRIMARY FACTORS OF ORGANIC EVOLUTION.

is constructed in the Pelycosauria almost exactly like
that of the Prototheria. The single occipital condyle
of the reptiles is not found in the Mammalia, but in
some of the Lacertilia (Uroplates, Gecco) there are
two condyles, the median (basioccipital) portion of the
single condyle being rudimental, and Seeley has re-
cently shown that it is deeply divided at the middle in
the Permian Cynognathidae of South Africa.. The
Pelycosauria could not, however, have given origin to
the Prototheria, since in that subclass of mammals there
is a well-developed coracoid. But in the Procolopho-
nina this element is developed as in the Prototheria.
Moreover, the Pelycosauria and the Procolophonina
have the interclavicle, which is an element of membran-
ous origin, while in the Prototheria we have the corre-
sponding cartilage bone, the episternum. This element
is present in the Permian order of the Cotylosauria,
which is nearly related to the Pelycosauria. This or-
der has, however, single-headed ribs, springing from
the diapophyses, which is not usual in the Mammalia.
But in some Cotylosauria the diapophyses are short,
and in the Monotremata the postcervical ribs are sin-
gle-headed, so this character is not an insurmountable
one. It is evident that the Mammalia were derived
from some type probably referable to a Permian rep-
tilian order of the Theromorous series, although to
which one is not yet known.

The Reptilia have been supposed by Haeckel to
have taken their origin from the Batrachia. I have
indicated that it is probable that the batrachian order,
which stands in this relation to the Reptilia, is the
Embolomeri of the Permian epoch. This conclusion
rests on the following considerations. The reptilian
order of the Cotylosauria approaches the Batrachia of

PHYLOGENY. 89

the subclass Stegocephali in the overroofing of the
posterior regions of the skull; in the presence of vo-
merine teeth, and in the absence of obturator foramen
of the pelvis. In some Cotylosauria (Diadectide) the
stegocephalian tabular bone of the skull is well devel-
oped. But in the Cotylosauria, the vertebral column
consists mainly of centra, while in the Stegocephali it
consists entirely or partly of intercentra. But in the
Embolomeri the centra are well developed, and are
larger than the intercentra anterior to the pelvis.
Hence this is the only order of Stegocephali from
which the Reptilia could have been derived.

Haeckel derived the Batrachia from the Dipnoi
(Dipneusta), and I followed him in this belief, being
strengthened in it by Huxley’s ascription of an auto-
stylic suspensorium of the mandible! to both divisions.
This phylogeny is questioned by Pollard? and by Kings-
ley,3 who would see the ancestry of the Batrachia in
the crossopterygian fishes on embryological grounds
derived from a study of Polypterus. In support of
their view I would cite the absence of the maxillary
arch in the Dipnoi, and its full development in the
Stegocephali, which are the ancestral Batrachia. The
large development of the dorsal and anal fins in the
Dipnoi is not favorable to the Haeckelian view; nor
do the paired fins approach as nearly to the limbs of
Batrachia as do those of some other fishes. It has been
shown by Huxley that the suspensorium of the Ba-
trachia is hyostylic in its earliest stages, and that it
becomes autostylic at a later period of development.

1 Proceedings Zoological Society of London, 1876, p. 59.

2 Anatomischer Anzeiger, VI, p. 338, 1891.

8 American Naturalist, 1892, p. 679. Kingsley would also derive the Dip-
noi from Crossopterygia.

go PRIMARY FACTORS OF ORGANIC EVOLUTION.

i
\)
i

: H ye % mR
Oe

Ny \ ) Winks Lae: ox
a oe SENS
=

Sey”
|

Fig. 24.—Zusthenopterum foordié Whiteaves; }4 natural size. Devonian of New Brunswick. From Whiteaves,

PHYLOGENY. gt

The Batrachia may then have originated from a hyo-
stylic teleostomous (i. e., one with complete maxillary
arch) fish. Among Teleostomata we naturally look for
forms with limbs which approach nearest the batrachian
type, and in which median fins are feeble or wanting.
Such are the Rhipidopterygia (formerly included in
the Crossopterygia), which include the families of
Holoptychiide, Tristichopteride, Osteolepidide, Co-
lacanthide, and perhaps some others. These fam-
ilies, except the last, abounded in. the waters of the
Devonian period, at the time when the ancestors of
the Batrachia also existed. All of them agree in pos-
sessing the median fins of greatly reduced proportions,
and the mesodermal or internal elements of the paired
fins more like the limbs of the Batrachia than are those
of any known fishes. The constitution of the superior
cranial wall is a good deal like that of the stegocepha-
lous Batrachia. The characters of the fins can be
learned from the accompanying figure of the Zusthe-
noplerum foordii Whiteaves, one of the Tristichopteridz.
The pectoral fin well-nigh realizes Gegenbaur’s theory
of the derivation of the Chiropterygium from the Ar-
chipterygium.

The ancestral type of fishes is probably the acan-
thodean order of the subclass of sharks (Elasmo-
branchii).1 Like other sharks, they are hyostylic and
have no maxillary arch or cranial bones. They have
the ptychopterygium, which is the primitive type of
fin. In this fin the osseous elements which support
the fin-rays are enclosed within the body-wall, the rays
only being free. Such a fin sustains the hypothesis
that the paired fins are parts of primitively continuous

1As represented by the Cladodontidae; see Dean, Trans. N.Y. Acad.
Scz., 1893, p. 124, and Cope, American Naturalist, 1893, p. 999.

92 PRIMARY FACTORS OF ORGANIC EVOLUTION.

longitudinal folds. This hypothesis is further sus-
tained by the acanthodean genus Climatius, where a
series of spines intervenes between the paired fins in

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line with them. From what the Acanthodeans can
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trace their ancestry ultimately to Branchiostoma (Am-
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PHYLOGENY. 93

nus represents.-the class Acrania, which is the ancestor
of craniate Vertebrata.

The phylogeny of the Vertebrata may be repre-
sented diagrammatically as follows:

Mammalia
Aves

Teleostomata (other) a
Telestémata (Rhipidopterygia)

Elasmobr. (Selachii)

Elasmobranchii— Acanthodii

Agnatha

Tunicata Acrania Enteropneusta

The Vertebrata exhibit the most unmistakable gra-
dation in the characters of the circulatory system. It
has long been the custom to define the classes by means
of these characters, taken in connection with those of
the skeleton. Commencing in the Leptocardii with
the simple tube, we have two chambers in the Marsi-
pobranchii and fishes ; three in the Batrachia and Rep-
tilia ; and four in the Aves and Mammalia. The aorta-
roots commence as numerous pairs of branchial arter-
ies in the Leptocardii ; we see seven in the Marsipo-
branchi, five in the fishes (with number reduced in
some); four and three in Batrachia, where they gen-
erally cease to perform branchial functions ; two and
one on each side in Reptilia; the right-hand one in
birds, and the left-hand one in Mammalia. This order
is clearly an ascending one throughout. It consists
of, first, a transition from adaptation to an aquatic, to

94 PRIMARY FACTORS OF ORGANIC EVOLUTION.

an aérial respiration; and, second, an increase in the
power to aérate and distribute a circulating fluid of in-
creased quantity, and of increased calorific capacity.
In other words, the circulation passes from the cold to
the hot-blooded type coincidentally with the changes
of structure above enumerated. The accession of a ca-
pacity to maintain a fixed temperature while that of
the surrounding medium changes, is an important ad-
vance in animal economy.

The brain and nervous system also display a gen-
eral progressive ascent. Leaving the brainless Acrania,
the Marsipobranchs and fishes present us with small
hemispheres with thin cortex, larger optic lobes, and
well-developed cerebellum. The hemispheres are really
larger than they appear to be, as Rabl Riickard has
shown! that the supposed hemispheres are only corpora
striata. But the superior walls are membranous, and
support on their internal side only a layer of epithelial
cells, as in the embryos of other Vertebrata, instead of
the gray substance. So that, although we find that the
cerebellum is really smaller in the Batrachia and most
Reptilia than in the fishes, the better development of
the hemispheres in the former gives them the pre-
eminence. The Elasmobranchii show themselves su-
perior to many of the fishes in the large size of their
corpora restiformia and cerebellum. The Reptilia con-
stitute an advance on the Batrachia. In the latter the
optic thalami are, with some exceptions, of greater
diameter than the hemispheres, while the reverse is
generally true of the reptiles. The crocodiles display
much superiority over the other reptiles in the larger
cerebellum, with rudimental lateral lobes. The greater
development of the hemispheres in birds is well known,

1Biologisches Centralblatt, 1884, p. 449.

PHYLOGENY. 95

while the general superiority of the brain of the living
Mammalia over all other vertebrates is admitted.

The consideration of the successive relations of the
skeleton in the classes of vertebrates embraces, of
course, only the characters which distinguish those
classes. These are not numerous. They embrace the
structure of the axis of the skull; of the ear-bones ; of
the suspensors of the lower jaw; of the scapular arch
and anterior limb, and of the pelvic arch and posterior
limb. Other characters are numerous, but do not enter
into consideration at this time.

The persistence of the primitive cartilage in any
part of the skeleton is, embryologically speaking, a
mark of inferiority. From a physiological or functional
standpoint it has the same significance, since it is far
less effective both for support and for movement than
is the segmented osseous skeleton. That this is a prev-
alent condition of the lower Vertebrata is well known.
The bony fishes and Batrachia have but little of the
primitive cartilage remaining, and the quantity is still
more reduced in the higher classes. Systematically,
then, the vertebrate series is in this respect an ascend-
ing one. The Acrania are membranous; the Marsi-
pobranchii and most of the Elasmobranchii cartilagi-
nous; the other Pisces and the Batrachia have the
basicranial axis cartilaginous, so that it is not until the
Reptilia are reached that we have osseous sphenoid
and presphenoid bones, such as characterize the birds
and mammals. The vertebral column follows more or
less inexactly the history of the base of the skull, but
its characters do not define the classes.

As regards the suspensor of the lower jaw, the scale
is in the main ascending. We witness a gradual change
in the segmentation of the mandibular visceral arch of

96 PRIMARY FACTORS OF ORGANIC EVOLUTION.

the skull, which clearly has for its object such a con-
centration of the parts as will produce the greatest ef-
fectiveness of the biting function. This is accom-

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plished by reducing the number of the segments, so as
to bring the resistance of the teeth nearer to the power,
that is, the masseter and related muscles, and their
base of attachment, the brain-case. This is seen in

PHYLOGENY. 97

bony vertebrates in the reduction of the segments be-
tween the lower jaw proper and the skull, from four to
none. In the fishes we have the hyomandibular, the
symplectic, the inferior quadrate, and the articular.
In the Batrachia, reptiles and birds, we have the quad-
rate and articular only, while in the Mammalia these
elements also are wanting.

The examination of the pectoral and pelvic arches
reveals a successive modification of the adaptation of
the parts to the mechanical needs of the limbs. In
this regard the air-breathing types display wide di-
versity from the gill-bearing types or fishes. In the
latter, the lateral elements unite below without the in-
tervention of a median element or sternum, while in
the former the sternum, or parts of it, is generally pres-
ent. Either arrangement is susceptible of much me-
chanical strength, as witness the siluroid fishes on the
one hand, and the mole on the other. The numerous
segments of the fishes’ pectoral arch must, however,
be an element of weakness, so that from a mechanical
standpoint it must take the lowest place. The pres-
ence of sternal elements, with both clavicle, epicora-
coid, and coracoid bones on each side, gives the Rep-
tilia the highest place for mechanical strength. The
loss of the bony coracoid seen in the tailed Batrachia,
and loss of coracoid and epicoracoid in the Mammalia,
constitute an element of weakness. The line is not
then one of uniform ascent in this respect.

The absence of pelvis, or its extremely rudimental
condition, in fishes, places them at the foot of the line
in this respect. The forward extension of the ilium in
some Batrachia and in the Mammalia, is to be com-
pared with its backward direction in Reptilia, and its
extension both ways in the birds. These conditions

7.
98 PRIMARY FACTORS OF ORGANIC EVOLUTION.

are all derived by descent from a strictly intermediate
position in the Batrachia and Reptilia of the Permian
epoch. The anterior direction must be regarded as
having the mechanical advantage over the posterior
direction, since it shortens the vertebral column and
brings the grip of the posterior nearer to the anterior
feet. The prevalence of the latter condition in the
Mammalia enables them to stand clear of the ground,
while the Reptilia move with the abdomen resting upon
it, excepting the higher Dinosauria, where the arrange-
ment is as in birds. As regards the inferior arches of
the pelvis, the Mammalia have the advantage again,
in the strong bony median symphysis connecting the
ischium and pubis.!_ This character, universal among
the land Vertebrata of the Permian epoch, has been lost
by the modern Reptilia and birds, and is retained only
by the Mammalia. So the lines, excepting the mam-
malian, have degenerated in every direction in the char-
acters of the pelvis.

The limbs of the Pisces are as well adapted to their
environment as are those of the land Vertebrata; but,
from an embryological standpoint, their structure is
inferior. The primitive rays are less modified in the
fin than in the limb; and limbs themselves display a
constantly increasing differentiation of parts, com-
mencing with the Batrachia and ending with the Mam-
malia. The details of these modifications belong to
the history of the contents of the classes, however,
rather than to the succession of the Vertebrata as a
whole. :

In review, it may be said that a comparison of the
characters which define the classes of the vertebrates
shows that this branch of the animal kingdom has

1 This is an advantage as a protection during gestation.

PHYLOGENY. 99

made with the ages successive steps of progress from
lower to higher conditions. This progress has not been
without exception, since, as regards the construction
of the scapular arch, the Mammalia have retrograded
from the reptilian standard as a whole.

In subsequent pages I shall take up the lines of the
classes separately.

6. The Line of the Pisces.

The fishes form various series and subseries, and
the tracing of all of them is not yet practicable, owing
to the deficiency in our knowledge of the earliest or
ancestral forms. Thus the origins of the three sub-
classes, Holocephali, Dipnoi, and Elasmobranchii, are
lost in the obscurity of the early Paleozoic ages. The
genus Paleospondylus of Traquair from the Carbonife-
rous probably represents an Agnathous type from
which all fishes may have sprung, although the genus,
as now known, has not sufficient antiquity to claim
this place. It may bea near descendant of the amphi-
oxus.

A comparison of the four subclasses of fishes shows
that they are related in pairs. The Holocephali and
Dipnoi have no distinct suspensory segment for the
lower jaw, while the Elasmobranchii and Teleostomata
have such a separate element. The latter, therefore,
present one step in the direction of complication be-
yond the former. It is, however, asserted by Huxley!
that the absence of suspensorium is due to its appro-
priation by the hyoid arch in the Holocephali, and its
rudimental condition in the Dipnoi. If this be the
case, the Holocephali and Dipnoi are peculiar speciali-

1 Proceedings Zoblogical Society, London, 1876, p. 45.

100 PRIMARY FACTORS OF ORGANIC EVOLUTION.

zations at one side of the main line of descent of the
fishes. We look then for the ancestral type of the true
fishes among the Elasmobranchii, and of these the
Ichthyotomi display the greatest resemblances to the
Teleostomata in all respects.

Too little is known of the history of the subclasses,
excepting the Teleostomata, for us to be able to say
much of the direction of the descent of their contained
orders. On the sharks much light is shed by the dis- -
covery of characters of the genus Cladodus Agass., in
which the support of the paired fins consists of a meta-
pterygium, which is enclosed in a lateral fold of the
body wall, and which gives rise to simple external
basilar rods only. Of the Teleostomata a much clearer
history is accessible. It has four primary divisions or
tribes which differ solely in the structure of the sup-
ports of the fins. In the first division, the Crossopte-
rygia, the anterior limbs have numerous basilar bones
which are supported on a peduncle of axial bones.
The posterior limbs are similar. In the second divi-
sion, or Podopterygia (the sturgeons, etc.), the pos-
terior limbs remain the same, while the anterior limbs
have undergone a great abbreviation in the loss of the
axial bones and the reduction of the number and length
of the basilar bones. In the third group, or Actino-
pterygia, both limbs have undergone reduction, the
basilar bones in the posterior fin being almost all atro-
phied, while those of the fore limb are much reduced
in number. In the fourth superorder, the Rhipido-
pterygia, the axial supports of the median fins are
greatly reduced in number, presenting a marked con-
trast to the other superorders ; while the axial elements

1 See Proceedings American Philosophical Society, 1884, p. 572, on the genus
Didymodus,

PHYLOGENY, IOI

of the paired fins are present and primitive, and re-
semble those of one of the suborders of sharks.

The phylogeny of the Teleostomata, as indicated
by the fin-structure, will commence with the Crosso-
pterygia. From this group the Podopterygia may be
theoretically derived, and from these the Actinoptery-
gia. The Rhipidopterygia appear to be a side group,
not in the main piscine line. But the oldest known
Crossopterygia are from the Carboniferous, while the
Rhipidopterygia are abundant in the Devonian. More-
over, the superorder Actinopterygia, with its contracted
fins, may have appeared in the Carboniferous, while
the Podopterygia (Paleoniscidz) certainly did so.

The descent of the fishes in general has witnessed,
then, a contraction of the limbs to a very small com-
pass, and their substitution by a system of accessory
dermal radii. This has been an ever-widening diver-
gence from the type of the higher Vertebrata, and
from this standpoint, and also a view of the ‘‘loss of
parts without complementary addition of other parts,”
may be regarded as a process of degeneration.

Taking up the great division of the Actinopterygia,
which embraces most of the species of living fishes,
we can trace the direction of descent largely by ref-
erence to their systematic relations when we have no
fossils to guide us.

The three subtribes adopted by Jordan represent
three series of the true fishes which indicate lines of
descent. The Holostei include the remainder of the
old ganoids after the subtraction of the Rhipidoptery-
gia, the Crossopterygia, and the Podopterygia. They
resemble these forms in the muscular bulbus arteriosus
of the heart, in the chiasm of the optic nerves, and in
the greater distinctness of the metapterygium. The

102 PRIMARY FACTORS OF ORGANIC EVOLUTION.

two former characters are complexities which the two
other divisions do not possess, and which, as descend-
ants coming later in time, must be regarded as inferior,
and therefore to that extent degenerate. Of these di-
visions the Malacopterygia approach nearest the Ho-
lostei, and are indeed not distinctly definable without
exceptions. The third division, or Acanthopterygia,
shows a marked advance beyond the others in: (1) the
obliteration of the primitive trachea, or ductus pneu-
maticus, which connects the swim-bladder and ceso-
phagus ; (2) the advance of the ventral fins from the

“abdomen forward to the throat ; (3) the separation of
the parietal bones by the supraoccipital ; (4) the pres-
ence of numerous spinous rays in the fins ; and (5) the
roughening of the edges of the scales, forming the cten-
oid type. There are more or less numerous excep-
tions to all of these characters. The changes are all
further divergencies from the other vertebrate classes,
or away from the general line of ascent of the verte-
brate series taken as a whole. The end gained is spe-
cialization ; but whether the series can be called either
distinctively progressive or retrogressive, is not so
clear. The development of osseous spines, rough
scales, and other weapons of defense, together with
the generally superior energy and tone which prevail
among the Acanthopterygia, characterize them as su-
perior to the Malacopterygia, but their departure from
the ascending line of the Vertebrata has another ap-
pearance.

The descent of the Acanthopterygian fishes has
probably been from Holostean ancestors, both with
and without the intervention of Malacopterygian forms.
This is indicated by increase in the number of basilar

PHYLOGENY. 103

bones? in the fins of families which have pectoral ven-
tral fins, and in the extinct genus Dorypterus.?

The Malacopterygia display three or four distinct
lines of descent. The simplest type is represented by
the order Isospondyli, and paleontology indicates clearly
that this order is also the oldest, as it dates from the
Trias at least. In one line the anterior dorsal verte-
bre have become complicated, and form an interlock-
ing mass which is intimately connected with the sense
of equilibrium in the water. This series commences
with the Characinide, passes through the Cyprinide,
and ends with the Siluride. The arrangements for
equilibration constitute a superadded complication,
and to these are added in the Siluroids defensive spines
and armor. Some of this order, however, are distinctly
degenerate, as the soft purblind Ageniosus, and the
parasitic Stegophilus and Vandellia, which are nearly
blind, without weapons, and with greatly reduced fins.

The next line (the Haplomi, pike, etc.) loses the
precoracoid arch and has the parietal bones separated,
both characters of the Acanthopterygia. This group
was apparently abundant during the Cretaceous period,
and it may have given origin to many of the Acantho-
pterygia.

Another line also loses the precoracoid, but in other
respects diverges totally from the Acanthopterygia and
all other Malacopterygia. This is the line of the eels.
They next lose the connection between the scapular
arch and the skull, which is followed by the loss of the
pectoral fin. The ventral fin disappeared sooner. The
palatine bones and teeth disappear, and the suspensor

1See Cope '‘ On the Homologies of the Fins of Fishes”; American Nat-
uralist, 1890, p. 401.

2See Proceedings of the American Association for the Advancement of Sct-
ence, 1878, p. 297.

104 PRIMARY FACTORS OF ORGANIC EVOLUTION.

of the lower jaw grows longer and loses its symplectic
element. The opercular bones grow smaller, and some
of them disappear. The ossification of most of the
hyoid elements disappears, and some of their cartila-
ginous bases even vanish. These forms are the marine
eels or Colocephali. The most extraordinary example
of specialization and degeneracy is seen in the abyssal
eels of the family Eurypharyngide. Here all the de-
generate features above mentioned are present in ex-
cess, and others are added, as the loss of ossification
of a part of the skull, almost total obliteration of the
hyoid and scapular arches, and the semi-notochordal
condition of the vertebral column, etc.

The Acanthopterygia nearest the Malacopterygia
have abdominal ventral fins, and belong to several or-
ders. It is such types as these that may be supposed
to have been derived directly from Holostean ances-
tors. They appear in the Cretaceous period (Derce-
tide), along with the types that connect with the Ma-
lacopterygia (Haplomi). Intermediate forms between
these and typical Acanthopterygii occur in the Eocene
(Trichophanes, Erismatopterus), showing several lines
of descent. The Dercetide belong apparently to the
order Hemibranchi, while the Eocene genera named
belong apparently to the Aphododiride, the immediate
ancestor of the highest Physoclysti, the Percomorphi.
The order Hemibranchi is a series of much interest.
Its members lose the membrane of their dorsal spinous
fin (Gasterosteide), and then the fin itself (Fistularia,
Pegasus). The branchial apparatus has undergone,
as in the eels, successive deossification (by retarda-
tion), and this in direct relation to the degree with
which the body comes to be protected by bony shields,
reaching the greatest defect in the Amphisilide. One

PHYLOGENY. 105

more downward step is seen in the next succeeding
order of the Lophobranchii. The branchial hyoid ap-
paratus is reduced to a few cartilaginous pieces, and the
branchial fringes are much reduced in size. In the
Hippocampidz the caudal fin disappears and the tail
becomes a prehensile organ by the aid of which the
species lead a sedentary life. The mouth is much con-
tracted and becomes the anterior orifice of a suctorial
tube. This is a second line of unmistakable degen-
eracy among true fishes.

The Acanthopterygia with pectoral ventral fins pre-
sent us with perhaps ten important ordinal or subordi-
nal divisions. Until the paleontology of this series is
better known, we shall have difficulty in constructing
phylogenies. Some of the lines may, however, be
made out. The accompanying diagram will assist in
understanding them.

The Anacanthini present a general weakening of
the organization in the less firmness of the ossecus
tissue and the frequent reduction in the size and char-
acter of the fins. The caudal vertebre are of the
diphycercal type. As this group does not appear early
in geological time, and as it is largely represented now
in the abyssal ocean fauna, there is every reason to
regard it as a degenerate type.! The Heterosomata
(flounders) found it convenient to lie on one side, a
habit which would appear to result from a want of mo-
tive energy. The fins are very inefficient organs of
movement in them, and they are certainly no rivals for
swift-swimming fishes in the struggle for existence,
excepting as they conceal themselves. In order to see
the better while unseen, the inferior eye has turned in-

1The general characters of the deep-sea fish-fauna are those of degen-
eracy.

106 PRIMARY FACTORS OF ORGANIC EVOLUTION,

ward, i. e., upward, and finally has penetrated to the
superior surface, so that both eyes areononeside. This
peculiarity would be incredible, if we did not know of

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its existence, and is an illustration of the extraordinary
powers of accommodation possessed by nature. The
Heterosomata (flatfishes) can only be considered a de-
generate group. The scyphobranch line presents a

PHYLOGENY. 107

specialization of the superior pharyngeal bones, which
is continued by the Haplodoci (Batrachide). This
cannot be called a degenerate line, although the fin-
rays are soft.

The double bony floor of the skull of the distegous
percomorph fishes is a complication which places them
at the summit of the line of true fishes. At the sum-
mit of this division must be placed the Pharyngogna-
thi, which fill an important réle in the economy of the
tropical seas, and the fresh waters of the Southern
Hemisphere. By means of their powerful grinding
pharyngeal apparatus they can reduce vegetable and
animal food inaccessible to other fishes. The result
is seen in their multifarious species and innumerable
individuals decked in gorgeous colors, and often reach-
ing considerable size. This is the royal suborder of
fishes, and there is no reason why they should not con-
tinue to increase in importance in the present fauna.

Very different is the line of the Plectognathi. The
probable ancestors of this division, the Epelasmia
(Chzetodontidz, etc.), are also abundant in the tropi-
cal seas, and are among the most brilliantly colored of
fishes. One of their peculiarities is seen in a shorten-
ing of the brain-case and prolongation of the jaws
downward and forward. The utility of this arrange-
ment is probably to enable them to procure their food
from the holes and cavities of the coral reefs, among
which they dwell. In some of the genera the muzzle
has become tubular (Chelmo), and is actually used as
a blow-gun by which insects are secured by shooting
them with drops of water. This shortening of the
basicranial axis has produced a corresponding abbre-
viation of the hyoid apparatus. The superior pharyn-
geal bones are so crowded as to have become a series

108 PRIMARY FACTORS OF ORGANIC EVOLUTION,

of vertical plates like the leaves of a book. These
characters are further developed in the Plectognathi.
The brain-case is very small, the face is very elongate,
and the mouth is much contracted. The bones sur-
rounding it in each jaw are codssified. The axial ele-
ments (pubes) of the posterior fins unite together, be-
come very elongate, and lose the natatory portion. In
one group (Orthagoriscidz) the posterior part of the
vertebral column is lost, and the caudal fin is a nearly
useless rudiment. In the Ostraciontide (which may
have had a different origin, as the pharyngeal bones
are not contracted) the natatory powers are much re-
duced, and the body is inclosed in an osseous carapace
so as to be capable of very little movement. The en-
tire order is deficient in osseous tissue, the bones be-
ing thin and weak. It is a marked case of degeneracy.

There are several evident instances of sporadic de-
generacy in other orders. One of these is the case of
the family of the Icosteidz, fishes from deep waters off
the coast of California. Although members of the
Percomorphi, the skeleton in the two genera Icosteus
and Icichthys is unossified, and is perfectly flexible.
Approximations to this state of things are seen in the
parasitic genus Cyclopterus, and in the ribbon-fishes,
Trachypteride.

Thus nearly all the main lines of the Acanthopte-
rygii are degenerate ; the exceptions are those that
terminate in the Scombride (mackerel), Serranidz,
and Scaride (Pharyngognathi).

c. The Line of the Batrachia.

We know Batrachia first in the Coal Measures.
They reach a great development in the Permian epoch,
and are represented by large species in the Triassic

PHYLOGENY. 109

period. From that time they diminish in numbers,
and at the present day form an insignificant part of
the vertebrate fauna of the earth. The history of their
succession is told by a table of classification such as I
give below:
I. Supraoccipital, tabular, and supramastoid bones present. Pro-
podial bones distinct. STEGOCEPHALI.
Vertebral centra, including atlas, segmented, one set of
segments together supporting one arch; Rhachitomi.

Vertebrze segmented, the superior and inferior segments
each complete, forming two centra to each arch;

Embolomert.
Vertebral centra, including atlas, not segmented, one to
each arch; Microsauri,

II. Supraoccipital and supramastoid bones wanting. Frontal and
propodial bones distinct ; URODELA.
a, An os tabulare.
A palatine arch and separate caudal vertebra ; Protetda
aa, No os tabulare.
A maxillary arch ; palatine arch imperfect ; nasals, pre-
maxillaries and caudal vertebrze distinct .
Pseudosauria}
No maxillary or palatine arches; nasals and premaxil-
liary, also caudal vertebre, distinct ; Zvachystomata.

III. Supraoccipital, tabular, and supramastoid bones wanting.
Frontals and parietals connate; propodial bones and caudal
vertebrz confluent ; SALIENTIA.

Premaxillaries distinct from nasals; no palatine arch;
astragalus and calcaneum elongate, forming a distinct
segment of the limb ; Anura,

The probable phylogeny of these orders as imper-
fectly indicated by paleontology is exhibited in the
diagram on the following page.

An examination of the above tables shows that
there has been in the history of the batrachian class a
reduction in the number of the elements composing

1 Includes the Gymnophiona.

110 PRIMARY FACTORS OF ORGANIC EVOLUTION.

the skull, both by loss and by fusion with each other.
It also shows that the vertebre have passed from a
notochordal state with segmented centra, to biconcave
centra, and finally to ball-and-socket centra, with a
great reduction of numbers. It is also the fact that
the earlier forms (those of the Permian epoch) show
the most mammalian characters of the tarsus and of
the pelvis. The later forms, the salamanders, show a
more generalized form of carpus and tarsus and of
pelvis also. In the latest forms, the Anura, the carpus
and tarsus are reduced through loss of parts, except

ra hystomata
Urodel

Salientia

REpTILia Proteida
Microsauri

Embolgmeri |
ea
Plc

that the astragalus and calcaneum are phenomenally
elongate. We have then, in the batrachian series, a
somewhat mixed kind of change; but it principally
consists of concentration and consolidation of parts.
The question as to whether this process is one of pro-
gression or retrogression may be answered as follows:
If degeneracy consists in ‘‘the loss of parts without
complementary addition of other parts,” then the ba-
trachian line is a degenerate line. This is only partly
true of the vertebral column, which presents the most
primitive characters in the early, Permian, genera
(Rhachitomi). If departure from the nearest approx-

PHYLOGENY. vee

imation to the Mammalia is degeneracy, then the
changes in this class come partly under that head. The
scapular and pelvic arches of the Rachitomi are more
mammalian than are those of any of their successors ;

Fig. 27.—Cricotus crassidiscus Cope, parts of individual represented in
Fig. 28; one-third natural size. From Permian of Texas. «, head from above;
6, part of belly from below. From Cope.

the carpus and tarsus are less so than that of the
Anura.

There are several groups which show special marks
of degeneracy. Such are the reduced maxillary bones

Fig. 28.—Cricotus crassidiscus Cope, vertebral column and pelvis; three-tenths natural size. Cope Coll. from the Per-
ischium; 22,

mian formation of Texas. Fig. a, proatlas; 4,c, cervical centra and intercentra; d, e, 7, g, caudal centra; zs,

ilium ; Pu, pubis; zs, ischium.

PHYLOGENY, 113

and persistent gills of the Proteida; the absence of
the maxillary bones and the presence of gills in the
Trachystomata ; the loss of a pair of legs and feeble-
ness of the remaining pair in the same; and the ex-
treme reduction of the limbs in Amphiuma, and their
total loss in the Czciliide. Such I must also regard,
with Lankester, the persistent branchiz of the sire-
dons. I may add that in the brain of the proteid Nec-
turus the hemispheres are relatively larger than in the
Anura, which are at the end of the line.

“It must be concluded, then, that in many respects
the Batrachia have undergone degeneracy with the
passage of time.

a. The Reptilian Line.

As in the case of the Batrachia, the easiest way of
obtaining a general view of the history of this class is
by throwing their principal structural characters into a
tabular form. As in the case of that class, I commence
with the oldest forms and end with the latest in the
order of time, which, as usual, corresponds, with the
order of structure. I except from this the first order,
the Ichthyopterygia, which we do not know prior to
the Triassic period :

I. The quadrate bone united with the adjacent elements by suture.
A. Temporal region of skull with a bony roof; no postorbital
bars.
Supramastoid bone present; an interclavicle; limbs
ambulatory ; Cotylosauria,
AA. Cranium with one postorbital bar; no sternum. (Sy-
naptosauria. )
a. Paroccipital bone distinct.
A supramastoid bone; ribs two-headed on centrum ;
carpals and tarsals not distinct in form from meta-
podials ; Ichthyopterygia,

114 PRIMARY FACTORS OF ORGANIC EVOLUTION.

No supramastoid ; sub- and postpelvic ossifications ; in-
terclavicle and clavicles separated from and below
scapular arch ; ribs one-headed on centrum ; coracoid
large, free posteriorly ; Testudinata.

ga, Paroccipital bone not distinct.

Ribs one or two-headed, capitulum intercentral; clav-
icles and interclavicles forming part of shoulder-
girdle; scapula simple; pubis and ischium plate-like
with small or no obturator foramen; no sub- or
post-pelvic bones; no supramastoid ; Theromora,

Supramastoid present ; ribs one-headed ; scapula trira-
diate ; no sternum ; pubis and ischium plate-like; no

sub: or postpelvic bones ; Plesiosauria,
AAA. Cranium with two postorbital bars ; asternum. (Archo-
sauria. )

Paroccipital bone not distinct ; no supramastoid.
Ribs two-headed; no interclavicle; external anterior
digits greatly elongate to support a patagium ;

Ornithosauria.

Ribs two-headed; no interclavicle; acetabulum per-
forate; limbs ambulatory ; Dinosauria,
Ribs two-headed; an interclavicle ; acetabulum closed ;
feet ambulatory ; Crocodilia.
Ribs one headed; an interclavicle ; acetabulum closed ;
feet ambulatory ; Rhynchocephalia,

II. The quadrate loosely articulated with the adjacent elements,

and only proximally. (Streptostylica.)
One postorbital bar, when present; a paroccipital ; su-
pramastoid not distinct ; ribs one-headed; Sguamata.

An inspection of the characters of these ten orders,
and their consideration in connection with their geo-
logical history, will give a definite idea as to the char-
acter of their evolution. The history of the class, and
therefore the discussion of the question, is limited in
time to the period which has elapsed since the Per-
mian epoch inclusive, for it is then that the Reptilia
enter the field of our knowledge. During this period
two remarkable orders of reptiles inhabited the earth,

PHYLOGENY. 115

those of the Cotylosauria and of the Theromora. The
important character and réle of these types may be
inferred from the fact that the Cotylosauria are struc-
turally nearer to the Batrachia and the Theromora to
the Mammalia than any other, and the former presents
characters which render it probable that all the other
reptiles derived their being from them. The phylogeny
may be thus expressed :

MAMMALIA
Pterosauria
Squamata !
Dinosauria
Crocodilia
Sauropterygia
Rhynchocephalia Anomodonta
Ichthyosauria Theriodonta Testudinata

otylosauri:

It is extremely probable that the characters of the
posterior parts of the cranium of reptiles, as seen in
the osseous bars posterior to the orbit, were derived
by a kind of natural trephining of the cranial roof of
the primitive order of the Cotylosauria. This order
has left remains in the Permian beds of North Amer-
ica, South Africa, and Germany. This is the theory
of Baur,?and I have rendered it probable by researches
on the Permian genera of North America.‘

1Some unknown type of Pythonomorpha will represent the ancestor of
the Ophidia, while it is uncertain whether this order originated from the
Theriodonta or the Rhynchocephalia.

2The Theromora include the Pelycosauria, Theriodonta, Anomodonta,
and other suborders.

8 American Journal of Morphology, 1889, p. 471.

4 Trans. Amer. Philos, Soctety, 1892, p. 13; American Naturalist, 1892, p.
407.

116 PRIMARY FACTORS OF ORGANIC EVOLUTION.

The diagrams on pages 117-11¢ illustrate the suc-
cessive changes in the structure of the posterior region
of the skull in the types mentioned. The orders and
suborders Pseudosuchia, Rhynchocephalia, Ichthyo-
pterygia, Dinosauria, Crocodilia, Sauropterygia, and
Testudinata commence at the beginning of Mesozoic
time, after the Permian had closed. The Squamata
(lizards and snakes) commence, so far as is certainly
known, in the later Mesozoic, in the Cretaceous period.

The line which terminated in the Lacertilia and
Ophidia (Squamata) may have originated directly from
the Theriodonta, or it may have descended from the
Rhynchocephalia. It departs from the former type in
two respects:

First, in the loss of the capitular articulation of the
ribs, and, second, in the gradual elongation and final
freedom of the suspensory bone of the lower jaw (the.
os quadratum). In so departing from the Theromora,
it also departs from the mammalian type. The ribs
assume the less perfect kind of attachment which the
mammals only exhibit in some of the whales, and the
articulation of the lower jaw loses in strength, while
it gains in extensibility, as is seen in the develop-
ment of the line of the eels among fishes. The end
of this series, the snakes, must therefore be said to be
the result of a process of creation by degeneration, and
their lack of scapular arch and fore limb and usual
lack of pelvic arch and hind limb are confirmatory
evidence of the truth of this view of the case.

Secondly, as regards the ossification of the anterior
part of the brain-case. This is deficient in some of
the Theromora, the ancestral series, which resemble in
this, as in many other things, the contemporary Ba-
trachia. The late orders mostly have the anterior walls

117

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120 PRIMARY FACTORS OF ORGANIC EVOLUTION.

membranous, but, in the streptostylicate series at the
end, the skull in the snakes becomes entirely closed in
front. In this respect, then, the latter may be said to
be the highest or most perfect order.

As regards the scapular arch, including the ster-
num, no order possesses as many elements as thor-
oughly articulated for the use of the anterior leg as the
Permian Theromora (excepting in the suborder Pelyco-
sauria). In all the orders there is loss of parts, except-
ing only in the Ornithosauria and the Lacertilia. In
the former the adaptation is to flying. The latter re-
tain nearly the theromorous type. An especial side
development is the modification of abdominal bones
into three pairs of peculiar elements to be united with
part of the scapular arch into a plastron, and the in-
clusion of the coracoid above them, seen in the Testu-
dinata.

The pelvic arch has amore simple history. Again,
in the Theromora we have the nearest approach to the
Mammalia. The only other order which displays sim-
ilar characters is the Ornithosauria (Dimorphodon,
according to Seeley). In the Dinosauria we have a
side modification which is an adaptation to the erect
or bipedal mode of progression, the inferior bones be-
ing thrown backward so as to support the viscera in a
more posterior position in birds. This is an obvious
necessity to a bipedal animal where the vertebral col-
umn is not perpendicular. And it is from the Triassic
Dinosauria that I suppose the birds to have arisen. The
main line of the Reptilia, however, departs from both
the mammalian and the avian type and loses in strength
as compared with the former. In the latest orders,
the Pythonomorpha and Ophidia, the pelvis is rudi-
mental or absent.

PHYLOGENY. 121

As regards the limbs, the degeneracy is well marked.
No reptilian order of later ages approaches so near to
the Mammalia in these parts as do the Permian Thero-
mora. This approximation is seen in the internal epi-
condylar foramen and well-developed condyles of the
humerus, and in the well-differentiated seven bones of
the tarsus. The epicondylar foramen is only retained
in later reptiles in the rhynchocephalian Sphenodon
(Dollo); and the condyles of the Dinosauria and all of
the other orders, excepting the Ornithosauria and some
Lacertilia, are greatly wanting in the strong charac-
terization seen in the Theromora. The posterior foot
seems to have stamped out the greater part of the tar-
sus in the huge Dinosauria, and it is reduced, though
toa less degree, in all the other orders. In the paddled
Plesiosauria, dwellers in the sea, the tarsus and carpus
have lost all characterization, probably by a process of
degeneracy, as in the mammalian whales. This is to
be inferred from the comparatively late period of their
appearance in time. The still more unspecialized feet
and limbs of the Ichthyosaurus (Ichthyopterygia) can
not yet be ascribed to degeneracy, for their history is
too little known. At the end of the line, the snakes
present us with another evidence of degeneracy. But
few have a pelvic arch (Glauconiide Peters), while
very few (Peropoda) have any trace of a posterior
limb.

The vertebrz are not introduced into the definitions
of the orders, since they are not so exclusively distinc-
tive as many other parts of the skeleton. They never-
theless must not be overlooked. As in the Batrachia,
the Permian orders show inferiority in the deficient
ossification of the centrum. Many of the Theromora
are notochordal, a character not found in any later or-

122 PRIMARY FACTORS OF ORGANIC EVOLUTION.

der of reptiles excepting in a few Lacertilia (Gecconi-
dz). They thus differ from the Mammalia, whose
characters are approached more nearly by some of the
terrestrial Dinosauria in this respect. Leaving this
order, we soon reach the prevalant ball-and-socket
type of the majority of Reptilia. This strong kind of
articulation is a need which accompanies the more
elongated column which itself results at first from the
posterior direction of the ilium. In the order with the
longest column, the Ophidia, a second articulation,
the zygosphen, is introduced. The mechanical value
of the later reptilian vertebral structure is obvious, and
in this respect the class may be said to present a higher
or more perfect condition than the Mammalia.

In review it may be said of the reptilian line, that
it exhibits marked degeneracy in its skeletal structure
since the Permian epoch; the exception to this state-
ment being in the nature of the articulations of the
vertebre. And this specialization is an adaptation to
one of the conditions of degeneracy, viz., the weaken-
ing and final loss of the limbs and the arches to which
they are attached.

The history of the development of the brain in the
Reptilia presents some interesting facts. In the dia-
dectid family of the Permian Cotylosauria it is smaller
than in a Boa constrictor, but larger than in some of
the Jurassic Dinosauria. Marsh has shown that some
of the latter possess brains with relatively very narrow
hemispheres, so that in this organ those gigantic rep-
tiles were degenerate, while the existing streptostyli-
cate orders have advanced beyond their Permian an-
cestors.

There are many remarkable cases of what may now
be safely called degradation to be seen in the contents

PHYLOGENY. 123

of the orders of reptiles! Among tortoises may be
cited the loss of one or two series of phalanges in sev-
eral especially terrestrial families of the Testudinide.
The cases among the Lacertilia are the most remark-
able. The entire families of the Pygopodide, the
Anniellidze, the Anelytropide, and the Dibamidz are
degraded from superior forms. In the Anguide, Te-
ide, and Scincidz, we have series of forms whose steps
are measured by the loss of a pair of limbs, or of from
one to all the digits, and even to all the limbs. In
some series the surangular bone is lost. In others the
eye diminishes in size, loses its lids, loses the folds
of the epidermis which distinguish the cornea, and
finally is entirely obscured by the closure of the oph-
thalmic orifice in the true skin.2, Among the snakes
a similar degradation of the organs of sight has taken
place in two suborders, which live underground, and
often in ants’ nests. The Tortricide and Uropeltide
are burrowing-snakes which display some of the earlier
stages of this process. One genus of the true colubrine
snakes even (according to Giinther) has the eyes ob-
scured as completely as those of the inferior types
above named (genus Typhlogeophis. )

e. The Avian Line.

The paleontology of the birds not being well known,
our conclusions respecting the character of their evo-
lution must be very incomplete. A few lines of suc-
cession are, however, quite obvious, and some of them
are clearly lines of progress, and others are lines of re-

1Such forms in the Lacertilia have been regarded as degradational by
Lankester and Boulanger.

2A table of the degenerate forms of Lacertilia is given in the chapter on
Catagenesis.

124 PRIMARY FACTORS OF ORGANIC EVOLUTION.

trogression. The first bird we know at all completely,
is the celebrated Archeopteryx of the Solenhofen slates
of the Jurassic period. In its elongate series of caudal
vertebrz and the persistent digits of the anterior limbs
we have aclear indication of the process of change
which has produced the true birds, and we can see
that it involves a specialization of a very pronounced
sort. The later forms described by Seeley and Marsh
from the Cretaceous beds of England and North Amer-
ica, some of which have biconcave vertebre, and all
probably, the American forms certainly, possessed
teeth. This latter character was evidently speedily
lost, and others more characteristic of the subclass be-
came the field of developmental change. The parts
which subsequently attained especial development are
the wings and their appendages; the feet and their
envelopes, and the vocal organs. Taking all things
into consideration, the greatest sum of progress has
been made by the perching birds, whose feet have be-
come effective organs for grasping, whose vocal organs
are most perfect, and whose flight is generally good,
and often very good. In these birds also the circula-
tory system is most modified, in the loss of one of the
carotid arteries.

The power of flight, the especially avian charac-
ter, has been developed most irregularly, as it appears
in all the orders in especial cases. This is apparent
so early as in the Cretaceous toothed birds already
mentioned. According to Marsh, the Hesperornithide
have rudimental wings, while these organs are well
developed in the Ichthyornithide. They are well de-
veloped among natatorial forms in the albatrosses and
frigate pelicans, and in the skuas, gulls, and terns,
and are rudimental in their allies, the auks. They are

PHYLOGENY. 125

developed among rasorial types in the sand-grouse,
and, among the adjacent forms, the pigeons. Then

K.Sch.gez,

Fig. 32.—Archeopteryx lithographica,
from the middle Odlite of Bavaria.

among the lower Passeres, the humming-birds exceed
all birds in their powers of flight, and the swifts and

126 PRIMARY FACTORS OF ORGANIC EVOLUTION,

some of the Caprimulgidz are highly developed in this
respect. Among the higher or true song birds, the
swallows form a notable example. With these high
specializations occur some remarkable deficiencies.
Such are the reduction of the feet in the Caprimulgide,
swifts, and swallows, and the fcetal character of the
bill in the same families. In the syndactyle families,
represented by the kingfishers, the condition of the
feet is evidently the result of a process of degenera-
tion.

A great many significant points may be observed
in the developmental history of the epidermic struc-
tures, especially in the feathers. The scale of change
in this respect is in general a rising one, though vari-
ous kinds of exceptions and variations occur. In the
development of the rectrices (tail-feathers) there are
genera of the wading and rasorial types, and even in
the insessorial series, where those feathers are of prim-
itive structure (Menuride), are greatly reduced, or
absolutely wanting. These are cases of degeneracy.

There is no doubt that the avian series is in gen-
eral an ascending one.

J The Mammatian Line.

Discoveries in paleontology have so far invalidated
the accepted definitions of the orders of this class that
it is difficult to give a clearly cut analysis, especially
from the skeleton alone. The following scheme, there-
fore, while it expresses the natural groupings and affin-
ities, is defective, in that some of the definitions are
not without exceptions: !

1This classification of the Mammalia was first published by the writer
inthe American Naturalist for 1885 ; was improved in the same, 1889 (October);
and appeared in a Syllabus of Lectures of the University of Pennsylvania,
July, 1891.

PHYLOGENY. 127

I. A large coracoid bone articulating with the sternum. An inter-
clavicle (Prototheria).

Epicoracoid and marsupial bones; fibula articulating

with proximal end of astragalus: 1. Monotremata.

II. Coracoid a small process codssified with the scapula (Eutheria).
a, Marsupial bones; palate with perforations (uterus divided ;
placenta and corpus callosum rudimental or wanting ; cere-

bral hemispheres small and generally smooth).

But one deciduous molar tooth : 2. Marsupialia

aa, No marsupial bones ; palate generally entire (placenta and
corpus callosum well developed).

8. Anterior limb reduced to more or less inflexible paddles
‘posterior limbs wanting (Mutilata).

Elbow-joint fixed ; carpals discoid, and with the digits
separated by cartilage ; lower jaw without ascending
ramus: 3. Celacea,

Elbow-joint flexible; carpals and phalanges with normal
articulations; lower jaw with ascending ramus:

4. Sirenia.
6. Anterior limbs with flexible joints. Ungual phalanges
compressed and pointed! (Unguiculata).
y. Feet taxeopodous (with exceptions in the carpus).
6. Teeth without enamel; generally no incisors.

Limbs not volant; hemispheres small, smooth :

\ 5. Edentata
6d. Teeth with enamel ; incisors generally present.

No postglenoid process; mandibular condyle not trans-
verse ; limbs not volant ; hemispheres small, smooth :

, 6. Glires

Anterior limbs volant ;' hemispheres small, smooth :

7. Chiroptera

A postglenoid process; mandibular condyle transverse ;
limbs not volant; no scapholunar bone?; hemi-
spheres small, smooth : 8. Bunotheria3

A postglenoid process ; limbs not volant, with a scapho-
lunar bone ; hemispheres larger, convoluted :

9. Carnivora,

1Except Mesonychiide.
2Except Erinaceus and Talpa.
3 With the suborders Pantotheria, Creodonta, Insectivora, and Tillodonta

128 PRIMARY FACTORS OF ORGANIC EVOLUTION.

yy. Feet diplarthrous.
Limbs ambulatory; a postglenoid process ; molars qua-
dritubercular : 10. Ancylopoda.
BBG. Anterior limbs with flexible joints and distinct digits ;
ungual phalanges not compressed and acute at apex} (Un-
gulata’).
e. Tarsal bones in linear series; carpals generally in linear
series.
Limbs ambulatory; teeth with enamel: 11. Zaxeopoda.®
ee. Carpal series alternating ; tarsal series linear.
Limbs ambulatory ; median digits longest; teeth with
enamel : 12. Toxodontia.
eee, Tarsal series alternating ; carpals linear.
Cuboid bone partly supporting navicular, not in contact
with astragalus ; 13. Proboscidia,
eece, Both tarsal and carpal series more or less alternating.
Os magnum not supporting scaphoides; cuboid sup-
porting astragalus ; superior molars tritubercular :
14. Amblypoda.
Os magnum supporting scaphoides; superior molars
quadritubercular : 4 15. Diplarthra}

1Except the Hapalide.
2 Lamarck, Zoologie Philosophique, 1809.
8 This order has the following suborders:
Carpal series linear; no intermedium; tibia not interlocking with astraga-
lus; no anapophyses; incisors rooted; hallux not opposable:

Condylarthra.

Carpal series linear; an intermedium; tibia interlocking with astragalus;
hallux not opposable: Hyracoidea

An incermedium ; fibula not interlocking; anapophyses; hallux opposable;
incisors growing from persistent pulps: Daubentonioidea,

An intermedium; fibula not interlocking; anapophyses; hallux opposable;
incisors rooted ; carpus generally linear: Quadrumana.

No intermedium;6 nor anapophyses; carpal rows alternating; incisors
rooted: Anthropomorpha,?

The only difference between the Taxeopoda and the Bunotheria is in the
unguliform terminal phalanges of the former as compared with the clawed or
unguiculate form in the latter. The marmosets among the former division
are, however, furnished with typical claws.

4Except Trigonolestes.

5 This order includes the suborders Perissodactyla and Artiodactyla. It
is the Ungulata of some authors.

6 Except in Simia and Hylobates.
7TIncludés the Anthropoid apes and man.

129

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130 PRIMARY FACTORS OF ORGANIC LVOLUTION,.

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132 PRIMARY FACTORS OF ORGANIC EVOLUTION.

The characters of the skeleton of the order Mono-
tremata showthat it is nearest of kin to the Reptilia, and
many subordinate characters, especially of the extrem-
ities, point to the Theromora as its ancestral source."
In the general characters the Marsupialia naturally
follow in a rising scale, as proved by the increasing
perfection of the reproductive system. The Monodel-
phia follow with improvements in the reproductive
system and the brain, as indicated in the table above
given. The oldest Monodelphia were, in respect to
the structure of the brain, much like the Marsupialia,
and some of the existing orders resemble them in some
parts of their brain-structure. Such are the Condylar-
thra and Amblypoda of extinct groups, and the Buno-
theria, Edentata, Glires, and Chiroptera, recent and
extinct. The characters of the brains of Amblypoda
and some Creodonta are, in their superficial char-
acters, even inferior to existing marsupials. The di-
vided uterus of the recent forms named, also gives
them the position next to the Marsupialia. In the
Carnivora, Hyracoidea, and Proboscidia, a decided ad-
vance in both brain-structure aud reproductive system
isevident. The hemispheres increase in size, and they
become convoluted. A uterus is formed, and the testes
become external, etc. In the Quadrumana and An-
thropomorpha the culmination in these parts of the
structure is reached, excepting only that, in the lack
of separation of the genital and urinary efferent ducts,
the males are inferior to those of many of the Artio-
dactyla. This history displays a rising scale for the
Mammalia.?

1Proceedings American Philosoph, Society, 1884, p. 43. Antea, p. 87.

2 See the evidence for evolution in the history of the extinct Mammalia
Proceedings of the American Association for the Advancement of Science, 1883.

PHYLOGENY. 133

Looking at the skeleton, we observe the following
successional modifications :

First, as to the feet, and (A) the digits. The Con-
dylarthra have five digits on both feet, and they are
plantigrade. This character is retained in their de-
scendants of the lines of Anthropomorpha, Quadru-
mana, and Hyracoidea, also in the Bunotheria, Eden-
tata, and most of the Glires. In some of the Amblypoda
and in the Proboscidia the palm and heel are a little
raised. In the Carnivora and Diplarthra the heel is
raised, often very high, above the ground, and the
number of toes is diminished, as is well known, to two
in the Artiodactyla and one in the Perissodactyla.
(B) The tarsus and carpus. In the Condylarthra and
most of the Creodonta the bones of the two series in
the carpus and tarsus are opposite each other, so as to
form continuous and separate longitudinal series of
bones. This continues to be the case in the Hyracoi-
dea and many of the Quadrumana, but in the anthro-
poid apes and man the second row is displaced inwards
so as to alternate with the first row, thus interrupting
the series in the longitudinal direction, and forming a
stronger structure than that of the Condylarthra. In
the bunotherian, rodent, and edentate series, the tar-
sus continues to be without alternation, as in the Con-
dylarthra, and is generally identical in the Carnivora.
In the hoofed series proper it undergoes change. In
the Proboscidia the carpus continues linear, while the
tarsus alternates. In the Amblypoda the tarsus alter-
nates in another fashion, and the carpal bones are on
the inner side linear, and on the outer side alternating.
The complete interlocking by universal alternation of
the two carpal series is only found in the Diplarthra.
(C) As to the ankle-joint. In most of the Condylarthra

‘azIs [PINJEU SYIUIT-OM} ‘VIYIE[APUOD Japio ay} Jo satjeyuasasdad ‘z2uvuU7100 snpormUsyg—OE ‘Sd

PHYLOGENY. 135

it is a flat joint or not tongued or grooved. In most
of the Carnivora, in a few Glires, and in all Diplar-
thra, it is deeply tongued and grooved, forming a more
perfect and stronger joint than in the other orders,
where the surfaces of the tibia and astragalus are flat.
(D) In the highest forms of the Rodentia and Diplar-
thra the fibula and ulna become more or less codssified
with the tibia and radius, and their middle portions
become attenuated or disappear. :

Secondly, as regards the vertebre. The mutual
articulations (zygapophyses) in the Condylarthra have
flat and nearly horizontal surfaces. In higher forms,
especially of the ungulate series, they become curved,
the posterior turning upward and outward, and the an-
terior embracing them on the external side. In the
higher Diplarthra this curvature is followed by another
curvature of the postzygapophysis upward and out-
ward, so that the vertical section of the face of this
process isan S. Thus is formed a very close and se-
cure joint, such as is nowhere seen in any other Verte-
brata.

Thirdly, as regards the dentition. Of the two types
of Monotremata, the Tachyglossus, and the Platy-
pus, the known genera of the former possess no teeth,
and the known genus of the latter possesses only a
single corneous epidermic grinder succeeding two de-
ciduous molars, like those of certain extinct forms, in
each jaw. As the theromorous reptiles from which
these are descended have well-developed teeth, their
condition is evidently one of degeneration. We prob-
ably have their ancestors in the Multituberculata,
which range from Triassic to lower Eocene time in
both hemispheres. In the marsupial order we havea
great range of dental structure, which almost epito-

136 PRIMARY FACTORS OF ORGANIC EVOLUTION.

mizes that of the monodelph orders. The dentition
of the carnivorous forms is creodont ; that of the kan-
garoos is perissodactyle, and that of the wombats is
rodent. Other forms repeat the Insectivora. I there-
fore consider the placental series especially. I have
already shown that the greater number of the types of
this series have derived the characters of their molar
teeth from the stages of the following succession.
First, a simple cone or reptilian crown, alternating
with that of the other jaw. Second, a cone with an-
terior and posterior lateral denticles. Third, the den-
ticles rotated to the inner side of the crown below, and
outer side above forming with the principal (median)
cone a three-sided prism, with tritubercular apex,
which alternates with that of the opposite jaw. Fourth,
development of a heel projecting from the posterior
base of the lower jaw, which, in mastication, meets
the crown of the superior, forming a tubercular-sec-
torial inferior molar. From this stage the carnivorous
and sectorial dentition is derived, the tritubercular
type being retained. Fifth, the development of a pos-
terior inner cusp in the superior molar, and the eleva-
tion of the heel in the inferior molar, with the loss of
the anterior inner cusp. Thus the molars become qua-
dritubercular, and opposite. This is the type of many
of the Taxeopoda, including the Quadrumana and In-
sectivora as well as the inferior Diplarthra. The higher
Taxeopoda (Hyracoidea) and Diplarthra add various
complexities. Thus the tubercles become flattened
and then concave, so as to form V’s in the section pro-
duced by wearing ; or they are joined by cross-folds,
forming various patterns, of which the most special-
ized is that of the horse. In the Proboscidia the latter

PHYLOGENY. 137

Fig. 37.—A, Phenacodus primavus, fore and hind limbs; 8B, Homo sapiens,
fore and hind limbs,

138 PRIMARY FACTORS OF ORGANIC EVOLUTION.

become multiplied so as to produce numerous cross-
crests.

The molars of some of the Sirenia are like that of
some of the Ungulata, especially of the tapirine group,
while in others the teeth consist of cylinders. In the
Cetacea the molars of the oldest (Eocene and Miocene)
types are but two-rooted and compressed, having much
the form of the premolars of other Mammalia. In ex-
isting forms a few have simple conical teeth, while in
a considerable number teeth are entirely wanting.

g. General Review of the Phylogeny of Mammatia.

In the accompanying table some of the characters
of the mammalian skeleton above described are thrown
into a tabular form. They are exhibited in the order
of their appearance in geological time, beginning with
the oldest horizon at the bottom of the left-hand col-
umn. Continued primitive types are enclosed in brack-
ets. These relations were pointed out by me in 1883,!
and every discovery made since that date has confirmed
their correctness. Some characters of the Mesozoic
Mammalia are now added.

Paleontology has cleared up the phylogeny of most
of the mammalian orders, but some of them remain as
yet unexplained. This is the case with the Cetacea,
the Sirenia, and the Edentata. The Marsupialia can
be supposed with much probability to have come off
from the Monotremata, but there is but little paleon-
tological evidence to sustain the hypothesis. Little
progress has been made in unravelling the phylogeny

1 Proceedings American Assoc, Adv. Science, p. 40. The successional gra-
dation inthe limbs and teeth was announced by me in 1873 (Proceeds. Acad-
emy Philadelphia, p. 371, and Journal of the Academy, 1874, p. 20), and that in

the size of the hemispheres of the brain by Marsh in 1874 (American Journal
Sct, Arts, p. 66).

139

PHYLOGENY.

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140 PRIMARY FACTORS OF ORGANIC EVOLUTION,

of the Cetacea and Sirenia. The results attained by
the study of the paleontology of the other orders may
be summarized as follows :

First. It is probable that the common ancestors of
the placental and implacental lines of Mammalia are
known to us in some of the types of the Jurassic per-
iod. Whether they were marsupial in the sense of
possessing an external pouch for the young or not, is
immaterial. They were probably marsupial in brain
characters, in the structure of their reproductive sys-
tem, and in the absence of placenta. To this source
the existing polyprotodont marsupials may be traced,
through such forms as Myrmecobius. The multi-
tuberculate type has a contemporary history, and one
distinct from that of the Polyprotodontia, and its an-
cestry has not yet been discovered. Their earliest
forms (of the Jurassic and Triassic) are already highly
specialized. They probably represent the Monotre-
mata of their time.

Second. The immediate didelphian ancestors of the
monodelphous Mammalia have not yet been certainly
discovered. In the oldest of the latter (of the Puerco
epoch) numerous points of approach to the insectivo-
rous Jurassic forms occur, especially in the prevalent
trituberculy of the molars in both epochs.

Third. The phylogeny of the clawed group has
been traced back to a common ordinal form which has
been called the Bunotheria. Of these the most genera-
lized are the Creodonta, from which we may trace the
Carnivora, the Insectivora, and the Tillodonta, and
probably all other Unguiculata. The Ancylopoda only
have undergone the alternation of the carpal and tar-
sal bones, which obtains in the diplarthrous Ungulata.

fourth. The phylogeny of the hoofed groups car-

PHYLOGENY, 141

ries us back to the order Condylarthra, the hoofed
cotemporary of the Bunotheria. The even and odd
toed hoofed mammals are traceable back to the Am-
blypoda, whose oldest representatives are the Panto-
donta of the Puerco. The Proboscidia and Hyracoidea
come directly from the Condylarthra. Moreover, the
phalanges of the lemurs are not distinguishable by any
important characters from the hoofs of the Hyracoidea
and Condylarthra. Not only this, but the structure of
the foot in these three groups is identical in regard to
the mode of articulation of the first and second rows
of the tarsal and carpal bones.

Fifth. The characters of the feet of the Condylar-
thra agree with those of unguiculate placental Mam-
malia, and bind the two series together. The synthesis
of the ungulate and unguiculate lines is accomplished
by exceptions to the characters which define them.
Thus the hoofs of Pantolambda (Amblypoda), Peripty-
chus (Condylarthra), and Mesonyx (Creodonta) do not
differ by any marked character. Claws occur in the
Hapalide of the quadrumanous line, and the ungues
of some Glires are absolutely intermediate between
the hoofs and claws. Many Edentata have claws on
the fore feet and hoofs on the hind feet. The Condy-
larthra with tritubercular molar teeth are then trace-
able to Bunotheria with tritubercular teeth, of which
many are known from the Puerco beds; and the quadri-
tubercular forms from corresponding quadritubercular
or tritubercular Bunotheria, of which latter, some are
known. .

Sixth. The anthropoid line may be traced directly
through the lemurs to the Condylarthra. The changes
which have taken place in the skeleton are slight, and

142. PRIMARY FACTORS OF ORGANIC EVOLUTION.

consist among other points in a rotation of the second
row of carpal bones inwards on the first row, in the
anthropoid apes and man, similar to that which has
occurred among the Ungulata, but it has not become
so pronounced.

As a result we get the general phylogenetic scheme
as shown on the following page.

In this diagram, divisions of greater and lesser rank
are mixed, so as to display better some of the relation-
ships. Thus all the divisions whose names stand on
the right side of the middle vertical line are unguicu-
lates ; and those on the left side of the line, excepting
Sirenia and Cetacea, are ungulates. The three names
in the middle vertical line are those of the suborders
of the Taxeopoda.

A review of the characters of the existing Mam-
malia as compared with those of their extinct ances-
tors displays a great deal of improvement in many
ways, and but few instances of retrogression. The
succession in time of the Monotremata, the Marsupia-
lia, and the Monodelphia, is a succession of advance
in all the characters of the soft parts and of the skele-
ton which define them (see table of classification). As
to the monotremes themselves, it is more than prob-
able that the order has degenerated in some respects
in producing the existing types. The history of the
Monotremata is not made out, but the earliest forms
of which we know the skeleton, Polymastodon (Cope)
of the Lower Eocene, is as specialized as the most
specialized recent forms. The dentition of the Juras-
sic forms, Plagiaulax, etc., is quite specialized also,
but not more so than that of the kangaroos. The pre-
molars are more specialized, the true molars less spe-
cialized than in those animals. The history of Marsu-

143

PHYLOGENY.

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144 PRIMARY FACTORS OF ORGANIC EVOLUTION,

pialia indicates that the primitive types were all in-
sectivorous, and possessed a larger number of molars
than any of the recent forms. The latter have then
followed the same. course as the placentals in the re-
duction of the number of teeth and specialization of
those that remain.

Coming to the Monodelphia, the increase in the
size and complication of the brain, both of the cere-
bellum and the hemispheres, is a remarkable evidence
of advance. But one retrogressive line in this respect
is known, viz., that of the order Amblypoda,! where
the brain has become relatively smaller with the pas-
sage of time. The successive changes in the structure
of the feet are all in one direction, viz., in the reduc-
tion of the number of the toes, the elevation of the
heel, and the creation of tongue and groove joints
where plain surfaces had previously existed. The
diminution in the number of toes might be regarded
as a degeneracy, but the loss is accompanied by a pro-
portional gain in the size of the toes that remain. In
every respect the progressive change in the feet is an
advance. In the carpus and tarsus we have a gradual
extension of the second row of bones on the first, to the
inner side. In the highest and latest orders this pro-
cess is most complete, and, as it results in a more
perfect mechanical arrangement, the change is clearly
an advance. The same progressive improvement is
seen in the development of distinct facets in the cubito-
carpal articulation, and of a tongue and groove (‘‘troch-
lear crest”) in the elbow-joint. In the vertebre the
development of the interlocking zygapophysial articu-
lations is a clear advance.

Progress is generally noticeable in the dental struc-

1See Naturalist, Jan,, 1885, p. 55.

PHYLOGENY. 145

tures; for, the earliest dentitions are the most simple,
and the later the more complex. Some of the types
retain the primitive tritubercular molars, as the Cente-
tide, shrews, and some lemurs, and most Carnivora
(above), but the quadritubercular and its derivative
forms are by far the most common type in the recent
fauna. The forms that produced the complicated mod-
ifications in the Proboscidia and Diplarthra appeared
latest in time, and the most complex genera, Elephas,
Bos, and Equus, the latest of all. The extreme sec-
torial modifications of the tritubercular type, as seen
in the Hyznide and the Felide, are the latest of their
line also.

Some cases of degeneracy are, however, apparent in
the monodelphous Mammalia. The loss of pelvis and
posterior limbs in the two mutilate orders is clearly a
degenerate character, since there can be no doubt that
they have descended from forms with those parts of
the skeleton present. The reduction of flexibility seen
in the limbs of the Sirenia and the loss of this charac-
ter in the fore limbs of the Cetacea are features of de-
generacy for the same reason. The teeth in both or-
ders have undergone degenerate evolution ; in the later
and existing forms of the Cetacea even to extinction.

The Edentata have undergone degeneration. This
is chiefly apparent in the teeth, which are deprived of
enamel, and which are wanting from the premaxillary
bone. A suborder of the Bunotheria, the Tillodonta
of the Lower Eocene period, display a great reduc-
tion of enamel on the molar teeth, so that in much-
worn examples it appears to be wanting. Its place is
taken by an extensive coat of cementum, as is seen in
Edentata, and the roots of the teeth are often undi-
vided as in that order.

146 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Local or sporadic cases of degenerate loss of parts
are seen in various parts of the mammalian series, such
as toothless Mammalia wherever they occur. Such
are cases where the teeth become extremely simple,
as in the honey-eating masupial Tarsipes, the carnivore
Proteles, the pteropod bats, and the aye-aye. Also
where teeth are lost from the series, as in the canine
genus Dysodus, and in man. The loss of the hallux
and pollex without corresponding gain, in various gen-
era, may be regarded in the same light.

In conclusion, the progressive may be compared
with the retrogressive evolution of the Vertebrata, as
follows: In the earlier periods and with the lower
forms, retrogressive evolution predominated. In the
higher classes progressive evolution has predominated.
When we consider the history of the first class of ver-
tebrates, the Tunicata, in this respect, and compare
it with that of the last class, the Mammalia, the con-
trast is very great.

h. The Phylogeny of the Horse.

As an example of special phylogeny I select that
‘of the horse, because it is the most completely repre-
sented by specimens in our museums.

I have already pointed out that the alternate type
of carpus and tarsus of the Diplarthra has been derived
from the linear of the Taxeopoda by a displacement
inwards of the bones of their second rows. In the pos-
terior foot this has changed the convex surface of the
head of the astragalus into a bifacetted face. Thus
was the condylarthrous astragalus modified into that
of the Diplarthra. At the beginning of the line of
the horses we find the condylarthrous genus of the
Wasatch Eocene, Phenacodus Cope, to differ in this

PHYLOGENY. 147

way from the perissodactylous genus Hyracotherium
Owen. Phenacodontide are indicated as the ances-
tors of all the Ungulata by their character as ‘‘buno-
dont pentadactyle plantigrades,”’ characters in which
they agree with the ancestors of all placental mam-
mals. That they are not the ancestors of all the latter
is shown by the fact that their molar type is quadritu-
bercular; but one has to go backwards but a short
distance in time to the Puerco epoch, to find their tri-
tubercular ancestors. Between these and Phenaco-
dus, comes the quadritubercular genus Euprotogonia
Cope, of the Puerco, which has simpler premolar teeth.

Between Phenacodus and Hyracotherium there is
room for two or more genera with fully facetted car-
pals and tarsals, longer feet, and a rudimental first toe
on the anterior foot, and first and fifth toes on the hind
foot. In Hyracotherium these digits have disappeared.
Further, in Hyracotherium the internal cusps of the
molars are more or less connected with the external
by low and indistinct ridges, which in the superior
molars include the small intermediate tubercles or
conules. Thus is the lophodont dentition foreshad-
owed. Hyracotherium was a contemporary of Phe-
nacodus and continued later in Eocene time. Some
of its forms developed an increased complexity of the
last premolars in both jaws, forming the genus Pliolo-
_phus, and foreshadowing the development of molar-
like premolars, which is so characteristic of the later
members of the horse line. In the genus Epihippus
Marsh, of one epoch later in time (the Uinta), two
such premolars are developed in each jaw. We have
seen very short interspaces next the canine teeth in
Phenacodus, and these have become longer in Hyra-
cotherium and Epihippus.

148 PRIMARY FACTORS OF OKGANIC EVOLUTION.

With the opening of the Neocene age, we have the
descendant of Epihippus in Mesohippus Marsh, which
differs from its predecessor as follows. There are but
three toes on all the feet; three premolars resemble
the true molars ; the crests which connect the internal
pair of cusps with the external in both jaws, are much
more elevated, and soon form on wearing a part of the
pattern of the crown. Hyracotherium already walked
on the ends of its toes, and the feet of Mesohippus
continue the character. The crowns of all the molars
are short like those of its ancestors. In the Middle
Neocene formations we have the genus Anchitherium
Kaup, where the incisor teeth show the addition of a
ridge, or cingulum round the inner side, which bounds
a cup; forming the cupped incisors so characteristic
of the horses. The species have been all the while
growing gradually larger.

Towards the end of Neocene time important pro-
gress was made. In the Loup Fork epoch the three
toed horses were very numerous in species, but their
lateral toes were all much shortened so that they did
not reach the ground. The crests of the molar teeth
were much stronger, and in the superior series the
conules had assumed a greater importance, extending
themselves posteriorly from the transverse crests, and
showing crescentic sections, resembling those of the
outer cusps, with which they are parallel. The an-
terior conule extended so far posteriorly as to join the
posterior one, resembling in this respect also the an-
terior external cusp. So the crown came to have six
modified cusps of which the two inner are the smallest
and remain unconnected with each other. The crowns
of the moiars vary in length in these later three-toed
horses. Some are short like the Anchitheriums, and

PHYLOGENY. 149

others are longer, approaching the true horses. In the
valleys between these high cusps cement is deposited,
as in the true horses and other mammals with long-
crowned molars. There are two types of these later
three-toed horses. In one the posterior inner cusp is
not joined to the conule by a transverse crest (genus
Hippotherium Kaup), or it is so joined (genus Pro-
thippus Leidy).

Plistocene times witnessed the perfection of the
horse line. The lateral toes dwindled into splints
concealed beneath the skin. The crowns of the molar
teeth became very long, and in the upper jaw the inner
posterior tubercle, now a column, joined the adjacent
conule, and became extended very much in fore and
aft diameter. The small anterior premolar disap-
peared, and the canines became the mark of the male
sex only, in general. The lower molars acquire some
additional complications, and the feet are longer than
in any of its ancestors. The genus Equus L. is fin-
ished, and remains a permanent member of the human
epoch, from which its only relatives, the rhinoceros
and the tapir, are gradually disappearing.

This history may be duplicated in ‘manner and
mode, by the lines of the camels, the dogs and bears,
the cats, the beaver, etc.

Examination of all these genealogical lines reveals
a certain definiteness of end and directness of approach.
We discover no accessions of characters which are
afterwards lost, as would naturally occur as a result of
undirected variation. Nor do we discover anything
like the appearance of sports along the line, the word
sport being used in the sense of a variation widely di-
vergent from its immediate ancestor. On the con-
trary, the more thorough becomes our knowledge of

150 PRIMARY FACTORS OF ORGANIC EVOLUTION.

the series, the more evident does it become that pro-
gressive evolution has advanced by minute increments
along a definite line, and that variations off this line
have not exerted an appreciable influence on the re-
sult.

2. The Phylogeny of Man.

In man the feet retain the pentadactyle plantigrade
type with scarcely grooved astragalo-tibial articula-
tion, which characterizes the Mammalia of the Puerco
epoch, and most of those of the Lower Eocene.!_ His
dentition is not lophodont, but is simply bunodont, like
that of the Phenacodontidez of the Lower Eocene. It
is only in the structure of the brain and the reproduc-
tive system that man shows an advance over the Eocene
type. In the former he greatly excels any mammal
that has appeared since; a superiority already apparent
in one of his early ancestors, the anaptamorphous lemur
of the Lower Eocene. In the reproductive system he
is about on a par with the higher Artiodactyla, although
the male, in the persistent union of the genital and urin-
ary efferent ducts is not so much specialized as some of
the latter, where they are distinct. It is an interesting
fact that man displays in his dentition strong tenden-
cies to a greater specialization by simplification beyond
the ordinary quadrumanous type, by reduction in the
number of the true molarsand incisors. Thus the M.3is
not unfrequently absent in the highest races, and some
families display a rudimental condition and absence of
the 1.2. :

Much importance attaches to the composition of
the molar dentition. Many years ago, Owen? called

1This fact was first pointed out by myself in the Penn Monthly Magazine,
1875; see Origin of the Fittest, p. 268.

2Odontography, 1840-5, p. 454.

PHYLOGENY. I51

attention to the fact that in the dark races the roots of
the last superior molar are distinct from each other,
while in the Indo-Europeans they are known to be

Fig. 38.—Fig «, skull of Anaptomorphus homunculus Cope, natural size.
Fig. 4, same, oblique view, displaying the large cerebral hemispheres. Fig.c,
superior view of skull, natural size. Fig. @, inferior view, three-halves natural
size. Lower figs. 2, 4, and ¢, left branch of lower jaw of Anaptomorphus emu-
dus Cope, twice natural size; a, from left side; 4, inner side; c, from above.

more or less fused together. These now well-known
characteristics of human dentition constitute one of
the examples of transition from a simian to a human

152 PRIMARY FACTORS OF ORGANIC EVOLUTION.

type. Ihave pointed out a corresponding modifica-
tion in the structure of the crown of the superior true
molars, viz.: the transition from a quadritubercular to a
tritubercular structure in passing from the lower to the
higher races. As this point has some interesting im-
plications in the earlier phylogeny of man, and as its
value has been disputed, I give it a little attention.
The facts of the case are as follows: I have dem-
onstrated! the fact that all forms of dentition exhibited
by the eutherian mammals have been derived from a
primitive tritubercular type. Professor Osborn says
that he expects to be able to do the same for the multi-
tuberculate (? Prototherian) dentition. I have also
shown that man exhibits a tendency to revert from his
primitive quadritubercular molar to this tritubercular
type.? As to the significance of these facts, I have
expressed the view that this acquisition of a tritubercu-
lar molar is a reversion to the lemurine type. This
conclusion is necessary because the lemurs are the last
of the families in the line of the ancestry of man which
present this dentition. The monkeys and anthropoid
apes are all quadritubercular, except a few limited col-
lateral branches of the former, which still retain the
lemurine type. There are also a few collateral types
of lemurs which have acquired one or more quadri-
tubercular niolars, but they are not typical. In many
tritubercular mammals, a precocious form or two can
be found, which has acquired the fourth tubercle. But
the further back we go in time, the fewer they become,
until, in the Puerco fauna, of eighty-two species of

1 Proceeds. Amer. Philos, Soc., Dec., 1883; Origin of the Fittest, 1887, pp
245, 347, 359-
2American Journal of Morphology, \1., 1883, p. 7.

PHYLOGENY. 153

eutherian mammals, but four have true quadritubercu-
lar superior molars. ;

I take this opportunity of saying, however, that re-
version is not necessarily a result of heredity. It may
be simply a retrogression on a line of advance already
laid down. What influence lemurine heredity may
have had in the case of man, it is not easy to know.
But it must be borne in mind that various forms of
degeneracy of molar teeth are possible other than the
resumption of the tritubercular type, yet the normal
reduction generally presented is just this lemurine and
primitive eutherian condition. The simplicity of the
elements involved, has something, but not everything,
to do with this reversion.

Dr. Paul Topinard has made an investigation ! of
the characters of the crowns of the molars in man, and
hasreached general conclusions identical with my own.
He remarks (p. 665): ‘‘It is demonstrated, in conclu-
sion, that the teeth of man are, at present, in process
of transformation, and that in some future which is re-
mote the inferior molars shall certainly be quadri-
cuspid, and the superior molars tricuspid. It will be
curious to have the statistics as to prehistoric man;
unfortunately, their crania are rare, and their molars
generally much worn.” In the details of his examina-
tion, there are some divergencies from my results.
Thus he finds the quadritubercular second and third
superior molar relatively of more frequent occurrence
in Europeans than I did. But the absence of Europeo-
Americans from his tables reduces the percentage of
trituberculars in the Indo-Europeans. He makes no
report of Esquimaux. Had he observed this type, he
would have found a higher per cent. of tritubercular

2L' Anthropologie, 1892, p. 641 {Nov., Dec.).

154 PRIMARY FACTORS OF ORGANIC EVOLUTION.

upper molars than in any race that he has recorded.
He confirms my conclusion as to the high percentage
of quadritubercular superior molars in the Malays,
Polynesians, and Melanesians.

The relation of this fact to phylogeny is to confirm
Haeckel’s hypothesis of the lemurine ancestry of man.
I have advanced the further hypothesis that the An-
thropomorpha (which include man and the anthropoid
apes) have been derived directly from the lemurs, with-
‘out passing through the monkeys proper. This close
association of man with the apes, is based on various
considerations. One of them is that the skeleton of
the anthropoid apes more nearly resembles that of
man in the most important respects than it does that
of the monkeys. This is especially true of the verte-
bral column, where the anapophyses are wanting in
the Anthropomorpha (insignificant rudiments remain-
ing on one or two vertebre, as pointed out by Mivart),
while they are well developed in the monkeys and
lemurs. The molar teeth of the apes and man resem-
ble each other more than either do those of the mon-
keys, since they lack the crests which connect the
cusps, which are general in the latter.

The frequent presence of the tritubercular molar in
man suggests the superior claim of the lemurs over the
monkeys to the position of ancestor. Another signifi-
cant fact pointing in the same direction is the existence
of large-brained lemurs with a very anthropoid denti-
tion (Anaptomorphidz) in our Eocene beds, which have
the dental formula of man and the Old World monkeys
andapes. This resemblance is very remarkable, much
exceeding that lately observed by Ameghino in certain
extinct forms of monkeys in Patagonia, which appear
to be ancestors of the existing South American mon-

PHYLOGENY. 155

keys (Cebidz), and possibly of the Old World monkeys
also. The superior molars of the Anaptomorphus are
tritubercular, while the premolars, canines, and in-
cisors are essentially anthropomorphous, and rather
human than simian. Anaptomorphus is probably at
the same time the ancestor of the Malaysian lemurine
genus Tarsius, and M. Topinard remarks that Tarsius
has as good claims to be regarded as ancestral to
Homo as Anaptomorphus. But M. Topinard must be
aware that in the existing genus the character of the
canine and incisive dentition is very unlike that of the
Anaptomorphus and Homo. It is specialized in a
different direction. The dentition of Anaptomorphus
being so generalized as compared with Tarsius, I sus-
pect that its skeleton will be found to present corre-
sponding characters. Of course, if it be found here-
after to have the foot structure of Tarsius (which I do
not anticipate), it cannot be included in the ancestry
of the Anthropomorpha.

It must be further observed that the ancestral line
of the Anthropomorpha cannot be traced through any
existing type of Lemuride, but through the extinct
forms of the Eocene period.! This is on account of
the peculiar specialization of the inferior canines, which
are incisor-like, and because of the peculiar character
of the incisors themselves, in the modern lemurs in
the restricted sense. But we have numerous lemurine
types of the Eocene of both America and Europe
which satisfy the conditions exactly, so far as the den-
tition is concerned. These are mostly referable to the
family Adapide.

Unfortunately, we do not know the entire skeletons

1On the Primitive Types of the Orders of the Mammalia Educabilia, 1873,
p. 8.

156 PRIMARY FACTORS OF ORGANIC EVOLUTION.

of these Eocene lemurs, but as far as we have them
(genera Tomitherium and Adapis) they are monkey-
like. But we have what is almost as useful, the skel-
eton of their Eocene and Puerco ancestors, the Con-
dylarthra. I long since pointed out that the latter
order (not the genus Phenacodus, as Lydekker has

ae pe

Fig. 39.—Tomitherium rostratum Cope, one of the Adapide, mandible,
natural size; a, from left side; 4, from above. Original, from Report U. S.
Geol. Survey Terrs., Vol. III.
represented me as saying) must be the ancestors of
the lemurs, basing my views expressly on the general
structure of the Phenacodus, Periptychus, and Menis-
cotherium. The structure of the ungual phalanges of
Periptychus is very significant, and even more so is
that in Meniscotherium, as recently shown by Marsh,

PHYLOGENY. 157

who adopts (without credit) my hypothesis of lemurine
affinities of the Condylarthra (which he renames the
Mesodactyla). From Condylarthra back to Creodonta
is an easy transition, and I have always assumed that
the Creodonta were derived from generalized polypro-

Fig. 40.— Tomitherzum ros-
tratum Cope, fore arm, five-

sixths natural size, Original,
6, ulna; ¢, radius.

todont Mursupialia. This view
has been entirely confirmed by
the recent discoveries of Ame-
ghino in Patagonia, where he.
has found forms whose remains
may be referred with equal pro-
priety to the one group or the
other. M. Topinard has been
rather hasty in reaching the
marsupial ancestry in suppos-
ing that Phenacodus belongs to
that order. All the evidence
shows that Phenacodus is a
generalized ungulate placental.
To return to the more im-
mediate ancestry of man. I
have expressed,! and now main-
tain as a working hypothesis,
that all the Anthropomorpha
were descended from the Eo
cene lemuroids. In my sys-
tem? the Anthropomorpha in-
cludes the two families Homi-
nide and Simiide. The sole

difference between these families is seen in the struc-
ture of the posterior foot; the Simiide having the

lAmerican Naturalist, 1885, p. 467.
2 Origin of the Fittest, 1887, p. 346, from American Naturalist, 1885, p. 344,
where the classification of the Taxeopoda should be in a foot-note; oc. cit.,

1889, October.

158 PRIMARY FACTORS OF ORGANIC EVOLUTION.

hallux opposable, while
in the Hominide the
hallux is not opposable.
This is not a strong
character, since it de-
pends ona slight differ-
ence in the form of the
entocuneiform bone. In
some vertebrates, as the
tree-frogs, the same and
similar characters (ge-
nus Phyllomedusa) are
not regarded as of fam-
ily value. It is then
highly probable that
Homo is’ descended
from some form of the
Anthropomorpha now
extinct, and probably
unknown at present, al-
though we do not yet
know all the charac-
ters of some extinct
supposed Simiide, of
which fragments only
remain to us. It cannot
now be determined
whether man and the
Simiidze were both de-
scended from a genus
with opposable hallux,
or without opposable
hallux, or whether from
a genus presenting an

Fig. 41.— Tomitherium rostratum Cope,
five-sixths natural size; a, ilium; 4, femur.
Original.

PHYLOGENY. 159

intermediate character in this respect. This genus
was, in arty case, distinct from either of the two existing
genera of Simiide, Simia and Hylobates, since these
present varied combinations of anthropoid resem-
blances and differences, of generic and specific value.

Professor Virchow in a late address! has thrown
down the gage to the evolutionary anthropologists by
asserting that ‘scientific anthropology begins with
living races,” adding ‘that the first step in the con-
struction of the doctrine of transformism will be the
explanation of the way the human races have been
formed,” etc. But the only way of solving the latter
problem will be by the discovery of the ancestral
races, which are extinct. The ad captandum remarks
of the learned professor as to deriving an Aryan from
a Negro, etc., remind one of the criticisms directed
at the doctrine of evolution when it was first presented
to the public, as to a horse never producing a cow,
etc. It is well known to Professor Virchow that hu-
man races present greater or less approximations to
the simian type in various respects. Such are the
flat coéssified nasal bones of the Bushmen; the qua-
dritubercular molars of the Polynesians; the flat ilia
and prognathous jaws of the Negro; the flat shin-
bones of various races; the divergent hallux of some
aborigines of farther India, etc. Professor Virchow
states that the Neanderthal man is a diseased subject,
but the disease has evidently not destroyed his race
characters; and in his address he ignores the important
and well-authenticated discovery of the man and wo-
man of Spy. These observations are reinforced by
recent discovery of a similar man by DuBois at Trinil

1 Popular Science Monthly, January, 1893, p. 373, translated.

160 PRIMARY FACTORS OF ORGANIC EVOLUTION.

in the island of Java. To these ancient people I will
now devote some space.
What had been long suspected is now established,

Fig. 42,_Megaladapis madagascariensis Forsyth Major, 4% natural size; lemuroid from Plis-
tocene bed of Madagascar, with tritubercular superior molars. From Forsyth Major.
through the discovery and descriptions of Messrs.
Fraipont and Lohest of Liége; viz. that there dwelt in
Europe during Paleolithic times a race of men which

PHYLOGENY. 162

possessed a greater number of simioid characteristics
than any which has been discovered elsewhere. ‘The
important discovery in the grotto of Spy of two skele-
tons, almost complete, served to unify knowledge of
this race, which had previously rested on isolated frag-
ments only. These skeletons proved what had been
previously only surmised, that the lower jaws of Nau-
lette, and of Shipka, and probably the skeleton of
Neanderthal, belong to one and the same race. The

Fig. 43.—Skull of the man of Spy. From Prof. G. F. Wright’s Man and
the Glacial Period. From a photograph.
simian characters of these parts of the skeleton are
well known. These are the enormous superciliary
ridges and glabella; the retreating frontal region; the
thickness of the cranial wall; the massive mandibular
ramus with rudimentary chin, and the large size of the
posterior molars. Messrs. Fraipont and Lohest have
added other characters to these, viz.: the tibia shorter
than in any other known human race; the sigmoid
flexure of the femur; the divergent curvature of the
bones of the fore-arm, and most important, a very

162 PRIMARY FACTORS OF ORGANIC EVOLUTION.

peculiar form of the posterior face of the mandibular
symphysis, already pointed out by Topinard in the jaw

From Fraipont and Lohest.

Fig. 44.—Outlines of calvaria; of the Neanderthal man in solid line; of the Spy man No.1 in dots, and

of the Spy man No. 2 in broken line.

of Naulette. On these characters the following re-
marks may be made.!
I. The prominent superciliary crests, which are

1 Archives Belges de Biologie, V11., 1886, p. 731, Gand.

PHYLOGENY. 163

characteristic of the Neanderthal race. No existing
race presents such a development, neither the Papu-
ans, Australians, nor Negroes of any race. But we
find the superciliary crests and underlying sinuses
identical in adult female orangs and chimpanzees and
young male gorillas. Inthe female chimpanzees the
crests are almost inferior in size to those of the man of
Spy.

II. The retreating forehead of the two crania of
Spy is not found in any existing human race, while it
is typical of that of Neanderthal. It is characteristic
of female orangs and gorillas and of the young males
of both species, and of adult males and female chim-
panzees. It appears in existing men in rare and iso-
lated cases; [probably as survivals].

III. The prominent transverse superior semicircu-
lar crest of the occipital bone is found in existing races
among the Fellahs of Africa and the Nigritos. It is
characteristic of the Neanderthal skulls, and presents
exactly the same characters as the young male and
female orang and gorilla and young male and adult
female of the chimpanzee.

IV. No human race presents the characters of the
lower jaw exhibited by those of Spy, Naulette, and
Shipka. In this part of their osteology the anthro-
poids depart widely from man, the most conspicuous
point in the latter being the presence of a chin. Ac-
cordingly, the angle formed by the anterior face of the
symphysis with the inferior border of the horizontal
ramus, is less than a right angle in man, and much
more than a right angle in the anthropoids. According
to Topinard, this angle in fifteen Parisians is 71.4°; in
fifteen African Negroes, 82.2°; in fifteen Neocaledo-
nians, 83.9°; in the jaw of Naulette, 94°. In the best

164 PRIMARY FACTORS OF ORGANIC EVOLUTION.

preserved jaw of Spy the angle is 107°, if measured
from the inferior symphysial border, or go° if meas-

A B
:)
c..
B
M~
Cc D E

Fig. 45.—Vertical sections of symphysis mandibuli of gorilla (Fig. 4), and
orang (Fig. 2), of chimpanzee (Fig. C), of Spy man No.1 (Fig. D), and Spy man
No. 2 (Fig. £). From Fraipont and Lohest.
ured from the inferior border of the ramus. There
is no chin in the jaw of the Spy race, and the large
angle approaches without nearly equaling that of the

PHYLOGENY. 165

anthropoids. But the posterior face of the symphysis
presents the most remarkable peculiarity. In the
symphysis of the apes (Fig. 54, 4, B, C) the posterior
border is a continuous slope from the alveolar border
to the inferior margin, interrupted by a slight concav-
ity below the middle. In the human jaw this line
slopes backward to near the middle, where are situated
the small tuberosities for the insertion of the genio-
glossal muscles. (B in the accompanying figures.) The
surface then slopes rapidly forward to pass into the
narrow inferior border of the chin (Fig. 46, 7, G). In
the jaws Naulette and Spy the structure is exactly in-
termediate between the two, and quite different from
both (Fig. 45, D, £). It commences above with a pos-
terior slope similar to that of the apes, exhibiting
what is called by Topinard ‘internal prognathism,”
as it appears in the lower human races. The surface
then descends abruptly, forming a vertical concavity,
which is bounded a considerable distance below by
another protuberance, the insertion of the genioglossal
muscles. This concavity is not present in the human
symphysis, while it is less developed in the simian.
The surface then slopes forward, as in the human sym-
physis, but this portion is shorter than in human jaws
generally. It is represented by a convex face in the
simian jaw. ‘This character, taken in connection with
the others cited, goes a long way toward justifying the
separation of the Neanderthal race as a distant species,
as has been done by some author under the name of
Homo neanderthalensis. This name is objectionable but
must be retained.

To these observations Messrs. Fraipont and Lohest
add the following.

V. The curvature of the ulna and radius, which

166 PRIMARY FACTORS OF ORGANIC EVOLUTION.

produces a wide interosseous space, is not found in any
human race, but is common to the apes. On the con-
trary, the shortness of these bones is entirely human.

VI. The anterior convexity of the femur, with its
round section, is only found among living races among
the Nigritos of the Philippine Islands. It is seen ina
less degree in femora of Neolithic men, and occasional
instances are seen among existing Europeans. It is
the normal condition in the apes.

VII. The tibia is shorter in its relation to the femur
than in any human race, and is more robust than in

fF G

Fig. 46.—Sections of symphysis mandibuli of modern Litgois (Fig. /)
and of an ancient Parisian (Fig. G). From Fraipont and Lohest.

most of them. This character, with the oval section,
while not identical with what is seen in the apes, forms
an approximation to it.

Messrs. Fraipont and Lohest have pointed out the
general characters of the dentition of the man of Spy.
They show that the molars increase in size posteriorly
to the same extent that they do in the apes, which is
the reverse of what is usual in man, where they dimin-
ish posteriorly, or, in a few lower races (Australians,
etc.), remain equal. They show that the superior mo-
lars are all quadritubercular, and that the internal root

4a 2a

Fig. 47.—Molar teeth of man. 1-2, man and woman of Spy; 3, Maori; 4, Tahitian; 5-6, Fan, 7, Esquimau.

168 PRIMARY FACTORS OF ORGANIC EVOLUTION.

is distinct in all of them. Through the kindness of
M. Lohest I received casts and photographs of these
teeth, and I give here figures of the former (Fig. 47),
which are more satisfactory than those in the memoir
from which J have already quoted so fully, where, in-
deed, the grinding faces are not represented at all.

The figures accompanying! show the large size of
the last superior molar, which exceeds in its propor-
tions those of the corresponding tooth in the chimpan-
zee. The fourth tubercle, or hypocone, is especially
large. In the male the crowns are more produced
posteriorly than in man generally, and remind one of
the character seen in the orang. The strong divergence
of the internal root of the last molar is shown in No.
2a, and the corresponding character in a Maori and a
Fan from tropical Africa is shown in Nos. 3 and 5a.
The quadritubercular crown of the last superior molar
of a Tahitian is shown in No. 4.4; and the roots, which
are exceptionally fused nearly as much as in the typi-
cal Indo-European, are shown in No. 4.

Dr. Eugene Dubois of the Army of the Netherlands
has recently published in Batavia, Java, in a brochure
in quarto, an account of some bones of an interesting
quadrumanous mammal allied to man, which were
found in a sedimentary bed of material of volcanic ori-
gin of probably Plistocene age, near a village called
Trinil. The remains consist of a calvarium which in-
cludes the supraorbital ridges and a part of the occi-
put; a last superior upper molar, and a femur. The
tooth was found close to the skull and belongs probably
to the same individual as the latter, while the reference
of the femur is more uncertain, as it was found some
fifty feet distant.

1From The American Naturalist, April, 1893.

PHYLOGENY. 169

The characters of the skull are closely similar to
those of the men of Neanderthal and of Spy, but the
walls are not so thick as those of the former, and more
nearly resemble those of the latter. The frontal region
is, therefore, much depressed, and it is also much con-
stricted posterior to the postorbital borders. The su-
tures are obliterated. Dr. Dubois states that the cranial
capacity is just double that of the gorilla, and two-thirds
that of the lowest normal of man, bridging the gap
which has long separated the latter from the apes.
Thus the capacity of the former is 500 cubic centime-
tres, and the latter is 1500 cubic centimetres. In the
Java man the capacity is 1000 cubiccentimetres. The
last upper molar has widely divergent roots,.as in apes
and inferior races of man, and the crown is large, with
the cusps not clearly differentiated, showing a character
commonly observed in the lower molars of the gorilla.
The femur is long, straight, and entirely human. This
discovery of Dr. Dubois adds to our knowledge of the
physical characters of the Paleolithic man, and espe-
cially to his geographical range.

As regards the proper appellation of this being,
Dr. Dubois is not happy. He proposes for him a
new genus Pithecanthropus (after Haeckel), and even
anew family, Pithecanthropide, without having shown
that he is not a member of the genus Homo. It is
not certain that he is not an individual of the species
Homo neanderthalensis. is cranial capacity is less, it
is true, than that of the man of Spy, but Virchow has
pointed out that some of the Nigritos possess a remark-
ably small cranial capacity, as little as 950 cubic centi-
metres, and an inhabitant of New Britain only 860
cubic centimetres, a capacity even smaller than that of
the man of Trinil. Until we learn the characters of

170 PRIMARY FACTORS OF ORGANIC EVOLUTION.

the lower jaw of the latter we shall be in doubt as to
whether this individual pertains to the Homo sapiens
or the Homo neanderthalensis.

The characters of the dentition, cranium, and limbs
which have been observed in the Paleolithic man, are
not without parallel in existing races, though the char-
acters do not generally occur together in the latter.
The supposition that all the Paleolithic men so far
found are all pathological subjects is not a probable
solution of the question, although this type was no
doubt subject to pathological conditions such as have
been found in the leg-bones of the men of Neanderthal
and Trinil. The characters of the symphysis of the
lower jaw are quite sufficient to separate the Neander-
thal man as a distinct species of the genus Homo.!
This character is not pathological but it is zodlogical,
and places that species between Homo sapiens and the
apes.

In conclusion, it may be observed that we have in
the Homo neanderthalensis a greater number of simian
characteristics than exist in any of the known races of
the Homo sapiens, although, so far as known, he be-
longs to the genus Homo. ‘The posterior foot, so far
as preserved, indicates this to be the case. The foot-
character, which distinguishes the genera Homo and
Simia still remains. There is still, to use the language
of Fraipont and Lohest, ‘‘an abyss’’ between the man
of Spy and the highest ape ; though, from a zoélogical
point of view, it is not a wide one.

The flints which were discovered in the stratum of
cave deposit containing the human remains, are of the
Paleolithic type known as Mousterien in France, which

1 This view was first insisted on in an article on the Genealogy of Manin
the American Naturalist, 1893, p. 331.

PHYLOGENY. I7I

are of later origin than the Chelléen or older Paleo-
lithic. The older Paleolithic man is not yet known.
It is interesting to observe that these flints (Mouste-
rien) are of the same form as the obsidian implements
which I collected at Fossil Lake, in Oregon, with the
bones of extinct Ilamas, horses, elephants, sloth, etc.
The animals which accompanied the man of Spy are,
Celodonta antiguitatis (wooly rhinocetos), Eguus ca-
ballus, Cervus elaphus, Cervus tarandus, Bos primigenius,
Elephas primigenius, Ursus speleus, Meles taxus, Hyena
spelea ; five extinct and four existing species.

As the evidence now stands, the most primitive and
simian of human races inhabited the Old World. No
trace of the Homo neanderthalensis has been found in
America. As, however, Paleolithic implements are
found in all continents, we may anticipate that this or
some similar species of man will be discovered there
also. The genealogy of man may be then represented
as follows:

CLASS & BRANCH ORDER AND FAMILY. GEOL. SYSTEM
Hominide Plistocene
Simiidze Neocene
Adapidz Eocene

Mammalia Condylarthra Cretaceous

Creodonta

Marsupialia polyprotodontia Jurassic
Monotremata Triassic

Reptilia Theromora Carbonic

Batrachia Batrachia Stegocephali Carbonic

Pisces Teleostomi Rhipidopterygia
Elasmobranchii Ichthyotomi

Agnatha q

Cephalochorda _Leptocardii

Vermes i

Ceelenterata 1.

Protozoa 1

1 Subordinate type not specified.

172 PRIMARY FACTORS OF ORGANIC EVOLUTION.

3. THE LAW OF THE UNSPECIALIZED.

The facts cited in the preceding parts of this chap-
ter show that the phylogenetic lines have not been
continuous, but that they may be represented by a
system of dichotomy. In other words, the point of
departure of the progressive lines of one period of time
has not been from the terminal types of the lines of
preceding ages, but from points farther back in the
series. Thus it is not the highly developed or spe-
cialized ‘plants which have given origin to the animal
kingdom, but the lowest forms or Protophyta, which
are not distinguishable from the Protozoa. Among
animals it is not the specialized Arthropoda or Mol-
lusca which present the closest affiliations with the
Vertebrata, but the simple Vermes or Tunicata, from
which the origin of the latter may be traced. In the
Vertebrata it is not the higher fishes (Actinopterygia)
which offer the closest points of affinity to the succeed-
ing batrachian class, but that more generalized type
of the Devonic period, the Rhipidopterygia, which
probably occupies that position. The modern types of
Batrachia (Urodela, Salientia) have plainly not fur-
nished the starting-point for the reptiles, but the an-
cient order of the Stegocephali, which are also fish-
like, is evidently their source. The Reptilia of the
Permian present us with types with fish-like vertebre
(Cotylosauria, Pelycosauria), from which the class
Mammalia may be distinctly traced. The later reptiles
diverged farther and farther from the mammalian type
with the advance of geologic time. The same prin-
ciple has been found to be true in tracing the history

PHYLOGENY. 173

of the subdivisions of the great classes, in the preceding
section.

Agassiz and Dana pointed out this fact in taxon-
omy, and I expressed it as an evolutionary law under
the name of the ‘‘ Doctrine of the Unspecialized.”
This describes the fact that the highly developed, or
specialized types of one geologic period have not been
the parents of the types of succeeding periods, but
that the descent has been derived from the less spe-
cialized of preceding ages. No better example of this
law can be found than man himself, who preserves in
his general structure the type that was prevalent dur-
ing the Eocene period, adding thereto his superior
brain-structure.

The validity of this law is due to the fact that the
specialized types of all periods have been generally in-
capable of adaptation to the changed conditions which
characterized the advent of new periods. Changes of
climate and food consequent on disturbances of the
earth’s crust have rendered existence impossible to
many plants and animals, and have rendered life pre-
carious to others. Such changes have been often espe-
cially severe in their effects on species of large size,
which required food in large quantities. The results
have been degeneracy or extinction. On the other
hand plants and animals of unspecialized habits have
survived. For instance, plants not especially restricted
to definite soils, temperatures, or degrees of humidity,
would survive changes in these respects better than
those that have been so restricted. Animals of om-
nivorous food-habits would survive where those which
required special foods, would die. Species of small
size would survive a scarcity of food, while large ones
would perish. It is true, as observed by Marsh, that

174 PRIM1RY FACTORS OF ORGANIC EVOLUTION.

the lines of descent of Mammalia have originated or
been continued through forms of small size. The
same is true of all other Vertebrata.

It is not to be inferred from the reality of the law of
‘‘the unspecialized” that each period has been de-
pendent on the simplest of preceding forms of life for
its population. Definite progress has been made, and
highly specialized characters have been gradually de-
veloped, and have passed successfully through the
vicissitudes of geologic revolutions. But these have
not been the most specialized of their respective ages.
They have presented a combination of effective struc-
ture with plasticity, which has enabled them to adapt
themselves to changed conditions.

In a large number of cases in each geologic age
forms have been successful in the struggle for existence
through the adoption of some mode of life parasitic on
other living beings. Such habits reduce the struggle
to a minimum, and the result has been always degen-
eracy. In other cases it is to be supposed that ex-
tremely favorable conditions of food, with absence of
enemies, would have occurred, in which the struggle
would have been almost nil. Degeneracy would fol-
low this condition also. On the other hand, extreme
severity of the struggle cannot have been favorable to
propagation and survival, so that here also we have a
probable cause of degeneracy. Degeneracy is a fact
of evolution, as already remarked, and its character is
that of an extreme specialization, which has been, like
an overperfection of structure, unfavorable to sur-
vival.

In general, then, it has been the ‘‘golden mean”
of character which has presented the most favorable
condition of survival, in the long run.

CHAPTER III.—PARALLELISM.

T IS now generally recognized that the successive
types of organic beings present characters which
are traversed in the embryonic life of those which at-
tain the greatest complexity of development, and which
occupy the highest places in the scale of life. This
fact was observed by the early embryologists, as Von
Baer and Agassiz, who did not admit its bearing on
the doctrine of evolution. But Darwin and Spencer
understood its significance, and Haeckel, Hyatt, and
the writer applied it directly to the explanation of phy-
logeny. At the present time one of the chief aims of
the science of embryology is to discover the record of
the history of the past, recapitulated in the stages of
embryonic life, and to unravel the phylogenesis of
plants and animals by this method. The utility of
these researches is attested by the results which they
have attained, though for obvious reasons, these are
not as definite and conclusive as those which are de-
rived from paleontology. The general conclusion is
however justified, i. e., that the records of embryology
and paleontology are closely similar, and that any dis-
cordance between them may be explained on compre-
hensible principles.

176 PRIMARY FACTORS OF ORGANIC EVOLUTION,

A number of illustrations of the parallelism be-
tween taxonomy, ontogeny, and phylogeny may now
be given.

1. PARALLELISM IN THE BRACHIOPODA.

For the following abstract I am indebted to Mr. C.
E. Beecher of New Haven, whose excellent work in
this field is well known.

The parallelism between the ontogeny and phy-
logeny in the Brachiopoda has been worked out in
numerous instances.! To illustrate these, some more or
less familiar genera may be taken as characteristic ex-
amples.

Lingula has been shown by Hall and Clarke (Pai.
New York, Vol. VIII., 1892) to have had its inception
in the Ordovician. In the ontogeny of both recent and
fossil forms, the first shelled stage has a straight hinge
line, nearly equal in length to the width of the shell.
This stage may be correlated with the more ancient
genus Paterina from the lowest Cambrian. Subsequent
growth produces a form resembling Obolella, a Cam-
brian and Ordovician genus. Then the linguloid type
of structure appears at an adolescent period, and is
completed at maturity. Thus, Lingula has ontogenetic
stages corresponding to (1) Paterina, (2) Obolella, and
(3) Lingula, of which the first two occur as adult forms
in geological formations older than any known Lin-
gula.

Paterina represents the radicle of the brachiopods.

1C. E. Beecher, ‘‘ Development of the Brachiopoda,” Part I., Introduc-
tion, Amer, Journ, Scz., Vol, XLI., April, 1891; ‘‘ Development of the Brachio-
poda,” Part II., Classification of the Stages of Growth and Decline, Amer.
Jour, Scz., Vol. XLIV., August, 1892; ‘‘ Development of Bilobites,’’ Aver.

Jour, Sc7., Vol. XLIL., July, 1891; ‘‘ Revision of the Families of Loop-bearing
Brachiopoda,”’ 7raus. Conn, Acad, Sci., Vol. 1X., May, 1893.

PARALLELISM. 177

It shows no separate stages of growth in the shell, is
found in the oldest fossiliferous rocks, and corresponds
to the embryonic shelled condition (protegulum) of
other brachiopods.

The genus Orbiculoidea of the Discinide first ap-
pears in the Ordovician and continues through the
Mesozoic. The early stages in the ontogeny of an in-
dividual are as in Lingula, first a paterina stage, fol-
lowed by an obolella stage. Then from the mechan-
ical conditions of growth a Schizocrania-like stage
follows, and completed growth results in Orbiculoidea.

The elongate form of the shell in Lingula, as well
as in many other genera, is determined by the length
of the pedicle and freedom of motion. The discinoid
or discoid of Orbiculoidea and Discinisca among the
brachiopods, and Anomia among pelecypods, is deter-
mined by the horizontal position of the valves, which
are attached to an object of support by a more or less
flexible, very short organ, a pedicle or byssus, without
calcareous cementation. This mode of growth is char-
acteristic of all the discinoid genera, but, as already
shown, the early stages of Paleozoic Orbiculoidea have
straight hinge lines and marginal beaks, and in the
adult stages of the shell the beaks are usually subcen-
tral and the growth holoperipheral. This adult disci-
noid form, which originated and was acquired through
the conditions of fixation of the animal, has been ac-
celerated in the recent Discinisca, so that it appears in
a free-swimming larval stage. Thus, a character ac-
quired in adolescent and adult stages of Paleozoic spe-
cies through the mechanical conditions of growth, ap-
pears by acceleration in larval stages of later forms
before the assumption of the condition of fixation which
first produced this character.

178 PRIMARY FACTORS OF ORGANIC EVOLUTION.

The two chief subfamilies of the Terebratellide
undergo complicated series of metamorphoses in their
brachial structure. Generic characters are based upon
the form and disposition of the brachia and their sup-
ports. The highest genera in one subfamily, which is
austral in distribution, pass through stages correlated
with the adult structure in the genera Gwynia, Cistella,
Bouchardia, Megerlina, Magas, Magasell, and Terebra-
tella, and reach their final development in Magellania
and Neothyris. The higher genera in another subfam-
ily, boreal in distribution, pass through metamorphoses
correlated with the adult structures of Gwynia, Cistella,
Platidia, Ismenia, Miihlfeldtia, Terebratalia, and Dal-
lina. The first two stages in both subfamilies are re-
lated in the same manner to Gwynia and Cistella. The
subsequent stages are different except the last two, so
that the Magellania structure is similar in all respects
to the Dallina structure, and Terebratella is like Tere-
bratalia. Therefore Magellania and Terebratella are
respectively the exact morphological equivalent to, or
are in exact parallelism with Dallina and Terebratalia.

The stages of growth of the genera belonging to
the two subfamilies Dallinine and Magellaniine are
further correlated in the accompanying tables.

The simplest genus Gwynia, as far as known, passes
through no brachial metamorphoses, and has the same
structure throughout the adolescent period, up to and
including the mature condition. In the ontogeny of
Cistella the gwyniform stage, through acceleration, has
become a larval condition. In Platidia, the cistelliform
structure is accelerated to the immature period, and
in Ismenia (representing an ismeniform type of struc-
ture in the higher genera), the gwyniform and cistelli-
form stages are larval, and the platidiform represents

MORPHOGENY FROM GWYNIA TO DALLINA.

PERIODS STAGES STAGES STAGES STAGES STAGES STAGES STAGES
Larval gwyniform? gwyniform gwyniform gwyniform gwyniform gwyniform gwyniform
. cistelliform cistelliform cistelliform cistelliform
Adolescent gwyuiform cistelliform cistelliform platidiform platidiform platidiform platidiform
ismeniform ismeniform ismeniform
miuhlfeldtiform miihlfeldtiform
terebrataliform
Mature Guwynia Cistella Platidia Ismenia Mihlfeldtia Terebratalia Dallina
MORPHOGENY FROM GWYNIA TO MAGELLANIA.
PERIODS STAGES STAGES STAGES STAGES STAGES STAGES STAGES STAGES
Larval gwyniform|gwyniform |gwyniform | gwyniform gwyniform gwyniform gwyniform gwyniform
cistelliform cistelliform cistelliform cistelliform cistelliform
Adolescent | gwyniform | cistelliform |cistelliform | bouchardiform] bouchardiform] bouchardiform] bouchardiform| bouchardiform
megerliniform | megerliniform | megerliniform | megerliniform
magadiform |magadiform {| magadiform
magaselliform | magaselliform
terebratelliform
Mature Guwyntia Cistella Bouchardia | Megerlina Magas Magasella Terebratella | Magellania

180 PRIMARY FACTORS OF ORGANIC EVOLUTION.

an adolescent condition. Similar comparisons may be
made in the other genera. Progressively through each
series, the adult structure of any genus forms the last
immature stage of the next higher, until the highest
member in its ontogeny represents serially, in its stages
of growth, all the adult structures, with the larval and
immature stages of the simpler genera. It is evident
that in the identification of specimens belonging to
the Terebratellida, whether recent or fossil, the strict
specific characters must be given first consideration.
Species, therefore, must be based upon surface orna-
ments, form, and color, within certain limits, and gen-
era only upon structural features developed througha
definite series of changes, the results of which are per-
manent in individuals evidently fully adult.

In each line of progression in the Terebratellide,
the acceleration of the period of reproduction, by the
influence of environment, threw off genera which did
not go through the complete series of metamorphoses,
but are otherwise fully adult, and even may show re-
versional tendencies due to old age; so that nearly
every stage passed through by the higher genera has
a fixed representative in a lower genus. Moreover,
the lower genera are not merely equivalent to, or in
exact parallelism with the early stages of the higher,
but they express a permanent type of structure, as far
as these genera are concerned, and after reaching ma-
turity do not show a tendency to attain higher phases
of development, but thicken the shell and cardinal pro-
cess, absorb the deltidial plates, and exhibit all the
evidences of senility.

(‘1ayoo0gq worg) ‘erueljeseW jo AuoZoysyd pue £ue8000 ‘ epodomprig ur wsr[aTereq—"gh “Sty

Vamarecane

Bouckar do, Re
iy"

tS,
PN. @

Megerlina
Cistella neopolitora

Nigflevestens

waokwoypboyy washyyeyoagaray, warhypsoboy wah yoboy, waohrurpaba yl wo rp soyonog warohrypysrg

182 PRIMARY FACTORS OF ORGANIC EVOLUTION,

2z. PARALLELISM IN THE CEPHALOPODA.

Among Mollusca it is well known that the Cepha-
lopoda form a number of series of remarkable regular-
ity, the advance being, in the first place, in the com-
plication of the folds of the external margins of the
septa, and, in the second place, in the degree of invo-
lution of one or both extremities of the shell to the
spiral ; third, in the position of the siphon.

Alpheus Hyatt, in an important essay on this sub-
ject, points out that the less complex forms are in
many cases identical with the undeveloped conditions
of the more complex. He says: ‘‘ There is a direct
connection between the position of a shell, in the com-
pleted cycle of the life of this order, and its own de-
velopment. Those shells occupying the extremes of
the cycle” (in time), ‘‘the polar forms, being more
embryonic than the intermediate forms. The first
epoch of the order is especially the era of rounded,
and, in the majority of the species, of unornamented
shells with simple septa; the second is the era of or-
namentation, and the septa are steadily complicating ;
in the third the complication of the septa, the orna-
mentation, and the number of species, about twice
that of any other epoch, all combine to make it the
zenith of development in the order ; the fourth is dis-
tinguishable from all the preceding as the era of re-
trogression in the form, and partially in the septa.

‘‘The four periods of the individual are similarly
arranged, and have comparable characteristics. As

\Memoirs of the Boston Society for Natural History, 1866, p. 193. Hyatt

was followed by Wirtenberger in Ausland, 1873, who entirely confirmed his
conclusions,

PARALLELISM. 183

has been previously stated, the first is rounded and
smooth, with simple septa; the second tuberculated,
and the septa more complicated; the third was the
only one in which the septa, form, and ornamentation
simultaneously attained the climax of individual com-
plication; the fourth, when amounting to anything
more important than the loss of a few ornaments, was
marked by a retrogression of the whorl to a more tabu-
lar aspect, and by the partial degradation of the septa.”
I am indebted to Professor Hyatt for the following
more detailed account of the results of his researches
in this interesting field. The evidence as to the na-
ture of evolution derived from the Cephalopoda is more
complete than that obtained from any other source.

- ‘Every group of nautiloids passes through, during
its evolution in time, either a part or the whole of a
certain series of changes. These modifications con-
sist: first, of a straight or nearly straight cone, ortho-
ceran; second, a curved cone, cyrtoceran; third, a
coiled cone, gyroceran, which does not come in con-
tact at any point; fourth, a coiled-cone, nautilian, which
does come in contact at the termination of the first vo-
lution and then during further growth remains in about
the same condition, all of the internal whorls being
visible as ina flat coil of rope; fifth, a coiled cone,
involute-nautilian, which ‘also comes in contact like
the fourth but then the whorl growing with greater
rapidity spreads internally, covering up more or less
of the internal volutions sometimes to such an extent
that even the centre is concealed from view. The ex-
amples which I have myself seen of the fifth kind range
from the Silurian to the Nautili of the existing fauna,
some being present in every period, and of other kinds,
the first, second, and third kinds die out gradually,

184 PRIMARY FACTORS OF ORGANIC EVOLUTION.

diminishing in the Devonian and Carboniferous and
ultimately ceasing their existence altogether in the
Trias. The fourth ceases in the Cretaceous, and the
fifth alone survives in the Tertiaries and is still living
in the Mautilus umbilicatus and pompilus, and two other
species.

‘«Wherever found, the young of shells of the fifth
kind are at first orthoceran or cyrtoceran like the first
and second kind, then gyroceran in curvature like the
third class, and then they become more or less rapidly
nautilian like the fourth class in succeeding stages. In
Silurian, Devonian, and Carboniferous forms this suc-
cession is so marked that about all of the young shells
of the fifth class may be described as palingenetic,
that is as cyrtoceran, gyroceran, nautilian, and then
involute-nautilian in their individual or ontogenetic
development. In the Trias, Jura, Cretaceous, Ter-
tiary, and present, as the fifth class increases in num-
bers, there is a decided tendency to shorten and su-
persede the gyroceran or third stage and introduce the
fourth kind or the tendency to spread by growth in-
wards, at earlier stages.

‘‘The characteristics of. the sutures are correlative
with these stages of development, and it may be said
in a general way, that all other characteristics corre-
late more or less when studied comparatively in dif-
ferent series with the differences in the curvature and
coiling of the whorls. - The curvature and amount of
involution is therefore the most important single char-
acteristic of the nautiloids,so far as the comparative
study of change by evolution is concerned; whether
the whole order be considered statistically as above,
1. e. with reference to the existence or non-existence
of certain forms orthoceran, cyrtoceran, etc., or gen-

PARALLELISM. 185

etically, i. e. with sole regard to the evolution of dis-
tinct series which may be traced from their origin to
their termination in time.

‘‘Of these last there are some in every period trace-
able with more or less completeness by gradations of
adults back to orthoceran or cyrtoceran ancestors. Of
these series of adults, some pass through only the or-
thoceran and cyrtoceran modifications, others have
the orthoceran, cyrtoceran, gyroceran, and nautilian,
but those having the latter and the nautilian-involute
are of extreme rarity until the Carboniferous is reached.
After this the nautilian shells begin to predominate in
every series, ultimately becoming the sole representa-
tives of genetic series.

‘«Such series are, of course, frequently so closely
parallel that it is possible to follow them, and show
they are distinct only by means of certain genetic char-
acters, the apertures, the structure of the siphuncle,
the sutures and septa, and sometimes, although very
rarely, all of these internal characters may show dif-
ferences peculiar to some one genetic series in which
the regular gamut of forms is passed through in the
usual succession. Neglect of the comparative study
of the stages of development and decline, and of the
obvious parallelisms between these and adults of an-
cestral forms, have caused naturalists, notably Bar-
rande, to make artificial classifications in which about
all straight forms, with the exception of some in which
the siphuncles were notably distinct to be classed as
Orthoceras, most of second kind as Cyrtoceras, most
of the third kind as Gyroceras, most of the fourth and
fifth kinds as Nautilus. ;

‘“*To such authors the involute-nautilian forms of
the Silurian and the existing fauna were considered to

186 PRIMARY FACTORS OF ORGANIC EVOLUTION.

be only specifically distinct, although any prolonged
study and comparison of the young would have shown
that they were widely separated in development and
really only morphic equivalents evolved from entirely
distinct ancestors.

“A good example of this is the Eudoceratide? in-
cluding the Silurian and Devonian Eudoceras and Trip-
teroceras, and probably gyroceran form Edaphoceras
of the Carboniferous and the close-coiled nautilian
shells of Endolobus of the Carboniferous. The pe-
culiar forms of this series and their remarkable sutures
enable the observer to follow the line both in the grada-
tions of the adults and by means of the parallelisms
of the development.

‘‘Another good series easily distinguished by the re-
markable sculpture of the shells is Zittelloceras of the
Silurian with cyrtoceran forms, and the gyroceran and
nautilian Halloceras of the Devonian.

“One of the best is Thoraceras, a rough spinous
cone of the Silurian, Devonian, and Carboniferous,
which has straight and cyrtoceran shells; the gyroceran
Triboloceras of the Carboniferous, and the nautilian
shells of Vestinautilus and its allies in the same period.

«There is no possible explanation of the parallel-
isms of development of these nautilian shells and the
adult stages of others except heredity in the same gen-
etic series. It is useless to waste time in discussion
unless the facts are specifically denied after having
been properly reéxamined.

‘When the ammonoids are taken up, it is easy to
demonstrate? by the study of the young of the Gonia-

1‘ Genera of Fossil Cephalopods,’’ Proc. Bost. Soc. Nat, Hist,, p. 287.
2 See ‘‘ Genera of Fossil Cephalopods,”’ Proc. Bost, Soc. Nat. Hist., XXII,
1883, p. 303.

PARALLELISM. 187

titinee that they had straight forms among their ances-
tors and that these forms have a central siphuncle and
suture as among nautiloids. The Devonian Goniati-
tine and some of the Carboniferous forms had also
gyroceran forms and loosely coiled nautilian forms, in-
dicating an ancestry with similar cones, but at these
stages the siphuncle is invariably ventral as in the
adults. The young of all of the Ammonitinz, however
involute the shell may afterwards become, have an in-
variably straight or curved cyrtoceran cone in the
apical part, and when they come in contact by growth,
the first whorl or whorls are equally invariably open
coils like the coils of the fourth grade in nautiloids.
The fifth kind of shell, the involute-nautilian, follows
in precisely similar succession to what it does in the
ontogeny of nautiloids. Farther than this the degree
of involution increases according to the species, with
age, and the amount of this involution is often an im-
portant part of the specific diagnosis.

“Among Ammonitine one finds at once that there
are no orthoceran or cyrtoceran shells except among
the large group designated by the author as Bactrites.
This genus begins early in the Silurian with shells that
are not distinguishable from true Orthoceras except
by having the siphuncle in adults and later stages
close to the venter. Some of these forms have no
bulb or protoconch and have a large scar on the apex
as in true Orthoceras, others have a calcareous bulb
or protoconch on the apex as in true Ammonitine.
There are also open or gyroceran shells in the adults
of the genus Mimoceras which are repeated in the
young of Anarcestes and other genera of Goniatitine
figured in my ‘Embryology of Fossil Cephalopods.’}

1Bull, Mus. Comp. Zodl., UI.

188 PRIMARY FACTORS OF ORGANIC EVOLUTION.

The shells of the Ammonitine, however, are of the
fourth and fifth kinds almost exclusively, and in xol-
lowing out the separate genetic series one has to dis-
tinguish the progressive gradations by means of the
greater or less amount of involution even in the Go-
niatitine of the Devonian and Carboniferous.

«« There are also some very remarkable facts show-
ing that the coiling is closer in the Mesozoic than in the
Paleozoic forms as a matter of hereditary derivation.
The young of the Silurian and Devonian forms have
the open, slowly coiling whorls figured by Sandberger
and Barrande and repeated by myself as referred to
above, but the young of all Mesozoic forms are close
coiled so far as known. This is shown in the centre
of the umbilicus by the perforation or central opening
which is extremely large in most of the Paleozoic Go-
nititinea but becomes almost obliterated in the true
Ammonitine of the Jura.

‘In tracing parallels between development of the
individual and the series among Ammonitine it has
been found by Branco and the author, that in orna-
mented shells the young are first like a nautilus in the
sutures, then have a goniatitic stage like the first rep-
resentatives of the order of ammonoids in the Paleo-
zoic, and that during these stages it is invariably
smooth and similar in general form to these same an-
cestors. After this nepionic stage is passed through
the sutures and the characteristics alter with greater
or less rapidity, but the stages show decisive parallel-
isms with the immediate ancestors of the same genetic
series. Some of the best examples of palingenetic de-
velopment of this kind, where the later stages of growth
present parallels with proximate ancestors, are cited in

PARALLELISM. 189

my ‘Genesis of the Ariétidaz’! and others have been
given by Buckman and Wiirtenburger.

««Some of the most remarkable occur in the least
expected quarters. As usual, when one has a true law,
it leads him into conclusions that are, perhaps, more
surprising to himself than to his readers, or to any
subsequent investigator. This was certainly my own
case in being led to recognise the perfect examples of
parallelisms in retrogressive series. Quenstedt and
all students since his time agree that the so-called
genera Crioceras, Hamites, Ancyloceras, Baculites,
forms that are successively more and more uncoiled
until in Baculites they are absolutely straight cones,
were derived from normal, close-coiled, involute-nau-
tilian shells of the Ammonitine. Their young have
been repeatedly shown to be close-coiled and they
grade into the normal progressive shells by all of their
adult characters.

«The ultimate fact in this demonstration has been
added by Dr. Amos Brown in the discovery of a close
coiled nepionic stage in the straight Baculites of the
Cretaceous, the only form whose development had not
been ascertained and whose exact ‘relations had not
been determined.

“It is now admitted by all students of Ammonitinz
that these retrogressive groups are not true genera;
but that as first demonstrated by Quenstedt, Baculites,
Crioceras, etc., are retrogressive stages in the evolu-
tion of distinct genetic series and that they do not ex-
ist as natural groups of species. In other words, dif-
ferent genetic series of the Ammonitine die out by
passing through a series of modifications which are
parallel and which are just the reverse of the parallel

1 Smithson, Contrib., 673, p. 41 et seq.

190 PRIMARY FACTORS OF ORGANIC EVOLUTION,

series of the orthoceran, cyrtoceran, gyroceran shells
with which each distinct complete genetic series of
nautiloids arose in time.

‘‘While the nautiloids coil up in their progressive
evolution and the Ammonitine increase this coiling up
tendency in the primitive and progressive forms of
each genetic series, the latter in becoming retrogres-
sive reverse the processes of progressive evolution.
They become more and more uncoiled, each complete
retrogressive series ending with a straight cone. All
other characters correlate with this uncoiling and in a
general way may be said to degenerate in greater or
less proportion to the amount of the uncoiling. To
make this extraordinary picture complete it is only
necessary to add that these retrogressive series followed
out to their ultimate development are distinctly parallel
with changes or stages of modification taking place in
the senile stages of individuals of the same genetic
group.

. In old age the highly ornamented shell gradually
parts with its spines and other ornaments, the whorls
slowly diminish, the involution decreases and even-
tually in extreme age it becomes separated from the
spiral and completely rounded and smooth. The aper-
ture becomes correlatively modified, and also the su-
tures. If an old ammonite could have its life pro-
longed, it would become Baculites, and the full-grown
part of the shell would, in some forms of Lytoceratinz
be very similar to the minute nepionic shell of the Ba-
culites as described and figured by Dr. Brown. If now
the coiled adult part of this imaginary shell were broken
off and lost, the straight senile fragment would be re-
ferred to the old genus Baculites. The morphic char-
acters of the gerontic or old-age stage of ontogeny are

PARALLELISM. 1gI

therefore parallel with the forms evolved in the para-
plastic or retrogressive stage of evolution of the phy-
lum. -In other words, the morphic modifications which
may occur as permanent, specific, and generic charac-
ters in the adults of retrogressive descendants of any
progressive individuals may be predicted from the
study of the similar changes that take place in the
senile stages of the progressive individuals. As it has
been stated by the writer on several occasions, the
embryonic, nepionic, and later stages of development
up to the adult repeat with greater or less clearness in
proportion to their removal in time and organization
from the point of the origin of the genetic group to
which they belong the permanent characteristic of
their ancestors; the adult gives the existing essential
differentials acquired by its own species, genus, and
group, being the index according to the time of its oc-
currence of the progression or retrogression of its
group; the old, in its invariably retrogressive course,
indicates the path that must be followed by degraded
series after the acme of the group to which the indi-
vidual belongs has been reached. This, of course, is
a generalized statement of the correlations of the on-
togenic cycle and the phylocycle when they occur as
in the Ammonitine, but it will be found eventually
that this law is true of all animals to some degree. It
is obvious from all past experience that every law of
correlation of structures cannot be true in any one
group without being found more or less in all organ-
isms. I have therefore ventured upon the basis of
this and Beecher’s, Clarke’s, and Schuchert’s re-
searches among Brachiopoda, corals, and trilobites,
Dr. Jackson’s among pelecypods, and after the con-
firmations by the independent researches of Wiirten-

192 PRIMARY FACTORS OF ORGANIC EVOLUTION.

burger and Buckman among Ammonitine, and those
of Bather among crinoids, to designate the complete
study of the correlations of the ontecycle and phylo-
cycle as Bioplastology. Bioplastology is easily sepa-
rable from the study of growth, and from that of hered-
ity, for which last I have proposed the term Genesi-
ology, and from that of Ctetology or the study of the
origin of acquired characteristics. By properly defin-
ing these different branches of research it is practicable
to see that bioplastology includes the results of the ac-
tion of growth, the laws of growth, as well as those of
genesiology and ctetology, but has a field entirely dis-
tinct from all of these in so far as it deals essentially
with the study of parallelism in all its phases.”

The parallelism of the gyroceras with an early stage
of all coiled Cephalopoda is represented in Fig. 119
page 410, as illustrative of the inheritance of an ac-
quired character.

3. PARALLELISM IN THE VERTEBRATA.

Parallels between the ontogeny and phylogeny are
well known in the Vertebrata. The primary relations
of the Vertebrata are discernible in the successive
types of structure of the nervous system, and of the
skeleton, but most clearly in those presented by the
circulatory system. It is well known that the central
organ—the heart, is, in the amphioxus, a straight
tube. In the next higher group, the Marsipobranchii
(lampreys), it is a bent tube, with a constriction which
divides it into two chambers. In the Pisces (fishes)
the heart is composed of two chambers related to each
other in a reversed longitudinal direction. In the Ba-

1 See Proceedings of the Boston Society of Natural History, 1893, p. 59.

PARALLELISM. 193

trachia and Reptilia the cephalad (auricular) division
is divided into two chambers by a septum; while in
the birds and Mammalia the caudad division (ventricle)
is also so divided, making four chambers in all.

‘The sources of the great vessels which distribute
the blood to the body and return it to the heart, dis-
play the same successional relation of types. In
the Acrania (amphioxus), the Marsipobranchii, and
most of the fishes, the vessel (truncus communis)
which receives the blood from the central organ, gives
off several branches on each side, which are distributed
to skeletal bars or arches which are in immediate con-
tact with water, which aerates the blood. They then
return, and, first sending the carotids anteriorly, unite
dorsad to the heart, and form the aorta posteriorly. In
the Batrachia, where aerial respiration succeeds to an
aquatic one during the life of the animal, the number *
of the vessels contributing to form the aorta is re-
duced from five to three in the sucessive types. One
of the arches is aborted as an arch, and sends the cir-
culating fluid to the modified swim-bladder of the fish,
or lung, where it is aerated. This aerated blood is
returned to the heart with non-aerated blood from
other organs, and the mixture is sent throughout the
body. In the reptiles we have essentially the same
system, but the aorta-origins are reduced to two, and
one, on each side. Next a division of the truncus com-
munis ensues, which corresponds functionally with
that in the ventricle, so that the impure blood from
one auricle is sent into the ventricle (right) which com-
municates with the lung; and the aerated blood is
then returned to the other auricle, which pours its
contents into the left auricle, which drives it into the
aorta, and thus throughout the body. Thus pure or

Fig. 49.—Circulatory systems; 1-2, fish; 3-4, batrachian; 5, reptile; 6, bird; all
from Gegenbaur. Figs, 7-8, human foetus, from His,

PARALLELISM. 195

aerated blood is distributed to the organs, and all but
one of the old roots of the aorta have ceased to function
as such.

This evolutionary succession is preserved with much
fidelity in the ontogeny of the respective classes of
Vertebrata. The representatives of each class pass
through the stages which are permanent in the classes
below them in the series. The Mammalia, as the
highest class, pass through all the stages. (Fig. 49.)
This series coincides also with phylogenetic succes-
sion. The order of appearance in time of the Verte-
brata is, first Agnatha, then Pisces, Batrachia, Rep-
tilia, and Mammalia.

In all the details of structure the same relation
may be observed. Referring to the illustrations of
phylogeny and variation of character described in the
preceding pages, many of the characters definitive of
natural divisions have been observed to appear in the
course of the embryonic life of those types which pos-
sess them. Those of greater systematic significance
appear earlier, and those of less importance in a tax-
onomic sense, later. I select some illustrations of this
principle.

I have shown that the primitive type of superior
molar in the placental Mammalia is tritubercular, the
fourth tubercle being added internally and posteriorly
in the later forms. Dr. Taeker has recently observed
that in the development of the superior molars in the
horse, at an early stage the crown is tritubercular, and
that the fourth cusp or hypocone is subsequently added,
as in the phylogenetic history. As the horse presents
the most complex molar among Mammalia, this sur-
vival of the record is interesting.

In the Artiodactyla and Edentata which lack su-

196 PRIMARY FACTORS OF ORGANIC EVOLUTION.

perior incisor teeth, rudiments of them can be found
in the early stages. We now know early extinct forms
of both of these types where these teeth are permanent
throughout life. In the toothless whalebone whales
the same phenomenon has been observed.

It is well known that the highest deer (Cervide)
add an antler to the simple spike horn in the third
year, and an additional antler with each successive
year for several years. Also they develop a basal snag
of the antler (see Cuvier, Ossem. Fossiles; Gray, Catal.
Brit. Mus.) at the third year. Nowa majority of those
of the New World (genera Cariacus, Coassus) never
develop it except in ‘‘abnormal”’ cases in the most
vigorous maturity of the most northern Cariacus (C.
virginianus); while the South American Coassus retains
to adult age the simple horn of the second year of
Cervus.

Among the higher Cervide, Rusa and Axis never
assume characters beyond an equivalent of the fourth
year of Cervus. In Dama the characters are on the
other hand assumed more rapidly than in Cervus, its
third year corresponding to the fourth of the latter,
and the development in after years of a broad plate of
bone, with points, being substituted for the addition
ot the corresponding snags, thus commencing another
series.

Returning to the American deer, we have Blasto-
cerus, whose antlers are identical with those of the
fourth year of Cariacus.

The oldest known deer (Palzomeryx) have no
horns, or they are undivided.

Among Batrachia excellent illustrations are fur-
nished by the two series of Salientia, the Arcifera and
the Firmisternia.

PARALLELISM. 197

The firmisternial structure is a modification of the
arciferous, which comes later in the history of growth,
and probably also in geological time. During the
early stages the Firmisternia have the movable shoul-

Fig. 50.—Succession of horns of Cervus elaphus L. from Gaudry. a, second year

represented by permanent horn of Coassus; 4, third year represented by permanent
horn of Furcifer; c, fourth year represented by permanent horn of Rusa; 4, fifth year;

é, sixth year,

der girdle which characterizes those of the arciferous
division, the consolidation constituting a modification
superadded in attaining maturity, Furthermore, young
Salientia are toothless, and one section of the species
of Arcifera never acquire teeth. In these (the Bu-

198 PRIMARY FACTORS OF ORGANIC EVOLUTION.

fonide) we have a group which is imperfect in two
points instead of one.

The genera of these salientian suborders exhibited
on a preceding page as forming indentical series in five
different families (pp. 66-67) are related to each other
as developmental stages in the history of the genera
that attain the extreme development on each line.
For example we select the family Hylidz of which
the terminal genus is Trachycephalus. Nearly allied

Fig. 51.—Shoulder girdles of Anura; a, of the arciferous type (Phyllomedusa
bicolor) ; b, Rana temporaria, tadpole with budding limbs; ¢, do., adult, firmis-
ternial type; 4 and c from Parker,

to it is the genus Osteocephalus, which differs in the
normal exostosis of the cranium not involving the
derm, as it does in the former. Close to this is Scy-
topis, where the fully ossified cranium is not covered
by an exostosis. Next below Scytopis is Hyla, where
the upper surface of the cranium is not ossified at all,
but is a membranous roof over a great fontanelle. Still
more imperfect is Hylella, which differs from Hyla in
the absence of vomerine teeth. Now, the genus Trachy-
cephalus, after losing its tail and branchie, possesses

PARALLELISM. 199

all the characters possessed by the genera Hylella
and Hyla, either at or just before the mature state of
the latter, as the ethmoid bone is not always ossified
in advance of the parietals. It soon, however, becomes
a Scytopis, next an Osteocephalus, and finally a Tra-
chycephalus. It belongs successively to these genera,
for an exhaustive anatomical examination has failed
to reveal any characters by which, during these stages,
it could be distinguished from these genera. The same
succession in development of the genera of the other
families is well known, the genus Otaspis of the Bu-
fonidez attaining a point beyond any of the others, in
the enclosure of its membranum tympani posteriorly
by dermoéssification.

Finally reaching in our review the relations of spe-
cific characters, the readers will call to mind that the
species of the lacertilian genus Cnemidophorus (page
41) are either striped, spotted, or cross-banded, and
that the Lacerta muralis agrees with them in this re-
spect. It was also shown that the young of all the
species are striped, and that the cross-banded forms
pass through not only a striped, but an intermediate
spotted stage, before attaining the adult coloration.

The young of spotted salamanders are without
spots (genera Amblystoma and Salamandrae g.); so
that unspotted species resemble the young of the
spotted. In many species of birds of more or less uni-
form patterns of coloration, the young are spotted. In
some of these the females remain spotted throughout
adult life. In some other species both sexes retain
the spotted coloration of the young. The young of
most deer are spotted. In the fallow-deer (Axis) the
adults retain the spotted coloration, thus resembling
the young of most of the species.

200 PRIMARY FACTORS OF ORGANIC EVOLUTION.

3. INEXACT PARALLELISM OR C/ENOGENY.

When the early or transitional stage of a higher
form is exactly the same as a permanent lower form,
the parallelism is said to be ‘‘exact.” Such is the re-
lation of a Cnuemidophorus gularis scalaris to a Cnemido-
phorus gularis gularis as to color characters ; and of an
Amblystoma tigrinum to a permanent breeding Siredon
lichenoides in characters of higher structural value.

When the transitional stage of the higher only re-
sembles the lower form in some one or more features,
but not in all, the parallelism is said to be ‘‘inexact.”
It is evident that ‘‘exact parallelism ” can only exist
between ancestor and descendant in the same re-
stricted line, and can be therefore only demonstrated
in the case of the nearest relatives, between which a
perfect phylogeny is known. So soon as new subordi-
nate characters are assumed, or a change in the order
of appearance of characters supervenes, the parallel-
ism becomes ‘‘inexact,’’ and such is the kind of paral-
lelism usually observed. And it is more inexact the
more widely removed in relationship are the forms
compared. ‘Thus the parallelism between the embryo
man with five branchial slits, and the adult shark, is
very inexact; but that between a true fish and a shark
is much less inexact. That between a higher and a
lower shark is still more exact, and so on. Exact par-
allelism in growth is called by Haeckel palingenesis
or palingeny. The growth which has, through changes
introduced subsequent to the origin of a line of de-
scent, become inexact, or ‘ falsified,” is termed by the
same author cenogenesis or cznogeny.

PARALLELISM. 201

The superposition of characters which constitutes
evolution, means that more numerous characters are
possessed by the higher than the lower types. This
involves a greater number of changes during the on-
togenetic growth of each individual of the higher type.
In other words, characters acquired during the phylo-
genetic history are continually assumed by the pro-
gressive form at earlier and earlier periods of life.
This process has been metaphorically termed by Pro-
fessor Alpheus Hyatt and myself ‘‘acceleration.” All
progressive organic evolution is by acceleration, as
here described. Retrogressive evolution may be ac-
complished by a retardation in the rate of growth of
the taxonomic characters, so that instead of adding,
and accumulating them, those already possessed are
gradually dropped; the adults repeating in a reversed
order the progressive series, and approaching more
and more the primitive embryonic stages. This pro-
cess I have termed ‘‘retardation.”” Retardation is not
however, always exact, even in retracing a true phylo-
genetic line, whence in such instances the process may
not be correctly described as retardation. Professor
Hyatt has applied to such types the term ‘‘senile,”
and gerontic ; and to the resulting condition, the term
‘¢senility.” His observations on this subject have been
made on Mollusca, and principally on the Cephalo-
poda, and are of fundamental importance in this con-
nection.

The history of a type which has passed through a
full cycle of life, from its earliest appearance to its ex-
tinction, is divided by Haeckel into three stages, viz.:
those of its rise; full vigor, as displayed by predomi-
nance of variations and numbers; and decadence.
For these stages he uses the expressions Anaplasis,

202 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Metaplasis, and Cataplasis. For the processes which
bring about the first and last of these conditions, Pro-
fessor Hyatt has used the terms Anagenesis and Cata-
genesis. Catagenesis is equivalent to degeneracy and
has played an important part in organic evolution. I
had used the term previously to Professor Hyatt for
the same process, but with a wider application; ex-
tending its use to inorganic nature as well.! (See
Chapter IV. of this book.)

Embryology has, however, revealed another series
of phenomena which in many instances obscure the
simplicity of the problem of ontogeny as presented in
the preceding pages. It was the merit of Haeckel to
generalize from the facts brought to light by this sci-
ence, so as to present the relations which subsist be-
tween the primitive stages of all multicellular animals.
This is known as the Gastrewa theory. He showed
that the primitive gastric cavity of all such animals is
produced by an invagination of a portion of the sur-
face of a primitive sphere or morula, which results
from the segmentation of the odsperm. This hollow
half-sphere he termed the gastrula, and the theoretical
primitive animal which corresponds to it he called the
Gastrea. Marine animals very similar to this Gas-
trea have been discovered. Haeckel showed, how-
ever, that gastrulas are not all alike, since they differ
in the extent to which the segmentation of the odsperm
may be carried, and the rate of segmentation of differ-
ent parts of it. Thus early do inexact parallelisms
arise. From this point onwards special peculiarities
of the various developmental lines appear, some of
which have especial reference to the necessities of em-
bryonic life. Hence the trochosphere stage of so many

lOrigin of the Fittest, p. 422.

PARALLELISM. 203

invertebrate forms, and the nauplius and zoza of the
Crustacea.

Such are the statoblasts which are resting-stages
for the embryos of fresh-water sponges and Polyzoa,
and the glochidia of the Unionide, which are wanting
in the marine forms of the same orders. Such are the
amnion and allantois of certain Vertebrata and the
placenta of certain Mammalia, which have no refer-
ence to any structures but their own residua, found in
the adults of those animals.

A remarkable instance of this state of things ap-
pears in the history of the evolution of the insects. It
is quite impossible to understand this history without
believing that the larval and pupal states of the high-
est insects are the results of a process of degeneracy
which has affected the middle periods of growth, but
not the mature results. The earliest insects are the
Orthoptera, which have active aggressive larve and
pup, undergoing the least changes in their meta-
morphosis (Ametabola), and never getting beyond the
primitive mandibulate condition at the end. The meta-
morphosis of the jawed Neuroptera is little more
marked, and they are one of the oldest orders.

The highest orders with jaws undergo a marked
metamorphosis (Coleoptera, Hymenoptera), the Hy-
menoptera even requiring artificial intervention in
some instances to make it successful. Finally, the
most specialized orders, the suctorial Diptera and
Lepidoptera, especially the latter, present us with very
unprotected more or less parasitic larval stages, both
active and inactive. These animals have evidently de-
generated, but not so as to prevent their completing a
metamorphosis necessary for purposes of reproduction.
Asis well known, many imagines (Saturniidz, CEstridz)

204 PRIMARY FACTORS OF ORGANIC EVOLUTION.

can perform no other function, and soon die, while in
some Diptera the incomplete larve themselves repro-
duce, so that the metamorphosis is never completed.

This history is parallel to that proposed by Dohrn
to account for the origin of the Ammoceetes larval
stage of the Marsipobranchii. He supposes this form
to be more degenerate than the corresponding stage of
its probable ancestral type in the ancestral line of the
Vertebrata. An inactive life in mud is supposed by
Dohrn to have been the effective cause. An inactive
life on the leaves of plants, or in dead carcases, has
probably been the cause of the same phenomenon in
the Lepidoptera and Diptera.

Thus we have developed an ontogeny within an
ontogeny, and a phylogeny within a phylogeny. These
facts do not, however, affect the general result in the
least. They only show us that the persistent larve
of those animals which possess them, have a history of
their own, subject to the same laws of evolution as
the adults. It results that in many cases the phy-
logeny can only be determined by the discovery and
investigation of the ancestors themselves, as they are
preserved in the crust of the earth. In all cases this
discovery confirms and establishes such definite con-
clusions as may be derived from embryology. It is
also clear that on the discovery of phylogenetic series
it becomes at once possible to determine the nature of
defective types. It becomes possible to ascertain
whether their rudimental parts represent the begin-
nings of organs, or whether they are the result of a
process of degeneration of organs once well devel-
oped.

An excellent illustration of inexact parallelism is
to be found on comparison of man with the lower Ver-

PARALLELISM. 205

tebrata. I have pointed out! that in the structure of
his extremities and dentition, he agrees with the type
of Mammalia prevalent during the Eocene period
(cfr. Phenacodus). Hence in these respects he re-
sembles the immature stages of those mammals which
have undergone special modifications of limbs and ex-
tremities, such as Ungulata in which cenogeny has
not obliterated the early stages from the embryonic
record. These forms are probably extinct. I have
also shown? that in the shape of his head man resem-
bles the embryos of all Vertebrata, in the protuberant
forehead, and vertical face and jaws. In this part of
the structure most Vertebrata have grown farther from
the embryonic type than has main, so that the human
face may be truly said to be the result of a process of
retardation. Nevertheless, in the structure of his ner-
vous, circulatory, and for the most part, of his repro-
ductive system, man stands at the summit of the Ver-
tebrata. It is in those parts of his structure that are
necessary to supremacy by force of body only, that
man is retarded and embryonic.

5. OBJECTIONS TO THE DOCTRINE OF PARAL-
LELISM.

An objection to the theory of parallelism in its full
sense has been recently put forward by Mr. C. Her-
bert Hurst. He says, ‘‘My object now is to show
that in neither case can a record of the variation at
any one stage of evolution be preserved in the ontog-

eny, much less can the ontogeny come to be a series of
1‘ The Relation of Man to the Tertiary Mammalia,’ Penn Monthly, 1875;
Origin of the Fittest, 268.

2 The Developmental Significance of Human Physiognomy,”’ American
Naturalist, June, 1883; Origin of the Fittest, 1887, p. 281.

3 Natural Science, 1893, p. 195-

206 PRIMARY FACTORS OF ORGANIC EVOLUTION.

stages representing in proper chronological order some
of the stages of adult structure which have been passed
through in the course of evolution.” Again: ‘The
early stages of the fish embryo are very like those of
the bird embryo. These two do correspond to each
other. The statement that the embryonic structure
of a bird follows a course which is from beginning to
end roughly parallel with, but somewhat divergent
from, the course followed by a fish, is borne out by
the actual facts. A bird does not develop into a fish
and then into a reptile, and then into a bird. There is
no fish-stage, no reptile-stage, in its ontogeny. The
adult resembles an adult fish only very remotely. Every
earlier stage resembles the corresponding earlier stage
of the fish more closely. There is a parallelism be-
tween the two ontogenies. There zs no parallelism be-
tween the ontogeny and the phylogeny of either g bird or
any other animal whatever. A seeming parallelism will
fall through when closely examined.” <“ The promise
that this theory gave of serving as the guide to knowl-
edge of past history without the labor involved in pale-
ontological research, was indeed tempting : and where
the royal road to learning has been shown by it, itis not
surprising that some zodélogists should have entered
for the race along this road. To what goal that road
has led may be learned by a comparison of the nu-
merous theories as to the ancestry of the ‘Chordata’
which have been put forward by those who have
adopted the theory without enquiring as to its valid-
ity.”

I have made this quotation as showing the point of
view from which the doctrine of parallelism when in-
correctly stated may be assailed. There is truth in
the author’s accusation that embryologists who have

PARALLELISM. 207

not used their results with proper caution, have been
frequently led to incorrect and even absurd results.
The errors of this class of biologists are mainly due to
their ignorance of species in the adult state, and their
ignorance of systematic biology or taxonomy. They
profess to regard this branch of the science as only
suitable for beginners, and as comparatively unim-
portant, as compared with their own; yet one might
as well attempt the study of philology without a knowl-
edge of alphabets, as to study phylogeny without the
knowledge of natural taxonomy. The correct discrim-
ination of species, genera, etc., imposes much greater
burdens on the faculty of judgment, than does any-
thing to be found in any science which includes obser-
vation and record only. But Mr. Hurst’s statement is
somewhat overdrawn, and he does not give embryolo-
gists the credit which is due to their theory of recapitu-
lation. I think he will find the following, which I wrote
in 1872! to be a correct statement of the facts, and a
fair induction as to principles.

‘<The smaller the number of structural characters
which separate two species when adult, the more
nearly will the less complete of the series be identical
with an incomplete stage of the higher species. As
we compare species which are more and more differ-
ent, the more necessarily must we confine the asser-
tion of parallelism to single parts of the animals, and
less to the whole animal. When we reach species as
far removed as man and a shark, which are separated
by the extent of the series of vertebrated animals, we
can only say that the infant man is idéntical in its nu-
merous origins of the arteries from the heart, and in
the cartilaginous skeletal tissue, with the class of

1 Penn Monthly, 1872, Origin of the Fittest, 1887, p. 8.

208 PRIMARY FACTORS OF ORGANIC EVOLUTION.

sharks, and in but few other respects. But the im-
portance of this consideration must be seen from the
fact that it is on single characters of this kind that the
divisions of the sodlogist depend. Hence we can say
truly that one order is identical with an incomplete
stage of another order, though the species of the one
may never at the present time bear the same relation
in their entirety to the species of the other. Still more
frequently can we say that such a genus is the same in
character as a stage passed by the next higher genus;
but when we can say this of spécies, it is because their
distinction is almost gone. It will then depend on the
opinion of the naturalist as to whether the repressed
characters are permanent or not. Parallelism is then
reduced to this definition: that each separate charac-
ter of every kind, which we find in a species, repre-
sents a more or less complete stage of the fullest
growth of which the character appears to be capable.
In proportion as those characters in one species are
contrasted with those of another by reason of their
number, by so much must we confine our comparison
to the characters alone, and the divisions they repre-
sent; but when the contrast is reduced by reason of
the fewness of differing characters, so much the more
truly can we say that the one species is really a sup-
pressed or incomplete form of the other The denial
of this principle by the authorities cited has been in
consequence of this relation having been assigned to
orders and classes, when the statement should have
been confined ¢o single characters, and divisions char-
acterized by them. There seems, however, to have
been a want of exercise of the classifying quality or
power of ‘abstraction’ of the mind on the part of the
objectors.”

PARALLELISM. 209

It is nevertheless true that the records brought to
light by embryologists are very imperfect, and have to
be carefully interpreted in order to furnish reliable evi-
dence as to the phylogeny of the species examined.
An illustration of this is the fact that the species char-
acters appear in many embryos before those which de-
fine the order or the family, although it is certain that
the latter appeared first in the order of time. Most of
the important conclusions as to the phylogeny of Ver-
tebrata demonstrated by paleontology have never been
observed by embryologists in the records of the spe-
cies studied by them. Thus I have shown that it is
certain that in the amniote vertebrates the intercen-
trum of the vertebral column has been replaced by the
centrum ; yet no evidence of this fact has been ob-
served by an embryologist. If we could study the em-
bryonic development of the vertebral column of the
Permian and Triassic Reptilia, the transition would be
observed, but in recent forms cenogeny has progressed
so far that no trace of the stage where the intercentrum
existed can be found.

Again I have demonstrated by paleontological evi-
dence that the lines of the ungulate Mammalia origi-
nated from a buncdont pentadactyle plantigrade an-
cestor ; but embryonic research has failed to discover
the preservation of a record of this fact in the ungu-
lates at present existing. The embryo of the horse is
not pentadactyle, nor even tridactyle, although tri-
dactyle horses persisted late in geologic time. Nor
has embryonic research demonstrated a four-toed
stage in the Bovide (oxen, etc.), although there is no
doubt that they descended directly from an ancestor
so characterized. Any number of similar cases might
be cited to show the prevalence of inexact parallelism

210 PRIMARY FACTORS OF ORGANIC EVOLUTION.

or cenogeny. If we could study the embryology of
the many extinct forms of life, the missing stages
would all be found, but as we have not the opportun-
ity of pursuing this important research, we have to
rely on paleontology for our phylogeny. Paleontology
is and always will be imperfect, but all that we get is
palingeny, or the phylogeny itself, and not an inverted
and distorted record of it.

CHAPTER IV.—CATAGENESIS.

E HAVE been principally occupied so far with
progressive evolution or anagenesis. Reference
has, however, been made to retrogressive evolution or
degeneracy, in Chapter III., in describing the evolution
of the Vertebrata, and will be in Chapter V., under the
caption ‘‘Disuse in Mammalia.” Degeneracy has, how-
ever, played a more important part in creation than
would be suspected from these references, and I pro-
pose in the present chapter to go more fully into its
phenomena, which, in the broadest sense, I have called
collectively Catagenesis.

As evidence for degeneracy as a factor in evolution
we naturally appeal first to examples in the life histo-
ries of plants and animals which are known to us; and
then examine the records of the past, in the light thus
gained, for evidence of degeneracy in vegetable and
animal phylogeny. In both directions we are met by
an embarras de richesse, and a few conspicuous cases
will have to suffice.

The parasitic copepod Crustacea undergo a retro-
grade metamorphosis, which commences at different
periods of the growth history of different genera. Says
Claus: ‘Many parasitic Copepoda, however, pass

212 PRIMARY FACTORS OF ORGANIC EVOLUTION.

over the series of nauplius forms [which are traversed
by other copepods] and the larva, as soon as hatched,
undergoes a moult, and appears at once in the youngest
Cyclops form with
antenne adapted
for adhering, and
mouth-parts for
piercing. From this
stage they under-
go a retrogressive
metamorphosis, in
which they become
attached to a host,
lose more or less
completely the seg-
mentation of the
body, which grows
irregular in shape,
cast off their swim-
ming feet, and even
lose the eye, which
was originally pres-
ent (Lerneapoda).
The males, how-
ever, in such cases
often remain small

Fig. 52.—Lernca branchialis ; a, male; 6, non- and dwarfed, and
degenerate female; c, female after fertilization adhere, frequently
undergoing metamorphosis; d, do. with egg sacs,
natural size. From Claus. more than one,

firmly to the body
of the female in the region of the genital opening. In
the Lern@a such pigmy males were for a long time
vainly sought for upon the very peculiarly shaped body

of the large female (Fig. 52), which carries egg-tubes.

CATAGENESTS. 213

At last it was discovered that the small Cyclops-like
males lead an independent life and swim about freely
by means of their four pairs of swimming feet, and
that the females in their copulatory stage resemble the
males, and that it is only after copulation that they
(the females) become parasitic and undergo the con-
siderable increase in size and modification of form
which characterizes the female with egg-tubes.”

A degeneracy of the females of a remarkable char-
acter occurs in the insects of the order Strepsiptera.
Here the female during the larval stage, bores its way
into the body of a hymenopterous insect and soon un-
dergoes a moult. At this time they shed their three
pairs of well-developed legs, and become a parasitic
maggot, which lives on the body of the host. The
males do not undergo this degeneracy but retain the
six legs and two pairs of wings common to the class
Insecta.

A notorious example of degeneracy among the Mol-
lusca is offered by the Lntoconcha mirabilis. Says J.
S. Kingsley: ‘‘So greatly has parasitism altered the
form of the body, and all of the organs, that the proper
position of this form among the gastropods is far from
certain, some placing it near Natica. Indeed, were it
not for the characters afforded by the young, its posi-
tion among the Mollusca would not be suspected.
Some thirty years ago [before 1885] Johannes Miiller
found in some specimens of Syxapta digitata an inter-
nal worm-like parasite, attached by one extremity to
the alimentary canal, while the other end hung free
in the perivisceral cavity.” ‘‘In one specimen of Syn-
apta out of one or two hundred this strange form oc-
curs. Itisasac, the upper part bearing the female,
and the lower the male reproductive organs, while the

214. PRIMARY FACTORS OF ORGANIC EVOLUTION,

centre of the body serves for a while as a broodpouch,
the embryos later passing out from an opening at the

Fig. 53.—A Synapta digitata with para-
sitic Entoconcha; B, a portion of Synapta,
with Entoconcha (/) enlarged; a, point of
attachment; 4, blood vessels; /, female por-
tion; z, intestine; 7z, male portion; me, me-
sentery. From Kingsley.

free end of the body
of the parent. The
eggs undergo a toler-
ably regular develop-
ment, producing a
velum, shell, and oper-
culum, the later stages
being found free in the
body-cavity of the
host.”

The preceding ex-
amples illustrate the
degenerating or cata-
genetic effect of a
parasitic life. We will
now observe the cor-
responding effect of a
sedentary life, which
may be called earth-
parasitism. Asan ex-
ample of this I select
the well-known case
of the lowest of the
Vertebrata, the Tuni-
cata, ,

The embryo ascid-
ian has the form of
a tadpole-like larva
which swims actively

through the sea by vibrating its long tail. After a
short free-swimming existence the fully developed,
tailed larva fixes itself by its anterior adhering papille

CATAGENESIS. 215

to some foreign object, and then undergoes.a remark-
able series of retrogressive changes, which convert it
into the adult ascidian. The tail atrophies, until noth-
ing is left but some fatty cells in the posterior part of
the trunk. The adhering papille disappear and are
replaced functionally by a growth of the test over neigh-
boring objects. The nervous system with its sense-
organs atrophies, until it is reduced to the single small
ganglion placed on the dorsal edge of the pharynx,
and a slight nerve-cord running for a short distance
posteriorly. Slight changes in the shape of the body
and a further growth and differentiation of the branchial
sac, peribranchial cavity, and other organs now pro-
duce gradually the structure found in the adult ascid-
ian (Herdman). It is, however, to be noted that in
the order Larvacea, this retrograde metamorphosis
does not take place. It embraces the single family
Appendiculariide, which includes Tunicata which pre-
serve the tail, notochord, and other larval features, and
lead a free-swimming existence in the ocean.

On the Tunicata, Herdman makes the following
general observations. ‘‘(1) In the ascidian embryo
all the more important organs (e. g. notochord, neural
canal, archenteron) are formed in essentially the same
manner as they are in amphioxus and other Chordata.
(2) The free-swimming tailed larva possesses the es-
sential characters of the Chordata, inasmuch as it has
a longitudinal skeletal axis (the notochord), separat-
ing a dorsally placed nervous system (the neural canal)
from a ventral alimentary canal (archenteron) ; and
therefore during this period of its life history the ani-
mal belongs to the Chordata. (2) The Chordata larva
is more highly organized than the adult ascidian, and
therefore the changes by which the latter is produced

DIPLOGLOSSA LEPtTo
Pygopodide | Zonuridz Anguide Teide Gerrhosauridz
I. Limbs, two pair .
a. Digits 5-4 Tejus
6. Digits 4-5 Tretioscineus
Micrablepharus
Gymopthalmus
c. Digits 4-4 Sauresia Scolecosaurus | Saurophis
ad. Digits 4-3
e. Digits 3-4
SJ. Digits 3-3 Microdactylus
&. Digits 3-2 Herpetochalcis
h. Digits 2-4
z. Digits 2-3
yj. Digits 2 2
k, One or both Chamesaura| Panolopus_ | Cophias Cetia
monodactyle Ophiognomon
II. Fore limbs only Propus (digits 0)
Ill. Hind limbs only | Pygopus Mancus Pseudopus
Cryptodelma Opheodes
Delma Hyalosaurus
Pletholax
Aprasia
Lialis
IV. No limbs Opheosaurus'
Dopasia
Anguis

GLOSSA

ANNIEL-
LOIDEA

ANNULATI

Scincidze

Acontiide

Dibamidz

Anelytropsidz

Anniellidz

Hagria

Heteropus
Ristella
Menetia

Gongyloseps
Chiamela
Rhinoseineus
Tetradactylus
Miculia
Chalcidoseps
Blepharactisis
Sphenops

Zygnopsis

Allodactylus

Tridentulus
Chalcides
Hemiergis
Siaphus
Phaneropis
Sepomorphus
Sphenoscineus
Sepsina

Nessia

Hemipodium

Anisoterma

Lerista
Eumecia
Heteromeles

Dimeropus
Chelomeles

Brachystopus
Oncopus
Brachymeles
Anomalopus
Coloscincus
Furcillus
Dicloniscus

Evesia

Euchirotivz (di-
gits 3-5)

Ollochirus
Dumerlia
Scelotes
Soridia
Podoclonium

Dibamus

Opheoscincus
Herpetosaura
Sepophis
Herpetoseps
Opheomorus

Acontias
Typhlacontias

Anelytropsis
Feylinia
Typhlosaurus

Anniella

Amphisbana
Rhineura
Lepidosternum
Trogonophide

218 PRIMARY FACTORS OF ORGANIC EVOLUTION.

from the former may be regarded as a process of de-
generation. The important conclusion drawn from all
this is, that the Tunicata are the degenerate descend-
ants of a group of the primitive Chordata” (= Verte-
brata).

The degeneracy of the Tunicata follows imme-
diately their assumption of the sessile condition. Some
of the degenerate forms which are not sessile, are sup-
posed to be the free descendants of sessile forms.

Among -the craniate Vertebrata, most conspicuous
examples of degeneracy are to be seen in the reduction
and loss of limbs in certain Batrachia and in many
Reptilia. In both classes successive loss of phalanges
and digits form series in several groups of salamanders
and lizards, and in both these orders there are forms
with the limbs rudimental or altogether wanting. In
Batrachia, the genus Amphiuma displays rudimental
limbs with minute digits numbering two or three on
each limb. In the Ceciliide, the limbs are wanting.
Both types are subterranean in their habits. I give the
annexed table of the Lacertilia with degenerate limbs,
which it will be observed are found in eleven distinct
families. (Pp. 216-217.)

Finally, in the snakes (Ophidia) the limbs have
totally disappeared, rudiments only remaining in the
boas and pythons and their allies.

Paleontology renders it clear that this reduction is
a case of degeneracy, since both the Ophidia and La-
certilia can be traced to Reptilia of the Permian epoch,
which have well-developed limbs. This degeneracy is
allied to subterranean or terrestrial habits. It is prob-
able that the primitive snakes sought concealment in
cavities of the earth and beneath rocks and logs, and
spent much of their time in narrow quarters, where

CATAGENESTS. 219

limbs would be of no use to them. Some of them, the
Angiostomata, are now subterranean in their habits,
and most of them are blind, or nearly so. These forms
present rudiments of limbs, which leads to the supposi-
tion that they are near to the ancestral types. From
such forms they developed a type which has proved
competent to compete successfully with other verte-
brates on the ground, in the water, and in the trees of
the forest.

From what has gone before it is now clear that
while kinetogenesis is a factor in progressive evolu-
tion, the reverse process, or akinetogenesis, is as defi-
nite a factor in degeneracy. The evidence derived
from parasitism and sedentary modes of life is conclu-
sive in this direction.

I now cite another example of catagenesis which
throws much light on the origin of the vegetable king-
dom. I have advanced the hypothesis! that plants
are the degenerate descendants of protozoan animal
ancestors, and I will now produce some of the evi-
dence on which the hypothesis rests. The Myxomy-
cetes or Mycetozoa occupy debatable ground between
the vegetable and animal kingdoms. They seem at
one period of their history to pertain to the former and
at another to the latter.

These organic beings are claimed by both botanists
and zodlogists, the former placing them with the
Fungi, the latter including them in the Protozoa.
The fact is that in their mature form they enter the
Fungi, while in their early stages they are Protozoa.
They have distinct reproductive structures, which pro-
duce spores. From each spore issues a ‘‘ flagellula,”
which is a simple cell with a flagellum, not apparently

1 Origin of the Fittest, pp. 431-432.

220 PRIMARY FACTORS OF ORGANIC EVOLUTION.

different from a monad. The flagellum is early lost,
and the cell is then termed an amcebula, since it does
not differ materially from an amceba. Its movements
are similar, and it puts forth short pseudopodia. When
these amcebule come in contact with each other they

Fig. 54.—Mycetozoa (from Lankester after Du Bary). 1-6, Germination
of spore (1) of 7rchea varia, showing the emerging flagellula; (4-5) and its
conversion into an ameebula(6). 7-18, Series leading from spore to plasmo-
dium phase of Chondrioderma difforma; 7, spore; 10, flagellula; 12, ame-
bula; 14, apposition of two ameebule; 15-17, fusions; 18, plasmodium. 19-
20, Spore-fruit (cyst) of Physarum leucopheum X 25; the former from the sur-
face, the latter in section with the spores removed to show the sustentacular
network or capillitium. 21, Section of the spore-cyst of Dydymium squamutlo-
sum, with the spores removed to show the radiating capillitium x, and the
stalk.

fuse, often in large numbers, forming a continuous
gelatinous sheet, the plasmodium (Fig. 54), which
may have several square inches, and even feet of sur-
face. At the proper time reproductive organs form
on this surface in the form of capsules (sporangia),
which may or may not be supported on peduncles, and

CATAGENESIS. 221

which are filled with minute cyst-like masses of proto-
plasm, or spores. As already stated, these spores
give issue to flagellula.

We have in the life of the Mycetozoa, if not the
actual origin of the vegetable from the animal king-
dom, a case closely similar to it in a collateral phylum.
The process is one of degeneracy through the assump
tion of a sessile life, or earth-parasitism ; an example of
akinetogenesis. The paleontology of animals has ab-
solutely established the fact that the predecessors of
all characteristic or specialized types have been un-
specialized or generalized types, ‘‘neither one thing
nor another.” It may then be regarded as almost cer-
tain that the ancestors of the present higher types of
plants were more animal-like than they; that the forms
displaying automatic movements were more numerous,
and the difficulty of deciding on the vegetable or ani-
mal nature of a living organism greater than it is now.
Hence it may be concluded that ‘‘animal” bathmism
has from time to time undergone retrograde meta-
morphosis producing as a result the permanent form
of life which we call vegetable. Given spontaneous
movement (i. e. growth) and surrounding conditions,
and the resultant product must be structures adapted
to their surroundings, just as the plastic clay is fitted
toitsmould. And this is essentially the distinguishing
character of vegetable teleology as compared with ani-
mal. In the average plant we see adaptation to con-
ditions permitted by unconscious nutrition and repro-
duction ; in the animal, adaptation to a greater variety
of conditions, due to the presence of sensation or con-
sciousness.

In closing Part I. of this book, I desire to point
out the conclusion which has, I think, been reached.

222 PRIMARY FACTORS OF ORGANIC EVOLUTION.

It has been proved, as it appears to me, that the vari-
ation which has resulted in evolution has not been
multifarious or promiscuous, but in definite directions.
It has been shown that phylogeny exhibits a progres-
sive advance along certain main lines, instead of hav-
ing been indefinite and multifarious in direction.

It is not denied that many lines of variation have
been at one geologic period and another discontinued.
It is also true that certain divergences from the main
lines have appeared, and that minor and secondary
variations have occurred. Such variations do not seem
to have had any material effect on the general course
of evolution. In many cases such variations from
main lines might be compared to the undulations in
the course of a stream, which nevertheless seeks its
lowest level in spite of all temporary obstacles. Pro-
fessor Scott has termed these temporary variations ‘‘nu-
tations,’’ in an able article on the subject.! ‘*Sports”
seem to have been of no importance in evolution what-
ever.

American Journal Sc?. Arts, Vol. XLVIII., 1894, p. 355.

PART IL.

THE CAUSES OF VARIATION.

PRELIMINARY.

N Part II., which treats of the causes of variations,
I propose to cite examples of the direct modifying
effect of external influences on the characters of indi-
vidual animals and plants. These influences fall nat-
urally into two classes, viz., the physico-chemical
(molecular), and the mechanical (molar). The modi-
fications so presented are supposed to be the result of
the action of the causes in question, continued through-
out geologic time. To the two types of influence
which thus express.themselves in evolution, I have
given the names Physiogenesis! and Kinetogenesis.
The inheritance of character is assumed in this sec-
tion, and the ‘reason for so doing will be considered
later, in the third section of this book.

In the animal kingdom we may reasonably suppose
that kinetogenesis is more potent as an efficient cause
of evolution than physiogenesis. In the vegetable
kingdom it is quite evident that evolution is more
usually physiogenetic than kinetogenetic. Atmospheric
and terrestrial conditions play a major réle in the

1‘ The Energy of Evolution.” Amerzcan Naturalist, March, 1894. ‘‘ The
Origin of Structural Variations” in New Occaszons, Chicago, May, 1894. C.H.
Kerr & Co. :

226 PRIMARY FACTORS OF ORGANIC EVOLUTION.

determination of plant-structure, but motion has also
had an important influence. The motion, however,
has originated in small degree in the plant itself, but
has been derived from without. Some importance
must be ascribed to the effects of winds, but the prin-
cipal source of the especial strains to which plants
have been subjected, has been the insect world. In-
sects have been inhabitants of land-plants since their
origin in early Paleozoic ages, and the mutual relations
of plants and insects have ever been intimate. As has
been insisted by Miller and Henslow, the uses to
which the floral organs have been put by hymenopte-
rous and other insects have been probably a principal
cause of the forms assumed by the former. From this
direction has been derived the kinetogenetic influence
in plant evolution. The few independent movements
displayed by plants may have had some influence on
the evolution of their structure. We have no reason
as yet to suppose that such movements have any other
than purely physical factors.

CHAPTER V.—PHYSIOGENESIS.

OTANISTS and gardeners are familiar with the
effects of physical causes in producing modifica-
tions in the characters of plants. That modifications
so produced have become hereditary is known to be
the fact, and we may therefore infer that the evolution
of plant forms has been produced in large degree by
similar agencies in past geological ages. Says Hens-
low :1 «*M. Carriére raised the radish of cultivation,
Raphanus sativus L., from the wild species, R. rapha-
nistum L., and moreover found that the turnip-rooted
form resulted from growing it in a heavy soil, and the
long-rooted one in a light soil. Pliny records the same
fact as practised in Greece in his day, saying that the
male (turnip form) could be produced from the female
(long form) by growing it in a ‘‘cloggy soil.” The
rule may be laid down that a species [of plant] may
be constant as long as its environment is constant, but
no longer. I have changed the spiny Ononis spinosa
L., the rest-harrow, both by cuttings and.by seed into
a spineless form, undistinguishable from the species
O. repens L. in two years; but it would have, I doubt

1 Natural Science, 1894, pp. 259-260.

228 PRIMARY FACTORS OF ORGANIC EVOLUTION.

not, at once reverted to the O. spinosa if I had re-
planted it on the poor soil from which I took it. It
seems, therefore, to be a very hazardous and fallacious
method of testing the value of specific or other char-
acters by cultivation. A wild plant may or may not
change at once. Thus the carrot, Daucus carota L.,
proved refractory with Buckman, but not with Vilmo-
rin, who converted this annual into a hereditary dzen-
nial by sowing the seed late in the season, till the
character of flowering in the second season became
fixed.”

The prevalence of spinous plants in dry and desert
regions has often been described.1 The same is true of
reptiles, although spines appear on some species in
fertile regions. Spines of plants are believed to be
twigs, petioles, leaves, etc., partially aborted under the
influence of drought, or the absence of the water neces-
sary to the tissues of the parts in question. Wallace
points out, however, that there are spinous plants in
humid climates, citing the Gleditschia (honey locust)
as an example. The spines of such plants may be sur-
vivals of periods of drought in previous geologic ages.
Or desiccation of certain parts of a plant might be a
form of abortion of those parts, a phenomenon which
is confined to no region, and is evidently due to causes
other than drought in some cases. Henslow (/. c.)
says: ‘‘They [spines] originate, I maintain, as a mere
accidental and inevitable result of the arrest of the
organ in question, such arrest being maznly due to
drought.”

One of the best expositions of the influence of the
physical characters of the environment on the struc-
ture of animals is to be found in Semper’s work, Ani-

1 Natural Science, 1894, September, p. 179.

PHYSIOGENESIS. 229

mal Life, to which I refer my readers for a fuller ex-
position than can be given here.

a. Relation of the Size of Shells of Mollusca to the En-
vironment.

' It has been observed that both in natural condi:
trons and in confinement, shells of fresh-water Mol-
lusca grow to a larger size in larger bodies of water,
and become reduced in size as the bulk of water in
which they live is reduced. Varigny has shown that
the reduced size follows a reduction of the air-surface
of the water rather than a reduction of the actual bulk,
though the two conditions may often coincide. He
also shows that, other things being equal, the size of
individuals is inversely as their numbers in a given
enclosure. ,

b. The Conversion of Artemia Into Branchinecta.4

In 1871 the spring flood broke down the barriers
separating the two different lakes of the salt works
near Odessa, diluting the water in the lower portion |
to 8° Beaumé, and also introducing into it a large
number of the brine shrimp, Artemia salina. After the
restoration of the embankment, the water rapidly in-
creased in density, until in September, 1874, it reached
25° of Beaumé’s scale, and began to deposit salt. With
this increase in density, a gradual change was noticed
in the characters of the Artemiz, until late in the
summer of 1874 forms were produced which had all
the characters of a supposed distinct species, 4. mwel-
hausenit. The reverse experiment was then tried. A
small quantity of the water was then gradually diluted,

lAbstracted from an account by J. S. Kingsley, Standard Natural His-
tory, Vol. Il. x

230 PRIMARY FACTORS OF ORGANIC EVOLUTION.

by M. Vladimir Schmankewitsch, who conducted the
experiments, and though continued for only a few
weeks, a change in the direction of A. salina was very
apparent. Led by these experiments, he tried still
others. Taking Artemia salina, which lives in brine of
moderate strength, he gradually diluted the water, and
obtained as a result a form which is known as Brancht-
necta schafferit, the last segment of the abdomen hav-
ing become divided into two. Nor is this change pro-
duced by artificial means alone. The salt pools near
Odessa, after a number of years of continued washing,
became converted into fresh-water pools, and with the
gradual change in character, Artemia salina produced
first a species known as Branchinecta spinosa, and at a
still lower density Branchinecta ferox, and another spe-
cies described as B. media. Here not only new species
were produced, but a new genus.

c. The Production of Colors in Lepidopterous Pupe.

The following important contribution to this sub-
ject has been made by Poulton.! As an illustration of
the direct effect of the environment in the production
of color-changes, it is of the greatest value. Several
lepidopterists, among others Weismann and Merrifield,
had shown that by exposing the pupa of butterflies to
low temperatures material changes in the coloration
of the mature insects can be produced. Says Poulton:
“In 1867 Mr. T. W. Wood exhibited to the Entomo-
logical Society of London a number of chrysalides of
the large and small garden white butterflies (Preris
brassice and P. rape), which corresponded in color to
the surfaces to which they were attached. Dark pupe

1 The Colors of Animals, International Scientific Series, Vol. LXVIII, by
E. B. Poulton, London, 1890.

PHVSIOGENESIS. 231

had been found on tarred fences and in subdued light;
light ones on light surfaces; while green leaves were
shown to produce green chrysalides, at any rate in cer-
tain cases.

‘During the following nineteen years, gradual con-
firmation of Mr. Wood’s central position was afforded.
In 1873 Professor Meldola supported the observations
upon the chrysalides of the ‘‘garden whites.” He
compared large numbers of individuals and found that
the pupe upon black fences were darker than those
upon walls.

“<In 1874 a paper by Mrs. M. E. Barber, and com-
municated by Mr. Darwin to the Entomological So-
ciety of London, was printed in the transactions of
that society. Mrs. Barber had experimented with a
common South African swallow-tailed butterfly (Papz-
fia nireus), and had found the chrysalis wonderfully
sensitive to the colors of its environment. When the
pup were attached among the deep green leaves of
the food-plant, orange, they were of a similar color;
when fixed to dead branches covered with withered,
pale, yellowish-green leaves, they resembled the latter.
One of the caterpillars affixed itself to the wood frame
of the case, and then became a yellowish pupa of the
same color as the wooden frame.

‘¢Mr. Maurel Weale also showed that the color of
certain other South African pupz can be modified, and
Mr. Roland Trimen made some experiments upon an-
other African swallow-tail (Papilio demoleus) confirm-
atory of Mrs. Barber’s observations. He covered the
sides of the cage with bands of many colors, and found
that green, yellow, and reddish-brown tints were re-
sembled by the pupz, while black made them rather
darker. Bright red and blue had no effect. The larve

232 PRIMARY FACTORS OF ORGANIC EVOLUTION,

did not exercise any choice, but fixed themselves in-
discriminately to colors which their pupa could re-
semble and those which they could not.. Inthe nat-
ural conditions the latter would not exist, for the pupze
can imitate all the colors of their normal environ-
ments.

“‘T began work with the common peacock butter-
fly (Vanessa io), of which the chrysalis appears in two
forms, being commonly dark gray, but more rarely,
bright yellowish-green ; both forms are gilded, espe-
cially the latter. Only six caterpillars could be obtained,
and these were placed in glass cylinders surrounded by
yellowish-green tissue-paper. Five of them became
chrysalides of the corresponding color; the sixth was
removed immediately after the caterpillar skin had been
thrown off, and was placed in a dark box lined with
black paper, but it subsequently deepened into a green
pupa exactly like the others.. Obviously the surround-
ings had exercised their influence before the pupa was
removed.

‘Being unable to attain more larve of the pea-
cock, I worked upon the allied. small tortoise-shell
butterfly (Vanessa urtice), which can be obtained in
immense numbers. In the experiments conducted in
1886, over seven hundred chrysalides of this species
were obtained and their colors recorded. Green sur-
roundings were first employed in the hope that a green:
form of pupa, unknown in the natural state, might be
obtained. The results were, however, highly irregular,
and there seemed to be no susceptibility to the color.
The pupe were, however, somewhat darker than usual,
and this result suggested a trial of black surroundings,
from which the strongest effects were at once wit-
nessed : the pupz were ds a rule extremely dark, with

PHYVSIOGENESIS. 233

only the smallest trace, and often no trace at all, of the
golden spots which are so conspicuous in the lighter
forms. These results suggested the use of white sur-
roundings, which appeared likely to produce the most
opposite effects. The colors of nearly one hundred
and fifty chrysalides obtained under such conditions
were very surprising. Not only was the black color-
ing matter asarule absent, so that the pupz weré
light-colored, but there was often an immense devel-
opment of the golden spots, so that in many cases the
whole surface of the pupz glittered with an apparent
metallic lustre. So remarkable was the appearance
that a physicist, to whom I showed the chrysalides,
suggested that I had played him a trick and had .cov-
ered them with gold-leaf.

‘These remarkable results led to the use of a gilt
back-ground as even more likely to produce and in-
tensify the glittering appearance. By this reasoning
I was led to make the experiment which had been sug-
gested by Mr. Wood nineteen years before. The re-
sults quite justified the reasoning, for a much higher
percentage of gilded chrysalides, and still more re~
markable individual instances, were obtained among:
the pupz which were treated in this way.

‘«These observations and experiments had been
made when I began to work at the subject in 1886:
they appeared to prove that the power certainly exists,
but nothing was really known as to the manner in
which the adjustment is effected. Mr. S. W. Wood’s
original suggestion, that the ‘skin of the pupa is pho-
tographically sensitive for a few hours only after the
caterpillar’s skin has been shed,’ was accepted by most
of those who had worked at the subject. And yet the
suggestion rested upon no shadow of proof; it de-

234 PRIMARY FACTORS OF ORGANIC EVOLUTION,

pended upon a tempting but overstrained analogy to
the darkening of the sensitive photographic plate un-
der the action of light. But the analogy was unreal,
for, as Professor Meldola stated in the discussion which
followed Mrs. Barber’s paper, ‘ the action of light upon
the sensitive skin of a pupa has no analogy with its
action on any known photographic chemical. No
known substance retains permanently the color re-
flected on it by adjacent objects.’ The supposed ‘pho-
tographic sensitiveness’ of chrysalides was one of those
deceptively feasible suggestions which are not tested
because of their apparent probability. It would have
been very easy to transfer a freshly formed pupa from
one color to another which is known to produce an
opposite effect upon it; and yet if this simple experi-
ment had been made the theory would have collapsed,
for the pupa would have been found to resemble the
first color and not the second. Furthermore, Mr.
Wood’s suggestion raised the difficulty that chrysa-
lides which had become exposed in the course of a
dark night would have no opportunity of resembling
the surrounding surfaces, for the pupal colors deepen
very quickly into their permanent condition.

‘‘Having thus defined the time of susceptibility.
the next question was to ascertain the organ or part of
the larva which is sensitive. At first it appeared
likely that the larve might be influenced through their
eyes (ocelli), of which they have six on each side of
the head. Hence, in many experiments the eyes of
some of the larve were covered with an innocuous
black opaque varnish, and they, together with an equal
number of normal larve from the same company, were
placed in gilt or white surroundings. The pupe from
both sets of larve were, however, always equally light-

PHYSIOGENESIS. 235

colored. It then seemed possible, although highly im-
probable, that the varnish itself might act as a stimulus
similar to that caused by gilt or white surroundings,
and therefore the experiments were repeated with black
surroundings in darkness, but the pupz of the two sets
were again almost identical, so that it appeared cer-
tain that the eyes can have nothing to do with the in-
fluence.

‘Tt then seemed possible that the large branching
bristles, with which the larve are covered, might con-
tain some organ which was affected by surrounding
colors, but experiments in which half of the larve were
deprived of their bristles showed conclusively that the
sensitive organs must have some other position, for
the pupz from both sets of larve were identical.

‘‘T was thus driven to the conclusion that the gen-
eral surface of the skin of the caterpillar is sensitive to
color during stage ii, and part of stage iii. In order
to test this conclusion, I wished to subject the body of
the same larve to two conflicting colors, such as black
and gold, producing the most opposite effects upon
the pupa. Such an experiment, if successfully carried
out, would decide some important points. If the part
of the body containing the head was not more sensi-
tive than the other part, a valuable confirmation of the
blinding experiments would be afforded. Mrs. Bar-
ber’s suggestion that particolored pupz may be pro-
duced by the influence of two colors would be tested
in a very complete manner ; if particolored pupz were
obtained, it seemed probable that the light acts di-
rectly upon the skin, but if they could not be obtained,
it seemed more probable that the light influences the
termination of nerves in the skin, and that the pupal
colors are produced through the medium of the nervous

236 PRIMARY FACTORS OF ORGANIC EVOLUTION.

system. The experiments were conducted in’ two
ways. In the first, the larve were induced to suspend
themselves from sheets of clear glass, by placing them
in wide shallow boxes, so that the ascent to the glass
roof was easily accomplished. As soon as suspension
(stage iii.) had taken place, each larva was covered
with a cardboard tube, divided into two chambers by
a horizontal partition, which was fixed rather below
the middle. There was a central hole in the partition
just large enough to admit the body of the larva. The
tube was fixed to the glass sheet with glue; the upper
chamber was lined with one color, e. g. gilt, and the
lower chamber with the opposite color, e. g. black,
with which the outside of the cylinder was also cov-
ered, in case the larva should stretch its head beyond
the lower edge. The partition was fixed at sucha
height that the larval head and rather less than half of
the total surface of skin were contained in, the lower
chamber, while rather more than half of the skin sur-
face was contained in the upper chamber.

‘The second method of conducting the conflicting
color experiments was superior in the more equal illu-
mination of the upper and lower colors. The bottom
of a shallow wooden box was covered with alternate
areas of black and gilt papers, and partitions were
fixed along the lines where the two colors came in
contact. Each partition was gilt toward the gilt sur-
face, and black toward the black surface, and was per-
forated close to the bottom of the box with holes that
would just admit the body of a larva. The box was
then placed in a vertical position towards a strong
light, so that the partitions became strong shelves,
while the black and gilt surfaces were uppermost alter-
nately. As soon as a larva was suspended to a glass

PHYSIOGENESIS. 237

sheet, the boss of silk was carefully scraped off and
was pinned on the upper color, above one of the holes,
so that the head and first five body-rings passed
through the hole on to the color beneath, which tended
to produce opposite effects. Other larva were simi-
larly fixed between the shelves upon one color only, so
as to afford a comparison with the results of the con-
flicting colors.

“‘A careful comparison of all the pupe obtained in
the conflicting’ color experiments showed that, when
the illumination of the two surfaces was equal, the ef-
fective results were produced by that color to which
the larger area of skin had been exposed, whether the
head formed part of that area or not. Particolored
pupz were never obtained. It therefore appears to be
certain that the skin of the larva is influenced by sur-
rounding colors during the sensitive period, and it is
also probable that the effects are wrought through the
medium of the nervous system. The latter conclu-
sion receives further confirmation from other observa-
tions.” .

Professor Poulton has since produced remarkable
color-changes in the larve of Lepidoptera by confin-
ing them to the branches of plants of distinct colors.
Thus geometrid larve confined to the stems of a black
color, became correspondingly dark; while those re-
stricted to white twigs became very pale. These larve,
and, still more strikingly, those of Cossus ligniperda,
when confined on branches which supported lichens,
became of variegated colors, corresponding with those
of the lichens, and affording an admirable means of
concealment.

238 PRIMARY FACTORS OF ORGANIC EVOLUTION.

d. The Effect of Light on the Colors of Flatfishes.

It is well known that the side of the body which is
uppermost in the normal position in the flatfishes
(Pleuronectidz) is colored generally with dark tints,
and frequently with a distinct pattern, while the lower
side is white. This is due to the absence from the
lower side of the chromatophore or pigment-contain-
ing cells, which are abundant on the upper side. The
young fish has chromatophore on both sides as it has
its eyes also in the normal position, but as the fish
turns the left side upwards and the right eye gradually
rotates to the left side, the chromatophore disappear |
from the right side, which thus becomes colorless.

Prof. J. T. Cunningham! experimented with young
flounders taken at the beginning or middle of their
metamorphosis, by placing a mirror below the aqua-
rium in which they were kept, at an angle of 45°, and
cutting off the light from above by an opaque cover.
In the great majority of the specimens treated in this
way, after several months, although no effect was pro-
duced upon the eyes, more or less of the skin of the
lower side was pigmented. He thus showed that the
absence of pigment on that side in the normal fish is
due to its position in shadow, where little light can
reach it.

e. The Effect of Feeding on Color in Birds.

Mr. F. E. Beddard cites the following remarkable
example of the direct effect of internal physical causes
in producing change of coloration.”

1 Zoologischer Anzeiger, 1891.

2 Animal Coloration, an Account of the Principal Facts and Theories Relat-
ing to the Colors and Markings of Animals, By Frank E. Beddard, M. A.
Oxon., F.R. S. E. With Four Colored Plates; and Wood-Cuts in the Text.
London. Swan Sonnenschein & Co. New York: Macmillan & Co. 1892.

PHYSIOGENESIS. 239

‘«That the yellow color of canaries can be altered
to an orange red by mixing cayenne pepper with their
food, has been known for along time. This curious
fact was first discovered in England, as was also the
fact that the different races of canaries vary in their
susceptibility to the action of the pepper; some kinds
are more, others are less, affected, while one race is
absolutely without any power of having its coloration
altered by these means. The color-change is pro-
duced by feeding the newly hatched young with the
pepper conveyed in their food or the old birds while
sitting upon the nest are furnished with food contain-
ing the cayenne, which they in turn feed their offspring.
The color change can, in fact, be only brought about
in very young birds whose feathers are not completely
matured ; it is quite impossible to produce any altera-
tion upon the full-grown canary. Clearly, therefore,
here is an instance of the direct effect of food upon
color. An interesting paper upon the subject, which
has also furnished me with the facts already men-
tioned, has lately appeared,! and it will be of interest
to give some account of the author’s (Dr. Sauermann’s)
experiments for reasons that will appear. Cayenne
pepper, of course, is a composite substance, from which
a number of distinct chemical substances can be ex-
tracted: the red color is caused by a pigment termed
capsicin, which can be separated from the pepper ;
and it might easily be supposed that the change from
yellow to red in the feathers of the canary was simply
caused by a transference of the pigment, as in the
cases mentioned on page 127; but Dr. Sauermann
shows that it is not so. Yellow-colored canaries were

lArchiv fiir Anatomie und Physiologie, 1889. Physiologische Abtheilung,
543-

240 PRIMARY FACTORS OF ORGANIC EVOLUTION.

not in the very slightest degree affected by the 'pig-
ment alone; but, curiously enough, particolored birds
did react,—the brown parts of the feathers became
distinctly lighter in hue. It isa fatty substance (trio-
lein) which appears to convey the pigment, and to pro-
duce thus a changing of the color from yellow to red ;
and further experiments were made with other birds,
showing that it is not only canaries which are influenced
by their food in this way, Some white fowls, belong-
ing to a special breed, showed traces of yellow among
the feathers after feeding with cayenne; but in this
_case there were not racial but individual differences in
susceptibility, for all the specimens of birds experi-
mented with did not react to the stimulus.

‘“‘A similar series of experiments was made with
some other colors: it was found with carmine that the
yellow color was destroyed and the birds became white.
This unexpected effect is explained by the fact that a
mixture of violet and yellow produces white. The fact
that the fatty constituent, triolein, plays the chief part
in the coloring of the feathers may perhaps help to ex-
plain the very singular fact that the Amazon parrots
change from green to yellow when fed upon the fat of
_certain fishes.

‘With regard to the white fowls referred to, the
experiments made by Dr. Sauermann were particularly
interesting. The interest lies in the fact that the pig-
ment was not absorbed equally by all the feathers ;
only special tracts were affected ; the breast feathers,
for instance, became red, while the head remained
white. It is therefore quite credible that in a state of
nature partial alteration of color may be produced by
a change of diet.”

in a chapter of Dr. Beddard’s book relating to pro-

PHYSIOGENESITS. 241

tective resemblances will be found an account of sev-
eral examples of animals which have apparently ac-
quired a resemblance to their surroundings by the
transference of pigment to their bodies in their food.

J. The Blindness of Cave-Animals.

Neo-Lamarckian writers have always ascribed the
absence or rudimentary condition of the eyes charac-
teristic of animals which dwell exclusively in caves, to
disuse consequent on the absence of light. Lamarck
ascribed the rudimentary condition of the eyes in the
mole to this cause. As the removal of so important
an organ as the eye is not accomplished in a single
generation, the element of heredity enters the propo-
sition. This subject is reserved for Part Third of this
book; nevertheless, for the present suspending judg-
ment as to this question, it has been rendered exceed-
ingly probable by embryological investigations into the
history of dwellers in darkness, that the Neo-Lamarck-
ian view is the correct one.!_ Says Packard:

‘«In my essay on Zhe Cave Fauna of North America
(p. 139), I record the fact that in the young of the
blind crayfish (Orconectes pellucidus), the eyes of the
young are perceptibly larger in proportion to the rest
of the body than in the adult, the young specimen ob-
served being about half an inchin length. Previously
to this, Dr. Tellkampf, in 1844, remarked that ‘the
eyes are rudimentary in the adults, but are larger in
the young.’ Mr. S. Garman states, regarding the blind
Cambarus of the Missouri Cave: ‘Very young speci-
mens of C. sefosus correspond better with the adults of
C. bartonii; their eyes are more prominent in these

1] am indebted for a résumé of this subject to Packard, American Nat-
uvalist, 1884, P. 735.

242 PRIMARY FACTORS OF ORGANIC EVOLUTION.

stages, and appear to lack but the pigment.’ In the
blind cave-shrimp (Troglocaris) of Austria, Dr. Joseph
discovered that the embryo in the egg is provided with
eyes.

“In this connection should be recalled the observa-
tions of Semper in his Animal Life (pp. 80, 81) on Pin-
notheres holothuria, which lives in the ‘water-lungs’
of holothurians, where, of course, there is an absence
of light. The zoéa of this form has large ‘ well-de-
veloped eyes of the typical character. Even when
they enter the animal they still preserve these eyes;
but as they grow they gradually become blind or half-
blind, the brow grows forward over the eyes, and
finally covers them so completely that, in the oldest
individuals, not the slightest trace of them, or of the
pigment, is to be seen through the thick skin, while,
at the same time, the eyes seem to undergo a more or
less extensive retrogressive metamorphosis.’

‘In this connection may be mentioned the case of
the burrowing blind shrimp (Ca/ianassa stimpsonit),
which has been found by Prof. H. C. Bumpus, at
Wood’s Holl, Mass., living in holes at a depth of be-
tween one and two feet. He has kindly given me a
.specimen of the shrimp, which is blind, with reduced
eyes, smaller in proportion to the body than those of
the blind crayfish. He has also obtained the eggs,
and has found that the embryos are provided with dis-
tinct black, pigmented eyes, which can be seen through
the egg-shell.

‘‘Recently, Zeller has studied the embryology of the
Proteus of Adelsberg Cave, and has confirmed the
statement of Michahelles, who, in 1831, discovered
that the eyes of this animal are more distinct in the

PHYSIOGENESIS, 243

young and somewhat larger than in the adult. We
quote and translate from Zeller’s account:

‘<« The development of the eyes is very remarkable ;
they are immediately perceived and present themselves
as small, but entirely black and clearly drawn circular
points, with a slit which is very narrow, and yet, at
the same time, well defined, and which penetrates
from the lower circumference out to the middle.

««<«Tndeed, one can hardly doubt that this astonish-
ing development of the eye has been accomplished by
the influence of light, as has also the pigmentation of
the skin, the reddish-white ground-color of which ap-
pears thickly studded with very small brownish-gray
points mixed with detached white ones, over the upper
surface of the head and over the back, down over the
sides of the yellowish abdomen. Even on the edge of
the fins (Flossensaum) the pigment is found. On the
other hand, there is a whitish spot over the snout, as
is likewise the case in the adult creatures which have
been colored by the light. Both the under surface of
the head and the entire abdomen are shown free from
pigment like the limbs. .

“«¢«T cannot specify very exactly as to when the pig-
mentation of the skin begins, but, in any case, it is
very early, and often earlier that the first beginning of
the eyes can be discovered. The latter occurs toward
the end of the twelfth week, at which time a thin, light
gray line, which still appears overgrown, may be per-
ceived, forming a half-circle, open underneath. Then
while this line subsequently becomes clearer and
darker, and its ends grow further under and towards
each other, there also takes place simultaneously a
progression of the pigment larger towards the middle
point, and the circle finally seems closed and filled up

244 PRIMARY FACTORS OF ORGANIC EVOLUTION.

to the narrow slit mentioned above, which proceeds
from the lower circumference and penetrates to the
middle of the eye’ (pp. 570, 571).

‘But the most striking discovery bearing on this
subject is that of the condition of the eyes in the em-
bryo and young compared with the adult of the blind
goby of San Diego.

‘(In his essay on The Fishes of San Diego, Professor
Eigenmann briefly refers to and gives four figures
(Fig. 55) of the embryo of Typhlogobius, Mr. C. L.
Bragg having been fortunate enough to discover the
egg in the summer of 1891. ‘The eyes develop nor-
mally, and those of No. 4 differ in no way from the
eyes of other fish embryos.’ In this case, then, we
have the simplest and clearest possible proof of the
descent of this blind fish from individuals with eyes as
perfect as those of its congeners.

‘We have been permitted by the Director of the
United States National Museum to reproduce Profes-
sor Eigenmann’s excellent figures on the embryo,
which tell the story of degeneration of the eye from
simple disease of the organ, the species being exposed
to conditions of life strikingly different from those of
its family living in the same bay.

‘‘Before the discovery of the eggs, the youngest in-
dividual ever seen is represented in Fig. 55, No. 1, its
eyes being, though small, yet distinct, and ‘appar-
ently functional.’

“From these data it is obvious that future embryo-
logical study on cave-animals will farther demonstrate
their origin from ancestors with normal eyes.”

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CHAPTER VI.—KINETOGENESIS.

NDER the head of kinetogenesis (development by
motion) comes the consideration of the effect of
use and disuse. Use necessarily conditions the evolu-
tion of useful characters. These characters are such
by reason of their adaptation to the life-functions of
the beings which possess them. It is perfectly well
known, however, that all plants and animals possess
more or less numerous peculiarities which are not use-
ful to their possessors. Such are the mamme of male
animals; the incisions forming palmate or pectinate
leaves and petals of plants; rudimental organs of all
kinds; great elongation of the vertebral column, espe-
cially of the caudal series in certain species ; patches
of color, or of hairs, at particular places, etc. These,
and many others may be arranged in divisions accord-
ing to their probable origin, as follows:

I. Excess of growth energy.

Examples: the recurved tusks of the mammoth, babirussa,
etc.; the elongate feathers of some birds, etc.

Il. Defect of growth-energy.

1. Atavism: examples; the tritubercular superior molar of
certain races of man.

KINETOGENESIS. 247

2. Degeneracy from disuse: examples; the rudimental legs
and digits of numerous lizards.

3. Degeneracy from disuse and complementary excess else-
where : examples; reduction in number of molars and in-
cisors in man; reduced mamme in male Mammalia; re-
duction of lateral digits in the true horses (Equus).

4. Physico-chemical causes: here must be probably included
various color-patches and color-tints, for which no other

explanation is accessible. ,

Darwin considers several of the above conditions,
and endeavors to explain some of them as consequences
of natural selection. Equivalent to the Section I.
above, he enumerates extraordinary developments of
particular parts.1 Hesays, ‘‘A part developed in any
species in an extraordinary degree or manner in com-
parison with the same part in an allied species, tends
to be highly variable.” He does not attempt any ex-
planation of the origin of such characters, except
through natural selection. Of the characters coming
under Section IJ. above, he says, ‘‘ Multiple, rudimen-
tary and lowly organized structures are variable.” Of
these he remarks, ‘‘I presume that lowness here means
that the several parts of the organism have been but
little specialized for particular functions; and as long
as the same part has to perform diversified work, we
can perhaps see why it should remain variable, that
is, why natural selection should not have preserved or
rejected each little deviation of form so carefully as
when the part has to serve for some one special pur-
pose.” Here Mr. Darwin well illustrates his unwilling-
ness to look to disuse as the cause of the conditions he
describes. Under ‘‘Compensation and Economy of
Growth” he quotes from Goethe that ‘‘In order to

1The Origin of Species, Ed. 1872, p. 119.

248 PRIMARY FACTORS OF ORGANIC EVOLUTION.

spend on one side, nature is forced to economize on
the other side.” I have expressed the same view in
the following language :}

“« The complementary diminution of growth-nutrition
follows the excess of the same in a new locality or or-
gan, of necessity, if the whole amount of which an
animal is capable be, as I believe, fixed. In this way
are explained the cases of retardation of character seen
in most higher types. The discovery of truly comple-
mentary parts is a matter of nice observation and ex-
periment.” An apparent illustration is that of the in-
crease of the median digits in the diplarthrous Ungu-
lata contemporaneously with the diminution and atro-
phy of the lateral digits. This is, however, an exam-
ple of the relative effects of use and disuse, which pro-
ceed contemporaneously, and it is probable that most
if not all cases of complementary growth-relations may
be expressed in this way. Thus the orthognathism of
the higher human races is accompanied by full frontal
development, the two modifications constituting a re-
tardation of the postembryonic growth of the face.
But this change can be traced to use, increased brain
action enlarging that organ, and expanding its osseous
case, probably at the expense of lime salts which would
otherwise go to the jaws. Reduction of teeth in Ar-
tiodactyla and in man cannot be regarded as a useful
character in itself, but it is complementary to the de-
velopment of other characters which are useful.

Under the same head may come perhaps, the facts
included by Mr. Darwin under the head of ‘‘ Correlated
Variation.” Of these he says, ‘‘I mean by this ex-
pression that the whole organization is so tied together

1“ Method of Creation,” Proceedings of the American Philosophical Society,
1871, p, 257; Origin of the Fittest, 1887, p. 201.

KINETOGENESIS. 249

during its growth and development, that when slight
variations in any one part occur, and are accumulated
through natural selection, other parts hecome modi-
fied.” After referring to various characters of compo-
site and unbelliferous plants in illustration of such a
law, he says (/. ¢., p. 116), ‘‘ Hence modifications of
structure, viewed by systematists as of high value, may
be wholly due to the laws of variation and correlation,
without being, so far as we can judge, of the slightest
service to the species.” Here Mr. Darwin admits the
insufficiency of natural selection as an explanation of
the origin of such characters; for he says (p. 119),
‘Natural selection, it should never be forgotten, can
act solely for the advantage of each being.” He goes
further, and admits (p. 114) that the Lamarckian doc-
trine has some claims to credence, where he says, ‘‘On
the whole we may conclude that habit, or use and dis-
use, have in some cases, played a considerable part in
the modification of the constitution and structure ; but
that the effects have often been largely combined with,
and sometimes overmastered by the natural selection
of innate variations.”

1. KINETOGENESIS OF MUSCLE.

The fundamental condition of the molar movements
of organic beings is the contractility of protoplasm. In
the Amceba this contractility is a generally diffused
characteristic of its body-substance, and this is the
case with Rhizopoda generally. In higher Protozoa
the contractility is already especially developed in cer-
tain regions where most needed for the movement of
the body in definite directions ; generally immediately
beneath the denser sarcode of the external surface. In

250 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Stentor this substance presents the appearance of
longitudinal threads; in Gregarina they encircle the
body. From these simple beginnings we can follow
the muscular tissue to its various expressions in all
classes of animals; to the concentric threads of the
Ccelenterata ; to the longitudinal bundles beneath the
integument of worms; and the variously directed
masses attached to the external skeleton of the Arthro-
poda, and the internal skeleton of the Vertebrata. The
ease with which muscular tissue is grown in the higher
animals under use, permits us to infer that its develop-
ment in all animals has been due to the same cause.
Muscular structure is directly related to the needs of
the structures to which it is attached, in the perform-
ance of movements. In rudimental limbs muscles are
reduced in both size and number, distinct slips or
bodies becoming fused. In enlarged limbs the reverse
process takes place. Muscular bellies increase in size,
and in number by subdivision. The muscular system
in the middle and higher Vertebrata is variable, and its
plasticity to the stimuli to movements is well known.
It is evident that definite muscular bands have been
developed in the lines of resistance which it has been
necessary to overcome in moving the body or parts of
it. The movable segments which have become adapted
for contact with the surrounding media, by development
of hardness or extent of surface, as limbs (feet, wings),
and jaws, have naturally become the points of origin
of the most efficient muscular bands. No one can
doubt the mutual stimuli which the muscular and
skeletal systems have exchanged during the process of
evolution, since they are necessary to each other from
a mechanical point of view.

KINETOGENESIS. 251

Hiiter,! a distinguished specialist in the diseases of
the joints, gives the following positive information as
to the easy formation of new modifications of muscu-
lar structure:

‘‘Muscular tissue everywhere possesses the capa-
city to shorten itself in consequence of continued ap-
proximation of its points of insertion; that is, to be-
come shorter by the disappearance of tissue, in pro-
portion to the duration of the approximation. This
law is of the greatest importance for the muscular con-
traction of joints, that is, for such restriction of the
freedom of movement of the articulations as has its
origin in muscular movements. We have experimen- —
tal opportunities for the observation of this fact, such
as the effect of a stiff bandage on an articulation. When
it is necessary, in consequence of a fracture of the fore-
arm, to fix the elbow-joint for several weeks in a right-
angled flexure, we find on the removal of the bandage
that the power of extension of the fore-arm has been
much restricted. That the cause is nutritive change
is proven by the fact that considerable force of mus-
cular contraction is necessary before the normal ex-
tension can be effected.”

Similar phenomena are to be observed in conse-
quence of a prolonged lying in bed, where no injury
to the innervation exists.

‘¢The muscles adapt themselves to the permanent
positions of the articulations, as in joint-contractions
which are due to muscular paralysis. Those muscles
which are habitually stretched, increase in length,
while those whose insertions are approximated, are
shortened, producing joint-contraction.” He then goes

lHtter, ‘Studien an den Extremitatengelenken Neugeborener und Er-
wachsener.” Virchow’s Archiv fir pathologische Anatomie, Bd. XXV., 6-8.

252 PRIMARY FACTORS OF ORGANIC EVOLUTION.

on to describe the effect of such fixation of joints on
the bones themselves, to which I will refer on a later
page, under the head of the origin of articular sur-
faces.

Professor Eimer of Tubingen has given us a synop-
sis of the nature of the evolution of the characters of
the muscular tissue, which is highly instructive, and
of which I present here an abstract.1_ The conclusions
reached by Eimer are derived from a general study of
the subject, both in the laboratory and in the litera-
ture. He says:

“(1) It is apparently continued contractions of the
protoplasm in definite directions, which have produced
muscular masses. Since plants do not display con-
tinuous and vigorous movements, they have not de-
veloped muscular bodies. ,

“‘(2) Undoubted facts indicate that from a primi-
tively identical substance muscular tissue has devel-
oped in the direction of effective contractions, while
connective tissue has developed where no contractions
have been present.

“«(3) Muscle-masses first appeared almost every-
where in the external layer of the contractile region:

‘qa, in Protozoa in the outer layer of the body;

‘$6, in Metazoa in the tegumentary sheath of
the body.

‘¢, They consist first either of muscle-cells, or
muscle-fibers, from which develop man-
tle muscle-cells and mantle muscle-fibers.
Mantle muscle-fibers compose the other-
wise highly developed striped muscles of

1“ Die Entstehung und Ausbildung des Muskelgewebes, insbesondere
der Querstreifung desselben als Wirkung der Thatigkeit betrachtet.” Ze7t-
schrift fiir wissenschaftliche Zoologie, LIII., Suppl., 1892, p. 67.

KINETOGENESIS. 253

Arthropoda, and some Vertebrata (Batra-
chia). And when the entire muscle-fiber is
divided into fibrille, there can appear an
external layer of muscular threads.

*‘(4) That muscle cells and fibers first appear in
the external stratum of the active body of animals, is
due to the especially active movements necessary to
this part of the body. This is'a simple mechanical
consequence of the fact, that in a more or less longi-
tudinally extended body of protoplasm, whether it be
Protozoén or worm, or muscle-cell or muscle-fiber, that
its movements must be more vigorous on the external
than the internal portion of it. Therefore, the former
would first display muscular structure.

‘«(5) If the first stage is the development of masses
of plasma, which display contraction in definite direc-
tions, the next step is the division of such masses into
muscle-threads or fibrille. These threads must be re-
garded as a result of contractions, whose inequality
produces subdivisions of the original mass. A com-
pound structure is also more effective than a simple
one in effecting contractions.

“«(6) The next stage of evolution of muscular tissue
consists of the appearance of the cross-striping. The
mechanical effect of the cross-striping is to distribute
the contractility equally throughout the length of the
fiber. The contractions of the unstriped muscular
fiber are less vigorous, and also less uniformly dis-
tributed than those of the striped fiber. Zhe cross-
striping ts a result of contractions. it commences as
simple undulations of the surface of the fiber. The
contraction of the plasma is wave-like and is propa-
gated rapidly through the fiber, and is not due to a
flow and return of the contained protoplasm. The

254 PRIMARY FACTORS OF ORGANIC EVOLUTION.

frequent repetition of these local contractions and en-
largement of the fiber have resulted in a permanent
difference in its intimate structure, the alternate waves
becoming fixed as cross-bands.”

As evidence of the truth of this proposition, (6),
Eimer cites many facts. ‘In the muscles of the Mol-
lusca, striped fibers occur in those forms, as Pecten,
where the closing of the shell is especially vigorous,
this being their mode of progress through the water.
In other forms, where the muscles have no such vigo-
rous use, the fibers are smooth.. In Arthropoda, the
muscles of the legs of swiftly running forms are striped,
while those of the alimentary canal are smooth. It is
a general law that muscles which have energetic con-
tractions are striped, while those in which the con-
tractions are slow or feeble, are smooth. In the com-
mon house-fly, Eimer records some remarkable obser-
vations. Flies examined in winter, during the period
of torpidity, were found to have the fibers of the tho-
racic muscles smooth. With advance of the spring
the striping gradually made its appearance, and in the
summer it was fully developed. An artificial imitation
of winter, by refrigeration in an ice-cellar, caused the
cross-striping to disappear. The striping in some
other animals is shown by Eimer to be strongly in-
fluenced by physical conditions.

In fact, muscular tissue is highly plastic, and as it
is directly under the control of nervous or equivalent
stimuli, the effect of the latter in building structure is
evident. That the motion communicated to the hard
parts through the agency of the muscular system is
effective in building the hard structures will be shown
in a subsequent section.

KINETOGENESIS. 255

2. KINETOGENESIS IN MOLLUSCA.

a. The Origin of the Platts in the Columella of the
Gastropoda.

Mr. W. H. Dall has developed the mechanics of
evolution in the Gastropoda, and I quote extracts from
one of his papers to show the harmony of his views
with those of other Neo-Lamarckians.! ‘‘ The question
which first arises is as to the origin of the columellar
plications and their function. In considering the dy-
namic relations of the animal to its shell we may ob-
tain satisfaction on this point. In the fusiform Rha-
chiglossa an anatomical difference exists to which I
believe attention has not hitherto been called. In-
deed, unless the principles of dynamic evolution are
granted, it is a difference which would appear to have
little or no significance. These principles, however,
afford a key which seems to unlock this and many
other mysteries. In the recent forms of this sort the
adductor muscle, which in all gastropods is attached
to the columella at a certain distance within the aper-
ture, is attached decper within the shelf than in non-
plicate forms. The point of attachment may be an
entire turn, or even more, behind the aperture, while
in short globose few-whorled shells and in the non-
plicate forms it is, as a general rule, little more than
half a turn behind the aperture.

«¢ Now let us consider the dynamics of the case. We
have, reduced to its ultimate terms, a twisted, shelly,
- hollow cone, subangulate or even channelled at two ex-

1 Transactions of the Wagner Free Institute of Science, Philadelphia, Aug.,
1890, p. 58.

256 PRIMARY FACTORS OF ORGANIC EVOLUTION.

tremes corresponding to the canal and the posterior
commissure of the body and outer lip. Inside of this
we have a thin, loose epithelial cone, the mantle, of
which the external surface, especially toward the mar-
gin, is shell-secreting ; lastly, inside of the mantle-
cone we have a more or less solid third cone, consist-
ing of the foot and other external parts of the body of
the animal, which can be extended beyond the mantle-
cone outwardly, as the mantle-cone can be beyond the
shell-cone. The body-cone and the mantle-cone are
attached at one of the angles of the shell-cone some
distance within the opening of the spiral of the latter.
The two outer cones constitute a loose, flexible funnel
within a rigid, inflexible funnel, while the body-cone
forms a solid, elastic stopper inside of all.

<¢ What will happen according to mechanical prin-
ciples (which can be tested by anybody with the sim-
plest apparatus) when the mantle-cone is withdrawn
into a part of the shell-cone too small for the natural
diameter of the contracted mantle-cone? It must
wrinkle longitudinally. Where will the wrinkles come?
They will come at the angles of the shell-cone first ;
they will be most numerous toward the aperture, since
toward the aperture the mantle-cone enlarges dispro-
portionately to the caliber of the shell, owing to its
processes, the natural fold of the canal, etc., etc.; the
deepest and strongest wrinkles will be on the pillar,
owing to the fact that the attachment of the adductor
prevents perfect freedom in wrinkling and the groove
of the canal will mechanically induce the first fold in
that vicinity. The most numerous small wrinkles will
be near the aperture opposite the pillar, because of
the mantle-edge this is the most expanded part, and
there will be a tendency to a ridge near the angle of

KINETOGENESIS, 257

the posterior commissure. Repeated dragging of a
shell-secreting surface, thus wrinkled, over a surface
fitted to receive such secretion, will result in the ele-
vated shelly ridges which on the pillar we call plica-
tions; and on the outer lip lire, if long, or teeth, if
short. The commonly existing subsutural internal
ridge on the body of the
shell near the posterior com-
missure will mark the spe-
cial conditions in that part
of the aperture.

««When the secreting sur-
face is thus wrinkled or cor-
rugated longitudinally, the
wrinkles and the concave
folds between them will be
directed in the sense or di-
rection in which the body
moves in emerging from or
withdrawing to the whorl.
The summits of the convex
wrinkles will be appressed
more or less forcibly against
the shell-wall exterior to
them in which they are con- Fig. 56.—Fusus parilis Con, the
fined. The semi-iuid, imy Imi vio“ opened soln
secretion of which the shell-
lining is built up, exuding from the whole surface of
the mantle, will be rubbed away from the lines of the
summits of the wrinkles and tend to accumulate in
lines corresponding to the concave furrows between
the wrinkles. This secretion hardens rapidly and
these lines would become somewhat elevated ridges
which would by their presence (when once initiated)

258 PRIMARY FACTORS OF ORGANIC EVOLUTION.

tend to maintain the furrows and wrinkles in the same
place with relation to the thus-initiated lire, as these
elevated lines are called when on the outer lip; or
plaits, when situated on the pillar.

««The modification referred to generally takes place
during resting stages of the animal’s growth, since
while the animal is rapidly extending its coil the se-
cretions seem to be directed toward the extreme mar-
gin, and the general mantle-surface resumes its secre-
tive function (or the latter becomes active) somewhat
later, after the formation of a definite varix, or thick-
ened margin ; indicating a resting stage in the animal’s
career. It is probable also that during rapid growth
there is less compression of the tissues than during the
resting-stages. The external sculpture and some of
the modifications of the aperture are connected with
the functions of the extreme edge of the mantle; those
we are at present considering relate more especially to
the function of its general surface by which the layer
which lines the whorls, the pillar, plaits, and lire are
solely secreted and deposited.

“«In species with the abductor attached to the pillar
near the aperture, the wrinkles would be fewer, and
their action, if any, confined to the vicinity of the mar-
gin of the aperture. The deeper the attachment, the
greater will be the compression of the secreting sur-
face and the distance over which it is constantly
dragged back and forth, and the consequent length of
the ridges of shelly matter deposited. If the inner or
mantle-cone had the whole cavity to itself, it is evident
that it could and would infold itself in a manner which
might not appress its folds against the inner surface
of the rigid outer or shell-cone. But there the mass
of the solid and elastic foot and external body comes

KINETOGENESIS. 259

into play, and by its withdrawal inward forces the
wrinkled mantle-cone against the shell. The mantle
is thus confined between a rigid outer and an elastic
inner surface, with the result that it cannot recoil from
the former and that a certain uniformity of size and

direction is imposed upon the

wrinkles, except where the re-
cess of the canal allows them to
become more emphatic, or to a
less degree the posterior angle
permits a slight expansion. The
mechanical principles involved
may be readily illustrated by the
experiment of pulling a hand-
kerchief through the neck of a
bottle, or funnel, followed by a
cork in the center. Of course,
the more nearly the apparatus
conforms to the form and twist
of a spiral shell, the more nearly
the results will approximate
those of nature. It is difficult,
however, to find any artificial
tissue which will correspond in
elasticity, or capacity for partial
self-contraction, to the living tis-
sues concerned in nature. Hence,
an exact conformity is not to be
expected, though the mechanical

Fig. 57.—Mitra lincolata
Heilprin, the body-whorl
opened, showing the pli-
cations of the columella.
From Dall.

principles may be reasonably well illustrated.

“‘A comparison of specimens will show that the
results exhibited agree with marvellous precision with
the results called for by the preceding hypothesis,
based on the dynamical status of the bodies concerned,

260 PRIMARY FACTORS OF ORGANIC EVOLUTION.

their motions and secretions. The agreement is so
complete as to amount to a demonstration, though in
certain cases there may be complications which need
additional explanation.

«<A point which may be noted in regard to the Vo-
lutide, to which my attention was called by Mr. Pils-
bry, is that in this group the mantle is greatly ex-
tended, and there would be more of it to be wrinkled
than in such forms as Buccinum, etc. It may be added
that the forms in which we note the
beginning of plaits for this family,
many of them, such as Liopeplum
and Volutomorpha, had the mantle
so extended as to deposit a coat of
enamel over the whole shell, as in
the modern Cypreza, so that here we
have an additional reason why plica-
tion should be emphasized in this
group.

‘¢Of course, as before noted, the
bone qe mechanical principles are the same
body-whorl opened, in any group of gastropods, but
rag a ie of among those in which the wrinkling

is confined to the region of the aper-
ture, or those shells which are lirate or dentate, as
opposed to plicate, several other principles come into
play which may be briefly referred to in passing. In
the first place, those species which have a very ex-
tended mantle, with hardly an.exception have a lirate
aperture (Oliva, Olivella, Cypraa, Trivia, etc.). With
species in which there is a widely expanded mantle
and yet no lirations, it will usually be found that the
mantle is not entirely withdrawn into the shell in such
forms, or is permanently external to the shell (many

KINETOGENESIS. 261

Opisthobranchs, Marseniide, Sigaretus, Harpa, etc.).
In a group like the Cypreidz, where nearly all the
species are lirate on both lips, there are a few which
want these lire, and these are species which have a
wider aperture in the adult than most of the genus,
and in which we should expect the wrinkles to be less
emphatic.”

b. Mechanical Origin of Characters in the Lamellt-
branchs (Pelecypoda).
_ Dr. Robert T. Jackson has pointed out! the history
of the characters of the retractor muscle and some of
those of the list, of bivalve Mollusca. I take the fol-
lowing abstract of his conclusions: ‘‘In the develop-
ment of pelecypods we find in a late embryonic stage
(the phylembryonic) that the shell has a straight hinge-
line. This is characteristic of Ostrea (Fig. 59), Car-
dium, Anodonta, and so many widely separated genera
that it apparently represents a primitive ancestral con-
dition common to the whole class. * Embryology shows
that the bivalve shell doubtless arose from the split-
ting on the median line of a primitive univalvular an-
cestor.. If that ancestor had a saddle-shaped? or a
cup-shaped? shell, as is probable, the first result of the
introduction of a hinge in the median line would have
been to straighten the shell on the hinge-line.- This
is asimple problem in mechanics, for if one tries to
break by flexion a piece of metal which is saddle-
shaped or cup-shaped, it will tend to form a straight
line on the axis of flexion. A parallel case is seen
in the development of a bivalve shell in ancient crus-

1 Memoirs of the Boston Society of Natural History, Vol. IV., No. 8, p. 277
July, 1890; American Naturalist, 1891, p. 11.

2Characteristic of young Dentalium.
8Characteristic of the extreme young of cephalous inollushs.

262 PRIMARY FACTORS OF ORGANIC EVOLUTION.

taceans. The ancient Ostracoda, Leperditia, Aristo-
zoe, etc., have a straight hinge-line and subcircular
valves, which are united dorsally by a ligament. The
resulting form of the early condition of the bivalvular
shell in these two distinct classes is so strikingly simi-
lar, that it lends weight to our supposition that the form
is induced by the mechanical conditions of the case.
‘7 think that the adductor muscles which close the
valves may also be demonstrated to be the necessary
consequence of the bivalvular condition. In the phyl-
embryo stage (Fig. 59) the
valves are closed by a single
adductor muscle, which is the
simplest condition mechan-
ically possible to effect the
desired end.! This muscle
does not seem homologous
with any muscle in other
classes of mollusks, and is
probably developed from the

Fig. 59.—Ostrea edulis, embryo;
a ad, anterior adductor muscle; mantle muscles as a conse-

m, mouth; a, anus; v, velum; 4, quence of the conditions of

hinge of shell. (After Huxley.) .
the case. In support of this

view, bivalvular crustaceans may again be cited. They
have an analogous adductor muscle, developed, of
course, on an entirely different line of descent, but under
closely similar mechanical conditions. At the completed
prodissoconch stage in all pelecypods, as far as known,
there are two adductor muscles, a second one having
developed in the posterior portion of the body. In
later life the anterior, the posterior, or both adductors

1This early adductor appears in the same position in many genera, and is
apparently characteristic of the class. It is the anterior of the two adductors
found in the later stages; but it may be retained or lost in the adult.

KINETOGENESTS. 263

may be retained, reduced, or lost, according as the
persistence or changes in correlated anatomical fea-
tures retain in use or bring into disuse the muscles in
question.

“Let us look at examples of the retention or loss of
the adductors. In typical dimyarian pelecypods, as
in Mya (Fig. 60) or Venus, the adductors lie toward
either end of the longer axis of the shell. As the hinge
occupies a position on the borders of the shell about
midway between the adductors, both muscles are nearly
or quite in a position to be equally functional in clos-

Fig. 60.—Mya arenaria. Lettering: af ax, antero-posterior axis; kar,
hinge axis; @ ad, anterior, and / ad, posterior adductor ‘muscle ; 7, mouth;
?l, palps; @, anus; g, gills; sd, pedal muscle; 7, foot; 4, byssus; 4, heart.
ing the valves. Asa result, both muscles are of about
the same size. The condition described is that existent
in the completed prodissoconch stage in all pelecy-
pods, as far as known. In later life, however, a revo-
lution of the axes of the soft parts may take place, so
that the antero-posterior axis (represented by a line
drawn through the mouth and middle of the posterior
adductor muscle), instead of being parallel to the
hinge-axis (the axis of motion of the valves) as in
dimyarians, may present a greater or less degree of
divergence from the parallel. In progressive series,

264 PRIMARY FACTORS OF ORGANIC EVOLUTION,

as in Modiola (Fig. 61), Perna, etc., as the adductor
muscle is brought nearer and nearer to the hinge-line,

Fig. 61.—Modzola plicatula. Lettering same as in Fig. 60.

where its mechanical action is less and less effectual
in closing the valves, we find that it is more and more
reduced until it finally dis-
appears from disuse and
atrophy, as in Ostrea (Fig.
62), and Pecten. Con-
versely, the posterior ad-
ductor in the same series in
the revolution of the axes is
pushed farther and farther
from the hinge-line and
nearer to the central plane
of the valves, where its me-
chanical action is most ef-
: fectual in closing the valves.

Fig. 62.—Ostrea virginiana, Let- With its increase in func-
Bea Se eee tional activity the muscle
increases in size. The revolved position of the axes,
and the consequent reduction or loss of the anterior
adductor and increase of the posterior adductor, is

KINETOGENESIS. 265

found in many widely separated genera of pelecypods,
as Ostrea, Mulleria, and Tridacna; thus proving the
development of the same features on different lines of
descent.! In Aspergillum the two valves have con-
cresced so as to form a truly univalvular, tubular shell,
so that the adductors would evidently be functionless if
existent. The posterior adductor has disappeared and
the anterior is reduced to a few disconnected shreds
(Fisher), though evidently existent in the young, as
attested by the form of the shell in the nepionic stage.

‘« Ordinarily there are two posterior retractor-mus-
cles of the foot in pelecypods, one situated on either side.
In adult Pecten either the left retractor alone exists,
or both retractors are wanting (the left doubtless al-
ways exists in the young). In studies of young Pecten
irradians, 1 found that the animal always crawled
while lying on the right side, with the foot extended
through the notch in the lower valve and pressed
against the surface of support. It is evident that while
crawling in this position the left retractor is in the
plane of traction, and it is retained ; on the other hand,
the right retractor would not be in the plane of trac-
tion, and it has disappeared through disuse and atro-
phy.? A similar disappearance of the right retractors
of the foot is seen in Azomia glabra, and is explained
on similar bases of argument.

“¢In Mya arenaria we find a highly elongated siphon.
In the young the siphon hardly extends beyond the
borders of the valves, and then the animal lives at or

1Dr. B. Sharp and I published almost simultaneously closely similar
views on the mechanical aspect of the relative size of the adductors. See
Proceeds, Phila, Acad., 1888, p. 122, and Proceeds, Boston Soc, Nat, Hist., Vol.
XXIII., 1888, p. 538.

2 Both retractors doubtless exist in the prodissoconch stage of Pecten and
allies.

266 PRIMARY FACTORS OF ORGANIC EVOLUTION,

close to the surface. In progressive growth, as the
animal burrows deeper, the siphon elongates, until it
attains a length many times the total length of the
valves. The ontogeny of the individual and the pale-
ontology of the family both show that Mya came from
a form with a very abbreviated siphon, and it seems
evident that the long siphon of this genus was brought
about by the effort to reach the surface, induced by the
habit of deep burial.

‘« The tendency to equalize the form of growth in a
horizontal plane in relation to the force of gravity act-
ing in a perpendicular plane, or the geomalic tendency
of Professor Hyatt, is seen markedly in pelecypods.
In forms which crawl on the free borders of the valves
the right and left growth in relation to the perpendic-
ular is obvious, and agrees with the right and left sides
of the animal. In Pecten the animal at rest lies on
the right valve, and swims or flies with the right valve
lowermost. Here equalization to the right and left of the
perpendicular line passing through the center of grav-
ity is very marked (especially in the Vola division of
the group); but the induced right and left aspect cor-
responds to the dorsal and ventral sides of the animal,
—not the right and left sides, as in the former case.
Lima, a near ally of Pecten, swims with the edges of
the valves perpendicular. In this case the geomalic
growth corresponds to the right and left sides of the
animal.

«« The oyster has a deep or spoon-shaped attached
valve and a flat or flatter free valve. This form, or a
modification of it, we find to be characteristic of all

1‘ Transformations of Planorbis at Steinheim, with Remarks on the Ef-
fects of Gravity Upon the Forms of Shells and Animals.’’ Proceeds, A. A. A.
S., Vol. XXIX., 1880.

KINETOGENESIS. 267

pelecypods which are attached to a foreign object of
support by the cementation of one valve. All are
highly modified, and are strikingly different from the
normal form seen in locomotive types of the group.
The oyster may be taken as the type of the form
adopted by attached pelecypods. The two valves are
unequal, the attached valve being concave, the free
valve flat ; but they are not only unequal, they are
often very dissimilar,—as different as if they belonged
to a distinct species in what would be considered typ-
icalforms. This is remarkable as a case of acquired
and inherited characteristics finding very different ex-
pression in the two valves of a group belonging to a
class typically equivalvular. The attached valve is
the most highly modified, and the free valve is least
modified, retaining more fully ancestral characters.
Therefore, it is to the free young before fixation takes
place and to the free, least-modified valve that we
must turn in tracing genetic relations of attached
groups. Another characteristic of attached pelecy-
pods is camerated structure, which is most frequent
and extensive in the thick attached valve. The form
as above described is characteristic of the Ostreide,
Hinnites, Spondylus, and Plicatula, Dimya, Pernos-
trea, Aetheria, and Mulleria; and Chama and its near
allies. These various genera, though ostreiform in
the adult, are equivalvular and of totally distinct form
in the free young. The several types cited are from
widely separated families of pelecypods, yet all, under
the same given conditions, adopt a closely similar
form, which is strong proof that common forces acting
on all alike have induced the resulting form. What
the forces are that have induced this form it is not
easy to see from the study of this form alone; but the

268 PRIMARY FACTORS OF ORGANIC EVOLUTION.

ostrean form is the base of a series, from the summit
of which we get a clearer view.”

c. Mechanical Origin of the Impressed Zone in Cepha-
lopoda.

Prof. Alpheus Hyatt has shown that the groove on
the dorsum or inside of each coil of the Cephalopoda
is due to the pressure exercised by contact with the
ventral side of the coil within it. He has shown that
this groove persists in cases where the shell in the
course of evolution has become more or less unwound,
and he regards this as an example of the inheritance
of a mechanically acquired character. This subject is
presented in greater detail in the part of this book de-
voted to heredity.

3. KINETOGENESIS IN VERMES AND ARTHROPODA.

It is believed with good reason that the Arthropoda
have descended from some of the forms included in
the branch Vermes, and perhaps Peripatus furnishes
the nearest living approach to that type. The ances-
tor, whatever it may have been, developed limbs from
processes of the body-wall, and used them to aid in
progression., Peripatus has soft flexible limbs, and a
non-chitinous integument generally. With the begin-
ning of induration of the integument, segmentation
would immediately appear, for the movements of the
body and limbs would interrupt the deposit at such
points as would experience the greatest flexure. The
muscular system would initiate the process, since flexure
depends on its contractions, and its presence in ani-
mals prior to the induration of the integuments in the
order of phylogeny, furnishes the condition required.
It is a matter of detail how the diverse segmentations

KINETOGENESIS, 269

of existing forms were produced. We can believe,
however, that, as in Vertebrata, there has been a
gradual elimination of less important segments of the
limbs, until the highest mechanical efficiency was at-
tained. We well know how the segments of the head
and body have been modified by fusion, etc.

Prof. B. L. Sharp has shown the mechanical con-
ditions of segmentation in Arthropoda as follows:1

“It occurred to me that if the theory [of kineto-
genesis] had a general application, some additional
proofs could be shown to exist among the inverte-
brates, where we have the action of muscular force
upon hard and resisting parts of the skeleton. Those
which present the best study for this purpose appear
to be the crustaceans, where we find an immense va-
riety of articulations in the body and in the limbs;
highly complicated locked joints, others allowing mo-
tion in but one plane, as well as loose joints, where
the hard parts scarcely come in contact with one
another, and cases of degeneration of the hard parts,
leading to total disappearance of a previously existing
joint. :

‘‘In the Annelides, from which, there is no doubt,
the arthropod branch sprang, we find no deposit of
inorganic salts in the epidermis. The outer layer of
the body is generally of a horn-like character, adher-
ing closely to the secretive cells of the epidermis, very
flexible, and thrown into folds by the vermicular mo-
tion of its possessor. In the leeches the body consists
of a flexible cylinder, made up of two sets of muscles,
an outer longitudinal cylinder and an inner cylinder of
circular fibers, the contraction of which causes the
animal to increase in length, while shortening is ef-

lAmerican Naturalist, 1893, p. 89.

270 PRIMARY FACTORS OF ORGANIC EVOLUTION.

fected by the contraction of the longitudinal layer.
The external surface of the medicinal leech, for exam-
ple, is thrown into a regular series of very fine folds, —
extending across the longitudinal axis of the body.
These folds do not correspond in numbers to the so-
mites of the body, which are not indicated externally,
five, six, or more of them belonging to one somite.
When the animal shortens its
length, these folds are deepened
and the segments thrown closely to-
gether ; when extension takes place,
the folds are flattened, spread open,
although not wholly disappearing,
as they are a fixed quantity, so to
speak. I believe these folds are
due to mechanical action; by the
disposition of the different fibers of
the longitudinal series, in being in-
serted in a series of planes bounded
by the valleys between the folds,
this being aided by some of the
circular fibers which pass through
Fig. 63.—Diagrammatic the longitudinal sheath, and find

representation of the seg- ie
ments of the leech, show- their attachment to the bases of the

ing the folds, valleys, and valleys.
muscular fibers.

‘Starting from this point, and
supposing the regularity of the folds to have become
established from preéxisting folds by the regularity and
stress of muscular action, we can conceive that when
deposits of calcareous matter took place, rings simi-
larly formed by a folding of a soft skin would receive
that deposit at the most prominent portion of this fold,
the convex face, and not in the protected valleys, as
there would be more friction or pressure from external

KINETOGENESIS, 271

causes, and no deposits would take place in the val-
leys themselves, because they would not be subject
to external friction, and their continual flexion would
prevent any such deposits. Should such a deposit
take place in the valleys, there would be a stiffening
of the whole surface, which would defeat motion. In
fact, in the leech the cuticle is already much thicker
on the crests of the folds than in the valleys.
“In the more .primitive Crus-
tacea, we find the animal made up
of rings extending over the whole
length of the body, similar to the
rings of the leech, save that there
is but one ring to one somite, and
instead of a perpendicular valley
between the folds, this valley has
an inward and a forward direction,
allowing the anterior edge of a
caudad ring to fit into the posterior
edge of a cephalad ring.
‘“‘In the higher Crustacea, sev-
eral of the anterior rings have co-
alesced and form a solid shield Fig. 64. —- Diagram-
- . matic representation of
which is known as the carapace. the rings of a primitive
This has no doubt arisen by the ctustacean,showing the
. : action of the muscles.
lessening of the action between the
anterior rings whén the posterior portion of the body
became the more active propelling organ. As the ac-
tion ceased forward the valleys came to rest, and be-
came exposed to friction and pressure, and conse-
quently a deposit of calcareous matter took place pro-
ducing the stiffening above hinted at.
‘¢ The formation of jointed appendages from para-
podic paddles of the annelids can be followed out in

272 PRIMARY FACTORS OF ORGANIC EVOLUTION.

the same manner, since the manner of mutual relation
of the segments is the same as in the case of the body-
segments.

«Tt has been stated that in the leech the folds do not
correspond in number to the somites of the body, while
they doin the Crustacea. All annelids do not move
by means of a muscular system built upon the plan
found in the leech. In many the circular layer has to
a large extent disappeared, for the longitudino-circular
plan is undoubtedly ante-annelidan. The movement
of the free medusoid forms, and of the Ctenophora, is
the result of a modified arrangement of this plan.

‘«With the disappearance of the circular layer, we
find a peculiar modification of the longitudinal layer.
This layer becomes broken up and the fibers act in
moving the sete, which answer to limbs. Ina seg-
ment of a setiferous annelid, we may observe that the
longitudinal muscles of the somite in section at the po-
sition of the seta are arranged like the letter ‘V’ in
the fork of which the seta lies, the fibers to the left
(anterior) pull the seta externally backward, those on
the right (posterior) pull the seta forward. The in-
troduction of the sete, the origin of which I do not
here attempt to explain, has no doubt been, together
with the establishment of the external segmentation, a
strong factor in causing the breaking up of the muscu-
lar tube into sections (myotomes), which by use and
consequent increase have extended each arm of the
‘V’ into the segment on each side, while the insertion
of the end of the seta has caused a break in the muscle
by the formation of an aponurosis. This gives us the
peculiar disposition of a myotome to extend across the
union of two somites.

“«If we examine the segments of the so-called ab-

KINETOGENESIS. 273

domen of the macrurous Crustacea, as the lobster, we
will find that the anterior face of one abdominal ring
is pulled into the posterior orifice of the ring lying an-
terior to it, forming a kind of tubular ball and socket-
joint, but with a flexible part of the integument with
no calcareous deposit, folded upon itself, and acting
physiologically as a tubular Zigamentum teres. On ex-
amining the different joints, we will find that com-
mencing at a fixed point, as at the base of the thorax,
the movable ring of the first abdominal somite is pulled
znto the fixed part. Then the first abdominal somite be-
comes the fixed point for the movable ring posterior to
it, and so on, so that we find that as the rings proceed
away from the thorax, each is pulled into the opening
of the one in advance. This is true of all those forms
where the abdomen is well formed, strong, and an ac-
tive organ in the economy of the animal; when this
organ, the abdomen, ceases to be an active organ of
motion, as in the burrowing forms, as in Callianassa,
Gebia, some of the Squillide, etc., or where it is folded
upon the sternum of the thoracic region, the muscles
becoming weaker through disuse, the rings are not
subject to the powerful muscular strain, and they as a
rule overlap but little, if dt all, but lie so that the edge
of one ring rests upon the edge of another. In those
forms where degeneration of the abdomen has pro-
ceeded so far as not to have even the usual deposit of
calcareous matter, as in the hermit crabs, there are
simply indications of rings on the abdomen, and this
organ is but little more than a fleshy sac containing
some of the viscera, and supplied with a few muscles
which act together, with the form of the organ, to keep
the abdomen curled so that it may hold as a hook, the

274 PRIMARY FACTORS OF ORGANIC EVOLUTION.

animal within the molluscan shell which it habitually
inhabits.

¢¢When the limbs are examined, the same rule will

be found to hold good, viz.: that the movable part is

pulled into the fixed part. A modification of this is

well illustrated in the evolution of the large chelz. In

some forms, take for example Ibacus, the first pair,

and in fact all of the thoracic limbs end in a sharp-

pointed segment, there being not the slightest sugges-

tion of achela. In Crangon, on the other hand, the

terminal segment is pulled

against the broad face of the

penultimate one thus making

a shift for a chela. In the

Stomatopoda this step has

been developed, for the last

segment can be drawn against

the whole length of the pen-

ultimate one (which is some-

times grooved to protect the

points of the spines of the

. 3 latter) and forms with it a

Fig. 65.—Diagrams of, «, hand very effective grasping or-

of a form of Crangon; 2, handofa gan. The continual use of

iii the terminal segment, the

increase of the muscular power will tend to draw this

terminal segment backward (into) on the penultimate

which enlarges with the increase of bulk of muscle, so

that a well-developed chela, as in the lobster is found,

where the ultimate segment is pulled backward to
about the middle of the penultimate segment.”

KINETOGENESIS. 275

4. KINETOGENESIS IN THE VERTEBRATA.

I have already adduced the evidence in support of
the doctrine that the structures of the hard parts of
invertebrates have been produced by muscular move-
ments. In turning to the Vertebrata we shall find that
the evidence indicating that the details of their hard
parts have had a similar origin, is quite convincing.
This branch of the animal kingdom presents two dis-
tinct advantages for this study. First, we have a more
complete paleontologic series than in any other. Sec-
ond, we have the best opportunity for observation and
experiment on their growth processes, since we our-
selves, and our companions of the domesticated ani-
mals, belong to this branch of the animal kingdom.

I shall show first, the conditions under which ab-
normal articulations of the skeleton have been formed ;
and then the process involved in the formation of
normal articulations. [I shall then apply these facts
to the phylogeny of the Mammalia as we know it, and
then in a more general way to the Vertebrata as a
whole.

i. KINETOGENESIS OF OSSEOUS TISSUE.

a. Abnormal Articulations.

Hitter, from whom I have quoted under the head
of ‘* Kinetogenesis of Muscle,” thus describes the effect
of abnormal conditions of joints on the articular sur-
faces of the bones which form them. He says: ‘*We
have abundant opportunity to investigate the change
of condition which the joints undergo during a year of
fixed muscular contraction.

‘¢ The ligaments and burse undergo similar changes

276 PRIMARY FACTORS OF ORGANIC EVOLUTION,

to those described for the muscles concerned. They
elongate at points where the articular surfaces are
spread apart, and correspondingly shorten where the
flexure produces a folding. These changes proceed
more slowly than those of the muscles and tendons.
Very remarkable are the changes undergone by the
articular cartilages. When a joint is permanently
flexed, a part of the extremity of each bone is separated
from contact with the other, and the articulation is
finally destroyed at this point, because the cartilage
begins to vanish. One must conclude that the exist-
ence of the articular cartilages is dependent on their
mutual contact ; for dislocated articular surfaces which
remain in contact with soft tissues only, lose their car-
tilaginous covering. ... Finally it is possible by a
consideration of the etiology of the effects of joint con-
tractions to reach some hitherto unnoticed conclusions
regarding the changes of articular surfaces, and bone
forms. The results of joint-contraction are most con-
spicuous when the latter occurs in childhood. During
maturity, a dislocation which causes an articular bor-
der or prominence to rest abnormally on the opposed
' articular face in the act of walking, will be followed by
the penetration of the former into the latter, and a de-
formation of the articulation ; but the corresponding
changes under like conditions in the growing skeleton
are much more conspicuous.”

Hiitter thus describes the formation of new artic-
ular surfaces as a consequence of dislocation of joints.
‘Tf the head of the femur or humerus leaves its socket,
and rests on the side of the ilium or the scapula, the
periosteum of the bone which receives the new impact
is excited to active bone-production, and the result is
the deposit of new osseous tissue. The thin bones

KINETOGENESIS. 277

become thicker, not uniformly, but in correspond-
ence with the periphery of the head of the humerus or
femur, rather than with the point of contact of the
latter. This point is irritated, but the contact of the
ball restrains osseous deposit. So it occurs that grad-
ually a new socket is developed, whose mechanical
relations correspond exactly with those of. the articu-
lating bone. The head also acquires a strictly spher-
ical shape, by such contractions and atrophies as are
necessary to produce that result. Further, cartilage
appears in the place of the periosteum of the socket,
which functions like the primitive articular cartilage.
It is characteristic of both connective and periosteal
tissue to develop cartilage under the stimulus of con-
tinued friction of hard surfaces, such as occurs in dis-
locations and fractures.”

These observations of Hitter have been confirmed
by Henke, Reyher, Moll, and Lesshaft. Henke and
Reyher state that the artificial prevention of flexure of
articulations in young dogs renders them immobile,
and their restraint of flexure to one direction, results
in a curving of the articular faces in that direction.

I cite here two examples of modifications of struc-
ture under abnormal conditions which imposed new
impacts and strains on the parts. I have described
these cases, which are examples of false elbow-joints
in man and in the horse, in the Proceedings of the Amer-
ican Philosophical Society for 1892.

In the first case, that of the human elbow, the
cubitus was luxated posteriorly, so that the humeral
condyles articulate with the ulna anterior to the coro-
noid process. The head of the radius is in contact |
with the external epicondyle on its posterior inferior
face. The results.are as follows. A new coronoid

278 PRIMARY FACTORS OF ORGANIC EVOLUTION.

process was developed in front of the abnormal posi-
tion of the humeral condyle to an elevation above the
shaft of the ulna exceeding that of the normal coro-
noid. Between it and the normal coronoid was devel-
oped a perfectly functional cotylus which embraces
the humeral condyle like the normal cotylus. The
latter has its articular surface, buried under osseous
deposit, so as to be no longer visible. The region of
contact between the head of the radius and the external
epicondyles, has developed in the latter a large artic-
ular cotylus which permits of both rotary and ver-
tical movement of the former. The articular surface
of the humeral condyles, except where in articulation
with the ulna, is roughened, and partially overgrown
with exostoses, so as to alter its form to a great extent.
The opportunity of examining this specimen I owe to
Provost Pepper of the University of Pennsylvania, in
whose museum it is preserved.

In the case of the horse’s elbow, the luxation of
the cubitus is inward, so that the olecranon articulates
with the external epicondylar surface, and the humeral
condyles are not adapted to the head of the radius;
their internal border falling considerably internal to
the inner border of the radius. The horse from which
this specimen was derived lived for two years after the
luxation took place, and became able to use the limb
in some degree. The effect on the articulation is as
follows.

A large part of the inferior extremity of the poste-
rior rib of the shaft of the humerus, which is the place
of insertion of the external flexor metacarpi muscle, has
been removed, so as to present a wedge-shaped out-
line with the apex downward. This removal permits
the close articulation of the inner face of the olecranal

KINETOGENESTS. 279

process with the epicondyle, which has developed a
considerable articular face, on which movement takes
place in extension and flexion. The posterior border
of this face has developed a ridge which borders the
facet behind, and retains the olecranon in place. Two
other facets are developed on the humeral condyles,
and two on the head of the radius. The most impor-
tant of the latter is a bevel of the external part of the
surface to the border, due to the contact of the ex-
panded internal humeral condyle. The articular face
of the olecranon is much depressed in consequence of
its articulation with the external epicondyle of the
humerus. Besides these new and changed facets, the
effect of the luxation is seen in the development of os-
seous crests at the points of insertion of the articular
ligaments. One of these on the humerus has been al-
ready referred to. Another is concentric with and
posterior to the internal humeral facet of the olecranar
process, and serves as a guide to the humeral crest
above described. A third is an extensive osseous de-
posit on the internal face of the head of the radius,
which partially builds an extension of the head of the
radius, which if completed would articulate with the
overhanging portion of the internal humeral condyle.
A third modification of normal structure is similar to
that observed in the human elbow. It consists of os-
seous deposit beneath the synovial bursa at points
where the luxation causes a gaping of the surfaces.
This occurs at the trochlear groove of the head of the
radius, which is partially filled up with exostosis.

The preceding observations lead to the following
conclusions:

First. Continued excessive friction removes osse-
ous tissue from the points of contact until complete

Fig. 66.—Elbows of man and horse.

‘asioy yo Moq)q—'49 “31d

282 PRIMARY FACTORS OF ORGANIC EVOLUTION.

adaptation is accomplished and the friction is reduced
toa normal minimum. Then a normal articular sur-
face is produced.

Second. Where the normal friction is wanting,
and an inflammatory condition is maintained by a pull-
ing stress on the investing synovial membrane, excess
of osseous deposit is produced.

Third. Stress on the articular ligaments and ten-
dons stimulates osseous deposit at their insertions,
which deposit may be continued into their substance.
This is a pulling stress.

These observations therefore show that osseous de-
posit is produced by different forms of mechanical
stimulus.

EXPLANATION OF FIGURES 66 AND 67.

1-5, Homo sapiens, \uxated elbow joint (one-half natural size); 1, luxated
elbow joint, from within; 2, luxated elbow joint, from outer side; 3, humerus,
posterior view of distal region; 4, humerus, distal view; 5, ulna and radius,
anterior (superior) view; 6-11, bones of abnormal left elbow joint of horse
(one-half natural size) ; 12, 13, normal bones of elbow joint of horse (one-half
natural size); 6-12, humerus, distal views; 7-13, cubitus, proximal views; 8,
humerus, external view of distal extremity; 9, humeral articulation of cubi-
tus, from above; 10, cubitus, internal view; 11, cubitus, external view. Let-
tering.—H, humerus; U, ulna; A, radius; C, coronoid process; C2, second
(abnormal) coronoid process; O, olecranon; £x, entepicondyle; Zc, ectepi-
condyle; £zo, entepicondylar exostosis ; Eco, ectepicondylar exostosis; Co,
condylar exostosis; Cos, superior condylar exostosis; Coz, inferior condylar
exostosis; 7, humeral facet ; X/, radial facet; U*, ulnar facet; Of, olecranar
process of ulna; C%, coronoid process of ulna; Og, olecranar groove of hu-
merus; 7c, trochlear crest of humerus; 7g, trochlear groove of humerus;
Ehc, external humeral facet of coronoid process; /kc, internal humeral facet
of coronoid process; sa, abnormal facet for coronoid process of ulna; 74,
do. for internal roller of humerus; sc, do. for abnormal facet of humerus;
1d, do, for internal border of radius; ze, do. for olecranar process of ulna;
if, do. for trochlear crest of humerus; 2a, 24, 2c, exostoses of radius and ulna
to fill vacuity between humerus and radius and ulna; 3a, abnormal crest
which serves as a guide to the olecranar process of the humerus; 34, abnormal
crest which serves as a guide to abnormal crest 72; 3c, exostosis extending
head of radius inwards to equalize its width with inward luxation of humerus;
gd, exostoses of external epicondyle of humerus, to equalize its width with
outward luxation of radius; je, abnormal exostosis of insertion of external
Aexor metacarpi muscle; 2/, 3g, abnormal crest at insertion of external ar-
ticular ligament on olecranar process of ulna.

KINETOGENESIS. 283

&. Normal Articulations.

The origin of condyles and their corresponding
cotyli has been made the subject of investigation by
several German anatomists. L. Fick! expressed the
opinion that the concavo-convex surfaces were pro-
duced by a wearing away of the surface which became
concave, by the free action on it of the surface which
became convex, the former being fixed, and the latter
free. He found the conditions of muscular insertions
to correspond with the conditions of fixity and free-
dom required ; for the insertions are always nearer to
the concave surface than to the convex surface. He
constructed plaster models of joints, and by moving
one on the other obtained a convex surface on the
moving, and a concave surface on the fixed extremi-
ties. These observations were confirmed by Henke,?
but he very properly does not regard the result as due
to wearing, but to the stimulation of metabolic action
in the required directions. R. Fick? has confirmed
these positions in an extended memoir, and recently
Dr. E. Tornier has devoted a still more thorough re-
search to the same subject.*- R. Fick applied his ob-
servations to the question of the phylogeny of the ar-
ticulations, but did not see in it proof of the operation
of mechanical causes, but ascribed it to ‘inheritance
and natural selection”? in accordance with the mean-
ingless formula usual at the time he wrote. W. Roux,®
however, in reviewing Fick’s article saw in the obser-

1 Ueber die Ursachen der Knochenformen, Experimental - Untersuchung,
1859, Géttingen, G. Wiegand.

2 Anatomie und Mechanik der Gelenke, Leipsic, 1863, p. 57.

8 Archiv fiir Anatomie und Physiologie, 1890, p. 391.

4 Archiv fiir Entwickelungsmechanik, 1., 1894, p. 157.

8 Biologisches Centralblatt, 1891, p. 188.

284 PRIMARY FACTORS OF ORGANIC EVOLUTION.

vations of Fick proof of a direct mechanical cause of
the structure. I have pointed out the phylogeny of
the articulations in the Mammalia in various papers
from 18771 to 1889,? and in 1881 I advanced the view
that their successive evolution was due to impacts and
strains (American Naturalist, July, 1881 ; Origin of the
Fittest, p. 373). The opinion of Roux entirely sup-
ports my position, and it is further established by the
elaborate memoir of Tornier just cited. This author
adopts the view that bone-development is controlled
by Druck und Zug or impact and strain, and he adds
some important considerations to those previously ad-
vanced. He asserts that ‘‘in all existing Vertebrata
true bones may appear as secondary structures, since
all of these animals possess bands and threads of con-
nective tissue which possess the latent capacity to be
changed wholly or in part into cartilage.” Thus is
accounted for the development of sesamoid bones in
tendons, in which category is included the patella.
Tornier also shows that the concave articular face
(cotylus) is that to which the flexor and extensor mus-
cular insertions are nearest, while the convex face
(condyle) is the one most remote from the muscular
insertions.

It must be observed that Tornier adopts the lan-
guage of the American Neo-Lamarckians in using the
expression ‘‘impact and strain.” Impact and strain.
are different modes of motion. ‘*Impact” implies
pressure, while “‘strain ” implies a pulling stress, either
direct or torsional. It is therefore alleged by Tornier,
as it has been by myself, that opposite modes of mo-

1 Report U.S. Geol. Survey W. of rooth Meridian, 1875, Vol. IV., p. 277-
279. Proceeds. Amer. Philosoph. Soc., 1884, p. 44.

2 Amer. Journal Morphology, 1889, p. 163.

KINETOGENESTS. 285

tion may produce metabolic changes in osseous tissue.
For this reason it is possible to account for the length-
ening of the limb-bones in heavy animals, as an effect
of impact, while the astragalus of bats may have been
elongated by a stretching strain.

c. The Physiology of Bone Moulding.

Dr. Koelliker has summarized the results of the
observations made by himself and his predecessors on
the processes of the growth and absorption of bone,
which determine the forms of the elements of the skel-
eton.!

Bone is deposited through the agency of uninuclear
cells, or osteoblasts, which may under peculiar condi-
tions become enlarged and multicellular, when they
are termed osteoclasts. These osteoclasts produce an
absorption or destruction of the bone or dentine with
which they are in contact, the bone or dentine being
passive under the operation. How this is done is not
known. Pieces of ivory which have been used to re-
place bone removed by surgical methods, have been
found to be both corroded by osteoclasts, and overlaid
by layers of living bone by osteoblasts.

In explanation of the causes which induce the for-
mation and action of the osteoclasts, Koelliker remarks
that: ‘«the totality of changes of the jaws during the
development of teeth appears to show that it is pres-
sure by the soft parts which causes the absorption of
bone. One can admit in the case of the jaw that the
dental sacs in process of growth produce by their en-
largement a state of irritation in the layer of osteo-
blasts which originally border the alveolar edge, and

1“ The Normal and Typical Absorption of Bones and Teeth," Verhandi.
der Phys. Med. Ges. von Wiirzburg, I1., IIL, 1872.

286 PRIMARY FACTORS OF ORGANIC EVOLUTION.

that in consequence of this irritation the cellules trans-
form themselves into osteoclasts, and acquire a new
power, that of absorbing bone. The function will
cease as soon as the teeth are formed, by the termina-
tion of pressure, and then the formative action of the
cellules adjacent to the bone will repair it as a conse-
quence of a retransformation of these elements into
osteoblasts.

‘‘T will not push further this first attempt at an
explanation of the normal absorption of bone, but I
content myself with observing, that in any case, pres-
sure exercised by the soft parts counts for much in this
phenomenon. Who does not remember in the face of
these facts, numerous cases of pathological absorption
of bone due to aneurisms, tumors, and hypertrophied
organs? Who will not admit the great effect of the
disappearance or arrest of development of organs on
the size of their osseous surroundings; as Fick, for-
merly professor of anatomy at Marburg, has shown to
take place in the orbit after the extirpation of the eye?
It is possible to go a step further in the proposition,
that external pressure has much to do with absorp-
tion. Thus the growth of the brain and spinal cord
produce the resorption seen in the interior of the skull
and of the spinal canal; that of the eye and of the
nasal mucosa, and of the cranial vessels and nerves,
have resulted in the enlargement of their cavities ; and
in the case of foramina, in their wider expansion... .
The medullary cavities of bones are produced in the
process of growth by the corrosive activity of osteo-
clasts.”

It is then pressure which produces the excavations
which form new cotyli in the construction of new ar-
ticulations due to dislocations. By such excavations

KINETOGENESIS. 287

elevated portions remain adjacent to them. Other
elevations, as already described, are due to deposit of
bone stimulated by the absence of accustomed pres-
sure, as in the filling up of the old ulnar cotylus in
the human subject above described. Other elevations
or osseous deposits such as occur at muscular and
ligamentous insertions appear to follow a pulling stress.

Many other examples of the abnormal production
of articulations might be cited, but the above are suf-
ficient to show the plasticity of osseous tissue. It is
also evident that if such results follow the stimulus of
the parts during a short period of months or years,
the continuance of the appropriate mechanical stresses
through geologic ages must have been quite sufficient
to produce all the characters which we observe in the
articulations of the vertebrate skeleton.

I will now present the inferences which may be de-
rived from consideration of the facts hitherto presented
in this chapter. We have not been witnesses of the
‘process of evolution, yet we believe that it has been
in active operation. We have not been able to observe
its modus operandi, but we may safely infer what it
has been from the facts which are before us. Kineto-
genesis having been observed in both the soft sarcode
(muscle) and in the hard parts of animals, the law of
uniformity obliges us to believe that similar changes
have taken place in past ages whenever the necessity
arose, and the energy at nature’s disposal was suff-
cient.

ll. MOULDING OF THE ARTICULATIONS.
a. The Limb Articulations.

This part of the subject has the advantage of many
facts of paleontology in our possession. We have

288 PRIMARY FACTORS OF ORGANIC EVOLUTION.

now discovered the outlines of the phylogeny of many
mammalian types, and many detailed histories of spe-

cial lines of descent are known.

Our knowledge is

most complete in the unguiculate and ungulate pla-:

Fig. 68.—Periptychus rhabdodon
Cope, a condylarthrous genus of the
Puerco epoch of New Mexico; poste-
rior foot, one-half natural size, show-
ing pentadactyle plantigrade foot with-
out groove of astragalus, as in the
probable ancestor of the Diplarthra.
From Scott and Osborn.

centals, while it is least
as regards the Mutilata,
and the implacentals. We
have excellent series of
skeletal parts, and I have
given the successional
modifications of some of
them on page 139.

In the first place, I
will select an illustration
of the effects of use on
the articulations of the
limbs and feet of the
Mammalia. I take first
the ankle and wrist-joints.
In the ruminating animals
(ox, deer, camel, etc.) and
in the horse, among other
living. species, the ankle-
joint is a very strong one,
and yet admits of an ex-
tensive bending of the foot
on the leg. It is a treble
tongue-and-groove joint ;
that is, two keels of the

first bone of the foot, the astragalus, fit into two grooves
of the lower bone of the leg, the tibia, while between
these grooves a keel of the tibia descends to fill a cor-

responding groove of the astragalus.

Such a joint as

this can be broken by force, but it cannot be dislocated.

KINETOGENESTS. 289

Now, in all bones the external walls are composed of
dense material, while the centers are spongy and com-
paratively soft. The first bone of the foot (astragalus)
is narrower, from side to side, than the tibia which
rests upon it. Hence the edges of the dense side-walls
of the astragalus fall within the edges of the dense
side-walls of the tibia, and they have pressed into the
more yielding material that forms the end of the bone,
and causing bone absorption, pushed it upward, thus
allowing the side-walls of the tibia to embrace the
side-walls of the astragalus. Now, this is exactly what
would happen if: two pieces of plastic dead material,
similarly placed, should be subjected to a continual
pounding in the direction of their length. And in
view of the facts already cited we cannot ascribe any
other immediate origin to it in the living material.
The same active cause that produced the two
grooves of the lower end of the leg produced the groove
of the middle of the upper end of the astragalus. Here
we have the yielding lower end of the tibia resting on
the equally spongy material of the middle of the as-
tragalus. There is here no question of the hard ma-
terial cutting into soft, but simply the result of con-
tinuous concussion. The consequence of concussion
would be to cause the yielding faces of the bones to
bend downward in the direction of gravity, or to re-
main in their primitive position while the edges of the
astragalus were pushed into the tibia. If they were
flat at first they would begin to hollow downward, and
a tongue above and groove below would be the result.
And that is exactly what has happened. This inclu-
sion of the astragalus in the tibia does not occur in the
reptiles, but appears first in the Mammalia, which de-
scended from them. See Figs. 68-69. I have shown

290 PRIMARY FACTORS OF ORGANIC EVOLUTION.

that without exception, every line of Mammalia com-
menced with types with an astragalus which is flat in
the transverse direction, or without median groove.

}
ii
i !

Hh ®
HI

Fig. 69. Fig. 70.
Fig. 69.—Hind foot of primitive cameloid Poébrotherdum labiatum Cope,

showing grooved astragalus and first toe-bones without keel in front at lower
end. (From Colorado.)

Fig. 70.—Hind foot of three-toed horse (Prothippus sezunctus Cope) (from
Colorado), showing grooved astragalus, and trace of keel on front of lower
end of first bone of middle toe.

KINETOGENESIS, 291

From early Tertiary times to the present day, we can
trace the gradual development of this groove in all

the lines which have acquired it.
became first a little concave ;
the concavity gradually became
deeper, and finally formed a well-
marked groove.

The history of the wrist-joint is
similar. The surface of the fore-
arm bones which joins the fore-
foot is in the early Tertiary Mam-
malia uniformly concave. In the
ruminating mammals it is divided
into three fosse, which are sep-
arated by sharp keels. These fos-
se correspond with the three
bones which form the first row of
the carpus or palm. The keels
correspond to the free sutures be-
tween them. The process has been
evidently similar to that which has
been described above as produc-
ing the side-grooves in the end of
the tibia. The dense walls of the
sides of the three bones imping-
ing endwise on the broad yielding
surface of the fore-arm (radius)
have gradually, under the influence
of countless blows, impressed
themselves into the latter. On
the contrary, the surface above

The upper surface

Fig. 71.— United first
bones of two middle toes
of deer-antelope (Cosoryx
Jurcatus Leidy), showing
extension of keel on front
of lower end. (From Mio-
cene of Nebraska.*

the weaker lines between the bones not having been
subject to the impact of the blows, and influenced by

292 PRIMARY FACTORS OF ORGANIC EVOLUTION.

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gravity, remains to fill the
grooves, and to form the
keels which we observe. (See
Fig. 72.)

There is another striking
instance of the same kind in
the feet of Mammalia’; that
is, in the development of the
keels and grooves which ap-
pear at the articulation of the
first set of bones of the toes
(metapodials) with the bones
of the second set (phalanges).
These keels first appear on
the posterior side of the end
of the first set of bones, pro-
jecting from between two
flexor tendons. These ten-
dons, in many mammals, con-
tain two small.bones, one on
each side, each of which acts
like the knee-pan, and resem-
bles it in miniature, which are
called sesamoid bones. These
tendons and bones exercise
a constant pressure on each
side of the middle line, when
the animal is running or
walking, and this pressure,
together with the concussion
with the ground, appears to
have permitted the protru-
sion of the middle line in the
form of a keel, while the

KINETOGENESIS. 293

lateral parts have been supported and even com-
pressed. The reptilian ancestors of the mammals do
not possess: these keels.

Now, I have shown that the lines of mammalian
descent displayed by paleontology are characterized,
among other things, in most instances, by the gradual
elevation of the heel above the ground, so that the
animal walks on its toes. It is evident that in this
case the concussion of running is applied more directly
on the ends of the bones of the foot than is the case
where the foot is horizontal. As a consequence we
find the keel is developed farther forward in such ani-
mals. But in many of these, as the Carnivora, hip-
popotamus, and the camels, there is developed under
the toes a soft cushion, which greatly reduces this con-
cussion. In these species the keel makes no further
progress. In other lines, as those of the horse, the
pig, and of the ruminants, the ends of the toes are ap-
plied to the ground, and are covered with larger hoofs,
which surround the toe, and the cushion is nearly or
quite dispensed with. These animals are especially
distinguished by the fact that their metapodial keels
extend entirely round the end of the bone, dividing
the front, as well as the end and back (Fig. 71); since
the front of the metapodial is out of the reach of the
sesamoid bones, its keel would seem to be a mould-
ing to the groove of the first phalange, which is itself
moulded by the middle and posterior part of the meta-
podial keel (Wortman.)

A third and similar example is furnished by the
elbow-joint of the Quadrumana and Diplarthra. In
the lower’ Mammalia, including the Carnivora (Fig.
73), the distal end of the humerus presents a subme-
dian groove, which receives the ulna, and on the inner

294 PRIMARY FACTORS OF ORGANIC EVOLUTION.

side of it, a more or less convex, surface, which is ap-
plied. to the head of the radius. The coronoid process
of the ulna is narrow, and its dense bounding walls
impinge on the broad face of the humeral condyle in
flexion and extension, and transfers to it the force of
impact when the foot strikes the ground. In either
case strong pressure has been brought to bear on
the humeral condyle, and it has
yielded to the denser body of the
ulna, thus forming the groove in
question. In such Mammalia the
effect of impact of the limb on the
ground has been to impress the
head of the radius on the humeral
condyle upwards. The dense
edges of the former have im-
pressed themselves on the latter,
while the unsupported middle
portion has yielded in the direc-
tion of gravity, and the result is
what we find, i. e., a cup-shaped
surface of the head of the radius,
7 and a convexity of the humeral
clit: —Bhowicint ot condyle adapted to it.
hyena) seen from behind ; #, Among specializations of the
humerus; 7, radius; ~, ulna. soe :
grease elbow-joint, I call attention to
two. In Quadrumana the head of
the radius, probably owing to continued supination of
the manus, occupies a position at the external side of
the coronoid process of the ulna, and impinges on the
outer part of the condyle of the humerus. The con-
cavity of its head, and the convexity of the humeral
condyle, are visible as before, but a prominent tongue
or keel, which has been called the intertrochlear crest,

KINETOGENESIS. 295

separates the ulnar and radial surfaces of the humerus
(Fig. 74). This keel occupies the groove or interval
which separates the head of the radius from the coro-
noid process of the ulna. It is plain that we have here
another tongue and groove-joint, produced by the mu-
tual adaptation of parts under strain, pressure, and
impact. The other extreme of elbow-joint is found in
that of the diplarthrous Ungulata (Fig. 75). Here the
head of the radius, while retaining its normal position
on the inner side of the fore-arm, is extended to the
external side of the ulna and
even beyond it, adapting it-
self to the entire width of the
humeral condyles. The same
structure is found in the spe-
cialized forms of both series
of Diplarthra, the Perisso-
dactyla and Artiodactyla.
This expansion of the head of
the radius appears to be in di-
rect relation to the duration
through long geologic ages _Fig. 74.—Elbow-joint of chim-
of the impacts which have ?2"2°¢ from behind.

affected the limbs of these, the swiftest of the Mam-
malia. That the head of the radius should be spread
so as to fit the entire surface of the humerus, under all
circumstances, seems to be a mechanical necessity.
But in addition to this we find a tongue-and-groove
adaptation, in which the crest (which I have called the
trochlear crest) articulates with a groove in the head
of the radius. The internal articulation of the humerus
with the radius has the usual form, convex and con-
cave distad. The trochlear crest marks the external
border of the olecranar groove of the humerus. But

296 PRIMARY FACTORS OF ORGANIC EVOLUTION.

the external part of the humeral condyles is converted
into aroller which is set off from the trochlear crest by
the abrupt contraction of its diameter ; while the cor-
responding part of the head of the radius projects to
fit it exactly.

A probable explanation of the form of this roller
may be derived from a consideration of the almost
identical structure of the meta-
‘podio-phalangeal articulation of
the Artiodactyla. -The internal
and external sides of the distal
metapodial condyles are not sim-
ilar, the external being more
strongly impressed than the in-
ternal (Fig. 77D). This is simply
due to the unequal pressure ex-
erted on the two extremities of
the condyle by the phalanges,
owing to the divergent direction
of the digits when serving asa
support. In the distal end ‘of
the humerus the same effect is

Hace ameoaeak Seems the external part of the con-
Cervus elaphus (red deer) dyle nearly resembling the corre-
sonnel sponding part of the metapodial
bones. This is traceable to the same cause, viz.: the
divergent position assumed by the fore arm on the hu-
merus, when the weight is supported on one fore leg
only. This brings the line of pressure through the ex-
ternal part of both the head of the radius and the hu-
meral condyle (Fig. 77A). That the higher ungulates
are ‘‘knock-elbowed” may be readily observed by
watching their gaits (Fig. 76).

KINETOGENESTS. 297

A distinct consequence of combined impact and
strain is seen in the evolution of the carpus and tarsus
of the Diplarthra. In primitive Mammalia, as in
most Unguiculata, the
bones’ of the carpus
and tarsus succeed
each other in such a
way that the principal
lines of separation be-
tween the elements
coincide in the two
rows, thus producing
a linear relation be-
tween the former. In
the Diplarthra, on the
other hand, the ele-
ments of the two rows
alternate with each
other so as to produce
a strong interlocking.
I have shown that in
the primitive Ungu-
lata, the Taxeopoda,
the linear arrange-
ment is observed,
while in three orders
of ungulates, the Pro- Fig. 76.—Cervus canadensis in motion:
boscidea, Toxodontia, from Muybridge’s Aximal Motion ; showing
and Amblypoda, there In¢hmckelton" psion of the freien
are various degrees of
alternation intermediate between the linear type of the
Taxeopoda and the completely interlocked condition
of the Diplarthra. It has been already pointed out in
the chapter on phylogeny that the taxeopodous type

298 PRIMARY FACTORS OF ORGANIC EVOLUTION.

of foot preceded the diplarthrous in time. Besides the
alternation mentioned, it is quite general in both types
for the metapodial bones to possess a facet for con-
tact with that element of the carpus and tarsus next
exterior to the one to which they have their principal
articulation. From these facts it is evident that the
bones of the second carpal and tarsal rows have, in

Fig. 77.—Cervus elaphus; A, B, C, humero-radial articulation; A and B,
with the radius in position; C, with radius twisted; D, Z, metatarsophalan-
geal articulation; D, front; Z, distal view, twisted.

the process of evolution, assumed a position interior
-to their primitive position, with reference to the first
row proximad to them, and the metapodials distad to
them. The cause of this shifting of position is to be
found in the movements of the limbs in progression,
and especially in rapid progression (Fig. 78).

If we observe the movements of the limbs ina

KINETOGENESIS. 299

diplarthrous ungulate, we shall see that as the foot is
planted on the ground the prominent flexures of the
limbs, the elbow and gambril joints, are turned in-

at | Radius | ~ B Radius Ulna

Scaphoid [=] Cuneif. | Scaphoid | cuneif
afer [><] [22 ][ oo } srofe| arene a> ee

Pelt, “weer

Pollex Indeg Med? Ann? Minim? Index Med? Ann’

Fig. 78.—Diagram of carpus of a Taxeopod (A) and (8) of a diplarthrous
ungulate. From Osborn.

wards, so that the limb, were it free from the ground,
would be twisted or rotated on its long axis from
within, forwards and outwards. As the foot rests on

Fig. 79.—Raccoon pacing, showing right fore foot just before recovery.
From H. Allen.
the ground, the limb experiences a torsion strain in
the directions mentioned. This throws the weight on
the interior bones of the lower legs, the radius and the
tibia. Thus these bones have acquired a great supe-

300 PRIMARY FACTORS OF ORGANIC EVOLUTION.

riority in dimensions over the external elements (ulna
and fibula) in all the Diplarthra. The bones of the
inner side of the first carpal and tarsal rows have thus
transmitted an ever-increasing share of the impact, as
the radius and tibia have developed, and have grown

se. (U.S Gu
make
( Va)

Fig. 80. Fig. 81.

Fig. 80.—RAznocerus unicornis carpus. Arrow ending in P, line of impact
in plantation; do. ending in X, line of strain in recover.

Fig. 81.—Z£guus cabalius fore foot. Sc, scaphoid; Z, lunar; Cz, cunei-
form; 7Yoz, trapezium and trapezoideo; Um, unciform; mg., magnum.
with their growth at the expense of the external ele-
ments, the cuneiform in the carpus, and the calcaneum
in the tarsus, which have become very narrow elements
in the higher Diplarthra. As the pressure has been
obliquely from within outwards, the growth of the
proximal elements, the scaphoid and lunar in front,

From Brehm.

Fig. 82.--Gazella dorcas, gazelle.

302 PRIMARY FACTORS OF ORGANIC EVOLUTION,

and the astragalus behind, has been in the same direc-
tion. It has been shown by Dr. H. Allen that just
before the recover of the foot, the latter is directed
outwards from a line parallel with the axis of the body,
so that the weight falls on the inner part of the sole of
the former. This naturally causes the bones of the
foot to press inwards on the heads of the metapodials,
so that the latter tend to grow outwards on the second
tarsal row. In this way were produced the facets on
the external side of the heads of the metapodials.
Thus is accounted for, on simple mechanical princi-
ples, the phenomenon of carpal and tarsal displace-
ment exhibited in its highest development, by the Dip-
larthra.

It is significant that diplarthrism has not appeared
in mammals which possess an elastic pad of connec-
tive tissue on the soles, as in Unguiculata generally,
and,especially in the Carnivora. Diplarthrism is pres-
ent in the camels, which have a pad, but I have shown
that this pad did not appear until a comparatively late
geologic epoch, and long after diplarthrism had be-
come established in the camels’ ancestors, the Poébro-
theriidz.

The faceting of the head of the astragalus as the
result of impacts, is seen on comparison of the astra-
gali of Phenacodus and Hyracotherium in Ungulata
(Figs. 33-35), and of Dissacus and Mesonyx among
the Creodonta. In this last genus we have the only
faceted astragalus among carnivorous mammals, but
this genus is at the same time subungulate.

b. The Forms of Vertebral Centra.

The mutual articulations of the vertebral column
are those of the centra and of the zygapophyses. Many

KINETOGENESIS. 303

important modifications in these articulations are to be
seen in Vertebrata, the Reptilia presenting the great-
est variety, excepting in the zygapophyses, which are
tolerably uniform in that class. In the Mammalia.
modifications of the central articulations are not more
striking than are those of the zygapophyses.

The forms of central articulation are four, viz.: the
amphiccelous, the ball-and-socket, the plane, and the
saddle-shaped. The first type is only seen in a very
imperfect degree in Mammalia and in but very few
vertebrz, where it is indeed but a modification of the
plane. The ball-and-socket is chiefly found in the
neck of the long-necked Mammalia, as the higher
Diplarthra, and to a less degree in their lumbar re-
gions, while the dorsal vertebre present an approach
to the same type in the same groups. The saddle-
shaped centrum is only found in Mammalia in the
necks of certain genera of monkeys. The majority of
Mammalia present the plane articulation of all the ver-
tebral centra.

In Mammalia in which movement of the vertebre
on each other has become impossible, the centra co-
éssify, as for instance in the sacrum. In this region the
number of vertebrz coésified is directly as the length
of the iliac bone, which supports and holds them im-
movable. Such is their condition throughout the
dorsal region in the extinct Edentata of the family
Glyptodontide, where the carapace is, as in the tor-
toises, inflexible, and which therefore limits the possi-
bility of motion of the vertebral column. Another
illustration is seen in the necks of the balenid Ceta-
cea, and to some degree in the Delphinide and Physe-
teride. The lack of present mobility of this part of
the column is due to its extreme abbreviation, a char-

304 PRIMARY FACTORS OF ORGANIC EVOLUTION.

acter which has been gradually developing during Ce-
nozoic time ; since the earliest Cetacea had consider-
ably longer necks than the later ones, and had their
vertebral centra distinct. It appears to me probable
that the shortening was the result of disuse. This
disuse would arise from gradually increasing powers
of locomotion through the water, a progress, which,
judging from the character of the limbs of the Zeuglo-
don, was evidently made after the time of the Eocene.
The increase of speed would enable the animal to over-
take and capture its prey, without the necessity of
using a long prehensile neck in seizing it in the pur-
suit.

The ball-and-socket articulation of the vertebre is
well known to be the predominant condition in the
Reptilia, and the fact that it is necessarily associated
with the flexibility of the column is equally well under-
stood. The flexibility is directly as the weakness of
the limbs, for in the large and long-limbed terrestrial
Reptilia of the order Dinosauria, the vertebral articu-
lations of the dorsal region, at least, are plane. That
it is chiefly confined to, and best developed in, the
most flexible regions, i. e., the cervical and lumbar, of
the column of the Mammalia, also shows this neces-
sary connection. There can be no doubt but that the
ball-and-socket vertebral articulation has been pro-
duced by constant flexures of the column in all direc-
tions, as has been suggested by Marsh.

lll. INCREASE OF SIZE THROUGH USE.

Under this head I enumerate examples where the
mechanical causes in operation are less self-evident
than those included under the preceding section. They

KINETOGENESIS, 305

are, however, probably due to the same process, viz.,
impact and strain.

a. The Proportions of the Limbs and of Their Segments.

The length of the legs of terrestrial Mammalia has
increased with the passage of time. The inferior types
of Mammalia now existing, as Marsupialia, Glires,
Insectivora, Edentata, have short legs, with a few
cases of extreme specialization as exceptions, such as
kangaroos, rabbits, and jerboas (hind legs only), the
Dolichotis patachonica, the Rhynchocyonide, and the
sloths. In the orders which stand at the summit of
the series, as the Diplarthra, Proboscidia, Carnivora,
and Anthropomorpha, the legs are much increased in
length, and this is especially marked in certain forms
which stand in all respects at the summit of their re-
spective orders. Thus in Diplarthra, the deer, ante-
lope, and horse are distinguished for length of limb;
in the Proboscidia, the elephant; in the Carnivora,
the large cats and hyenas; in the Anthropomorpha,
the fore limbs are long in all, the hind ones especially
so in man.

The cause of this elongation is apparently use. It
is the hind legs that are elongated in a straight line in
animals that walk on them, as man; and both, in those
that walk on both, as the elephant. In animals that
leap with the hind legs these are still more elongated,
and are folded when at rest, and rapidly extended
when in motion. In animals that climb with the fore
legs, these are elongated, as in the Anthropomorpha,
except man. In those that climb with all fours, all
are elongate, as in the sloths. It must be remembered
that these elongations are the sum of increments added
one to the other through long ages of use in geologic

306 PRIMARY FACTORS OF ORGANIC EVOLUTION.

time. The mechanical character of that use has not
been identical. It is of two principal kinds, viz.: im-
pact and longitudinal strain. These two forms of en-
ergy move in directions opposite to each other; the
one as compression in the direction of the length of
the bone; the other, as a stretching in the direction of
the length of the bone. Both processes alike appear
to have stimulated growth in the direction of the length
of the bone.

The increase in the length of the legs has not been
always due to increase in length of the same segment.
In a majority of the higher mammals, the increase has
been principally in the foot, and especially in the meta-
podials and digits, producing digitigradism. In the
forms which have remained plantigrade, the femur
(Proboscidia), or femur and tibia (Quadrumana), or
all three segments (Tarsius), have been the seat of the
elongation. We can again trace these especial elonga-
tions to special uses. In animals which leap, the dis-
tal segments of the limbs are elongated; in those
which do not leap, but which merely run or walk, it is
the proximal segments of the limbs which are elon-:
gated.

Animals which run by leaping are divided into
those which run and leap with all fours, as Diplarthra ;
and those which run and leap with the posterior limbs
only, as the jerboas and kangaroos. In both types,
the distal segments of the hind limb are elongated, and
in the Diplarthra, those of the fore limb also.

Animals which do not leap in progression (ele-
phants, Quadrumana, bears) are always plantigrade,
and have very short feet, but elongate thighs, and,
mostly, tibias.

These facts show that those elements which receive
e

KINETOGENESIS. 307

the principal impact in progression are those which
increase in length. In digitigrade animals it is the feet
which receive the impact of the repeated blows on the

Fig. 83.—Pes of (A) Merychocherus montanus from Scott; (B) Bos taurus,
much reduced. Ca, Calcaneum; As, Astragalus; Va, Navicular; Med, Na-
viculocuboid ; Cz, Mec, Ecto-mesocuneiform ; /¢, Metatarsals (cannon bone);
Enc, Entocuneiform.
earth while in progression, while supporting the weight
of the body at every stage of the process. In planti-
grade animals it is the soles of the feet, and the bones
of the leg in line with them. which receive the impact,

308 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Fig. 84.—Anterior feet of primitive Ungulata, reduced. A, Phenacodus primevus. B, Coryphodon elephantopus,
Hyracotherium venticolum,

KINETOGENESIS. 309

while the feet beyond this point receive none, and do
not support the body, except very partially at the mo-
ment of leaving the earth.

b. The Number of the Digits.

The reduction in the number of toes is supposed to
be due to the elongation of those which receive the
greater number of strains and impacts in rapid pro-
gression, and the complementary loss of material
available for the growth of those not subject to this
stimulus. This is rendered probable from the fact
that the types with reduced digits are dwellers on dry
land, and those that have more numerous digits are
inhabitants of swamps and mud, or are more or less
aquatic. That this inequality is due to these mechan-
ical causes is still further indicated by the fact that in
those forms where the soles are thickly padded (Car-
nivora, Proboscidia) the reduction has either not taken
place, or has made little progress, amounting to the
loss of only one digit. (An apparent exception in the
case of the camels will be mentioned later.) A still
more important body of evidence which shows that
the inequality in size and number of digits is due to
impacts and strains unequally distributed, has been
brought forward by Ryder. He points out that defi-
nite results are to be observed in those limbs of a given
type of animal which experience correspondingly defi-
nite influences; while in the limbs where the strains
are equal, the modifications do not appear. Examples
of this kind are to be found in the unguiculate Mam-
malia and in the Marsupialia. Thus in the jerboas
which use the hind limbs in leaping, these only dis-
play reduced digits, the fore limbs remaining of prim-

310 PRIMARY FACTORS OF ORGANIC EVOLUTION.

itive character. The same is true of the kangaroos.
In digging genera, the fore limbs experience the modi-

Ni
Hi |
Hi

ai rh }
i

Fig. 85.—A, Right posterior foot of Prothippus sejunctus Cope, from Colo-
rado, about one-half natural size. From U.S. Geological Survey of Territo-
ries, F. V. Hayden, IV. 8, Right posterior foot of Poébrotherium labiatum
Cope, from Colorado, three-fifths natural size. From Hayden's Report, IV.,
Plate CXV.

fications, while the hind limbs are more normal, as in
Chrysochloris and various Edentata.

KINETOGENESIS. 3Ir

Ryder sums up the evidence in two propositions,
as follows :1

«I. The mechanical force used in locomotion dur-
ing the struggle for existence has determined the digits
which are now performing the pedal function in such
groups as have undergone digital reduction.

“IT. When the distribution of mechanical strains
has been alike upon all the digits of the manus or of
the pes, or both, they have remained in a state of ap-
proximate uniformity of development.”

The application of the impact, or strain, or both,
in progression, is easily understood. In recover (see
Pp. 299), the leg is bent on the foot as it rests on the
ground, and those digits which then leave the ground
last, sustain greater strain than those which leave it
sooner. In replacing the foot on the ground (planta-
tion), those digits which strike it first experience greater
force of impact than those which strike it later. Sup-
posing the five primitive digits to have been of equal
length, the distribution of the impact and of the strain
will depend on the angle at which the foot is directed -
with reference to the direction of motion. If the feet
are pointed forwards, the middle digits will experience
strain and impact ; if outwards, the inner digits bear
the weight; if inwards, the external digits receive it.

Observation on five-toed plantigrade: mammals
shows that their feet are turned neither inwards nor
outwards in progression, but straight forwards. It is
probable that the primitive Mammalia moved in the
same manner. ‘This is also to be inferred from the
fact that they were plantigrade, so that the leverage
transversely in or out which results from the elevated
heel of the digitigrade leg was very much less in them.

lAmerican Naturalist, 1877, p. 607.

312 PRIMARY FACTORS OF ORGANIC EVOLUTION.

In progression of this type, the middle digits of course
leave the ground last and strike it first. Thus the
middle toes have been stimulated at the expense of the
lateral ones, so that in the Diplarthra, either the mid-

ssmiztay ‘S Ssnz0jzay ‘b sens‘ ‘snuvjog

-odpy ‘t ‘snuevjogodgery ‘t ‘AYSABTEMOY UIOIJ | paonpal YONur ‘e[AjOepory Jo snueW—'9g “BIg

dle one (Perissodactyla) alone remains, or the middle
two (Artiodactyla). In the kangaroos the external toes
have been chiefly used, so that the fourth and fifth
digits have been principally developed. In man, who

KINETOGENESIS. 313

now turns his feet out when using them as bases of re-
sistance to muscular labor, the inner digit has become
most robust. The mechanical history of the human
great toe is however yet unknown.

As regards the equal development of the third and
fourth digits in the Artiodactyla, as distinguished from
the development of the middle digit of the Perisso-
dactyla, I have advanced the following hypothesis. I
have supposed that the primitive members of this for-
mer division sprung from pentadactyl plantigrades who
dwelt in swamps and walked on very soft ground.
‘The effect of progression in mud is to spread the toes
equally in all directions and on each side of the me-
dian line. Such feet remain in the mud-loving hippo-
potamus, and to a lesser degree in the true pigs. From
such ancestry the cloven-footed Diplarthra derived
their characters. The Hyracotheriinz, the ancestors
of all Perissodactyla, display on the other hand evi-
dence of a life on harder ground, especially in the pos-
terior foot, where articulations are already rigidly de-
fined, and the third digit is longer than the others.
Some of their descendants love swamps, as one or two
species of tapirs and rhinoceroses, but others live on
the dryest ground, as the Andean tapir and the African
rhinoceros. As to the highest members of both even
and odd toed groups, the Bovide and the Equida,
their habitat is in the vast majority of cases the dry
land (Figs. 80-81).

Continued and excessive prehensile strain with
weight on the longest digits, must be assigned as the
cause of the especial elongation; and disuse as the
cause of the loss of the external and shorter digits, of
the sloths; so that there remain but two and three
(Choleepus and Bradypus), and in the climbing ant-

314 PRIMARY FACTORS OF ORGANIC EVOLUTION.

eater (Cycloturus) but one principal toe and two rudi-
ments. The excessive strain and impact experienced
by certain digits in leaping, accounts for the digital
reduction in the hinder foot of the kangaroos and jer-
boas, precisely as in the perissodactyle ungulates.

c. The Horns.

Horns are developed in Mammalia and other Ver-
tebrata on similar parts of the skull, principally on the
posterior lateral angles, as in various Batrachia, Rep-
tilia, and Mammalia, and on the nose, as in a few
Mammalia and several reptiles, recent and extinct.
These parts are the ones which are especially brought
into contact with resisting bodies; the nose in pushing
a path or way for the head and body; the lateral occi-
pital region in defence and assault, when the sensitive
nose and eyes are protected: by being held near the
ground. In the latter position the posterolateral an-
gles, when present, receive more frequent collision
with, and vigorous stimulation from, a body attacked
or resisted, and in accordance with the observed re-
sults of irritation on dermal and osseous tissues, addi-
tional matter has been deposited. In Lacertilia and
Batrachia Salientia there are distinct posteroexternal
cranial angles; in Batrachia Urodela such angles are
less prominent. In unguiculate Mammalia and in all
others with a sagittal crest there are no such angles;
hence this type of skull has never developed posterior
horns. The rhinoceros has developed the dermal
nasal horn, and the Elasmotherium, a median osseous
horn, since posterolateral angles of the skull are want-
ing or close together. Inthe Dinocerata and the Ar-
tiodactyla, where the temporal crests are lateral, leav-
ing a wide fronto-parietal plane with posterior lateral

KINETOGENESIS. 315

angles, horns are developed. In members of both
groups horns have been developed over the orbits also
(Fig. 87), and in the Dinocerata on the extremities of
the nasal bones as well. These growths are all on
parts which are subject to especial irritation by contact
with other bodies, animate and inanimate.

Among Artiodactyla, the deer (Cervide) are espe-
cially distinguished by the periodical shedding of all
but the bases of their horns. Extinct forms found in
the Upper Miocene of the United States and France
(the Loup Fork series) furnish the explanation of the
origin of this remarkable peculiarity. In the genus
Cosoryx we find that the horns may or may not pos-
sess a burr near the base of the beam, like that of the
deer; the same species being indifferently with it or
without it. This observation has been made on three
species,—the C. necatus, C. furcatus and C. ramosus.
The following explanation of these facts has been pro-
posed by myself.1 “From the facts of the case the
following inference may be derived, premising that it
is very probable that a genus allied to the present one
has given origin to the family of the deer. It is ob-
vious that the horns of (Dicrocerus) Cosoryx did not
possess a horny sheath as in the Bovide, from the fact
of their being branched. As the sheath grows by ad-
dition at the base, the presence of branches which
necessarily obstruct its forward movement, would be
fatal to the process. There is much to be said in favor
of the view that the horns were covered with an integu-
ment, probably furred, as in the giraffe and young
stage in the deer. Thus there are grooves in the sur-
face of the beam for superficial blood-vessels, which

1U.S. G. G. Survey West of the rooth Mer., G. M. Wheeler: IV., Paleon-
tology, 1877, Pp. 348.

316 PRIMARY FACTORS OF ORGANIC EVOLUTION,

must have been protected by skin (I do not observe
these grooves on the beam of C. ¢eres). The retention
of the broken extremity of an antler, so as to be re-
united, as described (Fig. 87, C), could not have been
accomplished without an integument. The presence
of the burrs cannot be
accounted for on any
other supposition, as
there are no foramina
to give exit to nutrient
vessels at’ the point
where they exist; the
irregularity of those
positions also forbids
the latter idea, and
adds to the probability
that the arteries which
furnished the deposit of
phosphate of lime were
contained in a super-
ficial dermal coating.
The supposition is also
strengthened by the fact
that the only existing
ruminants (the giraffes)

Fig. 87.—A, B, Cosoryx necatus Leidy;
A, without, &, with, burr on antler; C, D,
Cosoryx ramosus Cope; C, antler broken With permanent horns

and reunited; D, beam with burr; one- :
half natural size; original; from Report without horny sheaths

U.S. Gov. Geol, Expl. rooth Mer, G.M» have them covered with
eee hairy skin.

‘“‘It appears that in the antlers of the Cosoryx the
deposit of a burr was immediately associated with the
death of the portion of the horn beyond it, so that it
disintegrated and disappeared. This was not the case
with the beam in the specimens observed. Neverthe-

KINETOGENESIS. 317

less it is probable that the death of the horn would be
associated with the deposit of the burr in this case
also, were the conditions the same. What those con-
ditions were we can only surmise. It was very prob-
ably the death of the integument which invested and
nourished the horn that produced that result; and
this would more readily occur in the exposed antlers
than in the more protected basal portion of the beam.
It is very probable that this result would follow blows
and laceration of the surface received during combat,
or accidental contact with hard substances. The in-
tegument would be stripped up to near the junction of
the antlers with each other, or of the beam with the
cranium, and the arteries would be constricted or
closed at those points. It is near these junctions that
all of the burrs are found. But as such lesion would
be necessarily less complete at the point where the °
horn has greatest circumference, so the entire death
of the horn might be less usual than that of the
branches. Should such lesions have occurred for a
long period at the breeding season, nature’s efforts to
repair by redeposit of bony tissue might as readily be-
come periodical as the increase in size and activity of
the reproductive organs and other growths which char-
acterize the breeding season in many animals. The
subsequent death of the horn would be at some time
followed by its shedding by the ordinary process of
sloughing.”

Cosoryx is not the true ancestor of the Cervida, as
its teeth have already attained the prismatic type of
the higher Bovide. But Blastomeryx is most prob-
ably the ancestor of the deer. The remains of this
genus occur with those of Cosoryx, but the burr has
not yet been observed on its horns.

318 PRIMARY FACTORS OF ORGANIC EVOLUTION.

lv. THE MECHANICAL ORIGIN OF DENTAL TYPES.

In investigating the origin of dental types it is
necessary to become acquainted with the nature of the
mutual movements of the series of the opposing jaws.
I have classified them as follows :1

I. Inferior molars work within superior molars, but not between
them. Psalidodect mastication.
1. The inferior molars shear on the interior side of the su-
perior : Triconodontide.
II. Part or all of inferior molars work alternately to and between
superior molars. Amoebodect mastication.
2. The inferior molar shears forwards on the superior mo-
lar. Proterotome mastication: Creodonta; Carnivora.
3. The inferior molars shear posteriorly against the superior
molars. Opisthotome mastication :
Coryphodontide, Uintatheriide.
III. Molar teeth of both jaws oppose each other. Antiodect mas-
tication.
4. The movement of the lower jaw is vertical. Orthal mas-

tication : Suotdea, Tapiride,
5, The movement of the lower jaw is from without inwards.
Ectal mastication : many Perissodactyla.

6. The movement of the lower jaw is from within outwards.
Ental mastication :

most Artiodactyla; some Perrissodactyla,

7. The movement of the lower jaw is from before backwards,

Proal :

some Monotremata Multituberculata and most Glires.

8. The movement of the lower jaw is from behind forwards.

Palinal : Proboscidea (Ryder).

The distinction of teeth into incisors, canines, and
molars appears independently at various points in the
line of Vertebrata. Incisors and molars are distin-

1Mechan, Origin Hard Parts of Mammalia, 1889, p. 226.

KINETOGENESIS. 319

guished in sparoid fishes, and in placodont and dia-
dectid reptiles. Canine-like teeth, or pseudo-canines,
appear in clepsydropid and crocodilian reptiles, and
in saurodont fishes. Canine-like incisors appear in
the Clepsydropide. The variety of character in these
structures presented by the Mammalia to be consid-
ered is great, and the principles deduced from obser-
vation of them are applicable to the Vertebrata in
general.

As mechanical causes of the origin of dental modi-
fications, I have enumerated the following :

1. Increase of size of a tooth, or a part of a tooth,
is due to increased use, within a certain maximum of
capacity for increased nutrition.

2. The change of direction and use of a tooth take
place away from the direction of greatest, and in the
direction of least resistance.

3. It follows, from their greater flexibility, that
crests of crowns of teeth yield to strains more readily
than do the cusps.

4. The increase in the length of crests and cusps
in all directions, and therefore the plications of the
same, is directly as the irritation from use to which
their apices and edges are subjected, to the limit set
by the destructive effects of such ‘use, or by the re-
cuperative energy of nutrition.

5. The direction of growth of the branches of a V,
or of the horns of a crescent, will be the direction of
movement of the corresponding parts of the opposite
jaw.

Before giving a review of the various dental types
of Mammalia, I wish to describe some special exam-
ples where the effect of mechanical causes is most ob-
vious. I therefore first repeat the observation of Ryder

320 PRIMARY FACTORS OF ORGANIC EVOLUTION.

as to the origin of the selenodont molars of the Artio-
dactyla; and my own as to the origin of a similar
structure in the molars of certain multituberculate Pro-
totheria. In the former the mastication is ental; in
the latter it is proal, as shown by Osborn.

In the accompanying figure from Ryder the move-
ments of the lower jaw in mastication of lophodonts,
are diagrammatically represented. @ represents the
movement in Carnivora, and in the orthal bunodonts,
as the pigs. 4 shows a slight lateral movement be-
lieved by ee to exist in the wart hog (Phacoche-

MNOS

Fig. 88.—Diagram of excursion of lower jaw in mastication; from Ryder;
a-b, orthal; c-/, ental.

rus). ¢ represents the movement in kangaroos, pha-
langers, and tapirs. Ind a theoretical intermediate
movement is represented, such as Ryder supposed to
have characterized the Anchitherium. In ¢ the usual
movement among ruminants is depicted, as is seen in
the deer, etc. In / the wider excursion of the jaw is
that seen in the giraffe, camel, and ox. In these move-
ments from 4 to f, the lower jaw is moved transversely
across the upper jaw from one side to the other.
Some of the Diplarthra masticate on one side of the
jaw when performing this movement, and some on the
other. That is, in passing the lower jaw across the
face of the upper, some masticate the food on the side

KINETOGENESIS. 321

where the external face of the lower jaw crosses the
upper jaw from within outwards (ental); while in other
types the food is masticated on the side where the
lower jaw passes the external edge of the upper jaw
from without inwards (ectal). While masticating with
one side of the jaws, the opposing dental series of the
other side are not in contact. All mutual effect of the
teeth of one jaw on the other could therefore appear
on the side temporarily used for mastication only.
Among recent Un-
gulata the rumi-
nants present the
ental mastication ;
the rhinoceros and
horses, the ectal ;
and rodents, the
proal. Ryder is of
the opinion that the
mastication of the
Proboscidia is pali-

nal, but I have not Fig. 89.—Cervus, molars: a, superior, exter-

been able to satisfy nal view ; 4, do. inferior view; c, inferior molars,
superior view; from Ryder.

myself of this.

When the crests of the inferior molars were devel-
oped, their relation to the crests of the superior molars
was always anterior in mastication. That is, the in-
ferior crest, in the closing of the jaw, collides with the
crest of the upper molar, with its posterior edge against
the anterior edge of the latter. This is because: first,
as to position, the two anterior cusps of the lower
molar are the remains of the anterior triangle which
fit originally between two superior molars, and: be-
cause, in the closing of the jaw, these cusps continue
to hold that position ; and second, as to function, be-

322 PRIMARY FACTORS OF ORGANIC EVOLUTION.

cause the canine in the ungulate series diminishes in
size, and does not, therefore, draw the inferior molars
forwards by wedging on the superior molar, as in the
Carnivora, but allows free scope to the posterior trac-
tion of the temporal muscle in its exercise on the lower
jaw.

In those forms which masticate from the inside out-
wards (the ental type), the cusps of the inferior molars,
passing between those of the superior molars, would
tend to flatten the sides on which they exerted fric-
tion, and to extend those sides outwards beyond the
median apex of the cusp. (Fig. 90.) The result would
be, and taking into view the yielding of the tissue to

Fig. g90.—Cusps of superior premolars and molars: a, external cusps of
molar of Sarcothraustes; 4, of Phenacodus; c, of Anthracotherium; d, of
Oreodon; ¢, half of inferior molar of Cervus; /, superior premolar of Cory-
phodon; from Ryder.

such strain, has been, to modify the shape of the cusp
by pushing its side walls, so that a horizontal section
of it would become successively more and more cres-
centic. The effect on the inferior teeth would be to
produce the same result in their external cusps, but in
the opposite direction. The sides of the cusps would
be pushed inwards, past the apex, giving a crescentic
section more or less perfect, as the operation of the
cause had been of long or short duration. The result
of the lateral movement in mastication may be under-
stood by reference to the accompanying cut, Fig. gr.
The external crescents of the inferior molars (4) are
seen to pass between the internal crescents of the

KINETOGENESIS. 323

superior molars (2). The mutual interaction and effect
on the form of the crescents may be readily under-
stood. In Fig. go the successive stages of this effect

Fig. 91 —Two true molars of both jaws of a ruminant: @, superior molars,
their inner crescents; 4, inferior molars, their external crescents; the arcs
show directions of motion of jaws in mastication; from Ryder.
on one or two cusps may be seen, beginning with a
cone (@) and terminating with crescents (¢/). Thus is
the origin of the selenodont dentition of the highest

Fig. 92.Transverse vertical sections of superior molar teeth, showing
transition from bunodont (4) type to lophodonts (8, C). A, Sus erymanthius.
B, Ovis amaltheus. C, Bos taurus, From Gaudry. Letters: d, dentine; e,

enamel; c, cementum.

artiodactyle explained by Ryder, and, I believe, cor-
rectly.

Kowalevsky and I have shown that the types with
selenodont (crescent-bearing) molars, have descended

324 PRIMARY FACTORS OF ORGANIC EVOLUTION.

from tubercle-bearing (bunodont) ancestors. This de-
scent has witnessed an increased depth of the infold-
ing of the crown, as represented in the accompanying
figure. Now, in the table of masticatory types above
given it is shown that in the bunodont type of the
Suoidea the mastication is orthal, and a gradual in-
crease in the length of! the lateral excursions of the
lower jaw has been shown to have resulted in the ental
mastication. Thus has structure kept pace with func-
tion in the evolution of the selenodont dentition.

Fig. 93.— Chzrox plicatus Cope, palate and molar teeth from below, three-
halves natural size. From Puerco bed of New Mexico. From American Nat-
uralist, 1887, p. 566.

The general structure of the dentition in the Proto-
theria Multituberculata is similar to that of the Glires.
The incisors in the Plagiaulacide, Chirogide, and Poly-
mastodontide have structure and functions generally
similar to those of that order. The result in the
form and function of the molar dentition has been sim-
ilar to that observed in the Glires. The postglenoid
process is probably absent in these animals; in any
case the mandibular condyle is rounded, and is not
transverse. Prof. H. F. Osborn has pointed out to
me that mastication was performed by a fore-and-aft

KINETOGENESIS. 325

movement of the inferior molars on the superior in
Plagiaulacide. This was no doubt the case in the
other families named. The molar teeth of the lower
types, as Tritylodon from the Trias, present conical
tubercles in longitudinal series, two in the lower and
three in the upper jaw. The two series of the lower
jaw alternate with the three in the upper jaw, moving
in the grooves between the latter, while the three se-
ries of the upper molars reciprocally embrace the two
of the lower molars. This is demonstrated by the
mutual wear of the tubercles
seen in Ptilodus and Chirox
(Fig. 93). The trituration
was probably the same in Tri-
tylodon, but in Polymastodon
the increased thickening of
the tubercles prevented their
interlocking action in masti-
cation. In this genus the tu-
bercles slid over each other, Fig. 94.—4, Meniscobssus conquis-
and truncated the apices i eae a oT
until in old specimens they twicenatural size. B, Meniscoéssus,
were entirely worn away. In second species, from Osborn.

Meniscoéssus (Fig. 94) and Stereognathus we have an
interesting illustration of the effect of the action of
cusps on each other when under prolonged mutual
lateral thrust. Their external sides have been drawn
out into angles in the direction of thrust, converting
their transverse sections from circles to crescents. As
the thrust is in the Multituberculata longitudinal, the
crescents are transverse to the axis of the jaw. Inthe
selenodont Artiodactyla, where the thrust is transverse
to the line of the jaw, the crescents are longitudinal.
That similar effects should accompany similar move-

326 PRIMARY FACTORS OF ORGANIC EVOLUTION.

ments in two groups of Mammalia so widely separated
as these two is strong evidence in favor of the belief
that the two facts stand in the relation of cause and
effect.

I now present an example of the effect of strain, as
shown by the direction of the inferior incisors of the
lemurine Quadrumana. These teeth project horizon-
tally from the extremity of the mandible, so as not to
oppose the superior incisors, in consequence of which
they are useless as organs of prehension. But they

Fig. 95.—Lemur collaris, dentition from below and above; natural size;
original.

are used by their possessors as a comb for the fur,
drawing them from below upwards when thus employ-
ing them. The strain is always in one direction, and
must have resulted in developing the procumbent posi-
tion which they now display (Fig. 95). This is a di-
rect deduction from the fact that the incisor teeth are
similarly displaced by the pressure of the tongue in
cases of the abnormal enlargement of that organ in
man.

I now describe the general character of mammalian
dentition, with the view of pointing out how strong, in

KINETOGENESIS, 327

the light of the facts already cited, is the evidence of
their origin through mechanical strains and impacts.

a. The Origin of Canine Teeth.

The origin of canine, pseudo-canine, and canine-
like incisor teeth is due to the strains sustained by
them on account of their position in the jaws at points
which are naturally utilized in the seizing of prey, or
the fighting of enemies. In some reptiles (Dimetro-
don) the end of the muzzle has been utilized ; in croco-
diles, the side of the jaw; while the intermediate
position has been most used by Mammalia. The rea-
son why the canine instead of the incisor teeth have
been selected by carnivorous Mammalia for prehensile
purposes is not at present clear to me. In accordance
with Rule I., its increased size has been due to the
especial and energetic strains to which it has been
subjected while in use as a prehensile or offensive
weapon, when buried in the body of its prey or enemy.
The superior canine would acquire larger size earlier
in time than the inferior canine, since it bears the
greater part of such strain, as attached to the more
fixed head and body of its possessor. The anterior
teeth of the lower jaw would be less available for use,
since they offer weaker and less fixed resistance to the
opposing body. That the first tooth behind the canine
was not generally enlarged is (under I.) due to the
fact that its posterior position prevents it from having
the same amount of use, and experiencing the strain
that a tooth more anteriorly placed necessarily re-
ceives. It is excluded from considerable use by the
projecting muzzle above and in front of it. That it
was not drawn out into a horizontal position was due
to the presence of teeth anterior to it.

328 PRIMARY FACTORS OF ORGANIC EVOLUTION.

That the increased size of canine teeth is due to
strains is strongly indicated by the huge development
of these teeth in the walrus. This animal uses its ca-
nines for the breaking of ice, and for lifting itself from
the water on to the edge of strong ice. The fact that
canines and not incisors have been thus developed is
a necessary result of the fact that the walrus is a de-
scendant of a line of animals which had already re-
duced incisors and larger canines.

Fig. 96.—Esthonyx burmeisterii Cope, dentition: @, profile; 4, superior;
c, inferior dentition, grinding faces. Reduced.

6. Development of the Inctsors.

The history of the incisor teeth of the Mammalia
exhibits three processes, viz.: hypertrophy (e. g.
Glires), specialization (e. g. Galeopithecus, Lemur-
ide), and atrophy (e. g. Bodidea, Phacochcerus, Glos-
sophaga, etc.).

KINETOGENESIS. 329

Of hypertrophy we have two types: the first repre-
sented by the Glires, Multituberculata, Tillodonta and
their ancestors; and second, by the Proboscidia, the
narwhal and certain Sirenia. As the uses of the inci-
sors present two types corresponding with their struc-
ture, we have ground for believing the uses in question
to have been the efficient agent in producing the lat-
ter. Esthonyx furnishes us with an example (Fig. 96)
where all the incisors are present in the lower jaw, and

Fig. 97.—Psittacotherium multifragum Cope, mandibular ramus, one-half
natural size; «, profile; 4, from above.

where the function of one pair of them (the second)
has evidently been partially rodent in character; that
is, it has served as a scraper and gouger of food sub-
stances. Persistent use has apparently developed the
size of this pair of teeth, until we find in Psittacothe-
rium (Fig. 97) they have reached a greater efficiency,
and that the external incisors of the lower jaw have
disappeared. This disappearance can be accounted
for on the ground of disuse, a retirement from service
due to position, and the increased growth of incisor

330 PRIMARY FACTORS OF ORGANIC EVOLUTION.

No. 2. In Calamodon the first incisor has become ru-
dimentary from the same cause, and in Anchippodus
it has disappeared altogether, leaving a truly rodent
incisor dentition, consisting of the second incisors
only, in the lower jaw. Continued use as chisels has
developed these teeth to the great proportions seen
in such Glires as Castoroides, etc. (Fig. 107).

The use which the Proboscidia and Sirenia (Hali-
core) give their incisors, is, from a mechanical point
of view, like that which the Carnivora give their ca-
nines ; that is, it consists of impacts in the long axis,
and strains transverse to the long axis of the tooth.
The elephants use their tusks for prying up the vege-
tables on which they feed, or for pushing aside the
vegetation through which they wish to pass. The an-
cestors of the Proboscidia are not certainly known,
but they possessed incisors of enlarged proportions,
such as we find in the Toxodontia and other late rep-
resentatives of some of the primitive Ungulata. Use
of such teeth in the manner referred to, without oppo-
sition from the inferior incisors, will account for the
tremendous proportions which they ultimately reached
in some of the species of Elephas.

The use made by the narwhal of its single huge
superior incisor, that of an ice-breaker, indicates the
origin of its large dimensions. So with the straight
incisors of the hippopotamus; use as diggers has
straightened them to a horizontal from their primitive
vertical direction, a change which is also partially ac-
complished in the true pigs (Sus).

In the Sirenian genus Halicore the upper incisors
have been used in excavating vegetable growths from
the banks and bottom of shallow seas. The transition
from three incisors (Prorastomus) to two (Dioplothe-

KINETOGENESIS. 331

rium), and to one (Halicore), is identical with what
has taken place in the Proboscidia and Glires, and
has resulted in the production of an effective digging-
tool. In other genera it may be supposed that their
habits of browsing on soft growing materials did not
necessitate the use of digging incisors, hence these
teeth became atrophied, as in the manatee and Rhy-
tina.
c. Development of Molars.

In fishes and reptiles where teeth occasionally pre-
sent very primitive conditions, the theory of the origin
of particular types of molar teeth is more simple than
in the case of Mammalia. The observations of Hiiter
on the action of osteoblasts under stimulus show that
under moderate irritation osseous tissue is deposited,
while under severe pressure osseous tissue is removed.
Koelliker has shown that the action of these bodies is
the same in dentine as intrue bone. Hence modifica-
tions of dental structure must stand in close relation to
the uses to which they are put. Thus severe pressure
on a simple tooth crown would, if long continued, cause
it to expand laterally, or in the direction of least re-
sistance, and to grow but little in its vertical axis, i. e.,
in the direction of greatest resistance. The molar
teeth have been subjected to much more severe direct
irritation from use than any others in the jaws, and
this will account for their increased diameters.

In the case of the eutherian Mammalia, molar teeth
are not traceable back to ancestral types of reptilian mo-
lars, but to simple conic (haplodont) reptilian teeth.
The process of the evolution of the complex mamma-
lian molars from these, forms the subject of a paper in
the American Journal of Morphology for 1889, from which
I quote extensively in the present work.

332 PRIMARY FACTORS OF ORGANIC EVOLUTION.

I have there shown that the greater number of the
types of this series have derived the characters of their
molar teeth from the stages of the following succes-
sion. First a simple cone or reptilian crown, alternat-
ing with that of the other jaw (haplodont type). Sec-
ond, a cone with lateral denticles (the triconodont
type). Third, the denticles to the inner or outer side
of the crown, forming a three-sided prism, with tritu-
bercular apex, which alternates with that of the oppo-
site jaw (tritubercular type). Fourth, development of
a heel projecting from the posterior base of the lower
jaw, which meets the crown of the superior, forming a
tuberculosectorial inferior molar. From this stage
the carnivorous and sectorial dentition is derived, the
tritubercular type being retained. Fifth, the develop-
ment of a posterior inner cusp of the superior molar
and the elevation of the heel of the inferior molar,
with the loss of the anterior inner cusp. Thus the
molars become quadritubercular, and opposite. This
is the type of many of the Taxeopoda, including the
Quadrumana and Insectivora as well as the inferior
Diplarthra. The higher Taxeopoda (Hyracoidea) and
Diplarthra; add various complexities. Thus the tu-
bercles become flattened and then concave, so as to
form V’s in the section produced by wearing ; or they
are joined by cross-folds, forming various patterns. In
the Proboscidia the latter become multiplied so as to
produce numerous cross-crests.

@. Origin of the Carnivorous Dentition.

The anterior cusplet of the triconodont crown is
(Fig. 98 A), in the upper jaw, the paracone, and in the
lower jaw the paraconid ; and the posterior cusplet is
the metacone or metaconid, respectively. As the prin-

KINETOGENESIS. 333

cipal cusps, or protocone and protoconid, alternate with
each other, the cusplets stand opposite to them in the
closing of the jaws, and a certain amount of interfer-
ence results. As the lesser cusps are the less resistant
to the wedging pressure of such contact, their position
would change under its influence, rather than the large
central cusps. The lower jaw fitting within the upper,
the effect of the collision between the major cusps of
the one jaw, and cusplets of the other, would be to
emphasize the relation still more ; that is, the cusplets
of the upper jaw would be wedged outwards, while
those of the lower jaw would be pressed inwards, the
major cusps retaining at first their original alternate
position. With increase of the size of the teeth the
cusps would soon assume in each jaw a position more
or less transverse to that of the other jaw, producing,
as a result of the crowding, a crown with‘a triangular
section in both. The process may be rendered clear
by the following diagram :

_: 2Q@okR Wc OQ'‘on

ses BUAY

B
Fig. 98.—Diagrammatic representations of horizontal sections of tricuspi- ‘
date molars of both jaws in mutual relation; the shaded ones represent those
of the upper jaw: A, Triconodon; &, Menacodon; C, ideal tritubercular mo-
lars, approached by Menacodon, B.

It is supposed on the contrary by Rése and Kiken-
thal that mammalian molars which support more than
one cusp have been formed by the fusion of several
simple reptilian cones. So far as regards the higher
Mammalia this hypothesis is in opposition to all the
facts of paleontology and is not worthy of discussion.

334 PRIMARY FACTORS OF ORGANIC EVOLUTION.

The only question that can arise is with reference to.
’ the origin of the multituberculate molar of the'Proto-
theria.

It is further questioned by Forsyth-Major, whether
the tritubercular molar has been derived from the tri-
conodont. He believes, on the contrary, that it is de-
rived from the multitubercular type by reduction.
There are two objections to this view: (1) the cones
of the tritubercular tooth or trigon should be subequal,
were they derived from a multitubercular source. On
the contrary, the two external cones of the upper, and
the two inner cones of the lower series are in the
earliest (Jurassic), as well as most of the tritubercular
types, smaller than the single opposite cusp or proto-
cone, precisely as are the anterior and posterior cones
of the triconodont molar. (2) No paleontologic series
from the multitubercular to the tritubercular types has
been traced, while the series from the.triconodont to
the tritubercular is well known. Forsyth-Major’s evi-
dence that such a transition exists in the Glires, is
better explained by tracing the moderate complexity
he describes to a tritubercular origin.

It is also alleged by Allen and Scott that the inter-
nal cusps of the premolars, when present, originate by
the development of internal cingula, and have no prim-
itive tritubercular ancestry. The evidence at our dis-
posal from paleontological sources is in favor of this
view; hence it is reasoned that the history of the mo-
lar teeth must have been identical. This however does
not follow, especially as the paleontologic evidence
points the other way. The history of the two series
has been different. In the first place the premolars
have been subjected to much less use than the true
molars; hence they retained the primitive reptilian

KINETOGENESIS. 335

simplicity for a much longer period, a simplicity which
they retain in the Carnivora, except the 1, which be-
came the sectorial. Secondly, the premolars, instead
of increasing in size, have in many types decreased ;
the Diplarthra alone presenting an exception to this
rule. That the internal cusps of the premolars may
have arisen by growth of cingula in this order, is by no
means improbable. We seem to have here an excel-
lent illustration of the origin of two identical struc-
tures by different evolutionary routes.

The first modification of the tritubercular molar of
the lower jaw is the addition of a low cingulum at the
posterior base. This is seen in a rudimentary condi-
tion in various living species of the Centetide and
Chrysochloridz of the insectivorous order (Fig. 100);
but in these existing forms the superior molar has
added a posterior cingulum also, which widens inter-
nally, or towards the palate (Fig. 101). In the evolu-
tion of the dentition, the inferior posterior cingulum,
or ‘‘heel,” was developed first, as in the Deltatherium,
Centetes, and Stypolophus (Figs. 9g, 100, 102), where
it is quite large; while the superior cingulum is want-
ing in Stypolophus and Didelphodus, but is present in
a very rudimentary condition in De/tatherium fundamt-
nis. Inallof these genera the external cusps of the
superior series have been pressed inwards, and more
or less together, and are therefore removed in this re-
spect from the primitive condition. The more primi-
tive state of the superior cusps is seen in some species
of Mioclenus, where, however, a posterior cingulum
may be developed. The primitive type of tritubercular
superior molar is that of Sarcothraustes, and in the
same genus the inferior molar only differs from the
primitive type in having a well-developed heel. Among

336 PRIMARY FACTORS OF ORGANIC EVOLUTION.

recent Mammalia the carnivorous and insectivorous
Marsupialia generally have the tritubercular lower mo-
lar with heel. In the Chiroptera and many Insectivora
the heel is largely developed, and supports two cusps,
as it does in some Creodonta.

eo780 Set tteey,
. a
; mee,

Fig. 99.—Deltatherium fundaminis Cope, fragmentary skull, two-thirds
natural size; from the Puerco bed of New Mexico. a, 4, c, from one individ-
ual; @, from a second animal; a, right side of cranium; 4, palate from be-
low; c, mandible, part from above; d@, left ramus, outer side; from the Re-
port of the U.S. Geol. Surv. Terrs., Vol. UI.

From this point the evolution of the tritubercular
molar must be considered from two standpoints. The
first is the mechanical cause of the changes of its form ;
and the second is the mechanical cause of its definite

KINETOGENESIS, 337

location in a particular part of the jaw. For it has
been already stated that in the evolution of the secto-
rial dentition of the Carnivora, the number of molars
and premolars has considerably diminished, while
those that remain have become relatively much larger.

In the tritubercular dentition the crowns proper of
one jaw alternate with those of the other (Fig. 100);
but when heels are added in either jaw, they will op-
pose such part of the crowns of the teeth in the oppo-

Fig. 100,—Centetes ecaudatus: A, skull, side seen obliquely from below;
B, superior molars from below; C, inferior molars from above.
site jaw as comes in contact with them when in use.
The development of the heel in the inferior molars
produced a type which is known as the tuberculosec-
torial. This type characterizes the Creodonta and a
few Carnivora. In the former there are generally
three such teeth, in the latter but one.

In the tuberculosectorial type of inferior molar the
primitive tritubercular part of the crown (trigonid of
Osborn) stands principally anterior to the posterior

338 PRIMARY FACTORS OF ORGANIC EVOLUTION.

root of the tooth. It appears that the posterior root
has been extended backwards, so as to occupy a posi-
tion below the middle of the superior molar, while the
tritubercular crown has been confined to the space be-
tween the crowns of the superior molars. This would
follow of necessity from the alternating action of the
crowns of the opposite series, in connection with a
general increase in size of the teeth. In the opening of

prt

Fig. 101.—Series of inferior molar crowns representing the transition from
the simple (haplodont) to the quadritubercular, From Osborn.

the jaws in a Creodont, the elevated portion of the in-
ferior crown shears by its posterior face against the
anterior face of the superior molar, thus restraining its
extension posteriorly. The stimulus of use, however,
develops a low extension posteriorly, or a heel, which
covers the posterior root, and opposes in mastication
the internal extremity or tubercle of the crown of the
superior molar above it. Thus a molar element in

KINETOGENESIS. 339

mastication is added to the sectorial in some Creodonta,
and in Canide and Urside, etc., among Carnivora.
This function predominates over that of the anterior
triangle in the Lemuride. (Fig. 95.)

I have already pointed out the successive modifica-
tions of form which have resulted in the existing spe-
cialized single inferior sectorial tooth of the Felide.
They consist in the gradual obliteration of the poster-
ior-internal cusp, and of the heel, and the enlargement
of the external and anterior internal tubercles of the
primitive triangle. The modification in the character
of the dentition taken as a whole was shown to consist

Fig, 102.—Stypholophus whitie Cope; diagram representing the apposition
of the inferior and superior molars. The superior are in light, the inferior
in heavy lines. The numbers represent the molars and premolars: C, canine;
poc, protocone; fac, paracone; wc, metacone; POC, protoconid; PAC, para-
conid ; C, metaconid ; 4c, hypocone; HC, hypoconid.
in the reduction of the number of the teeth, including
the sectorials, until in Felis, etc., we have almost the
entire function of the molar series confined to a single
large sectorial in each jaw.

The genesis of the superior sectorial tooth has
been explained as follows. In consequence of the
fact that the lower canine tooth shuts anterior to the
superior canine, the result of the enlargement of the
diameters of those teeth will be to cause the crowns
of the inferior teeth to be drawn from behind forwards
against those of the superior teeth when the jaw is
closed (Fig. 102). Thus a shearing motion would re-

340 PRIMARY FACTORS OF ORGANIC EVOLUTION.

sult between the anterior external edge of the lower
triangle and the posterior internal edge of the superior
triangle. Now the characters of the true sectorial teeth
consist in the enormous extension of these same edges
in a fore and aft direction, the inferior shutting inside
of the superior. To account for the development of
these blades we must understand that the oblique pres-
sure of the front edge of the lower tooth, on the hind
edge of the superior tooth, has been continued for a
very longtime. We must then observe that the inter-
nal tubercle of the superior triangle has been pushed
continually forwards and been reduced to a very small
size. Why should this occur? Why should not the
corresponding tubercles of the inner side of the lower
crown have been pushed backwards, since action and
reaction are equal? The reason is clear: The superior
tubercle is on the internal apex of the trigon, and is
supported by but one root, while the resistant portion
of the inferior crown is the base of the trigonid, and
is supported by two, thus offering twice the resistance
to the pressure that the superior does. But why should
the anterior part of the inferior tooth move forwards?
even if it be in the direction of least resistance? This
is due to the regular increase in size of the teeth them-
selves, an increase which can be traced from the be-
ginning to the end of the series. And this increase is
the usual result of use (Fig. 102).

The mechanics of the above proposition I believe
to be correct, but I have had occasion to modify the
statement as to the initiatory cause of the process. In
many primitive Ungulata the canines have been as
well developed as in the Carnivora, yet the forward
pressure of the inferior molars on the superiors has
not resulted, or has not been sufficient to produce sec-

KINETOGENESIS. 341

torial molars in those types. In the Amblypoda, the
lower molars even shear backwards on the upper ones.
It seems then that this growth of the canines is not in
all instances sufficient to cause a proterotome masti-
cation. I suspect that the more usual cause is to be
found in the voluntary effort of the primitive flesh-
eater, to masticate flesh by the manipulation of his
lower jaw and the body to be divided. The presence
of the inferior canine forbids a posterior shearing move-
ment of the molars, so that the anterior shear is the
only one possible to most of the Creodonta. The ab-

Fig. 103.—Cynodictis geismarianus Cope; skull one-half natural size: w,
right side; 4, left side from below.

sence of preglenoid crest in primitive Creodonta will
permit a manipulation such as we observe in various
ungulates to-day. The formation of a habit of a pro-
terotome mastication would result, and the structural
results would succeed as above pointed out.

The excess of the forwards pressure of the inferior
teeth against the superior over any backwards pres-
sure, has left the posterior internal cusp of the triangle
of the inferior molar (metaconid) without contact or
consequent functional use. It has, consequently, grad-
ually disappeared, having become small in the highest

342 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Canidz, and wanting in some Mustelide, and all Fe-
lide. The heel of the same tooth has had a similar
history. With the diminution in size of the first supe-
rior tubercular, with which it comes in opposition in
mastication, its functional stimulus also diminished ;
and it disappeared sometimes a little sooner (Felide)
and sometimes a little later (Hyznidz) than that tooth.

The specialization of one tooth to the exclusion of
others as a sectorial, appears to be due to the follow-
ing causes. It is to be observed in the first place that
when a carnivore devours a carcass, it cuts off masses
with its sectorials, using them as shears. In so doing

Fig. 104.—Aelurodon sevus Leidy; diagram representing coadaptation of
crowns of superior and inferior molars in mastication; lines and lettering as
in Fig. 102.

it brings the part to be divided to the angle or canthus
of the soft walls of the mouth, which is at the front of
the masseter muscle. At this-point the greatest amount
of force is gained, since the weight is thus brought
immediately to the power, which would not be the case
were the sectorial situated much in front of the mas-
seter. On the other hand, the sectorial could not be
situated farther back, since it would then be inacces-
sible to a carcass or mass too large to be taken into
the mouth.

The position of the sectorial tooth being thus shown
to be dependent on that of the masseter muscle, it re-
mains to ascertain a probable cause for the relation of

KINETOGENESIS. 343

the latter to the dental series in modern Carnivora.
Why, for instance, were not the last molars modified
into sectorial teeth in these animals, as in the extinct
Hyznodon, and various Creodonta. The answer ob-
viously is to be found in the development of the pre-
hensile character of the canine teeth. It is probable
that the gape of the mouth in the Hyznodons was
very wide, since the masseter was situated relatively
far posteriorly. In such an animal the anterior parts
of the jaws with the canines had little prehensile power,
as their form and anterior direction also indicates.
They doubtless snapped rather than lacerated their
enemies. The same habit is seen in the existing dogs,
whose long jaws do not permit the lacerating power
of the canines of the Felidz, though more effective in
this respect than those of the Hyznodons. The use-
fulness of a lever of the third kind depends on the ap-
proximation of the power to the weight ; that is, in the
present case, the more anterior the position of the
masseter muscle, the more effective the canine teeth.
Hence it appears that the relation of this muscle to
the inferior dental series depended originally on the
use of the canines as prehensile and lacerating organs,
and that its relative insertion has advanced from be-
hind forwards in the history of carnivorous types.
Thus it is that the only accessible molars, the fourth
above and the fifth below, have become specialised as
sectorials, while the fifth, sixth, and seventh have,
firstly, remained tubercular as in the dogs, or, sec-
ondly, have been lost, as in hyenas and cats.

The reduction of the number of molars in relation
to the increase in the size of the canines commenced
as early as the Jurassic period. It is seen in the gen-
era Triconodon (Owen) and Paurodon (Marsh), where

KINETOGENESIS. 345

the canines are large and the molars few. In the
Plagiaulacide a similar relation is: seen between the
development of the incisors and the reduction in num-
ber of the molars. This is the modification of relation

From Gaudry.

Fig. 106.—Sections of crowns of molars of Ungulata from Dinotherium to Eiephas

primigenius, A,B, Dinotherium; C, D, Mastodon; Z, /, G, Elephas.

observed in existing Mammalia of the orders Probos-
cidia and Glires, which will be mentioned later, under
the head of proal dentition.

e. Origin of the Dental Type of the Glres.

The peculiarities of the rodent dentition consist, as is
well known, in the great development of the incisors ;

346 PRIMARY FACTORS OF ORGANIC EVOLUTION.

the loss of the canine and of all but one, or rarely of
two, of the premolars, which leave a wide diastema ;
and the posterior position of the molar teeth, as relates
to the rest of the skull. A peculiarity which belongs to
the highest types of the order is the prismatic form of
the molars, and the deep inflection of their always
transverse enamel folds both laterally and vertically.
A peculiarity of the masticating apparatus, which is the
basis of distinction from the bunotherian order, is the
lack of postglenoid process, and the consequent freedom
of the lower jaw to slide backwards and forwards in
mastication. Appropriately to this motion the condyle
of the mandible is either subglobular, or is extended
anteroposteriorly, and the glenoid cavity is a longitudi-
nal instead of a transverse groove.

The mechanical action of the development of the
rodent dentition has been as follows. The first factor
in the order of time and importance was the increasing
length of the incisor teeth. Those of the lower jaw
closed behind those of the upper in the progenitors of
the Glires (e. g. Psittacotherium) as in other Mamma-
lia. Increase of length of these teethin both jaws would
tend to keep the mouth permanently open, were it not
for the possibility of slipping the lower jaw backwards
as it closed on the upper. This backward pressure
had undoubtedly existed, and has operated from the
earliest beginning of the growth of the rodent incisors.
The process has been precisely the opposite of that
which has occurred to the Carnivora, where the pres-
sure has been ever forwards owing to the development
of the canines. The progressive lengthening of the
incisors through use has been dwelt on by Professor
Ryder (2 ¢.). The posterior pressure on the lower
jaw, produced by its closing on the upper, has been

KINE TOGENESIS. 347

increased directly as the increase in the length of the
incisors, especially those of the lower jaw.

The first effect of this posterior pressure will have
been to slide the condyle of the mandible posteriorly

ae
:

ng ramus: c,
; e, foramen infraorbitale; from Hall and Wyman.

over the postglenoid surface, if any were present, as is
probable, in the bunotherian ancestor of the rodent.
Continued repetition of the movement would probably
push the process backwards so as to render it ineffec-
tive as a line of resistance, and ultimately to flatten it

348 PRIMARY FACTORS OF ORGANIC EVOLUTION.

out against the otic bulla, and atrophy it. The lower
jaw would thus come to occupy that peculiarly pos-
terior position which it does in all rodents.

The anteroposterior (proal!) type of mastication
becoming necessary, an appropriate development of
the muscles moving the lower jaw, with their inser-
tions, follows, parz passu. As a result we see that the
insertion of the temporal muscle creeps forward on the
ramus, until in the highest rodents (Cavia) it extends
along the ramus to opposite the first true molars. The
office of this muscle is to draw the ramus backwards
and upwards, a movement which is commenced so
soon as the inferior incisor strikes the apex of the su-
perior incisor on the posterior side. By this muscle
the inferior molars are drawn posteriorly and in close
apposition to the superior molars. Connected with
this movement, probably as an effect, we find the co-
ronoid process of the mandible to have become grad-
ually reduced in size to complete disappearance in
some of the genera, e. g. of Leporidz. In these gen-
era the groove-like insertion of the temporal muscle
develops as the coronoid process disappears.

As third and fourth effects of the posterior position
of the lower jaw, we have the development of the in-
ternal pterygoid and masseter muscles and their inser-
tions and origins. The angle of the ramus being forced
backwards, these muscles are gradually stretched back-
wards at their insertions, and their contraction be-
comes more anteroposterior in direction than before.
The internal pterygoid becomes especially developed,
and its point of origin, the pterygoid fossa, becomes
much enlarged. The border of the angle of the man-
dible becomes more or less inflected. In their effect

1Page 318.

KINETOGENESIS. 349

on the movements of the ramus they oppose that of
the temporal muscle, since they draw the ramus for-
wards. They are the effective muscles in the use of
the incisor teeth ; that is, in the opposition of the in-
ferior incisors against the superior from below and
posteriorly. Hence the great development of the in-
ternal pterygoid, and, in a less degree, of the masse-
ter. Both muscles tend also to close the jaws, but at
a different point in the act of mastication from that at
which the temporal acts. If we suppose the mouth
to be open, the action of the masseter and internal
pterygoid muscles draws the mandible forwards and
upwards until the incisors have performed their office,
or the molars are in contact with each other or with the
food. They then relax, and their temporal muscle
continues the upward pressure, but draws the ramus
backwards to the limit set by the adjacent parts, caus-
ing the act of mastication.

A fifth effect of the development of the incisors and
of the proal mastication, is seen in the position of the
molar teeth. The indefinitely repeated strain and
pressure applied to the superior molars from forwards
and below has evidently caused a gradual extension of
the maxillary bone backwards, so that the last molars
occupy a position much posterior to that which they
do in other orders of mammals. This is especially the
case in such forms as Bathyergus, Arvicola, and Cas-
toroides (Figs. 107-108), where the last molars are be-
low the temporal fossa, and posterior to the orbit.

A sixth effect of the causes mentioned has been re-:
ferred to by Ryder.!. This is the oblique direction of
the axes of the molar teeth. These directions are op-
posite in the two jaws ; upwards and forwards for the

1 Proceedings Philadelphia Academy, 1877, Pp. 314.

350 PRIMARY FACTORS OF ORGANIC EVOLUTION.

lower, and downwards and batkwards for the upper.
The mechanics of this change of direction from verti-
cal in the primitive forms (Sciuridz) to oblique in the

Fig. 108 —Castoroides ohioensis Foster ; two-thirds natural size; skull from
below. a, incisine foramen; 4, pterygoid fossa; c, internal pterygoid plates;
d, fossa in basioccipital bone; ¢, external auditory meatus; /, mastoid pro-
cess; g, occipital condyles; 4, tympania bulla, after Hall and Wyman.

genera with prismatic molars, is simple enough. The
inferior crowns when closely appressed to the supe-
rior, and drawn posteriorly in the direction of the long
axis of the jaw, press and strain the teeth in the two

KINETOGENESIS, 351

directions mentioned. The development of the long
prismatic crowns which has proceeded under these
circumstances, has been undoubtedly affected by the
pressure and strain, and the direction we find has been
the result.

The seventh effect is in the detailed structure of
the teeth themselves. Beginning with short crowns
with simple transverse crests (Psittacotherium and Sci-
uride, Figs. 106, 109),
we reach through inter-
mediate forms, crowns
with vertical lamine of
enamel, which some-
times divide the crown
entirely across (Chinchil-
lide, Caviide, Castoroid-
ide) or appear only on
the side of the crown,
through the - continued
coalescence of the prisms
of which each molar
crown is composed (Arvi-

Fig. 109.—Jschyromys typus Leidy, from
3 the White River beds of Colorado; orig-
cola). In many instances inal; from the Report U.S. Geol. Surv

Terrs.: b, cranium from below; @, man-

the crowns increase iN 4:10 from above.

transverse at the expense

of their longitudinal diameter (Castor, Lepus). The
vertically laminated structure is evidently due to the
crowding together of transverse crests by the same
pressure which has given the crowns their oblique di-
rection. In many genera the lengthening of the crown
has included the lengthening of the longitudinal con-
nection between the transverse crests, as in Arvicola,
Castor, and Hystricide generally. In others this con-
nection has not been continued, so that the crown is

‘

352 PRIMARY FACTORS OF ORGANIC EVOLUTION.

composed of prisms which are separate to near the
base, as in Amblyrhiza and Geomyidz. In others, con-
nection between the prisms has been lost by cenogeny,
as in Chinchillide and Caviide generally. The latter
families display also the greatest amount of crowding.

Vv. DISUSE IN MAMMALIA.

Modifications of structure of the mammalian skel-
eton accompany the disuse of parts, no less distinctly
than in other divisions of animals. That these modi-
fications are the direct consequences of this disuse
may be reasonably inferred as the antithesis to the
thesis of development of structure through use, main-
tained in the preceding pages. The evidence is more
convincing from the fact that the same structures are
observed to be related to similar dynamic conditions
in groups of different taxonomic position. I select
four illustrations from the Mammalia, from types in
which the phylogeny is known, so that there is no
question as to the degeneracy of the parts described.

a. Natatory Limbs.

The limbs have undergone great modifications of
form in their gradual adaptation to aquatic habits.
The stages of this process are to be observed first in
the sea-otter (Enhydra), then in the seals, then'in the
sirenians, and last in the Cetacea. This succession
of groups is not given here as a phylogeny, for paleon-
tology does not warrant any such history, but the phy-
logeny of the limbs has been similar in the order of
succession.

The use of a limb as an oar for propulsion in the
water requires that it shall be, so far as the blade is
concerned, inflexible. Such a structure has existed in

KINETOGENESIS. 353

all thoroughly aquatic Vertebrata. This implies the
immobility of the articulations, which is due to the
loss of their condylar surfaces. This may be traced
to disuse of such articulations. This disuse would be
at first voluntary, the limb being held stiffly while used
as an oar in the act of swimming. Loss of power of
extension and flexion. is well
known to result from disuse.
It is well known that the flex-
ors and extensors of the manus
have become atrophied in the
Cetacea. Not so, however,
with the flexors and extensors
of the humerus, which become
those of the entire limb. In
the whales the first segment of
the fore limb is enclosed within
the integument of the body,
so that its motion being much
restricted, the insertional
crests are reduced in size. In
the eared seals (Otariidz) the
hind limbs are somewhat free
from the body integument, so
that they can be turned for- Fig. 110,.—Balena mysticetus
ward when on land. They are oo from Cuvier, Oss, Fos
further enclosed in the true

seals (Phocidz) so that their motion is very slight and
they cannot be used for progression on land, and are
available only for swimming.

b. Abortion of Phalanges in Ungulata.

In the heavy Ungulata the longitudinal diameter
of the phalanges is greatly reduced in relation to their

354 PRIMARY FACTORS OF ORGANIC EVOLUTION.

The successive increase in depression in

the bones of the feet with the advance of time is to be

transverse.

a b ¢

Fig. 111.—a, Pantolambda bathmodon, digit of posterior foot. 4, Right posterior foot of a species of Cory-
phodon from New Mexico, one-half natural size. From Cope, Report Expl. W. of rooth Mer., G. M. Wheeler, IV.,
Pl. LIX. c, Zobastleus mirabilis, right posterior foot; from Marsh, Dinocerata.

most readily seen in the order Amblypoda, where we
pass from Pantolambda to Coryphodon and Uintathe-

KINETOGENESIS. 355

rium (Fig. 111.) A similar successive reduction is to be
seen in the lines of the Perrisodactyla, as we pass from
the smaller and lighter to the heavier and more bulky
types. Such series are those which commence in the
Lophiodontidz, and terminate in the Menodontidz on
the one hand, and the rhinoceroses on the other. The
elephants display the end of a similar line, which com-
mences in the Condylarthra. In all of these bulky
mammals the weight in progression is borne on the
extremities of the metapodial bones, and the phalanges
take but little share in it. They are turned forwards
and are nearly useless. Their great reduction in di-
mensions in these forms appears to me to have fol-
lowed disuse, and this is then the probable cause of it.

c. Atrophy of the Uina and Fibula.

Successive atrophy of the ulna and fibula has been
already referred to (p. 135). This is coextensive with
reduction of the number of the digits in the ungulate
Mammalia, and with the development of the digital
patagium in the bats. This is in broad contrast to the
subequal development of the ulna and radius in the
Cetacea, where the fore limb functions as the blade of
anoar. The cause of the reduction of the two ele-
ments in the Ungulata is the restriction of the func-
tions of the fore and hind limb to the radius and tibia
respectively. The distal extremities of the ulna and
fibula are supported by the external bones of the carpal
and tarsal series respectively. The reduction of the
external digit deprives the external bones in question
of their share in the support of the general weight, and
consequently relieves them of the impact which passes
through the longer median digits which remain. The
median digits, on the other hand, support the radius

356 PRIMARY FACTORS OF ORGANIC EVOLUTION.

and tibia through the medium of the carpus and tar-
sus, and it is these elements therefore which function
in the use of the limb. We have here an evident
illustration of. the effect of disuse in effecting the
atrophy of an element, and of use in increasing the
size and complexity of an adjacent element, of the
same organism. No other explanation seems possible,
for the elements which are reduced and those which
are enlarged, are subjected in every other respect to
the same conditions.

ad. Atrophy of Incisor Teeth.

This is complete in both jaws of existing Edentata ;
the upper jaw of Dinocerata and many Artiodactyla,
and is partial in the upper jaw in various Chiroptera
and Lemuride. We have already seen (p. 326) that
the superior incisors of certain Lemuride are without
utility, owing to the conversion of the inferior incisors
into a horizontal comb. I have ascribed the reduction
of the superior incisors of bats to disuse consequent on
the adoption of a frugivorous diet.1_ Further reason,
which is common to the living members of the orders
mentioned, is to be found in the disuse which has fol-
lowed the use of the tongue as an organ for the pre-
hension of food. The fruit-eating bats with most re-
duced incisors (Glossophaginz) carry the soft parts of
fruits into the mouth with the tongue. The Edentata
use the tongue for the collection of both insect and
vegetable food, projecting it far exterior to the mouth.
The Artiodactyla without superior incisors however,
combine the prehensile use of the tongue with a use of
the lower incisors, which bite off the grass thus seized,

1Mechan. Origin, etc., Mammalia, 1889, p. 224. See also Dr, H. Allen,
Proceeds, Academy, Philadelphia, 1891, p. 451.

KINETOGENESIS, 357

while it is pressed against the pad which replaces the
superior incisors. Why the superior incisors should
have disappeared in this group is not yet clear to my
mind.

In this connection Dr. Allen (/. c.) reminds us that
in hypertrophy of the tongue in man, the inferior in-
cisors are thrown forward and are widely separated
from each other. He considers it reasonable to infer
that in lower animals where the tongue is used for pre-
hension, the similar change which takes place in the
teeth, from a vertical to a horizontal position, is induced
by this cause.

Vi. HOMOPLASSY IN MAMMALIA.

The direct evidence in favor of kinetogenesis above
adduced is greatly strengthened by corroborative tes-
timony presented by distinct phyla of animals. Re-
stricting myself here to Mammalia, I will enumerate a
number of cases where the same structures have ap-
peared in distinct lines of descent under similar me-
chanical conditions, a phenomenon already referred to
on page 72 under the name of Homoplassy.

Before reviewing the subject, I cite what is the
most remarkable example of homoplassy in the Mam-
malia which has yet come to the knowledge of paleon-
tologists. Ameghino has discovered in the Cenozoic
formations of Argentina a group of Ungulata which he
calls the Litopterna, and which I regard as a suborder
of the Taxeopoda, allied to the Condylarthra (p. 128).
Ameghino placed the group under the Perissodactyla,
but the tarsus and carpus are of a totally different char-
acter, and indicate an origin from the Condylarthra
quite independently of that division. The carpal and
tarsal bones are in linear series, or if they overlap, it is in

358 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Fig. 112.Feet of Proterotheriide, from Ameghino. 4, fore foot of Proterotherium cavum Ameghino;

B, C, fore and hind feet of Diadiaphorus majusculus Ameghino ; D.
crepidatum Ameghino, Much reduced.

£, fore and hind feet of Thoatherium

KINETOGENESIS. 359

a direction the opposite of that which characterizes the
order Diplarthra (= Perissodactyla and Artiodactyla).
But the Litopterna present a most remarkable paral-
lelism to the Perissodactyla in the characters of both
the feet and the dentition. No genus is known as yet
which possesses more than three toes before and be-
hind, and these are of equal length in Macrauchenia
Owen. In this genus the teeth are not primitive but
are much modified. The most primitive dentition is
seen in the genus Proterotherium (Ameghino) where
the superior molars are tritubercular as in many Con-
dylarthra. In this genus (Fig. 112, 4), there are three
toes, but the lateral ones are reduced, about as in the
Equine genus Anchitherium (p. 148). In the next
genus, Diadiaphorus Ameghino, the superior molars
are quadritubercular and crested, while the lateral toes
are reduced still more, being quite rudimental (Fig.
112, B, C), as in the equine genera Hippotherium and
Prothippus (p. 149; Fig. 70). The superior molars
have not progressed so far as in these genera, but are
not very different from those of Anchitherium. Inthe
third and last type (Thoatherium Ameghino), the lat-
eral digits have disappeared from both fore and hind
feet (Fig. 112, C, D), so that the condition is that of
the genus Equus (Fig. 81), but the splints in the 7hoa-
therium crepidatum Ameghino are even more reduced
than in the known species of horse. The superior
molars have not assumed the pattern of the genus
Equus, but resemble rather those of Macrauchenia,
and could have been easily derived from those of Dia-
diaphorus.

Here we have a serial reduction of the lateral digits
and their connections with the leg, and increase in the
proportions of the middle digit and corresponding in-

360 PRIMARY FACTORS OF ORGANIC EVOLUTION.

crease in the proximal connections, exactly similar to
that which took place in the horse-line, in a different
order of Mammalia.

In review I now cite as examples of homoplassy:

First, as regards the development of the tongue-
and-groove ankle-joint. This has been developed in-
dependently along four distinct phyla, viz., in the lepo-
rid Glires, the Carnivora, and the even and odd toed
Diplarthra.

Second, the wrist-joint. The faceting of the radial
surface has appeared independently in the perissodac-
tyle and artiodactyle lines, but is best developed in the
latter. Also it appeared independently in the separate
suoid and bo@id lines in the latter suborder.

Third, the trochlear crest of the elbow-joint ap-
peared independently in the perissodactyle and artio-
dactyle Diplarthra, and in the leporid Glires (the rab-
bit family).

Fourth, the round head of the radius appeared in-
dependently in the lines of the Edentata (ant-eater)
and Quadrumana, under the stress of supination of
the hand.

Fifth, the development of cusps with crescentic sec-
tion out of cusps with round section has occurred in
the widely different groups of the multituberculate
Prototheria, and the selenodont Artiodactyla. In the
former the crescents are transverse, since the thrust of
the teeth in use is longitudinal; in the latter they are
longitudinal, since the thrust of the jaws is transverse.

Sixth, the deep plication and hypsodénty of molars
appeared independently in the Glires, Tiliodonta, Pro-
boscidia, Sirenia, Perissodactyla, and Artiodactyla;
and probably in the Edentata and Toxodontia.

Seventh, increase in the length of the legs has en-

KINETOGENESIS. 361

sued in the Marsupialia, Glires (Lepus, Dolichotis,
Dipus), Carnivora, Ungulata, Quadrumana. :

Eighth, reduction of digits has occurred under sim-
ilar conditions in Marsupialia, Glires, Insectivora,
Carnivora, Ungulata.

Ninth, the atrophy of the ulna and fibula occur in
the distinct lines of the Perissodactyla and Artiodac-
tyla, and the atrophy of the fibula in the leporid
Glires ; all in limbs which function in the most rapid
progression.

Further confirmation of the law of kinetogenesis is
to be found in those cases where different structures
appear in different parts of the skeleton of the same
individual animal, in direct correspondence with the
different mechanical conditions to which these parts
have been subjected. Examples: the diverse modifi-
cations of the articulations of the limbs in consequence
of the uses to which they have been put, in mammals
which excavate the earth with one pair of limbs only;
as in the anterior limbs of the fossorial Edentata, In-
sectivora, and Glires. The reduction of the number
of the digits in the posterior limb only when this is
extensively used for rapid progression, as in leaping:
this is seen in the kangaroo and jerboas, in the orders
Marsupialia and Glires.

The development of a dental structure of premolars
identical with that of the molars, from a different struc-
tural origin, in the Perissodactyla.

From the preceding facts I have inferred that in
biologic evolution, as in ordinary mechanics, édentical
causes produce tdentical results.

362 PRIMARY FACTORS OF ORGANIC EVOLUTION.

vil.A HYPOTHESIS OF THE ORIGIN OF THE DIVISIONS OF
THE VERTEBRATA.

In order to estimate the part which has been
played by the movements of the Vertebrata in chang-
ing their environment in past geologic ages, we have to
rely principally on inferences derived from the present
physical characteristics of the earth. Formerly, as
now, conditions of temperature, humidity, soil, shel-
ter, food, etc., were avoided or appropriated by ani-
mals, through their capacity for moving from place to
place. What concerns us chiefly here, is the effects
on their structure produced by the movements of Ver-
tebrata. In examining this question I will take it up
in systematic order, so as to observe whether kineto-
genesis has been the principal or only a subordinate
agency in the evolution of this branch of the animal
kingdom.

The most conspicuous index of the serial succes-
sion of the vertebrate classes, is, as has been already
remarked, the circulatory system. The modifications
of this system have been immediately connected with
those of the method of respiration, which the exigen-
cies of the environment induced in vertebrates. The
existence of branchial arteries and veins dates from
the earliest vertebrate, if not from prevertebrate life.
They are already established in the Tunicata, and con-
tinued throughout the rising scale in diminished num-
bers, so long as Vertebrata were exclusively aquatic
in their modes of life. When at the close of the De-
vonian system the land masses assumed great propor-
tions in both the Eastern and Western Hemispheres,
it is probable that many fishes were entangled in shal-

KINETOGENESIS. 363

low water, which rapidly freshened, and ultimately
were desiccated, and respiration by the swallowing of
air into the alimentary canal began to take the place
of respiration by gills. It is well known that respira-
tion by this means may be carried on by fishes of va-
rious genera, e. g. Cobitis; and Professor Gage has
shown that the same habit exists in Batrachia and in
certain tortoises (Tronychide). In the middle Car-
boniferous shales tracks of land animals occur, and
the bones of Batrachia abound in the coal measures.
Already in the Permian these Batrachia are accompa-
nied by numerous Reptilia, and air breathers of ter-
restrial habits had become numerous on the earth.
The habit of holding in the esophagus large quan-
tities of air while engaged in seeking food in foul
water, or on land, on the part of vertebrates which
normally oxygenated the blood by means of gills, was
probably the mechanical cause of the development of
a pouch, and afterwards of a diverticulum of the
cesophagus, which became ultimately a swim-bladder
oralung. In vertebrates in which a return to aquatic
life became necessary, it became the former; in those
which remained for a shorter or longer period of time
on land it became the latter.! It is noteworthy that
among fresh-water fishes generally, the swim-bladder
is more complex than among marine forms, showing’
that the varying conditions of shore and fresh-water
life have been mainly responsible for its development.
The development of a lung at once produced a
change in the uses to which the various branchial
arches were put. The posterior, which supply the
lung, would be subjected to greater pressure owing to
the increased blood supply demanded by the lung,

1This view is adopted by C. Morris, American Naturalist, 1892, p. 975.

364 PRIMARY FACTORS OF ORGANIC EVOLUTION,

and a correspondingly diminished pressure would be
experienced by the now unused branchial portions of
the bows. The first would retain the importance of its
basal portion, as the source of the carotids, while the
middle arches would continue their existence as the
bases of the central dorsal aorta. The loss of the right
aorta-root in Mammalia was probably due to the fact
that the great arteries which supply the digestive sys-
tem are primitively branches of the left aorta-root, as
they are to-day in the crocodiles and in many of the
Batrachia. The right aorta-root disappeared through
disuse. Probably in the immediate ancestors of the
birds, as in the crocodiles, the right aorta-root gave
off the carotides and the subclaviz. As the birds de-
mand an excessive blood-supply for the fore limbs, we
have here probably the reason why the right root re-
mained in this subclass.

The next index of successional development in Ver-
tebrata is the brain. Our belief that use under stimu-
lus has been the cause of its successive growth, can
only be based on the analogy of our own experiences
in the matter of education. No part of the human
organism is so susceptible to stimuli as the nervous
system, and the marvellous effects on faculty of con-
tinued exercise are well known to everybody. Since
the changes of mental states are necessarily due to
corresponding structural changes no one will find in
ignorance of the mechanics of brain-evolution a serious
obstacle to believing that it has taken place under the
influence of the innumerable stimuli always present to
animal life.

It is in the skeleton that we have the actual record
and evidence of the effect of movement on structure.
It must be remembered in this connection that skeletal

KINETOGENESIS. 365

and dental tissues exhibit the phenomena of nutrition
and waste (metabolism), common to all living organic
matter. Hence even the hardest osseous tissues are
plastic and are subject to mechanical influences to a
degree which is not possible to dead matter of equal
density.

Fundamental differences between Vertebrata are
displayed by their organs of movement, but before
specially considering these I will refer briefly to cer-
tain other fundamental characters displayed by the
skull. In advancing from the fishes to the Mammalia
we observe a successive consolidation of the mandibu-
lar arch, and of its mode of connection with the cra-
nium. The mandibular arch in its entirety displays in
the fishes a segmented condition, generally compar-
able to that which characterizes the branchial arches.
Among Batrachians and Reptilia various degrees oi
fixation of its suspensor (hyomandibular, quadrate) to
the cranium exist, and in some of them it is closely
united by immovable suture. The complete fusion
with the squamosal seen in the Mammalia is its final
status. The segmentation of the mandibular portion
of the arch seems, from the discoveries of Ameghino,
to have continued among some of’ the Lower Eocene
mammals, but that finally disappeared, so that in the
modern mammals the movable mandibular arch con-
sists of a single element on each side. In this history
we see an instance of the progressive codssification of
parts, which results from the constant strain of use, of
which many other normal and abnormal examples are
known. This use is the act of mastication. Where
there is no mastication, and the jaws are used only as
prehensile organs, this codssification does not occur,
as, for instance, in the snakes. In this most special-

366 PRIMARY FACTORS OF ORGANIC EVOLUTION.

ized and modern type of Reptilia, the segmentation is
complete.

The segmentation of the limbs in the Vertebrata is
a simple mechanical problem. Paleontology and em-
bryology concur in proving that the limbs originated
in primitive folds in the external integument, and that
their connection with the internal skeleton was of later
accomplishment, has been shown by Wiedersheim.
At first free, they sought points of support on the
skeleton, but did not lose their free mobility when
this contact was attained. Appropriately to the me-
chanical conditions of rigidity and flexibility neces-
sary to their use in a fluid medium, they were orig-
inally composed of slender rods which were segmented
by interruptions at suitable points. The articulations
of the fin-rays of fishes have been made the subject
of an interesting research by Ryder, who finds them
to be fractures, due to flexures during motion in the
water medium.! The limb of land vertebrates (the
chiropterygium) was derived from one of the forms of
fins (rhipidopterygium) of water vertebrates. This is
the simple type of primitive fin displayed by the Pale-
ozoic Teleostomi of the superorder Rhipidopterygia.
Whether the subdivisions of the chiropterygium, the
propodial, metapodial, and phalangeal bones, etc.,
were divided from the primitive branches of the archi-
pterygium, as held by Gegenbaur, or whether they
have developed by sprouting from a simple axial series
of segments, as held by Baur, or whether, as I have
suggested, it is a derivation from the rhipidopterygian
type of paired fin, is not yet decided. In either case,
the limbs of the first land animals were segmented and
flexible at the joints between the segments. The ne-

1 Proceedings of the American Philosophical Society, 1889, p. 547.
&

KINETOGENESIS. 367

cessities of such limbs are twofold: first, to serve as
supports when at rest or in progression ; second, to be
applied to the body in protection from enemies, or in
aiding the functions of feeding, reproduction, etc.
The first function requires principally mobility at the
point of connection with the body. The second, flexi-
bility at some point on the shaft of the limb. The two
kinds of movements in question would conserve two
principal points of flexure, and these would be for the
fore limb, just what we find, the shoulder and elbow
joints; and for the hind limbs, the hip and knee joints.
The two median joints are directed in opposite ways,
the elbow backwards and the knee forwards. This
diversity is clearly due to the diverse positions of the
functioning regions. The opposite extremities of the
alimentary canal, the posterior including the exits of
the urogenital organs, requires that the fore limbs
should bend forwards, and the posterior limbs back-
wards. And the constantly recurring necessity for the
exercise of these flexures must necessarily have devel-
oped the appropriate articulations in preference to all
others. The terminal flexure, that of the wrist or
ankle, has been evidently due to a similar mechanical
cause, viz., the flexure due to pressure of the weight
of the body on the terminal segments when in contact
with earth. The distal segments are the most slender
in all types, and least able to maintain a linear direc-
tion under pressure, hence, they have flexed easily and
thus the line of separation between leg and foot had
its origin. The ankle and wrist in the Batrachia Uro-
dela is still a mere flexure.

Mr. Herbert Spencer has endeavored to account for
the origin of the segmentation of muscles into myo-
tomes, and the division of the sheath of the notochord

368 PRIMARY FACTORS OF ORGANIC EVOLUTION.

into vertebre, by supposing it to be due to the lateral
swimming movements of the fishes, which first exhibit
these structures.! With this view various later authors
have agreed, and IJ have offered some additional evi-
dence of the soundness of this position with respect to
the vertebral axis of Batrachia,? and the origin of limb
articulations.’ It is true that the origin of segmenta-
tion in the vertebral column of the true fishes and the
Batrachia turns out to have been less simple in its pro-
cess than was suggested by Mr. Spencer, but his gen-
eral principle holds good, now that paleontology has
cleared up the subject.

The Echinodermata, Mollusca, Arthropoda, and
Vertebrata possess external or internal calcareous or
chitinous skeletons for the most part. The lower forms
of all these branches, however, are more or less deficient
in this kind of protection, and embryology indicates
that all of them are the descendants of the Vermes or
worms, which are mostly without such hard supports
and protections. Whether this be demonstrated or
not, we have plenty of evidence to show that the prim-
itive Vertebrata were without hard skeletons, and that
their bodies were composed internally and externally
of perfectly flexible tissues.

If we now imagine that either the integuments, or
an axial rod, of a worm-like animal has become the seat
of a calcareous or chitinous deposit, it is evident that
the movements of the animal in swimming or creeping
must have interrupted the deposit at definite points of
its length. The lateral flexure of the body would be
restricted to certain points, and the intervening spaces

1 Principles of Biology, 1873, pp. 198-204.
2 Origin of the Fittest, 1887, p. 305.
3 Mechanical Causes of Origin of Hard Parts of Mammalia, 1889, p. 163.

KINETOGENESIS. 369

would become the seat of the deposit. At the lines of
interruption joints would be formed, and if the move-
ments were habitually symmetrical, these interruptions
would be equidistant. In this way the well-known
segmentation of the external skeletons of Arthropoda,
and the internal skeletons of Vertebrata would be
formed. We have more detailed evidence that this
has been the case. Thus the segmentation of the os-
seous sheath of the chorda dorsalis in both primitive
fishes and batrachians has been accomplished in wedge-
shaped tracts precisely as may be observed in the fold-
ing of a tolerably stiff sleeve of a coat which ensheathes
the arm, under the influence of lateral flexures. The
wedge-shaped tracts are superior and inferior, the
apices directed towards each other. Seen from the
side they form two wedges with their apices together,
and their bases one up and the other down. Now, if
a person who wears a coat of rather thick material will
examine the folds of his sleeve as they are produced
on the inner side of his arm, he will see a figure nearly
like that of the segments of the vertebral column de-
scribed. The folds will correspond to the sutures, and
the interspaces to the bony segments. He will find
that the spaces are lens-shaped, or, when viewed in
profile, wedge-shaped, with the apices together. This
arrangement results from the necessary mechanics of
flexure to one side. In flexure of a cylinder like the
sleeve, or like a vertebral column, the shortest curve
is along the line of the greatest convexity of the cylin-
der. Here is the closest folding of the sheath, and
here, consequently, the lines of fold in soft material,
or interruption in hard material, will converge and
come together. That is just what they do in both the

370 PRIMARY FACTORS OF ORGANIC EVOLUTION.

sleeve and the rhachitomous vertebral column, the
only difference being that in the animal it is exhib-

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ited on both sides,
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one direction.

It results from
the above obser-
vations that the
structure of the
rhachitomous ver-
tebral column Aas
been produced by
the movements of
the body from side
to side, as in swim-
ming, during the
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posit of mineral ma-
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See figures 113
to 114@ where the
coat-sleeve is com-

pared with the ‘“‘rhachitomous” vertebrz of primitive

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372 PRIMARY FACTORS OF ORGANIC EVOLUTION,

fishes (Merospondyli1) and Batrachia (Rhachitomi).
Such was the origin of the segmentation in the primi-
tive sharks, Pleuracanthus, whose structure has been
pointed out by Sauvage, and Hybodus, whose charac-
ters have been demonstrated by Smith Woodward.
The segmented (or rhachitomous, as I have termed it,)
condition may be then regarded as the primitive one of
the osseous column in the Vertebrata. From the rha-
chitomous column two divergent lines have arisen as
already remarked (pp. 89,209). The inferior segment
has been retained in the fish-batrachian line, whence I
have termed their vertebre ‘‘intercentral,” while these
bodies have disappeared or become rudimental in the
higher Vertebrata.. The pleurocentra (Figs. 113-1142,
c, pl.) have, on the other hand, developed downwards,
and, mesting below, have formed the effective centrum
of the vertebra. Hence, in the Monocondylia and
Mammalia the vertebre are ‘‘central.”

The Reptilia display a greater variety of vertebral
articulation than any of the classes of Vertebrata.
After the primitive biconcave (amphiccelous) type was
abandoned, the two principal types assumed are the
ball and socket (proccelous and opisthoccelous), and
the plane (amphiplatyan). In those families in which
the body is more or less in contact with the ground,
owing to the absence, shortness, or position of the
limbs (Lacertilia, Ophidia), the vertebral bodies ex-
hibit the ball-and-socket articulation, while in types
with longer limbs which supported the body in pro-
gression, so that the latter never reached the ground
(Dinosauria), the articulations are plane. The ball-and-
socket articulation may be inferred to have been pro-

1Zittel, Handbuch der Paleontologie, I11., p. 138, 1887, where this charac-
ter is first clearly pointed out in fishes.

KINETOGENESIS. 373

‘

duced by vermiform movements which utilize points of
resistance on the earth as aids to progression, while the
plane articulation has probably resulted from the per-
sistence of the fixed relation which is appropriate to a
body which should be relieved by the legs of all share
in movements necessary to progression. That this
position is correct is sustained by the fact that the cer-
vical vertebrz of various reptiles and mammals which
have plane dorsal vertebre have the ball-and-socket
structure. This is probably due to the constant flex-
ures to which that part of the column has been sub-
jected, as compared with the fixity of the dorsal re-
gion.

Owing to the comparatively advanced state of our
knowledge of the phylogeny of the Mammalia (Chap-
ter II.), this class furnishes especial opportunities for
the study of kinetogenetic evolution. But our knowl-
edge is not yet sufficiently complete to enable us to
account on mechanical grounds for the origin of all
the characters which distinguish all its subdivisions.
This being the case, I have not presented the subject
in taxonomic order, but have contented myself with
offering it in the order of evidential value. I have first
described certain cases where the action of kinetogen-
esis is self-evident. This has been followed by the
presentation of cases where the evidence amounts to a
high degree of probability.

Referring now to the table of definitions of the or-
ders of Mammalia on pages 127-128, I will go over the
characters serzatim, and show how far our knowledge
warrants us in giving a kinetogenetic explanation of .
their origin. No mechanical cause can be at present
assigned for the loss of the coracoid and episternal
bones in the Eutheria. In the Eutheria the presence

374. PRIMARY FACTORS OF ORGANIC EVOLUTION.

of the marsupial bones of the Didelphia is a survival,
and it may be that their absence in the Monodelphia
is due to disuse, on the withdrawal of strain on the
abdominal walls which followed the abandonment of
the oviparous habit of the Prototheria, and the young-
bearing habit of the Marsupialia. The very consider-
able weight actually borne by existing forms and prob-
able weight carried by extinct forms will probably
account for the development of these bones through
strain on the prepubic cartilage. The perforate palate
is a reptilian survival, and the closure of the fonta-
nelles may have been due to the increased strain due
to the increased energy of mastication which early en-
sued, owing to the increased size and specialization of
the molar teeth. Of the three divisions of the Mono-
delphia, the Mutilata, Unguiculata, and Ungulata,
the Unguiculata possess modifications of a character
of ungual phalanges inherited from the Reptilia, while
the other two groups have experienced still greater
modification. The limbs of the Mutilata display the
result of disuse as to the posterior ones, and special
use as to the anterior, as I have already pointed out.
The Sirenia display a less degree of modification than
the Cetacea. The hoofs of the Ungulata may well
have assumed their laterally expanded and transverse
forms by the extreme pressure and impact on the
earth, incident to their function as supports.

The origins of most of the dental characters which
characterize the orders of Mammalia have already been
referred to mechanical causes, and have been already
treated of. The same is true of tarsal and carpal
characters, which are of so much importance among
the Ungulata.

The characters enumerated on page 139 as indicat-

KINETOGENESIS. 375

ing progressive modification in time have also been
mainly accounted for on mechanical grounds.

5. OBJECTIONS TO THE DOCTRINE OF KINETOGENESIS

It has been objected that Neo-Lamarckians are
self-contradictory and illogical in their defense of the
doctrine of the development of structures by use, or
by motion. It is asserted that they believe that stimuli
of different kinds produce similar results, and that
stimuli of the same kind may produce different re-
sults. The charge that Neo-Lamarckians hold those
views is correct, but it is not correct to suppose that
they are illogical or self-contradictory. This criticism
is one of those generalities which will not bear exam-
ination, while the doctrine of kinetogenesis will bear
examination.

Thus ‘it has been experimentally shown that bone
irritation will produce both bone deposit and bone ab-
sorption, according to the degree of irritation. Mode-
rate irritation produces deposit, and greater irritation
produces absorption. Hence it is that both impact
and strain, or pressure and stretching, will elongate a
bone, by stimulating growth, if not excessive. We
have the illustrations in the elongation of ligaments
and cartilages and their ossification under stretching,
and the shortening of both in absence of use, from
which we may infer their lengthening under use. The
continued lengthening of the limbs and teeth of the
higher Mammalia, in the course of geologic time, is
an illustration of the effect of continued impact and
transverse strain; while the lengthening of the limb
bones of the sloth, and of the tarsal bones of many
bats, is a consequence of longitudinal strain.

376 PRIMARY FACTORS OF ORGANIC EVOLUTION.

The differing directions of the elements entering
into the articulations of the limbs of Mammalia may
be cited in illustration of the supposed inconsistency
of supposing them all to be the result of impact and
strain. Thus most of the condyles are directed distad,
but the heads of the humerus and femur, and the prox-
imal surfaces of the carpus and tarsus are directed
proximad (except the trochlear groove of the astraga-
lus when present). So far as regards the distal ends
of the radius and tibia (fore arm and leg) I have
pointed out that here dense layers disposed longitudi-
nally impinge on a similar layer disposed transversely,
with the natural consequence the latter has yielded to
the excess of impact so produced. The direct relation
of the sculpture of the surfaces concerned, to the
lengthening of the foot and increase of speed of the
animal, and hence increase of force of impact, leads
irresistibly to this conclusion. As regards the con-
vexity of the heads of the humerus and femur, or rather
the concavity of the corresponding surfaces of the
scapula and acetabulum the explanation has been al-
ready given. Henke was apparently the first to call
attention to the fact that the concavity and convexity
of the articular surfaces is directly related to the posi-
tions of the insertions of the muscles which move them.
He shows that a concave surface is developed at the
extremity which is nearest to the muscular insertion,
while the convex surface is developed on the extremity
which is most remote from its muscular insertion.
Thus is accounted for the apparently contradictory
evidence of the limb articulations mentioned. In some
cases at least, as those of the glenoid cavities of the
scapula, ilium, and phalanges, the muscular insertions
are so near to their borders, as to suggest that the

KINETOGENESIS, 377

growth of the latter is due to a pulling strain on them,
as well as to the greater mobility of the element which
becomes convex, as supposed by Fick.

It is claimed in the preceding pages, that impacts
on the extremities of a bone or tooth, gradually in-
crease its length. It may be hastily supposed that in
this assumption I derive elongation of the shaft of a
bone from the same stimulus which produces excava-
tion and therefore abbreviation of its extremities. In
the gross this charge is correct; but the position I
have assumed is defensible, because in detail it is easy
to perceive that effect of the use of a limb on an ar-
ticular surface of a bone is quite distinct from that
which it has on the shaft. At the articular faces we
have discontinuity; and therefore friction ; in the shaft
we have only the concussions produced by impact, to-
gether with some torsion strain. That the former
movement stimulates the development and activity of
the osteoclasts has been shown by Koelliker; that the
latter may stimulate the activity of osteoblasts is ren-
dered highly probable from the facts of pathological
anatomy. These show that a very slight modification
of stimulus is sufficient to change the building cells
into the absorbent cells and back again. For the same
reason belief in the elongation of bones under stretch-
ing strain may not be inconsistent with belief in an
elongation under impacts.

Cary makes specific objections against the kineto-
genesis of the articulations of the mammalian skele-
ton.! After a study of the carpus of the Eocene peris-
sodactyle genus Palzosyops he concludes that the
trapezoid bone is too small to express properly the di-
rect result of purely mechanical causes. He says that

lAmerican Journal of Morphology, 1892, p. 305.

378 PRIMARY FACTORS OF ORGANIC EVOLUTION

in reaching this result he has applied geometrical meth-
ods. ‘First, the volume of the bones was got at.
Next the area of the bearing surfaces and their inclina-
tion to the digits were measured. Then giving to the
thrust of each metacarpal a value proportional to its
volume, the distribution of that thrust can by resolu-
tion and composition of forces, be traced through the
foot, and the pressure on each surface and bone ap-
proximately obtained.” Further than this the author
does not explain how he reached the result that the
trapezoid is too small. It is quite essential that this
demonstration should be given if we are expected to
accept his conclusion. An essential part of the prob-
lem is, however, unnoticed by Mr. Cary; and that is
the condition of the trapezoid in the reptilian ances-
tors of the Mammalia. The phylogeny of an element
must be known, since it furnishes the ‘‘ physical basis”
of the problem. The fact is that the trapezium, trape-
zoides, and the magnum owe their small size to their
being the only carpal elements which have not been
produced by the fusion of two or more primitive ele-
ments of the batrachian and reptilian carpus. The
trapezoides moreover occupies a place in a longitudinal
series of three elements in the primitive carpus, while
the trapezium forms one of a series of only two ele-
ments. For similar reasons the cuneiforms are the
smallest elements of the tarsus.

Mr. Cary then proceeds to criticize the explana-
tions offered by Professor Osborn and myself, in ac-
counting for the origin of certain structures. He finds
our explanations to be self-contradictory, and that we
also contradict each other. Osborn has supposed that
the conules of the molars are produced by friction of
the molars of opposite series on each other. I have

KINETOGENESIS. 379

expressed the opinion that the shear of the sectorial
teeth of Carnivora was produced by lateral friction
during vertical movement of the lower tooth on the
upper. Ihave also asserted that the forms of facets
of limb articulations are due to pressure. Mr. Cary
sees here the attempt to explain the origin of totally
different structures through identical mechanical pro-
cesses, and believes that the attempt is a failure.
Were the conditions of the problems alike, as Mr.
Cary thinks them to be, he would have good reason
for his opinion. But the conditions in the three cases
are entirely different, and our author’s conclusion is
due to neglect of the elementary facts of the proposi-
tion.

The development of conules at the points indicated
by Professor Osborn, has been supposed by him to
be due to friction between existing ridges of enamel
which cross each other when in action, at the points
in question. In the case of the development of the
sectorial shear, the faces between which the shearing
motion takes place are smooth, and without ridges or
crests. Hence the entire surface receives a homo-
geneous friction. In the third case, that of the foot
articulations, there is no friction, but there is pressure
which when abruptly applied in movement becomes
impact. There is really no parity between the three
cases.

The author of this paper also thinks that the ex-
planation of the elongation of bones through use of
different kinds is not a permissible hypothesis. He
cites my attempt to account for the elongation of the
leg bones of higher mammals through impact-stimulus ;
and of other limb bones of other mammals through
stretching. But he does not prove that similar results

380 PRIMARY FACTORS OF ORGANIC EVOLUTION.

may not flow from mechanical stresses applied in dif-
ferent ways. I suppose that any mechanical stress
which determines nutritive processes to a part, will in-
crease its size, ceteris paribus; and the stretch as well
as the impact has this effect. I have in fact shown, in
the observations already cited (pp. 277-279), on the
production of artificial elbow joints, that osseous de-
posit is stimulated by pulling strain as well as by push-
ing or impact.

In concluding, Mr. Cary admits one of the two con-
tentions of the Neo-Lamarckians in his two closing
propositions. He says ‘‘ Plasticity of bone, using the
word plasticity not in a physical sense merely, but to
include absorption under pressure, will probably ac-
count for much structure in the foot and elsewhere,
especially the connection with the joints, and in the
fields of variation and correlation.” In the second
proposition he says that facts have been adduced by
him which are inconsistent with the theory that the
size of bones has been increased by the stimulus they
receive, and with the theory that regions of growth are
determined by regions of pressure and strain. ‘‘The
testimony of the literature as to the latter point,” he
says, ‘‘is conflicting.” I have shown that the supposed
conflict is due to a misunderstanding on the part of
the author of this paper. The proposition that pres-
sure does not affect growth is in contradiction to the
admission made by the author in his first proposition,
where he admits that pressure determines structure ;
for in such change of structure there is always growth.
Finally Mr. Cary remarks ‘‘That race changes follow
those produced in the individual life, or that they are
directly caused by their mechanical surroundings, I
do not think it has been satisfactorily shown.” The

KINETOGENESIS. 381

fact that the characters of bone structure admitted by
Mr. Cary to have had a mechanical origin appear in
the young before birth, is evidence that race characters
are produced, in other words, that they are inherited.

Another objection proposed by Tomes, and quoted
by Poulton and Wallace with approval, has reference
to the kinetogenesis of teeth of Mammalia as described
by Ryder and myself. Tomes asserts that it is quite im-
possible that the crowns of the teeth could have been
altered by mechanical impacts and strains, since their
form is determined in the recesses of the dental grooves,
entirely removed from all the mechanical influences
which affect the external surfaces of the jaws. But
the observations of Koelliker and others show that
osteoclasts are as active in dental as in ordinary osse-
ous tissue. It is altogether probable that the modifi-
cations of dental structure have been produced by
strain and friction under use in the adult, precisely as
in the skeleton, and that the share that the unerupted
crowns have in the process is that of inheritance only,
as in the case of the skeleton. That teeth deposit den-
tine as process of repair in adult mammals is well
known, and this repair is in direct relation to use.
That the effects of dental wear are inherited is proven
by the fact cited by Tomes and Wallace.

Another objection to the doctrine of kinetogenesis
which has been made by some of the Neo-Darwinians
is, that if growth under stimulus be true, how can it
have limits, so long as the stimulus of use exists. “In
other words, what is to prevent, in the case of the
vertebrate skeleton, of an indefinite increase in the
length of the legs, of the teeth, and of their cusps, etc.
The answer to this objection will vary more or less
with the part of the structure considered. In general,

382 PRIMARY FACTORS OF ORGANIC EVOLUTION,

however, it may be assumed that stimulus is stress
due to a want of harmony between an organism and
its environment, and that kinetogenesis is the result of
the effort of the organism to adjust itself. So soon as
equilibrium is attained, the stress of stimulus ceases
or is much reduced, and evolution in this direction
ceases. Such equilibrium is attained when the mechan-
ism of an animal is sufficient for the satisfaction of its
needs. When this is the case severe exertion is no
longer necessary, and a period of easy use follows
which is sufficient to maintain the mechanism in work-
ing condition. In the case where circumstances should
become so favorable for the easy satisfaction of the
necessities of life, as to call for little or no exertion,
degeneracy of the organism is sure to follow. The
well-known phenomena of degeneracy from disuse
show that a large part, and in some cases all, of the
stimulus of use, is only sufficient for the maintenance
of the organism in working condition, and that there is
no surplus to be expended in progressive evolution.

It is however true that some organs are stimulated
to excessive growth by active use. Such are some of
the teeth, which, if not worn at the crown by the op-
position of those of the opposite jaw, soon grow to an
inconvenient length. This occurs in the hypsodont
molars of horses and artiodactyles, and in the pris-
matic molars and incisors of Glires. Hypsodonty in
general is an illustration of continuous growth induced
by long-continued stimulus in those orders of Mam-
malia, and in the Toxodontia and Proboscidia. The
excessive growth of the canines in the South American
saber-tooth tiger, and of the incisors of the mammoth,
are cases where the energy of growth has not subsided
in time to prevent excess.

KINETOGENESIS. 383

Several years ago Prof. August Miiller and I called
attention nearly simultaneously to the probability that
many of the forms of the reproductive organs of plants,
especially the flowers, are due to the strains and other
effects produced by their use by insects. Rev. George
Henslow has written a book in which this subject is
set forth in detail.! It is impossible to demonstrate
this point with the same certainty as the kinetogenetic
origin of the articulations of the vertebrate skeleton
and their characters, owing to the absence of paleon-
tologic evidence. Henslow, however, says: ‘‘ When
we find innumerable coincidences all tending in one
direction, coupled with an indefinite capacity for vary-
ing in response to forces in all parts of plants, I still
maintain that [this] theory does not utterly break
down,” as asserted by Mr. Wallace.* Wallace argues
that since many regular flowers have been subject to
the irritation of insects and have not become irregu-
lar, there is no reason to suppose that this is the cause
of the irregularity in question. To this Henslow re-
plies:? [Mr. Wallace] ‘will see that existing regular
flowers being mostly terminal, have no lower petals at
all, but are so situated as to offer access to insects
from all points of the compass. Moreover, when a
plant with normally irregular flowers (which are always
situated close to the axis, so that insects can only en-
ter them in one way) produces a blossom in a terminal
position (as foxglove, larkspur, horse-chestnut, etc.,
often do), it at once becomes quite regular.” This
change may be brought about artificially, for, says

1The Origin of the Floral Structures by Insect and Other Agencies. Inter-
national Science Series, Vol. LXIV.

2Natural Science, 1894, p. 178.
38Natural Science, 1894, p. 262.

384 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Henslow, ‘flowers normally irregular in nature often
revert to their ancestral regular forms under cultiva-

tion in the absence of insects, and then come true from
seed, as the Gloxinias.”

CHAPTER VII—NATURAL SELECTION.

ATURAL SELECTION is the process of dis-
crimination of variations, by which those which
are most in harmony with the environment survive. It
is, in short, as expressed by Spencer, ‘‘the survival of
the fittest.” Fitness is of various kinds, and is only
determined by the nature of the environment. The
success of a variety which appears in aquatic sur-
roundings will depend on characters different from
those which bring success in a forest. Variations
which favor survival and increase among carnivorous
animals differ from those useful to the life of herbivo-
rous forms. So survival in human society depends on
characters different from those which secure the same
result among the lower animals, etc. It is thus evi-
dent that natural selection is of many kinds and that
forms survive for various reasons ; and it is hence of
universal application. The reasons for survival may
be divided into those which depend for survival on the
relations of a type to the non-living environment, and
those which depend on the living. The former may be
divided into those which are passive and those which
are active. The particular influences may be imper-
fectly enumerated as follows:

386 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Non-living environment.
a, Passive.
Isolation of areas ; continuity of areas; building material ;
food ; place of concealment; temperature; humidity.

aa, Active.
Pressure of earth, water, and air.

II. Living environment.

Food ; reproductive potency; sexual selection; digestive
and other physiological power; muscular strength; su-
perior weapons and other special mechanisms ; intelli-
gence.

I have already (page 4) quoted the language of
Darwin, where he states that the supposition that nat-
ural selection is a cause of the origin of variations is a
mistake. From the nature of selection, Darwin’s po-
sition thus expressed, is self-evidently sound. The
attempt has, however, been made to apply the term
selection to the efficient cause of all variation, and to
divide its exhibitions into two kinds, natural and arti-
ficial selection. If the primary assumption involved
in this position is illogical, the dual division proposed
is absurd. As may be readily seen in the table in the
preceding paragraph, in which the factors of natural
selection are enumerated, the conditions necessary to
selection are mostly identical, whether imposed by na-
ture or by the hand of man; i. e., whether natural or
artificial. The physiological effects of food, tempera-
ture, exercise, etc., do not differ, whether due to nat-
ural conditions, or to the influence of man. The ob-
servation of man’s influence is indeed especially in-
structive in increasing our knowledge of the effects of
natural causes, since in the former case we have the
process in action within our control, while in ‘the latter
case it is not.

The subject of natural selection has been ably

NATURAL SELECTION, 387

treated by Darwin, Wallace, and other writers, and it
is one on which much further research may be profita-
bly expended. It is the science of adaptations, and
the name Chorology has been framed for it by Haeckel,
but the earlier term CEcology is now generally used. It
was not overlooked by biologists prior to Darwin and
Wallace, and is stated in general terms by Lamarck in
his Philosophie Zoologigue, but it was reserved for the
two authors just mentioned to create the science. I
shall here only refer to a few aspects of the subject.

Isolation naturally tends to emphasize any pecu-
liarities of structure which may harmonize with the
conditions of the environment, by the barrier which it
sets up against the entrance and mixture of forms from
other localities where the environments are more or
less different, and where the characters are correspond-
ingly proportionately diverse. Isolation conversely
prevents the emigration of forms, and the consequent
mixture with the differing forms of other regions.
Breeding in and in is produced on a large scale. Geo-
graphical isolation is a result of the formation and
population of islands, whether this be accomplished
by submergence below or by elevation above sea level.
A noteworthy illustration of the former case is seen in
the West Indian Islands, which represent the elevated
regions of a former continent. Here the faunz of the
respective islands have been separated from each other
since late Pliocene time. We find that while most of
the genera of land Vertebrata are generally distributed,
each island possesses peculiar species. This is even
true of the birds, whose powers of migration are quite
sufficient to enable them to pass from island to island.
The restriction of land mollusca is still greater, several
islands having genera peculiar to them.

388 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Isolation is also produced by inequalities of land-
surface, resulting from the elevation of mountain
ranges, plateaus, etc. This is well seen in Mexico
and Central America where the number of species of
Vertebrata is large, owing to the fact that many of
them are restricted to very narrow areas bounded by
impassable barriers. The restriction of species of land
Mollusca to each of the numerous valleys of the Ha-
waiian Islands has been made the subject of an espe-
cial study by Dr. Gulick, who treats of them with
especial reference to the evolution of their forms.

The assimilation of inorganic matter necessarily
preceded that of organic matter, so that this function
characterized the first organic beings, whether animal
or plant-like in other respects. Among animals we
may regard the vegetable feeders as having by a little
preceded the carnivorous forms. Omnivorous forms
must have come into existence soon after, and from
these, both classes of feeders have been from time to
time recruited ever since. The primitive Vertebrata
were probably carnivorous, and most of the fishes and
Batrachia have always been such. Herbivorous forms
have arisen from time to time among Reptilia, and of
granivorous birds there are many. The early Mamma-
lia were divided between omnivorous (Multitubercu-
lata) and insectivorous types (Protodonta, Pantothe-
ria); while the higher Mammalia of all kinds were de-
rived from more or less omnivorous forms (primitive
Condylarthra and some Creodonta). We may account
primitive insects to have been largely herbivorous, even
more than they are at the present time, while Carnivora
predominate in marine invertebrate life. It is not diffi-
cult to understand that circumstances of the environ-
ment would determine the food of animals, and would

NATURAL SELECTION. 389

divert omnivorous forms into carnivorous or herbivo-
rous habits as abundance of food and competition of
rivals might dictate.

Sexual selection is of two general classes, that in
which the male selects, and that in which the female
determines the result. In the former case the most
vigorous males, or those in which the mechanisms for
seizing the females are most effective, propagate their
kind most successfully. It is well known that in many
animals, especially the Arthropoda, the males are fur-
nished with especial organs of prehension. In verte-
brates similar organs are especially conspicuous in
some of the Batrachia Salientia. (See p. 65.)

The species of Arcifera exhibit peculiar structures
during the breeding season ; either an extension of the
natatory membrane, or the development of corneous
plates or spurs, as aids to prehension. There is much
variety and efficiency displayed in this point (except
in Bufonide), in especial contrast to the apparent ab-
sence of all but the weakest modifications among the
Ranidz. This is in compensation for the structure of
the sternum, whose lateral halves, being movable on
each other, offer a slighter basis of resistance for the
flexor and extensor muscles of the fore limbs of the
male. In the Firmisternia the halves of the shoulder
girdle do not overlap below on the middle line, but
abut against each other, thus preventing compression
(Fig. 51, page 198).

While no appendages of the season have been ob-
served in some Cystignathide, in several genera two
acute spurs appear.on the superior aspect of the thumb
and more rarely spur-like tubercles on the breast ; the
body is sometimes shielded with hardened points on
the rugosities, or the lip surrounded by an arched

390 PRIMARY FACTORS OF ORGANIC EVOLUTION.

series of corneous ruge. In the Leptodactylus penta-
dactylus Laur. a huge acute process of the metacarpal
of the thumb, projects inwards. Its apex is covered by
a horny cap, and it is a formidable grappling-hook to
aid the male in retaining his hold. There is added to
this in the same species a horny plate on each side of
the thorax of the male, from which project three acute
points. With these fixed in her back and the thumb
spikes in her breast the females cannot escape. Struc-
tures like this do not appear in the Firmisternia.
Here the inferior elements of the scapular arch abut
against each other, so that the thoracic cavity does
not contract on pressure, and the possibility of the
male retaining a firm grip on the female is thereby
greatly increased. In the Cystignathus pachypus the
males exhibit a permanent enlargement of the bra-
chium, dependent on largely developed anterior and
posterior ale of the humerus. (Vide Ginther, Ann.
Mag. N. H., 1859.)

Another kind of male selection is accomplished by
the combats of males for the possession of the females.
This is usual in polygamous birds and Mammalia, and
in some promiscuous species of both. Of the birds the
Galline form the best known example; and of the
mammals, most Ungulata, and the eared seals (Otari-
ide), are illustrations. In this way the weak males
are eliminated either by death, or by exclusion from
the opportunity of reproduction. The males in such
species are armed with spurs, horns, or large teeth,
except in some of the Perissodactyla, which have
neither.

Female selection is seen in another direction. Here
the male attracts by the superior brilliancy of his colors
or peculiarity of physical appearance, as well as by

NATURAL SELECTION. 391

his notions. The available growth-energy of the male
being superior to that of the female in most animals,
his structure is more liable to excess of development
in useless directions. In many of the Arthropoda,
especially the Insecta, the males possess processes of
the head and thorax besides the especially useful pre-
hensile peculiarities of the limbs. Among Vertebrata
the male generally possesses the more brilliant colors.
This is especially noteworthy in fishes and birds. It
is also frequently the case in lizards, although in one
genus (Liocephalus) the female has the brighter hues.
The selection (taking no account of the origin of these
characters) acts in the probable preference by the
females for the most brilliant colors and most impres-
sive forms, thus propagating both, and in the neglect
of those males in which these characters are not so well
developed. The plainness of the females aids in their
concealment and enables them to perform their ma-
ternal functions in safety.

The desire of the males to attract the favor of the
females leads to many peculiar performances among
birds. The males display their plumage by spreading
their wings, tail, tail-coverts, etc., and strut and go
through many antics in the presence of the females.
Familiar examples are seen in our barnyards in the
turkeys, peafowls, and pigeons. In the paradise-bird
the most remarkable exhibitions occur, according to
Wallace. In song-birds thé male is frequently the only
or the best songster, and the development of the vocal
powers resulting from the sexual impulse is most re-
markable. Among Mammalia the female selection is
less common than male selection. In the case of
some of the old world monkeys (Macacus, e. g.) the
female presents the greater physical indication of ex-

392 PRIMARY FACTORS OF ORGANIC EVOLUTION.

citement in the extraordinary development of the nates
at the season of heat. Mankind, appropriately to the
high development of the mental powers, is selected
with reference to qualities of mind as well as with re-
gard to the physical attractions. Mental advantages
being equal, beauty is preferred, but beauty is often
neglected in favor of superior moral and intellectual
characteristics. Both sexes take part in the selection ;
in the lower races chiefly the male, while in the higher
races the choice rests ultimately with the female. It
is probable that in future civilized mankind will exer-
cise more care than now in the prevention of marriage
of persons affected with serious physical and mental
defects, such as chronic diseases, insanity, alcoholism,
criminality, etc.; but beyond this, supervisory selec-
tion cannot go. The supposition which is sometimes
entertained by some persons, that mankind will ina
state of higher civilization prefer physical to mental
perfection, is certainly ill founded. And among men-
tal qualities, a high value will always be attached to
those which render social life easiest and most pleasant ;
the standards of ease and pleasure being innumerable.

Among the most conspicuous examples of the ac-
tion of natural selection are to be found those resem-
blances in color or form between animals and their
environment which serve to conceal them from ene- |
mies. Animals possessing such protective appear-
ances naturally escape the observation of enemies
which prey on them, while those which do not possess
them are more readily captured and eaten. Much is to
be found of interest on this attractive subject in the
writings of Wallace, Poulton, Beddard, and others.
The two authors first named ascribe these color and
form characters to natural selection as a cause. This is,

NATURAL SELECTION. 393

however, impossible; yet natural selection has un-
doubtedly been the cause of their survival. Professor
Poulton has demonstrated (p. 230) that the protective
colors in lepidopterous pup are produced directly
by the influences of light on the nerves of the ani-
mal and its reflex action on the pigment depository
process.

The first objection to the belief that natural selec-
tion is the primary cause of organic evolution has
been already stated as follows: ‘‘A selection cannot
be the cause of those alternatives from which it se-
lects. The alternatives must be presented before the
selection can commence.” But the supporters of the
view that natural selection is the origin of variation
allege that it produces this result by the continued
survival of minute differences which are useful, thus
accumulating variation. That minute advantageous
differences will secure survival no one can doubt, but
it must be remembered that the variations which con-
stitute evolution have been in a vast number of cases
too minute to be useful. But the general question is
not affected by the supposition that advantageous va-
riations may be sometimes minute. Minute or great,
they have to be assumed in the argument for selec-
tion; and whether minute or great, they have a def-
inite cause.

* ‘ x

In conclusion of Part II. of this book, I trust that I
have adduced evidence to show that the stimuli of
chemical and physical forces, and also molar motion
or use or its absence, are abundantly sufficient to pro-
duce variations of all kinds in organic beings. The va-
riations may be in color, proportions, or details of struc-
ture, according to the conditions which are present.

PART IIE

THE INHERITANCE OF VARIATION.

)

PRELIMINARY.

N THE first section of this book I have endeavored
to show that variation of character is not promis-
cuous or multifarious, but that it is limited to certain
definite directions. That this rule applies to all kinds
of characters, whether they are of the less fundamen-
tal kind which distinguish species, or of the more fun-
damental kind which distinguish the higher divisions.
In the second section I have endeavored to show
that many characters, both those of the more super-
ficial and those of the profounder kinds, are the direct
result of chemical and physical stimuli, and of molar
motion or use, or of the absence of the latter or dis-
use.

It now remains to ascertain whether the characters
or variations so produced are inherited ; that is, whether
characters so acquired are transmitted to succeeding
generations. Unless this proposition is demonstrated,
our knowledge of the method of evolution remains in-
complete, and we must look for some new explana-
tion of the progressive increments and decrements of
structure which constitute the history of organic life.
The present part of this book will be devoted to an
examination of this question, and to the exposition of
such laws as may be derived from such examination.

CHAPTER VIII.—HEREDITY.

1. THE QUESTION STATED.

T IS the popular belief that characteristics of par-
ents are transmitted to their offspring through the
medium of the reproductive cells. This opinion is
founded on an infinitude of observations easily made
on plants, animals, and men, and in fact it is not de-
nied as a general statement by anybody. It is a fact
of ordinary observation that many and apparently
most of the structural characteristics of one generation
are inherited by its offspring. Not only is this the
case, but the functionings of organs which depend on
minute histological peculiarities are inherited. Such
are points of mental and muscular idiosyncrasy; of
weakness and strength of all or any of the viscera,
and consequent tendencies to disease or vigor of spe-
cial organs. Darwin has collected in his work on the
Descent of Man numerous instances of the inheritance
of various tricks of muscular movement of the face,
hands, and other parts of the body. But it is a fact
of equally ordinary observation that some peculiarities
of parents are not, or may not be inherited, and among
these may be enumerated mutilations and injuries, as
well as characters which are normal. It is then a
question of essential importance to ascertain what

HEREDITY. 399

kinds of characters are inheritable, and what are not
inheritable.

It has been insisted by Weismann and others that
characters which are newly acquired by an organism
are not inherited, whether they be products of normal
or abnormal conditions. In support of this view, he
points to the early isolation in embryonic life of the
reproductive cells from the remainder of the organism,
and their continued isolation during later life, so that
they are protected from the stimulating influences
which affect the remainder of the body. He also
points to the permanence of this isolation of the germ
plasma from generation to generation, which insures
only the transmission of those characters which it
contains, as distinct from those which are found in
the remaining cells of the organism, which constitute
the body orsoma. The characters which are inher-
ited, and which are present at birth are termed con-
genital, while those which appear in the body under
the influence of external stimuli are termed acquired.
The theory of Weismann then is, that the acquired
characters are not inherited.

Besides the fact that sporadic injuries and mutila-
tions of the soma are not inherited, there have been
cited various cases of the non-inheritance of mutila-
tions which have been often repeated and for long
periods of time. Thus the rupture of the hymen in
human females has not been followed by its abolition.
The practice of circumcision by the Jews has not re-
sulted in the disappearance from that race of the por-
tion of the body thus artificially removed. The con-
tinued cutting of the hair of men of many races has
not made it less abundant. The practice of distorting
the feet of a class of their women by the Chinese has

400 PRIMARY FACTORS OF ORGANIC EVOLUTION,

not modified the shape of that part of the structure in
the race. I have myself cut off the tails of nine suc-
cessive generations of mice without producing the
slightest effect on the length of the tails of the tenth.

Nevertheless such negative evidence only demon-
strates that such modifications of the structure may
not be inherited. A single undoubted example of the
inheritance: of a mutilation would prove that no in-
surmountable barrier to such inheritance exists. And
well authenticated examples of such cases are known
and will be mentioned later on. But it is not with
mutilations that the paleontologist has to do. The
rupture of the hymen and circumcision, and most muti-
lations, can only occur once in the life of the individual,
and generally they produce no appreciable direct effect
on his or her metabolic physiology. Moreover, the
mutilations above cited as not inherited are experi-
enced by but one sex, except in the case of the tails
of the mice. The question is widely different with re-
gard to the parts of the structure in which we observe
the real differences between organic types. The defi-
nitions of natural divisions rest to a great extent on
the diversities displayed by the organs of motion and
nutrition. Now these are in use in animals during
most of the hours not spent in sleep. Their move-
ments are perpetual, and their activities only cease
with death. It is then quite unreasonable to cite the
history of mutilations as evidence against the inheri-
tance of natural characters produced by oft-repeated
and long continued natural causes.

It has been shown in Part Second of this book that
structural characters are produced by use and other
stimuli to growth. It has also been shown in Part
First that the characters so produced show a progres-

HEREDITY. 401

sive increment or evolution from earlier or later geo- .
logic periods. There are two possible explanations
of this phenomenon. The one is that the characters
of one generation are inherited by the next, which
adds to them by the activity of the same stimuli which
gave them origin, thus producing progressive increase
of growth. The alternative is, that these structural
characters are produced by each generation for itself.
It is obvious that the latter hypothesis provides for
no additional development of a character in one gen-
eration above another. There are other objections to
the latter view, but letting these pass for the present,
it is only necessary to examine the embryonic history
of animals to show that it is entirely untenable. For
if some or all of these acquired characters can be
found present in the early stages of growth, as in the
egg, the pupa, the fcetus, etc., it becomes clear that
such acquired characters have’been inherited. That
such is the fact is abundantly demonstrated by embryo-
logical researches. This fact alone is sufficient to set
at rest by an affirmative answer the question as to the
inheritance of acquired characters. And that this
answer applies to all time and to all evolution is made
evident by the fact, which is disclosed by paleontology,
that all characters now congenital have been at some per-
tod or another acquired.

2. EVIDENCE FROM EMBRYOLOGY.
a. Vertebrata.

I have already (p. 292) pointed out the gradual
evolution through mechanical causes of the tongue and
groove-joints in the Mammalia as exhibited by the
distal ends of the metapodial bones of the feet where

402. PRIMARY FACTORS OF ORGANIC EVOLUTION.

they articulate with the phalanges. Mr. Carey having
agreed with me that those have been produced by me-
chanical causes, he alleges that they are not inherited,
but are produced by each generation for itself. To
this Dr. J. L. Wortman remarks as follows:

‘‘With reference to Mr. Carey’s first proposition
that the metapodial crests are produced during the life
of each individual by the necessary interaction of parts,
it appears to me to bea very simple one indeed. If
they are produced, by pressure during the lifetime of
each individual, and are not inherited, then clearly we
should find the crests absent in new born animals that
had never walked, and in which the metapodials had
not been subjected to any impact or pressure what-
ever. Ihave taken the trouble to examine a number
of such examples in which the distal ends of the bones
were entirely cartilaginous, and I find that the keels
and grooves are as well developed as they are in the
adult animal. I will cite one case in particular in
which I happen to know the history completely. Dur-
ing the past winter, a young hippopotamus was born
in the Zodlogical Gardens in Central Park, New York,
and it was stated to have been a premature birth ; the
animal lived but twenty-four hours, and I was informed
by the keeper that it never stood upon its feet. An
examination of the feet shows that the distal ends of
the metapodials are entirely cartilaginous, and in them
the keels are as well prefigured in cartilage as they are
formed in bone in the adult animal. I have also found
the same to be true of new-born rabbits and guinea-
pigs. In another case of a young buffalo calf preserved
in the American Museum Collection, the distal keels
of the metapodials are complete notwithstanding the
fact that the epiphyses of all the bones are very im-

HEREDITY. 403

perfectly ossified. This evidence, it appears to me,
effectually disposes of the question of the production
of these structures during the lifetime of the individ-
ual. They are as truly inherited as is the number of
digits or any other important organ in the animal econ-
omy.”

Such observations may be repeated indefinitely.
Thus the astragali of the higher Mammalia are already
grooved before birth, and are not flat up to that time
as in their Puerco ancestry. The reduction of digits
appears very early in foetal life, and the ball and socket
articulations of the cervical vertebre of the Diplarthra
are by no means introduced after birth.

The teeth possess the normal structure of their
crowns while yet in the alveoli before eruption. In
some cases the transition from a primitive to a modern
type of tooth has been observed to take place in the
embryo.

Dr. A. von Brunn! has shown that in the embryos
of the rat, the enamel-producing epithelial layer of the
molar teeth undergoes a remarkable change at the
places where the transverse crests of the crowns are
to appear. Before the enamel layer is deposited, the
portion of the epithelial layer corresponding to the
cross-crests undergoes degeneration, as a result of
which it acquires the character of a stratified squamous
epithelium. Thus no enamel is laid down on the sum-
mits of the cross-crests, which present the exposed
dentine when erupted. Now it is a fact that the crowns
of the molar teeth of the ancestors of the genus Mus,
were covered with enamel at maturity, like all other

1“ Notiz tiber unvollkommene Schmelzentwickelung auf den Mahlzahnen
der Ratte, Mus decumanus’’: Archiv fir Mikroskopische Anatomie, 1880, XVII,
Pp. 241-243, Pl. XXVII. Ryder, American Naturalist, 1888, p. 547.

404 PRIMARY FACTORS OF ORGANIC EVOLUTION.

primitive Glires. The removal of the enamel from the
apices of the tubercles and crests of their descendents
is due to the abrasion consequent on ordinary use.
On this Ryder (/. c.) remarks: ‘‘ The great value which
is to be attached to the fact that abrasions of the
enamel of the adult, which have reacted upon the
functional activity of the enamel organ of the embryo
rat, so that such mechanically induced alterations could
be inherited, does not consist so much in the proof it
affords that mutilations can be inherited, as it does
that mutilations incurred in the ordinary struggle for
existence, may, under Certain conditions in certain
practically feral species, be transmitted.”

Having shown by these examples that acquired
characters can be inherited, I offer some other illus-
trations which are at hand.

b. Arthropoda.

It has been already rendered probable if not certain
(p. 268) that the segments of the body and limbs of the
Arthropoda were originally produced by the movements
of definite tracts on each other, during the period that
the external surfaces were becoming hardened by chi-
tinous or calcareous deposits. It is well known that this
segmentation is no longer produced by this mechanical
cause during the adolescent or any other post-embry-
onic stage of the life of the individual, but that it ap-
pears during the various stages of embryonic life, and
is therefore inherited. Thus segmentation of the body
appears in the embryo while still attached to the yolk.
During the larval life of many insects the process of
segmentation is suspended, but during the repose of
pupal life, it goes on with great rapidity. In this stage
while protected from external mechanical stimuli, the

HEREDITY. 405

limbs with their specialized segments are fully devel-
oped, so that the individual is mature as it issues from
its prison. This illustration of inheritance derives its
point in the present connection from the fact that it
presents an example of the inheritance of characters
which were plainly acquired by mechanical stimuli
during post-embryonic life of the primitive ancestors
of the Arthropoda.

3. EVIDENCE FROM PALEONTOLOGY.

a. The Impressed Zone of the Nautiloids.

I have already quoted Professor Hyatt on the par-
allelism which is characteristic of the various series of
nautiloid Cephalopoda, as discovered by paleontologic
research. (P.182.) The impressed zone is a character
which has been produced by mechanical causes (pres-
sure), and Prof. Hyatt has observed cases where this
acquired peculiarity has been inherited in instances
where the mechanical cause which produced it no longer
existed. He describes these instances as follows :1

‘¢The characteristic dealt with in the paper of
which this is an abstract, is of essential importance
among nautiloids and ammonoids or all of the Cepha-
lopoda having chambered shells and living within their
shells. It consists mainly of an impression made on
the inner side or dorsum of each outer whorl during
the coiling up, as the whorl grows and is moulded over
the venter or outer side of the next inner whorl.

“‘This matter will be better understood, if a short
description is given of the following figures. Fig. 115
shows an almost complete fossil cast of a full grown

lAmerican Naturalist, 1893. October, p. 865. Professor Hyatt has person-
ally looked over and corrected these quotations.

‘

406 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Metatoceras cavatiformis Hyatt, and some of the lines
or sutures made in the external surface of the cast by
the intersections of the partitions or septa that cut
up the coiled tube of the living shell into air cham-
bers. Fig. 116 shows a broken specimen of the same
species, but with the outer and older whorls in large
part removed. The innermost septum near the center
of the coil was built across the interior after the animal
had constructed the hollow apex or point. It then
moved along, adding to the external wall of the tube,

Fig. 115.

which has been destroyed and removed from this cast,
and built the second septum, and so on until it reached
the tenth septum. By some freak of fossilization a
number of the septa beyond this have been destroyed,
so that if we were to remove the fragment of the ex-
ternal whorl and take out the center which has just
been described, this would have the exact aspect of a
cast of a young shell with ten air chambers.! The

1The shaded area in the center, shaped like a large inverted comma, was
an open space in the living shell. This is almost invariably filled by the

HEREDITY, 407

eleventh air space or chamber being open and without
divisions would then appear to be the living chamber
which the animal occupied when it built the tenth sep-

Fig. 116.

tum. Normally the shell really continued to progress
from the tenth septum by additions to the outer wall
and put in new septa behind it, together with the con-

Fig. 117.

necting tube until it reached s’, and finally the last
septum, /s. This one, /s, was really the last one built

rocky matrix in which the shells occur and is often, as in this specimen, al-
lowed toremain. Seealso 4, 5, 6, of Fig. 119, which show the comma shaped
umbilical perforations or openings left at the center through the crytoceran
form of the young.

408 PRIMARY FACTORS OF ORGANIC EVOLUTION.

and it formed the floor of a true living chamber, Zc,

formerly occupied by the animal at the time of its

death and burial in the sediment of the carboniferous

period. Fig. 115 shows a similar fossil but with a

longer, although still incomplete living chamber. If

the external wall of shell had been preserved none of

these structures could be seen. Fig. 117 shows a fossil

Temnochilus crassus, a shell

of the same family, with this

external wall preserved, and

all these internal structures

covered up. The impressed

zone is the reéntrant curve

shown in all these figures

me and especially marked in

Mee the lower outline of an outer

whorl of another carboniferous species, Metacoceras
adubium Hyatt, Fig. 118, zm. 2.

‘«It is not necessary to go into a discussion of the
details of internal structures and their relations to the
impressed zone in this abstract, but it is essential to
give a general description of the morphogeny of the
order of nautiloids.

‘« This group of chambered Cephalopods contains
the following classes of forms: first, straight, conical
shells, type Orthoceras, Fig. 119, No. 1; second, curved
cones, Cyrtoceras, Fig. 119, No. 2; third loosely coiled,
open whorled cones, do., No. 3; fourth, coiled cones
with the whorls more or less enveloping, do., No. 5.
The fourth and fifth forms are usually included in
the old genus, Nautilus. Practically, it is better to
designate the first class as orthoceran, the second as
cyrtoceran, the third as gyroceran, and the fourth and
fifth as nautilian. In tracing genetic series through

HEREDITY. 409

time they are found to diverge in their evolution, start-
ing with the orthoceran and passing through parallel
lines of forms, many of the genetic series having in
succession cyrtoceran, gyroceran, and even nautilian
forms of the fourth and fifth classes. Others are not
so perfectly parallel, stopping short with the cyrto-
ceran class of forms or the gyroceran. Many also
begin with cyrtoceran shells, while others diverge from
the gyroceran, and still other series have only nautilian
shells of different grades of close coiling and involu-
tion.

«<The application of the law of repetition in hered-
ity to the chambered shell-covered cephalopods, shows
that the straight orthoceran shells, Fig. 119, No. 1,
were repeated in the young of the curved cyrtoceran
forms, Fig. 119, No. 2, and these forms in their turn
in the young of the gyroceran forms, Fig. 119, No. 3;
and this may be seen by comparing the young or api-
cal part of each shell represented in outline with the
full-grown shells of the preceding figures. The apex
of No. 2, with the whole of No. 1; the apex of No. 3,
with the whole of No. 2. It will be understood, of
course, that the figures in outline represent full-grown
shells, except when otherwise explained, and that they
were built like the shells of Nos. 1-2, by an animal
living in their interiors and adding band after band of
shelly matter to the exterior, but in these outlines the
shell is supposed to be perfect and the internal struc-
tures concealed.! The young of Fig. 119, No. 4,
which represents the fourth class of forms repeats the
‘cyrtoceran form, then curves more closely, and just
Wefore it comes in contact there is a short time when

1Except in No. 9, in which a portion of the shell is broken away. showing
the cast of the interior and the sutures.

opoda,

Cephal

HEREDITY, 411

EXPLANATION OF FIG. 119.
LETTERING.

a. Apex of sHell. This usually bears a scar on the point, as shown in
Nos. 14 and 15, but this has no bearing on the question discussed, and has
not been described. This also represents the youngest (nepionic) or cyrto-
ceran stage in the growth of the shell, No. 8 being a young shell with complete
living chamber. This letter also indicates the location of the sections corre-
spondingly lettered in the figures.

4 is used to indicate the section of the cyrtoceran stage in Nos. 11-13.

6' is used to indicate the place of the sections, Nos. 4-54’, upon the whorls
of Nos. 4-5. They were taken through the whorl in the gyroceran stage.

cis used for the adolescent (neanic) stage of growth in the whorl and the
corresponding sections.

c'is used for the full-grown (ephebic) stage in the growth of the whorl and
the corresponding sections.

@ for the first part of the senile (gerontic) stage.

e for the final and most degenerative part of the senile stage.

zz for the impressed zone.

v venter or outer side of the shell, the dorsum being the inner side of the
whorl.

w for the whorls, thus 1 w in Nos. 3 and 4 means the end of the first whorl,
2w the beginning of the second whorl, 3 w that of the third whorl. These
letters serve to show the progressive increase in numbers of the whorls in the
ditferent classes of forms.

FIGURES.

No. 1. Outline of an orthoceran shell.

No. «. Outline of cyrtoceran shell.

No. 3. Outline of gyroceran shell.

No. 4. Outline of nautilian shell, having a larger umbilical perforation
at (2) and fewer whorls at the same age, than in No. 5; in other words, it is
less tightly and completely coiled up than the class of shells represented by
that figure.

No. 5. A nautilian shell with tighter coils than in No. 4 and the whorls
coming in contact and the impressed zone beginning at an earlier stage.

No. 6. Barrand as bohemi (sp. Barrande) Hyatt, showing the most
involute of the Silurian shells so far as known; No. 6 is reduced in size, but
the section No. 7 is natural size.

No. 8. A young shell of the same, natural size, with complete living
chamber.

Nos. 9-10. Coloceras globatum (sp. De Koninck) Hyatt, adult. No.9 has
a part of the outer shell broken off, showing the edges of the septal partitions
(sutures) as lines on the strong cast of the interior.

Nos. 11-13. Same to show the cyrtoceran stage and section, with its im-
pressed zone.

No. 14. Cenoceras clausum, Hyatt.

Nos. 15-16. Nautilus pompilius, to show the cyrtoceran stage with its im-
pressed zone.

412 PRIMARY FACTORS OF ORGANIC EVOLUTION.

it overlaps the apex without touching it. At this time
it is plainly gyroceran, like the whole of No. 3. After
it touches the first whorl just beyond the apex it re-
mains in contact, and the inner side or dorsum of the
second or overlapping whorl begins to show a flatten-
ing as a result of this collision of the whorls. The sec-
tions of the orthoceran, cyrtoceran, and gyroceran
whorls show no such flattening in any of the speci-
mens examined, although hundreds of different kinds
have been studied. The sections are designated on
the plate by the same letters as the supposed lines of
the sections made through the tube, and although dia-
grammatic figures, they give a sufficiently clear gen-
eral explanation of the facts observed. More specific
figures could have been given in abundance and will
be given in the paper now in course of preparation.}

“Fig. 119, No. 5, shows the same phenomena as
No. 4. The young is at first cyrtoceran like the adult
whorl of No. 2, and open, then becomes gyroceran in
curvature and finally overlaps the apex when it has
arrived at the end of the first volution, but does not at
first touch it. Then coming into contact it acquires a
flattened area or faint impressed zone on the dorsum
or inner side of the second volution, as is shown in
the section No. 5c. This is similar to the section of
No. 4 shown in No. 4c’, which represents a cut through
an adult whorl of the fourth class of forms. It differs
only in being smaller, on account of the younger stage
of growth at which it occurs.

‘The entire series of forms from orthoceran to nau-
tilian is more or less represented, even in the earliest
period at which the nautiloids appear, namely, in the

1See ‘‘Phylogeny of an Acquired Characteristic,’’ Hyatt, Proceedings
American Philosophical Society, Philadelphia, XXXII., No. 143.

| HEREDITY, 413

rocks of the Quebec group. There is, however, this
qualification: the fifth classof forms, or the involute
nautilian, are relatively rare and become more abun-
dant in successive periods. The young of nautilian
shells of the earlier periods are also apt to be lessclosely
coiled, or, in other words, remain open and similar to
cyrtoceras for a longer time during their growth. This
is shown by the large size of the central hole, or um-
bilical perforation, left in the center of full-grown
shells. This perforation is much larger, as a rule, in
Paleozoic than in the Mesozoic forms.

‘In each period the genetic series or groups of nau-
tilian forms have peculiarities of structure in the su-
tures, ornaments, apertures, etc., by which they can
be separated from each other, and these peculiarities
are the same as those possessed by gyroceran, cyrto-
ceran, and often orthoceran shells which occurred often
earlier in time, so that one can trace each group of
nautilian shells back to its ancestors through the par-
allel stages of evolution above described. The groups,
in other words, are parallel in their morphogenesis,
like two individuals of the same parents in their de-
velopment from youth to old age.

‘‘As a general rule the impressed zone originates,
as described above, after the whorls come in contact,
rarely before this time in the growth of any individ-
uals. Barrandeoceras is one of the most involute shells
known in the Silurian, and Fig. 119, No. 6, gives a
true sketch of this species ; No. 7, shows a section of
a full-grown shell with a decided impressed zone, and
No. 8 is the young. This last is a purely cyrtoceran
form with a compressed elliptical section like that of
No. 7, but no impressed zone, the inner side being
rounded like the diagram of Cyrtoceras, No. 2. The

414 PRIMARY FACTORS OF ORGANIC EVOLUTION,

impressed zone is not present in the young of Ophidi-
oceras, the closest coiled of all these forms, nor in the
young of most species of the Silurian before the whorls
touch, and all of the species likely to present this pecu-
liarity have been investigated.

‘¢The impressed zone is also, as a rule, lost in the
oldest stage of the whorl of every individual when the
whorls cease to continue to grow in contact. This
condition is represented in the last part of the outer-
most whorl of Nos. 4 and 5 in sections, Nos. 4e¢, 5¢,
and in the outlines of their apertures, which are ellip-
tical. The sections represent cuts through the whorls
when, as is the case in extreme age, these cease to in-
crease in size. As soon as this senile contraction be-
gins to occur, the sides shrink, becoming narrower,
the amount of involution becomes less, and the im-
pressed zone shrinks in breadth, as shown in the sec-
tions. When the whorl finally parts company in
consequence of continued contraction, the already
shrunken impressed zone, Nos. 44, 5d, rapidly dis-
appears, and the apertures of such shells are frequently
as round and free from indentations on the inner as on
the outer side, as is shown at the free end of Nos. 4
and 5.

“<In normally uncoiled forms, usually named Litu-
ites, when the adult or young is coiled, and the suc-
ceeding stages, whether representing adults or old
shells, are uncoiled, the phenomena are similar. The
impressed zone is lost after the growth ceases to bring
the whorls of the shell into contact.

«The young and the adults of many of these forms
have now been observed in the earliest periods, and it
is, therefore, obvious that during these early times the
impressed zone must have been a modification of the

HEREDITY. 415

whorl which took place in consequence of the mechan-
ical effects produced by close coiling. This charac-
teristic is slight when the coiling is slight and is de-
veloped in precise proportion to the increase of coiling
or involution of the whorls, and, on the other hand,
when through degeneration due to age, or to other
causes, the whorls cease growing in contact, the im-
pressed zone gradually disappears.

««Thus it generally appears preceded and accompa-
nied by an observable tendency in the mode of growth
toward closer coiling and that this tendency is quite
capable of producing the impressed zone can hardly
be denied with any show of reason, since the charac-
teristic tends to disappear in proportion as the pressure
is relieved through the degeneration of the powers of
growth-force to continue the normal rate of progres-
sive increase of bulk in old or young or prematurely
degenerate shells and in uncoiled whorls of all kinds
and all ages.

‘« The shells of Devonian series of nautiloids have
also been extensively examined, especially in the more
involute nautilian forms of the genus Nephriticeras,
and so far not one has been found with the slightest
indication of the presence of an impressed zone in
the cyrtoceran or gyroceran stages of development.
In several examples also, the disappearance of this
characteristic has been observed in the last stages of
old whorls. There is, therefore, every reason for re-
garding the impressed zone as a ctetic characteristic
acquired in the later stages of growth and not heredi-
tary so far as is known in any shells of the earlier Pa-
leozoic periods.!

1Certain exceptions have been found since this was written, but their evi-
dence is purely negative, it is impossible to say of them at present whether

416 PRIMARY FACTORS OF ORGANIC EVOLUTION.

««The same statement may also be made with regard
to the majority of Carboniferous shells. There is, how-
ever, a notable exception in Coloceras globatum (sp.
De Kon.) Hyatt, and very likely some other species
of closely coiled nautilian shells. In C. globatum of
Visé, Belgium, I found in seven specimens that the
impressed zone appeared while the whorl was still in
the cyrtoceran (or open) stage. Fig. 119, Nos. g-10,
give outlines of the adult of this species, and Nos. 11—
12, of the young and the zone, showing that the im-
pression appeared long before the whorls touched each
other and began to assume nautilian characters. Sec-
tion, No. 134, shows the impressed zone occurring in
the cyrtoceran stage while the venter or outer side of
the whorl was rounded. Such facts admit of but one
explanation, namely, that in this species the impressed
zone had become hereditary and was in consequence
repeated at an early age, previous to the occurrence
of close coiling which usually produced it in the ances-
tral forms of the same group.

‘There are certain correlative characters which
lead me to think that this is only a partial statement and
perhaps a more complete and better one would be as
follows: that the impressed zone, together with a pe-
culiar broadening out of the dorsum and helmet-shaped
section of the whorl, and perhaps also certain forms of
sutures occurred in the early stages of some Carbonif-
erous species before the nautilian stage, and conse-
quently they must have been introduced by heredity
into the development of this species before the ten-
dency to close coiling had completed the first whorl.

the impressed zone appeared as a genetic character or as a mechanical neces-
sity. Either view can be taken, but the positive evidence is that they are very
rare, and the impressed zone appears in them as a parallel character of dis-
tinct diverging series of forms.—A. #7.

HEREDITY. 417

Thus these characters, although purely ctetic in origin,
were repeated before the usual conditions recurred in
the ontogeny of this species which had obviously and
repeatedly produced them in the nautilian forms of the
earlier Paleozoic and the more generalized genetic
series of the Carboniferous. That this species, Co/.
globatum, is a highly specialized species is shown by
other characteristics, especially the early inheritance
of a furrowed abdomen, shown at vin Fig. 119, No.
11, and a peculiar aperture.

“‘The Triassic period is unimportant in this con-
nection since it has but few nautilian species that are
deeply involute and also sufficiently well known to
throw any light upon this problem. All of the true
orthoceran, cyrtoceran, and gyroceran forms diminish
in the Carboniferous and disappear with the Trias.

‘‘The Jura contains a considerable number of nau-
tilian shells of different genera of which the cyrtoceran
stages are sufficiently well known. Cenoceros aratum,
of which several specimens have been studied, shows
the impressed zone and correlative characters in this
stage; C. lineatum is the same; C. clausum, same;
C. intermedium, same. Fig. 119, No. 14, shows the
cyrtoceran stage ina shell of C. clausum, with a well
developed impressed zone, z. z. Endolobus is a char-
acteristic Paleozoic type and there is a single survivor
of this series in the Jura, End. (Vaut.) excavatum sp.
D’Orb. It is, therefore, very interesting and instruc-
tive to note that this species has the impressed zone,
according to D’Orbigny’s figure, during the cyrtoceran
stage. This species has a large umbilical perforation
and is slower in coiling up than other Jurassic species.
The evidence that the impressed zone and its correla-
tive characteristics are inherited in most species of the

418 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Jura before the habit of close coiling could have acted
‘ upon the whorls so as to produce this modification is,
therefore very general and convincing.

‘The leading characteristic of parallelism in all
genetic series of nautiloids is, as may be inferred from
the facts cited, a tendency toward closer coiling and
greater involution in the more specialized forms of
each separate series and a correlative increase in the
profundity of the impressed zone. When the impressed
zone becomes inheritable in some closely coiled and
involute specialized shells of the Carboniferous and
in similar shells in all of the genetic series of the
Jura this result is also directly connected with the ob-
served fact of the quicker development of the coiling
up tendency in the young of these Jurassic shells. This
is shown by the small diameter of the umbilical per-
foration in the centers of the shells of the Carbonif-
erous. It is also connected with the fact that the prim-
itive uncoiled forms, orthoceran, cyrtoceran, and gy-
roceran shells begin to die out in the Carboniferous
and cease with the Trias as mentioned above.

««This demonstration of the characters that accom-
pany progress in close coiling, enables me to fill a gap
which occurs in the evidence during the Cretaceous.
In this period the existence of the impressed zone dur-
ing the cyrtoceran stage of individuals has not been
clearly established by observation except in two spe-
cies, a form allied to Cymatoceras pseudoelegans D’Or-
bigny, from Faxoe,and Cymatoceras elegans from Rouen.
In other shells, although a considerable number have
been broken down, the state of preservation has been
invariably imperfect. The coiling, however, in the
young of all the shells examined is notably more ac-
celerated than in the similar shells of the Jura, and the

HEREDITY. 419

whorls broader and having more specialized charac-
teristics correlative with closer coiling and the early
existence of an impressed zone. It is, therefore, fair
to infer that the evidence when accessible will confirm
the facts observed in previous periods.

‘“‘The same arguments apply also to the tertiary
forms as far as known.

‘<The terminal members of the nautiloids are, of
course, the existing species. Maudzlus pompilius and um-
bilicatus have been examined in a considerable number
of specimens, and in all of these the impressed zone
and correlative helmet-shaped whorl and broad flat-
tened dorsal side appears during the cyrtoceran stage.
Fig. 119, Nos. 15-16, are outlines of the shell of pompz-
dius during the cyrtoceran stage exhibiting the helmet-
shaped whorl, broad dorsum, or inner side, and its
impressed zone, zz. Thus, when the whorls touch, as
in all the nautilian shells of the Carboniferous, Jura,
and Cretaceous, in which the same acceleration of de-
velopment also occurs, the whorl is already prepared
to become involute and to mould itself more readily
and rapidly over the surfaces of the apex and the side
of the succeeding whorls. In other words, heredity
has begun the work before the whorls touch, and be-
fore the deepening and enlargement of the impressed
zone through the pressure of close coiling is begun.
There are quite a number of characteristics of the spe-
cies of existing Nautili which lead to the inference
that they are survivors of Jurassic and generalized
Cretaceous and Cenozoic forms; the size of the um-
bilical perforations, the smoothness of the shells, the
simplicity of the sutures, and so on. These facts are

1This inference has been fully sustained by subsequent investigations.—
A, Hyatt.

420 PRIMARY FACTORS OF ORGANIC EVOLUTION.

of importance only in so far as they show that the ex-
isting Nautilus does not represent the acme of pro-
gress of its order, but is a descendant of shells with
less complicated structures than many of the genera of
the Carboniferous, Jura, and Cretaceous.”’

In these cases it seems that the mechanically ac-
quired impressed zone is inherited from the greater
part of the soma where it existed to a part of the soma
of the young where it could not be produced by me-
chanical causes, by reason of the non-contact of the
parts. This acquisition appears in a few Carboniferous
species, and then it is present in the cyrtoceran or
mesozoid stage of all the Jurassic, Cretaceous, and
Cenozoic species. Professor Hyatt, in his ‘‘ Phylogeny
of an Acquired Characteristic,” thus summarizes his
conclusions :

‘«The facts and arguments brought forward seem
to justify the following conclusions:

«‘t, The impressed zone is primitively a contact
furrow, an acquired characteristic of the dorsum of the
whorls of nautilian shells having large umbilical per-
forations, which appeared either in the ananeanic or
metaneanic (maturing) substages, and rarely later in
their ontogeny. There is abundant positive evidence
that in these primitive forms this furrow is a purely
mechanical result of the nautilian mode of growth, not
appearing in the ontogeny before contact, and either
partially or entirely disappearing on the free gerontic
(senile) volution.

‘¢2, The impressed zone does occur independently
of contact on the free dorsum of the paranepionic (ado-
lescent) substage as a dorsal furrow in some close-
coiled, highly tachygenic (accelerated) nautilian shells
in the Quebec group and in the Devonian.

HEREDITY. 421

‘¢3, While there is no positive proof that the dor-
sal furrow originated through heredity in the parane-
pionic substages of these nautiloids of pre-Carbonife-
rous age, there is also no satisfactory evidence that it
originated in the young of such species as have this
character, through purely mechanical agencies.

“«4. There is positive evidence that the similar dor-
sal furrow which also appears at the same age in the
young shells of Coloceras globatum and perhaps Celo-
gasteroceras canaliculatum among Carboniferous nauti-
loids can be explained only when it is considered as a
transmitted, tachygenetic (accelerated) characteristic.

‘«5. This fourth conclusion is supported by the
presence of a similar dorsal furrow in the paranepionic
(adolescent) substage of the young shells of all the
nautiloids of the Jura, so far observed.

‘¢6. The fourth and fifth conclusions are rendered
still more probable by the presence of the dorsal fur-
row at an earlier age, the metanepionic substage, in
all of the nautiloids so far observed, from the begin-
ning of the Cretaceous, through the Tertiaries, to and
including the living species of the genus Nautilus. Its
presence on this cyrtoceran volution in Cretacic shells
can be explained only when it is considered as a trans-
mitted, tachygenetic (accelerated) characteristic de-
rived from ancestral nautilian shells of the Jura, which
have the same characteristic at a later age, i. e., in the
paranepionic substage.

‘«7, The first conclusion is also sustained by the
parallel phylogeny of the impressed zone in the ances-
tral forms of the Ammonoidea, the Nautilinide, and
especially in the Mimoceras, the radical genus of this
family.

«¢8. The fourth, fifth, and sixth conclusions are

422 PRIMARY FACTORS OF ORGANIC EVOLUTION,

also supported by the presence of a contact furrow on
the dorsum of the earliest age of the conch in the spe-
cialized and highly tachygenic forms of the Goniati-
tine of the Devonian and of all the remaining ammo-
noids to the end of the Cretaceous.

‘¢g, These cumulative results favor the theory of
tachygenesis (acceleration) and diplogenesis, and are
opposed to the Weismannian hypothesis of the sub-
division of the body into two essentially distinct kinds
of plasm, the germ-plasm, which receives and trans-
mits acquired characteristics, and the somatoplasm,
which, while it is capable of acquiring modifications,
either does not or cannot transmit them to descend-
ants.” (Proceedings American Philosophical Soctety, Vol.
XXXII., p. 615).

4. EVIDENCE FROM BREEDING.

Under this head I cite the results of experience of
breeding of the domesticated Vertebrata. It is here
that we have had the best opportunity of testing the
possibility of the inheritance of acquired characters,
since the species in question have been the objects of
observation and experiment for a long period of time.
I especially avail myself of the writings in this con-
nection of Prof. Wm. H. Brewer, of Yale University,
President of the Agricultural Society of Connecticut.
The result of his long-continued observations is con-
tained in a series of papers in the journal Agricultural
Science of the years 1892-1893. He considers the sub-
ject under the following heads, viz.: The inheritance
of characters which are due to nutrition ; of those due
to the exercise of function ; of those due to disease ;
of those due to mutilation and injuries ; of those due
to habit, training, and education; of those due to. re-

HEREDITY, 423

gional influences and to a combination of causes ; and
of those of acquired plasticity and adaptation. I com-
mence with an example of the

a. Inheritance of Characters Due to Nutrition.

“«One class of ‘acquired characters,’ the transmis-
sion of which by heredity is especially denied by Weis-
mann, includes all ‘those which are directly due to
nutrition.’

‘« This denial strikes at the very foundation of what
has heretofore been considered an essential factor in
the practical improvement of breeds as to size. The
size attained by adult, healthy domestic animals de-
pends practically upon two causes—heredity and nu-
trition. Heredity is of course the chief one, for no
amount of feeding will make the Shetland pony equal
the Norman horse in size ; but whatever the heredity,
the size of the adult individual as compared with the
average of others of the same breed depends usually
upon its food. The ultimate weight of the mature
animal varies of course with the amount of fat assimi-
lated, which may occur long after maturity; but the
size as dependent upon the frame, such as the weight,
length, and general proportions, is modified by the
quantity and quality of food available during the grow-
ing period of early life. This fact no one questions ;
and if these acquired characters are in no degree what-
ever transmitted, then certain practices of breeders,
which are founded upon the contrary belief are delu-
sive and expensive mistakes.

‘‘Practical breeders have hitherto believed that
these characters are to some degree transmitted, and
practice accordingly. I have searched extensively the
writings of practical breeders to see if I could find a

424. PRIMARY FACTORS OF ORGANIC EVOLUTION,

single one who questions it, and I fail to find even so
much as an intimation of any such belief. All the
recorded observations founded upon actual practice
appear to point the other way, and consequently the
fact of partial transmission is assumed.

‘« The practical value given to this factor is now
much smaller than formerly given, but that it is a fac-
tor of some value is universally assumed.

««During the last century, and early part of this,
many graziers had a maxim that in the profitable pro-
duction of animals for slaughter, ‘feed is more than
breed,’ but now both breeders and graziers know that
heredity or ‘breed,’ is the more important. But no
breeder claims that a breed is or can be kept up to
extra size by selection alone. This belief is so uni-
versal, and is apparently so grounded upon long and
extensive experience, that I cannot find there has ever
been an attempt to increase the size of any breed with-
out special attention to this factor, and consequently
conclusive and direct experiment is entirely wanting.
Positive proof either way cannot be deduced from the
actual experiments of breeders ; their belief that feed
as well as selection is necessary, is a deduction from
the observation of many facts which bear upon the
question.

‘«In this connection it must be borne in mind that
all the best breeders recognize the rule laid down by
Darwin, that those characters are transmitted with
most persistency which have been handed down
through the longest line of ancestry. Breeders do not
believe that the characters acquired through the feed-
ing of a single ancestor, or generation of ancestors,
can oppose more than a slight resistance to that force
of heredity which has been accumulated through many

HEREDITY. 425

preceding generations, and is concentrated from many
lines of ancestry. Yet the belief is universal that the
acquired characters due to food during the growing
period has some force, and that this force is cumula-
tive in successive generations. All the observed facts
in the experience with herds and flocks point in this
direction. It is the same whether the observations re-
late to the increase in the size of breeds, which has
been brought about by systematic selection and feed-
ing directed with this special aim, or to the local de- -
velopment of breeds under the combined influence of
the food supply and unsystematic selection.

«Where both large and small breeds have been in
process of improvement in the same region at the
same time and with the same ‘kinds of food, liberal
feeding along with systematic selection is always prac-
tised where an increase of size is aimed at, and under-
feeding during growth is practised when it is desired to
reduce the size. We have examples of these going on
together contemporaneously. Breeding for increase
of size is more common than that for reducing, but the
latter occurs not only in the small fancy breeds of
poultry and dogs, but even of cattle. When small and
delicate Alderney cows were a fashionable ornament for
parks and lawns, some of the most successful breeders
practised starving systematically, and at least one
eminently successful breeder of these animals so under-
fed the growing calves that it led to legal interference
by a local Society for the Prevention of Cruelty to
Animals.

‘So far as I know, all the breeds of especially
large horses, cattle, and sheep have originated in dis-
tricts of abundant food, usually in fertile valleys or on
plains, and excepting fancy breeds of poultry and pets,

426 PRIMARY FACTORS OF ORGANIC EVOLUTION.

all the smaller breeds have originated in districts of
scantier forage. This can hardly be due to accident,
for it is as true of local varieties of’wild animals under
natural selection as of domestic animals under artifi-
cial selection.”

b. Inheritance of Characters Due to the Exercise of
Function.

This class of cases has an especial bearing on the
doctrine of kinetogenesis. We have a very conspicu-
ous example of such inheritance in the case of the
evolution of the trotting horse, which is described by
Professor Brewer as follows:

“«We have a copious literature relating to the de-
velopment of this breed, and the ‘records’ of speed
provide the data for a mathematical history of the rate
of progress, and also the measure of amount of cumu-
lative variation that has occurred up to this time.
These data give to this breed a special interest for
scientific study. :

“‘The facts briefly stated are as follows: Trotters
had their uses for ages, but fast trotters were not
wanted until the improvement in roads and in wheeled
vehicles during the last quarter of the last century
caused an increasing demand for faster roadsters for
light draft. Trotting is the gait of traction, as run-
ning is for riding, and trotting as a sport sprang up in
nearly all the countries of Europe as well as in Amer-
ica so soon as faster trotters were needed for the road.
Then trotting-horses began to be bred, and long be-
fore the close of the century there were trotting-stal-
lions of considerable fame. There were also recorded
statements as to the speed attained.

“‘Lawrence, a lover of trotters, in his 7reatise on

HEREDITY. 427

Horses (London, 1796), considered that ‘the utmost
speed of the English trotter’ (which he believes to ex-
cel all others), to be a mile in two minutes and fifty-
seven seconds. During the next twenty years there
were very many recorded trials of speed, and a few of
the best animals, both here and in Europe, trotted a
mile in three minutes, but none in less time than that
given by Lawrence.

‘Considering the number of animals that were
tested, the widespread interest in the matter, and that
these records were the best of both Europe and Amer-
ica, it is fair to assume that this was the utmost speed
actually attained by the best trotting-horses until after
1820, although some specific selection in breeding trot-
ters had been going on for half a century, and possibly
much longer.

«« By 1810, the taste for trotting as a sport had died
out in western Europe, but it increased here, and in
1818 it became a recognized sport under specific rules.
This is practically the beginning of technical ‘trotting
records’ as we now know them. It soon became
fashionable to drive a single horse for pleasure, a so-
cial factor in breeding that was lacking in the Old
World. This created a demand for trotters, as well
as increased the taste of trotting asasport. Asso-
ciations were chartered for the promoting of trotting,
and special tracks built for the exercising and training
of trotters.

‘At the end of 1824, six years after the first ac-
cepted three-minute record, the record had fallen to
2:34, a reduction of twenty-six seconds. This great
reduction so rapidly effected was, doubtless, due chiefly
to better training, but also in part to special exercise
of function, in part to heredity, and in part to the

428 PRIMARY FACTORS OF ORGANIC EVOLUTION.

larger number of animals trained. It is not probable
that mere exercise of training could materially further
increase this speed, for the next ten years lowered the
record only two and a half seconds, and twenty-one
years more passed before the first 2:30 record in har-
ness was made.

«‘By 1848, the record was lowered to 2:29%, and
we have now a 2:30 class, with two or three horses
technically in it, and perhaps half a dozen that had
actually trotted at that speed. Now we began to have
distinctively trotting blood, and heredity began to tell.

‘<The next decade lowered the record five seconds;
and the next (ending in 1868), lowered it seven.and a
fourth seconds more; there were several horses in the
2:20 class, and nearly one hundred and fifty in the
2:30 list.

«¢The next decade lowered the record four seconds;
and the next (ending in 1888), four and a half seconds,
and the number of 2:30 horses had increased to 3,255
animals.. At the close of last year, the record had
been further lowered half a second, to 2:08 ; there
were 5,908 in the 2:30 list, 507 in the 2:20 list, and
seven in the 2:10 list. This is the history for seventy-
three years of ‘records.’

“«¢ Parallel with the evolution of this breed has been
the development of a breed of pacers. The fast ani-
mals are not so numerous, but the speed is greater,
and the gait, as a fast gait, is more distinctly artificial.
The instincts involved will be discussed in a later pa-
per; here I will notice only the development of speed,
because that is the direct and obvious result of func-
tional development, and because we have mathematical
data as to the rate and amount of actual evolution.

‘«That the gain in speed has been cumulative, and

HEREDITY. 429

that for three-fourths of a century, that it has gone on
along with systematic exercise of special function in
successive generations of the present fast trotters, is
indisputable and very evident. Selection has doubt-
less determined the proper correlation of the various
organs involved in the special evolution, but the in-
crease in speed has only come along with the func-
tional development, which was enhanced by special
exercise in the individuals of successive generations.
The cumulative value of this, if transmitted, would be
vastly more than enough to account for all the increase
that has actually occurred, great as that is. Viewed
as phenomena, there is every appearance and indica-
tion that the changes acquired by individuals through
the exercise of function have been to some degree
transmitted, and have been cumulative, and that this
has been one factor in the evolution of speed. The
cumulative variation has been most marked since we
have had a 2:30 class, that is, since we have produced
animals that are swift by heredity, and whose ances-
tors, as well as themselves, have been exercised and
trained to trot. Studied as phenomena, there is not a
particle of evidence that these special changes ac-
quired by the individuals were totally lost to each suc-
cessive generation, and that all that was ‘transmitted
by heredity,’ was a something that did not exist in
either parent or in any ancestor. There is nothing
whatever in the actual phenomena observed anywhere
along the line of this development of speed that would
lead us to even suspect that the changes due to exer-
cise of function had zo¢ been a factor in the evolution,
and there is not a particle of evidence, other than met-
aphysical deductions, much less proof, that it would

430 PRIMARY FACTORS OF ORGANIC EVOLUTION.

or could have gone on just the same by mere selection
and adventitious variation.”

c. Inheritance of Characters Due to Disease.

Under this head Brewer cites a well-known case.
He says: ‘‘The most extensive and complete set of
experiments yet published on the artificial production
of disease by mechanical injuries are those of Dr.
Brown-Sequard on the artificial production of epilepsy.
This is a disease which is certainly sometimes heredi-
tary and which may also be produced by art in previ-
ously sound animals. He experimented with guinea
pigs and produced many artificial epileptics, and by
breeding these he produced many congenital epilep-
tics. The disease artificially produced in the parents
was transmitted to the offspring in numerous cases.
The acquired characters in those cases were certainly
transmitted to the offspring and became hereditary.
These experiments were continued and repeated by
his assistant and pupil Depuy, and the results abund-
antly confirmed. It was shown, moreover, that in
many cases it was the ¢endency to become epileptic that
was transmitted rather than the disease itself. Just
as ina great majority of cases of strictly hereditary
disease it is the constitutional tendency rather than
the disease itself that is commonly transmitted.

“«These experiments have now been before the
world some years, during which time ideas have greatly
changed as to the causes of disease, and the nature of
hereditary tendencies, but as yet there are no pub-
lished accounts of experiments indicating that those of
Brown-Sequard and of Depuy were not carefully per-
formed, or that the conclusions were illusive. Medical
literature abounds with alleged instances where ner-

HEREDITY. 431

vous diseases acquired by parents through environ-
ment have been transmitted in some shape to children,
but this evidence is not nearly so conclusive as the ex-
perimental proof cited.

‘«In conclusion we may say that the drift of all the
collated observations on both man and brute seem to
indicate that certain of the changes produced in the
animal body by disease are often to some degree trans-
mitted, that these may be cumulative and lead to de-
generation if not indeed to the extinction of families.
The experience of breeders as well as the observations
of medical men practically establishes the fact that ac-
quired weakness and defects occurring in successive
generations may result in truly hereditary unsound-
ness.”

a. Inheritance of Characters Due to Mutilation and
Injuries.

While characters of this kind are relatively rarely
inherited, there is little doubt that they can be. Dr.
Brewer cites a few cases for illustration ; ‘‘some of
them have been already published, others have not.
They are not the most striking, but are chosen because
they are representative.

“‘a. A mare in foal had an eye seriously injured by
burdocks entangled in the forelock. She suffered with
violent ophthalmia, and in due time dropped a foal (a
filly) which had the corresponding eye aborted. She
afterwards bore several normal foals.

“«(This case came under the observation of the
eminent veterinarian, Professor Law of Cornell Uni-
versity. Papers American Public Health Association,
2, Pp. 254.)

‘*d, A game-cock, in his second year, lost an eye

432 PRIMARY FACTORS OF ORGANIC EVOLUTION.

inafight. Soon after, and while the wound was very
malignant (it never entirely healed), he was turned
into a flock of game hens of another strain. He was
otherwise healthy and vigorous. A very large propor-
tion of his progeny had the corresponding eye defec-
tive. The chicks were not blind when hatched, but
became so before attaining their full growth; some at
the time of acquiring the pin-feathers, others later and
before reaching maturity. The hens afterwards pro-
duced normal chickens with another cock. Both
strains had been purely bred for ten or more years,
and none of the fowls had been blind unless from
fights. —

“<(This case was reported to me’by an educated
and reliable breeder of game-fowls. )

“¢¢, A hunting mare had a split pastern and was
then used for breeding. Her first, third, and fourth
foals were sound, the second one had ‘almost an exact
reproduction of the mare’s unsoundness.’

‘(This is on the authority of the celebrated veteri-
nary surgeon, Clement Stevenson, as occurring under
his own observation, ‘not hearsay.’ Live Stock Jour-
nal, London, November 23, 1888, p. 508.)

‘‘d@. A female (and very prolific) cat, when about
half grown met with an accident. ‘Her fine, long tail
was trodden on and had a compound fracture, two ver-
tebrz being so displaced that they ever after formed a
short offset between the near and far end of the tail,
leaving the two out of line. At first I noted that out
of every litter of kittens some had a tail with a querl
in it.’ With successive litters the deformity increased,
until ‘not a kitten of the old cat had a straight tail,
and it grew worse in her progeny until now we have
not a cat with a normal tail on the premises,’ (in a cat-

HEREDITY. 433

population of six or eight, exclusive of young kittens).
‘The tails are now in part mere stumps, some have a
semicircular sweep sideways, and some have the orig-
inal querl. Perhaps the deformity was somewhat
aggravated by in-and-in breeding and by artificial se-
lection practised by my Chinaman, who, with the per-
versity of his race, preferred the crooked tails, and
thus preserved them in preference to the normal kit-
tens. There are no other abnormally-tailed cats in
the neighborhood.’

‘«This is the essential part of an unpublished letter
from that keen observer and eminent scientist, Prof.
Eugene W. Hilgard of the University of California.

«Numerous cases have been recorded as occurring
with mankind. I will give but two, both of which
have not before been published.

‘¢e, A person, when a boy of ten years, cut the
terminal phalange of the little finger of his left hand
with a sickle. The joint was not injured, nor was the
function of the finger seriously impaired. There was,
however, an obvious deformity. The finger was ill-
shaped and crooked, and the nail abnormal. He mar-
ried and had two children, the first a son, with normal
fingers, the second a daughter, who had the little fin-
ger of the corresponding (the left) hand deformed
from birth in the same manner. The function of the
finger was not seriously injured, but the deformity was
precisely the same in shape, even to the malformation
of the finger-nail. She died at thirty, without chil-
dren, consequently no observation on a succeeding
generation could be noted. None of his other kindred
had malformed fingers, nor had any ancestor of the
child for at least three generations, and there was no
knowledge of any such in the more remote ancestry.

434 PRIMARY FACTORS OF ORGANIC EVOLUTION.

“«(This case was related to me in full detail by the
father with the deformed finger, and with whom I was
personally acquainted. He was an eminent physician,
the president of a large and reputable medical college,
and his name is well known to the profession.)

««f A woman thirty-five years of age had both
kneepans broken. Erysipelas and other complications
prevented the use of the usual surgical appliances for
keeping the severed parts together while healing, so
they never united by bony union, but became joined
by intervening cartilage. The hurt was peculiarly
painful and slow of healing, because of the complica-
tions alluded to, but the general health was fully re-
stored. Forsome years after healing there was a very
pronounced groove or furrow along the line of fracture
over the connecting cartilage, especially in the right
knee. The outer edges of the fractured bone were
sharp at first, but ultimately became rounded by ab-
sorption. Both fractures were V-shaped. The right
knee had the parts wider separated at the time of ‘the
accident, and was again partially torn asunder three
and a half months later, and the furrow consequently
remained very much broader and deeper than in the
other knee. About. four months (124 days) after the
first accident, and while still unable to walk, she gave
birth toa son. No abnormal appearance was noticed
at the time, and later was not looked for until the
child was ten or more years old, when he called atten-
tion to the matter himself. There was then a deep
and well-defined groove across the surface of the right
kneepan, very plainly perceivable through the skin.
It corresponded precisely in shape and position with
the fracture and the later furrow in the corresponding
bone in the mother. It was most pronounced before

HEREDITY. 435

the age of sixteen. After that the edges became modi-
fied by growth or absorption, becoming less sharp,
following in this respect the changes that gradually
occurred in the shape of the bone in the mother. The
son is otherwise normal. Three other children of the
same parents, one born before and two after the birth
of the one described, are entirely normal. The ances-
tors of both parents are known for several generations
(from three to éight in the several lines) and all were
normal, so far as is known.”

‘(This case has been under my own observation
during the whole period.)

“Tt will be noticed that in the cases a, 4, and f, the
injury to the parent occurred shortly before or during
gestation, and that the healing had not taken place
until after the birth of the offspring. Also, that the
function of the organ involved, an important organ in
the animal economy, was at the time suspended. Also
that in all these cases, later offspring were normal.”

e. Inheritance of Characters Due to Regional Influences.

Characters of this kind mostly come under the head
of Physiogenesis. A case of inheritance is thus re-
corded by Brewer.

‘¢ The texture and certain other characters of wool
which are of practical importance to manufacturers,
depend in part on the breed and health of the animals,
in part on the kind of food and on its uniformity of
supply, and in part on local conditions of climate,
soil, and forage. The wool grown in some regions is
harsher than that grown in others, and this is certainly
an acquired character in that it takes place in flocks
taken from one region to another. I have specimens
of wool alleged to have been taken from the same

436 PRIMARY FACTORS OF ORGANIC EVOLUTION,

flock, the same individual animals, when pastured at
two stations. The first were shorn when the sheep
were pastured in southeastern Ohio, where the sheep
were bred, a region noted for certain excellencies of
its wool. Taken to a certain portion of Texas, and
pastured on an alkaline soil, the wool of those sheep
took another character, affecting both its texture and
also its behavior with dyes. Treated in the same vats,
as to dye, lac and mordant, the difference is very ob-
vious.

“A certain harshness. of the wools produced in
some regions where the soil is alkaline or salt, the
climate dry, and the forage plants characteristic of
such regions, is widely known and is considered a de-
fect by manufacturers. It is stated that when a flock
is taken from a favorable region to such a less favor-
able one the change in the character of the wool begins
immediately, but is more marked in the succeeding
fleeces than in the first. It is also alleged that the
harshness increases with succeeding generations, and
that the flocks which have inhabited such regions sev-
eral generations produce naturally a harsher wool than
did their ancestors, or do the new-comers.

‘“«Now, in this case, the deterioration in successive
generations cannot possibly be due to panmixia, the
withdrawal of selection; on the contrary, selection
goes on under the new conditions just as carefully as
under the old, and often more so, for this is the means
used to lessen the evil.

‘«Tf this increase in the harshness of the wool of
succeeding generations is due in part to the inheri-
tance of an acquired character, it is very understand-
able. That it is a congenital adventitious variation

- HEREDITY. 437

coincident in all the individuals of immense flocks, is
a mathematical absurdity.

‘We have an analogous regional character in the
hoofs of horses. From early times it has been a known
fact that the feet of horses produced in mountainous
and hilly regions stand travel on hard roads and on city
pavements better than those bred on softer low lands,
however rich and fertile the latter may be. European
writers of previous centuries are very specific on this
point. Jacquet, over two centuries ago, cites it as a
fact true alike in Spain, Italy, and other countries of
Europe. I have interviewed the livery-stable men in
various eastern cities as to the relative character in
that particular of the horses bred in the hilly regions
of New England, New York, and Pennsylvania, com-
pared with those produced on the prairies, and the
testimony is almost unanimous to the same effect.
The old Vermont bred horses are still famous.

‘« This regional character cannot be a matter of se-
lection and adventitious variation. It must be related
to the environment alone, and environment can only
act on the living individual. If this fact is due to the
inheritance of acquired characters, it is very easily
understood. The different effects of exercise of the
feet of the growing animal in the one case on the hard,
stony soil of the hills, in the other, on the softer and
fine soil of the prairies, makes a difference in the ac-
quired characters, a difference of the very kind spoken
of, and which becomes congenital.”

At the close of this series of papers Brewer re-
marks: ‘‘The art of breeding has become in a meas-
ure an applied science; the enormous economic inter-
ests involved stimulate observation and study, and
what is the practical result? This ten years of active

438 PRIMARY FACTORS OF ORGANIC EVOLUTION.

promulgation of the new theory has not resulted in the
conversion of a single known breeder to the extent of
inducing him to conform his methods and practice to
the theory. My conclusion is that they are essentially
right in their deductions founded on their experience
and observations, namely, that acquired characters
may be, and sometimes are, transmitted, and that the
speculations of the Weismann school of naturalists are
unfounded.”

5 THE CONDITIONS OF INHERITANCE.

Since the evidence adduced must be regarded as
proving that characters acquired by an organism may
be transmitted by inheritance, we next endeavor to
ascertain what information is within our reach which
can throw light on this mysterious process. Although
Weismann has demonstrated the isolation and stability
of the germ-plasma to exceed that of other tissues, he
has not proven that it is entirely inaccessible to exter-
nal influences. He admits that its continual subdivi-
sion by the development from it of the embryonic
soma, would have speedily reduced it to an infinitesi-
mal quantity, were it not that it grows by accession of
nutritive material like other tissues, which nutritive
material is furnished by the soma. The accessibility
of the germ-plasma to stimuli which affect the soma is
then clearly possible.

The effect of the specialization of tissues on their
nutrition and repair after injury, is well known. Nu-
trition of each tissue produces only that tissue. Re-
pair or restoration of parts is confined to the repro-
duction of a tissue similar to the part lost, or similar
to some unfinished or embryonic stage of it. The
lower we descend in the scale of life, the more com-

HEREDITY. 439

plete is the reproduction of a lost part. The special-
ization of the higher organisms deprives the tissue of
the capacity for exact reproduction. As an example
of the reduction of this capacity, I cite the reproduc-
tion of the tail of lizards, where no vertebrz are repro-
duced, but in its place a notochord; while the squa-
mation presents a simpler character than that of the
normal tail. The possibility of reproducing the entire
organism is restricted, in the multicellular animals, to
the germ-plasma, which therefore may be regarded as
retaining the characteristic of the protozoén, which
reproduces itself by division. But in the multicellular
plants the power of reproduction of the entire organ-
ism from any of its parts, is retained to a much greater
degree than in multicellular animals. The reproduc-
tion of plants by cuttings, buds, tubers, and even by
single leaves, is well known; a characteristic which is
due to the general distribution of unspecialized proto-
plasm throughout the organism. Inheritance of char-
acters is in these cases known to be very exact, and
there can be here no isolation of the germ-plasma. This
isolation is progressively more pronounced as we rise
in the scale of specialization of structure, but that it
ever becomes absolute, the facts before us forbid us to
believe.

Having thus seen that the plasma of the germ-cells
is open to the influence of stimuli, let us see how it is
possible that such stimuli can be transmitted to it, and
how they could affect growth, of the embryo.

It has been shown that impressions experienced by
an animal during one stage of development may be
effective in causing the appearance of new structure in
a later stage. I have already quoted (Chap. V.) from
Poulton the results of experiments on the colors of

440 PRIMARY FACTORS OF ORGANIC EVOLUTION

Lepidoptera by several English entomologists. By
exposure to different colors, of larvee which were ap-
proaching the period of pupation, corresponding colors
were produced in the pupe. Thus black, dark, green,
and yellow larve, and larve with gilt spots or entirely
gilded, were produced at will. In this instance the
dynamic effect produced by the exposure was stored
for the period which elapsed between the exposure of
the larva and the full development of the pupa. In
another experiment, larvee which were in the act of
weaving cocoons, on exposure to certain colors, were
induced to-weave cocoons of corresponding color.
This experiment demonstrates that a stimulus may be
transmitted to a gland so as to modify the character
of its secretion in a new direction. From both experi-
ments we learn the transmissibility of energy from the
point of stimulus to a remote region of the body, and
its conversion into growth energy (in this case by
Physiogenesis). This prepares us to look upon hered-
ity as an allied phenomenon, i. e., the transmission of
a special energy from a point of stimulus to the germ-
cells, and its composition there with the emphytogenic
(inherited) energy into bathmism (or evolutionary en-
ergy). |

The relation of inherited and acquired characters
in a series of generations may be graphically repre-
sented as follows: Let S represent the aggregate of
character of the body (soma) of a given species in pro-
cess of progressive evolution or acceleration. Let g
represent the aggregate of characters potential (or dy-
namically present) in the germ cells of the same indi-
vidual. For the sake of simplification of the problem
I consider here only one sex, and imagine the repro-
duction to be parthenogenetic. Let 4 represent the

HEREDITY. 441

new character acquired by the soma under the appro-
priate stimulus, and let @ represent the same charac-
teristic as it is impressed on the germ-plasma of the
same individual at the same time, and in consequence
of the same stimulus. The history of the acquisition
and incorporation of newly acquired characters by the
line of descent originating with the species Sg, may
be represented as follows, for successive generations,
which are numbered 1, 2, 3, etc.

ISA + :

2 ee gill :

cg)

3S + Cah a2 g3
458 7” ca! a2 a3 at
5§ i cal a2.q3.a9as

oe 2A”
Fig. 120.—Diagram explanatory of Diplogenesis.

Under the appropriate stimulus the soma S acquires
A, and the germ plasma g the identical a! as the first
stage. The character 4a! being only inheritable va
the germ-plasma, it is represented by a! in the second
stage or generation, where it appears as an addition
to the characters of S and g, so that the soma of the
second generation is represented by the expression
Sa}, and the germ-plasma by g(e1); (on the supposi-

442 PRIMARY FACTORS OF ORGANIC EVOLUTION,

tion that .S.4-+ ga! represents the first of a line in which
a given character appears). A new character or an
additional increment of the same character, appears
in the second stage of acceleration ‘‘2,” and is repre-
sented as before, by 4a’, the 4 appearing in the soma,
and the a? being added to the character of the germ-
plasma. In the third stage, the new character a? ap-
pears in the soma, which now becomes Sala?. The «?
acquired by the germ-plasma of the second stage, is
inherited by that of the third, which is therefore rep-
resented by g(ala?). To the third stage is now added
the acquisition 4a. The a? is again incorporated into
the soma of the succeeding or fourth stage, which is
therefore represented by the expression S a!a?a3; while
the germ-plasma of the same (fourth, ‘ 4,’’) stage, is
represented by g(aa’a®), and so on. The lines of im-
mediate inheritance are represented by straight lines.
The vertical lines represent the descent of characters
from one type of the germ-plasma to a succeeding
one; and the oblique lines represent the transmission
of the same characters to the soma into which it grows,
as the succeeding generation or stage.

The letters a1, a, etc., expressive of characters ac-
quired by the germ-plasma, are numbered for identifi-
cation only. Should the influences derived from the
ancestry of the other sex be added to the diagram its
complexity would become inconvenient, and they are
therefore omitted. It is to be also observed, that the
enumeration of generations as immediately successive,
as I-2-3 etc., is to be understood as indicating succes-
sion only, and not any exact number of generations.

In the hypothesis of heredity above outlined, it is
insisted that the effects of use and disuse are two-fold ;
viz.: the effect on the soma, and the effect on the

‘

HEREDITY. 443

germ-plasma. Those who sustain the view that ac-
quired characters are inherited, must, I believe, un-
derstand it as thus stated. The character must be
potentially acquired by the germ-plasma as well as ac-
tually by the soma. Those who insist that acquired
characters are not inherited, forget that the character
acquired by the soma is identical with that acquired
by the germ-plasma, so that the character acquired by
the former is inherited, but not directly. It is acquired
contemporaneously by the germ-plasma, and inherited
from it. There is then truth in the two apparently op-
posed positions, and they appear to me to be harmon-
ized by the doctrine above laid down, which I have
called the Theory of Diplogenesis, in allusion to the
double destination of the effects of use and disuse in
inheritance.

From the preceding considerations we learn that a
new character is not inherited unless it is acquired by
germ-plasma, as well as by the soma. Should it fail
of the former it will not be inherited, although it may
appear in the soma. It is also evident that the same
character appears in the soma of later generations by
virtue of its inheritance by their germ-plasma. Hence
should it fail to appear in the adult soma of one gen-
eration, it might arise in a later one; and hence the
possibility of atavism, and an alternation of genera-
tions. Intermittent stimulus might be followed by in-
termittent activity of growth energy. This would be
especially apt to occur during the assumption of sex-
uality by animals and plants whose reproduction had
been performed by cell-division or budding only. And
such is the character, of most types of alternate gene-
rations ; a sexual type alternates with a non-sexual
type. The advantages being on the side of sexual re-

444 PRIMARY FACTORS OF ORGANIC EVOLUTION.

production on account of its increased opportunity of
variation, it has replaced the more primitive method
by the process of natural selection.

The time when the impressions of physical habits
are conveyed to the reproductive elements has an im-
portant bearing on the question of inheritance. Pro-
fessor Osborn! has thus classified the agencies which
lie at the basis of organic evolution. Opposite to each
he states the theories which have been proposed to
account for them:

A, Ontogenic Variations,

a, Gonagenic, i. e., those aris-
ing in the germ-cells, including
“blastogenic "' in part of Weis-
mann, the ‘‘ primary variations”
of Emery.

6. Gamogenic, i.e., those aris-
ing from maturation and fertili-
zation, including the ‘‘ blasto-
genic” in part of Weismann,
and secondary or Weismannian
variations of Emery.

«. Embryogenic, i.e., those oc-
curring during early cell-divi-
sion, including the blastogenic
and somatogenic of Weismann.

d, Somatogenic, i.e., those oc-
curring during larval and later
development after the formation
of the germ-cells.

Theoretically connected with
pathological, nutritive chemico-
physical, nervous influences, in-
cluding the doubtful phenomena
of Xenia and Telegony.

Theoretically connected with
influences named above, also
with the combination of diverse
ancestral characters, Amphi-
mixis of Weismann.

Theoretically connected with
extensive anomalies due to ab-
normal segmentation, and other
causes observed in the mechan-
ical embryology of Roux, Wil-
son, Driesch, and others.

Connected with reactions be-
tween the hereditary develop-
ment forces of the individual
and the environment.

B. Phylogenic Variations,

Variations from types originating in any of the above stages

which become hereditary.

American Naturalist, 1895, p. 426: ‘(On the Hereditary Mechanism and
the Search for Unknown Factors of Evolution "'

HEREDITY. 445

Osborn points out that Buffon appealed to the
‘‘direct action of the environment” as a cause of evo-
lution, in so general a way, as to embrace all the con-
ditions above enumerated. St. Hilaire dwelt on the
embryogenic influences, while Lamarck laid stress on
the somatogenic. Darwin only discussed variation
after it came into being.

The distinctions pointed out by Osborn relate to
the period of life at which modifying influences are
experienced ; that is, they are time distinctions. They
must all, however, be included under two heads when
the sources of influence are considered. That is, they
must proceed from the organism itself, or from the en-
vironment directly. Those proceeding from the or-
ganism may also be divided into two classes, viz.,
those which are inherent in the physical and chemical
characters of protoplasm, and those which have been
acquired by generations prior to any given one under
consideration. In this work I attend first to the prob-
ably efficient or phylogenetic causes, and these may be
regarded as having been at some time or another dur-
ing the history of the phylum as somatogenic. On
this view, I have regarded the life of an animal as
uivided into three periods ; those of embryonic life, of
adolescence, and of maturity. During embryonic life
impressions are exclusively somatic, and can be only
obtained through or from parental stimulus and parental
environment. Such will reach the embryo through nu-
trition, and through the direct mechanical contacts and
strains of theenvironment. The environment of unpro-
tected embryos is external to the parent; that of long
protected embryos is the walls of the oviduct, uterus,
etc., within the parent. Ryder has alleged with much
reason that the nature of the contact of the chorion with

446 PRIMARY FACTORS OF ORGANIC EVOLUTION,

the walls of the oviducts or uterus has determined the
shape of the placenta ; and that the invagination of the
embryo which resulted in the development of the am-
nion is a result of gravitation. While these facts have
an important bearing on the study of inheritance, they
have but a collateral relation to evolution; since the
embryo, whether in utero or in ovo, has little oppor-
tunity of experiencing the external influences which are
only possible at later periods of life. It is during ado-
lescence that the normal activities of maturity, except
reproduction, are first practised, whether inherited or
learned for the first time. The superior capacity of the
adolescent stage for acquisition in all directions is well
known, and it is reasonable to suppose that since growth
is not completed, changes in its details can be most
readily introduced. It is tothis period of life then that
we must look for the effective influence of the factors
of evolution in the acquisition of new characters of the
soma. And if the nervous, muscular and other tissues
react at this period most readily to external stimuli,
it is to be supposed that the developing reproductive
cells possess the same characteristic, and record in
their molecular movements the influences which are
experienced by the entire body. Such influences on
the reproductive cells, repeated millions of times from
generation to generation, must produce a definite effect
on them, in spite of the conservatism which their com-
parative isolation imposes on them.!

The transmission of acquired characters is evi-
dently accomplished during the adult period. While
the influence on the soma is greatest during ado-
lescence, the influence on the germ-plasma is prob-
ably important during maturity, because habits formed

lAmerican Naturalist, December, 1889, ‘‘On Inheritance in Evolution.”

HEREDITY. 447

during adolescence are now practised with especial
energy and frequency. The influence on the constantly
renewed germ-plasma is correspondingly greater, and
transmission is of course more certain. Some charac-
ters seem to have been mainly acquired during matur-
ity. Such is the permanent dentition of the higher
Mammalia, which does not appear until or after ma-
turity. In this case the influence of use on the germ-
plasma must be more energetic than that on the soma.
It is, however, not unlikely that the fundamental char-
acters of mammalian dentition were laid during ado-
lescence by direct influence on the temporary dentition.
The tritubercular molar was established at that time
and owes its present existence to inheritance. Only
the sectorial and lophodont types have been added
since the extensive development of the milk dentition
in geologic time.

The chief source from which acquired characters
are introduced into the germ-plasma, and hence into
the soma of the next generation, is probably the sper-
matozo6id, since it is endowed with a greater kinetic
energy than the ovum. The latter furnishes nutritive
material for the supply of the needs of growth. That
the male is the chief source of variation is also indi-
cated in the numerous cases when he is more active
than the female, and hence more capable of supplying

the stimulus of use.
The manner in which influences which have af-

fected the general structure are introduced into the
germ-cells remains the most difficult problem of biol-
ogy. For its explanation we have nothing as yet but
hypotheses. The one which has seemed to me to be
the most reasonable belongs to the field of molecular
physics, and it must be long before it is either proved

448 PRIMARY FACTORS OF ORGANIC EVOLUTION.

or disproved. I have termed it a ‘‘dynamic theory,”
and it is in some respects similar to that subsequently
proposed by Haeckel under the name of the ‘peri-
genesis of the plastidule.” I have already referred to
the phenomena of the building or growth of the added
characters which constitute progressive evolution as
evidence of the existence of a peculiar species of en-
ergy, which I termed bathmism. This is to be ex-
plained as a mode of motion of the molecules of living
protoplasm, by which the latter build tissue at par-
ticular points, and do not do so at other points. This
action is most easily observed in the beginnings of
growth, as in the segmentation of the odsperm, the
formation of the blastodermic layers, of the gastrula,
of the primitive groove, etc. In the meroblastic em-
bryo the energy is evidently in excess at one part of
the odsperm, and in defect at another. This is a sim-
ple example of the ‘‘location of growth force or bath-
mism.” In all folding or invagination there is ex-
cess of growth at the region which becomes the con-
vex face of the fold; i. e., a location or especial ac-
tivity of bathmism at that point. All modifications of
form can be thus traced to activity of this energy at
particular points. A basis is thus laid for a more or
less complex organism, and the channels of nutritive
pabulum being once estabiished, the location or dis-
tribution of the energy is assured in the directions in
which they lead. Thus with the establishment of cir-
culating channels nutrition is definitely guided to par-
ticular points. It is evident that on this hypothesis
the bases of evolutionary change are laid in the em-
bryonic tissues, where bathmism displays its activity
in producing the base forms on which all subsequent
structure is moulded.

HEREDITY, 449

The building energy being thus understood to bea
mode of molecular motion, we are not at liberty to
suppose that its existence is dependent on the dimen-
sions of the organic body which exhibits it. It is as char-
acteristic of the organic unit or plastidule as the mode
of motion which builds the crystal is of the simplest
molecular aggregate from which the crystal arises.
Bathmism has, however, no other resemblance to
crystalloid cohesion. The latter is a simple energy
which acts within geometrically related spaces, with-
out regard to anything else but the present compulsion
of superior weight-energy. In bathmism we see the
resultant of innumerable antecedent influences, which
builds an organism constructed for adaptations to the
varied and irregularly occurring contingencies which
characterize the life of living beings. As this resultant
is distinctive for every species, bathmism must be
regarded as a generic term, and the characteristic
growth-energy of each species as distinct species of
energy, which presents also diversities expressive of
the peculiarities of individuals.

The preceding statements do not, of course, con-
stitute an explanation of the exact manner in which a
stimulus which effects say the contraction of a muscle,
effects molecular movements of the nuclei of the re-
productive cells. This is a question of organic molec-
ular physics, a science which has made scarcely a be-
ginning. That the transmission of such influence is
through nutritive channels, by the intermediation of a
nervous structure where one exists, may be supposed.
Poulton’s experiments on Lepidoptera, already cited,
led him to believe that the effect of color-environment '
was transmitted to the pigment-cells through the me-
dium of the nervous system. That the modus operandi

450 PRIMARY FACTORS OF ORGANIC EVOLUTION.

is similar to that which produces reflexes may be also
reasonably supposed. How the record of these move-
ments become reflexes, is concentrated in a reproduc-
tive cell, is a question to be solved only in a more ad-
vanced stage of knowledge of organic physics than we
now possess.

Speculation in this direction takes the following
forms. According to one view the energy or molecu-
lar movement must be transmitted to the germ-plasma
through a material or molecular basis. This basis, it
may be supposed, must be that which receives the
mechanical impression which is to produce a corre-
sponding modification of growth-energy in the ovum
or spermatozoéid; that is, in the case of a modified
bone-articulation, particles of matter must pass from
the latter through the medium of the circulation to
the reproductive cells. The alternative hypothesis is,
that the energy which causes the active region to make
or omit to make a given movement, the result of which
is to be structural modification in the young, is im-
pressed through protoplasmic channels on the germ-
cells of either sex. In this case the transmission of
particles of matter is not necessary, as material connec-
tion through the cells, nervous or other, already exists.

To the first of these points of view belong the pan-
genesis theory of Darwin, and the modified pangenesis
of Weismann. These hypotheses present the difficulty
that we must conceive of each particle or ‘‘gemmule”
derived from a given part of the organism finding its
way through the circulation to its exact place in the
growing embryo; or otherwise, of transmitting its pe-
culiar mode of motion to the correct molecules of the
embryo, without error as to locality. The difficulties
to be encountered in accomplishing such a feat seem

HEREDITY. 451

to be insuperable. Hyatt well expresses these in the
following language: ‘Every purely corpuscular throng

- must not only account for a difficulty as great as
that of the camel and the needle’s eye, but must also
account for putting the numberless characters derived
from the entire caravan of its immediate progenitors
and remote wild ancestors and their progenitors back
to the origin of their phylum, through the same nar-
row tunnel. This physical difficulty is still further
enhanced by the fact that the ova and spermatozoa do
not increase in size in proportion to the increasing
number of characters transmitted.” (Proc. Boston Soc.
WV. H., 1893, p. 70.)

The transmission of a mode of motion organized in
a central nervous system, is less inconceivable. This
central system is the seat of a composition of incoming
stimuli and of outgoing energies, the resultant of both
combined constituting the active agency in the pro-
duction of automatic adaptive or intelligent adaptive
movements of any and allof the organs. It appears
to me that we can more readily conceive of the trans-
mission of a resultant form of energy of this kind to
the germ-plasma than of material particles or gem-
mules. Such a theory is sustained by the known cases
of the influence of maternal impressions on the grow-
ing foetus. Going into greater detail, we may compare
the building of the embryo to the unfolding of a record
or memory, which is stored in the central nervous or-
ganism of the parent, and impressed in greater or less
part on the germ-plasma during its construction, in the
order in which it was stored. This record may be
supposed to be woven into the texture of every organic
cell, and to be destroyed by specialization in modified
cells in proportion as they are incapable of repro-

452 PRIMARY FACTORS OF ORGANIC EVOLUTION,

ducing anything but themselves. The basis of mem-
ory is reasonably supposed to be a molecular (or
atomic) arrangement from which can issue only a
definite corresponding mode of motion. That such
an arrangement exists in the central nervous organism
is demonstrated by automatic and reflex movements.
It is also demonstrated by the fact that the memory
of the position and parts of amputated limbs is re-
tained by the sensory center, so that irritation of the
stump is referred to the lost limb. That the entire
record is not repeated in automatic and reflex acts,
but only that part of it which was last acquired, may
be regarded as due to the muscular and other systems
concerned in it having performed it most recently, and
having for a longer or shorter period omitted to per-
form the older movement, because the latest struc-
tures of the organs would render the performance of
the old movements impossible. In other words, the
physiological division of labor extends to memory at
the basis. In the case of the germ-plasma no other
specialization exists, so that the entire record may be
repeated stage after stage, thus producing the succes-
sion of type-structures which embryology has made
familiar to us. In the process of embryonic growth,
one mode of motion would generate its successor in
obedience to the molecular structural record first laid
down in the ovum and spermatozooid, and then com-
bined and recomposed on the union of the two in the
odspore, or fertilized ovum.

If the doctrine of kinetogenesis be true, this energy
has been moulded by the interaction of the living be-
ing and its environment. It is the recorded expression
of the habitual movements of the organism which, have
become impressed on, and recorded in, the reproduc-

HEREDITY. 453

tive elements. It is evident that these and the other or-
ganic units of which the organism is composed possess
a memory-structure which determines their destiny in
the building of theembryo. This is indicated by the re-
capitulation of the phylogenetic history of its ancestors
displayed in embryonic growth. This memory has
perhaps the same molecular basis as the conscious
memory, but for reasons unknown to us, consciousness
does not preside over its activities. The energy which
follows its guidance has become automatic, and it
builds what it builds with the same regardlessness of
immediate surroundings as that which is displayed by
the crystallific growth-energy. It is incapable of a
new design, except as an addition to its record.

Were all cells identical in characters, every one
would retain the'’structural record, or memory of its
past physical history, as do the unicellular organisms.
Evolution has, however, so modified most of the struc-
tural units of the organic body that none but the ner-
vous and reproductive cells retain this record, in
greater or less perfection. The nervous cells have
been specialized as the recipients of new impressions,
and the excitors of definite corresponding movements
in the cells of the remainder of the organism. The
somatic cells retain only the record or memory of their
special function. On the other hand, the reproduc-
tive cells, which most nearly resemble the independent
unicellular organisms, retain first the impressions re-
ceived during their primitive unicellular ancestral con-
dition; and second, those which they have acquired
through the organism of which they have been and are
only a part. The medium through which they can
receive such impression is continuous protoplasm.
Whether, in the higher animals, it is effected through

454 PRIMARY FACTORS OF ORGANIC EVOLUTION.

that system of cells called the nervous system, which
has been specialized through use and natural selection
to receive impressions from without, and to transmit
them to such parts of the organism as are capable of
receiving them, or whether it is transmitted through
other media, as in lower animals and in plants which
possess no such system, is unknown. The only cells
which can retain the entire record in the higher ani-
mals are the reproductive cells. In the lower animals
and plants it is well known that germ-plasma is not
confined to reproductive organs, but is widely dissemi-
nated throughout the organism. In some forms it
seems that all of the sarcode is capable of reproduction.
This is the logical result of the considerations
which have occupied the preceding pages, and is the
carrying out of the bathmism theory of heredity, of
which I have given hitherto only the bare outline.
Since Darwin, successive contributions have been
made to the theory of heredity in its relation to evolu-
tion. In 1868 and 1871 the present writer advanced
the dynamic hypothesis, but made no attempt to ex-
plain the mode of conveyance of dynamic impressions
and modifications to the germ-cells. The theory of
“‘ perigenesis,’’ proposed by Haeckel in 1873, is of the
same character, and is deficient in the same way. The
modified pangenesis theory of Brooks, published in
1883,! attempts to supply the defect found in the pre-
vious conceptions, but does so by assuming with Dar-
win the intermediation of gemmules, a hypothesis to
which sufficient objection has been made by Galton
and others. Brooks’s theory also fails to admit the
origin of variations through mechanical stresses, al-
though he seeks for the origin of gemmules through.

1The Law of Heredity, Baltimore, 1883, p. 80.

HEREDITY 455

the lack of equilibrium between the organization and
its environment, which embraces that proposition
without definite specification. To Weismann we are
indebted for the exposition of the separate origin and
relative isolation of the germ-plasma, but no sufficient
explanation of the origin and inheritance of new char-
acters is offered. Ryder! has especially dwelt on the
physiological division of labor seen in the tissues of
the organism, and on the special function of the germ-
plasma as the recipient of impressions through the
processes of metabolism; but he does not go into
greater detail.

What is true of the somatic cells is also true of
those which follow immediately the segmentation of
the odsperm. Each division contains the entire record,
until a point is reached in which specialization of its
growth-capacities begins.

Dr. Chalmers Mitchell thus discusses the question
as to the location of specialized growth in the oésperm :?

‘¢Loeb uses the term heteromorphosis to denote
the power of organisms, under the stimulus of outer
conditions, to produce organs on parts of the organism
where they do not occur normally, or the power to re-
place lost parts by parts unsimilar to them. Regenera-
tion is the reproduction of like parts. Heteromorpho-
sis is the reproduction of unlike parts.

“Tf one cuts off part of the stem of almost any
plant, on placing the stem in suitable soil, roots will
grow out, although roots are not natural to that part
of the stem. The prothallus of fern produces the male
and female organs on the lower side turned away from
the light. If the prothallus be darkened on the upper

1 American Naturalist, 1890, p. 85.
2 Natural Sczence, 1894, p. 187.

456 PRIMARY FACTORS OF ORGANIC EVOLUTION.

surface, and illumined by reflected light on the lower
surface, then the antheridia and archegonia will be
produced on the upper surface. Galls are produced
under the stimulus of the insect almost anywhere on
the surface of the plant. Yet in most cases these galls,
in a sense grown at‘random on the surface of a plant,
when placed in damp earth will give rise to a young
plant. Inthe hydroid, Tudularia mesembryanthemum,
when the polyp-heads are cut off, new heads arise.
But if both head and root be cut off, and the upper end
be inserted in the mud, then from the original upper
end not head-polyps, but root-filaments, will arise,
while from the original lower end, not root-filaments,
but head-polyps will grow. In Ciona intestinalis, round
a slit cut into the body-wall, a tubular process grew out,
forming a new mouth, while around the base of this, a
series of eye-spots, corresponding to the eye-spots
round the real mouth, appeared. In all these cases,
it is plain that there were present in parts affected, the
determinants, to use Weismann’s term, not only of the
normal parts, but also of parts, which, under normal
conditions, would never have appeared there; and
these new parts growing in the unwonted places bore
the normal species-stamp as characteristically as sim-
ilar parts grown in their normal places. It can hardly
be supposed that the architecture of the germ-plasm
contains special determinants to be ready for occur-
rences so casual, especially as these are called into
existence by circumstances quite foreign to the normal
environment of the organisms. On the other hand,
the facts are consonant with Hertwig’s belief that, as
all division is heirs-equal division, all the species-
characters that depend upon cells are latent in every
cell.

HEREDITY. 457

‘‘The experiments of Driesch, Wilson, and Hert-
wig upon the early stages of developing ova show that
heteromorphosis begins with the very earliest divisions
of the egg. Thus Driesch, working upon echinoderm
embryos, was able to flatten out the stage where there
was a sphere of sixteen cells into a flat plate where all
the cells were in the same plane. In such a plate, the
nuclei of the cells occupied relative positions very dif-
ferent from the normal conditions. Yet from these
Driesch obtained normal plutei larve. It was, in fact,
as if the cells could be pushed about like billiard balls
without destroying the future shape and characters of
the embryo. Did each cell contain only the determi-
nants that would correspond to the structures that
would arise from it under normal conditions then
change of its normal position would have arrested de-
velopment. Each cell must, on the other hand, have
contained the determinants for all the animal, and
have allowed those to come into operation that were
required by the new positions into which the cells were
forced. Driesch, by separating the first two and the
first four segmentation-spheres of an Echinus ovum,
obtained two or four normal plutei, respectively one-
half and a quarter of the normal size. Here again
each sphere must have contained all the determinants
for the whole organism. Heirs-equal division must
have occurred. So, also, in the case of Amphioxus,
Wilson obtained a normal, but proportionately dimin-
ished, embryo with complete nervous system from a
separated sphere of a two or four or eight-celled
stage.

‘‘Hertwig himself, some years ago, published the
results of experiments he made upon the development
of frogs’ eggs under abnormal conditions. He showed

458 PRIMARY FACTORS OF ORGANIC EVOLUTION,

that there could be no question of imperative divisions
separating the germ-plasm into right and left halves,
and so forth, but that the method of division was de-
termined by pressures and relative gravities. Altera-
tion of these made the ova divide into novel but sym-
metrical forms. Chabry obtained normal embryos in
cases where some of the segmentation-spheres had
been artificially destroyed.

‘¢ These cases all show that in its possibilities each
segmentation-sphere is identical; that as a result of
heirs-equal division, each cell contains all the material |
necessary to cause the development of a complete em-
bryo. Weismann would have to suppose that in all
these cases, in addition to its half of the nuclear mat-
ter resulting from heirs-equal division, it had also a
stock of unaltered germ-plasm ready to be called into
activity by unwonted stimuli. But even this hypothesis
would not account for cells distorted by compression
responding with the production of unwonted symme-
tries.”

6. OBJECTIONS TO THE DOCTRINE OF INHERITANCE
OF ACQUIRED CHARACTERS.

I will now mention some objections to the theory
of epigenesis, or the inheritance of acquired charac-
ters. Some of them appear at first to have consider-
able force, but the explanations which have been of-
fered seem to me to be sufficient.

Weismann’s merit consists in having directed at-
tention to the isolation and continuity of the germ-
plasma, factors which must be taken account of in any
theory of inheritance. The continuity of reproductive
function which this substance displays is a fact of great

HEREDITY. 459

interest, and one which has given rise to the statement
that it is under normal conditions, immortal.

Isolation of the germ-plasma is however doubt-
fully complete anywhere, and in the vegetable king-
dom it scarcely exists. Most plants may be propa-
gated either by roots, cuttings, bulbs, buds, or even
by leaves. The germ-plasma is evidently as widely
distributed in these multicellular organisms, as it is in
a Protozoén. The greater degree of isolation exhib-
ited by the higher animals is one of their many spe-
cializations, but that it is not complete is shown by the
facts already cited in the preceding pages. The con-
tinuity of protoplasm in the organism is likely to be
true of the germ-cells as of other cells; and they are
not deprived of nutrition, so that they are evidently
accessible to influences from or through the soma. As
regards the immortality of the Protozoén there is rea-
son to believe, that like its descendent the germ-cell,
it requires renewal from another cell to escape death.
According to Maupas, the Protozoa after reproducing
by self-division for many generations, require conju-
gation, or they dwindle and die.

The old formula that variation is due to ‘‘natural
selection and heredity” has derived new life from the
fact that sexual conjugation is necessary for the re-
newal of the vitality of the ovarian cell. It is sup-
posed by Weismann that variation as well as repro-
ductive energy is introduced in this way, the process
being termed by him Amphimixis. But like the old
formula this explains nothing, for if the parents are
the sources of variation, the question as to the source
of the variation is simply relegated to the parents for
answer. Moreover, Brooks, who made this suggestion
prior to Weismann, points out that it has less force

460 PRIMARY FACTORS OF ORGANIC EVOLUTION,

than appears at first sight to belong to it. He shows!
that the ancestors of the individuals of a given species
are in greater or less degree identical persons, and
that they are on this account less numerous than has
been sometimes assumed. Thus, if the population of
a given district had for ten generations married first
cousins, the total ancestry of each person for that
pericd would number only thirty-eight persons. If,
on the contrary, all the ancestors of each person had
been distinct individuals, the total number of ances-
tors in ten generations would be two thousand and
forty-six persons. An investigation into the ancestry
of three persons, not nearly related, living on an island
on the Atlantic coast where the records are complete
for seven and eight generations, shows that the ances-
try of each of the three averages only three hundred
and eighty-two persons. That this consideration is of
even greater importance in estimating the ancestry of
the lower animals than in man, is evident from the
fact that no consideration of kinship modifies their re-
productive habits.

The fact that mutilations are not generally inherited
is cited as evidence against the inheritance of acquired
characters. A particular mutilation, however, as al-
ready remarked, rarely happens more than once or
twice in the lifetime of a single individual; in fact its
occurrence more than once is, in many cases, as in
amputations, impossible. Such sporadic events must
necessarily have little influence as stimuli to the organ-
ism, in comparison with the habitual movements of ani-
mals, or the continued exposure to especial physical
conditions, as is experienced by both plants and ani-
mals, and are not worth considering in this connection.

1 Science, 1895, February, p. 121.

HEREDITY. 461

One of the cases which is cited in opposition to the
view here sustained, is the alleged fact that the artifi-
cial contraction of the feet undergone by high-caste
Chinese female children, resulting in deformity of the
feet of the women, is not inherited. That this abnor-
mality has never been transmitted has not yet been
satisfactorily shown ; but in any case there are some
reasons why it should not be inherited. One of these
is, that the deformity is confined to one sex. The
male, who is without it, has the advantage of an an-
cestry possessing normal feet extending backwards
indefinitely, while the modification of the female is a
very modern interference with the law of the species.
Moreover, a positive stimulus to ontogenetic growth,
such as is in this instance furnished by the male, is
always likely to be prepotent as.compared with the
negative part played by the female.

Professor Poulton, whose interesting experiments
in the production of color changes in lepidopterous
larve and pupa have been previously cited, states that
none of the color varieties which he has obtained, have
been inherited. I cannot regard this result as con-
clusive until the experiments have been continued for
a longer period than has yet been possible to devote
to them.

Perhaps the strongest case that can be made out
against the theory of use-inheritance as defended in
the present book, is that of the variety of structure
displayed by the neuter members of the colonies of
ants and termites. Mr. W. P. Ball describes these
briefly as follows: 1

‘«But there happens to be a tolerably clear proof
that such changes as the evolution of complicated

1The Effects of Use and Disuse, Nature Series, 1890, p. 24.

462 PRIMARY FACTORS OF GRGANIC EVOLUTION.

structures and habits and social instincts can take
place independently of use-inheritance. The wonder-
ful instincts of the working-bees have apparently been
evolved (at least in all their later social complications
and developments) without the aid of use-inheritance—
nay, in spite of its utmost opposition. Working-bees,
being infertile ‘neuters,’ cannot, as a rule, transmit
their own modifications and habits. They are de-
scended from countless generations of queen-bees and
drones, whose habits have been widely different from
those of the workers, and whose structures are dissim-
ilar in various respects. In many species of ants there
are two, and in the leaf-cutting ants of Brazil there
are three, kinds of neuters which differ from each other
and from their male and female ancestors ‘to an al-
most incredible degree.’! The soldier caste is distin-
guished from the workers by enormously large heads,
very powerful mandibles, and extraordinarily different
instincts. In the driver ant of West Africa one kind
of neuter is three times the size of the other, and has
jaws nearly five times as long. In another case, ‘the
workers of one caste alone carry a wonderful sort of
shield on their heads.’ One of the three neuter classes
in the leaf-cutting ants has a single eye in the midst of
its forehead. In certain Mexican and Australian ants

1 Origin of Species, pp. 230-232; Bates's Naturalist on the Amazons. Dar-
win is surprised that no one has hitherto advanced the demonstrative case of
neuter insects against the well-known doctrine of inherited habit as advanced
by Lamarck. As he justly remarks, ‘‘it proves that with animals, as with
plants, any amount of modification may be effected by the accumulation of
numerous slight, spontaneous variations, which are in any way profitable,
without exercise or habit having been brought into play. For peculiar habits
confined to workers, however long they might be followed, could not possibly
affect the males and fertile females, which alone leave any descendants.”
Some slight modification of these remarks, however, may possibly be needed
to meet the case of ‘‘factitious queens,’’ who (probably through eating par-
ticles of the royal food) become capable of producing a few male eggs.

HEREDITY. 463

some of the neuters have high spherical abdomens,
which serve as living reservoirs of honey for the use of
the community. In the equally wonderful case of the
termites, or so-called ‘white ants’ (which belong, how-
ever, to an entirely different order of insects from the
ants and bees), the neuters are blind and wingless,
and are divided into soldiers and workers, each class
possessing the requisite instincts and structures adapt-
ing it for its tasks. Seeing that natural selection can
form and maintain the various structures and the ex-
ceedingly complicated instincts of ants and bees and
wasps and termites in direct defiance of the alleged
tendency to use-inheritance, surely we may believe
that natural selection, unsupported by use-inheritance,
is equally competent for the work of complex or social
or mental evolution in the many cases where the strong
presumptive evidence cannot be rendered almost in-
disputable by the exceptional exclusion of the modified
animal from the work of reproduction.

«‘Ants and bees seem to be capable of altering their
habits and methods of action much as men do. Bees
taken to Australia cease to store honey after a few
years’ experience of the mild winters. Whole com-
munities of bees sometimes take to theft, and live by
plundering hives, first killing the queen to create dis-
may among the workers. Slave ants attend devotedly
to their captors and fight against their own species.
Forel reared an artificial ant-colony made up of five
different and more or less hostile species. Why can-
not a much more intelligent animal modify his habits
far more rapidly and comprehensively without the aid
of a factor which is clearly unnecessary in the case of
the more intelligent of the social insects.”

The explanation of this phenomenon will be prob-

464 PRIMARY FACTORS OF ORGANIC EVOLUTION,

ably some day found by paleontological discovery.
We may suppose, on the basis of discoveries already
made in other animals, that the primitive ants and
termites presented homogeneous colonies, and that
the varied structures which they present to-day have
been primarily due to the usual process of specializa-
tion through use-inheritance. It is necessary to sup-
pose that the varied functions of the different members
of the community have modified the structures of the
parts essential to their performance. It is probable
that the earliest ants in an early geologic period be-
came soldiers under the usual exigencies of their strug-
gle for existence, and having thus secured a place in
the economy of nature, certain members of the com-
munities underwent degenerative changes, appropriate
to their respective functions, of a less exacting charac-
acter. In a second stage of evolution the community
would present the character of a family of varied forms
all of whose members would produce any or all of the
types of form to be found in it, under slight diversi-
ties of conditions, just as now, all species produce
young of two sexes. The differences between the
members of an ant community are considerable in ap-
pearance, but not so great essentially as that between
sexes.

Finally, in a third stage of the history, the func-
tions of reproduction come to be the special office of
afew members of the community. This may have
been due to starvation, or to excessive labor on the
part of certain individuals aborting the reproductive
powers; but whatever may have been the cause, a
majority of individuals became sterile. The repro-
ducing members of the community, however, have
continued to produce all the forms of the community.

HEREDITY, 465

They produce sterile workers and soldiers, sometimes
of several forms, although themselves unlike most of
their progeny. ‘‘This,’”’ says Mr. Ball, ‘‘is evidence
that inheritance can have no share in the process.” He
believes that each one of the structural types of the
community is produced by the treatment accorded to—
the young by the workers, each generation for itself.

As we have seen that the embryonic and paleonto-
logic histories distinctly negative the idea that each
generation has been produced by itself without inheri-
tance, let us endeavor to read the riddle in the light
of the knowledge we have gained from paleontology.
I assume that the most specialized types, the soldiers,
represent the type of the species in Mesozoic and pos-
sibly earlier time. They are already known from early
Cenozoic formations (Scudder). The process of change
into workers and breeders has been degenerative. I
suppose, however, that in ants, as in the case of many
other animals, slight differences in the supply of nutri-
tive energy will prevent or produce these degenerative
processes, as it appears to do in the case of the pro-
duction of the sexes. (Experiments on lepidopterous
larve have shown that excessive food supply produces
females, and deficient supply produces males). In
bees the larve of the female (queen) receives the larg-
est food supply ; those of the males less ; and those of
the neuters the least of all. How the food supply
came to be varied so as to produce the several types
in accordance with the exigencies of the community,
is a question to be solved by future research. Perhaps
it was due to variations in the supplies available at
particular times of the year; and perhaps the ants ul-
timately learned the secret, and now practice it intelli-
gently. It is enough for my present purpose to have

466 PRIMARY FACTORS OF ORGANIC EVOLUTION.

shown that the basis of the entire community, the most
specialized form, the original fertile soldier, acquired
his characters in the usual way, by use, and that all
other forms have been derived from him by inheritance
modified by disuse, or degeneracy, under the influence
of variations in the food supply.

This reply to Mr. Ball’s argument was made by
me at a meeting of the Philadelphia Academy of Nat-
ural Sciences on May 23, 1893. In the latter part of
the same year an almost identical answer was pub-
lished by Herbert Spencer. My remarks were not pub-
lished until the end of the year.

Mr. A. R. Wallace! presents the fact of change of
character under external stimulus as evidence of the
non-inheritance of acquired characters. Thus he cites
the cases of change of species of Artemia, in conse-
quence of increased salinity of water (antea, p. 229) ;
and of the change of color of a Texan Saturnia, when
its normal food-plant /uglans nigra was replaced by
J. regia. Under the new conditions the old characters
were not continued. In the same way the appearance
of all new characters might be assumed to prove non-
inheritance of the old ones. The obvious interpretation
of these facts is the one generally given them ; that is,
they demonstrate the superior potency of certain new
stimuli over the inherited type of growth-energy. They
demonstrate that the energy of inheritance is not un-
changeable in its type, which is the condition of the
possibility of evolution. They do not demonstrate
that acquired characters cannot be inherited.

Objections have been made to the supposition that
the simian characters of the lower human races are
due to inheritance because it has been shown that

1 Nature, 1893, p. 267.

HEREDITY. 467

some of them are due to mechanical causes acting
after birth.

The demonstration of the mechanical origin of a
given peculiarity, however, by no means precludes
that such peculiarity may not be an inheritance from
or reversion to pithecoid ancestors. It has been al-
ready pointed out that all of the form characters of
the vertebrate skeleton, and for that matter, of the
hard parts of all animals, have been produced by mus-
cular pressures and contractions, and the friction,
strains, and impacts, due to these. The demonstra-
tions by Virchow and others that such is the origin of
the platycnemic human tibia, is directly in the line of
Neo-Lamarckian evolutionary doctrine, and shows us
that atavistic and reversionary characters are found in
the muscular system as well as in the skeleton. Such
characters are inheritable as well as those of the skel-
eton. But the characters of the skeleton can generally
be shown to be inherited, because they appear before
birth, and are found at some stage or another of fcetal
life. The later appearance of the muscular structures
in the ontogeny, is simply a case of cenogeny, where
the record has been falsified by retardation of the parts
in question.

The variations in the characters of the human skel-
eton are of very various significance and value, and
the zodlogist and paleontologist can perceive that they
are sometimes misinterpreted by archeologists. Thus
the presence of wormian (Inca) bones, and of a per-
foration of the olecranar fossa, have no zodlogical
value; while the prognathous jaws, tritubercular mo-
lar, and platycnemic tibia have such avalue. The
tufted hair of the negro has a human value only, as it
does not occur in any of the Quadrumana. But arche-

468 PRIMARY FACTORS OF ORGANIC EVOLUTION,

ologists who are not zodlogists are not careful to point
out these distinctions.

If the platycnemic tibia has been produced by mus-
cular pressure in man, it has been probably so pro-
duced in the apes, where it is a universal character.
If the early fusion of the sagittal suture is produced
by the vigorous contractions of the temporal muscle
as suggested by Brinton, in the black race, due to
prognathous jaws, this is probably why it is a universal
character of the apes, where the jaws are still more
prognathous. What may be the cause of prognathism
is not explained by archeologists, but has been dis-
cussed in my book on the Origin of the Fittest, and by
Dr. C. S. Minot. That the prognathous jaws and
platycnemic tibia are not found in the foetus by no
means proves that they are not inherited characters.
Besides the fact already mentioned, that we are by
this only thrown back on an inherited muscular struc-
ture, it is further to be remarked that characters which
indicate the evanescence or degeneracy of parts, do
not usually appear in the fcetus, but are disclosed at
later stages. The prognathous jaws are disappearing
from the higher races, and the process of disappear-
ance is in this point accomplished by a retention of
the foetal face, which is excessively orthognathous.
Prognathism is characteristic of most of the lower
Mammalia, and whenever man displays it, if he be, as
evolutionists believe, descended from some other mam-
mal, he is simply continuing to develop the old char-
acter in the old manner. The same reasoning applies
to the platycnemic tibia and the tritubercular molar.

As regards the lemurine character of the trituber-
cular molar, the term is a good one, as indicating the
nearest of kin to man which present such molars. But

HEREDITY. 469

this type can with equal propriety be called, as I have
shown, the primitive placental molar. The lemur is
the highest form next to man which displays it, but it
was universal among the placentals at one geological
epoch. It is possible that Topinard’s suggestion as
to the cause of its appearance in man is the correct
one, as I made the same many years before, but that
does not affect its value as an evidence of reversion,
as in the cases already cited. There are various other
ways in which molar teeth may degenerate, besides
reversion to trituberculy, with which dentists are fa-
miliar, and which may be explained as Topinard and
I have done ; i. e., by change of food; but why the
regular and normal mode should be trituberculy, and
not one of those other modes, requires additional ex-
planation. This explanation is that a regular or nor-
mal retrogressive modification of a structure is likely
to be areturn on the line by which it advanced. This
is atavism or reversion.

That the anthropoids have been directly derived
by descent from the false lemurs rather than from the
Old World monkeys (Cercopithecidz) is probable for
various reasons which I have pointed out on page 157.
I mention now that this view is somewhat confirmed
by the recent discovery by Forsyth-Major, in Mada-
gascar, in beds of Plistocene age, of a skull of a new
genus of Lemuride with tritubercular molars, whose
single species is nearly as large as a chimpanzee.

In closing these remarks, I call attention to the
frequent muscular and occasional cerebral anomalies
found in the negro, which are of simian character, and
which indicate simian descent. An excellent synopsis
of these has been given by Dr. Frank Baker in his
address at Cleveland in 1888 as Vice-President of the

470 PRIMARY FACTORS OF ORGANIC EVOLUTION,

American Association for the Advancement of Science,
and by Prof. H. F. Osborn in 1891 in the Cartwright
lecture before the New York College of Physicians.

It is evident that evolutionists are reaching greater
harmony of opinion on the question of inheritance.
In fact, the discussion is sometimes a logomachy de-
pendent on the significance which one attaches to
the term ‘‘acquired characters.” Thus Von Rath! re-
marks: ‘There is nothing in the way of the opinion
that by the continued working of such external in-
fluences and stimuli the molecular structure of the
germ-plasma also experiences a change which can lead
to a transmission of transformations. Above all, it
ought not to be forgotten in this case that the somatic
cells are in no way the first to be modified by the stim-
ulus, and that then by some sort of unexplained pro-
cess (pangenesis or intracellular pangenesis), this
stimulus is transmitted gradually by these cells to the
plasma of the germ-cells. The influence on the germ-
plasm is rather a direct one, and if by continued in-
fluence a transformation of the structure of this plasm
takes place and transmission occurs, we have then
simply a transmission of blastogenic, and by no means
of somatogenic characters, and therein is not the
slightest admission of the transmission of acquired
characters.”

This paragraph contains an admission of the doc-
trine of diplogenesis, and does not regard the phe-
nomena as including a transmission of acquired char-
acters. Nevertheless the stimuli traverse the soma in
order to reach the germ-plasma. Such an energy is
evidently then not of blastogenic origin, although it is

1 Berichte der naturforschenden Gesellschaft zu Freiburg in Baden, Bd.VI.,
Heft 3.

HEREDITY. 471

such in its effects. Moreover, Von Rath omits to men-
tion the fact that in traversing the soma, the stimulus,
frequently, if not always, produces effects on the latter
similar to those which it produces on the germ-plasma.
I should call this process the inheritance of an acquired
character, even in the case where no corresponding
modification appears in the soma, since the causative
energy is acquired by the soma and is not derived from
the existing germ-plasma.

Romanes! says, in reviewing the opinions of Weis-
mann: ‘‘(1) Germ-plasm ceases to be continuous in
the sense of having borne a perpetual record of con-
genital variations from the first origin of sexual propa-
gation. (2) On the contrary, as all such variations have
been originated by the direct action of external conditions
[italics mine], the continuity of the germ-plasm in this
sense has been interrupted at the commencement of
every inherited change during the phylogeny of all
plants and animals, unicellular as well as multicellular.
(3) But germ-plasm remains continuous in the re-
stricted though highly important sense of being the
sole repository of hereditary characters of each succes-
sive generation, so that acquired characters can never
have been transmitted to progeny ‘representatively,’
even though they have frequently caused those ‘spe-
cialized’ changes in the structure of germ-plasm, which
as we have seen, must certainly have been of con-
siderable importance in the history of organic evolu-
tion.”

Here the inheritance of characters acquired by the
soma is admitted, and the process is after the method
of diplogenesis. According to Romanes, Galton origin-

1An Examination of Wetsmannisn, Chicago, 1893, p. 169.

472, PRIMARY FACTORS OF ORGANIC EVOLUTION,

ally propounded this doctrine. Galton’s language? is
as follows:

‘«Tt is said that the structure of an animal changes
when he is placed under changed conditions; that his
offspring inherit some of his change; and that they
vary still further on their own account, in the same
direction, and so on through successive generations
until a notable change in the congenital characteristics
of the race has been effected. Hence, it is concluded
that a change in the personal structure has reacted on
the sexual elements. For my part, I object to so gen-
eral a conclusion, for the following reasons. It is
universally admitted that the primary agents in the
processes of growth, nutrition, and reproduction, are
the same, and that a true theory of heredity must so
regard them. In other words, they are all due to the
development of some germinal matter, variously lo-
cated. Consequently, when similar germinal matter
is everywhere affected by the same conditions, we
should expect that it would be everywhere affected in
the same way. The particular kind of germ whence
the hair sprang, that was induced to throw out a new
variety in the cells nearest to the surface of the body
under certain changed conditions of climate and food,
might be expected to throw out a similar variety in the
sexual elements at the same time. The changes in
the germs would everywhere be collateral, although
the movements where any of the changed germs hap-
pen to receive their development might be different.”

This is the first statement of the doctrine of diplo-
genesis with which I have met, and it appears to fur-
nish the most rational basis for the investigation into
the dynamics of the process.

1 Contemporary Review, 1875, pp. 343-344; Proc. Royal Society, 1872, No. 136.

CHAPTER IX.—THE ENERGY OF
EVOLUTION.

F we view the phenomena of organic life from the
standpoint of the physicist, the first question that
naturally arises in the mind is as to the kind of energy
of which it is an exhibition. Ordinary observation
shows that organic bodies perform molar movements,
and that many of them give out heat. A smaller num-
ber exhibit emanations of light and electricity. Very
little consideration is sufficient to show that they in-
clude among their functions chemical reactions, a con-
viction which is abundantly sustained by researches
into the physiology of both animals and plants. The
phenomena of growth are also evidently exhibitions of
energy. The term energy is used to express the mo-
tion of matter, and the building of an embryo to ma-
turity is evidently accomplished by the movement of
matter in certain definite directions. The energy which
accomplishes this feat is, however, none of those which
characterize inorganic matter, some of which have just
been mentioned, but, judging from its phenomena, is
of a widely different character. If we further take a
broad view of the general process of progressive evo-
lution, which is accomplished by successive modifica-
tions of this growth-energy, we see further reason for

474. PRIMARY FACTORS OF ORGANIC EVOLUTION.

distinguishing it widely from the inorganic energies.

In considering the dynamics of organic evolution,
it will be convenient to commence by considering the
claims of natural selection to include the energy which
underlies the process. That natural selection cannot
be the cause of the origin of new characters, or varia-
tion, was asserted by Darwin ;! and this opinion is
supported by the following weighty considerations :

1. A selection cannot be the cause of those alterna-
tives from which it selects. The alternatives must be
presented before the selection can commence.

2. Since the number of variations possible to or-
ganisms is very great, the probability of the admirably
adaptive structures which characterize the latter hav-
ing arisen by chance, is extremely small.

3. In order that a variation of structure shall sur-
vive, it is necessary that it shall appear simultaneously
in two individuals of opposite sex. But if the chance
of its appearing in one individual is very small, the
chance of its appearing in two individuals is very much
smaller. But even this concurrence of chances would
not be sufficient to secure its survival, since it would
be immediately bred out by the immensely preponder-
ant number of individuals which should not possess
the variation.

4. Finally, the characters which define the organic
types, so far as they are disclosed by paleontology,
have commenced as minute buds or rudiments, of no
value whatever in the struggle for existence. Natural
selection can only effect the survival of characters when
they have attained some functional value.

In order to secure the survival of a new character,
that is, of a new type of organism, it is necessary that

1 Origin of Species, Ed. 1872, p. 65.

THE ENERGY OF EVOLUTION. 475

«
the variation should appear in a large number of indi-
viduals coincidentally and successively. It is exceed-
ingly probable that that is what has occurred in past
geologic ages. We are thus led to look for a cause
which affects equally many individuals at the same
time, and continuously. Such causes are found in the
changing physical conditions that have succeeded each
other in the past history of our planet, and the changes
of organic function necessarily produced thereby.

1. ANAGENESIS.

It is customary to distinguish. broadly between in-
organic and organic energies, as those which are dis-
played by non-living and living bodies. This classifi-
cation is inexact, since, as already remarked, nearly
all of the inorganic energies are exhibited by living
beings. A division which appears to be, with our
present knowledge, much more fundamental, is into
the energies which tend away from, and those which
tend toward, the phenomena of life. In other words,
those which are not necessarily phenomena of life, and
those which are necessarily such. And the phenom-
ena of life here referred to are the phenomena of growth
and evolution, as distinguished from all others. I have
termed! these classes the Anagenetic, which are ex-
clusively vital, and the Catagenetic, which are phys-
ical and chemical. The anagenetic class tends to up-
ward progress in the organic sense; that is, toward
the increasing control of its environment by the organ-
ism, and toward the progressive development of con-
sciousness and mind. ‘The catagenetic energies tend
to the creation of a stable equilibrium of matter, in

1 The Monist, Chicago, 1893, p. 630.

476 PRIMARY FACTORS OF ORGANIC EVOLUTION,

which molar motion is not produced from within, and
sensation is impossible. In popular language the one
class of energies tends to life; the other to death.
Herbert Spencer has defined evolution as a process
of ‘‘integration of matter and dissipation of motion ”’;1
‘the absorption of motion and the diffusion of matter”
he terms dissolution. If by evolution Mr. Spencer
referred only to that of inorganic bodies and masses,
his definition must be accepted; but the evolution of
organic bodies, since it has proceeded in a direction
the opposite of the inorganic, cannot be so character-
ized. Organic evolution has passed beyond the do-
main of the inorganic, and the terms applicable to the
latter process cannot be correctly applied to the former.
In organic anagenesis there is absorption of energy;
dissipation of energy is only known in the functioning
of organic structures, which is catagenetic; not in
their progressive evolution, which is anagenetic.
Huxley, in a lecture delivered in 1854,? remarks:
“¢Tendency to equilibrium of force and permanency of
form then are the characters of that portion of the
universe which does not live, the domain of the chem-
ist and the physicist. Tendency to disturb existing
equilibriums, to take on forms which succeed one
another in definite cycles, is the character of the living
world.” In the letter to Professor Tyndall, prefatory
to the volume Lay Sermons and Addresses, in which this
essay appeared, Huxley says: ‘‘The oldest essay of
the whole, that on ‘The Educational Value of the
Natural History Sciences,’ contains a view of the dif-
ferences between living and not-living bodies, which I
have long since outgrown.” Whatever might have

1 First Principles, ed. 11., 1873, p. $42.
2Lay Sermons and Addresses, 1880, p. 75.

THE ENERGY OF EVOLUTION. 477

been the cause of this change of opinion in Huxley’s
mind, the cause which has produced a similar change
in the minds of many men, has been the discovery of
means of producing in the laboratory numerous organic
compounds, which, it had been previously supposed,
could not be produced excepting through the action of
living things, vegetable and animal. But it has been
shown that all of these substances are the result of the
running down of protoplasm, and are, hence, catage-
netic, and not anagenetic.

That the catagenetic energies, whether physical or
chemical, tend away from life is clear enough. Thus
molar motion, unless continuously supplied, or directed
by a living source, speedily ceases, being converted by
friction into heat, which is dissipated. The same
is true of molecular movements, under the same con-
ditions. Chemical reactions, which are fundamental
in world-building, result in the production of solids
and the radiation of heat. This is the general result,
although in the process, as it occurs in nature, irregu-
larities occur, owing to local and temporary elevation
of temperature. This arises from the decomposition
of organic substances, which liberates heat; the oxy-
dization of carbon, which owes its position as a ter-
restrial element to vegetable and animal organisms ;
and the access of heat from the interior of the earth,
or from the sun’s rays. Finally cosmic creation in-
volves the perpetual radiation of heat into space, and
the gradual reduction of all forms of matter to the
solid state.

The endothermic chemical reaction, where inor-
ganic matter undergoes a change of molecular aggre-
gation the reverse of that just mentioned, with the ab-
sorption of heat, as in the case of several nitrogen

478 PRIMARY FACTORS OF ORGANIC EVOLUTION.

compounds, is rare in nature, where free from organic
complications, and is necessarily soon reversed by
further reactions.

In the anagenetic energies, on the other hand, we
have a process of building machines, which not only
resist the action of catagenesis, but which press the
catagenetic energies into their service. In the assimi-
lation of inorganic substances they elevate them into
higher, that is more complex compounds, and raise
the types of energy to their own level. In the devel-
opment of molar movements they enable their organ-
isms to escape many of the destructive effects of cat-
agenetic energy, by enabling them to change their
environment; and this is especially true in so far as sen-
sation or consciousness is present to them. The ana-
genetic energy transforms the face of nature by its
power of assimilating and recompounding inorganic
matter, and by its capacity for multiplying its individ-
uals. In spite of the mechanical destructibility of its
physical basis (protoplasm), and the ease with which
its mechanisms are destroyed, it successfully resists,
controls, and remodels the catagenetic energies for its
purposes.

The anagenetic power of assimilation of the inor-
ganic substances is chiefly seen in the vegetable king-
dom. Atmospheric air, water, and inorganic salts
furnish it with the materials of its physical basis. Then
from its own protoplasm it elaborates by a catagenetic
retrograde metamorphosis, the non-nitrogenous sub-
stances, as wood (cellulose), waxes, and oils, and the
nitrogenous alkaloids, and it may take up inorganic
substances and deposit them without alteration in its
cells. Many of the compounds elaborated by plants
and animals have been manufactured of latter time by

THE ENERGY OF EVOLUTION. 479

chemists. The discovery that the living organism is
not necessary for the production of these substances
has led to the hasty conclusion that the supposed dis-
tinction between ‘‘organic”’ and ‘‘inorganic” energy
does not exist. But the elaboration of these substances
is not accomplished by anagenetic or ‘‘vital” energy,
but by a process of running down of the higher com-
pound protoplasm, which is catagenesis. No truly
anagenetic process has yet been imitated by man.

All forms of functioning of organs, except assimi-
lation, reproduction, and growth, are catagenetic. That
is, functioning consists in the retrograde metamorpho-
sis of a nitrogenous organic substance or proteid with
the setting free of energy. The proteid is decomposed
in the functioning tissue into carbon dioxide, water,
urea, etc., and energy appears in the muscle as con-
traction, in the glands as secretion, and in all parts of
the body as heat. The general result of physiologic
research is, that the decomposition of the blood is the
source of energy, while the tissue of each organ deter-
mines the character of that energy. That the tissue
itself suffers from wear, and requires repair, is also
true, but to a less extent than was once supposed.

In the anagenetic process of the growth of the em-
bryo the case is different. Here the processes of func-
tioning of organs are in complete abeyance, the plasma
of the odsperm is not sensibly broken down in chemical
decomposition, but it isin great part elaborated into
tissues and organs. All the mechanisms necessary to
the mature life of the individual are constructed by the
activity of the special form of energy known as growth-
energy or Bathmism. It is the modifications of this
energy which constitute evolution, and it is these to
which we will hereafter direct our attention. Its sim-

480 PRIMARY FACTORS OF ORGANIC EVOLUTION.

plest exhibition is the subdivision of a unicellular pro-
toplasmic body into two or more individuals or struc-
tural units of a multicellular organism. Further divi-
sion of the latter does not abolish the individual, but
extends it, and we now observe the elaboration of dif-
ferent structural types to become the conspicuous func-
tion of this form of energy. In other words, a once
simple energy becomes specialized into specific ener-
gies, each of which, once established, pursues its mode
of motion in opposition to all other modes not more
potent than itself. Besides the evident truth of the
proposition that a mode of building is a mode of mo-
tion, we have another very good reason for believing
‘in the existence of a class of bathmic or growth-ener-
gies. This is found in the phenomena of heredity.
The most rational conception of this inheritance of
structural characters is the transmission of a mode of
motion from the soma to the germ-cells. This is a far
more conceivable method than that of the transmis-
sion of particles of matter, other than the ordinary ma-
terial of nutrition. The bathmic theory of heredity
bears about the same relation to a theory of transmis-
sion of the pangenes of Darwin, or the ids of Weis-
mann, as the undulatory theory of light and other
forms of radiant energy does to the molecular theory
of Newton. I have therefore assumed as a working
hypothesis the existence of the bathmic energy, and
have inquired how far the facts in our possession sus-
tain it. In doing so it has been necessary to elaborate
the theory so as to render clearer its application to spe-
cific cases. The fact to be accounted for is its spe-
cialization into so many diverse specific forms.
A further indication of the existence of the bathmic
energy is the quantitative limitation to which growth

THE ENERGY OF EVOLUTION. 481

is obedient. Thus the successive stages of embryonic
growth are limited in number in each species. The
dimensions of most species are limited within a def-
inite range. The duration of life, or of the functioning
organic machine, has a definite limit in time. All this
means that a certain limited quantity of energy is at
the disposal of each individual organism.

In the preceding pages I have endeavored to show
what causes have been and are efficient in the produc-
tion of different types of organic life, through the
modifications of the bathmic energy. We will now
briefly consider the question of the origin of the living
substance, protoplasm or sarcode, which exhibits bath-
mism.

On this subject Professor Manly Miles remarks :}
‘«Qmitting subordinate details, which represent the
separate links in the chain of events, the processes of
nutrition may be summarized in general terms as fol-
lows: In plants the chemical elements and binary com-
pound on which they feed, are built up by successive
steps of increasing complexity and instability into pro-
toplasm, with a storing of the energy made use of in
the constructive process, which is derived from the
heat and light of thesun. The constructive processes
are expressed by the term anabolism, and the products
of the different upward steps are called anastatic. Pro-
toplasm, the most complex and unstable of organic
substances, is the summit of the ascending steps of
anabolism ; and katabolism, which represents the suc-
ceeding downward steps of metabolism, then follows,
and its products or katastates are starch, cellulose,
proteids, etc., or what we recognize as the proximate

1Proceeds. Amer Assoc, Adv, Scz., 1892, p. 203.

482 PRIMARY FACTORS OF ORGANIC EVOLUTION.

constituents and tissues of plants.” I interject here
the remark, that from a chemical point of view, pro-
toplasm is, under certain conditions, not unstable.

If the tendency of the catagenetic energies is away
from vital phenomena, it is impossible that they, or
any of them, should be the cause of the origin of liv-
ing matter. This logical inference is confirmed by the
failure of all attempts to demonstrate spontaneous gen-
eration of living organisms from inorganic matter.
Further, the principle of continuity leads us to infer
that the energy which produced organic matter must
be identical with or allied to that which is the efficient
agent in progressive evolution of organisms, and is,
therefore, anagenetic. Such a conclusion may seem
to lead to a dualism which is itself opposed to the
principle of continuity or uniformity, and which is op-
posed to experience of the phenomena of energy in
general. How is uniformity to be harmonized with
the hypothesis of two types of energy acting in differ-
ent directions, apparently in opposition to each other?
Since facts and logic do not support the derivation of
the anagenetic from the inorganic energies, can the re-
verse process, the derivation of the catagenetic from
the anagenetic be and have been the order of nature?
In support of this hypothesis, we have the universal
prevalence of the retrograde metamorphosis of energy
in both the inorganic and organic kingdoms. Phe-
nomena of structural degeneracy are well known in
the organic world, and purely chemical phenomena in
both organic and inorganic processes are all degenerate.
It appears, then, much more probable that catagenesis
succeeds anagenesis as a consequence, and does not
precede it as a cause. In other words, it is more

THE ENERGY OF EVOLUTION. 483

probable that death is a consequence of life, rather than
that the living is a product of the non-living. I have
therefore given to that energy which is displayed by
the plant in the elaboration of living from non-living
matter the name of antichemism.! Thus, while the
heat of the sun is necessary to the building of proto-
plasm, within a certain range of temperature this form
of energy has its opportunity.

The actual demonstration of this hypothesis can
only come from researches into the thermochemistry
of proteids and protoplasm. As these substances have
not been made in the laboratory, these researches are
not yet possible. We may, however, consider the
problem as follows. In the process of making pro-
toplasm, three gases, oxygen, hydrogen, and nitrogen
are converted into a semisolid. In this case heat
should be dissipated, to an amount reduced by the
molecular dissolution of carbon. This is however
not the case, for heat is absorbed with an integration
of atomic bonds. In other words, it would seem that
the manufacture of protoplasm by plants is an endo-
thermic process. This view is strengthened by the dis-
covery by Berthollet? that the production of numerous
solid organic substances, in which organic bases are
used, isalso endothermic. These facts confirm the in-
ference above recited, that the phenomena of organic
growth involve the absorption of energy and not its
dissipation.

Referring to the composition of protoplasm CO
N, Ihave called attention to the fact that each of its
elements represents one of the great divisions defined

American Naturalist, 1884, p. 979; Origin of the Fittest, 1887, p, 431.
2Annales de Chimie et de Physique, V1, 1895, Pp. 232+

’

484 PRIMARY FACTORS OF ORGANIC EVOLUTION,

by their valency, into which the ultimate substances
of nature naturally fall. This combination I have sug-
gested might account for the chemical inertness of
protoplasm, through the mutual inhibition which each
of these elements might be supposed to exercise over
the other, owing to the diversity of their modes of
chemical action.

In order to present more clearly the views enun-
ciated in the preceding pages, I give a synoptic table
of energies.

: Antichemism
I. Anagenetic Organic Bathmism
Exclusively Neurism
organic Myism

II. Catagenetic Rechant Enetey

Inorganic and Chemism
Cohesion
organic Gravitation

2. BATHMOGENESIS.

The innumerable structures which are due to the
activity of bathmisms may be supposed to result from
the composition of the inherited form with energies
which are derived from sources external to the germ-
plasma, whether within the soma or external to it.
These interferences produce new and specific types of
energy. The inherited bathmism I have termed ‘‘sim-
ple growth force,” and the modified forms I have termed
‘¢grade growth force.”! It appears that these types of
energy should be distinguished by special names.
Hence I have proposed to restrict the term bathmism

Proceedings American Philosophical Society, 1871, p. 253.

THE ENERGY OF EVOLUTION. 485

to the modified or ‘‘grade” growth force, and to term
the inherited or ‘‘simple” type of growth force, em-
phytism.! Asa matter of fact, pure emphytism can
only be observed in the embryos of sexless or parthe-
nogenetic origin, and in the repair of tissues.

Ryder has called the exhibition of growth-energy
-ergogenesis, and he calls attention to the fact that it
appears under two aspects. In the first, ergogenesis
is due to mechanical causes resident in the organism
exclusively, and consists of the physical tensions in-
herent in protoplasm under all the conditions of
growth. With these the growth-energies have to
reckon, as they are the conditions which underlie them.
They are not, however, strictly speaking, growth-
energies, but would be exhibited by any similar col-
loid under similar conditions. To the movements due
to physical causes under these circumstances, Ryder
gives the name of Statogenesis.2 The second aspect
of the energies necessary to growth is present under
the two forms already referred to, as emphytism and
bathmism. The latter class, or interference energies,
are naturally differentiated into those which are due
to physical (or chemical) external agencies (molecular
movements), and those that are due to molar move-
ments as expressed in tissues, as impact, strain, etc.
To the former I have given the name of physiobath-
mism, to the latter, kinetobathmism.?

The relations of these forms of energy may be rep-
resented in tabular form as follows:

1] have supposed in a late paper (American Naturalist, 1894, p. 212) that
this is the statogenic energy of Ryder. This mistake has been corrected.

2 Proceedings American Philosophical Soctety, 1893, P- 194.

8American Naturalist, 1894, p. 214. The two types of growth are then
physiogenesis and kinetogenesis. (Origin of the Fittest, 1887, p. 423.)

486 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Ergogenesis
Catagenetic Statogenesis

Inherited Lmphytogenesis
Anagenetic | With inter- Molecular
ference Bathmogenesis Phystogenesis

Molar <Kinetogenesis

Emphytogenesis I shall hereafter endeavor to show
is an automatic (catagenetic) product of bathmogen-
esis, and a stationary factor in evolution.

The above table is designed to be a classification
and formulation of the innumerable well-known facts
of organic growth and evolution. It does not pre-
tend to be an explanation of the processes involved,
but it is the first step to be taken in attempting the
explanation, i. e. a discrimination and classification of
its factors.

Ryder thus expressed the relation between stato-
genesis and kinetogenesis.!

‘So universal is this interference of the statical
conditions of the plasma of segmenting ova with the
ontogenetic processes, that not a single metazoan or-
ganism can be named, the development of which is not
thus marred in some way or other. It is often a long
time relatively after development has begun that there
is any obvious delineation of the embryo. In fact,
this cannot take place until the statical energies of
surface-tension which have kept the egg globular are
overridden. Inso far as the ontogeny of any organ-
ism is marred by statical conditions of energy-display,
its embryonic form is also modified. In so far as such
statical interference affects the figure of the organism
they are morphogenetic or form-determining. In so
far the figure of a developing being is disturbed or

1Proceeds, Amer, Philos. Society, 1893, pp. 197-201. j

THE ENERGY OF EVOLUTION. 487

modified by statical agencies its figure may be said to
be subject to statogenetic influences. No existing
larval form has escaped the influence upon its own
shape of a constantly active statical equilibrium of its
own substance. There is, therefore, a constant strug-
gle going on during development between the phylo-
genetic and ontogenetic forces, determining the se-
quence and relations of the successive cleavages of the
egg and the statical equilibria that obtain amongst its
several parts. Statogenetic processes are, therefore, as
constant and universal as the phylogenetic and onto-
genetic. One may even go so far as to say that possi-
bly the relations thus tending to be established by
statical conditions may tend to become transmissible
as hereditary tendencies. Such indeed is the view up-
held by Prof. E. B. Wilson in his remarkable paper on
‘The Cell-Lineage of Nereis.’ I have myself seen no
less than three consecutive recurrences of the same
statical conditions in a fish egg, none of which can,
for this reason, be definitely proved to be purely onto-
genetic.

‘¢While such phenomena as those of the genesis
of the heterocercal or upwardly deflected condition of
the axis in the tails of fishes, or the downwardly de-
flected condition of the axis in Ichthyosauri are almost
purely kinetogenetic, the multiplicity of factors con-
cerned, statogenetic as well as ontogenetic and phylo-
genetic, must always be considered and each given its
due weight and importance in achieving the morpho-
genetic result. That there is an absolute conflict be-
tween statogeny and kinetogeny on the one hand, and
of phylogeny and ontogeny on the other, in the case
of the development of the ova of multicellular forms
admits of no doubt. All metazoa pass through larval

488 PRIMARY FACTORS OF ORGANIC EVOLUTION,

stages in which the statical conditions of equilibrium
of the plasma of the egg is gradually, in a great meas-
ure, overriden by the hereditary energies represented
by phylogeny and ontogeny. That there still remain
traces of the effects of kinetogeny and statogeny in the
adult organism cannot be denied in view of the facts
to be derived from the shapes of tissue elements, and
even of organs, as the foregoing paragraphs show.”

The first appearance of bathmogenetic action is the
first modification of the statogenetic and emphytogen-
etic energies from whatever source. Changes may be
effected in the weight, color, and in functional capacity
by temperature, humidity, food, etc., thus exhibiting
physiogenesis. Or changes in the size and forms of
parts of the body may be produced by movements of
the organism, or of its environment, so displaying ki-
netogenesis. So long as these modifications of struc-
ture should be confined to the individuals thus modi-
fied, there would be no evolution. A second genera-
tion, if not subjected to the same stimuli, would not
possess the modifications ; and their possession of them
would depend entirely on the amount of stimulus. In
other words, there would be no accumulation of modi-
fication. It has, however, been generally believed that
these modifications are inherited, and I think it has
been shown that this belief rests on asolid basis. Mean-
while I have called the bathmogenesis which does not
extend beyond the generation in which it appears,
autobathmogeny.

The quantitative relation which necessarily exists
between bathmism and its sources may be expressed
as follows, with due recognition of the fact that such
expression does not rest upon any experimental tests.
Emphytogenesis is work done in the construction of

THE ENERGY OF EVOLUTION. 489

tissues like those of the parent and without interfer-
ence. Here we have the molecular energy of the par-
ent converted into the molar movements observed to
be concomitants of segmentation ; to be represented
in the completed tissue by the mutual tensions by vir-
tue of which each structural element maintains its in-
tegrity. It is evidently a process of metamorphosis of
energy in which there is less waste than in any other
known to us. Embryonic growth is.accompanied by
a very slight dissipation of heat, since a slight rise
of temperature is noticeable in the eggs of cold-blooded
animals and in flowers, when reproduction is active.
The products of breaking down are equally rare in
embryonic growth, and both this and the dissipation
of heat are perhaps largely due to the changes wrought
in non-cleavable nutritive substances with which the
yolks are sometimes charged. It is probably to ac-
complish this process that the oxygen necessary for the
embryonic growth is used. How much loss is due to
cell-division itself is not known, but it must be very
little if any. We have probably here a nearly perfect
conversion of energy. Theoretically we have ana-
genesis wherever the up-building exceeds the down-
breaking.

The attempt to realize in the imagination the
modus operandi of bathmic energy in embryo-building
takes the following form. It is to be supposed that
movement which has been most frequently repeated,
and for the longest period, is prepotent, and takes
precedence of all others. This is clearly simple cell-
division, which follows the nutrition supplied by the
spermatozoon, and which represents the first act of
animal life. Hence, segmentation of the odsperm is
the first movement of bathmism. Each subsequent

490 PRIMARY FACTORS OF ORGANIC EVOLUTION.

movement appears in the order of potency, which is,
other things being equal, a time order, or the order of
record. The cause of the localization of tissues and
structures is much more difficult to understand than
the cause of the order of their appearance. The more
energetic part of the process naturally requires the
greater space for its products. The ectoderm, which
becomes the seat of the nervous axis and its muscular
adjuncts, occupies the superficial portions of the yolk.
Hence, we may regard this expression of the struc-
tural record of these functions as more energetic than
that of the record-structure of the nutritive functions,
which displays itself below the ectoderm. In mero-
blastic and amphiblastic embryos, the segmentation
which develops the nutritive tissues is evidently more
sluggish, for the cells are larger and fewer in number
than those of the ectoderm.

In evolution external stimuli modify the course of
emphytogeny above described, and by producing new
structural records, cause a new form of energy, due to
composition of the new with the old, and the process
of growth then becomes bathmogeny. The external
stimuli are molecular or molar, determining physio-
bathmism or kinetobathmism.

The effect of motion or use on the soma may be
conveniently termed autokinetogenesis. Moderate use
of a muscle is known to increase its size. Irritation
of the periosteum is known to cause deposit of bone.
Friction and pressure of the epithelium increases its
quantity or changes its form. Increased activity of
the functions of nervous tissues increases their relative
proportions, as in the enlargement of nerves which re-
place others which are interrupted by mutilations, etc.

THE ENERGY OF EVOLUTION. 491

On the other hand, it is equally well known that disuse
produces diminution of muscular tissues, and through
it, a reduction in the quantity of the harder tissue
(bone, chitin, etc.) to which it is attached (as muscu-
lar insertions, etc.) It was the observation of such
well-known phenomena as these that led Lamarck to
advance his doctrine of evolution under use and dis-
use, and which has led many others to give their ad-
herence to such a view.

Thus much for cell-growth. Another class of mod-
ifications of a similar kind may be found in the parts
of an organism which consist of a complex of cells, or
tissues. Thus the lumen of a small artery is enlarged
under the influence of pressure when it is compelled
to assume the function of a larger vessel through the
interruption of the latter. A part of an internal or
external skeleton which is fractured will form an arti-
ficial joint at the point of fracture, if the adjacent sur-
faces are kept in motion. Marey (Animal Mechanism,
pp. 88-89) says, ‘‘After dislocations the old articular
cavities will be filled up and disappear, while at the
new point where the head of the bone is actually placed,
a fresh articulation is formed, to which nothing will be
wanting in the course of a few months, neither articu-
lar cartilages, synovial fluid, nor the ligaments to re-
tain the bone in place.” I have given some illustra-
tions of this fact, which have come under my observa-
tion, and which have an important bearing on the
origin of the articulations of the vertebrate skeleton as
I have traced them throughout geological time. f
have, as I think, conclusively shown that these varied
structures have been produced by impacts and strains,

1Page 275 and Proceeds. Amer. Philos. Soc., 1892, p. 285.

492 PRIMARY FACTORS OF ORGANIC EVOLUTION.

which are concomitants of the movements of the ani-
mals, acting through long periods of time.!

The term mnemogenesis is employed by Professor
Hyatt? to characterize the manner in which kinetogen-
esis is supposed to produce results in inheritance. I
have suggested that the phenomena of recapitulation,
characteristic of ontogeny (American Naturalist, Dec.,
188g), are due to the presence of a record in the germ
cells, having a molecular basis similar to that of mem-
ory. This view is adopted by Professor Hyatt. I have
already referred to it in the preceding pages.

A general statement of this doctrine was made by
Mr. Sedgwick in The British and Foreign Medico-Chir-
urgical Review for July 1863 in the following language:
‘For atavism in disease appears to be but an instance
of memory in reproduction, as imitation is expressed
in direct descent; and in the same way that memory
never, as it were, dies out, but in some state always
exists, so the previous existence of some peculiarity in
organization may likewise be regarded as never abso-
lutely lost in succeeding generations, except by ex-
tinction of race.” The next formulation of mnemo-
genesis is by Hering in 1870.8

It is concentrated in the following paragraph:

‘‘The appearance of properties of the parental or-
ganism in the full-grown filial organism can be noth-
ing else but the reproduction of such processes of
organized matter as the germ when still in the germi-
nal vesicles had taken part in; the filial organism re-
members, so to speak, those processes, and as soon as

1‘ Mechanical Origin of the Hard Parts of the Mammalia," Amer, Journal
of Morphology, 1889. Origin of the Fittest, 1887, pp. 305-373.
2 Proceeds. Boston Soc. Nat. History, 1893, p. 73.

3 Address before the Imperial Academy of Sciences of Vienna, May 30,
1870, by Ewald Hering; English translation, Chicago, 1895.

THE ENERGY OF EVOLUTION. 493

an occasion of the same or similar irritations is offered,
a reaction takes place as formerly in the parental or-
ganism, of which it was then a part and whose desti-
nies influenced it.” In explanation of this theory,
Hering says: ‘‘We notice, further on, that the process
of development of the germs which are destined to
attain an independent existence, exercises a powerful
reaction both on the conscious and unconscious life of
the whole organism. And this isa hint that the organ of
germination is in closer and more momentous relation
to the other parts, especially to the nervous system,
than any other organ. In an inverse ratio, the conscious
destinies of the whole organism, it is most probable,
find a stronger echo in the germinal vesicles than else-
where.”

If heredity is a form of memory, its laws may re-
semble those of the psychic memory. In the latter,
everything depends on what we call the strength of
the impression. A single impression is often easily
forgotten, and the certainty of recollection is largely
dependent on the frequency of repetition of the stimu-
lus. This is the essence of mental education, and it
is probably the law of education of the germ-plasma
as well. Thus may be understood how stimuli end-
lessly repeated through long geologic ages, must pro-
duce results far more profound and lasting than spo-
radic impressions of modern and artificial origin.

It must be here remarked for the benefit of the
reader who may be unfamiliar with the explanation of
the psychic memory, that it is the conscious part of
memory which gives it its psychic character. This
side is due to a fundamental molecular arrangement
caused by stimuli, which may be retained for long
periods without expression in consciousness. Thus

494 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Bain regards memory as consisting of an unconscious
and a conscious stage, and the latter he terms rem-
iniscence. Other psychologists in common with man-
kind generally, use the word memory for the conscious
expression. J have termed the unconscious condition
of the molecular basis of mind, cryptopnoy.

CHAPTER X.—THE FUNCTION OF
CONSCIOUSNESS.

1, CONSCIOUSNESS AND AUTOMATISM.

ONSCIOUSNESS is a general term, which em-
braces all forms of self-knowledge. Sentiency is
sometimes used with an identical meaning. Conscious-
ness must be distinguished from self-consciousness,
which implies introspection. Consciousness may or
may not be characterised by attention. There are two
widely different types of consciousness, viz., the pre-
sentative and the representative. The former includes
sense-perception only; the latter includes all the com-
binations of sense-perception which characterize men-
tal action, from simple memory to the most compre-
hensive classification and conception. Most, if not
all, animals appear to possess sense-perception, and
all such possess the representative faculty of memory;
but the higher grades of representative mental function
are not so general among animals, and the extent of
their occurrence is yet in dispute.

In the preceding pages I have endeavored to show
that the factors of evolution are bathmogenesis cor-
rected by natural selection. Bathmogenesis embraces
the two factors physiogenesis and kinetogenesis, or the
products of molecular and molar motion, respectively.

496 PRIMARY FACTORS OF ORGANIC EVOLUTION,

These two forms of motion have been coéxtensive
with the existence of life, neither one preceding the
other in time. Statogenesis is the expression of a form
of energy which characterizes inorganic matter, while
bathmogenesis is entirely peculiar to living things.
Kinetogenesis is the fundamental principle in organic
evolution, since it determines the amount and kind
of physiogenesis, because it creates the environment
which furnishes the conditions of physiogenesis. Pro-
gressive organic evolution may, then, be described as
due to kinetogenesis corrected by natural selection.
At the basis, however, molar organic motion, i. e., con-
traction of protoplasm, is probably molecular, but it is
distinguished from other forms of molecular motion in
the vast aggregate of molecules which move simultan-
eously in one direction, as in an amceba or a muscle,
thus effecting a change in the position of all or a part
of an organism. Hence the distinction is a real one.

Molar motion being, then, of such fundamental im-
portance as a factor in evolution, the cause of such
motion is also a capital question. Contraction of
protoplasm is caused by stimuli, such as currents of
electricity and chemical reagents; but such stimuli are
not those which ordinarily produce the contractions to
which the molar movements of living animals are due.
In those animals which possess a nervous system it
has been shown that contractions only follow stimuli
which are conveyed to the contractile elements by
nervous threads, and the.internal energy which repre-
sents the external stimulus, is called nervous energy
orneurism. In animals without a nervous system, and
in plants, external stimuli must be justly supposed to
be converted into the same form of energy, which in
such organisms has a general circulation throughout

THE FUNCTION OF CONSCIOUSNESS. 497

the contractile protoplasm. The important point about
these movements in most animals is, that their direc-
tion directly subserves the attainment of some position
which is favorable for the procurement of relief from
some unpleasant sensation, or the acquisition of some
agreeable one, or both. We have the best reasons for
believing this to be true of the vast majority of animals,
because their structure is fundamentally like our own,
and the inference that the same is true of the lowest
forms of life is justifiable until it is proven to be mis
taken.

Lamarck has attributed the movements of animals
to the necessity of satisfying their instincts, without
entering into the metaphysical questions which this
involves. I have regarded the question as a meta-
physical one by asserting that the necessary prelim-
inary to movement is ‘‘effort,” referring to what are
called ‘‘voluntary” as distinguished from automatic
motions.

Without special organs of movement, a great part of
the phenomena of kinetogenesis would have no exis-
tence, precisely as natural selection cannot act unless
the materials for selection (i. e. variations) are already
in existence. In explanation of the origin of organs
of movement we have the general ability of the primi-
tive animal, or protozoén, to project portions of its
body-substance as pseudopodia, which, in more spe-
cialized forms, become persistent and more or less
rigid, as flagella, cilia, etc.; which are the first distinct
organs which subserve the transportation of the body
from place to place. The causes which lead to these
changes are as yet obscure, but that the use of these

1 Proceeds. Am. Philos. Soc., 1871, p. 18. Origin of the Fittest, 1887, p. 194.
390 rd

498 PRIMARY FACTORS OF ORGANIC EVOLUTION.

organs when once called into existence is due to stimuli
similar to those which affect the motions of the limbs
of the higher animals, is altogether probable. What-
ever be its nature, the preliminary to any animal move-
ment which is not automatic, is an effort. And as no
adaptive movement is automatic the first time it is per-
formed, we may regard effort as the immediate source
of all movement. Now, effort is a conscious state, and
is a sense of resistance to be overcome. When an act
is performed without effort, resistance has been over-
come, and the mechanism necessary for the performance
of the act has been completed. The stage of automa-
tism has been reached. At the inception of a new
movement resistance is necessarily experienced. Itis
generally believed that a mental state, as a sensation
or a desire, which may or may not stimulate a rational
process as an intervening element in the circuit, is
concerned in overcoming this resistance..

A different view is held by certain physiologists and
thetaphysicians, ase. g. Wundt and Héoffding. Hux-
ley thus states his opinion in his Belfast address of
1874,1 @ propos of Descartes’s doctrine that all animals
below man are automata. ‘*The consciousness of
brutes would appear to be related to the mechanism of
their body simply as a collateral product of its work-
ing, and to be as completely without any power of
modifying that working as the steam-whistle which
accompanies the work of a locomotive-engine is with-
out influence on its machinery. Their volition, if they
have any, ts an emotion indicative of physical changes, not
a cause of such changes.” (Italics mine.) In other
words, stimulus excites conscious states, but the state
thus produced has no influence on the resulting act.

MScientific Culture and Other Essays, p. 243.

THE FUNCTION OF CONSCIOUSNESS. 499

That sense-perceptions are stimuli to the immediate
appearance of structural changes or movements is ad-
mitted. This is shown by the production of color
changes in animals through changes in the condition
of the organs of sight. Pouchet showed that the extir-
pation of both eyes of the turbot, and of a Gobius,
paralyzed the chromatophorous cells, so that the usual
color-adaptations to the color of the surface of the bot-
tom on which they rested, could not be made. He also
produced the same effect on one side of a trout by re-
moving the eye of the opposite side. The chromato-
phore were permanently expanded, and the colors dark.

Some experiments which I tried with tree frogs of
the species Hyla gratiosa, and Hyla carolinensis, are as
follows: The color is usually green in both species,
but it changes to dark brown where the frog rests ona
brown surface, as of bark, etc. It appears that the
maintenance of the brown color requires a more vigor-
ous nervous stimulus than the green. ‘The frogs are
green at death ; and limbs which I ligated remained
green when the remainder of the surface became
brown. Now in individuals with extirpated eyes, the
color was always green, no matter what the surface on
which they rested. The power of assuming the brown
color was lost.

In these experiments it is difficult to coanest the
expansion of the chromatophorous cells as any effect
of consciousness of color, by direct proof. If, how-
ever, muscular cells can be contracted under the in-
fluence of mental states, a similar mechanism may be
supposed to exist in the case of chromatophore. The
fact that the process may be now reflex does not ex-
clude the other fact of the influence of consciousness

500 PRIMARY FACTORS OF ORGANIC EVOLUTION.

at the inception, and its necessity for the continuance
of the habit.

If we examine muscular movements, the evidence
of control by consciousness becomes more distinct.
New conditions bring forth new acts in animals too
frequently to permit us to believe otherwise. Thus
Mr. Belt tells of a procession of ants which crossed a
railroad in Panama. Many were killed on the rail, so
the column excavated a passage beneath the rail, and
thus escaped further injury. No one can reasonably
deny the intervention of a conscious state of a high
order, as directly controlling the muscular movements
of those ants. According to Beauchamp, termites in
the same region display similar intelligence. A num-
ber of them were confined in a deep glass vessel with
smooth sides which they could not scale. They there-
upon deposited drops of their building secretion, which
hardens on drying, on the glass, ascending backwards,
and so made a stair out of their prison, by which they
escaped.

A Cebus capucinus in my possession imitated some
carpenters who were working in the room with a draw-
ing-knife. He used a triangular piece of tin, and,
holding the corners, drew the edge towards him over
the surface of a piece of squared wood on which he
sat. He did this rapidly and repeatedly, with many
grimaces. A Cebus afella in the Philadelphia Zodlogi-
cal Garden lights matches whenever he can get them.
He always selects the proper end, and holds it at a
proper distance, so that the stick is not broken and his
fingers are not burned. He strikes them on the rough
outside of his drinking-kettle. My Cedus came direct
from the forests of Venezuela, and he had not been
educated among carpenters. The history of the apella

THE FUNCTION OF CONSCIOUSNESS. 501

I do not know, but he had not probably been brought
up among matches, and his act was in any case not
reflex.

As an illustration of the simplest of movements,
and their physical conditions, I cite those of the Myx-
omycetes, from Stahl.!

‘‘The movement of Myxomycetes is influenced by:

‘‘1, Moisture (Hydrotropism): In their young
stages they wander from the parts of the substratum
(i. e. of the deposit on which they are creeping), which
are gradually drying up, toward those which continue
moist longer; ‘it is even possible, by bringing moist
bodies into the proximity of any ramifications, to cause
the production of pseudopodia, which elevate them-
selves from the substratum, and soon come into con-
tact with the moist object, so as to enable the whole
mass of the plasmodium to migrate on to it.’ On the
entrance of the plasmodia into the fructifying condi-
tion, positive hydrotropism gives place to negative ;
the myxomycete quits the moist substratum and creeps
upwards on to the surface of dry objects.

‘<2, Unequal distribution of warmth in the sub-
stratum, and

“¢3. Unequal supplies of oxygen also cause loco-
motion in the myxomycete.

««4, Chemical substances soluble in water have a
similar action. Contact of the plasmodia on one side
with solutions of common salt, saltpetre, or carbonate
of potash, cause them to withdraw from the danger-
ous spot, while infusion of tan, or a dilute solution
of sugar, produces a flow of the protoplasm and ulti-

1E, Stahl, ‘‘Zur Biologie der Myxomyceten,” Botan, Zeztung, 1884, No.
zo-12. Abstract in Sitzungsbericht der Jenaischen Gesellschaft fiir Medizin
und Naturwissenschaft, 1883, Sitzung vom 16. November.

502 PRIMARY FACTORS OF ORGANIC EVOLUTION,

mately translocation of the whole plasmodial mass
towards the source of nourishment. Some solutions
have an attractive or repulsive effect, according to
their degree af concentration.

‘¢5. Finally, they withdraw from light (negative
heliotropism).

‘With regard to the sceaciaaod or definite direc-
tion of movement produced entirely by stimuli, com-
pare the following:

‘«The knowledge of the remarkably delicate reac-
tion of the plasmodia under external influences enables
us to comprehend how these tender structures, desti-
tute of every kind of external protection, are able to
carry on their existence. The plasmodia which are
not yet ripe for reproduction are kept in the moist sub-
stratum by positive hydrotropism, which is assisted by
negative heliotropism.

‘¢But within the darkness and moisture of the sub-
stratum the plasmodia by no means remain in one
place, because the differences in the chemical compo-
sition of the substratum cause continual migrations.
The plasmodia have the faculty in a wonderful way of
avoiding harmful substances, and, traversing their
substratum in all directions, of taking up the materials
they require.

“¢ When the internal changes have proceeded so far
that the plasmodia approach the fructifying condition,
they are brought by the negative hydrotropism which
now sets in, from the moist parts of the ground in the
forest or wood to the surface, where they creep up
various upright objects, often only forming rigid re-
productive capsules at some height from the ground.

«‘When in autumn the substratum becomes grad-
ually colder a change which takes place from the sur-

THE FUNCTION OF CONSCIOUSNESS. 503

face downwards, the plasmodia migrate into deeper
regions still having a higher temperature. When the
cooling proceeds very gradually, which especially hap-
pens in large tan-heaps, the plasmodia may, in their
migration reach somewhat considerable depths, where
they then change into sclerotia. To find the sclerotia
of #thalium in winter it is, therefore, not seldom
necessary to search through the mass of tan to a depth
of several feet. When the temperature again begins
to rise, the sclerotia again germinate, and movement
in the opposite direction takes place from the deeper
and cooler parts to the upper portions already warmed.

“<In the locomotion of the Myxomycetes, then, we
see extremely interesting cases of movements due to
stimulation. Heliotropism, geotropism, hydrotropism,
trophotropism, in general, are stimulus-movements,
and ultimately all growth depends on stimulus-move-
ment. It is the most primitive kind of protoplasmic
movement. Stimuli in fixed directions and constantly
repeated, produced, but only secondarily, fixed paths
of conduction, and responses of a quite definite kind
(reflexes). Thus arose nerves, and finally apparatus
for stirring up stimuli, arose sensation and will—as
acquired and inherited faculties.”

In this lowest type of organic movement it is diffi-
cult to discern any cause for it different from those
which actuate higher organisms. What form of inor-
ganic energy can be cited as sufficient to cause the
organism to change its position with regard to stimuli
to self-preservation, and without regard to gravita-
tion, or any known form of attraction or repulsion?
In the Fuligo (tan flowers) a most pronounced ex-
ample of designed movement has been observed.
This form, in the amcebula stage, will, according

504 PRIMARY FACTORS OF ORGANIC EVOLUTION.

to H. J. Carter, ‘‘confine itself to the water of the
watch-glass in which it may be placed, when away.
from the sawdust and chips of wood among which it
has been living ; but if the watch-glass be placed upon
the sawdust it will very soon make its way over the
side of the watch-glass and get to it.” This act probably
depends on a sense-perception of the presence and posi-
tion of the tan-bark, and of a feeling of desire to reach
it. This may have been due to a sense of discomfort.
due to the surrounding water, or to a recollection of
superior comfort associated with the tan-bark.
Ordinary observation of most animals leads to the
belief that their movements are provoked by sensa-
tions, as of hunger, thirst, temperature, etc.; also of
sight, hearing, smell, etc., when they possess those
senses. There are physiologists who deny that such
is the case, but I must insist on the importance of a
psychological rather than a physiological study of ani-
mals as a most important source of information in
this direction. The students of dead or mutilated
animals miss important evidence as to the phenomena,
of consciousness. The attempt has been made to
identify hunger, for instance, with chemical energy, a
proposition which is simply irrational. It may be none
the less true, however, that hunger is a necessary con-
comitant of a molecular condition. Observation on
living animals shows in the most conclusive manner
that by far the greater number of species are capable
of the performance of acts in response to new situations
and circumstances for the performance of which no
automatic mechanism exists. Memory is clearly pres-
ent in them, and, as a consequence, judgments are
formed which determine the succeeding acts. The
process, be it ever so simple, is ‘‘representative,” and

THE FUNCTION OF CONSCIOUSNESS. 505

thus a mental act, at least one stage beyond sense-
impression. The doctrine that conscious states have
preceded organisms in time and evolution I have called
archesthetism. It seems to have been first clearly for-
mulated by Erasmus Darwin, who believed that growth
has been stimulated by ‘‘irritations ” (of hunger, thirst,
etc.) and by the pleasurable sensations attending those
irritations, and by exertions in consequence of painful
sensations, similar to those of hunger and suffocation,’
etc.

The weakness of the doctrine of archzsthetism con-
sists in our ignorance of the characters of the Proto-
zoa, with respect to the presence or absence of con-
sciousness or sensation. While many of the acts of
these low organisms need not be explained by suppos-
ing its presence, others seem to be impossible without
it. We are, however, led to infer its presence rather
on uniformitarian grounds, than by any certainty of
explanation of the phenomena. We can trace sensa-
tion so far down in the scale of animal life, that it
seems unreasonable to deny its presence when the
same phenomena are exhibited by the Protozoa. We
are confirmed in our belief in the presence of sensation
in these low forms, by the knowledge that reflex acts
are the product of conscious acts, whereas we have no
evidence that conscious acts are the product of the re-
flex.

Although it is frequently alleged or assumed that
designed conscious acts are the product of reflexes, no
one has yet shown how this is possible. On the other
hand, the development of automatic acts out of con-
scious ones is of ordinary occurrence, and is known
under the name of education.

1Zoonomia, KXXIX., 3; Osborn, From the Greeks to Darwin, p. 148,

506 PRIMARY FACTORS OF ORGANIC EVOLUTION,

The relation of consciousness to the physical basis
is as yet a profound mystery, but that they exercise
over each other a definite mutual control is unques-
tionable. The processes which produce thought, as
conception, judgment, etc., are, however, not qualita-
tively related to the amount of nutritious proteids
consumed in the central nervous system, but only
quantitatively; yet it is the outcome of these processes
that directs animal movements, when they are not auto-
matic. In other words, the forms of thought, which
have no weight, direct the movements of muscles,
which have weight. This is not in accord with the
doctrine of the correlation of energy. But what has
the formation of a concept, or the development of a
judgment, to do, per se, with the correlation of energy?
I may give this idea a more definite expression by the
following diagram :1!

I 2
AFFIRMATIVE. NEGATIVE. AFFIRMATIVE. NEGATIVE,
I 5 I 3
6 2

2 4
3 5
4 6

Let each square represent the grammes of energy
necessary for the maintenance in consciousness of six
propositions. Judgment issues from the side of the
predominating number of propositions. They arrange
themselves in consciousness in accordance with their
qualities, in two aggregations represented by columns
in the squares. Now if they arrange themselves in
four affirmative and two negative, as in square 1, the

1This is in explanation of the same proposition as stated by me in the
Proceedings of the American Philosophical Society, 1889, p. 504.

THE FUNCTION OF CONSCIOUSNESS. 507

judgment is affirmative. If, on the other hand, they
arrange themselves in two affirmative and four nega-
tive, as in square 2, the judgment is negative. The
energy expended in the two cases is the same. So also
in forming different concepts from the same set of par-
ticular sense-impressions or memories. Is there any dif-
ference in the energy expended in forming from them
the concept of bigness as compared with that of red-
ness? While, therefore, every mental process is ex-
pensive as a whole, the mental content is obedient to
the forms of thought rather than the correlation of
energy. This is what mind is. While it is doubtful
whether any animal below man can form a concept
(with a very few possible exceptions), the formation
of simple judgments is general. Any decision based
on experience is a judgment.

In order to render this proposition clearer, I have
formulated it in the following language, although it is
possible that the definition of energy will not bear the
strain of the statement.

‘¢ The formal statement of this phenomenon may be
found in the thesis, that exergy can be conscious. If true,
this is an ultimate fact, neither more nor less diffi-
cult to comprehend than the nature of energy or
matter in their ultimate analyses. But how is sucha
hypothesis to be reconciled with the facts of nature,
where consciousness plays a part so infinitesimally
small? The explanation lies close at hand, and has
been already referred to. ergy become automatic is
no longer conscious, or is about to become unconscious.
That this is the case is matter of every-day observa-
tion on ourselves and on other animals. What the
molecular conditions of consciousness are, is one of
the problems of the future, and for us a very interest-

508 PRIMARY FACTORS OF ORGANIC EVOLUTION.

ing one. One thing is certain, the organization of the
mechanism of habits is its enemy. J? zs clear that in
animals, energy, on the loss of consciousness, undergoes a
retrograde metamorphosis.

‘«To regard consciousness as the primitive condi-
tion of energy, contemplates an order of evolution in
large degree the reverse of the one which is ordinarily
entertained. ‘The usual view is, that life is a deriva-
tive from inorganic energies as a result of high or com-
plex molecular organization, and that consciousness
(=sensibility) is the ultimate outcome of the nervous
or equivalent energy possessed by living bodies. The
failure of the attempts to demonstrate spontaneous
generation will prove, if continued, fatal to this theory.
With our present evidence it may be affirmed that not
only ‘has life preceded organization,’ but that con-
Sclousness was coincident with the dawn of life.”

The facts cited, and the doctrines defended in the
preceding pages lead to one inference as to the relation
of consciousness to its physical basis. The condition
of matter necessary to the maintenance of conscious-
ness is, in the language of morphology, generalized; in
the language of chemistry, zeutra/; in the language of
physics, zon-eguilibrated. The materialist and the ani-
mist can alike agree as to this generalization. The
difference between the two positions is a difference of
view as to the mutual relations of the two members of
the partnership. Is the permanent absence of equi-
librium of living protoplasm due to control by con-
sciousness ? or is consciousness a product of an absence
of equilibrium, which is due to chemical and physical
action? The latter proposition is untenable, because
the inevitable tendency of chemical and physical ener-
gies is to an equilibrium. Is, therefore, the other al-

THE FUNCTION OF CONSCIOUSNESS. 509

ternative true? There seems to be no escape from it,
and it accords also with our personal human experi-
ence of the agency of conscious states in our various
activities, physical and mental.

2. THE EFFECTS OF CONSCIOUSNESS.

From the facts cited it is evident that sensation
(consciousness) has preceded in time and in history,
the evolution of the greater part of plants and animals,
both unicellular and multicellular. It appears also
that if kinetogenesis be true, consciousness has been
essential to a rising scale of organic evolution.

Animals who do not perform simple acts of self-
preservation must necessarily perish sooner or later.
In fact it is impossible to understand how the lowest
forms of life, utterly dependent as they are on physi-
cal conditions of many kinds, should not have been
all destroyed, were they not possessed of some degree
of consciousness under stimuli at least. And the case
is even plainer with the higher forms. We have only
to picture to ourselves the condition of a vertebrate
without general or special sensation, to perceive how
essential consciousness is to its existence. If now, as
maintained in Chapter IV., use has modified struc-
ture, and so, in coéperation with the environment, has
directed evolution, we can understand the origin and
development of useful organs. And we can under-
stand how by parasitism or other mode of gaining a
livelihood without exertion, the adoption of new and
skilful movements would become unnecessary, and
consciousness itself would be seldom aroused. Con-
tiued repose would be followed by subconsciousness,
and later by unconsciousness. Such appears to be the
history of degeneracy everywhere, and such is, per-

510 PRIMARY FACTORS OF ORGANIC EVOLUTION.

haps, the history of the entire vegetable kingdom.
From their ability to manufacture protoplasm from
inorganic substances, plants do not need to move
about in search of food, so that they require no con-
sciousness of conditions to guide their movements.
They become fixed, and their entire organization be-
comes monopolized by the functions of nutrition and
reproduction. Movements rarely occur, and when
present are confined to those of one part of the struc-
ture or another. They are mostly rhythmic or rotary,
and very seldom exhibit the quality of impromptu de-
sign. The satisfactory explanation of those that ex-
hibit general design, as the adaptation for transporta-
tion often seen in seeds, may be chance coincidence
and natural selection.

The ascending scale of development of intelligence
observed among animals is strong evidence in support
of the hypothesis here outlined. There can be no
doubt that in the long run the most intelligent have
survived. They have survived because they were
capable of the most successful designed acts, thus
directing their movements to the most useful ends.
These movements ultimately modified their structure
usefully, to the perfecting of mechanisms in every way
important to their possessors. This much having been
established as to the cause of anagenesis, let us look
more closely into the history of catagenesis.

Movements of organic beings on frequent repeti-
tion become automatic, reflex, and finally, as it is
termed, organic. This means the running down of
energy through various grades, beginning with the
highest or conscious stage, and ending with the purely
reflex, which is as unconscious of changes in the en-
vironment as is any one of the physical energies. The

THE FUNCTION OF CONSCIOUSNESS. 511

conscious stage is evidently the most susceptible to
the stimuli of the environment, and the process of
catagenesis is one of degeneracy to less and less sensi-
tive and to more and more mechanical conditions.
The resemblance of the lowest grade of organic activ-
ities to physical mechanical energy is so great that it
is almost universally supposed by evolutionists to be
of purely mechanical origin, but I have endeavored to
show that they are of totally different origin, and that
the only explanation of their characteristics is the hy-
pothesis of catagenesis.

In accordance with this view, the automatic ‘‘in-
voluntary’? movements of the heart, intestines, repro-
ductive systems, etc., were organized in primitive and
simple animals in successive states of consciousness,
which stimulated ‘‘voluntary” movements, which ulti-
mately became rhythmic; whose results varied with
the machinery already existing and the material at
hand for use.. It is not inconceivable that circulation
may have been established by the suffering produced
by an overloaded stomach demanding distribution of
its contents. The structure of the Infusoria offers the
structural conditions of such a process. A want of
propulsion in a stomach or body-sack occupied with
its own functions would lead to a painful clogging of
the flow of its products, and the ‘‘ voluntary” contrac-
tility of the body or tube-wall being thus stimulated,
would at some point originate the pulsation necessary
to relieve the tension. Thus might have originated
the ‘‘contractile vesicle” or contractile tube of some
protozoa ; its ultimate product being the mammalian
heart. So with reproduction. Perhaps an excess of
assimilation in well-fed individuals of the first animals
led to the discovery that self-division constituted a re-

512 PRIMARY FACTORS OF ORGANIC EVOLUTION.

lief from the oppression of too great bulk. With the
increasing specialization of form, this process would
become necessarily localized in the body, and growth
would repeat such resulting structure in descent, as
readily as any of the other structural peculiarities. No
function of the higher animals bears the mark of con-
scious origin more than this one, as consciousness is
still one of the conditions of its performance. While
less completely ‘‘ voluntary” than muscular action, it
is more dependent on stimulus for its initial move-
ments, and does not in these display the unconscious
automatism characteristic of many other functions.
There remain, however, some phenomena which do
not yield so readily to this analysis. First, we have the
conversion of inorganic substances into protoplasm by
plants. It is also well known that living animal or-
ganisms act as producers, by conversion, of various
kinds of inorganic energy, as heat, light, sound, electri-
city, motion, etc. It is the uses to which these forces are
put by the animal organism, the evident design in the
occasion of their production, that gives them the stamp
of organic life. We recognize the specific utility of the
secretions of the glands, the appropriate distribution of
the products of digestion and adaptation of muscular
motion to many uses. The increase of heat to protect
against depression of temperature ; the light to direct
the sexes to each other; the electricity as a defence
against enemies—display unmistakably the same util-
ity. We must not only believe that these functions
of animals were originally used by them under stimu-
lus, for their benefit, but, if life preceded organism,
that the mechanism which does the work has devel-
oped as the result of the animal’s exertions under stim-
uli. This will especially apply to the mechanism for

THE FUNCTION OF CONSCIOUSNESS. 513

the production of motion and sound. The production
of heat, light, chemism, and electricity doubtless re-
sult from molecular aptitudes inherent in the constitu-
tion of protoplasm. But the first and last production
of even these phenomena is dependent on the motions
of the animal in obtaining and assimilating nutrition.
For without nutrition all energy would speedily cease.
Now the motion required for the obtaining of nutrition
has its origin in the sensation of hunger. So, even for
the first steps necessary to the production of inorganic
forces in animals, we are brought back to a primitive
consciousness. This hypothesis I have termed Ar-
chesthetism.

‘‘It maintains that consciousness as well as life
preceded organism, and has been the primum mobile in
the creation of organic structure. This conclusion
also flows from a due consideration of the nature of
life. I think it possible to show that the true defini-
tion of life is, exergy directed by sensibility, or by a mech-
anism which has originated under the direction of senst-
bility. Tf this be true, the two statements that life has
preceded organism, and that consciousness has pre-
ceded organism are coéqual expressions.

‘Granting the existence of living protoplasm on
the earth, there is little doubt that we have some
of its earliest forms still with us. From these sim-
plest of living beings both vegetable and animal king-
doms have been derived. But how was the distinc-
tion between the two lines of development, now so
widely divergent, originally produced ? The process
is not difficult to imagine. The original plastid dis-
solved the salts of the earth and appropriated the gases
of the atmosphere and built for itself more protoplasm.
Its energy was sufficient to overcome the chemism

514 PRIMARY FACTORS OF ORGANIC EVOLUTION.

that binds the molecules of nitrogen and hydrogen in
ammonia, and of carbon and oxygen in carbonic diox-
ide. It apparently communicated to these molecules
its own method of being, and raised the type of energy
from the polar non-vital to the adaptive vital by the
process. Thus it transformed the dead inorganic world,
perhaps by a process of invasion, as when a fire com-
municates itself from burning to not burning combust-
ible material. Thus it has been doing ever since, but
it has redeposited some of its gathered stores in vari-
ous non-vital forms. Some of these are in organic
forms, as cellulose ; others are crystals imprisoned in
its cells ; while others are amorphous, as waxes, resins,
and oils. But consciousness apparently early aban-
doned the vegetable line. Doubtless all the energies
of vegetable protoplasm soon became automatic. The
plants in general, in the persons of their protist ances-
tors, soon left a free-swimming life and became sessile.
Their lives thus became parasitic, more automatic,
and in one sense degenerate.

“« The animal line may have originated in this wise...
Some individual protists, perhaps accidentally, de-
voured some of their fellows. The easy nutrition which
ensued was probably pleasurable, and once enjoyed
was repeated, and soon became a habit. The excess
of energy thus saved from the laborious process of
making protoplasm was available as the vehicle of con-
sciousness and motion. From that day to this, con-
sciousness has abandoned few if any members of the
animal kingdom. In many of them it has specialized
into more or less mind. Organization to subserve its
needs has achieved a multifarious development. There
is abundant evidence to show that the permanent and
the successful forms have ever been those in which

THE FUNCTION OF CONSCIOUSNESS. 515

motion and sensibility have been preserved, and most
highly developed.

We must remember, however, that in the matter
of the evolution of plant-types we have an especial
factor in the influence which insects have exerted on
the conditions of almost all of their organs. Insects
originated early in geological time, and have closely
accompanied plants in their evolution. As the source
of the food, and as the dwelling-places of great num-
bers of insects, they have been subjected to a class of
stimuli and strains similar to those which animals have
experienced. It is believed that the forms of the or-
gans of fructification and especially of the flowers,
have been greatly modified by the influence of insects.?
The general evolution of plants, however, presents us
with a greater predominance of physiogenetic or simple
dynamical conditions over the bathmic, than in the case
of animals. Thus many peculiarities of the inflores-
cence directly result from the shortening of the axial
growth in complementary relation to the increase of
peripheral growth. Such is evidently the origin of
flowers themselves ; secondly of the umbel as com-
pared with the spike or panicle and finally of the com-
posite head as compared with the other modes of in-
florescence. To the cohesion of the elements of a
whorl, possible only in the case of an abbreviated axis,
can we ascribe the formation of a seed vessel from dis-
crete carpels, and a gamopetalous from a polypetalous
corolla. Degeneracy or specialization is to be seen
everywhere, as in the abortion of ovules, carpels, and
perianth.

«‘ Catagenesis of living organisms has been epito-

lOrigin of the Fittest, p. 428, 432.

2 Henslow.

516 PRIMARY FACTORS OF ORGANIC EVOLUTION.

mized in the following language: ‘Evolution of living
types is then a succession of elevation of platforms,
on which succeeding ones have built. The history of
one horizon of life is that its own completion but pre-
pares the way for a higher one, furnishing the latter
with conditions of a still further development. Thus
the vegetable kingdom died, so to speak, that the ani-
mal kingdom might live, having descended from an ani-
mal stage to subserve the function of food for animals.
The successive types of animals first stimulated the
development of the most susceptible to the conflict,
in the struggle for existence, and afterwards furnished
them with food.’ In the occupation of the world’s
fields, the easiest and nearest at hand have been first
occupied, and successively those which were more dif-
ficult. The digging animals are generally those which
first abandoned the open field to more courageous or
stronger rivals ; and they remain to this day generally
of low type compared with others of their_classes (e. g.
Monotremata, Glires, Insectivora). Alloccupations have
been filled before that one which requires the greatest
expenditure of energy, i. e. mental activity. But all
other modes of life have fallen short of this one in giv-
ing the supremacy over nature.”

We now approach an explanation of the phenome-
non of anagenesis. Why should evolution be pro-
gressive in the face of universal catagenesis? No other
ground seems discoverable but the presence of sensa-
tion or consciousness, which is, metaphysically speak-
ing, the protoplasm of mind. The two sensations of
hunger and sex, have furnished the stimuli to internal
and external activity, and memory, or experience with
natural selection, have been the guides. Mind and
body have thus developed contemporaneously and

THE FUNCTION OF CONSCIOUSNESS. 517

have reacted mutually. Without the coéperation of
all these factors, anagenesis seems impossible.

From this point of view the study of the evolution
of mind and its relation to the organic world assumes
a newimportance. Circumstances have forbidden my
entering on this subject in the present volume, but I
hope to be able to devote especial attention to it at a
future time. One fundamental postulate of mental
evolution may, however, be mentioned here. That is,
as Spencer has pointed out, the instinct of hunger is
at the basis of the activity which has developed the
intelligence, while that of sex is at the basis of the de-
velopment of the altruistic or social instincts and affec-
tions. With this proposition I leave this interesting
part of the doctrine of evolution.

CHAPTER XI.—THE OPINIONS OF
NEOLAMARCKIANS.

AMARCK ascribed some of the evolutionary changes
of structure to changes in the environment, some
to the motions of organic beings, and others to both
combined.! Spencer in 1865? devoted a short chapter
to the effect of motion in producing variations, and
specified the mechanical effect of flexure in producing
segmentation of the vertebral column. The present
writer in 18715 insisted on the importance of motion
as a factor in determining growth, and in 1872! I ap-
proached the subject more definitely in the following
language: ‘‘ The first physical law is that growth force
. must develop extent in the direction of least re-
sistance, and density on the side of greatest resist-
ance.” In 1877 Ryder further applied the principle
of motion to the origin of structural changes, chiefly
reduction of digits, in the feet of Mammalia in lan-
guage® which I have quoted on page 311.
1Philosophie Zoologigue, Chap. VII., 1809; translation in American Nat-
uralist for 1888.
2 Principles of Biology, 11., pp. 167 and 195.

3Proceeds, Amer, Philosoph, Soc., 1871, p. 259. Origin of the Fittest, 1887, p.
210.

4 Penn Monthly Magazine, July, 1872. Origin of the Fittest, 1887, p. 30.
6 American Naturalist, 1877, p. 607.

‘THE OPINIONS OF NEO-LAMARCKIANS. 519

-In the same year, in discussing the origin of the
great development of the incisor teeth in the Roden-
tia,1 Professor Ryder, in summing up, ventured ‘the
reflection that the more severe strains to which they
were subjected by enforced or intelligently assumed
changes of habit, were the initiatory agents in causing
them to assume their present forms, such forms as
were best adapted to resist the greatest strains with-
out breaking.” In 1878 the writer? advanced the fol-
lowing proposition: ‘‘ Change of structure is seen to
take place in accordance with the mechanical effect of
three kinds of motion, viz., by friction, pressure, and
strain.”” In the same year Professor Ryder went into a
discussion of the specific application of strains in the
evolution of the dental types of the diplarthrous Un-
gulata, and prepared the field for work in the Rodentia
and Proboscidia.? In 1879 the writer gave mechan-
ical reasons for the reduction of the sectorial teeth of
Carnivora to one, and for their present position in the
jaws. In 1881 the writer described the specific ac-
tion of impacts and strains in the production of the
existing characters of the articulations of the limbs in
the higher Mammalia. In 1887 the same subject, to-
gether with that of the mechanical origin of the char-
acters of the molar teeth, was more fully investigated
‘in a paper on the Perissodactyla.® In 1888 the writer
published a paper on the mechanical origin of the sec-
torial teeth of the Carnivora,? one on the mechanical

1 Proceeds. Phila, Acad., 1877, p. 318.

2 American Naturalist, January, 1878. Origin of the Fittest, p. 354.

8 Proceeds. Phila, Acad., 1878, p. 45.

4 American Naturalist, March, 1879.

5 American Naturalist, April and June, 1881.

6 American Naturalist, 1887, pp. 985, 1060.

7 Read before the American Association for the Advancement of Science,

New York, 1887, p. 254.

520 PRIMARY FACTORS OF ORGANIC EVOLUTION.

origin of the peculiar dentition of the Glires,! and a
third on the mechanical origin of the dentition of the
Amblypoda.? In 1889 I discussed the mechanical
causes of the structures of the elbow and other joints
in the Artiodactyla and the origin of the peculiar in-
tervertebral articulations in that order.? In the same
year I published a résumé of the work done on this
subject with reference to the Mammalia.‘ Since that
time important contributions to the subject have been
made by Ryder, Osborn, Wortman, Dall, Jackson,
and others, to which reference will now be made.

Hyatt says as a result of his exhaustive studies
of the phylogeny of the Cephalopoda®; ‘‘The ac-
tion of physical changes takes effect upon an irrit-
able, plastic organism which necessarily responds to
external stimulants by an internal reaction or effort.
This action from within upon the parts of organisms
modifies their hereditary forms by the production of
new growths or changes, which are therefore adapted
or suitable to the conditions of the habitat, and are
therefore physiologically and organically equivalent to
the physical agents and forces from which they directly
or indirectly originated. In so far then, as causes and
habits are similar, they probably produce representa-
tion or morphological equivalence in different series of
the same type in similar habitats: and in so far as
they are different, they probably produce the differen-

lAmerican Naturalist, January, 1888, p. 3.

2 Proceeds. Amer, Philosoph. Soc., 1888, p. 80.

3 American Naturalist, March, 1889.

4 The American Journal of Morphology, September, 1889, pp. 137-277, ‘On
the Mechanical Causes of the Development of the Hard Parts of the Mam-
malia.”

5 The Genesis of the Arietide, by Alpheus Hyatt; Smithsonian Contribu-
tions to Knowledge, and Memoirs of the Museum of Comparative Zodlogy, Vol.
XVL., No. 3, 1889.

THE OPINIONS OF NEO-LAMARCKIANS 521

tials which distinguish series and groups from each
other.”

Packard! in discussing the causes of the blindness
of cave animals, says: ‘‘Such a phrase as ‘natural
selection,’ we repeat does not to our mind definitely
bring before us the actual working-causes of the evo-
lution of these cave organisms, and no one cause can
apparently account for the result. The causes are
‘change in the environment,’ disuse of certain organs ;
‘adaptation,’ ‘isolation,’ and ‘heredity’ operating to
secure for the future the permanence of the newly orig-
inated forms as long as the physical conditions remain
the same.”

In 1889, Ryder described the ontogenetic origin of
the articulations of the cartilaginous fin-rays of the
Salmo fontinalis, and used the facts observed as evi-
dence that these articulations are due to the mechan-
ical strain experienced by the rays in use as motors of
the body of the fish in the water.?

Prof. H. F. Osborn in 18g03 discussed thoroughly
the mechanical causes for the displacement of the ele-
ments of the feet of the ungulate Mammalia from
linear to alternating relations. (See antea, p. 299.)
In an article in Wa¢ure,* the same distinguished natu-
ralist remarks: ‘‘The following views are adopted
from those held by Cope and others, so far as they con-
form to my own observations and apply to the class
of variations which come within the range of paleon-
tological evidence. In the life of the individual, adap-

1 On the Cave Fauna of North America,” Memozrs of the U. S, National
Academy of Sciences, IV, pt., I., p. 137.

2 Proceedings of the American Philosophical Society, 1889, p. 546.

8 Transactions of the American Philosophical Society, XV1., February, 1890,

p. 531.
4January 9, 1890, p. 277.

522 PRIMARY FACTORS OF ORGANIC EVOLUTION.

tation is increased by local and general metatrophic
changes of necessity correlated, which take place most
rapidly in the regions of least perfect adaptation, since
here the reactions are greatest; the main term of vari-
ation is determined by the slow transmission, not of
the full increase of adaptation, but of the disposition
to adaptive atrophy or hypertrophy at certain points ;
the variations thus transmitted are accumulated by the
selection of the individuals in which they are most
marked, and by the extinction of inadaptive varieties
or species; selection is thus of the ensemble of new
and modified characters. Finally, there is sufficient
paleontological and morphological evidence that ac-
quired characters in the above limited sense, are trans-
mitted. ... Excepting in two or three side-lines the
teeth of all the Mammalia have passed through closely
parallel early stages of evolution, enabling us to formu-
latealaw: Zhe new main elements of the crown make
their appearance at the first points of contact, and chief
points of wear of the teeth in preceding periods. ‘What-
ever may be true of spontaneous variations in other
parts of the organism, these new cusps arise in the
perfectly definite lines of growth. . . . Now, after ob-
serving these principles operating in the teeth, look at
the question enlarged by the evolution of parallel spe-
cies of the horse series in America and Europe, and
add to the development of the teeth what is observed
in progress in the feet. Here is the problem of corre-
lation in a stronger form even than that presented by
Spencer and Romanes. To vary the mode of state-
ment: what must be assumed in the strict application
of the selection-theory? (@) that variations in the lower
molars correlated with coincident variations of reversed
patterns in the upper molars, these with metamorpho-

THE OPINIONS OF NEO-LAMARCKIANS. 523

sis in the premolars and pocketing of the incisor-
enamel; (4) all new elements and forms at first so
minute as to be barely visible, immediately selected
and accumulated; (¢) in the same individuals favor-
able variations in the proportions of the digits involv-
ing readjustments in the entire limbs and skeleton, all
coincident with those in the teeth; (7) finally, all the
above new variations, correlations, and readjustments
not found in the hereditary germ-plasm of one period,
but arising fortuitously by the union of different strains,
observed to occur simultaneously and to be selected at
the same rate in the species of the Rocky Mountains,
the Thames Valley, and Switzerland! These assump-
tions, if anything, are understated.”

I have already referred to the contribution by Dall
to the doctrine of kinetogenesis which has resulted
from his investigations of the origin of the characters
of the lamellibranchiate (or pelecypod) Mollusca.! He
observes: ‘In reflecting upon the origin of the com-
plicated mechanical arrangements in bivalves which
we call the hinge, I have come to the conclusion that
here, as in the cases of the mammalian foot and tooth
elaborated so clearly by Cope and Ryder, we have the
result of influences of a mechanical nature operating
upon an organ or apparatus in the process of develop-
ment. ... The shell is in one sense the product of se-
cretion from the mantle, as the mammalian tooth is
derived from the ectoderm of the jaw, or the skeleton
from the periosteum and cartilages. Both are that
and much more. It would be as reasonable to say
that a steam boiler in process of construction is the
product of the boy inside who holds the rivet-heads,
as to claim that the shell has no more significance

8 American Journal of Science and Arts, December, 1889, p. 447.

524 PRIMARY FACTORS OF ORGANIC EVOLUTION.

than is implied in the term ‘secretion of the mantle.’
The original theoretic protoconch may have been so,
but ‘as soon as it came into being, its development was
governed by the physical forces impinging upon it
from all sides, and through it influencing the growth
and structure of the soft parts beneath. The gastropod
shell is the result of the action and reaction between
the physical forces of the environment, and the evolu-
tionary tendencies of the organic individual’ In the
pelecypod we have the mechanical stresses and reac-
tions of one valve upon the other, added to the cate-
gory of influences. *To some extent it is doubtless as
true that the animal is moulded by its shell, as it is
that the shell is shaped by the soft parts of the ani-
mal.’

Dr. Dall in an able paper on the ‘‘Dynamic In-
fluences in Evolution,” read before the Biological So-
ciety of Washington, March 8, 1890, writes thus forci-
bly:

‘¢It is often assumed, in discussing variation, that
the possibility of variation is equal in every direction.
A consideration of the dynamic conditions of life show
that this is not the case, or, at least, if we grant its
theoretic truth, in practice it can never be true. Un-
der any conditions which would permit it, the result-
ing organic forms would have to pass their existence
in constant rotation. The moment that any one of
them came to rest, it would begin to be subjected to
unequal stresses relatively to its different parts. Light,
gravity, friction, opportunities for nutrition, would be
unequally distributed, with the result of forcing an
unequal growth, development, and specialization of
its regions. Inequality of form once established, if it
were a moving organism, friction and resistance of the

THE OPINIONS OF NEO-LAMARCKIANS. 525

circumambient medium, would confirm the inequality,
and put individuals of its kind at a disadvantage when
they varied towards the original shape.”

This is an excellent statement of kinetogenesis in
concentrated form.

Prof. A. S. Packard in an important essay ‘On
the Evolution of the Bristles, Spines, and Tubercles
of Certain Caterpillars,” etc., remarks as follows :}
‘‘The Lamarckian factors (1) of change (both direct
and indirect) in the mz/ieu, (2) need, (3) habit, and the
now generally adopted principle that a change of func-
tion induces change in organs, and in some or many
cases actually induces the hypertrophy and specialisa-
tion of what otherwise would be indifferent parts or
organs. These factors are all important in the evolu-
tion in the colors, ornaments, and outgrowths from
the cuticle of caterpillars. .. .

‘¢So far as Iam aware no one has suggested why
these horns and high tubercles and often pencils of
hairs are restricted to these particular segments. As
a partial explanation of the reason, it may be stated
that the presence of these high tubercles, etc., is cor-
related with the absence of abdominal legs on the seg-
ments bearing the former. It will also be noticed that
in walking the apodous segments of the caterpillar are
more elevated and prominent than those to which the
legs are appended. They tend to bend or hump up,
particularly the first and the eighth abdominal, the
ninth segment being reduced to a minimum, and the
tenth simply represented by the suranal and paranal
plates, together with the last pair of legs.

‘‘As is well known, the loopers or geometrid worms,
while walking elevate or bend up the part of the body

1 Proceedings of the Boston Society of Natural History, 1890, p. 493, 510-513.

526 PRIMARY FACTORS OF ORGANIC EVOLUTION.

situated between the last thoracic and first pair of ab-
dominal legs, which are appended to the seventh
euomere. Now in the larva of Mematocarpa filamentaria
which bears two pairs of remarkable filamental tuber-
cles rolled up at the end, it is certainly very sugges-
tive that these are situated on top of the loop made
by the caterpillar’s body during progression, the first
pair arising from the second, and the hinder pair from
the fourth abdominal segment.

‘«It seems, therefore, that the humps or horns arise
from the most prominent portions of the body, at the
point where the body is most exposed to external stim-
uli; and the force of this is especially seen in the con-
spicuous position of those tubercles which are volun-
tarily made to nod or so move as to frighten away
other creatures. Perhaps the tendency of these seg-
ments to loop or hump up, has had a relation of cause
and effect in inducing the hypertrophy of the dermal
tissues entering into the composition of the tubercles
or horns.”

Prof. W. B. Scott! says: ‘*To sum up the results
of our examination of certain series of fossil mammals,
one sees clearly that transformation, whether in the
way of the addition of new parts or the reduction of
those already present, acts just as zf the direct action
of the environment and the habits of the animal were
the efficient cause of the change, and any explanation
which excludes the direct action of such agencies is
confronted by the difficulty of an immense number of
the most striking coincidences. . . . So far as I can see
the theory of determinate variations and of use-inheri-
tance, is not antagonistic, but supplementary to nat-
ural selection, the latter theory attempting no explana-

lAmerican Journal of Morphology, 1891, pp. 395, 398.

THE OPINIONS OF NEO.LAMARCKIANS. 527

tion of the causes of variation. Nor is it pretended for
a moment that use and disuse are the sole or even the
chief factors in variation.”

European authors, partly from their less favorable
situation for the obtaining of paleontologic evidence,
have not contributed as much as Americans to the
doctrine of bathmogenesis. Nevertheless, in England
Spencer, Cunningham, Henslow, and others have sus-
tained this doctrine, and in France Giard and Edmond
Perrier, and in Germany, Semper, Eimer, and others,
who lean principally in their writings to its physio-
genetic aspect. Says Eimer:!

“According to my conception, the physical and
chemical changes which organisms experience during
life, through light or want of light, air, warmth, cold,
moisture, food, etc., and which they transmit by her-
edity, are the primary elements in the production of
the manifold variety of the organic world, and in the
origin of species. From the materials thus supplied,
the struggle for existence makes its selection. These
changes, however, express themselves simply as
growth.”

Nageli discards completely the agency of natural
selection, and sees an internal ‘‘ Principle of Improve-
ment” as the active agent in evolution. He appar-
ently includes both statogenesis and bathmogenesis in
his conception.? He says:

“‘Such internal causes must necessarily be sup-
posed merely on the ground that modifications or vari-
ations of the phyla do actually take place in definite
directions, are not irregular. The internal causes effect

1 Organic Evolution, English Translation, 1890, p. 22.
2Mechanische physiologische Abstammungslehre, C. V. Nageli, Munich,
1884. :

528 PRIMARY FACTORS OF ORGANIC EVOLUTION.

a constant alteration of the phyla in definite directions,
towards greater perfection, that is, towards greater
complexity.” Accordingly Nageli describes his theory
of internal causes, as the ‘Principle of Improvement.”
‘« Superficial reasoners,” he says, ‘‘have pretended to
discover mysticism in this. But the principle is one
of a mechanical nature and constitutes the law of per-
sistence of motion in the field of organic evolution.
Once the motion of evolution is started it cannot cease,
but must persist in its original direction.”

For convenience of reference I give a list of pa-
pers by American authors on this subject. European
authors, beginning with Lamarck, and including Spen-
cer, have implicitly included in their theses the effects
of mechanical strains and impacts in developing the
structures of animals. Fick, Henke, Tornier, and
others have attempted an exact demonstration of the
manner in which these forms of mechanical energy
have produced the results. These attempts have great
merit as physiological studies, but they have not been
used by their authors as illustrations of specific evolu-
tion, owing to the fact that they have not carried their
researches into the field of paleontology.

LIST OF PAPERS BY AMERICAN AUTHORS WHO HAVE
CONTRIBUTED TO THE EVIDENCE
USED IN THIS BOOK.

1866. Hyatt, A. Memoirs of the Boston Society of Natural His-
tory, p. 203. On the Parallelism Between Stages in the
Individual and those in the Groups of Tetrabranchiata.

1866. Cope, E. D. Transactions of the American Philosophical
Society, p. 398. On the Cyprinidz of Pennsylvania.

1871. Cope, E. D. Proceedings of the American Philosophical
Society, p. 259. On the Method of Creation of Organic
Types; reprinted in Origin of the Fittest, 1887, pp. 210,
195, 199.

1872.

1877.

1878.

1879.

(880.

1881.

1883.

1885.

1886.

LHE OPINIONS OF NEO-LAMARCKIANS. 529

Cope, E. D. Penn Monthly Magazine; May-July. On Evo-
lution and Its Consequences ; reprinted in Origin of the
Fittest, 1887, p. 30.

Ryder, J. A. American Naturalist, p. 607. On the Laws
of Digital Reduction.

Ryder, J. A. Proceedings of the Academy of Natural Sci-
ences of Philadelphia, p. 314. On the Significance of the
Diameter of the Incisors of the Rodents.

Cope, E.D. American Naturalist, January. The Relation
of Animal Motion to Animal Evolution; reprinted in
Origin of the Fittest, 1887, p. 350.

Ryder, J. A. Proceedings Academy Natural Sciences, Phila-
delphia, p. 45. On the Mechanical Genesis of Tooth-
Forms.

Cope, E. D. American Naturalist, March. On the Origin
of the Specialized Teeth of the Carnivora; Origin of the
Fittest, 1887, p. 363.

Hyatt, A. Memoirs Boston Society Natural History, Fiftieth
Anniversary. Genesis of the Tertiary Species of Planor-
bis at Steinheim.

Cope, E. D. American Naturalist, April and June. On the
Origin of the Foot-Structures of the Ungulates. On the
Effect of Impacts and Strains on the Feet of Mammalia ;
Origin of the Fittest, 1887, pp. 368, 373.

Ryder, J. A. Popular Science Monthly, XIII., pp. 139-
145, 4 figs. The Gigantic Extinct Armadillos and Their
Peculiarities, [Discusses the mechanical genesis, degen-
eration, and coalescence of vertebral centra. ]

Ryder, J. A. American Naturalist, pp. 411-415. On the
Position of the Yolk-Blastopore as Determined by the Size
of the Vitellus.

Ryder, J. A. American Naturalist, pp. 815-819 and 903-
go7- On the Availability of Embryological Characters in
the Classification of the Chordata.

Ryder, J. A. American Naturalist, pp. 1013-1016. On the
Genesis of the Extra Terminal Phalanges in the Cetacea.

Ryder, J. A. American Naturalist, pp. 90-97. An Outline
of a Theory of the Development of the Unpaired Fins of
Fishes.

Ryder, J.A. American Naturalist, pp. 179-185. The Origin
of the Amnion.

530 PRIMARY FACTORS OF ORGANIC EVOLUTION.

1886.

1887.
1887.

1888.

1888.
1888.

1889.

1889.
1889.

1889.

1889.
1889.
18g0.
1890.

1890.

Ryder, J. A. Annual Report U. S. Commissioner of Fish
and Fisheries for 1884, pp. 981-1085, Pl. IX. On the
Origin of Heterocercy, etc.

Ryder, J. A. American Naturalist, pp. 780-784. A Theory
of the Origin of Placental Types, etc.

Cope, E. D. American Naturalist, pp. 985, 1060. The
Perissodactyla.

Cope, E. D. Proceedings of the American Association for
the Advancement of Science, p. 254. On the Mechanical
Origin of the Sectorial Teeth of the Carnivora.

Cope, E. D. American Naturalist, p. 3. The Mechanical
Causes of the Origin of the Dentition of the Rodentia.
Cope, E. D. Proceedings of the American Philosophical
Society, p. 80. The Mechanical Origin of the Dentition

of the Amblypoda.

Ryder, J. A. American Naturalist, p. 547. The Several
Functions of the Enamel Organ in the Development of the
Teeth of Mammals, and on the Inheritance of Mutilations.

Cope, E. D. American Naturalist, March. The Artiodac-
tyla. (The elbow-joint ; the zygapophyses. )

Cope, E. D. American Journal of Morphology, III., p. 137.
The Mechanical Causes of the Development of the Hard
Parts of the Mammalia.

Hyatt, A. Smithsonian Contributions to Knowledge, and
Memoirs of the Museum of Comparative Zodlogy, Cam-
bridge, XVI., No. 3. The Genesis of the Arietidz.

Dall, W. H. American Journal Science and Arts, XXXVIII.,
Pp. 445. Hinge of Pelecypoda and Its Development.

Osborn, H. F. Transactions American Philosophical So-
ciety, XVI., p. 531. (Published February, 1890.) The
Evolution of the Ungulate Foot; The Mammalia of the
Uinta Formation.

Ryder, J. A. American Naturalist, pp. 218-221. The Po-
lar Differentiation of Volvox, etc.

Ryder, J. A. American Naturalist, pp. 271-274. The Quad-
rate Placenta of Sciurus hudsonius.

Ryder, J. A. Proceedings American Philosophical Society,
XXVIII., pp. 109-159. The Origin of Sex, etc.

Ryder, J. A. American Naturalist, pp. 376-378. The Pla-
centation of the Hedgehog and Phylogeny of the Placenta.

Packard, A.S. Proceedings Boston Society Natural His-

1890.

1891.

1892.

1893.
1893.

1893.

1893.
1893.

1893.

THE OPINIONS OF NEO-LAMARCKIANS. 531

tory, XXIV., p. 493. Hints on the Evolution of Certain
Bristles, Spines, and Tubercles of Certain Caterpillars.

Dall, W. H. Proceedings of the Biological Society of
Washington, May. On Dynamic Influence in Evolution.

Jackson, R. T. Memoirs Boston Society Natural History,
IV., p. 277 (July); American Naturalist, 1891, p. 11.
Phylogeny of the Pelecypoda; The Aviculide and Their
Allies.

Dall, W. H. Transactions of the Wagner Free Institute of
Science, Philadelphia, ITI., p. 58 (September). American
Naturalist, 1894, p.go9. Origin of the Plaits on Columella
of Gastropoda.

Scott, W. B. American Journal of Morphology, p. 378.
On the Osteology of Mesohippus and Leptomeryx; On
Some of the Factors in the Evolution of the Mammalia.

Ward, Lester F. Proceedings Biological Society of Wash-
ington, Annual Address. Neo-Darwinism and Neo-La-
marckism.

Elliot, D.G. The Auk, IX., January. The Inheritance of
Acquired Characters.

Ryder, J. A. American Naturalist, pp. 923-929. A Geo-
metrical Representation of the Relative Intensity of the
Conflict Between Organisms.

Ryder, J. A. Proceedings Academy Natural Sciences, Phila-
delphia, pp. 219-224. On the Mechanical Genesis of the
Scales of Fishes.

Sharp, Benj. American Naturalist (February), p. 89. Joint
Formation Among the Invertebrata.

Ryder, J. A. Proceedings American Philosophical Society,
p. 192. Energy as a Factor in Organic Evolution.

Hyatt, Alpheus. Proceedings Boston Society Natural His-
tory, p. 59. Bioplastology and the Related Branches of
Biologic Research.

Riley, C. V. Proceedings Entomological Society Washing-
ton, II., June, No. 4. Parasitism in Insects.

Orr, Henry B. A Theory of Development and Heredity.
New York and London: Macmillan & Co. 8vo. pp. 255.

Hyatt Alpheus. Proceedings of the American Philosophical
Society, p. 349. The Phylogeny of an Acquired Charac-
teristic.

532 PRIMARY FACTORS OF ORGANIC EVOLUTION.

1894. Ryder, J. A. American Naturalist, p. 154. Orr’s Theory
of Development and Heredity.

1894. Cope, E. D. American Naturalist, p. 205. The Energy of
Evolution.

1894. Cope, E.D. New Occasions, No. 6 (May), Chicago. The
Origin of Structural Variations.

1894. Scott, W.B. American Journal Science and Arts, XLVIII.
P. 355. Mutation and Variation.

INDEX.

Abnormal articulations, 275.
Abortion of phalanges in ungulates,
353-
Acanthodeans, 92.
Acanthopterygia, 102, 103, 104, 105,
108,
Acceleration, 9, 201.
_Acquired characters, 10, 399, 401, 402,
458.
Acrania, 87, 94, 95, 193.
Acris, 71.
Actinopterygia, 100, 172.
Actinozoa, 82, 83.
Adapidae, 155.
Adirondacks, 50.
lurodon sevus Leidy, 342.
Ethalium, 503.
#Etheria, 267.
Affections, 517.
Africa, 73, 88, 115, 163, 168, 462.
Agamidae, 73.
Agassiz, A., 172, 175.
Ageleus pheniceus, 52.
Ageniosus, 103.
Aglossa, 63.
Agnatha, 99, 195.
Alaska, 49, 50.
Algae, 75, 77.
Allen, H. Dr., 47, 302, 334) 357+
Allen, J. A., 45.
Altruism, 517.
Amblypoda, 128, 132, 133, 141, 143,144,
2971 341, 354, 520.
Amblyrhiza, 352.
Amblystoma tigrinum, 58, 59, 200.
Amblystomidae, 58, 199.
Ameghino, 154, 157) 357, 365.
America, 426.

Ametabola, 203.
Ammoceetes, 204.
Ammonitinae, 187, 188, 189, 190
Ammonoids, 187, 188, 422.
Ammonoidea, 421.
Ameba, 76, 249.
Ameebodect mastication, 318.
Amphignathodontidae, 71.
Amphimizis, 459.
Amphioxus, 86, 457.
Amphisilidae, 104.
Amphiuma, 113, 218.
Anabolism, 481.
Anacanthini, 105, 106.
Anagenesis, 202, 475, 479, 516.
Anaplasis, 2o1.
Anaptomorphus, 155.
Anaptomorphidae, 154.
Anarcestes, 187.
Anchitherium, 148, 320, 359.
Ancistrodon contortrix, 22.
Ancyloceras, 189.
Ancylopoda, 128, 140, 143.
Anelytropidae, 123.
Anguidae, 123.
Annelides, 269.
Anniellidae, 123.
Anodonta, 261.
Anomia, 170, 177.
Anomia glabra, 265.
Anomodontia, 115.
Anthropomorpha, 132, 133, 143, 154
157, 158, 159, 305.
Antichemism, 484.
Antilocapra americana, 55.
Ants, 462, 500.
Anura, 107, I10, III, 113.
Aphrododiridae, 104.

534 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Appendicularidae, 87.

Archesthetism, 505, 513.

Archean beds, 83.

Archeopteryx, 124.

Archipterygium, 91.

Archosauria, 114.

Arcifera, 64, 65, 70, 71, 196, 197, 389.

Arctic Region, 52.

Argentina, 357.

Ariétidae, 189.

Artemia, 229, 230, 466.

Artemia salina, 229; A. mtuelhausenii,
229.

Arthropoda, 80, 81, 82, 83 172, 250, 253,
268. 269, 368, 369, 389, 391, 404.

Articulations, of Arthropoda, 269; of
Vertebrata, 275, 287.

Artiodactyla, 69, 132, 133, 150, 195, 248,
295, 296, 312, 313, 314, 315, 318, 320,
325, 359, 360, 361, 520.

Arvicola, 349, 351.

Aryan, 159.

Asia, 73.

Aspergillum, 265.

Astacus, hand of, 274.

Atrophy, of incisor teeth, 356; of the
ulna and fibula, 355.

Australia, 72.

Australians, 163, 166.

Austroriparian, 29.

Avian line, 123.

Axis, 196, 199.

Axolotl, 58.

Bactrites, 187.
Baculites, 189, 190.
Bain, 494.

Baird, S. F., 47.

Baker, F. Dr., 469.
Balena mysticetus, 353.
Ball, W. P., 461, 465, 466.
Barber, M. E., 231, 234.
Barrande, 185.
Barrandeoceras, 413.
Batavia, 168.

Bather, 192.

Bathmic energy, 480.
Bathmism, 449, 479, 484.
Bathmogenesis, 484, 486.
Bathyergus, 349.
Batrachia, 87, 88, 89, 91, 94, 95, 97, 98,

108, 115, 116, 121, 172, 193, 195, 196,
218, 253, 363, 364, 365, 368, 372, 388.

Batrachia, line of the, 108; respira-
tion of, 93, 193; remains of, 110; B.
salentia, 8, 63, 69, 70, 314, 389; B. uvo-
dela, 314, 367.

Batrachidae, 107.

Baur, G. 115, 366.

Bear, 21.

Beauchamp, 500.

Beard, Dr. 85.

Beaumé, 229.

Beddard, F. E., 238, 240, 292-

Beecher, C. E., 10, 176, 191.

Bees, 463, 465.

Belt, 500.

Berthollet, 483.

Bioplastology, 192.

Blastocerus, 196.

Blastomeryx, 317.

Blindness of cave animais, 241.

Boa constrictor, 122.

Bodidea, 328.

Bos, 144; B. taurus, 22,

Bouchardia, 178, 179.

Bovidae, 69, 209, 313, 315, 317.

Brachiopoda, 191.

Brachiopodus Mollusca, 58.

Bradypus, 313.

Bragg, C. L. 244.

Brain, vertebrate—development of
94.

Branchinecta ferox, 230; B, media,
230; B. schefferit, 230; B. spinosa,
230. '

Branchiostoma, 86, 92.

Branco, 188

Brazil, 462.

Breeding, 422, 437.

Brehm, 301.

Brevicipitidae, 70.

Brewer, W. H., 422, 426, 430, 431, 435,
437.

Bridger, 139.

Brinton, 468.

British America, 49.

Brooks, 86, 454, 459.

Brown, A., 189, 190.

Brown-Séquard, 430.

Brunn, A. von, 403, 446.

Buccinum, 260,

INDEX, +

Buckman, J., 23, 189, 228.

Bufonidae, 65, 70, 189, 199, 389.

Bumpus, H. C., 242.

Bunotheria, 127, 132, 133, 140, 141, 145.

Bushmen, 159.

Butterfly, peacock, 232; B., swallow-
tailed, 231; B., tortoise shell, 232,

Caciliidae, 113, 218.

Cenoceras aratum, 417; C. clausam,
417; C. intermedium, 417; C. linea-
tum, 417.

Czenogeny, 200, 209.

Calamodon, 330.

California, 50.

Callianassa, 273.

Callianassa stimpsonit, 242, 273.

Calyptocephalus gayi D. and B., 68,

Cambarus bartoniz, 241; C. setonzi,
241.

Cambrian, beds, 83; time, 176.

Camelidae, 69.

Canidae, 48, 49, 59, 339, 342.

Canis, 21, 59; /atrans, 48; lupus, 48.

Caprimulgidae, 126.

Carbonic, epoch, 99, 101, 108, 184, 188,
416, 417, 418, 419, 420; beds, 77, 363.

Cardium, 261.

Cariacus, 196.

Carnivora, 48, 50, 127, 132, 133, 135,
140, 143, 144, 293, 302, 305, 309, 318,
322, 330, 335, 340, 343, 346, 360, 361,
379, 388, 519.

Carpophyta, 77.

Carriére, M., 227.

Carter, H. J., 504.

Cary, 377, 378, 379, 380, 381, 402.

Cassina, 71.

Castor, 351.

Castoroides, 330, 349, 351.

Castoroides ohioensis, 347, 350.

Catagenesis, 202, 211, 475, 479, 516.

Cataplasis, 202.

Caterpillars, 230, 525.

Causes of variations, 223.

Cave animals, 241, 521.

Cavia, 348.

Caviidae, 351, 352-

Cebidae, 155.

Cebus apella, 500; C. capucinus, 500,

Cell-division, 489.

535

Cells, germ, 447, 480; glandular, 440;
muscle, 249; nerve, 450, 453; repro-
ductive, 446, 453; somatic, 453, 456.

Cenogenesis, 200.

Cenozoic, 304, 357, 419, 420.

Centetes, 335.

Centetidae, 145, 335.

Central America, 29, 49, 52.

Centrina, 53, 68, 388.

Cephalopoda, 8, 182, 183, 192, 218, 405,
408, 520.

Ceratobatrachidae, 71.

Ceratophrys, 71.

Cercopithecidae, 469.

Cervidae, 51, 69, 196, 315, 317.

Cervus, 196, 312.

Cervus canadensis, 297; elaphus, 298.

Cetacea, 127, 138, 140, 142, 143, 145, 155,
268, 303, 304, 352, 353, 355) 374-

Chabry, 458.

Chaetodontidae, 107.

Chama, 267.

Characiniidae, 103.

Chelmo, 107.

Chelydobatrachus gouldi? Gray, 68.

Chemism, 484.

Chilonyx, 117.

Chimpanzee, elbow-joint of, 295.

Chinchillidae, 351, 352.

Chirogidae, 324.

Chiroptera, 127, 132, 143, 336, 358.

Chiropterygium, 91.

Chirox, 325.

Chlorophyll, 75.

Choloepus, 313.

Chondrioderma difforme, 220.

Chondrotus tenebrosus, 58, 59.

Chordata, 86, 205, 215, 218.

Chorology, 387.

Chrysochloridae, 335.

Chrysochloris, 310.

Cicindela, variations in, 25.

Ciona intestinalis, 456.

Cladodus, roo.

Clarke, 176, 191.

Claus, 211.

Clepsydropidae, 319.

Climatius, 92.

Cnemidophorus, 199; color-variation
of, 41.

Cnemidophorus deppei, 41; C. gra-

536 PRIMARY FACTORS OF ORGANIC EVOLUTION,

hamii, 46; C. gularis, 41, 46, 200; C.
costatus, 46; C. scalaris, 46, 200; C.
semifasciatus, 43, 46; C. mariarum,
41, 45; C. sexlineatus, 41, 46; C. tes-
sellatus, 41, 46; C. melanostethus,
46; C. perplexus, 46; C. rubidus, 45,
46; C. septemvittatus, 46; C. vario-
losus, 46.

Coassus, 196.

Cobitis, 363.

Cobra de capello, 22.

Coelacanthidae, 91.

Coelenterata, 79, 81, 82, 83, 250.

Calogasteroceras canaliculatum, 421.

Cohesion, 484.

Colaptes auratus, 52.

Coleoptera, 203.

Colocephali, 104, 106.

Coloceras globatum, 4, 16.

Color changes, in Lepidoptera, 230;
in cocoons, 440; in birds, 238; in
fishes, 499; in tree-frogs, 499.

Color variations, in the genus Cicin-
dela, 25; in Osceola doliata, 29; in
Cnemidophorus, 41.

Colostethidae, 78.

Columba livia, 21.

Complementary growth-energy, 248.

Conditions of inheritance, 438.

Condylarthra, 84, 85, 132, 133, 134, 135»
141, 143, 157, 356, 357, 359, 388.

Coniferae, 77.

Conscious energy, 507.

Consciousness, 495, 505.

Consciousness and automatism, 495.

Conversion of Artemia into Branchi-
ata, 229.

Cope, E. D., 8, 528.

Copepoda, 211.

Cophylidae, 70.

Copperhead, 22.

Corvus americanus, 52.

Coryphodon, 354.

Coryphodontidae, 318.

Cosoryx, 315, 317.

Cosoryx furcatus, 315; C. necatus, 315;
C. ramosus, 315; C. teres, 315.

Cossus ligniperda, 237.

Costa Rica, 50,

Cotylosauria, 87, 88, 113, 115, 122, 172.

Crangon, hand of, 274.

Craniomi, 100.

Creodonta, 336, 337, 338, 339, 341, 343,
388.

Cretaceous, 139, 143, 184, 189, 419, 420,
421, 422.

Cricotus crassidiscus, 111,

Crioceras, 189.

Crocodilia, 94, 114, 116,

Crocuta maculata, 294.

Crossopterygia, 100, 101.

Crotalus horridus, 22.

Crustacea, 211, 271, 273.

Cryptopnoy, 494.

Ctenophora, 272.

Ctetology, 192.

Cunningham, J. L., 238, 527.

Cyanurus cristatus, 52.

Cyclops, 212.

Cyclopterus, 108.

Cycloturus, 314.

Cymatoceras elegans, 418.

Cynodictis getsmarianus, 341.

Cynognathidae, 88,

Cyprza, 260.

Cyprezidae, 261.

Cyprinidae, 103.

Cyrtoceras, 185, 408, 413.

Cystignathidae, 65, 70, 71.

Cystignathus pachypus, 390.

Dall, W. H., 10, 58, 255, 520, 530, 531-

Dama, 196,

Darwin, C., 3, 4, 5, 6,7, 14, 231, 247,
248, 249, 385, 387, 398, 474, 480.

Darwin, E., 10, 505.

Daubentonioidea, 128.

Degeneracy, 247; in birds, 126; in
plants, 76; in reptiles, 122; in crus-
tacea, 211; in mollusca, 213; in
vertebrata, 215.

Delphinidae, 303.

Deltatherium fundamintis, 335.

Dendrobatidae, 70.

Dendrophryniscidae, 70.

Dentition modification, in Canidae,
59; in Felidae, 60; in Homo, 60, 61;
in lemurs, 61; in lower placental
mammals, 61; in monkeys, 61.

Depuy, 430.

Dercetidae, 104.

Descartes, 498.

INDEX.

Designed action in animals, 500.

Devonic period, 77, 91, 101, 172, 184,
186, 188, 362, 415, 420, 422,

Diadectidae, 89.

Diadiaphorus, 359.

Dibamidae, 123.

Dicrocerus, 315.

Didelphodus, 335.

Didymium squamulosum, 220.

Digits, number of, 309.

Dimorphodon, 120.

Dimya, 267.

Dinocerata, 314, 315, 356.

Dinosauria, 98, 114, 116, 120, 121, 122,
304, 372.

Dioplotherium, 330.

Diplarthra, 84, 128, 133, 136, 143, 144,
146, 293, 295, 297, 300, 302, 305, 306,
312, 313, 320, 332, 360, 403.

Diplogenesis, 12, 441, 443) 470.

Dipneusta, 89.

Dipnoi, 89, 99.

Diprodontidae, 143.

Diptera, 203, 204.

Dipus, 361.

Disciniscus, 177.

Dissacus, 302.

Disuse in Mammalia, 352.

Dog-opossum, 22.

Dohrn, 204.

Dolichotis, 361; D. patachonica, 305.

Dollo, rar.

Domestic fowls, 21.

D’ Orbigny, 417.

Dorypterus, 103.

Driesch, 457.

DuBois, Dr., 159, 168, 169.

Duméril, 58.

Dynamical evolution, 524.

Dyscophidae, 70.

Dysodus, 59, 146.

Echidermata, 368.

Echinodermata, 80, 81, 82, 83.

Echinus, 457.

Ectal mastication, 318.

Edaphoceras, 186.

Edentata, 127, 132, 133, 138, 141, 143,
145, 186, 195, 303, 305, 310, 356, 360.

Education, 505.

Eels, 103.

537

Eftect of feeding on color in birds,
238.

Effect of light on the colors of flat-
fishes, 238.

Effects of consciousness, 509.

Efficient cause, 10, 497, 498.

Eigenmann, C., 244.

Eimer, 23, 45, 252, 254, 527.

Elasmobranchii, 91, 94, 95, 99.

Elasmotherium, 314.

Elbow-joint, of Cervus elaphus, 296;
of chimpanzee, 295; of horse, ab-
normal, 278; human, abnormal,277.

Elephas, 145, 330.

Elliot, D. G., 531.

Elosia nasus Licht, 68.

Embolomeri, 88, 109, 110.

Embryology, 202, 209, 401.

Embryonic variations, 444.

Emphytogenesis, 486.

Endoceras, 186.

Endolobus, 186; £. excavatum, 417.

Energies, specific, 480.

Energy, 448, 451, 506, 507, 512; Synop-
tic table of, 484; anagenetic, 478,
484; definition of, 473; of evolu-
tion, 473; catagenetic, 479, 484; cor-
relation of, 506; inorganic, 475, 484,
512: composition of, 490.

Engystomidae, 70.

Enhydra, 352.

Ental mastication, 318.

Entoconcha mirabilis, 213.

Environment, physical influences of,
436, 452, 475-

Eocene, 61, 104, 135, 138, 139, 142, 143,
145, 147, 150, 154, 155, 173, 205, 304-
365, 377-

Epigenesis, 13.

Epihippus, 147, 148.

Epilasmia, 107.

Epilepsy in Cavia, 430.

Equidae, 313.

Equilibrium, 508.

Equus, 145, 149, 359; Z. cabadlus, 84,
300.

Ergogenesis, 486.

Erinaceus, 127.

Erismatopterus, 104.

Eryops megacepalus, 371.

Esquimaux, 61, 153.

538 PRIMARY FACTORS OF ORGANIC EVOLUTION,

Esthonyx, 329.
Eudoceratidae, 186.
Euprotogonia, 147.
Europe, 55, 160, 426, 427.
Europeans, 166.
Europeo-Americans, 153.
Eurypharyngidae, 104.
Eusophus nebulosus Gir, 68.
Eusthenopteron foor diz, 91.
Eutenia, 63; Z. saurita, 21; E. strta-
lis, 21, 63.
Eutheria, 373.
Evolution, science of, 22.
Expression points, 25.

Faxoe, 418.

Feet of Chinese women, 399.

Felidae, 48, 49, 145, 342.

Felis, 339.

Felts concolor, 49; F. domestica, 21;
F. pardalis, 50.

Fellahs, 163.

Ferns, 77.

Fick, R., 283, 284, 286, 377, 528.

Firmisternia, 64, 70, 71, 196, 197, 389,
390.

Fisher, 91, 99, 101, 104.

Fishes, ancestral type of, 86, 91, 99.

Fistularia, 104.

Flatfishes, 238.

Flexure, 368,

Florida, 52, 56.

Flossensaum, 243.

Forel, 463.

Forsyth-Major, 334, 469.

Fraipont, 160, 161, 165, 166, 170.

France, 83, 470, 315.

Friction, 279, 519, 378, 490.

Fuligo, 503.

Functions of consciousness, 495.

Fungi, 70, 219.

Furcifer, 197.

Fusus parilis, 257,

Gage, 363.
Galeopithecus, 328.
Gallinae, 391.
Gallus sp., 21.
Galton, Dr., 12, 47%.
Ganocephali, 110,
Garman, S., 241.

Garter-snake, 21.

Gasterosteidae, 104.

Gastraea theory, 202.

Gastrechmia, 63.

Gastropoda, plaits in shell of, 255.

Gazella dorcas, 301.

Gebia, 273.

Gecconidae, 73, 88, 122.

Gegenbaur, 91, 366.

Gelocus, 312.

Genealogy, of man, 171; of the horse,
146.

Genesiology, 192.

Geomyidae, 352.

Giard, 527.

Glauconiidae, 121.

Gleditschia, 228.

Glires, 51, 127, 132, 133, 135) 141, 143,
305, 318, 324, 328, 329, 330, 331, 334s
345, 346, 360, 361, 404.

Glochidia, 203

Glossophaga, 328.

Glossophaginae, 356.

Gloxinia, 384.

Glyptodontidae, 303.

Gobius, 499.

Goethe, 247. .

Gonagenic variations, 444.

Goniatitinae, 186, 187, 188, 422.

Gravitation, 484.

Growth-energy, 449, 473; G. force,
484.

Gulick, 388.

Gulo luscus, 50.

Gtnther, 123, 390.

Gwynia, 178, 179.

Gymnosperms, 79.

Gyroceras, 185.

Haeckel, E., 7, 8, 85, 88, 89, 154, 169,
175) 201, 202, 387, 448, 454.

Halicore, 330, 336.

Hall, 176.

Halloceras, 186.

Hamites, 189.

Hapalidae, 141.

Haplodoci, 106, 107.

Haplomi, 103, 104, 106.

Harpa, 261.

Hawaiian Islands, 388,

Heliotropism, 503.

INDEX.

Hemibranchii, 104, 106.

Hemimantuis, 71.

Hemiphractidae, 71.

Henke, 277, 283, 528.

Henslow, G., 23, 226, 227, 228, 383, 384,
527.

Herdman, 215.

Heredity, 398.

Hering, 492.

Hertwig, 456, 457.

Hesperornithidae, 124.

Heteroglossa, 71.

Heterologous series, 71.

Heteromorphosis, 455.

Heterosomata, 105, 106.

Hilgard, S. W., 433.

Hinnites, 267.

Hippocampidae, 105.

Hippopotamidae, 69.

Hippopotamus, 330, 402.

Hippotherium, 84, 149, 359; /¥. sed7-
terraneum, B4.

Héffding, 498.

Holocephali, 99.

Holoptychiidae, gr.

Holostei, ror, 102.

Holostomi, 106,

Hominidae, 157.

Homo, 155, 158, 169, 170.

Homogeneous series, 71.

Homogeny, 72.

Homologous, series, 71.

Homology, 19.

Homo neanderthalensis, 170; HH. sa-
piens, 170; H. erectus, 169.

Homoplassy in Mammalia, 72, 357.

Homoplastic series, 71.

Hoplobatrachus, 71.

Horn, G. H., 25, 29.

Horns, 314; of Cervus elaphus, 197.

Horse, evolution of trotting, 426; H.
phylogeny of, 146, 522.

House-fly, 254.

Hunger, 504.

Hurst, C. H., 205, 207.

Hitter, 251, 275. 276, 331.

Huxley, 89, 99, 476.

Hyaenidae, 145, 342, 343-

Hyaenodon, 343.

Hyatt, A., 8,9, 10, 175, 182, 183, 201,

539

202, 266, 268, 405, 420, 451, 520, 528,
529, 530, 531.
ybodus, 332.
esDiguttatus, 22,
Hydroids, 82.
Hydrotropism, 501.
Hyla, 11, 198, 199; H. carolinensis, 499;
Al, gratiosa, 499.
Hylella, 71, 198, 199.
Hylidae, 65, 70, 198.
Hylobates, 159.
Hymen, 399.
Hymenoptera, 82, 203.
Hyopotamus, 312.
Hyperolius, 71.
Hypothesis of the origin of the divi-
sions of the Vertebrata, 362.
Hypsiboas donmercti D. and B., 68;
HI, punctatus Schu., 68.
Hyracoidea, 132, 133, 141, 143. 332.
Hyracotheriinae, 313.
Hyracotherium, 147, 148, 302.
Hystricidae, 351.

Ibacus, 274.

Ichthyocephali, 106.

Ichthyopterygia, 113, 116, raz.

Ichthyornithidae, 124.

Ichthyosaurus, 121.

Ichthyotomi, too.

Icichthys, 108.

Icosteus, 108.

Iguanidae, 73.

Impact, 277, 284, 287, 291, 302, 305, 311,
485.

Impressed zone of the nautiloids, 405.

Increase of size through use, 304.

India, 159.

Indo-Europeans, 153.

Inexact parallelism, 200,

Influence, of external stimulus on mo-
tions of animals, 496; of the mental
condition of the mother on the fo-
tus, 434, 451; of mind on coloration,
499; of mind on matter, 498.

Infusoria, 79, 511.

Inheritance, of acquired characters,
401, 405; of characters due to dis-
ease, 430; conditions of 438, 440,
of exercise of function, 426; of mu-

540 PRIMARY FACTORS OF ORGANIC EVOLUTION,

tilation and injuries, 399, 431; of
nutrition, 423; of regional influ-
ences, 435, 440.

Insecta, 213, 226,

Insectivora, 136, 140, 143, 305, 332, 336,
361.

Intelligence, animal, 500, 504.

Introduction, 4.

Ischyromys typus, Leidy, 351.

Ismenia, 178, 179.

Isolation, 387.

Isospondyli, 103, 106.

Jackson, R. T., 10, 191, 261, 520, 531.

Jaeger, 10. ,

Japanese spaniel, 60,

Java, 160.

Java man, 169.

Jayne, H. Dr., 60.

Jordan, Dr., ror.

Joseph, Dr., 242.

Judgment, 504, 506.

Juglans nigra, 466; J. regia, 466.

Jura, 122, 139, 140, 142, 143, 184, 188,
417, 418, 419, 420, 421.

Katabolism, 481,

Kinetobathmism, 485.

Kinetogenesis, 225, 246, 287, 375, 496;
in Mammalia, 288; in Mollusca,
255; of muscle, 249; objections to
the theory of, 375; of osseous tis-
sue, 275; under impact and strain,
519; under use in Vermes and Ar-
thropoda, 268; in Vertebrata, 275.

Kingsley, J. S., 89, 213.

Koelliker, Dr., 285, 331, 377, 381.

Kowalevsky, 323.

Ktkenthal, 333.

Lacerta muralis, 45, 195; L. m. albi-
ventris, 46; L. m.cantpestris, 46; L,
m, maculostriata, 46; L. m. punctu-
latofasciata, 46; L. m. reticulata,
46; L. mm, striatomaculata, 46; L.m.
tigris, 46.

Lacertilia, 88, 116, 120, 121, 122, 123,
218, 314, 372.

Lamarck, 2, 5, 7, 8, 12, 14, 241, 387,
497.

Lamellibranchs, 261.

Lankester, E. R., 71, 113.

Laramie, 139.

Larvacea, 215.

Law of the unspecialized, 172.

Law, Prof., 431.

Lawrence, 426, 427.

Laws of organic evolution, 3.

Laws of structural relations, 19.

Leidy, Professor, 351.

Lemur collaris, 326.

Lemuridae, 155, 328, 339, 356, 469.

Lemuroids, 157.

Lemurs, 61, 150, 154, 155, 156.

Leperditia, 262.

Lepidoptera, 203, 204, 237, 440, 441.

Leporidae, 348.

Leptodactylus pentadactylus, Laur.,
390.

Lepus, 351, 361; L. sylvaticus, 53.

Lernea branchialis, 212.

Lernzapoda, 212.

Lesshaft, 277.

Litge, 160.

Life, definition of, 513.

Light effect, of, on flatfishes, 238.

Lima, 266.

Limbs, moulding of articulations of,
287; vertebrate segmentation of, 367.

Line of the pisces, 99.

Lingula, 176, 177.

Liocephalus, 391.

Liopeplum, 260,

List of papers by American authors
on the law of kinetogenesis, 528.

Litopterna, 357, 359.

Lituites, 414

Loeb, 455.

Lohest, 160, 161, 165, 166, 168, 170.

Lophiodontidae, 355.

Lophobranchii, 105, 106.

Louisiana, 50.

Loup fork, 139, 148, 315.

Lucius estor, 21; L. nobilior, 21; L.
vermiculatus, 21.

Lytoceratinae, 190.

Macacus, 391.
Machrauchenia, 359.
Mackenzie River, 50.
Magas, 178, 179.
Magasella, 179,

INDEX.

Magellania, 178, 179.

Magosphera, 102,

Malacopterygia, 102, 103, 104.

Mammalia, characters of, 93; line
of the successional modifications of

* the feet and digits of, 133; verte-
brae of, 135; dentition of, 135; phy-
logeny of, 138; origin of, 87; brain
and nervous system of, 144.

Man of Spy, 161.

Maori, 168.

Marey, 491.

Marseniidae, 261.

Marsh, 122, 123, 156, 174, 304.

Marsipobranchs, 94, 95, 192, 193, 204.

Marsupialia, 127, 132, 138, 142, 143,
157; 305, 309, 336, 361, 374.

Mastodonsaurus, 117.

Maupas, 79, 459.

Mead, T. H., 31.

Mechanical, causes of dental modifi-
cations, 319; conditions of segmen-
tation in Arthropoda, 269; origin
of characters in Pelecypoda, 261;
origin of the impressed zone in
Cephalopoda, 26r.

Megerlina, 178, 179.

Melanesians, 154.

Meldola, Prof., 231, 234.

Meleagris gallopavo, 21.

Meniscoéssus conguistus, 325.

Meniscotherium, 156.

Menodontida, 355.

Mental, evolution, 510; degeneracy,
509; processes, 506.

Menuridae, 126.

Merospondyli, 106, 372.

Merrifield, 230.

Merychocherus montanus, 307.

Mesohippus, 148.

Mesonyx, 141, 302.

Mesozoic age, 79, 116, 188, 413.

Metabolism, 481.

Metaplasis, 202.

Metatoceras cavatiforme, 406; M. du-
bium, 408.

Metazoa, 252.

Mexico, 29, 48, 49, 388.

Michahelles, 242.

Microsauria, 109, t1o.

Miles, M., 481.

541

Milk-snake, 29.

Mind, development of, 364; its rela-
tion to matter, 507, 508.

Mimetic analogy, 392.

Mimoceras, 187, 421.

Minot, C. S., 468.

Miocene, 138, 139, 315.

Mioclenus, 335.

Mississippi, 57.

Mitchell, Dr. C., 455.

Mitra lineolata, 259.

Mivart, 154.

Mixophyes, 71.

Mnemogenesis, 492.

Modiola, 264.

Molar teeth, of man, 61, 152; of Es-
quimaux, 153; of Fan, 168; of man
and woman of Spy, 166; of Maori,
168 ; of Tahitian, 168.

Moll, 277.

Mollusca, 8, 80, 81, 82, 83, 172, 182, 213,
229, 254, 261, 368, 388, 523, 524.

Moloch, 72.

Monkeys, intelligence of, 500; in
Patagonia, 157.

Monocondylia, 87, 372.

Monodelphia, 132, 142, 144, 374.

Monotremata, 88, 127, 132, 135, 138,
140, 142, 143.

Morphogeny from Gwynia to Dal-
lina, 179.

Morris, C., 363.

Moschidae, 69.

Moulding of the articulations in the
Vertebrata, 287,

Mousterien type, 170.

Muhlfeldtia, 178, 179.

Miller, Aug., 226, 383.

Miller, Johannes, 213.

Mulleria, 265, 267.

Multituberculata, 135, 145, 318, 324,
325, 329, 388.

Muscle, kinetogenesis of, 239; striped,
254.

Mus decumanus, 403.

Mustela americana, 50; M. pennant?,
50.

Mustelidae, 342.

Mutations, 222.

Mutilata, 143, 288, 290, 291, 374.

Mutilations, 398, 431.

542 PRIMARY FACTORS OF ORGANIC EVOLUTION.

Mya arenaria, 263, 265, 266.
Mycetozoa, 219, 229.

Myism, 484.

Myrmecobius, 140.
Myxomycetes, 75. 219, 501, 503.

Nageli, 527, 528.

Narwhale, 330.

Natica, 213.

Natural selection, 247, 385, 474.

Nature of variations, 113, 115.

Naulette, 161, 162, 163, 165. °

Nautili, 183, 184, 185, 186, 408, 413, 417,
418, 419, 420, 421, 422.

Nautilinidae, 421.

Nautiloids, 405, 415, 421.

Neanderthal man, 159, 161, 163, 165,
169, 176.

Necturus, 1173.

Negritos, 163, 166, 169, 154.

Negro, 159, 163.

Nematocarpa filamentaria, 526.

Nematognathi, 106.

Neocaledonians, 163.

Neocene, 143, 148.

Neo-Darwinians, 381.

Neo-Lamarckians, 255, 284, 375, 389,
518,

Neo-Lamarckism, 241, 518.

Neolithic man, 166.

Neothyris, 178.

Nephryticeras, 415.

Neurism, 484, 496.

Neuroptera, 203.

New Britain, 169.

New England, 49, 52, 56, 437.

New Granada, 29.

Newton, 480.

New York, 50, 402, 437.

Nigritos, 154, 163, 166, 169.

Normal articulations, 283.

Norman horse, 423.

North America, 10, 29, 47, 48, 53, 55,
73, 115, 124.

Nutrition, 423.

Objections, to the doctrine of inheri-
tance of acquired characters, 458 ;
to kinetogenesis, 375; to the doc-
trine of parallelism, 205.

Obolella, 176,

Odessa, 224.

Ccology, v, 384.

Cistridae, 102.

Oliva, 260.

Olivella, 260.

Ononis repens, 227; O. spinosa, 227
228.

Ontogeny, 444.

Odphyta, 77.

Opheomorphus mimus, 29.

Ophidia, 116, 120, 122, 218, 372.

Ophidioceras, 414.

Opinions of Neo-Lamarckians, 518.

Opisthobranchs, 261.

Opisthotome mastication, 318.

Orbiculoidea, 177.

Orconectes pellucidus, 241.

Ordovician, 77, 83, 176.

Origin, of the animal line, 514; of
Batrachia, 89; of canine teeth, 327;
of carnivorous dentition, 332; of the
dental type of the Glires, 345; of
divisions of the vertebrates, 362; of
genera,9; of the plaits in the col-
umnella of the gastropods, 255; of
plants, 514; and survival of the fit-
test, 4; of hereditary individual
variation, 11.

Ornithosauria, 114, 120, 121.

Ornithostomi, 143.

Orr, H. B., 531.

Orthagoriscidae, 108.

Orthal mastication, 318.

Orthoceras, 185, 187, 408.

Orthognathism, 248.

Orthoptera, 203.

Ortyx virginianus, 52.

Osborn, H. F., 152, 320, 324, 337, 378,
379) 444, 470, 520, 521, 530.

Osceola doliata annulata, 30, 35, 39;
O. d. clerica, 31, 33, 39; O. @. cocct
nea, 30, 37,39; O. a. collaris, 31, 33,
39; O. ad. conjuncta, 30, 39; O. a.
doliata, 22, 29, 30, 33, 39; O. ad. gcn-
tilis, 30, 37, 39; O. ad. parallela, 30,
35,39; O. d. polyzona, 30, 37, 39; O.
d. syspila, 30, 35, 39; O. a. tempora-
tis, 31, 33. 39; O. d@. triangula, 31,
33, 39.

Osteocephalus, 198, 199.

Osteolepididae, 91.

INDEX.

Ostraciontidae, 108.

Ostracoda, 262.

Ostrea, 261, 264, 265.

Ostrea edulis, 262; O. virginiana, 264,
Ostreidae, 267.

Otariidae, 353, 390.

Otaspis, 199.

Owen, 150.

Oyster, 266, 267.

Pacific, 29, 51, 56. .

Packard, 241, §21, §25, 530.

Palzomeryx, 196.

Palzoniscidae, 181.

Palzospondylus, 99.

Palzosyops, 377.

Paleolithic, flints, 170; man, 169, 170;
time, 160. .

Paleozoic, 188, 226, 413, 415, 417.

Palinal mastication, 318.

Palingenesis, 200.

Paludicola, 71.

Pangenesis theory, of Brooks, 454; of
Darwin, 450.

Pantodonta, 141.

Pantolambda, 141, 354.

Pantotheria, 388.

Pantylus, 117.

Papilio demoleus, 231; P. nireus, 231.

Papuans, 163.

Paradise-birds, 391.

Parallelism, 20, 175; in the Brachio-
poda, 176; in the Cephalopoda, 182;
inexact, 200; objections to doctrine
of, 205; in the Vertebrata, 192.

Parasitism, 211, 214, 509.

Pariotichus, 117.

Parisians, 163.

Passeres, 124.

Patagonia, 157.

Paterina, 176.

Paurodon, 343.

Pavlow, M., 84.

Pea-fowls, 391.

Pecten, 254, 264, 265, 266.

Pediculati, 106.

Pegasus, 104.

Pelecypoda, 261.

Pelobatidae, 70.

Pelodytidae, 70.

Peltaphryne peltacephala D. & B., 68.

543

Pelycosauria, 87, 88, 120, 172.

Pennsylvania, 49, 437-

Pepper, Dr., 278.

Percomorphi, 104, 106, 108.

Perigenesis, 448, 454.

Periptychus, 141, 156, 268,

Perissodactyla, 133, 312, 313, 318, 355,
3571 359, 360, 361, 390, 519.

Permian, 87, 88, 98, 108, 110, 114, 115,
I2I, 122, 172, 209, 218, 363.

Perna, 264.

Pernostrea, 267.

Peropoda, 121.

Perrier, E., 527.

Phacochoerus, 328.

Phanerogamia, 77, 79.

Pharyngognathi, 106, 107, 108.

Phenacodontidae, 147, 150.

Phenacodus, 146, 147, 156, 157, 205,
302.

Phenacodus prim@evus, 130, 137; P.
vortmanit, 134.

Phillipine Islands, 166,

Phocidae, 353.

Phryniscidae, 70.

Phrynocephalus, 73.

Phrynosoma, 72.

Phyllomedusa, 158.

Phyllopod crustacea, 229.

Phylogenetic scheme of the Mamma-
lia, 127.

Phylogeny, general, 74, 444; of ani-
mals, 79; of the Batrachia, 108; of
the birds, 123; of the classes, 83; of
the fishes, 99; of the horse, 146; of
the Mammalia, 126, 138; of man,
150; of plants, 78; of the reptiles,
113; of the Teleostomata, 1o1; of
the Vertebrata, 83; of the Actino-
pterygia, ror.

Physarum leucopheum, 220.

Physeteridae, 303.

Physiobathmism, 485.

Physiogenesis, 225, 227, 435.

Physiology, ii, 479; of bone mould-
ing, 285.

Physoclysti, 104.

Pickerel, 21.

Pieris, 230; P. drassicae, 230; P. va-
pae, 230. f

Pigeon, 21.

544 PRIMARY FACTORS OF ORGANIC EVOLUTION,

Pike, 21.

Pilsbry, 260.

Pinnotheres holothuriae, 242.

Pipilo erythrophthalmus, 52.

Pisces, 87, 95, 98, 192, 195.

Plagiaulacidae, 324, 345.

Plagiaulax, 142.

Plant variation, 23.

Plants, fossil, 77; evolution of, 515.

Platidia, 178, 179.

Platypus, 135.

Plectognathi, 106, 107, 108.

Plectospondyli, 106.

Plesiosauria, 114, 121.

Pleuracanthus, 372.

Pleuronectidae, 238.

Plicatula, 267.

Pliny, 227.

Pliocene, 387.

Plistocene, 149, 168.

Podopterygia, 100.

Poébotheriidae, 302.

Pollard, 89.

Polygamy, 390.

Polymastodon, 142.

Polymastodontidae, 324.

Polynesians, 154.

Polyvedates, 68; P. guadrilineatus

D. & B., 68.

Polyprotodontia, 140, 143.

Polypterus, 89.

Polyzoa, 202.

Porifera, 80, 81.

Pouchet, 498.

Poulton, E. B., 230, 237, 381, 392, 393,
439, 449, 461.

Pre-Carboniferous age, 421.

Pressure, 286, 292, 295, 340, 405, 519.

Principle of improvement, 527.

Proal mastication, 318.

Proboscidia, 128, 132, 133, 136, 141,144,
297, 305, 306, 309, 318, 321, 329, 330,
331, 332, 345, 360, 382, 519.

Procolophonina, 87, 88.

Procyonidae, 48.

Production of colors in lepidopterous
Ppupe, 230,

Prognathism, 417.

Proportions of limbs and of their seg-
ments, 305.

Prorastomus, 330.

Protective colors, 392.

Proteida, 109, 110, III.

Proteles, 146.

Proterotherium, 359.

Proterotome mastication, 318.

Proteus, 242.

Prothallium, 455.

Prothippus, 149, 359-

Protodonta, 388.

Protophyta, 75, 76, 77, 172.

Protoplasm, composition of, 483.

Prototheria, 88, 324, 360, 374.

Protozoa, 75, 79, 81, 83, 172, 219, 249,
252, 505.

Protozoén, 459.

Psalidodect mastication, 318.

Pseudis, 71.

Pseudosauria, 109.

Pseudosuchia, 116.

Psittacotherium, 329, 346, 351.

Ptenophus garrulus Smith, 73.

Pteridophyta, 77, 79.

Pterosauria, 115.

Ptilodus, 324. a

Puerco, 139, 140, 141, 147, 150, 156, 403.

Putorius ermineus, 50.

Pygopodidae, 123.

Pythonomorpha, 120.

Pyxicephalus, 71.

Quadrumana, 132, 133, 136, 143, 293,
294, 306, 326, 332, 360, 361, 467.

Quebec group, 413, 420.

Quenstedt, 189.

Quiscalus purpureus, 52.

Rabl Rickard, 94.

Raccoon pacing, 299.

Rachitomi, 109, 110, 111, 372.

Radiant energy, 484.

Rana agilis Thomas, 68; R. catesbey-
ana, 68; R. chrysoprasina, 68; R.
clamata, 68; R, hexadactyla, 68; R.
temporaria, 64.

Ranidae, 65, 70, 71, 389.

Raphanus raphanistrum L., 227; R.
sativus L., 227.

Recapitulation, 453, 492.

Reduction of digits, 309.

Regeneration, 455.

Reptiles, degeneracy of the eye of

INDEX.

219; degeneracy of the limbs of,
218; degeneracy in the skeletal
structure of, 122; development of
the brain of, 122; line of, 113; suc-
cessive changes in the structure of
the skull of, 116; vertebral articu-
lation of, 121.

Reptilia, 88, 94, 95, 98, 110, 114, 116,
120, 122, 132, 172, 193, 195, 209, 218,
289, 303, 304, 363, 365, 366, 374, 388.

Retardation, 9, 201.

Retrogressive evolution in the Verte-
brata, 145.

Reyher, 277.

Rhinoceros, 313. 314.

Rhinocerus unicornis, 300.

Rhipidopterygia, 91, 100, 101, 172, 366.

Rhizopoda, 249.

Rhynchocephalia, 144, 116.

Rhynchocyonidae, 305.

Rhytina, 331.

Riley, C. V., 531.

Rodentia, 135, 519.

Romanes, Vi, 471.

Rése, 333.

Roux, W., 283, 284.

Rusa, 196.

Ryder, J. A., 79, 309, 311, 319, 320, 321,
323, 346, 349, 366, 404, 455, 485, 486,
518, 519, 520, 521, 529, 530, 531, 532.

Salamandra, 199.

Salientia, 109, 110, 172, 196, 197.
Sandberger, 188.

San Diego, 244.

Sarcothraustes, 335.

Saturnia, 466.

Saturniidae, 203.

Sauermann, Dr., 239, 240.
Sauropterygia, 115, 116.
Sauvage, Dr., 372.
Scaphiopidae, 65.

Scaphiopus holbrookii, 68.
Scaridae, 108.

Schismaderma carens Smith, 68.
Schizocrania, 177.
Schmankewitsch, V., 230.
Schools of evolutionary doctrine, 13.
Schuchert, 191.

Scincidae, 123.

Sciuridae, 351.

545

Scombridae, 108.

Scott, W. B., 222, 334, 526, 531, 532.

Scudder, S., 465.

Scyphophori, 106.

Scytopis, 198, 199.

Sectorial teeth, 139.

Sedgwick, 492.

Seeley, 88, 120, 123.

Segmentation of the external skele-
ton of the Arthropoda, 269; origin
of, 368.

Segmentation of the vertebral col-
umn, 368; origin of, 368.

Selenodont dentition, 320; origin of,
323.

Self-consciousness, 495.

Semper, 228, 242, 527.

Sense perception, 495.

Sensation, 495, 513.

Serranidae, 108,

Sex, 516.

Sexual selection, 389.

Sharp, B., 269, 531.

Shetland pony, 423.

Shipka, 161, 163.

Shoulder girdles of Anura, 64.

Sigaretus, 261.

Siluric, 77, 83, 183, 185, 186, 187, 413,
414.

Siluridae, 103.

Simia, 159, 170.

Simiidae, 157, 158.

Siphocyprea problematica, 260.

Siredon lichenoides,' 200; S. mexica-

num, 59.
Sirenia, 127, 142, 143, 145, 329, 330, 352,
360.

Skull, of man of Spy, 161 ; of Neander-
thal man, 162.

Smilodon neog@us, 344.

Solenhofen slates, 123.

Sonoran, 29.

South America, 50, 154.

Sioths, 305.

Spain, 437.

Spea h ait inter: tana, 68.

Spencer, H., 5, 6, 7, 175, 367; 385, 466,
476, 517, 518, 527.

Sphenodon, 121.

Spinous plants, 228.

Spondylus, 267.

546 PRIMARY FACTORS OF ORGANIC EVOLUTION,

Sponges, 80.

Sports, influence of, 24

Spy, 159, 161, 163, 164, 165, 166, 169,
170.

Squamata, 114, 115, 116.

Squillidae, 273.

Stahl, E., 501.

Starch, 481.

Statogenesis, 485, 496.

Stegocephali, 88, 109, 172.

Stegophilus, 103.

Stentor, 250.

Stereognathus, 325.

Stevenson, C., 432.

Strain, 305, 311, 313, 319, 326, 327, 349,
281, 485, 519, 521.

Strepsiptera, 213.

Streptostylica, 114.

Sturnella magna, 52.

Stypolophus, 335.

Stypolophus whitia, 339.

Successional relation, 19, 62.

Suidae, 69.

Suoidea, 318, 324.

Sus, 330.

Symphysis mandibuli of a, chimpan-
zee, 164; gorilla, 164; liegois, 166;
orang, 164; Parisian, 166; Spy man,
164; Spy woman, 164.

Synagodus, 59.

Synapta digitata, 213.

Systems of evolution, 13.

Table of the characters of the mam-
malian skeleton, 139.

Tachyglossus, 135.

Teker, 195.

Tahitian, 168.

Tapir, 313.

Tapiridae, 318.

Tarsipes, 146.

Tarsius, 155, 306.

Taxeopoda, 128, 136, 146, 297, 357; Car-
pus of,

Taxidea americana, 50.

Teeth, evolution of, 318, 522.

Teidae, 123.

Teleology, 20.

Teleostomata, 91, 99, 100, 101, 336.

Tellkampf, Dr., 241.

Terebratellidae, 178, 179, 180.

Termites, 500.

Tertiary, 184, 291, 421.

Testudinata, 114, 115, 116, 119, 123.

Texas, 50, 436.

Theory of internal causes, 527.

Theory of use and disuse, 3.

Theriodonta, 115, 116.

Thermochemistry, 483.

Theromora, 88, 114, 115, 116, 120, 121,
132.

Thoatherium, 359.

Thoraceras, 186.

Thoropa miliaris Sphix, 68.

Thylacinus cynocephalus, 22.

Tillodonta, 140, 143, 145, 329, 360.

Tomes, 381.

Tomitherium rostratum Cope, 156.

Topinard, P., 153, 155, 157, 168, 165.

Tornier, E., 283, 284, 528.

Tortoises, 114.

Tortricidae, 123.

Toxodontia, 128, 143, 297. 330, 360, 382.

Trachycephalus, 198.

Trachypteridae, 108.

Trachystomata, 109, III.

Tragulidae, 69.

Traquair, 99.

Trias, 108, 113, 135, 184, 209, 325, 417

Triboloceras, 186.

Trichea varia, 220.

Triconodon Owen, 343.

Triconodontidae, 318.

Trichophanes, 104.

Tridacna, 265.

Trilobita, 83.

Trimen, R., 231.

Trinil, man of, 159, 168, 169, 170.

Trionychidae, 303.

Tripteroceras, 186.

Tristichopteridae, 91.

Trityloden, 325.

Trivia, 260.

Trotting horses, 426.

Troglocaris, 242.

Tubularia mesembryanthemum, 456,

Tunicata, 172, 214, 218, 362.

Turbot, 499.

Tyndall, Prof., 476.

Typhlogeophis, 123.

Typhlogobius, 244.

INDEX.

Unconsciousness, 494, 507.

Uinta, 147.

Uintatherium, 354.

Uintatheriidae, 318.

Uma, 73.

Unguiculata, 140, 143, 374.

Ungulata, 138, 140, 142, 143, 147, 205,
248, 295, 297, 302, 321, 330, 340, 353,
355» 357, 361, 374, 390; Origin of, 209.

Unionidae, 203.

United States, 49, 53, 315.

Urochorda, 82.

Urodela, 109, 110, 172.

Uropeltidae, 123.

Uroplates, 88.

Ursus arctos, 21,22; U. maritimus, 21.

Unspecialized, doctrine of, 173.

Use and disuse, doctrine of, 9.

Vandellia, 103.

Vanessa 20, 232; V. urticae, 232.

Variation, 21.

Variation, of basal lobes of leaves,
5; causes of, 225; in cicindela, 25;
cnemidophorus, 41; embryogenic,
444; fortuitous, 444; gamogenic,
444; geographical, 47; gonagenic,
444; in North American birds and
mammals, 45; origin of, 225, 497;
ontogenetic, 444; in Osceola dolzata,
29; phylogenetic, 444.

Variations, of specific characters, 25 ;
somatogenic, 444; structural char-
acter, 58.

Varigny, 229.

Vermes, 80, 81, 82, 83, 172, 263, 268,
368, 437.

Vertebral centra, forms of, 302.

Vertebrata, brain and nervous sys-

tem of, 94, 139; classification of,

547

93; Circulating system of, 93, 192;
origin of, 81; phylogeny of, 81.

Vestinautilus, 186.

Vilmorin, 228.

Virchow, Prof., 159. 169, 467.

Visé, 416.

Vola, 266.

Volutidae, 260.

Volutimorpha, 260.

Volvox, 79.

Vom Rath, 470, 4713.

Von Baer, 175.

Von Brunn, 403.

Vulpes alopex, 48; V. cinereoargenta-
tus, 48; V. lagopus, 48; V. velox, 48.

Wallace, A. R., 3, 5, 228, 381, 383, 387,
392, 392, 466.

Ward, L., 531.

Wasatch, 139, 146.

Weale, M., 231.

Weismann, 10, II, 12, 23, 203, 399, 424
438, 450, 458, 459, 480.

West Indies, 387.

White River, 139.

Wiedersheim, 366.

Wilson, E. B., 457, 487.

‘Wood, T. W., 230, 231, 233, 234-

Woodward, A. S., 372.

Wortman, 293, 402, 520.

Wundt, 498.

Wiirtenburger, 189. 191.

Yucatan, 49.

Zeller, 242, 243.
Zenedura macrura, 52.
Zeuglodon, 304.

Zittel, Dr., 370.
Zittelloceras, 186,
Zygophyta, 77.

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